Does control of soil erosion inhibit aquatic eutrophication?

Much of the phosphorus (P) from erosive soils is transported to water bodies together with eroded soil. Studies clarifying the impact of soil erosion on eutrophication have sought largely to quantify the reserves of P in soil particles that can be desorbed in different types of receiving waters. Aquatic microbiology has revealed that the cycling of P is coupled to the availability of common electron acceptors, Fe oxides and SO4, through anaerobic mineralization in sediments. Eroded soil is also rich in Fe oxides, and their effect on the coupled cycling of C, Fe, S, and P has been neglected in eutrophication research. Soil erosion, and its control, should therefore be studied by considering not only the processes occurring in the water phase but also those taking place after the soil particles have settled to the bottom. We propose that in SO4-rich systems, Fe oxides transported by eroded soil may promote Fe cycling, inhibit microbial SO4 reduction and maintain the ability of sediment to retain P. We discuss the mechanisms through which eroded soil may affect benthic mineralization processes and the manner in which soil erosion may contribute to or counteract eutrophication.

► The bulk of the Fe flux to water systems originates from the catchment.
► Eroded soil affects eutrophication in receiving waters in different ways.
► Eroded soil may inhibit eutrophication if it promotes Fe cycling in sediments.
► Site-specific factors dictate whether soil erosion may contribute to or counteract eutrophication.