Factors controlling phosphorus speciation in a Mediterranean basin (River Guadalfeo, Spain)

Abstract

There is a lot of interest nowadays in the role of riverbed sediments in phosphorus cycling and particularly, in the processes that lead the exchange of phosphorus between the sediment and the water column. This study presents results on phosphorus forms and other properties from surface riverbed sediments of the River Guadalfeo and its main tributaries. Results show a wide range of spatial variability within the basin with differences of phosphorus concentration higher than an order of magnitude among different sites. The most abundant form is the apatite inorganic phosphorus (AIP) which accounts for 68 % of total phosphorus followed by total organic phosphorus (OP) that represents 29 %.

The high oversaturation of calcite reached during the summer and early autumn in most studied rivers, accounts for the dominance of AIP form in the sediment and should prove the importance of calcite-phosphorus co-precipitation as a self-cleansing mechanism that removes phosphorus from the water column. External factors such as the lithology of drainage area and sewage inputs are less important in the concentration of sediment phosphorus than physico-chemical and biological processes that take place in the rivers. Taking into account the low biodegradable characteristics of dominant phosphorus forms, it could be concluded that the surface sediment in the Guadalfeo basin acts as a phosphorus sink.