WATER QUALITY DEGRADATION IN SENECA LAKE, NEW YORK

Seneca Lake, in central New York State, is vital to the local region as a source of drinking water and a magnet for the tourist economy. The elongated lake, at 15.5 km³, 186 m deep, 57 lm long, up to 5 km wide, has a water residence time of ~19 years, and holds just over 50% of the water in the Finger Lakes region. Here, we present 20 years of water quality data from both the lake and its major tributaries. It reveals that water quality has declined over the past decade despite a decade-long, healthy standing crop of the filter-feeding, zebra and quagga mussels.

Routine collection of water quality data started in 1991 and was progressively more frequent and analyzed more parameters since 1996. Recently, lake sites were sampled weekly from April through October and focused on four representative sites in the northern portion of the lake. In August, 2010, nine sites were sampled, distributed along the long axis of the entire lake. Onsite data included a CTD cast, secchi disk depth, plankton tows, and alkalinity. Water samples were also collected from the surface (< 1 m depth) and bottom (within 5 m of the lake floor), and analyzed back in the laboratory for total and dissolved phosphates, nitrates, dissolved silica, chlorophyll-a, total suspended solids and major ions. Selected stream sites were typically sampled at the terminus of the stream on a weekly period during May and June (typically dry afterwards). Nearly all of the major tributaries were sampled once or twice a year, and recently augmented by weekly samples from four representative tributaries since January 2010. Onsite, we collected stream discharge, alkalinity, temperature, conductivity, pH, and dissolved oxygen data. Water samples were also collected for total and dissolved phosphates, nitrates, dissolved silica, total suspended solids, and major ion analyses back in the laboratory.

The data reveal that nutrient concentrations in the tributaries exceed those in the lake by up to 100 times. Critical nutrient point and non point sources include wastewater treatment facilities lacking tertiary treatment, on-site (septic) wastewater treatment, runoff from lawns, crop agriculture and animal husbandry, stream bank erosion, and others. The major ion data also indicate that Seneca is progressively becoming less saline, primarily due to decreasing Na and Cl concentrations.