SEASONAL TRENDS IN SPECIFIC CONDUCTANCE IN A SMALL TRIBUTARY WATERSHED OF LAKE CHAMPLAIN

A conductivity data logger was deployed in October 2015 to continuously monitor electrical conductivity (EC) and temperature in a small (3.16 km²) tributary watershed of Lake Champlain. The EC (and temperature-corrected specific conductance [SC]) of the stream are elevated due to the application of road salt in the winter months. SC is used in this study as a proxy for chloride concentrations. The watershed has no naturally-occurring sources of chloride and is a landscape with varying levels of development intensity (golf course, residential, commercial/industrial, airport, etc.) and few remaining forested areas (<16%). Seasonal variability is most pronounced during storms and snow melt events, when chlorides stored in roadside ditches (especially those along U.S. Route 9) are mobilized and transported to the stream and, ultimately, to Lake Champlain. Initial spikes in SC during these events are followed by troughs as additional stormwater runoff/snow melt from upstream areas dilutes the chloride concentration. The spikes are most severe during the winter and spring, although smaller spikes persist throughout the summer and fall. Following a stormwater/meltwater event, SC rebounds to a background level likely driven by baseflow and spring water discharging from fractured limestone bedrock into roadside ditches directly upstream of the monitoring site throughout the year. Sampling of springs within and adjacent to the watershed indicate elevated chloride concentrations in groundwater in the southern portion of the watershed. These are likely the result of salt application on roads and parking lots at Bluff Point, which is situated on a topographic high in the southern portion of the watershed.