An Overview of the Water Quality Data on this Website

This website presents water quality data that have been generated by volunteer monitoring partnerships around the southern end of the Cayuga Lake watershed beginning in 2002. Some 7,000 data items are grouped by the three kinds of locations where water samples are being collected by groups of volunteers: streams, Cayuga Lake, and public parks. All samples are analyzed by CSI’s certified laboratory (ELAP# 11790). In addition, volunteer groups and agency staff frequently perform field measurements of temperature, pH, dissolved oxygen and alkalinity. Monitoring of streams, parks and Cayuga Lake is ongoing. Water samples are collected and new data are generated every two to three months. Results are archived in MS Excel spreadsheets and used to update the graphs and tables on this website approximately every six months. The MS Excel files containing raw water quality data are available to interested parties at any time upon request.

Interpreting Water Quality Data from Streams

Interpreting long-term water quality data is challenging. Occasionally, results show clearly and consistently that a water quality standard is being violated. More often, however, results fall within accepted limits most of the time or all of the time. Interpreting water quality data then becomes a matter of assessing trends and deciding whether government needs to intervene to improve the management of water resources and, if so, what form of intervention would be most constructive and cost-effective.

Presented below are broad concepts that are helpful in interpreting monitoring data. More detailed information about water quality terminology may be found in the Glossary.

Water quality under base flow vs. high flow conditions:

A watershed is defined as an area of land through which water moves downhill to reach a stream or a lake. As a result, stream and lake water are directly affected by how the land in a watershed is used. Any impact that land uses may have on water quality is usually magnified following a rain or a snowmelt that saturates the ground and causes surface runoff. One reason is that under base flow conditions, most of the water in streams and lakes comes from groundwater, and soil acts as a filter to remove many pollutants. Under high flow or storm water conditions, water quality reflects a mixture of groundwater and surface runoff. Runoff usually contains a variety of pollutants that water picks up as it moves along the ground surface. The more rain or snowmelt, the more runoff there is and the more water quality declines.

Ideally, volunteer groups collect stream samples six to eight times per year or twice per season, once under base flow and once under high flow (storm water) conditions. This makes it possible to profile water quality at different times of the year and to assess how water quality is compromised by surface runoff in different seasons.

Time frame for collecting stream samples:

Volunteer groups collect water samples from all of the monitoring sites on their stream on the same day and within a few hours of one another. This provides a water quality “snapshot” of the stream under specific flow conditions. A “snapshot” makes it possible to assess the condition of the stream as a whole and to compare results for each monitoring site with the results at every other site.

Graphs analyzing stream data:

This website offers two types of graphs to analyze long-term water quality data on streams:

• Averages of results across the watershed: The average value for all monitoring events is reported for each water quality indicator at each monitoring site. In addition, the median value for all monitoring events is reported for total coliform bacteria, and the geometric mean is reported for E. coli bacteria. In the graphs, the distances of the monitoring sites from the headwaters of the stream are plotted on the x-axis, and the average, median or geometric mean is plotted on the y-axis. Monitoring sites on feeder streams are also plotted in terms of their distance from the headwaters of the main stream; their distance from the headwaters of the feeder stream on which they are located is indicated in the table below each graph. Water quality standards are indicated on each graph and are explained in legends and footnotes. — This type of graph makes it possible to assess water quality trends across the watershed as water flows from upstream to downstream (from left to right across the graphs). Second, it shows how water quality at individual monitoring sites rates, on average, compared to other sites. These two pieces of evidence: Changes in water quality indices as the stream flows through the watershed, and the relative values of water quality indices at individual monitoring sites, provide a basis for identifying sources of pollution in the watershed and, ultimately, for managing them.

• Values of water quality indicators in relation to stream flow: When it rains or when snow melts, water quality generally deteriorates as a result of pollutant-rich surface runoff mixing with groundwater in the stream. At the same time higher concentrations of pollutants are loaded to the stream from surface runoff, stream flow also increases following a rain or snowmelt. (Flow is defined as the volume of water passing down a stream per unit time, e.g., cubic feet of water per second). The combination of these two factors: Increased pollutant concentration and increased flow, results in a significant increase in the amounts of pollutants being transported to the mouth of a stream and loaded to the next body of water — in the case of our region, to Cayuga Lake. Excessive loadings of substances such as suspended sediment, phosphorus and nitrogen nutrients, and bacteria can lead to a deterioration of water quality in Cayuga Lake as well as its tributary streams over time. In the second approach to graphing water quality data on this website, the concentrations of water quality indicators at the monitoring site closest to the mouth of the stream and Cayuga Lake are plotted for each monitoring date. In addition, graphs show the flow at the mouth of the stream. In a second set of graphs, the concentration of each water quality indicator is plotted against stream flow, and the correlation between water quality indicator and stream flow is investigated using a simple linear regression equation. When the correlation is good, flow can be used to estimate the loading of a pollutant to Cayuga Lake over time.