Estimating ecosystem metabolism from continuous multi-sensor measurements in the Seine River

Abstract

Large rivers are important components of the global C cycle. While they are facing an overall degradation of their water quality, little remains known about the dynamics of their metabolism. In the present study, we used continuous multi-sensors measurements to assess the temporal variability of gross primary production (GPP) and ecosystem respiration (ER) rates of the anthropized Seine River over an annual cycle. Downstream from the Paris urban area, the Seine River is net heterotrophic at the annual scale (-226 gO m year or -264 gC m year). Yet, it displays a net autotrophy at the daily and seasonal scales during phytoplankton blooms occurring from late winter to early summer. Multivariate analyses were performed to identify the drivers of river metabolism. Daily GPP is best predicted by chlorophyll a (Chla), water temperature (T), light, and rainfalls, and the coupling of daily GPP and Chla allows for the estimation of the productivity rates of the different phytoplankton communities. ER rates are mainly controlled by T and, to a lesser extent, by Chla. The increase of combined sewer overflows related to storm events during the second half of the year stimulates ER and the net heterotrophy of the river. River metabolism is, thus, controlled at different timescales by factors that are affected by human pressures. Continuous monitoring of river metabolism must, therefore, be pursued to deepen our understanding about the responses of ecosystem processes to changing human pressures and climate.

Influence of Hydrological Perturbations and Riverbed Sediment Characteristics on Hyporheic Zone Respiration of CO2 and N2

“…The significance of biogenic CO 2 and N 2 gas production due to heterotrophic microbial activity in rivers and associated hyporheic zones to the overall carbon balance of rivers is poorly quantified, yet net heterotrophy is estimated to be 0.32 Pg C yr −1 , with half of terrestrial organic carbon stored or transformed in aquatic systems (Battin et al, ). While net heterotrophic conditions are common in inland waters (Escoffier et al, ), much less is known about controls on hyporheic zone contributions to biogenic CO 2 and N 2 gas production and fate of resulting C and N storage in subsurface biomass.…”

“…Hyporheic zones contribute to metrics of river net ecosystem productivity (NEP) through the consumption of O 2 from AR and NI and the production of CO 2 from both AR and DN. NEP is typically estimated with instream diel oxygen metabolism methods (i.e., Escoffier et al, ; Hall et al, ; Hotchkiss et al, ; Odum, ), as a balance between gross primary production (GPP), autotrophic respiration ( R a ), and river and hyporheic heterotrophic respiration ( R h1 + R h2 ) where the hyporheic heterotrophic component ( R h2 ) is typically neglected in the O 2 model (Figure ). Assuming a 1:1 ratio between O 2 consumption and CO 2 production ( ), and constant diffusion terms ( D ), hyporheic heterotrophic respiration ( R h2 ) is then estimated using river CO 2 mass balance closure with rates of R h2 found to vary between 1 and 2 g/m 2 /d of CO 2 (Hotchkiss et al, ).…”

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

“…Sampling was not performed during blooms, avoiding an impact of phytoplankton on fluxes. The Seine River is net heterotrophic at the annual scale (Escoffier et al, 2016), except during spring (due to the presence of diatoms) and summer (Chlorophyceae and diatoms) blooms (Garnier et al, 1995). Cyanobacteria are not common and were not observed in 2011 (Escoffier et al, 2016).…”

“…The Seine River is net heterotrophic at the annual scale (Escoffier et al, 2016), except during spring (due to the presence of diatoms) and summer (Chlorophyceae and diatoms) blooms (Garnier et al, 1995). Cyanobacteria are not common and were not observed in 2011 (Escoffier et al, 2016). More studies about nitrite fluxes during spring and summer blooms would shed light on the role of phytoplankton uptake and release on nitrite dynamics.…”

The potamochemical symphony: new progress in the high-frequency acquisition of stream chemical data

“…Automated approaches, developed using probes installed directly in the river (Rozemeijer et al, 2010a;Macintosh et al, 2011;Cassidy and Jordan 2011;Dåbakk et al, 1999;Glasgow et al, 2004;Zhu et al, 2010;Yang et al, 2008), or using online instrumental devices in which continuously pumped water is injected (Rozemeijer et al, 2010b;Zabiegala et al, 2010;Jordan and Cassidy, 2011), are alternatives to sampling methods requiring human intervention. Several papers have been published over the last decade reporting existing devices mostly focused on monitoring dissolved N or P and organic matter (Clough et al, 2007;Kunz et al, 2012;Aubert et al, 2013b;Escoffier et al, 2016). A recent overview of the potential of available conductivity, dissolved oxygen and carbon dioxide, nutrients, dissolved organic matter and chlorophyll in situ probes is given by Rode et al (2016).…”