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  • David R. DeWalle

Introduction to Water Quality in the Spring Creek Watershed

Beginning in 1999 monitoring of stream and spring water quality was initiated by the Spring Creek Watershed Association to provide data to citizens, business leaders and public officials to better protect and manage water resources. The Water Resources Monitoring Project involves quarterly sampling of 15 stream sites and 8 springs mainly during low flows (see Figs. 1-2 for locations of and Table 1 for descriptions of monitoring sites). Monitoring is largely supported by local municipalities and organizations. The PA Department of Environmental Protection provides water quality analysis services. Check out the website for more information.

Figure 1. Locations of stream monitoring stations within the Spring Creek watershed.

Figure 2. Location of spring monitoring sites within the Spring Creek watershed.

In addition, monitoring of precipitation chemistry is conducted at Rock Springs by the National Atmospheric Deposition Program at the PA-15 site (see here) located immediately south of the Spring Creek basin. Streamflow discharge and water chemistry measurements are measured by the U. S. Geological Survey at several locations within the basin (see here). This brief summary of water quality condition in the Spring Creek basin is largely based on data from this this network during 1999-2017. A paper describing water temperature variations in the Spring Creek basin already appears on this Atlas site.


1. Precipitation monitoring during 1988-2016 at Rock Springs on the southern boundary of the Spring Creek watershed shows relatively constant annual precipitation amounts and gradually declining levels of acid-producing sulfate and nitrate pollutants dissolved in rain and snow (Figure 3).

2. Geology in the Spring Creek watershed is a major control on water quality (Figure 4). Springs and streams flowing from forested uplands, where weather-resistant sandstone/shale rocks dominate, have very low hardness and low concentrations of dissolved solids. In contrast, waters in the valleys, where carbonate geology with more-soluble limestone and dolomite rocks dominate, causes hardness and high dissolved solids.

3. Low flows in Spring Creek basin are supported by a score of forest streams from sandstone/shale uplands which supply water with low chloride, nitrate and sediment concentrations to streams and springs in the valleys.

4. Chloride levels in springs and streams in the valleys have been increasing steadily over the past few decades especially in more heavily-developed urban areas (Figure 5). Widespread use of de-icing salts on roads and other paved surfaces in winter is likely the major cause of chloride increases. Levels of chloride sampled during low flows are currently below the drinking water standard of 250 ppm for Cl and are also below standards of 230 ppm Cl (USA) and 120 ppm Cl (Canada) recommended to protect aquatic organisms from chronic or long-term exposures. Elevated chloride levels can cause some aquatic organisms to dehydrate leading to mortality due to osmosis through semi-permeable membranes.

5. Spring Creek waters generally exhibit low suspended sediment concentrations. In fact, 73% of spring and 42% of stream water samples were below laboratory detection limits (<2 parts per million or ppm) for suspended sediment. Sediment deposition in stream channels can impair aquatic ecosystems and fish reproduction.

6. Millbrook Marsh appears to decrease levels of sediment which reach main Spring Creek from urbanized sections of Slab Cabin Run and Thompson Run. Trapping of sediment by vegetation in the marsh and dilution of suspended sediment by clearer spring waters in the marsh are believed responsible (Figure 6).

Figure 6: Comparison of mean concentrations of suspended sediment (SS in ppm) entering and leaving Millbrook Marsh during low flows in streams. Drop in concentration from Millbrook Marsh is attributed to sediment trapping and dilution by springflows within the marsh.

7. Despite rapid population growth and enhanced wastewater flows, nitrate levels in Spring Creek basin springs and streams are generally declining and remain well below drinking water standards of 10 ppm of nitrate-nitrogen (Figure 7). High nitrate and orthophosphate levels in streams can act as a fertilizer causing excessive aquatic plant growth and eventual reductions in dissolved oxygen for aquatic animals as plant matter decays (eutrophication).

8. Orthophosphate levels in streams and springs have fluctuated more than nitrate but also appear to be declining in recent years (Figure 8). The downward trend in both nitrate and phosphorus concentrations likely reflect combined effects of improved wastewater treatment and management along with declining levels of nitrogen in precipitation and improved soil and water conservation practices on agricultural lands in the basin.

9. While most springs have low levels of pollutants, some springs showed occasional high levels of suspended sediment, chloride or nitrate, likely due to proximity of pollutant sources and movement of pollutants through sinkholes and subsurface conduits typically found in the karst terrain.

10. Inputs of water from Big Spring in the lower portions of the watershed with its relatively low levels of hardness, chloride and nitrate helps to dilute pollutants and control export of pollutants from the watershed at Milesburg.


The “Canyon” section of Spring Creek between Houserville and Axemann Gauge sites produces the highest mean levels of nitrate and chloride at baseflow. Sources of this pollution are not well understood, but Benner Spring, two fish hatcheries, a sewage treatment plant, a bridge crossing by Interstate 99 and scattered housing and commercial development within the reach may play a role. Further study of this section of Spring Creek is warranted given its importance to recreational use, especially trout fishing.

Since monitoring was conducted only at low flows, patterns of water quality at high flows could be different. Some water quality indicators can be diluted at higher flows like hardness and others like chloride and suspended solids levels can increase dramatically at higher flows. Monitoring at higher flows at selected sites is needed for a more complete picture of water quality in the Spring Creek watershed.

Arguably, the major unresolved scientific issue in the Spring Creek watershed is whether stream chlorides will continue to increase with future urban/suburban development and what levels of chlorides are toxic for aquatic organisms, especially benthic macroinvertebrates which support the food-chain for trout. Without careful monitoring, future changes in chloride levels in the Spring Creek drainage and the likely corresponding subtle responses of aquatic insects to these changes may be missed.

Table 1. Description of Monitoring Sites within Spring Creek Basin


Dr. DeWalle is retired from teaching and research at Penn State in the Department of Ecosystem Science and Management. His research focused on impacts of climate change, land use and acid rain on water quality and hydrology of forest streams and watersheds.

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