NEW ENGLAND COASTAL BASINS NAWQA PROGRAM: PUBLICATIONS

WATER-QUALITY CHANGES IN THE MERRIMACK, BLACKSTONE, AND CONNECTICUT RIVERS DURING THE 20TH CENTURY

27th Annual Meeting of the New England Association of Environmental Biologists (NEAEB), 2003

Keith W. Robinson¹, Jean P. Campbell, and Norbert A. Jaworski

¹U.S. Geological Survey, 361 Commerce Way, Pembroke, NH 03275

Abstract

Water-quality data from the Merrimack, Blackstone, and Connecticut Rivers were used to describe trends in concentrations of sulfate, chloride, residue, nitrate, and total phosphorus during the 20 th century. All five water-quality indicators changed significantly during this period. Mean annual total phosphorus and sulfate concentrations decreased during the second half of the century. Mean annual concentrations of nitrate, chloride and residue increased throughout the century. In the Merrimack River, mean annual chloride concentrations increased by an order of magnitude from 3 to 25 mg/L. Mean annual nitrate concentrations also increased by an order of magnitude from 0.04 to 0.33 mg/L in the Merrimack River and from 0.04 to 0.35 mg/L in the Connecticut River. The data for each river were from multiple locations, but these locations are considered close enough so not to be a source of variability in the data.

These water-quality changes appear to be partially explained by national and regional data sets that describe changing human activities. Most notable are the increased usage of road de-icing salts in relation to increased chloride concentrations in rivers; increased agricultural use of nitrogen fertilizers and nitrogen oxide emissions in relation to increased nitrate concentrations; and the decreased agricultural use of phosphorus fertilizers in relation to decreased total phosphorus concentrations. For all the water-quality constituents assessed, concentrations were greatest in the Blackstone River than in the Merrimack and Connecticut Rivers. The Blackstone River Basin is smaller and more urbanized than the other basins studied. These study results indicate that long-term water-quality data-collection programs can provide valuable insight on the effects of changing human activities on river quality.

NECB publications
List of NH-VT District abstracts