Typical features of particulate phosphorus in the Seine estuary (France)

Abstract

International audienceDuring the 2001–2002 hydrological cycle, 8,000 tons P year−1 (44% as particulate phosphorus) originating from the Seine basin entered the Seine estuary. P content in suspended sediments (SS) is 2.9 g P kg−1 (80% as inorganic form) at Poses (the upstream limit of the Seine estuary). During the transfer from Poses to Caudebec (the limit of saline water intrusion), Particulate Inorganic Phosphorus (PIP) in SS decreases by 40% whereas Particulate Organic Phosphorus (POP) remains stable. This decrease is explained as the result of (i) a dilution by SS poorer in P, originating from storage zones (mudflats) within the estuary, and (ii) a loss of P by sedimentation, especially in the Rouen harbour where 15% to 20% of SS are yearly trapped and extracted. Downstream, in the turbidity maximum of the estuary, P content in SS is twice as low as at Poses (1.5 g P kg−1, 70% as inorganic form). PIP content is fairly homogeneous both vertically and throughout an annual survey. On the other hand, POP varies by season. Higher POP content is observed during vernal period with phytoplankton accumulation. In a salinity gradient from 0 to 30 (PSS78), PIP content further decreases by 30%. POP does not vary much in this gradient, leading to the assumption that PIP is submitted to desorption in response to the dilution by marine waters (poor in orthophosphates). Using 32P isotopic method, we establish a mathematical formulation of P exchangeable between the suspended solid and water phases of the Seine estuary. Particulate P in the turbidity maximum zone is shown to represent a possible source of dissolved P, available for algal growth in the Seine Bight. Instead of playing a role of nutrient retention, the turbidity maximum zone of the Seine estuary could favour coastal eutrophication

Addressing the measurement of particulate organic and inorganic phosphorus in estuarine and coastal waters

“…4). These contributions are similar or lower than those found by Van der Zee et al (2007) and Nemery and Garnier (2007) in the Scheldt and the Seine estuaries with similar methods, 65% and 66-75% respectively. They are even lower than those found when a sequential extraction of P forms was used, 70-80% in the Gironde estuary (Deborde et al, 2007).…”

“…Some studies on the speciation of TPP in coastal and estuarine waters have used the Aspila method (Yuan et al, 2009;Nemery and Garnier, 2007;Benitez-Nelson et al, 2004;Loh and Bauer, 2000). However the use of this method for SPM has not been discussed with regard to the different nature of SPM compared to particulate matter present in sediments.…”

An integrated modelling approach to forecast the impact of human pressure in the Seine estuary

“…Given that the estuarine section submitted to saline intrusion, i.e., the turbidity maximum zone, may play an important role in the transformation of particulate species, such as the particulate organic matter including the phytoplanktonic biomass (Even et al, 2004a, b) & Garnier, 2007), which may desorb, a three dimensional approach is currently being developed to include this 30 km long reach. As these processes can modify the nutrient ratios, the results discussed above, although representative of the upstream estuary, cannot be simply extrapolated to the coastal zone.…”

Nitrogen processes in coastal and marine ecosystems

“…Th is process, termed fl occulation, promotes sedimentation of riverine particulate organic matter in estuaries. Further, the salinity gradient has been shown to contribute to phosphorus desorption (Némery and Garnier, 2007 ) whereas silica dissolution could be ten times higher in the saline waters compared to the freshwater ones (Roubeix and Lancelot, 2008 ;Garnier et al ., 2006 ). All these estuarine processes may aff ect the nutrient fl uxes delivered to the marine waters.…”