Beef Cattle Pasture to Wetland Reconversion: Impact on Soil Organic Carbon and Phosphorus Dynamics

Authors: Sigua, Gilbert; Coleman, Samuel; Albano, Joseph

Submitted to: Ecological Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2009
Publication Date: 7/23/2009
Citation: Sigua, G.C., Coleman, S.W., Albano, J. 2009. Beef cattle pasture to wetland reconversion: Impact on soil organic carbon and phosphorus dynamics. Ecological Engineering. 35: 1231-1236.

Interpretive Summary: Basic information on the ecological understanding of the responses of systems to water regime change is essential in both the environmental integrity and productivity of the ecosystem. Progress in this area may facilitate some reversal of wetlands losses in the future. Re-wetting of formerly drained areas has become common practice in wetland restoration. Such variation could profoundly affect the processes underlying nutrient transformations in these systems. Partial drying of wet (previously inundated) soils will result in an increase of soil’s affinity for P and will produce a zone for nitrification coupled with denitrification. Hence, partial drying may reduce the availability of soil P. The study described in this paper was conducted on a 162-ha historic wetland that was largely drained and converted to improved beef cattle pasture in the early 1940’s, largely influenced by the passage of the Swamp Land Act of 1849. Our experimental data support field studies that showed that drainage of wetlands decreases TOC and significantly affected the different forms of soil P. The concentration of TOC was reduced by 96% over the periods of land use conversion. It appeared that conversion of wetland was proceeding toward a soil condition/composition like that of mineral soils. Cumulative concentrations of TP in soils (1,134 mg/kg) under dry condition are two to three times lower than those in soils (2,752 mg/kg) under wet condition over the periods of land use conversion, suggesting that P release from wetlands may be possible during the process of the conversion. These results are important in establishing useful baseline information on soil properties in pasture and wetland prior to restoring and converting pasture back to its original wetland conditions. The results further suggest that changes in soil properties due to changing land use and hydrologic conditions (drying and re-wetting) could be long lasting.

Technical Abstract: Many wetlands were lost in the coastal plain region of southeastern United States, primarily as a result of drainage for agricultural activities because of the passage of the Swamp Land Act of 1849. Wetland drainage could be analogous to subjecting wetlands to an extreme and long-term drought. There is an earnest need to understand the historical condition and chemical/biological functions of the ecosystems following a conversion of wetlands to agricultural functions. To better understand the dynamics of soil total organic carbon (TOC) and phosphorus (P) during wetland conversion to beef cattle pastures and beyond, soil core samples were collected from the converted beef cattle pastures and from the natural wetland at Plant City, FL in summer of 2002, 2003, 2005, 2006 and 2007. The levels of SOC and soil P were significantly affected by changing land use and hydrology. Draining natural wetlands to grazed pastures resulted in very pronounced reduction of SOC from 180.1 to 5.4 g/g. Cumulative concentrations of TP in soils (1,134 mg/kg) under dry condition are two to three times lower than those in soils (2,752 mg/kg) under wet condition over the periods of land use conversion. There was a declining trend (r = 0.82**; p=0.01) in total soil P from natural wetland (763 mg/kg) to altered pastures (340 mg/kg), largely as organic-bound P (natural wetland, 48%; grazed pastures, 44%; altered pastures, 29%). These results are important in establishing useful baseline information on soil properties in pasture and wetland prior to restoring and converting pasture back to its original wetland conditions. The results further suggest that changes in soil properties due to changing land use and hydrologic conditions (drying and re-wetting) could be long lasting.