Trends in Water Quality of New Jersey Streams, Water Years 1986-95

Trend tests were conducted on values of 24 water-quality characteristics measured at 83 surface-water-quality stations on streams in New Jersey during water years 1986-95. Characteristics tested include physical properties and concentrations of nutrients, bacteria, and major dissolved constituents. Seasonal Kendall uncensored tests and tobit regression were used to determine whether unadjusted values of water quality or flow-adjusted values of water quality increased or decreased during this period.

Results of tests on instantaneous streamflow measured at the time of water-quality measurements indicate that streamflow decreased during the period of study; 20 of the 81 stations tested showed decreasing values of instantaneous streamflow. No station showed increasing values of instantaneous streamflow. Because the locations of stations with decreasing streamflow are widespread, it is likely that these trends are due to changes in weather patterns rather than to changes in the amount of water withdrawals.

Results of tests on nutrients are consistent with the expected effects of upgrades to sewage-treatment plants, which occurred in the State of New Jersey during the period of study. For all nutrients tested other than total nitrate plus nitrite, more stations showed decreasing unadjusted and flow-adjusted values than showed increasing unadjusted and flow-adjusted values.

Results for eight major dissolved constituents--specific conductance, total hardness, and dissolved concentrations of solids, sodium, potassium, calcium, magnesium, and chloride--of the nine tested showed more stations with increasing values than stations with decreasing values. Only dissolved sulfate did not show more increases than decreases.