Amélie Darracq

Nutrient loads exported from managed catchments reveal emergent biogeochemical stationarity

Complexity of heterogeneous catchments poses challenges in predicting biogeochemical responses to human alterations and stochastic hydro?climatic drivers. Human interferences and climate change may have contributed to the demise of hydrologic stationarity, but our synthesis of a large body of observational data suggests that anthropogenic impacts have also resulted in the emergence of effective biogeochemical stationarity in managed catchments. Long?term monitoring data from the Mississippi?Atchafalaya River Basin (MARB) and the Baltic Sea Drainage Basin (BSDB) reveal that inter?annual variations in loads (LT) for total?N (TN) and total?P (TP), exported from a catchment are dominantly controlled by discharge (QT) leading inevitably to temporal invariance of the annual, flow?weighted concentration, Cf = (LT/QT). Emergence of this consistent pattern across diverse managed catchments is attributed to the anthropogenic legacy of accumulated nutrient sources generating memory, similar to ubiquitously present sources for geogenic constituents that also exhibit a linear LT?QT relationship. These responses are characteristic of transport?limited systems. In contrast, in the absence of legacy sources in less?managed catchments, Cf values were highly variable and supply limited. We offer a theoretical explanation for the observed patterns at the event scale, and extend it to consider the stochastic nature of rainfall/flow patterns at annual scales. Our analysis suggests that: (1) expected inter?annual variations in LT can be robustly predicted given discharge variations arising from hydro?climatic or anthropogenic forcing, and (2) water?quality problems in receiving inland and coastal waters would persist until the accumulated storages of nutrients have been substantially depleted. The finding has notable implications on catchment management to mitigate adverse water?quality impacts, and on acceleration of global biogeochemical cycles.

Long‐term development of phosphorus and nitrogen loads through the subsurface and surface water systems of drainage basins

We analyze and compare simulations and controlling processes of the past 60 years and possible future short-and long-term development of phosphorus and nitrogen loading from the Swedish Norrstrom d ...

Physical versus biogeochemical interpretations of nitrogen and phosphorus attenuation in streams and its dependence on stream characteristics

We investigate the influence of biogeochemical nutrient attenuation rates versus physical solute travel times on nutrient transport and attenuation in streams with different characteristics. Compar ...

Nutrient cycling and N2O emissions in a changing climate: the subsurface water system role

This study has quantified the subsurface (groundwater, soil, sediment) water system role for hydrological nitrogen (N) and phosphorus (P) loading to the coast and agricultural N2O emissions to the atmosphere in a changing climate. Results for different climate and hydrological model scenarios in the Swedish Norrstrom drainage basin show that the subsurface water system may largely control a long-term increase in the coastal nutrient loading, in particular for P, irrespectively of the realized future climate change scenario and our uncertainty about it and its water flow effects. The results also indicate an important subsurface water system role for current atmospheric N2O emissions from agriculture, and an even greater role for future ones. The current N2O–N emissions from agriculture are quantified to be about 0.05 g m−2 yr−1 over the basin surface area, or 3% of the direct N mass application on the agricultural land. These results are consistent with recent global emission estimates, and show how the latter can be reconciled with previous, considerably smaller subsystem emission estimates made by the IPCC (Intergovernmental Panel on Climate Change).