Effects of forested floodplain soil properties on phosphorous concentrations in two Chesapeake Bay sub-watersheds, Virginia, USA.

Abstract

Aquatic ecosystems are known to undergo fluctuations in nutrient levels as a result of both natural and anthropogenic processes. Changes in both extrinsic and intrinsic fluvial dynamics necessitate constant monitoring as anthropogenic alterations exert new pressures to previously stable river basins. In this study, we analyzed stream water and riparian zone soil phosphorous (P) dynamics in two third-order sub-watersheds of the lower Chesapeake Bay in Virginia, USA. The Ni River is predominantly forested (70% forested), and Sugarland Run is a more human impacted (>45% impervious surfaces) sub-watershed located in the suburbs of Washington D.C. Total stream P concentrations were measured during both high and low flows and Mehlich-3 methods were used to evaluate potential P fluxes in riparian soils. The results show total stream P concentrations in Sugarland Run ranged from 0.002 to 0.20ppm, with an average of 0.054ppm. In contrast, the forested Ni River had typical stream P concentrations <0.01ppm. Total soil P was significantly higher in the more urbanized Sugarland Run basin (23.8 ± 2.1ppm) compared to the Ni River basin (16 ± 3.7ppm). Average stream bank erosion rates and corresponding cut-bank P flux rates were estimated to be 7.98cmyear(-1) and 361kg P year(-1) for Ni River and 9.84cmyear(-1) and 11,600kg P year(-1) for Sugarland Run, respectively. The significantly higher values of total P in the stream water and floodplain cut-banks of Sugarland Run suggests erosion and resuspension of previously deposited legacy sediments is an important processes in this human-impacted basin.