Physical and Water-Quality Characteristics Affecting Trout-Spawning Habitat in the Quashnet River, Cape Cod, Massachusetts

Baevsky, Yvonne Halpern

This report presents the results of a reconnaissance study of the physical and water-quality characteristics of the Quashnet River by the US. Geological Survey, in cooperation with the Mashpee Water District, in 1988 and 1989. The Quashnet River, a ground-water sustained, trout-spawning stream on Cape Cod, has been designated an Area of Critical Environmental Concern by the Commonwealth of Massachusetts, because of the possible effects of current and projected population growth in the watershed. The concerns are that the development of new wells for water supply may deplete streamflow, which may adversely affect trout-spawning activity and that contamination of ground water by septic-system and agricultural wastes may degmde stream-water quality, which m y adversely affect trout-spawning. Hydrologic and water-quality conditions in a stream determine its viability as a trout habitat. Previous research has identified the importancec of groundwater discharge in maintaining the characteristics of water temperature, pH, and dissolved-oxygen concentration within the limits which are critical to successfil development of trout embryo. Selected physical characteristics of the river-stream width, depth, and velocity- were measured at up to five sites at five different times in the annual hydrologic cycle; selected water-quality characteristics of the river--tempemture, dissolved-oxygen concentration, pH, and specific conductance--were measured concurrently. The Quashnet River is normally sustained by ground-water discharge at all but the highest flow rates, which result from direct runoff ofprecipitation or the release of water stored in cranberry bogs. During base flow, when all the streamflow is from storage, about one-third of the streamflow below the spawning reach, in the reach from the estuary to the spawninggrounds that trout must travel through, is derived from ground-water discharge. The autumn spawning run of 1988 was found to coincide with the release of water from a cranberry bog, following harvest. During a 1- to 2-day interval when the spawning activity of the sea-run brown trout peaked, velocities reached 1.8 feet per second and the discharge peaked at 32 cubic feet per second at the center of the spawning area. In the spawning reach, during the spawning period of 1988, temperatures ranged from 10 to 11 degrees Celsius. Dissolved-oxygen concentrations ranged from 9.3 to 12.6 milligrams per liter. The pH ranged from 5.96 to 6.38 units and specific conductance ranged from 54 to 66 microsiemens per centimeter at 25 degrees Celsius. The effects of proposed ground-water withdrawals on the volume of streamflow in the river need to be assessed spatially and temporally in terms of the locations and reduction of ground-water discharge to the Quashnet Rivel: The effects of proposed withdrawals on the spawning reaches could be estimated with a digital ground-water flow model calibrated to simulate ground-water /stream interaction. The hydrologic and water-quality information obtained in this study of the Quashnet River establishes an initial data base for research on the interaction of hydrology and aquatic biology in an environment where fish-embryo development is directly affected by hydrologic conditions.

Physical and Water-Quality Characteristics Affecting Trout-Spawning Habitat in the Quashnet River, Cape Cod, Massachusetts

Series