Phosphorus inputs to wetlands following storm events after drought

This study investigated phosphorus (P) concentrations in Donana seasonal we tlands in southwestern Spain as the wetlands started to fill. following sto rm events after a drought. Both soluble and particulate P flowed into the D onana wetlands through runoff. A gradient in the soluble reactive phosphoru s (SRP) concentrations was found from the littoral to the pond center follo wing a 108.5-mm storm. The SRP concentration was 100 times higher 2 m from the shoreline than it was at the pond center. Neither the incoming. SRP nor the total P concentrations were related to the magnitude of storm events. They were always highest during the initial filling periods (first tyoweeks ) and lower after subsequent, even heavier storms (>100 mm) a month later. Deposited sediments were a net P sink during the initial filling period of ponds. Samples of fresh vegetation, soil, and manure from a wetland watersh ed were washed in distilled water for 19 h, and the SRP in the leachates wa s measured in the laboratory. The highest SRP concentration (1.5 mg gDW(-1) ) was leached from the fine (0.1 mm), organic-matter-rich (25% OM) soil dif fraction from uplands. The SRP concentration found in pasture soil was 1.3 rag gDW(-1), followed by fresh scrub (1.25 mg gDW(-1)), and manure (0.9 mg gDW(-1)). Only during periods of heavy rainfall does runoff drain from the uplands to the basin of the wetland watersheds. Therefore, we conclude that incoming P concentrations to Donana wetlands vary greatly from year to yea r according to changes in hydro-meteorological conditions.