A DECADE OF INCREASING PRODUCTIVITY IN THE SENECA LAKE WATERSHED

A decade of water quality investigations of Seneca Lake are presented to illustrate the overall quality of the tributaries, the lake, and their trends over time. Seneca Lake is the largest of New York's 11 Finger Lakes, and is essential to the economy and water resources of the region.

This study monitored the health of the lake and streams by periodically measuring nitrate, phosphate (TP and SRP), dissolved silica, chlorophyll-a (measured only in the lake), total suspended sediment (TSS), and dissolved oxygen (DO) concentrations, as well as secchi disk depths, conductivity and stream discharge. Samples were collected from 4 sites on the lake and near the end of seven larger streams in the watershed. Sites were monitored weekly, from Apr. – Oct. on the lake and May – Jul. in the streams, unless the streams dried up earlier. At these sites samples were collected and onsite analyses were gathered using probes and field titrations. Water samples were taken back to the lab and filtered for nutrient, chlorophyll, and TSS analyses.

By combining 2007 data with similar studies from the past decade an overall picture of water quality develops. Concentrations of nutrients were higher in streams that drain watersheds with more agricultural land and other anthropogenic sources like wastewater treatment plants. All nutrient concentrations were larger in the tributaries than the lake indicating nutrient loading to the lake. Phosphate is most problematic, as phosphate is the limiting nutrient in this lake. Annual averages of the lake and stream concentration data reveal an increase in dissolved silica, lake chlorophyll, and phosphates (TP and SRP), and a decrease in the lake secchi disk depth over the past decade. It suggests that nutrient loading is increasing lake productivity from an oligotrophic to mesotrophic. The trend is disturbing because increasing productivity leads to a decline in the health of the lake, due to an imbalance between nutrient and DO availability, creating nutrient depleted and anoxic zones. In conclusion water quality is noticeably deteriorating in Seneca Lake and corrective action should be implemented now before the lake becomes eutrophic.