Seasonal Nutrient Dynamics of Forested Floodplain Soil Influenced by Microtopography and Depth

Abstract

Edaphic and hydrologic influences on floodplain soil nutrient dynamics must be characterized in order to more fully understand ecosystem functions of forested floodplains. The objective of this study was to characterize the impacts of microtopography and depth on soil microbial processes related to nutrient dynamics in a forested floodplain soil. Nutritional and biological parameters were measured seasonally for 2 yr at paired plots representing two microtopographic classes (swales and slopes) and three soil profile locations—surface organic material, root zone (RZ, 0–0.1 m), and sub‐root zone (SR, 0.2–0.3 m)—on the Coosawhatchie River floodplain, South Carolina. Litter decomposition dynamics followed trends previously described in the literature: N and P concentrations increased relative to C following litterfall, and the relative increase was greater in swales than on slopes. Mineral soil on the Coosawhatchie floodplain was rich in total P compared with other sites. Soil N pools fluctuated together with C, while P was redistributed by floodwater independently of major C and N pools. As a result, P accumulated more in swale soil. Carbon/N ratios in RZ soil were seasonally constant, averaging 14 in swales and 19 on slopes. Carbon/total P ratios were more variable, ranging from 77 to 118 in swales and 151 to 246 on slopes. Microtopographic differences (<1 m) profoundly influenced nutrient dynamics, particularly P, of surface organic material and soil on this floodplain.