A Soils Perspective: Phosphorus Storage and Retention Within Degraded Isolated Wetlands of Agricultural Lands.
Ed Dunne, Mark W. Clark, and K. R. Reddy. Soil and Water Science Dept, Univ of Florida/IFAS, 106 Newell Hall, Gainesville, FL 32611
Water quality degradation caused by eutrophication is still a problem within many agroecosystems such as those present within Lake Okeechobee's Basin, Florida, USA. Presently, to combat this degradation, restoring the hydrology of historically isolated wetlands within grazing pasture ecosystems, to store and retain phosphorus (P), is being evaluated to help reduce the impact of agriculture on the receiving environment. The objectives of our study were to (i) investigate the ability of historically isolated wetlands to store and retain P in response to wetland hydrological restoration (increased wetland flooding) and (ii) at the sub-basin-scale, determine the soil chemical processes responsible for P storage and retention within isolated wetland ecosystems. The first study investigated four wetlands (two paired sites on two different cow-calf pastures) and the objective was to characterize ecosystem P storages prior restoration and then, monitor changes in ecosystem P storages through time (specifically soil), to determine if restoration reduces the impact of agriculture on the environment. Our initial results (site characterization) suggest that in terms of ecosystem P storage, soils (0-10 cm) stored greatest amounts of P (> 80%) compared to other ecosystem components such as above ground vegetation, litter (dead biomass) and below ground biomass (< 20%). Also, wetland soils stored greater amounts of P (mean ± SD; 14.7 ± 3 g P m-2) than surrounding grazed pasture soils (11.5 ± 2 g P m -2), which may suggest that wetland soils are accumulating P from these surrounding areas. Most of the P stored in wetland soils was associated with organic matter, while in grazed pasture soils most of the P was associated with soil mineral components. The second study is an intensive assessment of isolated wetland soils at the sub-basin-scale. Little is known about long-term P storage processes within isolated wetland soils other than, most P is stored in organic forms; our previous studies suggest this is about 70-80% in surface soils (0-10cm). We sampled 20 historically isolated wetlands within dairy, improved and unimproved agricultural lands. Soils were sampled to a depth of 30 cm. We hypothesize that (i) newly accreted surface soils will have different P characteristics than underlying soils, (ii) that P storage and retention is governed by organic matter accumulations in surface soils, (iii) the inorganic P that is stored in surface soils is governed by metallic cations associated with organic matter, and (iv) that P storage in underlying soils is controlled by Al and Fe. Findings of both studies will provide important information to water quality managers, state agencies, land owners and other stakeholders, in an effort to reduce the effect of agricultural production on the receiving environment within agroecosystems of Okeechobee Basin.