Trends in tributary water quality in a water supply reservoir

Abstract

The study that is the basis for this article evaluated water quality trends in tributaries of a drinking water source to assist in developing effective management strategies. Nutrient and total organic carbon (TOC) trends from 1998 to 2012 were assessed in major tributaries of the Wachusett Reservoir in Massachusetts. In this period, solute concentrations generally declined—in seven of eight tributaries for nitrate (all statistically significant at p < 0.05), four of eight tributaries for total phosphorus (all significant), and six of eight tributaries for TOC (three significant). Despite these changes, increased flows resulted in increased or constant daily loads. Installation of municipal sewer systems in selected subbasins between 2002 and 2008 coincided with decreased concentration trends in their tributaries and decreased loads in the most sewered tributary. These results illustrate the dominance of flow in determining loads and have implications for water managers seeking to quantify and manage solute transport.