Hydrological Alteration Index as an Indicator of the Calibration Complexity of Water Quantity and Quality Modeling in the Context of Global Change

Modeling is a useful way to understand human and climate change impacts on the water resources of agricultural watersheds. Calibration and validation methodologies are crucial in forecasting assessments. This study explores the best calibration methodology depending on the level of hydrological alteration due to human-derived stressors. The Soil and Water Assessment Tool (SWAT) model is used to evaluate hydrology in South-West Europe in a context of intensive agriculture and water scarcity. The Index of Hydrological Alteration (IHA) is calculated using discharge observation data. A comparison of two SWAT calibration methodologies are done; a conventional calibration (CC) based on recorded in-stream water quality and quantity and an additional calibration (AC) adding crop managements practices. Even if the water quality and quantity trends are similar between CC and AC, water balance, irrigation and crop yields are different. In the context of rainfall decrease, water yield decreases in both CC and AC, while crop productions present opposite trends (+33% in CC and -31% in AC). Hydrological performance between CC and AC is correlated to IHA: When the level of IHA is under 80%, AC methodology is necessary. The combination of both calibrations appears essential to better constrain the model and to forecast the impact of climate change or anthropogenic influences on water resources

Experimental evidences for the use of two macroalgal species, Ascophyllum nodosum and Fucus vesiculosus as biomonitors of N sources

Proyecto ANILE (CTM2009-08396, CTM2010-08804-E) Plan Nacional de I+D+i y Proyecto RADIALES (IEO)Postprint2,263

Translocation of isotopically distinct macroalgae : a route to low-cost biomonitoring?

Nitrogen stable isotope ratios (δ15N) in macroalgae are often used to identify sources of nitrogenous pollution in fluvial and estuarine settings. This approach assumes that the macroalgal δ15N is representative of the sources of the pollution averaged over a timespan in the order of days to weeks, but the preferential uptake of a particular nitrogen compound or potential for fractionation in the water column or during uptake and assimilation by the macroalgae could make this assumption invalid. Laboratory studies were therefore performed to investigate the uptake and assimilation of both nitrate and ammonium at a variety of concentrations using the vegetative (non-fertile) tips of the brown macroalgae, Fucus vesiculosus. Nitrate appeared to fractionate at high concentrations, and was found to be taken up more rapidly than ammonia; within 13 days, the macroalgae tips were in isotopic equilibrium with the nitrate solution at 500 μM. These experiments were complemented by an investigation involving the translocation of macroalgae collected from a site enriched in 15N relative to natural levels (Staithes, UK), to the River Tees, Middlesbrough (UK), a site depleted in 15N relative to natural levels. The nitrogen isotope signature shifted 50% within 7 days, with samples deployed nearer the surface subject to greater change. These findings suggest that the translocation of macroalgae with isotopically distinct signatures can be used as a rapid, cost-efficient method for nitrogen biomonitoring in estuarine environments

Unbounded boundaries and shifting baselines: estuaries and coastal seas in a rapidly changing world

This Special Issue of Estuarine, Coastal and Shelf Science presents contributions from ECSA 55; an international symposium organised by the Estuarine and Coastal Sciences Association (ECSA) and Elsevier on the broad theme of estuaries and coastal seas in times of intense change. The objectives of the SI are to synthesise, hypothesise and illustrate the impacts of global change on estuaries and coastal seas through learning lessons from the past, discussing the current and forecasting for the future. It is highlighted here that establishing impacts and assigning cause to the many pressures of global change is and will continue to be a formidable challenge in estuaries and coastal seas, due in part to: (1) their complexity and unbounded nature; (2) difficulties distinguishing between human-induced changes and natural variations and; (3) multiple pressures and effects. The contributing authors have explored a number of these issues over a range of disciplines. The complexity and connectivity of estuaries and coastal seas have been investigated through studies of physicochemical and ecological components, whilst the human imprint on the environment has been identified through a series of predictive, contemporary, historical and palaeo approaches. The impact of human activities has been shown to occur over a range of spatial and temporal scales, requiring the development of integrated management approaches. These 30 articles provide an important contribution to our understanding and assessment of the impacts of global change. The authors highlight methods for essential management/mitigation of the consequences of global change and provide a set of directions, ideas and observations for future work. These include the need to consider: (1) the cumulative, synergistic and antagonistic effects of multiple pressures; (2) the importance of unbounded boundaries and connectivity across the aquatic continuum; (3) the value of combining cross-disciplinary palaeo, contemporary and future modelling studies and; (4) the importance of shifting baselines on ecosystem functioning and the future provision of ecosystem services

Macroalgae δ 15 N values in well-mixed estuaries: indicator of anthropogenic nitrogen input or macroalgae metabolism?

International audienceAlthough nitrogen stable isotope ratio (d15N) in macroalgae is widely used as a bioindicator of anthropogenic nitrogen inputs to the coastal zone, recent studies suggest the possible role of macroalgae metabolism in d15N variability. Simultaneous determinations of d15N of dissolved inorganic nitrogen(DIN) along the landesea continuum, inter-species variability of d15N and its sensitivity to environmental factors are necessary to confirm the efficiency of macroalgae d15N in monitoring nitrogen origin in mixed-use watersheds. In this study, d15N of annual and perennial macroalgae (Ulva sp., Enteromorpha sp., Fucus vesiculosus and Fucus serratus) are compared to d15N-DIN along the Charente Estuary, after characterizing d15N of the three main DIN sources (i.e. cultivated area, pasture, sewage treatment plant outlet). During late winter and spring, when human activities produce high DIN inputs, DIN sources exhibit distinct d15N signals in nitrate (NO3-) and ammonium (NH4+): cultivated area (+6.5 ± 0.6 ‰ and +9.0 ± 11.0 ‰), pasture (+9.2 ± 1.8 ‰ and +12.4 ‰) and sewage treatment plant discharge (+16.9 ± 8.7 ‰ and +25.4 ± 5.9 ‰). While sources show distinct d15N - NO3- in this multiple source catchment, the overall mixture of NO3- sources - generally >95% DIN - leads to low variations of d15N - NO3- at the mouth of the estuary (+7.7 to +8.4 ‰). Even if estuarine d15N - NO3- values are not significantly different from pristine continental and oceanic site (+7.3 ‰ and +7.4 ‰), macroalgae d15N values are generally higher at the mouth of the estuary. This highlights high anthropogenic DIN inputs in the estuary, and enhanced contribution of 15N-depleted NH4+ in oceanic waters. Although seasonal variations in d15N - NO3- are low, the same temporal trends in macroalgae d15N values at estuarine and oceanic sites, and inter-species differences in d15N values, suggest that macroalgae d15N values might bemodified by the metabolic response of macroalgae to environmental parameters (e.g., temperature, light, DIN concentrations). Differences between annual and perennial macroalgae indicate both a higher integration time of perennial compared to annual macroalgae and the possible role of passive versus active uptake mechanisms. Further studies are required to characterize the sensitivity of macroalgae fractionation to variable environmental conditions and uptake mechanisms

Cycle benthique du silicium dans les estuaires (observations et modélisation à différentes échelles spatio-temporelles)

Les estuaires sont des zones complexes et hétérogènes, soumises à de fortes pressions anthropiques, qui peuvent avoir un rôle déterminant de filtre lors du transport et de la transformation de la matière vers les zones côtières. Le cycle du silicium (Si), essentiel à la croissance des diatomées qui constituent la base des réseaux trophiques sains, est encore mal défini au sein de ces interfaces. Cette thèse a pour objectif d étudier le cycle benthique du Si dans les deux principaux estuaires de la Rade de Brest. Afin d aborder les interactions d échelles propres aux estuaires, et de les intégrer aux estimations de flux, les hétérogénéités spatiales et les variations tidales du cycle benthique du Si ont été quantifiées et comparées aux variations saisonnières le long des estuaires. Dans le but d étudier les interactions entre les cycles de la matière (N, P, C, Si) exerçant un contrôle sur le fonctionnement des écosystèmes côtiers, les interactions entre Si et Pont été explorées et semblent favoriser la rétention de P. Enfin, le cycle benthique du Si a été étudié à l aide d u outil de modélisation de la diagénèse précoce, afin de palier à la difficile estimation directe des flux de dépôt dans les estuaires, et évaluer le rôle des estuaires dans la rétention et le recyclage de Si. Cette première contribution à l étude du fonctionnement du cycle du Si dans les estuaires de la Rade de Brest ouvre de nombreuses perspectives en termes d études de processus et de modélisation, que ce soit dans la perspective d un modèle intégré du continuum terre-mer de la Rade de Brest, ou d un modèle générique du cycle du Si ai sein des marges continentales.Estuaries are complex and heterogeneous areas, subject to many anthropogenic activities, which can have strong filtering capacities during transport and processing of terrestrial matter to coastal zones. The cycling of silicon (Si), which is essential for the growth of diatoms constituting the basis of healthy food webs, is coarsely defined at these interfaces (Dürr et al., 2011). This thesis aims to study the benthic Si cycle in the two main estuaries of the Bay of Brest. To address the interactions of scales and to integrate them in flux estimates spatial heterogeneity and tidal variations of benthic Si cycle were quantified and compared with seasonal variations along estuaries. In order to study the interactions between the different cycles of matter (N, P, C, Si) controlling the functioning of coastal ecosystems, the interactions between Si and P have been explored and appear to favor the retention of P. Finally, the benthic cycle of Si was studied using a diagenetic model to estimate deposition fluxes, that are difficult to estimate directly in estuaries, and to evaluate the retention and recycling of Si at a seasonal scale. This first contribution to the study of the Si cycle in the estuaries of the Bay of Brest offers many opportunities in terms of experimental studies and modelling, whether from the perspective of an integrative model of the land-sea interface in the Bay of Brest, or from the implementation of a generic model of the Si cycle in continental margins.BREST-BU Droit-Sciences-Sports (290192103) / SudocSudocFranceF

Landward Perspective of Coastal Eutrophication Potential Under Future Climate Change: The Seine River Case (France)

International audienceStudies quantifying the impact of climate change have so far mostly examined atmospheric variables, and few are evaluating the cascade of aquatic impacts that will occur along the land–ocean continuum until the ultimate impacts on coastal eutrophication potential. In this study, a new hydro-biogeochemical modeling chain has been developed, based on the coupling of the generic pyNuts-Riverstrahler biogeochemical model and the GR4J-CEMANEIGE hydrological model, and applied to the Seine River basin (France). Averaged responses of biogeochemical variables to climate-induced hydrological changes were assessed using climate forcing based on 12 projections of precipitation and temperature (BC-CORDEX) for the stabilization (RCP 4.5) and the increasing (RCP 8.5) CO2 emission scenarios. Beyond the amount of nutrients delivered to the sea, we calculated the indicator of coastal eutrophication potential (ICEP). The models run with the RCP4.5 stabilization scenario show low variations in hydrological regimes and water quality, while five of the six models run with the increasing CO2 emissions scenario (RCP8.5) leads to more intense extreme streamflow (i.e., higher maximum flows, lower and longer minimum flows), resulting in the degradation of water quality. For the driest RCP 8.5 projection, median biogeochemical impacts induced by decreasing discharge (until −270 m3 s−1 in average) are mostly located downstream of major wastewater treatment plants. During spring bloom, e.g., in May, the associated higher residence time leads to an increase of phytoplankton biomass (+31% in average), with a simultaneous −23% decrease of silicic acid, followed downstream by a −9% decrease of oxygen. Later during low flow, major increases in nitrate and phosphate concentrations (until +19% and +32% in average) are expected. For all considered scenarios, high ICEP values (above zero) lasted, indicating that coastal eutrophication is not expected to decrease with changing hydrological conditions in the future. Maximum values are even expected to be higher some years. This study deliberately evaluates the impact of modified hydrology on biogeochemistry without considering the simultaneous alteration of water temperatures, in order to disentangle the causes of climate change-induced impact. It will serve as a first comparative step toward a more complete modeling experiment of climate change impacts on aquatic systems

Nitrifying Kinetics and the Persistence of Nitrite in the Seine River, France

International audienceAlthough a higher oxidation rate for nitrite than for ammonia generally prevents nitrite accumulation in oxic waters, nitrite concentrations in the Seine River (1-31 mM) exceed European norms. We investigated the kinetics of in situ ammonia-and nitrite-oxidizing communities in river water and wastewater treatment plant (WWTP) effluents to determine the role of pelagic nitrification in the origin and persistence of nitrite downstream of Paris. The main source of nitrite is the major Parisian WWTP, and its persistence, up to tens of kilometers downstream of the plant, is explained by low ammonia and nitrite oxidation rates and high river flow. Furthermore, similar nitrite and ammonia oxidation rates preclude a rapid consumption of both preexisting nitrite and nitrite produced by ammonia oxidation. Maximum ammonia oxidation rates are two to three times higher downstream than upstream of the WWTP, indicating the input of ammonia oxidizers and ammonia from the WWTP. In both river water and WWTP effluents, nitrite oxidizers were unable to oxidize all available nitrite. In the human-impacted Seine River, this phenomenon might be due to mixotrophy. This study highlights the low resilience of the river to nitrite contamination as well as the importance of managing nitrite, nitrifiers, and organic matter concentrations in WWTP effluents to avoid nitrite persistence in rivers