Water Quality of the North End of Seneca Lake: 1991-2006

Abstract

The Seneca County Soil and Water Conservation District (SCSWCD) has collected limnological data on the waters of the northern end of Seneca Lake since 1991. This report updates the 1999 report (Makarewicz et al. 1999) with data taken by the SCSWCD from 1999 to 2006. The purpose of monitoring the northern portion of Seneca Lake was to determine the health of the Seneca Lake ecosystem and to determine if any temporal trends existed in Seneca Lake water quality. The water quality of Seneca Lake has been studied since the early 1900s when secchi disk readings were first taken. At that time, the trophic state of Seneca Lake was classified as oligotrophic; that is, nutrient concentrations and primary production were low and transparency high. Water clarity remained approximately the same up through the early 1930s. By the late 1970s, water clarity generally decreased, indicating that the lake’s trophic status was mesotrophic. Total phosphorus concentrations from the 1970s were into the mesotrophic range. Chlorophyll-a concentration also illustrated the trend toward more productive waters in Seneca Lake in the early to mid 1970s. Similarly, in the early 1970s, the transparency of Seneca Lake had decreased to within the eutrophic range. These low transparency values were observed into the early 1990s. Based on the sampling done by the Seneca County Soil and Water Conservation District from 1991 through 2006, an improvement in water quality of Seneca Lake is suggested – at least at the north end where the samples were taken. The trophic status of Seneca Lake is currently best described as oligotrophic. In conclusion, water quality of Seneca Lake appears to have improved since the early 1970s. However, the increase in total phosphorus levels from 2003 to 2005 represents an increase of some concern as they represent the highest values in the last 14 years.