Redistribution of Wetland Soil Phosphorus Ten Years after the Conclusion of Nutrient Loading

Abstract

There is considerable concern about ecological recovery in wetlands that have been enriched with P; however, there are few long‐term studies tracking the distribution of the soil P after the termination of P loading. The Blue Cypress Marsh Conservation Area in Florida contains areas with elevated soil P levels from historical loading. The local spatial variation of soil P was determined in a 750‐ by 150‐m area proximal to the historic surface water inflow point and a second area of the same size located in the center of the marsh with no record of historical P impacts. The average soil total P was estimated at 847 mg kg−1 in the P‐enriched area and 643 mg kg−1 in the marsh interior (unenriched). When compared with previously determined historical data, it was estimated that soil P has decreased in the P‐enriched area by about 61%. Meanwhile, there was an increase of 82% in P within the unenriched area during this same time period. These results suggest that P has been mobilized from the impacted areas toward the unimpacted marsh along the water flow patterns in the wetland. These observations have implications for restoration of high‐P wetland systems. Remobilization from P‐impacted to unimpacted areas can expand the area of increased nutrients despite termination of P inputs into the marsh. If remobilization predominates over burial, then it is also unlikely that the overall nutrient status of the system will return to pre‐impact levels within a reasonable management time frame (<25 yr).