Phosphorus fractionation and distribution in salt marsh soils affected by mine wastes and eutrophicated water: A case study in SE Spain

The study aimed to establish the distribution and fate of phosphorus in the soils of a coastal salt marsh affected by mine wastes and wastewater effluents. Water samples from two watercourses were analysed for soluble phosphorus and dissolved organic carbon and soil samples within the marsh were analysed for total P, Fe, N and CaCO3. In addition, a fractionation of the phosphorus was performed. The results indicate that high concentrations of soluble phosphorus (up to 12.3 mg PO43−P L− 1) and dissolved organic carbon (up to 36.5 mg L− 1) flowed from one of the watercourses into the salt marsh. Organic residual P was the most abundant P form in the soils, constituting between 38.6 and 76.6% of the total P, whereas P associated with humic acids was less abundant (less than 3%). Among the mineral soil components, Ca and Mg compounds were the most active in phosphorus retention (up to 50% of the total P), except in the plots most affected by mine wastes. In the latter sites, the highest Fe (up to 247 g kg− 1) and the lowest CaCO3 (8.9 g kg− 1) concentrations were obtained, and Fe- and Al-bound P was the most abundant fraction, reaching 23.9% of the total P. Unusually low total nitrogen/total phosphorus ratios (between 5.4 and 5.7) showed that marsh areas affected by wastewater effluents are acting as phosphorus sinks.