Spatial variability of organic matter and phosphorus cycling in Rhône River prodelta sediments (NW Mediterranean Sea, France): a data-model approach

the mediterranean sea (ms) is a large oligotrophic sea. its productivity may be sensitive to riverine nutrient inputs. understanding its productivity involves quantifying phosphorus (p) river supply which is crucial for calculating p mass balances in the anthropogenically disturbed sea. yet the precise role of the deltaic filter is not known, especially concerning the differential trapping/recycling of nutrients in deltaic sediments. a benthic dataset from the rhône river prodelta was coupled to an early diagenetic model, including the benthic p cycle. the dataset comprised porewater oxygen, nitrate, sulfate, dissolved inorganic carbon, ammonium, dissolved reduced and total iron, dissolved inorganic phosphorus (dip) and solid data (organic carbon, fe-bound p, ca-bound p and organic p) for 9 stations from the rhône river prodelta. the model results indicated that the intensity of biogeochemical processes occurring near the sediment–water interface decreased from the river mouth to the adjacent continental shelf. this decrease occurred according to oc fluxes to the seafloor, sedimentation rates and integrated rates of oc mineralization (from 160 mmol c m-2 d-1 near the mouth to 10 mmol m-2 d-1 on the shelf). the organic p mineralization was intense, especially near the river mouth (1196 µmol m-2 d-1), and its contribution to dip release was large (> 90%). fe-bound p had a key role in promoting ca-bound p precipitation in anoxic sediments. these sediments played an important role as a source of regenerated dip.a significant part of dip was recycled to the overlying waters (72-94%), representing 25% of the riverine discharge input of dip. while 6-28% of produced dip was buried as ca-bound p, which represented 3-6% of the riverine inputs.

地中海（MS）是一片广袤的寡营养型海域。其生产力可能对河流输入的营养物质敏感。理解其生产力涉及量化磷（P）河流供应，这对于计算人为干扰下海域的磷质量平衡至关重要。然而，三角洲过滤器的确切作用尚不清楚，尤其是在三角洲沉积物中营养物质的差异捕获/循环方面。来自罗讷河三角洲的底栖数据集与早期成岩模型相结合，包括底栖磷循环。该数据集包括来自罗讷河三角洲9个站点的孔隙水氧气、硝酸盐、硫酸盐、溶解无机碳、铵、溶解还原铁和总铁、溶解无机磷（DIP）及固体数据（有机碳、铁结合磷、钙结合磷和有机磷）。模型结果表明，在沉积物-水界面附近发生的生物地球化学过程强度从河口到邻近的大陆架逐渐减弱。这一减弱与向海底的氧碳通量、沉积速率和氧碳矿化综合速率（从河口附近的160 mmol C m-2 d-1降至大陆架上的10 mmol m-2 d-1）相符。有机磷的矿化作用强烈，尤其是在河口附近（1196 µmol m-2 d-1），其对DIP释放的贡献较大（> 90%）。铁结合磷在促进缺氧沉积物中钙结合磷的沉淀中发挥了关键作用。这些沉积物作为DIP再生来源发挥着重要作用，其中相当一部分DIP（72-94%）被循环回上层水体，占河流DIP输入的25%。而6-28%产生的DIP以钙结合磷的形式被埋藏，这代表了河流输入的3-6%。