EVALUATION OF THE INFLUENCE OF NITROGEN ON PRIMARY PRODUCTION USING RETROSPECTIVE DATA, REGRESSION ANALYSIS, AND MODELING

Abstract

Anthropogenic activities have negatively affected water quality in the Chesapeake Bay and its tributaries. The Potomac River (PR), the largest tributary, is a primary study site for water quality research and new management strategies. The Blue Plains Wastewater Treatment Plant (BP), located in the tidal fresh portion of the PR, is the largest total nitrogen (TN) point source. Retrospective examination of water quality data for the PR revealed relationships among discharge, N loading and concentration, light and primary production. Regression analysis revealed BP (TN) load was an important variable influencing production, coupled with local dissolved inorganic nitrogen concentrations and photic depth prior to installation of biological nutrient removal (BNR) at BP. After 100% BNR implementation, BP TN did not influence production. Four existing primary production models were evaluated for applicability to tidal fresh systems. Regression analysis demonstrated all models were significant but the BZpI0t model provided the most robust results.