GLORIA - A globally representative hyperspectral in situ dataset for optical sensing of water quality

The development of algorithms for remote sensing of water quality (RSWQ) requires a large amount of in situ data to account for the bio-geo-optical diversity of inland and coastal waters. The GLObal Reflectance community dataset for Imaging and optical sensing of Aquatic environments (GLORIA) includes 7,572 curated hyperspectral remote sensing reflectance measurements at 1 nm intervals within the 350 to 900 nm wavelength range. In addition, at least one co-located water quality measurement of chlorophyll a, total suspended solids, absorption by dissolved substances, and Secchi depth, is provided. The data were contributed by researchers affiliated with 59 institutions worldwide and come from 450 different water bodies, making GLORIA the de-facto state of knowledge of in situ coastal and inland aquatic optical diversity. Each measurement is documented with comprehensive methodological details, allowing users to evaluate fitness-for-purpose, and providing a reference for practitioners planning similar measurements. We provide open and free access to this dataset with the goal of enabling scientific and technological advancement towards operational regional and global RSWQ monitoring

QUAL-NET, a high temporal-resolution eutrophication model for large hydrographic networks

To allow climate change impact assessment of water quality in river systems, the scientific community lacks efficient deterministic models able to simulate hydrological and biogeochemical processes in drainage networks at the regional scale, with high temporal resolution and water temperature explicitly determined. The model QUALity-NETwork (QUAL-NET) was developed and tested on the Middle Loire River Corridor, a sub-catchment of the Loire River in France, prone to eutrophication. Hourly variations computed efficiently by the model helped disentangle the complex interactions existing between hydrological and biological processes across different timescales. Phosphorus (P) availability was the most constraining factor for phytoplankton development in the Loire River, but simulating bacterial dynamics in QUAL-NET surprisingly evidenced large amounts of organic matter recycled within the water column through the microbial loop, which delivered significant fluxes of available P and enhanced phytoplankton growth. This explained why severe blooms still occur in the Loire River despite large P input reductions since 1990. QUAL-NET could be used to study past evolutions or predict future trajectories under climate change and land use scenarios

Data for: Seasonal and event-based concentration-discharge relationships to identify catchment controls on nutrient export regimes

The water quality parameters included in this database were nitrate (NO3-), total phosphorus (TP) and soluble reactive phosphorus (SRP). From approximately 10 000 water quality stations present in the French national public database (http://www.naiades.eaufrance.fr/), we selected the stations meeting all the following criteria: i) C station can be paired with a Q station (data from http://www.hydro.eaufrance.fr/) when their catchments share at least 90% surface area; ii) all C catchments are independent; iii) C data contains at least 50 observations after outliers removal (i.e. values over 200 mgN L-1 and 5 gP L-1) over the period 2008-2015; iv) at least 30% of C observations occurred during “major” hydrological events (defined here as Q(t) > 1.5 x Q_baseflow); v) trends on C are non-significant over the period (p-value of Sen’s Slope test > 0.05, following Hipel and McLeod (2005)). Finally, stations where a single concentration value was observed more than 15% of the time were removed from the selection, a situation often seen in P surveys when concentrations are below quantification limits. This resulted in 219 unique catchments with respectively 179, 138 and 107 individual time series for NO3-, TP and SRP.THIS DATASET IS ARCHIVED AT DANS/EASY, BUT NOT ACCESSIBLE HERE. TO VIEW A LIST OF FILES AND ACCESS THE FILES IN THIS DATASET CLICK ON THE DOI-LINK ABOV

Eutrophication mitigation in rivers: 30 years of trends in spatial and seasonal patterns of biogeochemistry of the Loire River (1980–2012)

Trends and seasonality analysis from 1980 onward and longitudinal distribution, from headwaters to estuary, of chlorophyll <i>a</i>, nitrate and phosphate were investigated in the eutrophic Loire River. The continuous decline of phosphate concentrations which has been recorded since 1991 both in the main river and in the tributaries has led to the conclusion that it was responsible for the significant reduction in phytoplanktonic biomass across the whole river system, although <i>Corbicula</i> spp. clams invaded the river during the same period and probably played a significant role in the phytoplankton decline. While eutrophication remained lower in the main tributaries than in the Loire itself, they were found to contribute up to &approx; 35% to the total nutrient load of the main river. The seasonality analysis revealed significant seasonal variations for the different eutrophication metrics and calls into question the classical monthly survey recommended by national or international authorities. Reducing P inputs impacted these seasonal variations: the decline of seasonal amplitudes of chlorophyll <i>a</i> reduced the seasonal amplitude of orthophosphate and of daily variations of dissolved oxygen and pH but did not significantly affect the seasonal amplitude of nitrate. Thus, the influence of phytoplankton on seasonal variations of nitrate was minor throughout the period of study

Spatial and Temporal Variability in Concentration‐Discharge Relationships at the Event Scale

The analysis of concentration‐discharge (C‐Q) relationships from low‐frequency observations is commonly used to assess solute sources, mobilization, and reactive transport processes at the catchment scale. High‐frequency concentration measurements are increasingly available and offer additional insights into event‐scale export dynamics. However, only few studies have integrated inter‐annual and event‐scale C‐Q relationships. Here, we analyze high‐frequency measurements of specific conductance (EC), nitrate (NO3‐N) concentrations and spectral absorbance at 254 nm (SAC254, as a proxy for dissolved organic carbon) over a two year period for four neighboring catchments in Germany ranging from more pristine forested to agriculturally managed settings. We apply an integrated method that adds a hysteresis term to the established power law C‐Q model so that concentration intercept, C‐Q slope and hysteresis can be characterized simultaneously. We found that inter‐event variability in C‐Q hysteresis and slope were most pronounced for SAC254 in all catchments and for NO3‐N in forested catchments. SAC254 and NO3‐N event responses in the smallest forested catchment were closely coupled and explainable by antecedent conditions that hint to a common near‐stream source. In contrast, the event‐scale C‐Q patterns of EC in all catchments and of NO3‐N in the agricultural catchment without buffer zones around streams were less variable and similar to the inter‐annual C‐Q relationship indicating a homogeneity of mobilization processes over time. Event‐scale C‐Q analysis thus added key insights into catchment functioning whenever the inter‐annual C‐Q relationship contrasted with event‐scale responses. Analyzing long‐term and event‐scale behavior in one coherent framework helps to disentangle these scattered C‐Q patterns.Key Points: We compare event‐scale and inter‐annual concentration‐discharge relationships in four adjoined catchments with contrasting land use. The variability of event‐scale C‐Q relationships was shaped by land use and antecedent conditions for biogeochemically reactive but not for geogenic solutes. For biogeochemically reactive solutes, event‐scale C‐Q patterns can contrast the inter‐annual pattern obtained from all observations.Helmholtz Association http://dx.doi.org/10.13039/501100009318Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/50110000234

Multidecadal Trajectory of Riverine Nitrogen and Phosphorus Dynamics in Rural Catchments

ISI Document Delivery No.: GU6UJ Times Cited: 0 Cited Reference Count: 66 Dupas, Remi Minaudo, Camille Gruau, Gerard Ruiz, Laurent Gascuel-Odoux, Chantal Amer geophysical union WashingtonInternational audienceThe long-term evolution of nutrient dynamics in rivers under changing external forcings, termed hereafter trajectory, is influenced by local human activities and regional climatic variations. Here we investigate nitrogen (N) and phosphorus (P) dynamics in seven mesoscale agricultural catchments (median size 800 km 2) of western France from seasonal to multidecadal time scales (1970–2016). Results show that, in these catchments dominated by shallow groundwater, long-term nitrate exports responded to variations of the agricultural N surplus with time lags of approximately 10 years. Presence of legacy N storage, related to the catchments' denitrification capacity, was found to increase response times. In contrast, P trends were predominantly controlled by decreasing point source emissions during the study period, and P dynamics were influenced by in-stream retention/remobilization processes that hampered precise quantification of land-to-river diffuse transport processes. Occurrence of interannual climate variations during three 5-to 10-year dry-wet cycles, influenced by the North Atlantic Oscillation, affected N and P dynamics with persistent interannual hysteresis patterns among catchment and years. Thus, water quality assessment programs should cover at least five years to decipher the effect of mitigation measures from climate variations