Water Quality Trends

Project Summary

Water Quality Trends

Biotic Index
Dissolved Oxygen
Fecal Coliform Bacteria
Nitrate Nitrogen
Total Phosphorus

Water Quality Trends
Dissolved Oxygen

The amount of oxygen dissolved in a stream ecosystem can affect the health of aquatic organisms. Different levels of dissolved oxygen are necessary to support various types of aquatic life.For example, adult warm water fish (i.e. bass and pike) require oxygen concentrations of at least 5.0 milligrams per liter (mg/L) for normal growth and reproduction, and adult cold water fish (i.e. trout and salmon) require at least 6.5 mg/L of dissolved oxygen (US EPA 1986). Oxygen is dissolved into streams from the atmospheric supply when water is mixed in riffles and rapids. Oxygen is removed from streams when organic pollutant loads deplete the supply through biochemical oxygen demand.

Pennsylvania defines minimum dissolved oxygen concentrations for varying stream classifications. These definitions include:

High Quality Cold Water Fishes . . . . . . . . . . . . . 7.0 mg/L
High Quality Warm Water Fishes . . . . . . . . . . . . 6.0 mg/L
High Quality Trout Stocking . . . . . . . . . . . . . . . . . 6.0 mg/L
Exceptional Value Streams must maintain existing levels

The following graphs present county-wide trends in dissolved oxygen for each year that data were collected. High and low color values may exceed the maximum and minimum shown on the legend.

View Station Location Map | View Animated Graphic
1991	1992	1993
1994	1995	1996
1997	1998	1999
2000	2001