Valérie David
email: valerie.david@u-bordeaux.fr

Sébastien Tortajada

Nicolas Savoye

Martine Bréret

Nicolas Lachaussée

Olivier Philippine

François-Xavier Robin

Christine Dupuy

Martine Breret

Impact of human activities on the spatio-seasonal dynamics of plankton diversity in drained marshes and consequences on eutrophication

Keywords: drained marshes, functional diversity, plankton, human control, eutrophication

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

water temperature, low light availability and high flood is actually related to the dominance of tychopelagic phytoplankton and K-strategists zooplankton. Spring and summer were characterized by i) the succession of pelagic large cells, small cells and then taxa with alternatives food strategies due to nitrogen limitation and phosphorous desorption from the sediment leading to eutrophication processes and ii) the dominance of r-strategists for mesozooplankton.

The artificial summer replenishment acts positively on water quality by decreasing the eutrophication processes since the nitrogen inputs limit the proliferation of phytoplankton mixotrophs and diazotrophs and increase the ecological efficiency during the warm period.

Both small and large catchment basins may lead to summer eutrophication processes in drained marshes since the largest ones imply higher hydrodynamic features at the root of large inputs of nitrogen nutrient favoring the phytoplankton development while the smallest ones exhibit hypoxia problems due to high proliferation of macrophytes. Urbanized marshes are less subjected to eutrophication during summer than non urbanized marshes due to more recurrent nutrient inputs from urban waste. However they exhibited a lower ecological efficiency. The results suggest that a better management of the hydrodynamics of such anthropogenic systems can avoid eutrophication risks on coastal areas.

Introduction

Non tidal wetlands, such as marshes, provide several goods and services to human populations despite their low surface area at the global scale [START_REF] Costanza | The value of the world's ecosystem services and natural capital[END_REF]) -water flow regulation, waste treatment, nutrient cycling, moderation of disturbance and nursery services [START_REF] De Groot | Global estimates of the value of ecosystems and their services in monetary units[END_REF][START_REF] Mea | Millenium Ecosystem Assessment. Ecosystems and Human Well-being: General Synthesis[END_REF]. Nowadays, preservation and restauration of such systems appear thus essential to provide more water of better quality in a context of increasing human population and activities (industry, agriculture) on coastline as well as to prevent waste discharge to marine systems [START_REF] Lotze | Depletion, Degradation, and Recovery Potential of Estuaries and Coastal Seas[END_REF][START_REF] Lubchenco | The Sustainable Biosphere Initiative: an ecological research Agenda: a Report from the ecological Society of America[END_REF][START_REF] Meybeck | Water quality assessments -A guide to use of biota, sediments and water in environmental monitpring[END_REF][START_REF] Noges | Assessment of the ecological status of European surface waters: a work in progress[END_REF].

Through history, polderization such as drainage of wetlands for human uses has left few natural and pristine marshlands. In such systems, hydrodynamic flows are now controlled by human management. Drained marshes support a large range of anthropogenic activities, like shellfish and fish farming, agriculture, water purification facilities and cattle husbandry while maintaining at least a part of wetlands regulating services -e.g. ability to remove nitrate drained from culture soils on catchment basin [START_REF] Tortajada | Variability of fresh-and salt-water marshes characteristics on the west coast of France: A spatio-temporal assessment[END_REF]).

However, polder areas are particularly sensitives to climate change through storm floods events causing marine submersion and thus high risks for local economical activities and populations [START_REF] Chaumillon | Storm-induced marine flooding: Lessons from a multidisciplinary approach[END_REF]. In order to increase their resilience, socio-economic vulnerability of these areas support the idea of 'Growing with the sea' rather than 'fighting against it'. Management policies that restore natural coastal processes along coastline letting natural and socio-ecosystems interact more dynamically are thus more and more adopted by several countries [START_REF] Cormier | Marine and coastal ecosystem-based risk management handbook[END_REF][START_REF] Klein | Resilience and Vulnerability: Coastal Dynamics or Dutch Dikes?[END_REF]. However, country plannings lead to compromise states between natural coastal dynamic systems and artificial anthropogenic systems entirely protected by dutch dikes. They must thus be done in accordance with the stakeholders to be both environmentally and economically acceptable [START_REF] Klein | Resilience and Vulnerability: Coastal Dynamics or Dutch Dikes?[END_REF]. In others words, they should consider the better compromise between the profits that such systems provide through the human activities developed in and the services they may assure in more natural state. In this context, a better kwowledge of drained marshes functioning is essential to evaluate their ability to maintain ecological functions and thus related services to human in order to adapt their restauration in a context of sustainable development.

Water quality in freshwater marshes, in particular drained marshes, have been poorly studied worldwide . Due to their high vicinity to terrestrial inputs and human activities, they are even more sensitive to eutrophication than rivers and lakes due to water stagnation.

Moreover, catchment basins characterised by large agriculture areas may imply sulfate accumulation that may have consequences on the biogeochemical cycle of phosphorous [START_REF] Correll | The role of phosphorus in the eutrophication of receiving waters: a review[END_REF][START_REF] Lucassen | Effects of stagnating sulphate-rich groundwater on the mobility of phosphate in freshwater wetlands: a field experiment[END_REF][START_REF] Schindler | Evolution of phosphorous limitation in lakes[END_REF]. Previous works performed on freshwater drained marshes want to propose several hypothesis about the drained marshes management. They first showed that a higher water renewal through natural groundwater inputs or artificial replenishment by adjacent rivers during summer reduces the eutrophication processes. Moreover, a high risk of eutrophication linked to the size of the catchment basin, mainly dominated by agriculture is advanced [START_REF] Tortajada | Variability of fresh-and salt-water marshes characteristics on the west coast of France: A spatio-temporal assessment[END_REF]. Finally, highly urbanized marshes may also present such eutrophication risks through nutrients inputs by sewage discharges. Consequently, these first results suggest that a better knowledge about the role of these several activities on such anthropo-systems may provide a better management and thus limit the eutrophication risks on coastal areas. [START_REF] Tortajada | Variability of fresh-and salt-water marshes characteristics on the west coast of France: A spatio-temporal assessment[END_REF] suggested that a better understanding of the processes behind these risks should be performed by studying the structure of the planktonic food webs.

Ecosystem functioning is actually driven by the species that are living in [START_REF] Tilman | The influence of functional diversity and composition on ecosystem processes[END_REF][START_REF] Worm | Impacts of Biodiversity Loss on Ocean Ecosystem Services[END_REF]) and ecological functions and services are efficient especially as their biodiversity is high [START_REF] Cardinale | Biodiversity loss and its impact on humanity[END_REF]. Biodiversity plays actually a buffering role on the resilience of the ecological functions and services provided by the ecosystems to human [START_REF] Worm | Impacts of Biodiversity Loss on Ocean Ecosystem Services[END_REF]. Moreover, functional diversity may have a greater impact on ecosystem functioning than taxonomic diversity since the richness in functional roles may be a more powerful driver of the processes than the species richness [START_REF] Downing | Ecosystem consequences of species richness and composition in pond food webs[END_REF]Leibold 2002, Tilman et al. 1997). Functional diversity studies consist in aggregating the overwhelmingly diversity of organisms into groups of species sharing similar trait expression [START_REF] Mc Gill | Rebuilding community ecology from functional traits[END_REF]). The recent interest in functional diversity through the trait-based approach is explained by its ability to explain the organization of ecological communities and species niches (Litchman andKlausmeier 2008, Litchman et al. 2013). However, the methodological challenge is to find, among the increasing availability of traits, the ones available in the literature as well as the ones that best link communities to environment [START_REF] Anderson | Plankton functional type modelling: running before we can walk?[END_REF][START_REF] Dray | Combining the fourth-corner and the RLQ methods for assessing trait responses to environmental variation[END_REF][START_REF] Kleyer | Assessing species and community functional responses to environmental gradients: which multivariate methods?[END_REF].

The main objectives of this study are thus to use the functional diversity of two planktonic functional compartments, the nano-microphytoplankton (phytoplankton of size 2-200µm) and the mesozooplankton (zooplankton larger than 200µm), in order to better understand i) the drained marshes functioning and their related ecological functions, ii) the impacts of human control (replenishment) and human activities on the catchment basin (agriculture, urbanization). The several hypothesis proposed by [START_REF] Tortajada | Variability of fresh-and salt-water marshes characteristics on the west coast of France: A spatio-temporal assessment[END_REF] were tested: 1) higher nutrient inputs from the catchment basin or urbanized activities may limit the proliferation of diazotrophs and mixotrophs phytoplankton functional groups and thus favor the ecological efficiency, ii) lower nutrient inputs and higher stagnation of the water may favor the macrophytes development versus phytoplankton development.

Material and methods

Study site

The Charente-Maritime marshes represent the second-largest French wetland zone (100,000 hectares; 46°10' N, 01°12' W; Figure 1). This transitional area between continent, ocean and atmosphere exhibits a high diversity of drained marsh types with replenished and unreplenished drained marshes with anthropogenic uses such as agriculture or urbanization on their catchment basins. Drained freshwater marshes constitute artificial hydrographic networks of channels and ditches. For all marshes, human control on sea locks allows to prevent drying and flooding throughout the year. Moreover, for some marshes, a replenishment channel brings water from the Charente River to drained marshes and prevents artificially drying during summer while groundwater may assure a 'natural' form of a replenishment for certain marshes (i.e, replenished drained marshes).

Sampling strategy

The 7 stations were sampled monthly from February 2009 to February 2010 along a water renewal gradient. On one hand, one station corresponds to unreplenished drained marshes (stations 7; Figure 1) and six to replenished drained marshes with one natural replenishment (station 6). On the other hand, five station present an artificial replenishment from the Charente River (stations 20 and 21, 36, 39 and 40). The several sampling marshes presented different catchment basin surfaces with large culture areas that may influence their water quality ('large ', i.e, >4000ha, for station 6, 'median', about 2000ha, for stations 7, 21 and 40 and 'small', i.e, <1500ha, for 20, 36, 39). Moreover, the smallest catchment basins were characterized by a high proliferation of macrophytes, mainly duckweeds, especially during summer. Finally, an important urbanization was present for the station 20 with urban constructions presenting water treatment plant or houseold sewage discharges.

The replenishment effect was analyzed by confronting the station 7 (No replenishment) vs the stations 21, 40 (with replenishment) presenting a same catchment basin area ('median' size) and no urbanization at the vicinity. The effect of the catchment basin size was studied by confronting 3 groups: stations 6 ('large'), 21, 40 ('median') and 36, 39 ('small') which are replenished marshes with no urbanization at the vicinity. Finally, the urbanization effect was analyzed by comparing stations 36, 39 (none urbanization at the vicinity) versus station 20 (high urbanization) which are replenished marshes with small catchment basin areas (Figure 1).

For each marsh, samples were realised in the middle of the main channel of the network to avoid the edge effect. For each station/date (7 stations x 13 months), several physico-chemical and biological parameters were sampled. The four seasons were determined considering the calendar information (winter, spring, summer and fall) as well as the period of sea lock gates closing controlled by the stakeholders (usually between spring and summer).

Abiotic parameters

At each station/date, conductivity (Cond), water temperature (Twater), pH and dissolved oxygen were evaluated in situ with a probe (WTW CellOx325-3); It should be noted that dissolved oxygen is expressed in % relatively to the oxygen saturation throughout the manuscript. Nutrients concentrations were also estimated according to [START_REF] Masclaux | Planktonic food web structure and dynamic in freshwater marshes after a lock closing in early spring[END_REF]. Nitrates and Nitrites concentrations were pooled as NOx. The ratio N/P corresponding to the ratio (NO3 -+NO2 -+NH4 + )/PO4 3-was also considered.

Particulate material

Suspended particulate matter (SPM) as well as C and N elemental (C/N) and isotopic (δ 13 C and δ 15 N) ratios of particulate organic matter (POM) were assessed according to [START_REF] Savoye | Origin and composition of particulate organic matter in a macrotidal estuary: the Gironde Estuary[END_REF].

Planktonic communities

For each station/date, in situ water was prefiltrered on 200µm. Chlorophyll a concentrations was used as an index of phytoplankton biomass (Phyto). The latter were evaluated for three-size classes of phytoplankton (pico-, nano and microphytoplankton) using fractioned filtration: 200 µm prefiltrered water was successively filtered on a 20µm polycarbonate filter (microphytoplankton, ph3), a 3µm polycarbonate filter (nanophytoplankton, ph2) and then a GF/F filters (0.7 μm; picophytoplankton, ph1). Filters were analyzed as described according to [START_REF] Masclaux | Planktonic food web structure and dynamic in freshwater marshes after a lock closing in early spring[END_REF]. Triplicates were performed and averaged for each station/date (at least 100 mL filtered per replicate). Chlorophyll a concentrations were then converted into carbon via the carbon to chlorophyll a ratio for each size-class, C= 50 Chla; [START_REF] Banse | Determining the carbon-to-chlorophyll ratio of natural phytoplankton[END_REF] and were expressed in percent of the total chlorophyll biomass according to references referred above. The active chlorophyll a (Active Chla) was defined by the ratio Chla / (Chla + pheo) [START_REF] Irigoien | Light limitation and distribution of chlorophyll pigments in a highly turbid estuary: the Gironde estuary (SW France)[END_REF].

For each station/date, three subsamples of heterotrophic prokaryots (HP) and picophytoplankton were estimated according to [START_REF] Masclaux | Planktonic food web structure and dynamic in freshwater marshes after a lock closing in early spring[END_REF]. Abundances were averaged for each station/date and HP abundances were converted into carbon biomasses (HP) according to [START_REF] Lee | Relationships between biovolume and biomass of naturally derived marine bacterioplankton[END_REF]. Picophytoplankton were considered in order to consider all the biological compartments presents in the planktonic food web as well as HP and others environmental parameters.

Protozoa diversity, abundances of heterotrophic nanoflagellates and nanomicrophytoplankton were estimated by the Uthermohl method and converted in biovolumes (µm 3 ) by applying standard geometric formulae to each taxon [START_REF] Hillebrand | Biovolume calculation for pelagic and benthic microalgae[END_REF] according to [START_REF] Masclaux | Planktonic food web structure and dynamic in freshwater marshes after a lock closing in early spring[END_REF]. Cell carbon were computed per taxon/functional groups with conversion factors of 0.19 and 0.15 pgC µm -3 for ciliates and nanoflagellates, respectively [START_REF] Sakka Hlaili | The planktonic food web of the Bizerte lagoon (south-western Mediterranean) during summer: I. Spatial distribution under different anthropogenic pressures[END_REF]. Average abundances of each taxon/functional groups allowed then to calculate the total carbon biomass of nano-microzooplankton per station/date (Microzoo). Moreover, tychoplankton had been considered has as temporary plankton organism even if it may be also have a benthic status growing in the sediment.

Mesozooplankton was sampled at 1-m depth with a portable pump-based zooplankton sampler equipped with a microprocessor-that controlled flow sensor for precise determination of the volume of water processed by the sampler [START_REF] Nayar | A portable, low cost, multipurpose surfacesubsurface plankton sampler[END_REF]: Two hundred liters were pumped for each station/date and retrieved on a 200µm-mesh-size sieve. Mesozooplankton was fixed in 5% (final concentration) water/buffered formalin and identified to the lowest taxonomic level possible under a dissecting stereomicroscope (×63). The determination and measurements were performed on 200 individuals per sample [START_REF] Frontier | Calcul de l'erreur sur un comptage de zooplancton[END_REF]. Conversion in carbon biomasses per taxon was performed according to [START_REF] Masclaux | Planktonic food web structure and dynamic in freshwater marshes after a lock closing in early spring[END_REF] and allowed to estimate the total mesozooplankton carbon biomasses (Mesozoo).

The ecological efficiency was used as an index of the efficiency with which the energy is transferred from the first to the last trophic level in the Planktonic Trophic Pathway.

It was estimated as the ratio between mesozooplankton and total phytoplankton biomasses [START_REF] Grami | The plankton food web of the Bizerte Lagoon (South-western Mediterranean): II. Carbon steady-state modelling using inverse analysis[END_REF]).

Specific and functional diversity of planktonic compartments

Nano-microphytoplankton and mesozooplankton compartments present both a high diversity of functional groups that allows them to adapt to several environmental conditions [START_REF] Barnett | Functional diversity of crustacean zooplankton communities: towards a trait-based classification[END_REF][START_REF] Litchman | Trait-Based Community Ecology of Phytoplankton[END_REF][START_REF] Litchman | Trait-based aproaches to zooplankton communities[END_REF]) and a low lifespan that provides them a high reactivity to environmental changes of both climate and anthropogenic origins [START_REF] Beaugrand | Monitoring pelagic ecosystems using plankton indicators[END_REF], David et al. 2012).

• Nano-microphytoplankton

158 taxonomic units of nano-microphytoplankton were observed among 7 taxonomic groups: Bacillariophyta, Chlorophyta, Chrysophyta, Cryptophyta, Haptophyta, Dinophyta, Euglena and Cyanobacteria. They were classified according to several functional traits based upon their availability to metazooplankton grazers and their resource acquisition: both types of traits might traduce their relationships with others planktonic compartments involved in the planktonic trophic pathways as well as their Life habitat (Litchman andKlausmeier 2008, Reynolds 2006).

• The cell biovolume and surface: when counting, each individual cell was measured using a calibrated ocular micrometer. Biovolumes (µm 3 ) and surfaces (µm 2 ) were estimated by applying standard geometric formulae to each taxon [START_REF] Hillebrand | Biovolume calculation for pelagic and benthic microalgae[END_REF]).

• Morphological criteria: the surface/volume ratio and the maximum linear dimension*S/V proposed by Alves- [START_REF] Alves-De-Souza | Functional groups in marine phytoplankton assemblages dominated by diatoms in fjords of southern Chile[END_REF] were also used as indices of the C-S-R strategies for phytoplankton (Reynolds 2006, Reynolds et al. 2002).

• Cell shape: algal shapes might influence the ingestion ability by zooplankters [START_REF] Hartmann | Mechanisms of food selection in Daphnia[END_REF]: spheroid and cuboidal unicells (class 1) are easily ingested, elongated cells (class 2) are more difficult to orientate and thus loosely packed for ingestion while long filaments caused by colonial forms (class 3) are really quite difficult to ingest. Each taxon was classified according to their shape in these three classes.

• Nitrogen fixation: some cyanobacteria are able to use atmospheric nitrogen which represents a clear advantage when dissolved nitrogen is limited (Le [START_REF] Quéré | Ecosystem dynamics based on plankton functional types for global ocean biogeochemistry models[END_REF].

• Toxicity: the potential toxicity of any taxonomic units (mainly cyanobacteria) was also considered (Reynolds 2006).

• Trophy: some photosynthetic algae show capacities to ingulf prey cells (some dinoflagellates or chryptophytes) or absorb selected dissolved organic compounds (osmotrophy; certain euglenophyta) as a facultative or a typical life style, which is also a clear advantage under low dissolved nutrient conditions (Reynolds 2006). Each taxon was classified according to its feeding mode, either autotrophy or potential mixotrophy.

• Life habitat: each taxon was classified according to its tyckopelagic, pelagic or mixed life style.

• Environmental plasticity: According to their salinity tolerance, they were split into typical limnic species versus euryhaline species which present higher tolerance to brackish environment.

• Mesozooplankton

Fifty-one taxonomic units were observed among 6 taxonomic groups: cladocera, copepoda, ostracoda, rotifers, larvae of benthic mollusks, benthic decapods.

They were classified according to several functional traits based upon their Life strategies (r and K strategies), their resource acquisition and their Life habitat [START_REF] Barnett | Functional diversity of crustacean zooplankton communities: towards a trait-based classification[END_REF][START_REF] Litchman | Trait-based aproaches to zooplankton communities[END_REF]).

• The mean size: as each individual organism was measured using a calibrated ocular micrometer when counting, they were split by taxon into three size classes: small (mean length <0.3mm), median (0.3-0.6mm) and large (>0.6mm) according to [START_REF] Barnett | Functional diversity of crustacean zooplankton communities: towards a trait-based classification[END_REF].

• The maximum population growth according to literature was split in three classes ('high', 'median' and 'low';[START_REF] Barnett | Functional diversity of crustacean zooplankton communities: towards a trait-based classification[END_REF]))

• The fastest generation time (FGT) correspond to the time duration between 2 generations according to literature [START_REF] Barnett | Functional diversity of crustacean zooplankton communities: towards a trait-based classification[END_REF]. It was also split in three classes ('high'for about 1 day, 'median' for 0.8 ̶ 1 days and 'low' for <0.8 days). This trait was combined with the reproduction mode since 'high' FGT corresponded to taxa displaying only a sexual reproduction and 'low' FGT exhibited both sexual and asexual reproduction.

• Two traits as qualitative factors traducing their diet plasticity with the food size range and the degree of selectivity of their preys :'small', 'median' and 'large' for both traits [START_REF] Barnett | Functional diversity of crustacean zooplankton communities: towards a trait-based classification[END_REF] • Two traits were common with nano-microphytoplanktonic functional traits and traduce their habitat: the Life habitat: (tychopelagic, pelagic or mixed life style) and the environmental plasticity (limnic vs euryhaline with higher tolerance to brackish waters)

Data analysis

For charactering the environmental context of the drained marshes, Two-way analyses of variance (ANOVA) were applied to assess the spatio-temporal differences of all environmental parameters and ecological efficiency (ANOVA habitat:season): some parameters were previously log-transformed to assess the applicability conditions. Rare species were excluded using the abundance sorting method adapted from [START_REF] Ibañez | Comparaison des évolutions à long terme (1977-1990) de deux peuplements macrobenthiques de la baie de Morlaix (Manche occidentale): relations avec les facteurs hydroclimatiques[END_REF] for both phyto-and mesozooplankton databases: 54 units were kept, i.e. 34% of the total taxonomic units for phytoplankton and 27 taxa, i.e. 53% of the total taxonomic units for mesozooplankton [START_REF] David | Data Treatment in Environmental Sciences[END_REF], David et al. 2012). This method is based on an index mixing species abundances and frequencies, retaining only the frequent and locally abundant taxa at least at one station/date [START_REF] David | Data Treatment in Environmental Sciences[END_REF].

For both compartments, we used several traits proposed in the literature and described above [START_REF] Barnett | Functional diversity of crustacean zooplankton communities: towards a trait-based classification[END_REF][START_REF] Litchman | Trait-Based Community Ecology of Phytoplankton[END_REF][START_REF] Litchman | Trait-based aproaches to zooplankton communities[END_REF]) and the OMI-GAM coupled with the witOMI methodological approaches to select the most appropriate traits to relate communities to environment [START_REF] Karasiewicz | Within outlying mean indexes: refining the OMI analysis for the realized niche decomposition[END_REF][START_REF] Kleyer | Assessing species and community functional responses to environmental gradients: which multivariate methods?[END_REF].

The Outlying Mean Index (OMI) analysis was performed for the overall data (7 stations × 13 months) considering all the abiotic factors, the parameters describing POM quantity /quality and the planktonic communities described above. This analysis allowed to determine taxa niche positions and breadths. It was conducted for each database independently: phytoplankton -54 taxa-and mesozooplankton -27 taxa [START_REF] Doledec | Niche separation in community analysis: a new method[END_REF].

Moreover, 'subniches' or habitat estimations were conducted according to [START_REF] Karasiewicz | Within outlying mean indexes: refining the OMI analysis for the realized niche decomposition[END_REF] considering the 6 subsets reported in Figure 1 in order to analyze the effect of resplenishment, catchment basin size and urbanization. Taxa'subniche dynamics were estimated by comparing marginality (witOMIG) and tolerance to the origin: low witOMIG traducing a preference of the taxa for one habitat. Moreover, the subniche parameters to the subset mean habitat conditions used by one taxa (witOMIGk and tolerance k) highlighted the taxa distribution within the subset habitat conditions: low witOMIGk traducing a more common habitat for the taxa. Moreover, the realized niche for each habitat was calculated as the percentage of the polygon area occupied by the group in the plane Axis 2 vs Axis 1 of the OMI according to the total area occupied by each habitat. The statistical significance of OMI, witOMIG, witOMIGk and environmental parameters between subniches were tested by Monte Carlo permutation procedure with 10000 permutations [START_REF] Doledec | Niche separation in community analysis: a new method[END_REF][START_REF] Karasiewicz | Within outlying mean indexes: refining the OMI analysis for the realized niche decomposition[END_REF].

For each OMI (OMI-phytoplankton and OMI-mesozooplankton), the taxa scores on the first two axes were used as response variables in generalized additive models (GAMs) with functional traits as explanatory variables [START_REF] Kleyer | Assessing species and community functional responses to environmental gradients: which multivariate methods?[END_REF]. Multimodal inference based on all-subsets selection of GAMs was used per axis and the best GAM were obtained by using the Akaike information criterion. Functional groups of taxa were obtained using a Ward's hierarchical clustering based on Euclidean distances between taxa predicted values from inference-based GAMs on the first two OMI axis. The optimal number of functional groups was determined via the Calinsky and Harabasz index. These functional groups were then brought face to face to their position relatively to the first OMI axes and their related environmental parameters.

Taxonomic richness, Shannon-Wiener diversity and Pielou evenness were used to assess the structural diversity while functional richness, evenness, dispersion and divergence were calculated based on the functional traits highlighted by the OMI-GAM to analyze the functional diversity per station/date [START_REF] Laliberte | A distance-based framework for measuring functional diversity from multiple traits[END_REF]Legendre 2010, Villéger et al. 2008).

One-way Generalized Linear Models (GLMs) were used for testing the relationships of the total biomasses and the several taxonomic and functional diversity indices between season or habitat for both nano-microphyto-and mesozooplankton. Two-Ways Generalized Linear Models were used for testing the relationships of abundances, specific richness, witOMIG, tolerance, witOMIGk, tolerance k, realized niche percentage between functional groups and season or habitat (GLM functional groups:season or GLM functional groups:habitat). Gaussian link functions were used for quantitative indices while Poisson link function were applied for taxonomic and functional richness. Residuals normality and variance homogeneity were previously tested for each model. Abundances were logtransformed in order to fit these applicability conditions.

All tests were performed with the R software (R-Core-Team 2014) using the libraries

Results

Environmental context

Seasonal variations

All environmental parameters displayed significant seasonal variations except pH and POM δ 15 N (Two-way ANOVA, season factor, Table 1). Water temperature fluctuated between 8°C during winter and 22°C during summer. For nutrients, the highest values were recorded during winter and the lowest during summer (33 500 µmol L -1 vs 35000 µmol L -1 for NOx, 380 vs 40 µmol L -1 for NH4 + and 270 vs 70 µmol L -1 for PO4 3-, respectively). O2 saturation exhibited their lowest values during the fall (about 50%). HP and microzooplankton displayed their lowest biomasses during the winter and their highest values during the spring (44 vs 116 µgC L -1 and 4304 vs 6836µgC L -1 for HP and microzooplankton respectively). In contrast, the parameters describing the SPM and POM concentrations were the highest during summer and the lowest during winter: 73000 vs 31000 µg L -1 for SPM, 5646 vs 3060 µg L -1 for POC, 877 vs 450 µg L -1 for PON and 109 vs 44 µg L -1 for POP, respectively). POM δ 13 C exhibited low values during winter-spring and their lowest values during the spring period (-33.1‰). Moreover, ecological efficiency was the highest during the fall (0.022).

Human impacts • Replenishment effect (non-urbanized and median catchment basin)

Only pH, NOx, POM quantity, HP, microzooplankton and ecological efficiency presented significant differences between replenished and unreplenished marshes for a same catchment basin size (Two-way ANOVA, Habitat and Habitat*Saison effect, Table 1 andFigure 2). Replenished marshes displayed the lowest pH (7.7 vs 8.1 for resplenished and unreplenished marshes, respectively), the lowest parameters describing the POM quantity (38 vs 88 mg L -1 for SPM, 2375 vs 11621µg L -1 for POC, 446 vs 1768µg L -1 for PON and 57 vs 144 µg L -1 for POP, respectively), the lowest HP (66 vs 154µgC L -1 ) and microzooplankton biomasses (3737 vs 26551 µgC L -1 ) in particular from spring to fall. In contrast, they exhibited the highest NOx concentrations (27 vs 10 µmol L -1 ) from winter to summer and their highest ecological efficiencies (0.013 vs 0.0003) from spring to fall.

• Catchment basin effect (non-urbanized replenished marshes)

NOx, POM quantity, O2 saturation and ecological efficiency presented significant values between the marshes of different catchment basin sizes (Two-way ANOVA, Habitat effect and Habitat*saison effect; Table 1 and Figure 2). The smallest catchment basin habitat exhibited the lowest NOx concentrations (10 vs 26-27 µmol L -1 for smallest catchment basin vs others marshes, respectively) in particular during winter and the lowest O2 saturation during summer and fall. In contrast, the largest catchment basin habitat presented the highest POM quantity (62 vs 38-40 mg L -1 for SPM, 3433 vs 2375-2387µg L -1 for POC, 636 vs 446-379µg L -1 for PON and 85 vs 57-52 µg L -1 for POP, respectively), notably during summer and the lowest ecological efficiency (0.001 vs 0.01), in particular from spring to fall.

• Urbanization effect (for large catchment basin and replenished marshes)

NH4 + , PO4 3-, POM quantity, δ 15 N and ecological efficiency presented significant differences between urbanized and non urbanised resplenished marshes (Two-way ANOVA, Habitat effect and Habitat*season effect; Table 1 andFigure 2). Urbanized marshes displayed i) the highest NH4 + concentrations (0.73 vs 0.09 µmol L -1 for urbanized vs non urbanized marshes, respectively), especially during winter, ii) the highest PO4 3-concentrations all year round (0.51 vs 0.11 µmol L -1 ), iii) the highest parameters describing the POM quantity (50 vs 40 mg L -1 for SPM, 4321 vs 2387µg L -1 for POC, 854 vs 379µg L -1 for PON and 86 vs 52 µg L -1 for POP), in particular during summer and fall and the highest POM δ 15 N (10.9 vs 8.5‰).

In contrast, they exhibited the lowest ecological efficiency (0.007 vs 0.014), especially during summer. Moreover, O2 saturation was higher for urbanized than for non urbanized marshes.

Niche analysis and functional groups of nano-microphytoplankton and mesozooplankton

Both OMI analysis were significant (Monte Carlo permutation tests, p<0.001) with 43 and 20 taxa displaying significant realized niches for nano-microphyto-and mesozooplankton, respectively. The first two axis represented 82% and 73% of the projected inertia respectively. For nano-microphytoplankton, the first axis represented a higher part of this inertia (72%; Figure 3A) than for mesozooplankton (54%; Figure 3B).

Concerning the nano-microphytoplankton-OMI, the first axis was mainly explained by the opposition between inorganic nitrogen nutrients on the positive values and the parameters describing the POM quantity (POC, PON, POP) as well as the largest biomasses of nanomicrophytoplankton and HP on the negative values (Figure 3A). The second axis was related to water temperature and large biomasses of mesozooplankton. In contrast, the first axis was explained by water temperature, large mesozooplankton biomasses and NOx while the second axis by the parameters describing the POM quantity concerning the mesozooplankton-OMI (Figure 3B).

Phytoplankton functional groups

Over the 10 functional traits tested (described in section 2.2.4.), four were finally kept according to the Akaike criteria by the GAMs performed on the first two axis of the OMI analysis: Life habitat, nitrogen fixation, trophy and size (Figure 4C). The best GAM with the taxa scores on the first axis had an explained deviance of 36.5% with a higher contribution of the life habitat (17.5%) and secondly a contribution of nitrogen fixation (8.8%), cell size (7.8%) and trophy (6.8%) while the one conducted on the second axis was only explained by cell size (10%).

Five resulting functional groups were highlighted (Ward's clustering; Figure 4A). A first group (C1) was characterized by large tychopelagic and autotrophic cells, a second group (C2) by small tychopelagic and autotrophic cells, C3 by large pelagic autotrophic cells, C4 by small pelagic autotrophic cells and C5 by small pelagic mixotrophs and N2 fixators (Figure 4C). The first three groups were dominated by diatoms while others were more diversified with a high contribution of green algae for C4, and of euglena, dinoflagellates and cyanobacteria for C5 (Figure 4B).

Mesozooplankton functional groups

Over the 7 functional traits used (described in section 2.2.4.), three were finally kept (optimized GAMs obtained on the first two axis of the OMI analysis): Life habitat, population growth rate and fastest generation time combined with the reproduction mode (Figure 5C).

The best GAM with the taxa scores on the first axis had an explained deviance of 31.3% with a higher contribution of the population growth rate (29.2% of deviance explained) and secondly the Life habitat (22.2%). The best GAM conducted on the second axis had an explained deviance of 57.5% with a higher contribution of the population growth rate (98.5%) and secondly with the fastest generation time (80%).

Four resulting functional groups were highlighted based only on the significant life traits found with GAMs on the first two axis of the mesozooplankton-OMI (Ward's clustering; Figure 5A). A first group (C1) was characterized by K-strategists and mixed Life habitat and composed by a mix of copepods, ostracods and cladocerans, a second group (C2) by rather r-strategists with high growth rates dominated by cladocerans with mixed Life habitat, C3 by pelagic r-strategists with high growth rates (mainly rotiferas), C4 by tychopelagic K-strategists with median growth rates (copepods) (Figure 5B and5C).

Spatio-temporal variations of nano-microphytoplankton and mesozooplankton functional diversities

Seasonal fluctuations

Total biomasses displayed significant seasonal variations for both nano-microphytoand mesozooplankton (GLM, season effect, p<0.001). However, no significant differences were highlighted for the several specific and functional diversity indices for both compartments (GLM, season effect, p>0.05; Figure 6).

Among the dominant features for phytoplankton, small tychopelagic autotroph cells (C2) exhibited the lowest biomasses while large pelagic autotrophs cells (C3) the highest biomasses all over the seasonal cycle (GLM, season: functional groups effect, p<0.05; Figure 7). For mesozooplankton, K-strategists with mixed Life cycle (C1) presented the lowest biomasses while r-strategists pelagic taxa (C3) the highest biomasses over the seasonal cycle (GLM, season: functional groups effect, p<0.05; Figure 7).

Considering the seasonal cycle of phytoplankton, winter displayed the significant lowest total biomasses (GLM, season effect, p<0.05; Figure 6) with the highest biomasses of large tychopelagic autotrophs (C1), the highest taxa richness of tychopelagic cells, the largest pelagic autotrophs (C1, C2 and C3) and the lowest biomasses and richness of small pelagic functional groups (C4 and C5; GLM, season: functional groups effect, p<0.05; Figure 7).

Spring presented among the highest large tychopelagic autotrophs biomasses (C1) but with decreasing taxa richness of tychopelagic cells and large pelagic autotrophs (C1, C2 and C3) in contrast with increasing biomasses and richness of pelagic autotrophs and mixotrophs / N2 fixators (C3, C4 and C5 ; GLM, season:functional groups effect, p<0.05; Figure 7). Summer was marked by the highest total biomasses (GLM, season effect, p<0.05; Figure 6) with the highest biomasses and richness of small pelagic cells (C4 and C5) and decreasing biomasses of large tychopelagic autotrophs (C1; GLM, season:functional groups effect, p<0.05; Figure 7). Finally, fall exhibited decreasing biomasses and richness of small pelagic cells (C4 and C5; GLM, season:functional groups effect, p<0.05; Figure 7).

Considering mesozooplankton, winter was also marked by the lowest total biomasses (GLM, season effect, p<0.001; Figure 6) with the lowest biomasses of all functional groups except K-strategists with both pelagic and tychopelagic Life habitat (C1) and the lowest richness of pelagic r-strategists (C3; GLM, season: functional groups effect, p<0.05; Figure 7). Spring displayed increasing biomasses and richness of r-strategists (C2 and C3) and increasing biomasses of tychopelagic K-strategists (C4; GLM, season: functional groups effect, p<0.05; Figure 7). As for nano-microphytoplankton, summer exhibited the highest mesozooplankton biomasses (GLM, season effect, p<0.001; Figure 6) with the highest biomasses of all functional groups and the highest richness of pelagic r-strategists (C3; GLM, season: functional groups effect, p<0.05; Figure 7). Fall period exhibited no significant changes with summer period (Figure 7).

Human activity effect • Replenishment effect

Replenished marshes were characterized by the lowest total nano-microphytoplankton biomasses and functional divergence (Figure 8 and Table 2) and inversely the highest total mesozooplankton biomasses and functional dispersion (GLM habitat effect, p<0.05; Figure 9 and Table 2). In contrast, they exhibited the highest taxonomic and functional richness for both compartments (Figure 6) compared with unreplenished marshes (GLM habitat effect, p<0.05).

Concerning nano-microphytoplankton, all functional groups displayed lower witOMIG suggesting a preference for replenished marshes (GLM, functional group:habitat effect, p<0.05; Figure 8). Small pelagic autotrophs and mixotrophs/ N2 fixators (C4 and C5) exhibited higher tolerance and higher biomasses for unreplenished marshes (GLM, functional group:habitat effect, p<0.5; Figure 8). The higher biomasses of mixotrophs/ N2 fixators may also be related to their significant higher tolerance Gk (GLM, functional group:habitat effect, p<0.05; Figure 8) while C4 exhibited lower richness for unreplenished marshes. Small tychopelagic cells (C2) displayed significant higher biomasses and richness for replenished habitat probably related to their higher realized subniche (GLM, functional group:habitat effect, p<0.05; Figure 8).

Concerning mesozooplankton, r-strategists (C2 and C3) displayed lower witOMI G traducing a preference for replenished marshes with higher realized subniches, biomasses and taxonomic richness (GLM, functional group:habitat effect, p<0.05; Figure 9). The higher biomasses of K-strategist with both life style (C1) may be related to their higher tolerance k (GLM, functional group:habitat effect, p<0.05; Figure 9).

• Catchment basin area effect

The largest catchment basin marshes displayed the higher total phytoplankton biomasses (Figure 8) and inversely the highest specific richness and the lowest functional dispersion for mesozooplankton (GLM habitat effect, p<0.05; Figure 9 and Table 2). No significant differences were found for others biomasses and diversity indices between the three habitats exhibiting several catchment basin sizes (GLM habitat effect, p>0.05).

Concerning nano-microphytoplankton, all functional groups presented a significant lower preference and a less common habitat for the largest catchment basin marshes (higher WitOMI G and Gk; GLM, functional group:habitat effect, p<0.05; Figure 8). However, small pelagic cells (C4 and C5) exhibited higher biomasses for this habitat (GLM, functional group:habitat effect, p<0.05; Figure 8). The others functional groups did not exhibit significant differences in biomasses between the three catchment basin size marshes (Figure 8). In contrast, small tychopelagic cells (C2) presented significant lower realized niches for largest catchment basin marshes (GLM, functional group:habitat effect, p<0.05; Figure 8).

Finally, the large tychopelagic cells (C1) exhibited lower tolerance for the largest catchment basin marshes (GLM, functional group:habitat effect, p<0.05; Figure 8).

Concerning mesozooplankton, K-strategists with both Life style (C1) presented a significant higher preference and a more common habitat for the smallest catchment basin marshes (higher WitOMI G and Gk) which may be related to its largest realized subniche and explain its higher biomass for this habitat (higher WitOMI G and Gk; GLM, functional group:habitat effect, p<0.5; Figure 9). The r-strategists with both Life style (C2) exhibited also higher realized subniches and consequently largest biomasses for the smallest catchment basin marshes (GLM, functional group:habitat effect, p<0.05; Figure 9). The others functional groups did not present significant differences between the three catchment basin size marshes (Figure 9).

• Urbanization effect

No differences were observed for total biomasses and diversity indices between urbanized and non urbanized replenished marshes with the same catchment basin size for both nano-microphyto and mesozooplankton (GLM habitat effect, p>0.05; Figure 6, 8 and 9 and Table 2). mesozooplankton-while summer was marked by the highest biomasses. Winter period is actually not suitable to primary production due to temperature and probably to light limitation as suggested by [START_REF] Masclaux | Planktonic food web structure and dynamic in freshwater marshes after a lock closing in early spring[END_REF]. However, POC/Chla ratio presented a ratio of about 250 as most of the year (data not shown) traducing the large, even not totally dominant, part of the phytoplankton in the POM composition. However, POM δ 13 C exhibited their lowest values confirming the importance of terrestrial material mixed with freshwater microalgae in the POM composition at this season as highlighted by [START_REF] Savoye | Dynamics of particulate organic matter δ15N and δ13C during spring phytoplankton blooms in a macrotidal ecosystem (Bay of Seine, France)[END_REF][START_REF] Savoye | Origin and composition of particulate organic matter in a macrotidal estuary: the Gironde Estuary[END_REF]. Nanomicrophytoplankton was marked by a high contribution of large tychopelagic cells which may be due to high hydrodynamic features as demonstrated by Guarini et al. (2004b) and David et al. (2016). Moreover cryptophytes and tychopelagic diatoms are dominant at this season to the detriment of chlorophytes confirming resuspension processes: the latter taxonomic groups being less favored in turbulent environment [START_REF] Cañavate | Flushing-related changes of phytoplankton seasonal assemblages in marsh ponds of the warm temperate Guadalquivir river estuary (SW Spain)[END_REF][START_REF] Ramade | Dictionnaire encyclopédique des sciences de la nature et de la biodiversité[END_REF]). What's more, NOx and PO4 3-displayed actually their highest values during winter. The sea lock gates are actually opened to evacuate the surplus water coming from the catchment basin: drained marshes are thus characterized by running water that probably exerted an erosive action on the sediment that may explain tychoplankton resuspension [START_REF] De Jonge | Wind-and tide-induced resuspension of sediment and microphytobenthos from tidal flats in the Ems estuary[END_REF] and high inputs of nutrients drained from the culture soils as demonstrated by [START_REF] Tortajada | Variability of fresh-and salt-water marshes characteristics on the west coast of France: A spatio-temporal assessment[END_REF]. None information is available in our systems about a possible atmospheric nitrogen inputs that may play an additional source of nutrients for phytoplankton especially in others urban systems suggested by [START_REF] Peng | Atmospheric nitrogen pollution in urban agglomeration and its impact on alpine lake-case study of Tianchi Lake[END_REF]. However, according to our knowledge, the main anthropogenic activities are provided by wastewater treatment plant and those providing from private dwelling leaching or soil leaching: a few industrial activities are present on the catchment basin. On the other hand, mesozooplankton was dominated by tychopelagic K-strategists that are actually more competitive in cooler environment than rstrategists for which faster growth and high turnover is favored by warmer conditions (David et al. 2016b[START_REF] Elliott | Challenging paradigms in estuarine ecology and management[END_REF][START_REF] Jerling | Population dynamics and estimates of production for the calanoid copepod Pseudodiaptomus hessei in a warm temperate estuary[END_REF][START_REF] Litchman | Trait-based aproaches to zooplankton communities[END_REF].

This confirms the high contribution of tychopelagic species due to resuspension and thus the high benthos-pelagos coupling at this season.

The decreasing temperature and the increasing precipitation at the fall period lead to the human action such as the opening of the sea lock gates. This implies a running water that seems to contribute to the decrease of the taxa with alternative food diet. Hydrodynamic features may lead to a more detritical environment as testified by the highest value of POC/ Chla ratio (data not shown) that may be explained by the degradation of the accumulated POM according to [START_REF] Savoye | Dynamics of particulate organic matter δ15N and δ13C during spring phytoplankton blooms in a macrotidal ecosystem (Bay of Seine, France)[END_REF].

Drained marshes insure the ability to remove nitrate drained from culture soils on catchment basin since the winter NOx concentrations, brought from the catchment basin, was reduced by 99% as it was highlighted by [START_REF] Tortajada | Variability of fresh-and salt-water marshes characteristics on the west coast of France: A spatio-temporal assessment[END_REF]. However, eutrophication is marked during summer and may lead to hypoxia (lowest O2 saturation) and potential toxic environment. Actually, cyanobacteria may produce toxins [START_REF] Karjalainen | Ecosystem Consequences of Cyanobacteria in the Northern Baltic Sea[END_REF]) and protease inhibitors that limit their digestibility and may affect the higher trophic levels [START_REF] Agrawal | Acute inhibition of protease and suppression of growth in zooplankter, Moina macrocopa, by Microcystis blooms collected in Central India[END_REF]. No significant differences were highlighted concerning functional richness and divergence for both nano-microphyto-and mesozooplankton traducing a coexistence of the several functional groups over the seasonal cycle probably due to the high food availability as suggested by [START_REF] Hillerislambers | Rethinking Community Assembly through the Lens of Coexistence Theory[END_REF]: each group may find a favorable environment even if competition participate to the dominance of one or other according to the seasonal period.

Impact of human activities

Summer replenishment

The effect of artificial summer resplenishment from the adjacent Charente River was performed considering non urbanized marshes displaying the same size of catchment basin. This human action is an additional management on marshes allowing to maintain a sufficient stock of water to prevent the drying up of small channels and supplies both cattle husbandry and local maize culture occupying until 70% of the catchment basin area: the water level decreases actually of some centimeters per day during summer for unresplenished marshes.

Our data showed that replenishment decreases drastically the summer eutrophication.

This results confirm the typology of [START_REF] Tortajada | Variability of fresh-and salt-water marshes characteristics on the west coast of France: A spatio-temporal assessment[END_REF] that highlighted an increasing eutrophication with a decreasing replenishment. Moreover, [START_REF] Dembowska | A case study of the planktonic communities in two hydrologically different oxbow lakes, Vistula River, Central Poland[END_REF] suggested that replenishment had already been described as a structuring factor for phytoplankton. Phytoplankton biomasses were actually lower for replenished than for unreplenished marshes when the sea lock gates are closed and the replenishment active (from the end of spring to the beginning of fall). During summer, replenished marshes are characterized by smaller biomasses of small pelagic autotrophs and mixotrophs/ N2 fixators. However, the biological trait "motility" would have been interesting to consider for such system: motile species could have been favored by running water during summer. POM quantity, microzooplankton and HP accumulation are also less pronounced in replenished waters during summer as it was highlighted by [START_REF] Masclaux | Planktonic food web structure and dynamic in freshwater marshes after a lock closing in early spring[END_REF]. This traduces a lower N-nutrient limitation for replenished marshes: NOx displayed higher concentrations in replenished compared to unreplenished marshes during spring and summer since it is brought by the Charente River. Moreover, small tychopelagic cells displayed higher biomasses for replenished marshes probably due to the higher hydrodynamics all the year due to the running water induced by the connection with the River favoring tychopelagic resuspension (Guarini et al. 2004a). The connection with the River all year round may limit water stagnation, phosphorous release and thus eutrophication processes in replenished marshes.

The nitrogen-nutrient limitation explained the fact that mixotrophs and N2 fixators displayed higher biomasses for unreplenished marshes. Their tolerance to N-nutrient limitation is largest in the latter marshes compared with the others functional groups since they are more adapted to such environment than the others functional groups. Moreover, water stagnation and high temperature favor the proliferation of mixotrophic dinoflagellates for unreplenished marshes as suggested by [START_REF] Litchman | Phytoplankton niches, traits and eco-evolutionary responses to global environmental change[END_REF]. The higher functional divergence recorded for these systems may thus be explained by the higher contribution of mixotrophs/ N2 fixators during the summer period in contrast with replenished marshes.

Contrasting with the lower phytoplankton biomass, zooplankton biomasses displayed higher biomasses, richness and dispersion for replenished marshes with a higher contribution of all functional groups except tychopelagic K-strategists notably from spring to fall. This may be explained by the low nutritive quality or even toxicity that may exhibit certain phytoplankton taxa favored during the eutrophication processes that are larger for unresplenished marshes and may affect the higher trophic levels [START_REF] Agrawal | Acute inhibition of protease and suppression of growth in zooplankter, Moina macrocopa, by Microcystis blooms collected in Central India[END_REF]). This higher zooplankton biomasses contrasting with the lower phytoplankton biomasses might thus explain the higher ecological efficiency observed for replenished waters.

Catchment basin size/agriculture effect

The comparison between non urbanized and replenished marshes of different catchment basin size report the effect of agriculture on water quality and plankton diversity.

The largest catchment basin displayed the largest area of agriculture (4700ha and 2000 with 72% of agriculture occupation for station 6 and 20, respectively) compared with the smallest catchment basin size (900ha-37-40%).

Small catchment basin with lower agriculture activity implied a lower quantity of NOx brought during winter and explained thus the lower biomasses of nano-microphytoplankton all year round. Even if lower inputs of wintering NOx in small catchment basin should prevent the development of small pelagic taxa such as organisms with alternative food ressources (mixotrophs and N2 fixators): the latter functional groups did not displayed significant lower biomasses. In contrast, hypoxia periods (lowest O2 saturation) are more recurrent. Moreover, tychopelagic phytoplankton taxa are also disfavored for small catchment basin probably due to the lower hydrodynamics features compared to marshes with large catchment basin: a larger water volume is actually condensed in small channels favoring microphytobenthos resuspension during winter as suggested above. The lower hydrodynamics features as well the lower nutrient inputs lead to the development of macrophytes that are actually more competitive than phytoplankton in nutrient limited environment as demonstrated by [START_REF] Sand-Jensen | Interactions among phytoplankton, periphyton, and macrophytes in temperate freshwaters and estuaries[END_REF]. In contrast, [START_REF] Bronmark | Indirect effects of fish community structure on submerged vegetation in shallow, eutrophic lakes: an alternative mechanism[END_REF] suggested that high hydrodynamics features in marshes with large catchment basin may favor phytoplankton development from the beginning of the spring and may prevent macrophytes development.

Aquatic macrophytes play an important role in structuring communities in aquatic environments, increase habitat complexity and heterogeneity and may provide food sources for various organisms like invertebrates, fishes and waterbirds [START_REF] Thomaz | The role of macrophytes in habitat structuring in aquatic ecosystems: methods of measurement, causes and consequences on animal assemblages' composition and biodiversity[END_REF].

There are also known to greatly participate to heavy metal remediation [START_REF] Abdallah | Phytoremediation of heavy metals from aqueous solutions by two aquatic macrophytes, Ceratophyllum demersum and Lemna gibba L[END_REF]). However, our systems are dominated by free leaved macrophytes at the surface of the water column, mainly duckweeds. [START_REF] Janse | Nitrogen, the Confer-N-s[END_REF] suggested that a high cover of free-floating plant may implies anoxic conditions that have a negative effect on freshwater ecosystems reducing animal biomasses and diversity. Moreover, they are primacy for light.

In contrast, [START_REF] Chambers | Roots versus Shoots in Nutrient Uptake by Aquatic Macrophytes in Flowing Waters[END_REF] highlighted that rooted submerged macrophytes use a large part of their nutrient need from the sediment. while the presence of submerged macrophytes usually implies low plankton biomasses and low eutrophication in ponds [START_REF] Mukhopadhyay | The ability of aquatic macrophytes to maintain water clarity in two tropical ponds[END_REF]. Consequently, free-leaving plants out-compete submerged macrophytes due to light availability and cause a nutrient and light depletion in the water column that may cause eutrophication processes and lower plankton biomasses, notably during summer period [START_REF] Parr | Causes of low oxygen in a lowland, regulated eutrophic river in Eastern England[END_REF]Mason 2004, Scheffer et al. 2003).

Consequently, even if largest catchment basin and thus higher agriculture activity may lead to summer eutrophication processes since they imply higher NOx and POM concentrations as reported by [START_REF] Tortajada | Variability of fresh-and salt-water marshes characteristics on the west coast of France: A spatio-temporal assessment[END_REF], small catchment basin also presented eutrophication processes with higher hypoxia problems due to a high proliferation of free living plants at the surface of the water that limits light availability and favors mixotrophs/ N2 fixators during summer. Even if no significant differences in biomasses were highlighted, zooplankton exhibited a lower taxonomic richness for marshes with small catchment basin characterized by large covers of duckweeds. Some taxa, such as copepods and cladocerans seems to be disfavored in such habitat. Previous works showed actually that copepods may be disfavored by low oxygen concentrations [START_REF] Appeltans | Zooplankton in the Schelde estuary (Belgium/The Netherlands). The distribution of Eurytemora affinis: Effect of oxygen?[END_REF][START_REF] Mialet | Response of zooplankton to improving water quality in the Scheldt estuary (Belgium)[END_REF]) and that cladocerans abundances are mainly related to Chla (De los Rios and Soto 2007, [START_REF] Mialet | Response of zooplankton to improving water quality in the Scheldt estuary (Belgium)[END_REF]. This habitat displayed lower phytoplankton. However, due to the lowest phytoplankton biomasses, the marshes displaying the smallest catchment basin exhibited the lowest ecological efficiency and thus less food at least for higher trophic levels based on the planktonic trophic pathways.

Urbanization

The comparison between urbanized and non urbanized replenished marshes with small catchment basin report the effect of the presence of water purification facilities on the marsh as well as leaching water from housing. [START_REF] Mcclelland | Changes in food web structure under the influence of increased anthropogenic nitrogen inputs to estuaries[END_REF] suggest that the higher POM δ 15 N exhibited in urbanized marshes traduced the clear influence of urban waste in such habitat even though the lower contribution of N2 fixators during summer may also contributed to these high values.

No differences were observed for plankton biomasses between the two kinds of marshes contrasting with others studies that report a decreasing biomass when urbanization is present (Kentzer et al. 2010, Murakami and[START_REF] Murakami | Waterplant purification of eutrophicated water in mesocosm system with long-term observation[END_REF]. In contrast, urbanized marshes exhibited a higher contribution of small pelagic autotrophs and a lower contribution of organisms characterized by alternative food sources (mixotrophy/ N2 fixation). This may be explained by the largest concentrations of NH4 + and PO4 3-that are released from water purification facilities or leaching waters that prevent nutrient limitations. Oxygen depletion is thus lower during summer due to these lowest heterotrophic taxa contribution. Moreover, zooplankton assemblage was marked by a lower biomass of K-strategists in favour of r-strategists, in particular rotifers and cladocerans. Cladocerans are actually mainly related to Chla concentrations biomasses as suggested by De los [START_REF] De Los Rios | Eutrophication and dominance of daphnids (Crustacea) in a deep Patagonian lake (Lake Llanquihue, Chile)[END_REF] and [START_REF] Mialet | Response of zooplankton to improving water quality in the Scheldt estuary (Belgium)[END_REF] and may be thus favored by the highest contribution of small pelagic autotrophs during summer versus mixotrophs in our systems. Moreover, rotifers, especially Brachonius that dominated during summer exhibited low selectivity on small preys in contrast with the K-strategists copepods that are generally more opportunists according to the review of [START_REF] Barnett | Functional diversity of crustacean zooplankton communities: towards a trait-based classification[END_REF]. Cladocerans and rotifers may thus present asexual reproduction in this favorable nutritive environment that confer them higher growth rates and thus a higher competitivity than K-strategists in urbanized marshes as proposed by [START_REF] Litchman | Trait-based aproaches to zooplankton communities[END_REF].

Finally, urbanized marshes are thus less subjected to eutrophication during summer than non urbanized marshes due to more recurrent nitrogen-nutrient inputs from urban waste that prevent the proliferation of mixotrophs and N2-fixators. However, they exhibited a lower ecological efficiency and thus less available food for the higher trophic levels.

Inputs of a functional approach on the drained marshes functioning

The functional diversity approach complete greatly the knowledge about the functioning of such systems in aggregating the overwhelmingly diversity of organisms into groups of species sharing similar functions as suggested by [START_REF] Mc Gill | Rebuilding community ecology from functional traits[END_REF]. This approach underlines the pelagic-coupling during winter while the rest of the seasonal cycle was marked by an autochthonous pelagic production. It also brings information about the mechanisms behind the functioning of these systems due to nutrients limitation with the demonstration of a seasonal succession of large, small pelagic autotrophs and then small pelagic with alternative nutrition mode (mixotrophy and N2 fixation). The latter may provide toxic and unsuitable food for higher trophic levels decreasing thus the ecological efficiency during the warming periods. Finally, it is informative on the process of competition between macrophytes and phytoplankton: the former been more favored in less nutrient and hydrodynamics environment.

The results highlight thus the powerful of the trait-based approach to understand both the drained marshes functioning and their related ecological functions as well as the impacts of man control and human activities on the catchment basin. Previous works have actually prove its efficiency to explore the organization of ecological communities and species niches for plankton compartments even though the difficulties related to the bibliographic synthesis necessary to compile the traits for all species and the data treatment methodology [START_REF] Breton | Functional trait variation and nitrogen use efficiency in temperate coastal phytoplankton[END_REF], David et al. 2012, Kruk et al. 2002). The combination between the OMI-GAM proposed by [START_REF] Kleyer | Assessing species and community functional responses to environmental gradients: which multivariate methods?[END_REF] and witOMI analysis by [START_REF] Karasiewicz | Within outlying mean indexes: refining the OMI analysis for the realized niche decomposition[END_REF] has been particularly powerful in this work. The former allowed to find, among the available traits, the ones that best linked communities to environment and to determine functional groups [START_REF] Kleyer | Assessing species and community functional responses to environmental gradients: which multivariate methods?[END_REF] while the latter provide interpretations on niche dynamic by considering the several drained marshes as different habitat conditions [START_REF] Karasiewicz | Within outlying mean indexes: refining the OMI analysis for the realized niche decomposition[END_REF].

For nano-microphytoplankton, it was not surprising that size and trophy traits were significant functional features in relating communities to environmental conditions. Both kind of traits are actually a way to adapt to nutrient limitation through the surface/ biovolume ratio allowing small cells to better absorb nutrients in the case of a N/P desequilibrium and through a mixotrophs or N2 fixation nutrition mode when complete depletion of them. The high seasonal fluctuations of nutrients until complete depletion drive thus the functional assemblage of phytoplankton in drained marshes. Concerning mesozooplankton, growth rates and fastest generation time related to reproduction modes were significant traits explaining the assemblages in drained marshes. The functional groups obtained was related to the r and K Life strategies proposed for these organisms by the Litchman model [START_REF] Litchman | Trait-based aproaches to zooplankton communities[END_REF] adapted from the McArthur and Wilson theory (MacArthur and Wilson 1967). r-strategists presented high growth rates with the ability of asexual reproduction when environmental conditions are favorable and are characterized by a low energetic investment for defense and offspring protection. In contrast, K-strategists displayed low growth rates with only sexual reproduction and a great energetic investment for defense and offspring protection. Even if rstrategists are in theory less able to select their preys than K-strategists, the trait concerning food selectivity were not significant in our results. In contrast, r-strategists (cladocerans and rotifers) seemed favored by a certain food environment (high phytoplankton biomasses) contrary to K-strategists which were more dependent of abiotic environment. For both compartments, Life habitat was a significant functional trait related to the OMI niche. The hydrodynamics play actually a great role in plankton communities with high resuspension of tychopelagic forms during flood time.

How to perform such preliminary results

The most marshes of the world and specially in Europe are affected by human activity, such as artificial replenishment, urbanization and catchment basin size. However, a few works report the impact of human actions: the latter on plankton communities in relation with their impacts on planktonic communities. This work reports two functional approach but independently for nano-microphytoplankton and mesozooplankton. In this case is very difficult to analyze the processes between the two compartments. However, some traits used in this study provide several indications to make any assumptions about them. For nano-microphytoplankton 'Cell shape and biovolume' as well as 'potential toxicity' may influence their ingestion availability for zooplankters. Concerning zooplankton, 'K versus r strategists' deduced according to several traits may condition their availability to adapt to several kind of food. In that case, some assumption could be made about the potential 'top-down' and 'bottom up' control among the several planktonic pathways and thus about the impact of anthropogenic action within such pathways. For example, small catchment basin and unreplenished marshes during summer may imply the development of small phytoplankton, even toxic or indigestible preys to zooplankton and thus bottom up effect. However, the result of ecological efficiency are not so clear. Our study is not enough in-depth to explore such processes.

Even if functional approach includes usually both ecological (habitat preference related to abiotic tolerance or biotic interactions) and biological (e.g. Life history, physiological, behavioral or morphological features) traits [START_REF] Wu | Using river microalgae as indicators for freshwater biomonitoring: Review of published research and future directions[END_REF], only the latter type of traits were considered in this paper. Moreover, some of the biological traits, such as the motility, were not taken into account. This was due to the lack of information about the former kind of functional traits for a lot of species and could explain the part of unexplained deviance concerning the GAM on the two first axis revealed by the OMI analysis for both nanomicrophytoplankton and mesozooplankton.

In addition, it would have been interesting to access to i) a larger number of sampling marshes for each kind of habitat and ii) to reproduce this work several years (interannual survey) in order to confirm the results. Coastal systems are usually more marked by seasonal rather than interannual fluctuations of plankton communities and water quality [START_REF] David | Long-term changes of the zooplankton variability in a turbid environment: The Gironde estuary (France)[END_REF][START_REF] Tortajada | Variability of fresh-and salt-water marshes characteristics on the west coast of France: A spatio-temporal assessment[END_REF]). However, this was not practicable due to the heaveness of this work considering all the parameters that were sampled, both cost-and time consuming.

Nevertheless, the present study revealed novelty and interesting information about the seasonal and anthropogenic impacts on plankton communities in drained marshes.

Conclusions

In a context in which polder areas are particularly sensitives to climate change through storm floods events causing marine submersion and thus high risks for local economical activities and populations, a better understanding of how, socio-economic vulnerability of these areas support the idea of 'Growing with the sea' rather than 'fighting against it' to increase their resilience. However, this implies a better knowledge of how human impacts act on such systems, e.g. drained marshes.

The artificial summer replenishment, which represents an additional man control on drained marshes, acts positively on water quality i) by decreasing the eutrophication processes by assuring a recurrent input of nitrogen nutrient preventing the proliferation of mixotrophs and N2 fixators, ii) by increasing the ecological efficiency during the warmer period providing largest food for the higher trophic levels based on the planktonic trophic pathways.

Both small and large catchment basins may lead to summer eutrophication processes since the largest ones imply higher nutrients and POM concentrations and the smallest ones exhibit hypoxia problems due to higher proliferation of free floating macrophytes. However, the large catchment basin displayed lower ecological efficiency and thus less food for the higher trophic levels. Moreover, the latter may also cause harmful effects due to higher pesticides inputs.

Urbanized marshes are less subjected to eutrophication during summer than non urbanized marshes due to more recurrent nitrogen-nutrient inputs from urban waste, which prevent the proliferation of mixotrophs and N2 fixators, but exhibited a lower ecological efficiency and thus less available food for the higher trophic levels. Nevertheless, urban sewage inputs may also be a source of contaminant for coastal waters such as polycyclic aromatic hydrocarbons.

The several tools used in this analysis doubtless complete the informations provided by the works deployed on the protocols recommended by the Water Quality Evaluation System (WQES) for the European Water Framework Directive. This was suggested by previous results concerning the spatio-temporal fluctuations of drained marshes functioning and the effect of the several human activities. They confirm that a better management of the hydrodynamics of such anthropogenic systems submitted to diverse human controls (i.e. replenishment) and several levels of human impact according to its activity on the catchment basin (agriculture, urbanization occupation) can prevent eutrophication risks on coastal areas. This should be taken in consideration in a "growing with the Sea" policies in order to maintain ecological functions and related services and thus adapt their restauration in a context of sustainable development.

Preventing the eutrophication linked to PO4 3-desorption from the sediment during summer is a challenge for the management of such anthropo-system. Several strategies necessitate human actions. While decreasing the N/P ratio from the water purification installation or dragging sediment that is charged in nutrient are realists, others solutions such as adding aluminium sulfates to increase the phosphate adsorption, restoring the macrophytes cover or introducing phytoplanktonophage fishes are more dangerous for the autochtonous species and the ecosystem functioning. Aluminium sulfate may be harmful for the sediment biogeochemistry and the introduction of non-native species may disturb the ecosystem functioning.

Aknowledment

This study was performed by the personal of the university of Bordeaux, the university of la Rochelle as well as the 'Union des Marais de Charente Maritime' by the support of the Agence 'Ministère de l'enseignement et de la Recherche,' the water agencies Loire-Bretagne and Adour-Garonne, the 'Conseil general de Charente Maritime and the European Union. Frequency of the taxa recorded per functional groups according to their taxonomic groups.

[C] Frequency of the taxa recorded per functional groups according to their Life traits. Only the significant Life traits found with GAMs on the first two axis of the phytoplankton-OMI were kept.

50 Frequency of the taxa recorded per functional group according to their Life traits.

  [subniche], [vegan], [ggplot2] and[gam].

FIGURESFigure 1 :

 1 FIGURES

Figure 3 :

 3 Figure 3: Outlying Mean Index analysis on nano-microphytoplankton (54 taxa; left panel) and mesozooplankton (27 taxa; right panel).

Figure 4 :

 4 Figure 4: Phytoplankton functional groups based on the OMI-GAM approach C1, C2, C3, C4 and C5. [A]Dispersion of the taxa according to their functional groups on the first two axis of the OMI analysis.[B]

Figure 5 :

 5 Figure 5: Mesozooplankton functional groups based on the OMI-GAM approach C1, C2, C3, C4. Only the significant Life traits found with GAMs on the first two axis of the mesozooplankton-OMI were kept: [A] Dispersion of the taxa according to their functional groups the OMI analysis found with GAMs on the first two axis [B] Frequency of the taxa recorded per functional groups according to their taxonomic groups. [C]

Figure 7 :

 7 Figure 7: Seasonal variations of biomasses and richness per functional group for both nano-microphyto-(left panel) and mesozooplankton (right panel). Black bars hide standard errors.

Figure 8 :

 8 Figure 8: Between-Habitats variations per functional group of nano-microphytoplankton witOMIG, witOMIGk, respective tolerances, biomasses, realized subniche percentages and specific richness per functional groups. Black bars hide standard errors.

Figure 9 :

 9 Figure 9: Between-Habitats variations per functional group of mesozooplankton witOMIG, witOMIGk, respective tolerances, biomasses, realized subniche percentages and specific richness per functional groups. Black bars hide standard errors.

TABLETable 1 :

 1 Two-way ANOVA for environmental parameters end ecological efficiency

	Parameter	Habitat	Season	Interaction
		effect	effect
	Temperature	ns	***	ns
	Conductivity	ns	*	ns
	pH	* (Replenishment,	ns	* (Replenishment, Catchment
		Catchment basin)		basin)
	Oxygen saturation	* (Catchment basin)	***	* (Catchment basin)
	NOx NH4 + PO4 3-	*** (Replenishment) *** (Urbanization) *** (Urbanization)	*** ** **	* (Replenishment) *** (Urbanization) * (Urbanization)
	N/P	*	*	ns
	SPM	***	***	ns
	POC	*** (Replenishment,	*	* (Replenishment, Catchment
		Catchment basin,		basin, Urbanization)
		Urbanization)
	PON	*** (Replenishment,	**	* (Replenishment, Catchment
		Catchment basin,		basin, Urbanization)
		Urbanization)
	POC/Chla	ns	*	ns
	Chla	ns	**	ns
	Active Chla	ns	**	ns
	POM δ13C	ns	**	ns
	POM δ15N	** (Urbanization)	ns	* (Urbanization)
	HP biomass	*** (Replenishment)	***	* (Replenishment)
	Microzooplankton biomass *** (Replenishment)	*	* (Replenishment)
	Ecological efficiency	* (Replenishment,	Ns	* (Replenishment, Catchment
		Catchment basin,		basin, Urbanization)
		Urbanization)

Table 2 :

 2 Two-way GLM for biomasses, taxonomic and functional indices and OMI indices: ns= non-significant, * significant at least p<0.05

	Parameters	Habitat effect	Interaction	Habitat	Interaction functional
			functional	effect	groups :habitat
			groups :habitat
		NANO-MICROPHYTOPLANKTON	ZOOPLANKTON
	Biomasses	* (Replenishment,	* (Replenishment,	*	* (Replenishment, Catchmen
		Catchment basin)	Catchment basin,	(Replenish	basin, Urbanization)
			Urbanization)	ment)
	Taxonomic richness * (Replenishment,	ns	*	* (Replenishment)
		Catchment basin)		(Replenish
				ment)
	Functional	* (Replenishment)	*( Replenishment,	*
	richness		Urbanization)	(Replenish
				ment)
	Functional	*(Replenishment)	ns	*
	divergence
				*
	Functional dispersion			(Replenish
				ment,
				Catchment
				basin)
	witOMIG	*(Replenishment)	* (Replenishment,		* (Replenishment, Catchmen
			Catchment basin,		basin, Urbanization)
			Urbanization)
	Tolerance	ns	* (Replenishment,	ns	ns
			Urbanization,
			Catchment basin)
	witOMIGk	ns	* (Catchment basin,	ns	* (Catchment basin,
			Urbanization)		Urbanization)
	Tolerance Gk	ns	* (Replenishment)	ns	*
	Realized niche	ns	* (Replenishment,	ns	* (Replenishment, Catchmen
	percentage		Catchment basin,		basin, Urbanization)
			Urbanization)

Concerning nano-microphytoplankton, all functional groups presented a significant lower preference and a less common habitat (higher WitOMI G and Gk) as well as a higher tolerance and realized niches for urbanized marshes (GLM, functional group:habitat effect, p<0.5; Figure 8). However, only small pelagic autotrophs (C4) presented significant differences in biomasses and richness between the two habitats with higher biomasses which contrasted with a lower richness for urbanized marshes (GLM, functional group:habitat effect, p<0.05; Figure 8).

Concerning mesozooplankton, K-strategists with both life style (C1) presented a significant higher preference and a more common habitat (lower WitOMI G and Gk) for non urbanized marshes which is coherent with their higher realized subniches and biomasses for this habitat (GLM, functional group:habitat effect, p<0.05; Figure 9). In contrast, r-strategist (C2 and C3) presented a significant lower preference, a less common habitat (higher WitOMI G and Gk) and a lower tolerance for the urbanized marshes while they displayed higher realized subniches and biomasses for this habitat at least for C3 (GLM, functional group:habitat effect, p<0.05; Figure 9).

Discussion

Ecological functions and seasonal variations in drained marshes

Both nano-microphyto-and mesozooplankton displayed high seasonal variations linked to the environmental fluctuations. These results are in accordance with those obtained for water quality for which most of the parameters presented some significant seasonal fluctuations in the same freshwater drained marshes as demonstrated by [START_REF] Tortajada | Variability of fresh-and salt-water marshes characteristics on the west coast of France: A spatio-temporal assessment[END_REF]. Winter was characterized by a low biological activity with the lowest biomasses of all the planktonic compartments -heterotrophic procaryots, phytoplankton, micro-and