Julien Némery

Origin and fate of phosphorus in the Seine watershed (France): Agricultural and hydrographic P budgets

Phosphorus (P) sources (point and diffuse) in the human-impacted Seine basin (64,840 km2) were evaluated for the year 2000. An agricultural P budget showed that fertilizers represented 59% (20–25 kgP ha−1) of P inputs to the soils. A P surplus (2.5 kg P ha−1 y−1) contributed to P enrichment of the agricultural soils whose stocks amounted to 1800–5000 kgP ha−1. A hydrographic P budget showed that runoff (0.39–0.51 kgP ha−1) dominated the diffuse sources. These losses represented a very low percentage (0.01%) of the P stocks in soils and contributed to 19–25% of the total P inputs to the drainage network. Point sources remained the main source of P (75–81%), particularly in the downstream urbanized zone. Phosphorus retention in the river drainage network accounted for 9–15% of the total P inputs, indicating that it must not be ignored in large river P budget calculations. The Seine basin exported 8000 tP y−1 (44% as particulate P) to its estuary. The annual mean particulate P in suspended sediment at the outlet (2.9 gP kg−1) was fourfold greater than in headwaters and in rural zones. The similar increase of the particulate inorganic P/particulate organic P ratio in suspended sediment along the river continuum clearly indicated the increasing pressure of point sources. The close relation between P content of suspended sediment during the high-flow period and the P content of agricultural soils resulted in proposing a novel method to calculate the PP losses from runoff.

Tracing sediment sources in a tropical highland catchment of central Mexico by using conventional and alternative fingerprinting methods

Land degradation is intense in tropical regions where it causes for instance a decline in soil fertility and reservoir siltation. Two fingerprinting approaches (i.e. the conventional approach based on radionuclide and geochemical concentrations and the alternative diffuse reflectance infrared Fourier transform spectroscopy method) were conducted independently to outline the sources delivering sediment to the river network draining into the Cointzio reservoir, in Mexican tropical highlands. This study was conducted between May and October in 2009 in subcatchments representative of the different environments supplying sediment to the river network. Overall, Cointzio catchment is characterized by very altered soils and the dominance of Andisols and Acrisols. Both fingerprinting methods provided very similar results regarding the origin of sediment in Huertitas subcatchment (dominated by Acrisols) where the bulk of sediment was supplied by gullies. In contrast, in La Cortina subcatchment dominated by Andisols, the bulk of sediment was supplied by cropland. Sediment originating from Potrerillos subcatchment characterized by a mix of Acrisols and Andisols was supplied in variable proportions by both gullies and rangeland/cropland. In this latter subcatchment, results provided by both fingerprinting methods were very variable. Our results outline the need to take the organic carbon content of soils into account and the difficulty to use geochemical properties to fingerprint sediment in very altered volcanic catchments. However, combining our fingerprinting results with sediment export data provided a way of prioritizing the implementation of erosion control measures to mitigate sediment supply to the Cointzio reservoir supplying drinking water to Morelia city. Copyright

Tracing sediment sources in a tropical highland catchment of central Mexico by using conventional and alternative fingerprinting methodsTracing sediment sources in a tropical

Land degradation is intense in tropical regions where it causes for instance a decline in soil fertility and reservoir siltation. Two fingerprinting approaches (i.e. the conventional approach based on radionuclide and geochemical concentrations and the alternative diffuse reflectance infrared Fourier transform spectroscopy method) were conducted independently to outline the sources delivering sediment to the river network draining into the Cointzio reservoir, in Mexican tropical highlands. This study was conducted between May and October in 2009 in subcatchments representative of the different environments supplying sediment to the river network. Overall, Cointzio catchment is characterized by very altered soils and the dominance of Andisols and Acrisols. Both fingerprinting methods provided very similar results regarding the origin of sediment in Huertitas subcatchment (dominated by Acrisols) where the bulk of sediment was supplied by gullies. In contrast, in La Cortina subcatchment dominated by Andisols, the bulk of sediment was supplied by cropland. Sediment originating from Potrerillos subcatchment characterized by a mix of Acrisols and Andisols was supplied in variable proportions by both gullies and rangeland/cropland. In this latter subcatchment, results provided by both fingerprinting methods were very variable. Our results outline the need to take the organic carbon content of soils into account and the difficulty to use geochemical properties to fingerprint sediment in very altered volcanic catchments. However, combining our fingerprinting results with sediment export data provided a way of prioritizing the implementation of erosion control measures to mitigate sediment supply to the Cointzio reservoir supplying drinking water to Morelia city. Copyright

N, P, Si budgets for the Red River Delta (northern Vietnam): how the delta affects river nutrient delivery to the sea

The Red River Delta (RRD) (Vietnam), a region experiencing rapid population growth, industrialization, and economic development, concentrates 54% of the population of the whole Red River watershed in less than 10% of the basin area. Our study aimed at understanding and quantifying the processes by which the delta affects the nutrient fluxes coming from the upstream watershed before they reach the sea. A comprehensive budget of nitrogen (N), phosphorus (P), and silica (Si) fluxes associated with natural and anthropogenic processes in the terrestrial and hydrological system of the delta was established for five sub-basins of the delta for the period 2000–2006, based on official statistical data, available measurements, and our own sampling campaigns and enquiries. The results show that anthropogenic inputs of N and P brought into the delta area are higher than the amounts delivered by the river from the upstream watershed. However, the amounts of these two elements ultimately delivered to the coastal zone from the delta are lower than the amounts carried by the upstream river, showing extremely efficient retention of both the soils and the delta’s drainage network. For Si (taking into account both dissolved and amorphous solid forms), the retention is much lower. High retention of N and P and low retention of Si in the delta area have up to now protected the coastal zone from severe eutrophication problems.

Phosphorus budget in the water‐agro‐food system at nested scales in two contrasted regions of the world (ASEAN‐8 and EU‐27)

Phosphorus (P) plays a strategic role in agricultural production as well as in the occurrence of freshwater and marine eutrophication episodes throughout the world. Moreover, the scarcity and uneven distribution of minable P resources is raising concerns about the sustainability of long-term exploitation. In this paper we analyze the P cycle in anthropic systems with an original multiscale approach (world region, country, and large basin scales) in two contrasting world regions representative of different trajectories in socioeconomic development for the 1961–2009 period: Europe (EU-27)/France and the Seine River Basin, and Asia (ASEAN-8)/Vietnam and the Red River Basin. Our approach highlights different trends in the agricultural and food production systems of the two regions. Whereas crop production increased until the 1980s in Europe and France and has stabilized thereafter, in ASEAN-8 and Vietnam it began to increase in the 1980s and it is still rising today. These trends are related to the increasing use of fertilizers, although in European countries the amount of fertilizers sharply decreased after the 1980s. On average, the total P delivered from rivers to the sea is 3 times higher for ASEAN-8 (300 kg P km−2 yr−1) than for EU-27 countries (100 kg P km−2 yr−1) and is twice as high in the Red River (200 kg P km−2 yr−1) than in the Seine River (110 kg P km−2 yr−1), with agricultural losses to water in ASEAN-8 3 times higher than in EU-27. Based on the P flux budgets, this study discusses early warnings and management options according to the particularities of the two world regions, newly integrating the perspective of surface water quality with agricultural issues (fertilizers, crop production, and surplus), food/feed exchanges, and diet, defining the so-called water-agro-food system.

Atmospheric nitrate export in streams along a montane to urban gradient

Nitrogen (N) emissions associated with urbanization exacerbate the atmospheric N influx to remote ecosystems - like mountains -, leading to well-documented detrimental effects on ecosystems (e.g., soil acidification, pollution of freshwaters). Here, the importance and fate of N deposition in a watershed was evaluated along a montane to urban gradient, using a multi-isotopic tracers approach (Δ17O, δ15N, δ18O of nitrate, δ2H and δ18O of water). In this setting, the montane streams had higher proportions of atmospheric nitrate compared to urban streams, and exported more atmospheric nitrate on a yearly basis (0.35 vs 0.10 kg-Nha-1yr-1). In urban areas, nitrate exports were driven by groundwater, whereas in the catchment head nitrate exports were dominated by surface runoff. The main sources of nitrate to the montane streams were microbial nitrification and atmospheric deposition, whereas microbial nitrification and sewage leakage contributed most to urban streams. Based on the measurement of δ15N and δ18O-NO3-, biological processes such as denitrification or N assimilation were not predominant in any streams in this study. The observed low δ15N and δ18O range of terrestrial nitrate (i.e., nitrate not coming from atmospheric deposition) in surface water compared to literature suggests that atmospheric deposition may be underestimated as a direct source of N.