Nutrients, chlorophyll and biotic metrics in the Rappahannock River estuary: implications of urbanisation in the Chesapeake Bay watershed, USA

Abstract

In the Chesapeake Bay watershed, various endeavours such as the inter-state agreements and Chesapeake 2000 agreement have been implemented to improve water quality and ecological conditions, and have produced mixed results at best in various tributaries. So as to evaluate the management efforts on ecological conditions in the Rappahannock River watershed, we analysed the long-term variability in land use, nutrient content and ecological biotic metrics. It appears that the inter-annual variability in nutrient loadings and concentrations is largely influenced by changes in urbanisation and climate. Significant increases in urban development (35%) and population growth have exacerbated both point and non-point nutrient pollution in the Rappahannock River. The comparatively low N : P ratio in the tidal zone, with respect to the non-tidal zone, may be due to salinity-induced P leaching from sediments regulating the water quality along the river–estuary continuum. In addition, inter-annual variability in ecological biotic metrics demonstrates degrading ecological conditions in the Rappahannock River watershed, which are primarily due to increasing watershed urbanisation driving high nutrient loadings and altered nutrient stoichiometry.