Groundwater Modeling of a Eutrophic Lake Watershed in Northwestern Vermont: Lake Carmi, Franklin VT
This study investigates the role of groundwater as a control on algal blooms in a small eutrophic lake watershed in Franklin, Vermont. Lake Carmi situated in northwestern Vermont has long been subjected to high P loading resulting in water quality issues such as algal blooms, poor water clarity, and heavy aquatic plant growth (Holdren et al., 2018). In compliance with the Clean Water Act, Lake Carmi had a total maximum daily load (TMDL) implemented by the Vermont Agency of Natural Resources in 2008 to combat the high P concentrations (VTANR, 2008; Holdren et al., 2018). This policy reduced P inputs greatly from overland sources. However, Lake Carmi has continued to suffer from severe algal blooms despite the implementation of the 2008 TMDL. This suggests that the groundwater may be acting as a P reservoir, and slowly supplying a diffuse source of P into the Lake.
This study uses MODFLOW groundwater modeling of the subsurface to quantify P transport to the lake by groundwater flow. The model parameters are informed by monitoring well data, bedrock well data, precipitation data, topographic data, and soil data. For each of the 6 monitoring wells sampled in the study, a two-dimensional cross section was produced from well to lake, and the model outputs were used to extrapolate the hydrogeologic budget of the lake.
Groundwater modeling yielded a range of 7.5-51.7 kg of P loaded annually to Lake Carmi via surficial sediment groundwater transport. A lake-water budget approach yielded a larger range of 155-388 kg/yr. High P concentrations in monitoring well sediment cores indicate a natural bedrock source of P, with P contributions to Lake Carmi from groundwater to be expected yearly.
History
Institution
- Middlebury College
Department or Program
- Earth and Climate Sciences
Degree
- Bachelor of Arts
Academic Advisor
Dr. Peter RyanConditions
- Open Access