Phosphorus budget in the Marne Watershed (France): urban vs. diffuse sources, dissolved vs. particulate forms

Abstract

International audienceWe evaluated the P sources (point, diffuse), through a nested watershed approach investigating the Blaise (607 km2), dominated by livestock farming, the Grand Morin (1202 km2), dominated by crop farming, and the Marne (12,762 km2), influenced by both agriculture and urbanization. Fertilizers account for the main P inputs (>60%) to the soils. An agricultural P surplus (0.5–8 kg P ha–1 year–1) contributes to P enrichment of the soil. The downstream urbanized zone is dominated by point sources (60%, mainly in dissolved forms), whereas in the upstream basin diffuse sources dominate (60%, mostly particulate). Among the diffuse sources (losses by forests, drainage and runoff), losses by runoff clearly dominate (>90%). P retention in the alluvial plain and the reservoir represents 15–30% of the total P inputs. Dissolved and particulate P fluxes at the outlet of the Marne are similar (340 and 319 tons of P year–1, respectively). The Blaise sub-basin receives P from point and diffuse sources in equal proportions, and retention is negligible. The Grand-Morin sub-basin, influenced by the urbanized zone receives, as does to the whole Marne basin, 60% of P inputs as point sources. The total particulate phosphorus in suspended sediments averaged 1.28 g P kg–1, of which about 60% are inorganic and 40% organic P. Particulate phosphorus exchangeable in 1 week and 1 year (32P isotopic method) accounts for between almost 26% and 54% of the particulate inorganic phosphorus in the suspended sediment and might represent an important source of dissolved P, possibly directly assimilated by the vegetation

Influence of legacy phosphorus, land use, and climate change on anthropogenic phosphorus inputs and riverine export dynamics

“…eutrophication and subsequent potential for hypoxia, loss of aquatic biodiversity and harmful algal blooms (Han et al 2011a;Roy and Bickerton 2014;Morse and Wollheim 2014). Due to differences in human activities, hydroclimate, land use/land cover, geology, and geomorphology, substantial spatio-temporal variability in anthropogenic P inputs and riverine P exports exists across regions and years (Némery et al 2005;Russell et al 2008;Han et al 2011a;Kleinman et al 2011;Hong et al 2012;Bowes et al 2014). To effectively guide P management for protecting water quality, it is important to quantify factors regulating anthropogenic P inputs and riverine export dynamics.…”

“…5). Particle P loss via erosion, dissolved P leaching (diffuse source pollution) and waste discharge (point source pollution) are believed to be the major pathways for P entering rivers (Némery et al 2005;Gentry et al 2007;Sobota et al 2011). Higher precipitation enhances erosion and leaching and subsequently increases fractional export of NAPI by rivers (Borbor-Cordova et al 2006;Morse and Wollheim 2014, Fig.…”

Net anthropogenic phosphorus inputs: spatial and temporal variability in the Chesapeake Bay region

“…Point sources associated with the urbanized coastal plain section of the Chesapeake Bay watershed may be responsible for the higher proportion of inputs being discharged there. In urbanized watersheds, point sources can account for greater than 60% of all phosphorus discharges (Nemery et al 2005). Point source discharges efficiently transfer phosphorus inputs to streams and P discharges can be greater than 25% of P inputs to streams in urbanized areas (McMahon and Woodside 1997).…”

Nitrogen Behaviour and Nitrous Oxide Emission in the Tidal Seine River Estuary (France) as Influenced by Human Activities in the Upstream Watershed

“…The measurements of the nitrogen forms at twice-monthly intervals and of daily water fluxes allowed the calculation of the N fluxes at the boundaries of the freshwater estuary (Poses-Caudebec) using the procedure described by Verhoff et al (1980) and recommended by Walling and Webb (1985), and commonly used for the Seine Ne´mery et al 2005).…”