Robert Costanza Crawford

Richard B Howarth

Ida Kubiszewski

Shuang Liu

David I Stern
email: david.stern@anu.edu.au

Influential Publications in Ecological Economics Revisited

Keywords: Bibliometrics, ecological economics JEL Codes: A12, A14, Q57

We revisit the analysis of Costanzaet al. (2004, Ecological Economics) of influential publications in ecological economics to discover what has changed a decade on. We examine which sources have been influential on the field of ecological economics in the past decade, which articles in the journal Ecological Economics have had the most influence on the field and on the rest of science, and on which areas of science the journal is having the most influence. We find that the field has matured over this period, with articles published in the journal having a greater influence than before, an increase in citation links to environmental studies journals, a reduction in citation links to mainstream economics journals, and possibly a shift in themes to a more applied and empirical direction.

Introduction

Ecological economics is a transdisciplinary field of study.It is influenced by and has influence on a broad range of disciplines and topics. We revisit the analysis of [START_REF] Costanza | Influential publications in ecological economics: a citation analysis[END_REF] of influential publications in ecological economics to discover what has changed a decade on. We compare our findings with this previous work to determine how the journal and the field have changed in the intervening period. We analyze what literature has had the most influence on the field in the last decade, as indicated by citationsmade by articles published in Ecological Economics (EE), and which publications in the journal have had the most influence both on the field and on the wider scientific community.We also look at the most common topics of these influential papers to find which are the most important recent topics in the field.

There are, of course, well-known issues andlimitations related to using citation analysis to assessinfluence [START_REF] Costanza | Influential publications in ecological economics: a citation analysis[END_REF], including the following:

1. The influence of a publication can go wellbeyond academia, and citation analysis will notpick up this non-academic influence.

2. Quantity of citations is not the same as quality and does not indicate whether a publication has been cited in a positive or negative way, though the vast majority of citations are positive (Catalinet al., 2015).

3. The databases used contain only a subset (albeit large) of articles and citations.

4. The academic review process is slow and citationanalysis is, therefore, most useful for publicationsthat are at least a few years old. 5. Similarly, influential older publications tend to be obliterated from citation counts while their influence does not diminish as their information becomes incorporated into common scientificknowledge [START_REF] Merton | The Matthew Effect in science II: Cumulative advantage and the symbolism of intellectual property[END_REF].

6. Citation practices vary across disciplines and scientific communities, which means that comparisons across disciplines should be made carefully.

Despite these well-known limitations, citationanalysis is a powerful and increasingly popular quantitative guide to the relativeinfluence a publication has had on the academic community.Also, in this paper, we are looking at changes over time in comparison with the results of a previous study, and so we must use similar methods to those used in the previous study.

Another important caveat regarding our analysis is the question of whether the changes we find are due to changes in the field of ecological economics or due to changes in the management of the journal, Ecological Economics, and the market for publications in the field. In 2004, Robert Costanza had been editor for all but one year of our sample. In the past decade, Cutler Cleveland and Richard Howarth have been the editors. The numbers of submissions and published articles have both increased strongly and the journal has become more selective. There are also more alternative outlets for publications in this field. In our analysis, we attribute the changes we see to changes in the field itself, but recognize that these other factors may also be at play. [START_REF] Costanza | Influential publications in ecological economics: a citation analysis[END_REF] carried out an analysis along similar lines to the current study and found a broad range of influences on the field of ecological economics. As the field was still quite young, inward influence from classic articles in the broader environmental and economic literature were more influential on the field than were the articles actually published in EE. But the authors argued that this was likely to change as the field matured, as some articles published in the journal were receiving high numbers of citations per year. So, it is interesting to now follow up on that prediction. [START_REF] Ma | Environmental and ecological economics: a citation analysis[END_REF] They found that -there is a significant overlap between the two fields at the journal levelthe two journals cite similar journals‖ but that -ecological economics tends to cite (but not be cited by) general natural science journals more often than environmental economics does, environmental economics cites more heavily from journals rather than other publications, and citations in environmental economics are more concentrated on particular journals and individual publications.‖ (p491) There was much less similarity at the level of individual articles: -Non-market valuation articles dominate the most cited articles in JEEM while green accounting, sustainability, and the environmental Kuznets curve are all prominent topics in EE.‖ (p491)We are interested in finding out whether the pattern of citation links to the natural science literature has been sustained or not and how the topics of influential articles have evolved.

Literature Review

Castro e Silva and Teixeira (2011) showed how the topics covered in EE evolved from 1989 to 2009.They -note that ecological economics experienced an ‗empirical turn' reflected in a shift away from exclusively formalized papers towards exclusively empirical and, to a larger extent, ‗formal and empirical' ones‖(p849). An interesting question is whether there has also been such a shift in influential papers or whether theoretical papers remain the more influential. [START_REF] Hoepner | Environmental and ecological economics in the 21st century: An age adjusted citation analysis of the influential articles, journals, authors and institutions[END_REF] revisited the question of influential publications in environmental and ecological economics covering articles published in a group of 14 environmental and resource economics journals including EEin the period from 2000 to 2009. Their main indicator is citations per annum, which gives recently published papers more equal weight,and they distribute citations to authors and institutions on a fractional basis. They rank individual publications, authors,journals, and institutions with,at times, counterintuitive results. For example, Costanza ranks as the 61 st most influential author. [START_REF] Spash | Influencing the perception of what and who is important in ecological economics[END_REF] criticized this analysis mainly for combining ecological and environmental economics together and thus giving a heavier weight to mainstream environmental economics, as more such journals were included. As Spash stated, Hoepner et al.'s(2012) research design excludes important influences on ecological economics that are outside of the economic mainstream. These are included in our study. [START_REF] Plumecocq | The second generation of ecological economics: How far has the apple fallen from the tree?[END_REF] compares ecological economics research published in EEand Environmental Values with researchpublished in JEEM and Environmental and Resource Economics using textual data analysis.His results -point to the increasing importance of the evaluation of ecosystem services in ecological economic discourse‖. This causes him to -question the kind of transdisciplinarity promoted by ecological economics‖ (p458). Our results will show how the topics covered by the most cited papers in the field, including ecosystem services valuation, have evolved in the last decade.

Methods and Data

3.1.Identifying the influential publications

Our main analysis is based on a set of the most influential articles that we constructed as described in the following. First, we distinguish between inward and outward influence.

Inward influence occurs when publications are cited in articles published in EE. Outward influence occurs when articles published in EE are cited in other publications.

To measure inward influence, we compiled a database of all the sources cited in articles in EE over the 11 years,2004-2014, and selected those that received more than 15 citations in the journal in this period.We excluded institutional authors such as the IPCC and UN. We also collected the total number of citations to the identified publications in the Web of Science(WoS) as a whole and in Google Scholar(GS).We used avariety of techniques to ensure that we hada comprehensive list of publications that received more than 15 citations in the journal in the period, and that all of the citations to a publication were counted. First, we made a substantial effort to identify orphaned citations -citations to an article that should have been added to the total but were listed separately because of small variations in the recorded details of the publication. We examined all publications that have 10 or more citations and combined all orphaned citations. This gives a more comprehensive list of articles that received more than 15 citations. We used the following approach to collect WoS citations.For journal articles that have correct DOIs, we used these DOIs to identify the articles and collect the associated WoScitations. For journal articles whose DOIs were missing or entered into the database incorrectly, we used a combination of the author's name and year of publication to identify the publication and collect itsWoScitations.

For monographs and edited books, we followed the approach used byCostanza et al. (2004).

The titles of monographs and edited books recorded in the WoSdatabase show substantial variation. We first searched for the author's or editor's name(s) together with the publication year in order to pick up all the variations on a title in the WoSdatabase. Next, we searched for all these variations of the titles without the year and the author's and editor's name(s). This yields a large list of possible references to the volume. For example, we first searched for John Rawls'A Theory of Justice (1971) (using -Cited Reference Search‖) as: To measure outward influence, we examined the citations received by all articles published in the journal in the same period. We downloaded data on all the articles published in Ecological Economics in the designated period from WoS on 26 February 2015. The data include all citations included in the database up to that date. We found a total of 2960 published items for the 11 years of the sample. For the period from 1989 to 2003 there were 1364 items. We identified the most influential individual articles published in the journal based on citations inWoS as a whole.To deal with the varying age of articles and their corresponding variation in potential to be cited, we used the Thomson-Reuters -highly-cited‖ approach of picking the top fractile of most cited publications of all the publications in a

given year (Thomson Reuters, 2014). Though this selects papers in recent years that havelow numbers of citations so far, [START_REF] Stern | High-ranked social science journal articles can be identified from early citation information[END_REF] shows that early citations are quite strongly correlated with long-run cumulative citations and so many of these papers will turn out to be very influential. [START_REF] Costanza | Influential publications in ecological economics: a citation analysis[END_REF] selected 71 highly cited articles from the journal, which is about 5% of the total. We decided to extend coverage to 10% of items in each year.

We also collected the number of GScitations to each of the identified influential articles. We collected GScitations to these articles on 6 March 2015. If the borderline between the top 10% and the rest of the articles fallsinside a group of articles with a common number of citations we used the number of GScitations received to determine the cut-off point within that group. If articles on both sides of the 10% line still have the same number of GScitations, we thenremoved those articles that share the same number of citations as those over the borderline. This made the most difference to the 2014 articles,which often have onlyone citation. Table 1 presents the number of articles selected in each year and the cutoff points in terms of citations used in each year.We also counted the number of citations these articles received in EE alone.

3.2.Identifying the influential themes

Weidentifiedthe importance of the various subject themes of the most inwardly and outwardly influential publicationsby attaching a theme to each of the 679 most influential publicationsthat we identified.After eliminating duplicate publications that appear both in the inward and in the outward influencelists, we obtained635unique influential publications.

These publications arethen clustered following a descending hierarchical classification method [START_REF] Reinert | Uneméthode de classification descendantehiérarchique: application à l'analyselexicale par contexte[END_REF] applied to the vocabularyused in the titles of these publications. This clustering techniqueproceeds from a contingency table that enables us to count the presence or absence of words in a given title.All the words found in the titles (except pronouns, conjunctions, and some adjectives)are placedin rows; the 635 uniquepublicationsare placedin the columns. The hierarchical descending classification commencesby splitting the ensemble of columns into two contrastinggroups in terms of the presence or absence of the occurrence of words.These two clusters then contain mutually exclusive vocabularyso that words present in one cluster are relatively absent in the other one, and vice versa.We test whether there is a significant difference in the relative abundance of a word inside and outside the clusterusing a chi-square test evaluated at the 5% significance level.The classification then proceeds via an iterative process: the largestof the two clustersin terms of number of publicationsis divided into two contrasting groups; then amongst these three clusters, the largest is again divided; etc.The iterative process stops either when the number of clusters predefined by the analyst is reached, or when no significantly different vocabularycan be found in the largest cluster.We repeated this iterative process by progressively increasingthe number of clusters requested so as to get the finestpossible clustering. In our case, we obtained 53 clusters. We labeled these clusters according to their main theme words (based on chi-square values), and proceeded to reallocatepublicationsthat were misplaced and to amalgamateclusters that arevery close in theme. 2

Using this algorithm, we obtained 22 clusters (i.e. 22 themes). Only 5 publications remainedunclustered. Table 2 presents the full list of 22 clusters (themes) and some statistics.

2 Two types of misclassification were found. First, some clusters were formed on the basis of artifacts. For instance, publications using the word -question‖, and no other word significantly associated to other classes were clustered together, although they really belonged to very different themes. Second, some clusters might attract publications containing only one of a group of words, which characterized the cluster. For example, some publications mentioning -analysis‖ might be grouped with those mentioning -input-output analysis‖. These publications were regrouped.

3.3.Journal level data

In addition to this main analysis, werepeatthe analysis of [START_REF] Ma | Environmental and ecological economics: a citation analysis[END_REF]

Results

Inward influence

Table 2lists details of the top 30 publications,regardless of when they were published, ranked by number of EE cites in the 2004-14 period. Figure 1 One striking difference between Figure 1 and Figure 2, which presents outward citations,is the relative lack of correlation between WoS and EE cites in Figure 1 compared to Figure 2.

There are many articles in Figure 1 with very high WoS cites but relatively low EE cites.

These are publications such as Kuhn's (1962) The most inwardly influential publications in the 1989-2003 period dealt with the themes of ecological economics (15.6%), and conservation, ecosystems, biodiversity, and species (11.7%). Altogether these two themes represent only 9.5% of the citations in the second period. Instead the themes that became influential are valuation (9.5%), social aspects of environmental issues, including behavioral and institutional dimensions (7.9%), and the exploration of the relationships between the economy and the environment (7.3%).

Outward influence

Table 3 lists This article also has the highest average citations per year. However, it is not the most cited article in Ecological Economics. That is [START_REF] Engel | Designing payments for environmental services in theory and practice: An overview of the issues[END_REF] article on designing environmental service payments (PES). This shows a divergence between outward and inward influence that will be explored further below. Many of the most inwardly influential papersin this group (i.e. papers that were both highly cited in EE and highly cited in general) are on PES. Engel et al.'s paper is also the second most outwardly influential paperin terms of citations per year. 14 of the 33 top articles ranked by EE citations contain both the terms-ecosystem‖ and-service‖ or -environmental‖and -service‖ in their title and others appear to be on related themes, indicating the importance of this theme in EE in this period.We also observe a fairly strong correlation between EE cites and WoS cites for these papers, indicating that highly cited papers in EE are also highly cited elsewhere, with an average ratio of about 5 WoS cites for every 1 EE cite.This indicates the broader influence of papers published in EEbeyond the journal itself.This may also be because in the last 10 years the accessibility of journal articles has increased dramatically and where a paper is published now has less influence on who reads it and cites it.It could also indicate that more influential authors are now deciding to publish in EE.

How have things changed since [START_REF] Costanza | Influential publications in ecological economics: a citation analysis[END_REF]? First, some of the articles in Table 3and Figure 2 have very substantialWoScitations, which was not the case for articles published in the journal prior to 2004. [START_REF] Pearce | Capital theory and the measurement of sustainable development: an indicator of weak sustainability[END_REF] was the article that had received the most WoScitations at that point -a total of 75. Second, the most popular topics among the top articles prior to 2004 were sustainable development and mainstream environmental valuation methods as well as a number of papers on the foundations of ecological economics (receiving 16.8% and 16.7%, respectively, of the citations of the influential articles in the first period). These themes have changed dramatically, as shown in Table 4.In the 2004-2014 period,the influential papers published in EEon the three themes related to ecosystem services (payment for, valuation, and categorization)received the largest number of citations (12.6%, 10.1%, and 10%, respectively,32.7% altogether), while sustainable development and ecological economics decreased in importance and received only6.5% and 4.1% of the citations to influential articles, respectively.

Influential themes

Table 4 shows the results of the thematic clustering procedure. The largest cluster -on the theme of -behaviors and institutions‖ -contains 50publications, closely followed by 49 publications on -valuation.‖The smallest cluster-on the theme of -land use‖ -contains 9 publications. However, if we aggregate the three themes relatedto ecosystem services (payment for, biodiversity, and categorization) their total number of publications is 85, indicating the prevalence of this topic. In terms of citations, these three themes together had 25% of the total citations (an average of 78 citations per paper for these themes, compared to 43.4 citations on average for all identified influential publications), with the next largest cluster --valuation‖ -having only 6.9% of total citations.

The number of applied themes does suggest that there has been a move away from the dominance of the more foundational themes. However, it is hard to determine from the theme analysis whether EE has produced more influential applied papers in the last decade than previously. Wemight expect theoretical or review papers to be more influential in EE. 3 Looking at the top outward influential papers, we find theoretical or conceptual ones: [START_REF] Boyd | What are ecosystem services? The need for standardized environmental accounting units[END_REF]Banzhaf (2007) andFisher et al. (2009)provide classifications of ecosystem services, [START_REF] Engel | Designing payments for environmental services in theory and practice: An overview of the issues[END_REF] is an overview of concepts and issues in PES, [START_REF] Dinda | Environmental Kuznets Curve hypothesis: A survey[END_REF] While these studies are applied, their results and outcomes are very general so that they can easily be mobilized in other research to provide overview data that helps in framing more specific issues. Nevertheless, an analysis of the co-occurrence of the words contained in the titles suggests that the growing influence of (payments for) ecosystem services is coupled with an empirical trend. When splitting the timeframe into two periods, we can even distinguish two phases of this evolution: under the editorship of Cutler Cleveland, 9% of the influential publications associated the terms -theory‖ and -practice‖ in their titles; and 9% of the influential papers published under the editorship of Richard Howarth (from 2008) contained both the words -case‖ and -study‖ (ranked as the fifth most frequent association of words in the titles of articles published since 2008). It also seems that the emergence and influence in the last decade of themes such as PES or more broadly ecosystem services has led to more applied papers, especially under Richard Howarth's editorship (Table 3). Journals marked in bold are common to the lists in [START_REF] Ma | Environmental and ecological economics: a citation analysis[END_REF]

Discussion and Conclusions

We have described and analyzed the publications in the broader literature that have influenced EE(inward influence) based on their citation rates in EE, and the influence of articles published in EE(outward influence) based on citation rates in both the journal itself and the broader literature (WoS and GS). We have also described how these citations have changed over time and how the citation rates of major themes covered in EEhave changed over time.These patterns are complex, but we can draw a few conclusions.

EE is a unique, transdisciplinary, journal that cites and is cited by a broad range of other sources. In its first 14 years (1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003) it was building its reputation and the inward influence in citations was much larger than its outward influence.This has changed to some degree in the 2004-2014 period.As Figure 1 shows, papers published in EEnow average 5 citations in WoS for every one in EE, and some have garnered hundreds of WoS citations.

As for inward influence, publications in EE often cite publications from general interdisciplinary natural science journals and books, again a testament to its transdisciplinary nature. Citations to economics journals whether environmental and resource economics journals or core economics journals have declined and environmental and resource economics journals have also dropped down the citing journal list, as shown in Table 5.

Interdisciplinary environmental studies journals increasingly dominate both the cited and citing journal lists.

Of course, we cannot answer all questions about a journal's influence and themes from citation analysis, which only charts influence in the academic literature and is subject to other limitations as noted previously.There are certainly many other interesting questions to address concerning, for example, how opinions have evolved over time on particular topicslike ecosystem services, PES, and environmental Kuznets curves. These have been examined to some degree in previous research (e.g. [START_REF] Plumecocq | The second generation of ecological economics: How far has the apple fallen from the tree?[END_REF].

EE is now 26 years old.Its themes and publication patterns have changed dramatically over that period, but it has retained its commitment over three editors, to being a unique venue for research that transcends disciplinary boundaries.The world itself has also changed dramatically over the life of the journal, in part because of the work of ecological economists themselves and by many others who have been influenced by them, to one in which the topics covered in EE have become even more important to the future of humanity.We hope that the analysis of past patterns of publication in this paper can help future editors and authors to develop priorities for the future.

  followed up Costanza et al.'s analysis by comparing EEand the Journal of Environmental Economics and Management (JEEM) in order to understand the differences between transdisciplinary ecological economics and mainstream environmental economics.

Cited

  57 title entry variations, which we then used for the next searchusing the -Cited Work‖ search. 1 We collected WoSand GScitations to journal articles between April 17 and 23, 2015.We collected GScitations to books on 3 May 2015and WoS citations to booksbetween 17 April and 19 May 2015.

  on which journals are most cited by EE and which journals cite EEmost using data from the Journal Citations Reportfor the period 2004 to 2014.

Figure 1 .

 1 Figure 1. Inward Influence: Publications Highly Cited by EE Articles. The figure is a log-log plot of total WoS citations vs. EE citations. Circle size indicates the number of GS citations.

  is a log-log plot of the number of WoS cites vs. the number of EE cites for all the articles we included in our survey of inward influence, along with an indication of the number of GS cites by the size of the circles. It also shows the line where the number of EE cites is 1/10 of the number of WoS cites. Publications to the right of this line are 10 times or more cited in WoS relative to in EE.

Figure 3

 3 Figure 3 is a log-log plot of the relationship between EE citations in the 1989-2003 period vs. EE citations in the 2004-2014 period to show which articles have had continuing influence on EE citations. This plot, of course, only includes articles published before 2003. Most of these publications have continued to have ongoing influence. A few exceptions that have had waning influence with relatively fewer citations in the later period include Hanemann (1991), Pearceet al.(1989), and Costanza (1991), all -foundational‖ books.

Figure 2 .

 2 Figure 2. Outward Influence: Highly Cited Papers Published in EEfrom 2004 to 2014 The chart plots total WoS citations vs. EE citations. Size of the circle is number of GS citations. Darkness of color indicates publication year.

Figure 3 .

 3 Figure 3. Changes in Inward Influence: Relationship between EE Citations Received from 1989 to 2003 andEE Citations Received from 2004 to 2014.

  the top three articles published in EE ranked by WoS citations in each of the years 2004 to 2014 and their EE, WoS, and GS citations.Figure 2 is a plot of the outward influence of the most highly cited papers published in EE in the 2004-2014 period.The chart shows total WoS citations on the x-axis vs. total EE citations on the y-axis, with the size of the circles indicating the number of GS citations and the color of the circles indicating the year of publication. The most highly cited article published in EEacross the eleven years in both WoS and GSis Pimentel et al.'s (2005) article on the economic costs of invasive species.

  schemes. While these studies are applied, their results and outcomes are very general so that

Figure 4 .

 4 Figure 4. Inwardly and Outwardly Influential Themes

Table 1 . Outward Influence: Selection Criteria Year of Publication Total number of items Number selected Cutoff number of ISI citations

 1

	Cutoff number
	of GS citations

Table 2 . Inward Influence: The Top Thirty Articles

 2

		EE cites	EE cites	Total ISI	Total GS
	Publication	2004-14	1989-2003	cites	cites
	Costanzaet al.(1997) The value of the world's ecosystem services and natural capital, Nature.	139	68	5303	13350
	Ostrom (1990)Governing the Commons: The Evolution of Institutions for Collective Action.	129	40	5939	21419
	Greene (1993)Econometric Analysis.	107	18	14529	48504
	Wackernageland Rees (1996)Our Ecological Footprint: Reducing Human Impact on the Earth.	94	47	1350	6239
	Daily (1997) Nature's Services: Societal Dependence On Natural Ecosystems.	93	78	1995	5152
	Georgescu-Roegen (1971)The Entropy Law and the Economic Process.	91	65	1454	229
	Stern (2006) Stern Review: The Economics of Climate Change.	83	0	2222	13874
	Mitchelland Carson (1989)Using Surveys to Value Public Goods: The Contingent Valuation
	Method.	81	58	2098	5929
	Hardin (1968) The tragedy of the commons, Science.	79	30	6663	26262
	Grossman and Krueger (1995) Economic growth and the environment, Quarterly Journal of
	Economics.	75	29	1087	4225
	de Groot et al. (2002) A typology for the classification, description and valuation of ecosystem
	functions, goods and services, Ecological Economics.	72	2	786	2321
	Freeman et al.(2003)The Measurement of Environmental and Resource Values.	70	30	986	3588
	Miller and Blair (2009) Input-Output Analysis: Foundations and Extensions.	63	0	1213	4203
	Arrow et al.(1993) Report of the NOAA panel on contingent valuation, Federal Register.	60	19	1000	53
	Train (2003) Discrete Choice Methods with Simulation.	60	0	2672	7832

Table 3 . Outward Influence: Top Three Articles by Year

 3

		ISI	GS	EE
	Article	Citations	Citations	Citations
	Dinda (2004) Environmental Kuznets Curve hypothesis: A
	survey	311	1156
	Robinson (2004) Squaring the circle? Some thoughts on the
	idea of sustainable development	170	713
	Adhikariet al. (2004) Household characteristics and forest
	dependency: evidence from common property forest
	management in Nepal	109	326
	Pimentel et al. (2005) Update on the environmental and
	economic costs associated with alien-invasive species in the
	United States	1113	1992
	Jaffe et al. (2005) A tale of two market failures: Technology
	and environmental policy	196	668
	Max-Neef (2005) Foundations of transdisciplinarity	124	477	9
	Hein et al. (2006) Spatial scales, stakeholders and the valuation
	of ecosystem services	239	626
	Chapagainet al. (2006) The water footprint of cotton
	consumption: An assessment of the impact of worldwide
	consumption of cotton products on the water resources in the
	cotton producing countries	146	406
	Troy and Wilson (2006) Mapping ecosystem services: Practical
	challenges and opportunities in linking GIS and value transfer	135	322
	Boyd and Banzhaf (2007) What are ecosystem services? The
	need for standardized environmental accounting units	330	921
	Wiedmannet al. (2007) Examining the global environmental
	impact of regional consumption activities -Part 2: Review of
	input-output models for the assessment of environmental
	impacts embodied in trade	253	377
	Zhang et al. (2007) Ecosystem services and dis-services to
	agriculture	184	452
	Engel et al. (2008) Designing payments for environmental
	services in theory and practice: An overview of the issues	377	1017
	Wunderet al. (2008) Taking stock: A comparative analysis of
	payments for environmental services programs in developed
	and developing countries	233	640
	Peters (2008) From production-based to consumption-based
	national emission inventories	172	394

Table 4 . Themes: Number of Publications and Citations by theme

 4

				Total				Total
	Theme	Number of Inward Publications	Number of Outward Publications	Publications (eliminating double	Share in Total Publications	Inward Citations	Outward Citations	Citations (eliminating double	Share in Total Citations
				counting)				counting)
	Social aspects (behaviors and	33	20	50	7.9%	776	1002	1725	6.3%
	institutions) Valuation	35	16	49	7.7%	935	1011	1912	6.9%
	Environmental policy and	23	25	46	7.2%	659	831	1459	5.3%
	governance Technical change	17	26	43	6.8%	345	1419	1764	6.4%
	Ecological economics	24	15	37	5.8%	547	773	1277	4.6%
	Happiness and poverty	27	11	37	5.8%	600	627	1210	4.4%
	Impacts assessment	18	21	37	5.8%	388	1349	1701	6.2%
	Economy and the environment	28	10	36	5.7%	715	452	1119	4.1%
	Payment for ecosystem	19	26	33	5.2%	484	2356	2519	9.1%
	services/conservation Ecosystem services valuation	19	12	28	4.4%	526	1887	2346	8.5%
	Ecosystem services	9	23	27	4.3%	252	1881	2009	7.3%
	categorization/application Flow-stock models/Energy	11	16	26	4.1%	268	1095	1347	4.9%
	analysis/Metabolism Sustainable development	9	20	26	4.1%	189	1228	1350	4.9%
	Conservation, ecosystems,	15	8	23	3.6%	385	423	808	2.9%
	biodiversity, species Input-Output analysis	12	12	21	3.3%	349	871	1129	4.1%
	Ecological footprint	16	5	20	3.1%	446	247	669	2.4%
	Environmental Kuznets curve	18	3	20	3.1%	450	470	887	3.2%
	Statistics/Econometrics	18	0	18	2.8%	544	0	544	2.0%
	Environmental/neoclassical	16	1	17	2.7%	381	13	394	1.4%
	economics Limits to growth, steady state, and	12	5	16	2.5%	349	177	509	1.8%
	de-growth Epistemology/interdisciplinary	6	5	11	1.7%	154	325	479	1.7%
	Land use	3	6	9	1.4%	53	257	310	1.1%
	Varied	2	3	5	0.8%	34	58	92	0.3%
	Total	390	289	635	100.0%	9829	18752	27559	100.0%

  book The Structure of Scientific Revolutions that are very highly cited in general but have had only a moderate influence on EE.Costanza et al. (1997)was the most highly cited publication in EE in the 2004-14 period, and the second highest in the 1989-2003 period after Daily (1997), an edited book.Both these publications are on the topic of ecosystem services. It is also notable how many of the top

items are books

(including Ostrom (1990), Daily (1997)

,

Stern (2006), etc.)

. This is not surprising, since books in general garner higher overall citations than journal articles (LSE Public Policy Group, 2011). Only two articles published in EE appear in this top thirty listde

[START_REF] De Groot | A typology for the classification, description and valuation of ecosystem functions, goods and services[END_REF]

and

[START_REF] Engel | Designing payments for environmental services in theory and practice: An overview of the issues[END_REF]

-both of which are also on the topic of ecosystem services.

Table 5 . Most Cited and Most Citing Journals 2004-2014 Top 20 journals citing EE 2004-14 Top 20 journals cited by EE 2004-14

 5 Table5uses data from the Journal Citation Reports to list the 20 journals that most frequently cited EE and were most frequently cited by EE in the years 2004-2014. As noted by[START_REF] Ma | Environmental and ecological economics: a citation analysis[END_REF], EE cites the general science journals PNAS, Science,and Nature but is obviously cited by those journals much less. There is also a tendency to cite the mainstream environmental and resource economics journals Environmental and Resource Economics, JEEM, Land Economics, and American Journal of Agricultural Economics but to be much less cited by them. However, this less pronounced than in 2003 when those four journals were the four most cited in EE after the journal itself. Instead interdisciplinary environmental studies journals such as Global Environmental Change, J. Environmental Management, Ecology and Society, and Environmental Science and Technology are much more prominent. No core economics journal now appears in the top 20, whereas in 2003 the American Economic Review, J. Political Economy, and Quarterly Journal of Economics all featured. Energy Policy now is the second most cited journal and Energy Economics also features in the top 20 list, reflecting the expansion of publication in energy economics and policy in recent years. There has also been a reduction in the prominence of economics journals in the list of the top 20 journals citing EE and a rise in interdisciplinary environmental studies and energy journals as well as interdisciplinary mega-journal PLOS One.

	Journal	Citations Journal	Citations
	ECOL ECON	936	ECOL ECON	920
	ECOL INDIC	322	ENERG POLICY	165
	J CLEAN PROD	264	P NATL ACAD SCI USA	143
	SUSTAINABILITY-BASEL	231	ENVIRON RESOUR ECON	109
	ENERG POLICY	221	GLOBAL ENVIRON CHANG	92
	LAND USE POLICY	178	SCIENCE	90
	GLOBAL ENVIRON CHANG	153	J ENVIRON MANAGE	66
	PLOS ONE	142	ECOL SOC	63
	RENEW SUST ENERG REV	140	ENVIRON SCI TECHNOL	63
	J ENVIRON MANAGE	137	J ENVIRON ECON MANAG	62
	ECOL SOC	127	LAND ECON	57
	ENERG ECON	124	LAND USE POLICY	57
	ENERGY	112	ENERG ECON	56
	ENVIRON SCI TECHNOL	100	NATURE	52
	SCI TOTAL ENVIRON	96	WORLD DEV	51
	ENVIRON MANAGE	90	BIOL CONSERV	45
	FOREST POLICY ECON	81	AM J AGR ECON	43
	ENVIRON RESOUR ECON	71	CONSERV BIOL	42
	MAR POLICY	69	ECOL INDIC	42
	APPL ENERG	66	ECON SYST RES	38

In science as a whole, methods papers tend to receive the most citations (van Noordenet al., 2014) and reviews receive lower citations than original research in biomedicine(Lokker et al., 2009).

The search terms entered in this case were: Cited Work: 'THEORY JUSTICE ' OR '1971: A Theory of Justice' OR '1971: A Theory of Justice' OR '7HEORY OFJUSTICE' OR 'THEORY JUST' OR 'THEORY JUSTICE ROUTL' OR 'A THEORY OF JUSTICE' OR 'THEORY JUSTICE REV E' OR 'A theory of justice (Théorie de la justice) ' OR 'A theoryofjustice' OR 'THEORY SOCIAL JUSTIC' OR 'ATHEORY JUSTICE' OR 'J RAWLS THEORY JUSTI' OR 'THEORY JUSTICE' OR 'PREFACE THEORY JUSTI' OR 'STHEORY JUSTICE' OR 'TEORIA GIUSTIZIA' OR 'TEORY JUSTICE' OR 'THEOLY JUSTICE' OR 'THEOR JUSTICE' OR 'THEORIE GERECHTIGKEI' OR 'THEORY JSUTICE' OR 'THEORY JUCTICE' OR 'THEORY JUSETICE' OR 'THEORY JUSINCE' OR 'THEORY JUSITCE' OR 'THEORY JUSTIC' OR 'THEORY JUSTICD' OR 'THEORY JUSTICE 1' OR 'THEORY JUSTICE 90 91' OR 'THEORY JUSTICE CAMBR' OR 'THEORY JUSTICE FAIRN' OR 'THEORY JUSTICE OUP' OR 'THEORY JUSTICE OXFOR' OR 'THEORY JUSTICEE' OR 'THEORY JUSTICER' OR 'THEORY JUSTICEW' OR 'THEORY JUSTICS' OR 'THEORY JUSTICW' OR 'THEORY JUSTIDE' OR 'THEORY JUTICE' OR 'THEORY OFJUSTICE' OR 'THEORY PRACTICE' OR 'THEORY USTICE' OR 'THEORYJUSTICE' OR 'THEORYN JUSTICE' OR 'THEROY JUSITCE' OR 'THOERY JUSTICE' OR 'THOERY JUSTICT' OR 'THOEY JUSTICE' OR 'THOEYR JUSTICE' OR 'THORY JUSTICE' OR 'TREATISE JUSTICE' OR 'A Theory of Justice' OR '3HEORY JUSTICE' OR 'THEORY JUSTICE 3' OR 'THEORY JUSTICE TJ' OR 'A THEORY JUSTICE'


Vincent Regard
email: vincent.regard@get.obs-mip.fr

Sébastien Carretier

Jean-Loup Boeglin

Jules-Rémy Ndam Ngoupayou

Jean-Guy Dzana

Jean-Pierre Bedimo Bedimo

Jean Riotte

Jean-Jacques Braun

Denudation rates on cratonic landscapes: Comparison between suspended and dissolved fluxes, and 10 Be analysis in the Nyong and Sanaga River basins, South Cameroon

Keywords: Denudation rate, weathering, cosmogenic nuclides, Cameroon, craton Denudation rates from modern fluxes and cosmogenic nuclides, Cameroon

South Cameroon is located in a tropical and tectonically quiescent region, with landscapes characterized by thick highly weathered regolith, indicative of the long term predominance of chemical weathering over erosion. Currently this region undergoes huge changes due to accelerated mutations related to a growing population and economical developments with associated needs and increasing pressures on land and natural resources. We analysed two of the main South Cameroon rivers: the Nyong River and Sanaga River. The Sanaga catchment undergoes a contrasted tropical climate from sub-humid mountainous and humid climate and is impacted by deforestation, agriculture, damming, mining and urbanization, especially in the Mbam sub-basin, draining the highly populated volcanic highlands. By contrast, the Nyong catchment, only under humid tropical climate, is preserved from anthropogenic disturbance with low population except in the region of Yaoundé (Méfou sub-basin). Moreover the Nyong basin is dam-free and less impacted by agriculture and logging.

We explore both denudation temporal variability and the ratio between chemical and physical denudation through two catchment-averaged erosion and denudation datasets. The first one consists of an 11-year long gauging dataset, while the second one comes from cosmogenic radionuclides (CRN, here 10 Be) from sand sampled in the river mainstreams (time scale of tens to hundreds of thousands of years). Modern fluxes estimated from gauging data range from 5 to 100 m/Ma (10 to 200 t/km 2 /yr); our calculations indicate that the usual relative contribution of chemical vs physical denudation is 60% and 40%, respectively, of the total denudation. 10 Be denudation rates and sediment fluxes range from 4.8 to 40.3 m/Ma or 13 to 109 t/km 2 /yr, respectively, after correction for quartz enrichment. These fluxes are slightly less than the modern fluxes observed in Cameroon and other stable tropical areas. The highest 10 Be-derived fluxes and the highest physical vs. chemical denudation ratios are attributed to anthropogenic impact.

Introduction

Erosion rates are strongly impacted by anthropogenic activities such as agriculture, damming, mining and urbanization. However, in order to appreciate the importance of these processes with regards to global erosion requires knowledge of the prehistoric, long term denudation rates imposed on land surfaces solely by natural processes [START_REF] Wilkinson | Humans as geologic agents: A deep-time perspective[END_REF]. Quantitative understanding of the variability in weathering and erosion fluxes on modern Earth is important for assessing soil resources and the impact of human activities (e.g., [START_REF] Balthazar | Human impact on sediment fluxes within the Blue Nile and Atbara River basins[END_REF][START_REF] Bellin | Anthropogenic and climatic impact on Holocene sediment dynamics in SE Spain: A review: Quaternary International[END_REF][START_REF] Bellin | Natural and anthropogenic controls on soil erosion in the Internal Betic Cordillera (southeast Spain)[END_REF][START_REF] Syvitski | Impact of Humans on the Flux of Terrestrial Sediment to the Global Coastal Ocean[END_REF].

Continental tropical regions are often characterized by slow denudation in tectonically quiescent shield areas, which is the result of uplift and the base level likely due to eustatic changes such as those resulting from the advance and retreat of ice sheets in mid and boreal latitudes or from geodynamics (e.g., [START_REF] Conrad | Influence of dynamic topography on sea level and its rate of change[END_REF]. Thus, in general, the balance between erosion and weathering, i.e., the weathering regime, has been in favour of deepening of the regolith through chemical weathering (towards kinetically limited regime), rather than by erosive stripping (e.g., [START_REF] Chadwick | Shaping post-orogenic landscapes by climate and chemical weathering[END_REF][START_REF] Migoń | Weathering mantles and their significance for geomorphological evolution of central and northern Europe since the Mesozoic[END_REF]Monod et al., Accepted;[START_REF] Von Blanckenburg | Stable runoff and weathering fluxes into the oceans over Quaternary climate cycles[END_REF][START_REF] De Oliveira Carmo | 40Ar / 39Ar geochronology constraints on late miocene weathering rates in Minas Gerais, Brazil[END_REF]. In addition, successive periods of laterization (usually leading to the formation of thick regolith and different generations of iron crust) have resulted from climate changes [START_REF] Retallack | Lateritization and Bauxitization Events[END_REF][START_REF] Tardy | Derive des continents paleoclimats et altérations tropicales[END_REF].

Cosmogenic radionuclides (CRN), particularly 10 Be, have been widely applied to assess the total denudation rates (i.e. the sum of the physical erosion and chemical weathering rates) over 10 3 to 10 6 yr (e.g., [START_REF] Bierman | Refining estimates of 10Be and 26Al production rates[END_REF][START_REF] Brown | Denudation rates determined from the accumulation of in situ-produced 10Be in the luquillo experimental forest, puerto rico[END_REF][START_REF] Carretier | Slope and climate variability control of erosion in the Andes of central Chile[END_REF][START_REF] Covault | Spatial and Temporal Variations in Landscape Evolution: Historic and Longer-Term Sediment Flux through Global Catchments[END_REF][START_REF] Granger | Spatially averaged long-term erosion rates measured from in situ-produced cosmogenic nuclides in alluvial sediment[END_REF][START_REF] Portenga | Understanding Earth's eroding surface with 10Be[END_REF][START_REF] Vanacker | Constraining landscape development of the Sri Lankan escarpment with cosmogenic nuclides in river sediment[END_REF][START_REF] Von Blanckenburg | The control mechanisms of erosion and weathering at basin scale from cosmogenic nuclides in river sediment[END_REF]. Recent attempts have been made to compare these long-term pre-anthropogenic denudation rates to modern physical erosion and chemical weathering rates. For instance, in the steep, humid tropical highlands of Sri Lanka, [START_REF] Hewawasam | Slow advance of the weathering front during deep, supply-limited saprolite formation in the tropical Highlands of Sri Lanka[END_REF] showed that the short-term denudation rates (from river load gauging) exceed the total pre-anthropogenic denudation rates measured by cosmogenic nuclides by several orders of magnitude (90-1400 mm/kyr versus 10-20 mm/kyr). This study serves to highlight the severity of geomorphic change caused by human action. Other studies have shown lower shortterm denudation rate compared to long-term 10 Be-derived denudation rates (e.g., [START_REF] Carretier | Slope and climate variability control of erosion in the Andes of central Chile[END_REF][START_REF] Kirchner | yr, 10 k.y., and 10 m.y. time scales[END_REF][START_REF] Schaller | Large-scale erosion rates from in situ-produced cosmogenic nuclides in European river sediments[END_REF]. This difference has been interpreted as reflecting the lack of low frequency large floods in the river load records or climate change. This can be illustrated with a recent example in the Blue Mountains Plateau in the western Sydney Basin, Australia, for which [START_REF] Tomkins | Contemporary versus long-term denudation along a passive plate margin: the role of extreme events: Earth Surface Processes and Landforms[END_REF] explored the role of extreme events (wildfires and catastrophic floods) in landscape denudation along a passive plate margin by determining the denudation rates for the short-term (contemporary) by river gauging, the medium-term (5-500 kyrs) with cosmogenic nuclides and long-term (1-100 Myrs) with apatite fission track thermochronology and post-basalt flow valley incision. They found that the average of the contemporary denudation rates is several times lower than the long-term average (5.5 ± 4 mm/kyr versus 21.5 ± 7 mm/kyr). They suggest that a plausible combination of infrequent mass movement events and high fluvial discharge could account for a significant proportion of the discrepancy between contemporary and long-term denudation rates. Using to a synthesis of the limited number of studies in the literature comparing short-term and medium term denudation rates, Covault et al. (2013, fig. 11) generalize this observation (larger medium-term denudation rates than short-term ones) up to a certain catchment size. For large catchments (equivalent sediment mass load >10 Mt/yr), gauging data tends to be similar to CRN data. According to these authors, this similarity could be due to a buffering effect in larger catchments, smoothing the high-frequency variations in sediment load. All these studies emphasize the need to better understand the temporal link between denudation rates impacted by climatic events and/or anthropogenic activities.

Another motivation underlined by the present paper deals with the relationship between physical erosion and chemical weathering fluxes in low relief areas. The role of erosion in enhancing the chemical weathering of silicate rocks in mountain ranges, a process that consumes atmospheric CO2 over geological timescales, has been the focus of an intense debate for the past two decades (e.g., [START_REF] Raymo | Influence of late Cenozoic mountain building on ocean geochemical cycles[END_REF][START_REF] Willenbring | Long-term stability of global erosion rates and weathering during late-Cenozoic cooling[END_REF]. Recent papers suggest that large peneplain surfaces may matter along with or more so than mountain ranges in terms of CO2 consumption (e.g., [START_REF] Carretier | Mean bedrock-tosaprolite conversion and erosion rates during mountain growth and decline[END_REF][START_REF] Willenbring | Earth is (mostly) flat: Apportionment of the flux of continental sediment over millennial time scales: Geology[END_REF]. However, there is a shortage of data on erosion and weathering fluxes in large cratonic regions in order to estimate their contribution to global silicate weathering (e.g., [START_REF] Gaillardet | Global silicate weathering and CO2 consumption rates deduced from the chemistry of large rivers[END_REF][START_REF] Millot | The global control of silicate weathering rates and the coupling with physical erosion: new insights from rivers of the Canadian Shield[END_REF][START_REF] West | Tectonic and climatic controls on silicate weathering[END_REF]. This paper presents both fluxes in this type of region.

The present study focuses on the comparison of pre-anthropogenic and modern denudation rates in both the Sanaga and Nyong River basins, the main and adjacent river systems of South Cameroon flowing towards the Gulf of Guinea [START_REF] Bird | Effect of forest and savanna vegetation on the carbon-isotope composition of sediments from the Sanaga River[END_REF][START_REF] Dubreuil | Le Bassin de la rivière Sanaga: ORSTOM Monographies Hydrologiques[END_REF][START_REF] Olivry | Fleuves et rivières du Cameroun: Paris[END_REF]. Both basins, devoid of significant floodplains, are mainly developed on the silicate basements of the passive margin (South Cameroon Plateau). The Sanaga River basin experiences a contrasting tropical climate ranging from sub-humid mountainous to humid climates and is impacted by anthropogenic activities, mainly agriculture and damming. By contrast, the Nyong River basin, only under a humid tropical climate, is dam-free and less impacted by agriculture and logging.

The assessment of pre-anthropogenic denudation rates is based on an original dataset for cosmogenic radionuclides ( 10 Be) carried out on sandy sediments sampled in riverbeds. Modern physical erosion rates are assessed from river-gauged total suspended solids from 1968 to 1969 (Sanaga sensu stricto, [START_REF] Dubreuil | Le Bassin de la rivière Sanaga: ORSTOM Monographies Hydrologiques[END_REF]), 1970to 1971(Mbam, Dubreuil et al., 1975) and 1995[START_REF] Ndam Ngoupayou | Bilans hydrogeochimiques sous foret tropicale humide en afrique : du bassin experimental de Nsmi-Zoetele aux reseaux hydrographiques du Nyong et de la Sanaga au sud-Cameroun[END_REF][START_REF] Ndam Ngoupayou | Bilans hydrogeochimiques sous foret tropicale humide en afrique : du bassin experimental de Nsmi-Zoetele aux reseaux hydrographiques du Nyong et de la Sanaga au sud-Cameroun[END_REF] for the Sanaga River and from the SO BVET database (http://bvet.omp.obsmip.fr/index.php) for the Nyong River and its tributaries (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011).

Settings

The two main South Cameroon river basins are considered in this study: the Sanaga and Nyong River basins. The characteristics of the studied sub-basins (population density, climate, geomorphology, land use and land cover) are detailed in Table 1.

The Sanaga River basin (135,000 km 2 ) stretches between latitudes 3°38' N and 7°22' N and longitudes 9°38' E and 14°54' E and is the largest basin in Cameroon (Figure 1). The basin covers different climatic domains extending from a tropical climate with two seasons (mean annual rainfall, MAR, from 1500 to 1900 mm/yr) in the north and northwest, to an equatorial climate with four seasons (MAR from 1600 to 2500 mm/yr) in the south and southwest (Figure 1). In a large part of its basin, the Sanaga River drains the South Cameroon Plateau (650-850 m a.s.l.), a vast undulating landscape locally interrupted by inselbergs with successive steps at fault traces and mostly covered by thick mature lateritic regolith mainly developed on a granito-gneissic basement [START_REF] Ségalen | Les sols et la géomorphologie du Cameroun[END_REF]. The South Cameroon Plateau is referred to as a Miocene lower planation surface [START_REF] Guillocheau | Cenozoic Landscape Evolution in and Around the Congo Basin: Constraints from Sediments and Planation Surfaces, in Geology and Resource Potential of the Congo Basin (de Wit[END_REF]. It is bordered to the north and west by the Cameroonian Ridge, which is composed of a succession of high plateaus and volcanic massifs. This ridge can be subdivided into two very distinct regions: the Adamawa Plateau and the Western Highlands. These topographic units are composed of a Precambrian basement (comprising 89% plutonic and metamorphic rocks), which in places is covered by recent eruptive volcanic rocks and sedimentary formations (Regnoult, 1986). Two large sub-basins of the Sanaga River basin are considered in this study above the Ebebda Bridge: the upper Sanaga River basin sensu stricto and the Mbam River basin (Figure 1, Table 1).

The Nyong River basin (27800 km 2 ) lies between latitudes 2°48'N and 4°32'N and longitudes 9°54'E and 13°30'E. The Nyong River flows in the low-relief South Cameroon Plateau landscape and then joins the coastal plain by a series of falls corresponding to the scarp of the passive margin. The basement of the Nyong River basin is mostly silicates, composed of dominant granito-gneiss (Precambrian and Panafrican in age) intermingled with less abundant mafic to ultramafic rocks from Precambrian greenstone belts (Regnoult, 1986). The seasonal rainfall variations exhibit a typical bimodal distribution with MAR values between 1600 and 1800 mm/yr. The basin is entirely located in the tropical rainforest zone developed on deep mature lateritic regolith (reaching up to 50 m on the plateau) and hydromorphic soils in the valleys. The Upper Nyong basin is covered by semi-deciduous forest characterized by Stertuliaceae and Ulmaceae. Marsh forest and water meadows are found and raffias (Raphia montbuttorum) grow in the swampy depressed zones [START_REF] Santoir | Atlas régional Sud-Cameroun[END_REF] for 150 km upstream of the Upper Nyong basin. Downstream (westwards), the climate passes progressively to an equatorial monsoon climate (2000-3000 mm of rainfall). The climatic transition leads to a change in vegetation cover from semi-deciduous forest to the east to littoral forest (Lophira alata) to the west, passing by evergreen forest (Caesalpinaceae) in-between.

In the whole basin, the vegetation cover is significantly damaged by agroforestry, logging, and slash and burn practices. Human activities include moderate industrial forestry, traditional shifting cultivation (manioc and other tubers, banana, corn, peanuts, cocoa beans and tomatoes) without significant fertilizer inputs. The Nyong River is dam-free.

The Nyong River basin has been monitored since the 60's, but unfortunately not continuously [START_REF] Olivry | Fleuves et rivières du Cameroun: Paris[END_REF]

Sampling and methodology

Historical gauging stations for the Sanaga and Nyong River basins

The monitoring stations for the Sanaga River basin were set up by ORSTOM (now IRD) in partnership with the Centre de Recherches Hydrologiques of IRGM, Yaoundé, Cameroon. The Sanaga sensu stricto and Mbam Rivers have been monitored for discharge since the early 50's. The former stations at the outlet of the basins were located at Nachtigal for the Sanaga River sensu stricto and at Goura for the Mbam River [START_REF] Dubreuil | Le Bassin de la rivière Sanaga: ORSTOM Monographies Hydrologiques[END_REF]. For the Sanaga River sensu stricto the first TSS dataset is available for the years 1968 and 1969 before the Mbakaou dam was constructed.

For the Mbam River the water years 1970-1971 and 1971-1972 are recorded before Bamendjin and the Mape fillings. For the Nyong River, a nested watershed network from 0.5 to 27000 km 2 was sampled during the 2000-2011 period (Table 2).

Total Suspended Solids (TSS) and Total Dissolved Solids (TDS) for the Nyong River basin

The data presented in this study are from the SO BVET stations for the years 2000-2011 (Table 3). Bi-monthly (or higher frequency) water samples were collected between 30-50 cm below the water surface, preferentially where the flow velocity was high enough to allow for a good homogenization of the solid particles of different sizes. In fact, for the large streams of the tropical zone of Africa, including those of Cameroon, the sampling technique along one vertical which is rather simple, fast and practical, gives results that are satisfactory and relatively close to those of the full solid gauging method (e.g., [START_REF] Lienou | Régimes des flux des matières solides en suspension au Cameroun: revue et synthèse à l'échelle des principaux écosystèmes; diversité climatique et actions anthropiques / Regimes of suspended sediment flux in Cameroon: review and synthesis for the main ecosystems; climatic diversity and anthropogenic activities[END_REF]Ndam Ngoupayou et al., 2014;[START_REF] Olivry | Transport de matières sur les grands fleuves des régions intertropicales : les premiers résultats des mesures de flux particulaires sur le bassin du fleuve Congo[END_REF] The water samples were filtered on-site with cellulose acetate 0.45 µm membranes using a polycarbonate Millipore filtration unit of 500 mL. The filters are pre-dried (60°C) and weighted before the filtration procedure in order to determine the TSS. The particulate fractions retained on the filters is obtained by weighting the filter on a Mettler type balance (precision of 0.1 mg) and dried in the oven at 105°C, after desiccation. The estimation of the instantaneous TSS concentration is obtained from the difference in weight between the loaded filter and the filter before filtration for the volume of water brought up to 10 3 mL. For this procedure, Maneux (1998) calculated a theoretical error of 5%, when the suspended sediment concentration is less than or equal to 10 mg L -1 and 3% when it is more than 10 mg L -1 .

TDS is calculated after the following procedure. The filtered water is stored in acid washed Nalgene® polypropylene bottles, either acidified with ultrapure 15N HNO3 for the major cation analyses or non-acidified for the major anion analyses. Conductivity, pH, and water temperature measurements were taken out on-site. Major cations (Ca, Mg, K, Na) and anions (Cl, SO4, NO3) were determined by Ion Chromatography at Geoscience Environnement Toulouse (GET) (Table 3). The typical uncertainty was 5% and the detection limit ranged up to 1 µmol/L. Alkalinity is determined by titration with HNO3 and the Gran method [START_REF] Gran | Determination of the equivalence point in potentiometric titrations[END_REF]. The typical uncertainty was 5% and detection limit ranged up to 1 µmol/L. Aqueous silica concentrations were measured both by standard colorimetry (molybdate blue method) and ICP-MS. The usual incertitude was 5% and the detection limit approached 1 µmol/L. The international standard SLRS-3 was used as a reference.

The Volume Weighted Mean (VWM) of the TDS and TSS concentrations was calculated using Equation 1.

Equation 1 𝑉𝑊𝑀 = ∑ 𝐶 𝑖 𝑉 𝑖 𝑛 𝑖=1 ∑ 𝑉 𝑖 𝑛 𝑖=1 ⁄
The same equation is used to calculate the TDS and TSS VWM concentrations in the stream water, where Ci is the concentration of an instantaneous stream flow i and Vi is the discharge volume (L) for the period between two samplings; the denominator is the whole sampling period discharge. The TDS and TSS values are remarkably constant in the studied river systems with only 20% fluctuation over the sampling period, therefore the dependence of the concentrations on discharge is weak. Moreover, because of the long monitoring duration, the water sampling encompassed some of the highest discharge conditions, such that high magnitude events were properly sampled for the monitoring period.

Pre-anthropogenic denudation rates with 10 Be analyses

For the Sanaga sensu stricto and Mbam River basins, the sandbar sediments for cosmogenic analysis were collected at Ebebda, at the confluence of both rivers.

For the Nyong River basin, eight sampling sites were selected in the upper basin (on the South Cameroon Plateau) and two in the lower basin. On the South Cameroon Plateau, the sites encompass (i) the five stations of the SO-BVET project (Mengong at Nsimi, Awout at Messam, So'o at Pont-So'o, Nyong at Mbalmayo and Olama) and (ii) three additional stations (Bivesse at Zoulabot, Nyong at Ayos and Ebogo). The sampling sites downstream the escarpment of the passive margin encompass the Eseka and Dehane stations on the lower Nyong River. For the Zoulabot, Eseka and Dehane sites, two sand samples have been collected corresponding to different sandbars.

Sample preparation for the 10 Be analyses was carried out at Geosciences Environnement Toulouse (GET) using the procedure described by Von Blanckenburg et al. (1996). Samples were sieved into the 0.5-1 mm fraction. After chemical leaching with HCl and H2SiF6, the samples were etched in HF. A Be carrier (0.3 g of low noise carrier from A. Alimanovic, University of Melbourne, 1155 ppm, 10 Be/ 9 Be<10 -15 ) was added to the samples before complete dissolution in HF. Beryllium was extracted using chromatography as described in von [START_REF] Von Blanckenburg | Separation of 9Be and cosmogenic 10Be from environmental materials and SIMS isotope dilution analysis[END_REF]. Measured 10 Be ratios were corrected using blanks that were processed similarly to the samples. Finally, sample oxidation and targets were prepared and measured with the CEREGE LN2C and ASTER AMS facility (Table 4). The concentration of 10 Be, C 10 Be in the river sand samples allows us to estimate the mean denudation rate ε in the catchment upstream from the sampling site (e.g. [START_REF] Brown | Denudation rates determined from the accumulation of in situ-produced 10Be in the luquillo experimental forest, puerto rico[END_REF][START_REF] Granger | Spatially averaged long-term erosion rates measured from in situ-produced cosmogenic nuclides in alluvial sediment[END_REF]. The recorded denudation rate ε corresponds to the topsoil, because the typical penetration depth of cosmic rays is less than 1m (this problem is addressed in the discussion). We assume that C 10 Be corresponds to a secular equilibrium between the loss by erosion and the gain by production on the Earth's surface. The mean catchment denudation rate ε is calculated using Equation 2. where P is the average catchment production rate, ρ is the rock density (2.7 g/cm 3 for bedrock), Λ is the attenuation length depending on which secondary particle is producing 10 Be in the mineral (Λn = 160 g/cm 2 for neutrons, Λµs = 1500 g/cm 2 for negative muons and Λµf = 5300 g/cm 2 for fast muons; [START_REF] Braucher | In situ produced Be-10 measurements at great depths: implications for production rates by fast muons[END_REF]). Using the new muon contribution estimate of [START_REF] Braucher | Determination of muon attenuation lengths in depth profiles from in situ produced cosmogenic nuclides[END_REF] (with an attenuation length of 4300 g/cm 2 for muons without distinguishing between negative and fast muons), the erosion rates are 0.6% smaller. The 10 Be radioactive decay is usually neglected as proposed by previous works [START_REF] Brown | Denudation rates determined from the accumulation of in situ-produced 10Be in the luquillo experimental forest, puerto rico[END_REF][START_REF] Granger | Spatially averaged long-term erosion rates measured from in situ-produced cosmogenic nuclides in alluvial sediment[END_REF][START_REF] Von Blanckenburg | The control mechanisms of erosion and weathering at basin scale from cosmogenic nuclides in river sediment[END_REF]. Introducing radioactive decay allows for the formal calculation of ε, but it is possible to show that introducing radioactive decay would decrease ε by no more than λρ/Λn~0.3 m/Ma, which is very low in comparison with the erosion rates calculated below [START_REF] Brown | Denudation rates determined from the accumulation of in situ-produced 10Be in the luquillo experimental forest, puerto rico[END_REF][START_REF] Granger | Spatially averaged long-term erosion rates measured from in situ-produced cosmogenic nuclides in alluvial sediment[END_REF].

The above description is valid if all denudation comes from material that is eroded near the Earth's surface (the depth is smaller than the attenuation length). For a thick regolith like in Cameroon, the method needs to be modified or considered with regards to two specific points. (1) The density evolves from bedrock to topsoil. Denudation fluxes (F, kg/m3/yr) can be written without taking the density into account (Equation 3). Thus we treat denudation as a flux, rather than as a vertical velocity.

(2) The representativeness of the CRN concentration in quartz goes through the evaluation of quartz enrichment from bedrock to soil; as such it is commonly assumed that quartz is essentially insoluble and only removed by physical erosion, while the denudation of the bulk soil occurs by both physical erosion and chemical weathering (text inspired by [START_REF] Granger | Cosmogenic Nuclides in Weathering and Erosion[END_REF]; also see [START_REF] Dixon | The critical role of climate and saprolite weathering in landscape evolution: Earth Surface Processes and Landforms[END_REF][START_REF] Hewawasam | Slow advance of the weathering front during deep, supply-limited saprolite formation in the tropical Highlands of Sri Lanka[END_REF][START_REF] Riebe | Long-term rates of chemical weathering and physical erosion from cosmogenic nuclides and geochemical mass balance[END_REF]. This enrichment is calculated through the CEF (chemical erosion factor), defined by Equation 4:

Equation 4 𝐶𝐸𝐹 = 𝑅𝑠𝑝𝑟 (𝑅𝑠𝑠 (1 -𝑒 -𝜌 𝑠 ℎ 𝑠 Λ ⁄ ) + 𝑒 -𝜌 𝑠 ℎ 𝑠 Λ ⁄ )
where Rspr and Rss are the concentration ratios for an immobile element between saprolite and rock and between soil and saprolite, respectively; ρs and hs are the soil density and thickness [START_REF] Riebe | Quantifying effects of deep and near-surface chemical erosion on cosmogenic nuclides in soils, saprolite, and sediment[END_REF]. In the literature, the simplified expression CEF~Rsr (Rsr is an immobile element concentration ratio between soil and rock) can also be found (e.g., [START_REF] Dixon | The critical role of climate and saprolite weathering in landscape evolution: Earth Surface Processes and Landforms[END_REF][START_REF] Hewawasam | Slow advance of the weathering front during deep, supply-limited saprolite formation in the tropical Highlands of Sri Lanka[END_REF]. We use the information collected around the Nsimi watershed (pits 1L6 andIL5, Braun et al., 2005, 2012), expected to be representative of the Nyong watershed and at the Goyoum site (pits 319 and 341, [START_REF] Braun | Solid/Liquid REE Fractionation in the Lateritic System of Goyoum, East Cameroon: The Implication for the Present Dynamics of the Soil Covers of the Humid Tropical Regions[END_REF] located in the Sanaga catchment. We selected the immobile elements Zr and Th and found similar values for the two CEF evaluations: CEF~3.2 ± 1 (Nsimi) and CEF~3.3 ± 0.6 (Goyoum); thus in the following we choose a value of 3.2 ± 1 as representative for hillslopes. In alluvial valleys, the CEF may be lower, as suggested by chemical analyses of pit 313 at the Goyoum site (CEF~2.3 ± 1.3, Braun et al., 1998).

Results

Physical characteristics of the river basins

The Nyong River catchment can be divided into two parts. Upstream, it flows on the South Cameroon Plateau (~650 m, Figure 2), where the slope is low at 0.05 m/m. At Olama the slope is approximately 0.015%; but the values are higher for the upper basin (0.11% at Ayos) and for the stations on the tributaries (0.1 to 1.3%). Between the OLAM and ESE stations, the river crosses the plateau edge (Figure 2), but the average slope remains very gentle on the order of 0.5% (the vertical elevation seen in the profile in Figure 2 is exaggerated by a factor of ~1000). This may result from the resolution and precision of the SRTM DEM. Here, the slope is low and the data is likely dominated by the noise on the SRTM dataset. The catchment pre-anthropogenic denudation rates obtained by 10 Be are expressed in both mm/ky and t/km 2 /yr and are presented in Table 5. Once corrected for quartz enrichment, they range from 4.8 to 40.3 mm/kyr (4.8-40.3 m/Ma or 13-109 t/km 2 /yr), corresponding to relatively low denudation rates. These denudation rates are in the lower range of the worldwide dataset provided by [START_REF] Portenga | Understanding Earth's eroding surface with 10Be[END_REF]. In three sites we collected two samples in different parts of the riverbed (Bivesse River at Zoulabot, Nyong River at Eseka and Nyong River at Dehane): the concentrations never differ by more than 20% (Table 4). In practice, this denudation rate is integrated over a "characteristic time", which is the time needed to erode a strip of rock for which the thickness is the attenuation length (we only consider this for the most efficient producing rays: neutrons). Consequently, the lowest denudation rates are integrated over the longest period of time. This period is calculated to be between 48 and 399 kyrs; it is often more than 100 kyrs implying that this denudation rate integrates both glacial and interglacial climates (Table 5).

In Figure 3, we plotted the 10 Be-derived denudation rates as a function of the classically used geomorphic parameters: basin area and basin slope. Interestingly, and counter-intuitively, the denudation rate increases with the basin area while the two variables are expected to be independent. On the contrary, denudation is not clearly dependent on basin slope as observed elsewhere [START_REF] Carretier | Slope and climate variability control of erosion in the Andes of central Chile[END_REF].

Discussion

Contemporary versus long-term denudation rates in South Cameroon

The analyses presented here allow for the comparison of two time scales, from the decennial time scale (gauging) to several tens of kyrs ( 10 Be). The 10 Be time scale is smaller for higher denudation rates and varies from ~50 kyrs (MBAM, SANA, DEHJ, DEHR) to more than 200 kyrs (AYOS, EXUT, BIVB, BIVG, AWOU and PSOO): as a consequence, our analyses encompass multiple glacial/interglacial cycles for the low denudation rate samples, while it only integrates over the last glacial period for MBAM, SANA, DEHJ and DEHR.

In our dataset, the smallest 10 Be-derived denudation rates are observed for the smallest catchments, and Figure 3 indicates a simple relationship with the denudation rate that is proportional to the catchment area, at least up to 200,000 km 2 , i.e., for the Nyong catchment when it is only located on the South-Cameroon Plateau (the Eseka and Dehane stations are downslope from the plateau edge). The only exception is EBOG, for which the catchment is quite small (3096 km 2 ) and the 10 Be-derived denudation rate is quite large (33.04 t/km 2 /yr). It should to be emphasized that the EBOG sampling point is located downstream from the confluence with the Mefou tributary which drains the urban and peri-urban area of Yaoundé city; this could explain the increase in sediment river load at that specific location.

The catchment mean denudation rate (in m/yr or specific sediment yield in t/km 2 /yr) has been found to either decrease (e.g., [START_REF] Dedkov | The relationship between sediment yield and drainage basin area, in Sediment Transfer throngh the Fluvial System[END_REF][START_REF] Dendy | Sediment yield-runoff-drainage area relationships in the United States[END_REF][START_REF] Summerfield | Natural controls of fluvial denudation rates in major world drainage basins[END_REF][START_REF] Syvitski | Geology, Geography, and Humans Battle for Dominance over the Delivery of Fluvial Sediment to the Coastal Ocean[END_REF] or increase (e.g., [START_REF] Dedkov | The relationship between sediment yield and drainage basin area, in Erosion and sediment yield in mountain areas of the World[END_REF] with the catchment area. Based on a synthesis of these works and numerical modelling, [START_REF] Birkinshaw | Model study of the relationship between sediment yield and river basin area: Earth Surface Processes and Landforms[END_REF] concluded that a decrease mostly occurs in catchments dominated by hillslope erosion, whereas the reverse is observed in catchments where sediments are mainly produced by river bank erosion. These relationships may also be explained by a heterogeneous distribution of the erosive rainfall vegetation cover, natural or artificial sediment traps or land use (Birkinshaw and Bathurst, 2006 and references herein). In the Cameroon catchments, the forest-cover, which may limit sediment production, does not seem to decrease downstream, but the rainfall slightly increases downstream. In the Nyong River basin, there is a rainfall gradient with the Mean Annual Rainfall varying from 3000 mm/yr seaward to 1600 mm/yr inland (see the map in Fig. 7 provided in [START_REF] Braun | Present weathering rates in a humid tropical watershed: Nsimi, South Cameroon[END_REF]. Thus, the observed positive relationship between the catchment mean erosion rate and area could be explained by either by a significant contribution of river bank erosion or by a downward increase in rainfall in this very gentle topography. In the case of the Nyong River, the river banks are invaded by thick floating vegetation mats which may limit bank failure and physical erosion. Downstream, the combination of increasing rainfall and passive margin scarp would increase the river erosion capacity. Figure 4 displays the relationships between TSS, TDS and the 10 Be-derived denudation rates. First, the Nyong basins display very low physical denudation rates that are lower than the chemical rates. For the Sanaga River, both of these rates are quite stable but when using the physical denudation rates recorded before dam building, TSS is higher than TDS. For the Mbam catchment, the physical denudation rate dominates (~75%) the total denudation rate. With regards to the total short-term denudation rate vs. the 10 Be denudation rates, most of the catchment points are below the 2:1 line in Figure 4: the short-term denudation rate is less than half the 10 Be-derived denudation rate. The exact ratio is uncertain and this evaluation (the short-term rate is two times lower than the long-term denudation rate) must be taken with caution: as described above, these values have been corrected for quartz enrichment within the saprolite. This correction relies on two local pits and the uncertainty is likely to be 30% but may be up to 50% (see the Sampling and methodology section). Some catchment points, in contrast to the others, lie clearly above the 2:1 line. They correspond to catchments with either enhanced anthropogenic denudation (MBAM) or with anomalous solid discharge (AWOU and PSOO).

Our analysis sheds light on weathering processes and the saprolite equilibrium. If the weathering profile is at steady state, the weathering front propagates downward at the same velocity (w) as the surface downwears (ε). Physical denudation is φε= ε.ρsp , where ρsp is the saprolite density; similarly, the chemical denudation is φw = w (ρrρsp), where ρsp is the unweathered rock density. As discussed aboven, the immobile elements Zr and Th show that the CEF ~3.2 ± 1, implying that chemical and physical denudation accounts for 55-72% and 28-45% of the total denudation, respectively. This proportion is independently confirmed by the ratio between TDS and TSS (Table 5) indicating a usual chemical denudation proportion of ~60% out of the total denudation. This proportion is lower for PSOO and SANA (52%) and very low for MBAM (26%), indicating a higher contribution of physical denudation; this confirms the observations made beforehand that these catchments are affected by anthropogenic disturbances.

Comparison of the tropical cratonic denudation rates

Figure 5 shows various estimates of the cratonic denudation rates through different time scales. Gardner et al. (1987) proposed that the comparison of two time-dependent variables could introduce a bias when comparing various time-scales. They proposed a correction, which we used here following [START_REF] Beauvais | Modes, tempo, and spatial variability of Cenozoic cratonic denudation: The West African example: Geochemistry[END_REF]. However, this correction accounts for a maximum difference of 50%, and we prefer keeping the raw values in Figure 5. It appears from Figure 5 that our estimates fall within the ranges reported in the literature: 5-100 m/Ma (10-200 t/km 2 /yr) for river load measurements and 1-20 m/Ma (2-50 t/km 2 /yr) for CRN. The long-term estimates are smaller than the millennial CRN estimates. In turn, the river loads indicate that the modern-day erosion rates are higher.

Conclusion

Denudation rates in Cameroon have been estimated by gauging data and cosmogenic radionuclides (CRN, 10 Be) along the Nyong catchment draining the South Cameroon Plateau as well as in two large rivers in northern Cameroun: the Sanaga River and Mbam River. The two methods have very different characteristic time scales: 10 yrs and 100 kyrs for gauging and CRN data, respectively.

Modern fluxes (from gauging data) range from 5 to 100 m/Ma (10-200 t/km 2 /yr). The contribution of chemical denudation is typically 60% of the total denudation. When this ratio differs, anthropogenic effects may occur.

10 Be fluxes must be corrected as proposed by previous authors for sites with a thick regolith (saprolite + soil). These fluxes are slightly lower than modern-day fluxes, ranging from 4.8 to 40.3 m/Ma or 13 to 109 t/km 2 /yr; however, this difference is similar to that observed in other stable tropical areas. The data on the extent of chemical weathering from deep regolith weathering (used to derive the CEF) are confirmed by the data from the river loads (TDS/TSS ratio), suggesting that the relative importance of chemical weathering in the overall denudation of the landscape has remained relatively constant over time.

These fluxes are low and are typical of low-denudation areas with a tendency to increase with the catchment area.

Ackowledgements

In Cameroon, the multidisciplinary research carried on the Nsimi watershed began in 1994 under the control of IRD and IRGM-CRH (Institut de Recherche Géologique et Minière / Centre de Recherche Hydrologique, Yaoundé, Cameroon). Apart from the specific support from the French Institute of Research for Development (IRD), our project benefited from funding from the national programs PROSE/PEGI (Programme Sol Erosion/Programme Environnement Géosphère Intertropicale) and PNSE (Programme National Sol-Erosion) dedicated to a better understanding of the humid tropical ecosystems These programs were funded both by IRD and INSU / CNRS (Institut National des Sciences de l'Univers / Centre National de la Recherche Scientifique). The long term monitoring on Nsimi is supported by the project SO BVET (Service Observation Recherche en Environnement -Basins Versants Expérimentaux

Figure 1 .

 1 Figure 1. (Left) Study area shaded relief with the main stations and related catchments. Two rivers are investigated: the Sanaga divided into two tributaries, Sanaga (SANA) and Mbam (MBAM); and the Nyong river (AYOS, MBAL, BIV, AWOU, EXUT, EBOG, PSOO, OLAM, ESE and DEH). (Right, not present in published paper) Photograph of AWOU station.

  . Since 2001, a nested network of monitored stations has been set up on the Upper Nyong basin within the framework of the SO BVET project. It encompasses five hydrological stations in the So'o basin, a southern tributary of the Nyong River. These are, from upstream to downstream: Nsimi at the outlet of the small experimental Mengong watershed (14 km from Zoétélé, 120 km SSE from Yaoundé), Messam on the Awout stream, Pont So'o on the So'o River, Mbalmayo and Olama on the Nyong Rivers; water from the So'o Basin mix upstream from Olama with the water coming from the eastern Upper Nyong basin flowing into Mbalmayo (Erreur ! Source du renvoi introuvable.).

Table 3 .

 3 Water characteristics for the Nyong catchment stations from monthly sampling during 1998/99 cyclex: Temperature (temp.) is in °C, electric conductivity (E.C.) in µS/cm; major cations and anions, as well as dissolved silica concentrations, are in µmol/L; sum of cations (SCat, including protons) and sum of anions (SAn) in µeq/L; dissolved organic carbon (DOC), total of mineral dissolved species (TDS) and total of suspended solids (TSS) concentrations are in mg/L; given pH values correspond to field measurements, but for the calculation of SCat, SAn and bicarbonate concentrations, pH values determined at the laboratory were used; the arithmetic mean (mean), standard deviation (±σ) and discharge-weighted mean (DWM) are given for most parameters; fluxes are expressed in t/yr (except at spring and outlet of Mengong, in kg/yr), specific fluxes are in kg/km 2 /yr.

Table 4 .

 4 Cosmogenic 10 Be analytical data. N 10 Be: Concentration of 10 Be in the sample [ 10 Be] is the concentration in the sample and +/-its uncertainty.

  /𝑚 2 /𝑦𝑟] = 𝜀[𝑐𝑚/𝑦𝑟] × 𝜌[𝑔/𝑐𝑚 3

Figure 2 .

 2 Figure 2. Map and longstream profile of the Nyong River catchment, showing the sampling stations. Large dots correspond to stations along the Nyong main stream; small dots are locations on the studied tributary. All the stations except DEH and ESE are located on the South Cameroon Plateau. The profile was smoothed using a 5km sliding window.

4. 2 .

 2 Pre-anthropogenic denudation rates ( 10 Be) Specific fluxes come from the ORE-BVET project fot the Nyong stations (years 2000-2011), from Ndam (1997) for the Mbam and the Sanaga (cycle 1995/96). Erosion rates are calcutated for a upper soil density of 1,3.

Table 5 .

 5 Comparison between short-term (gauging) and medium-term ( 10 Be) denudation rates. P10Be is the catchment-averaged production of 10Be. E10Be and E10Be_c are the raw and corrected (with CEF) denudation rates from 10Be expressed in mm/kyr and t/km 2 /yr. ±σ is the 1σ uncertainty on the preceding column value. The contemporary denudation rate is the sum TDS and TSS. Chem. Denud. Prop. is the proportion of chemical denudation on total denudation.

Figure 3 .

 3 Figure 3. 10 Be denudation rates in function of catchment physical parameters: area, slope. The grey and bigger symbols are Mbam and Sanaga catchments.

Figure 4 .

 4 Figure 4. Contemporary vs 10 Be denudation rates. The contemporary denudation rate is the sum of TSS and TDS. Empty symbols represent the situation before dam building. Dashed lines are 1:1 and 2:1 lines.

Figure 5 .

 5 Figure 5. Cameroon denudation rates compared with other tropical cratonic denudation rates as compiled by Beauvais and Chardon (2013), updated with few recent studies (Bierman et al., 2014; Codilean et al., 2014; Mandal et al., 2015; Wittmann et al., 2010). Symbols indicate the methods used: river loads, CRN (cosmogenic radionuclides as 10 Be in this study), local relief (calculation of erosion of an ancient surface) and AFTA (Apatite Fission Track Analysis). Colors indicate the geographic location, grey symbols coming from the present dataset. Dashed lines connect samples various samples from the same area acquired with the same method.

Table 1 . Settings of the different studied basins.

 1

Table 2 . Gauging/sampling station and corresponding catchment characteristics. Asterisks denote SO BVET sites and italics estimated values.

 2

  Discharge is determined from the daily-measured water stages by local observers on limnimetric scales (staff gauges), using calibration curves drawn from a gauging

	dataset	for	each	station	(Table	2	and	http://bvet.obs-
	mip.fr/en/stations/cameroon/meteo-nyong).