Assessment of Nutrients in the Wachusett Reservoir Watershed: An Investigation of Land Use Contributions and Trends

Thursday, 10 December 2020
Amanda Carneiro Marques, Emily Kumpel, John E Tobiason and Christian Guzman, University of Massachusetts Amherst, Civil and Environmental Engineering, Amherst, MA, United States
The Boston Metropolitan Area, supplied with freshwater from the Quabbin-Wachusett system, depends on water quality management and adjustments based on environmental trends. The Wachusett Reservoir receives inflow from tributaries (French, Gates, Malagasco, Malden, Muddy, Trout, Waushacum, and West Boylston Brooks), the Quinapoxet and Stillwater Rivers, and the Quabbin Aqueduct transfer. Nutrient sampling data collected by the Department of Conservation and Recreation (DCR) monitors potential hotspots for water quality. Nitrate-N (NO3) and Total Phosphorus (TP) concentrations were analyzed temporally, considering seasonal inputs and trophic status, from 2000-2020 for eight tributaries, and the available dataset for the other two (from 2012-2020 and 2015-2020). The mean concentration results suggest rising (static, or declining) trends vary over time depending on tributary characteristics. Based on NO3, most of the tributaries (60%) are oligotrophic (< 0.3 mg/L). This is consistent for seasonal inputs during warm months (April-September). For cold months (October-March), the number of eutrophic tributaries (0.5-1.5 mg/L) slightly increases. Based on TP, all tributaries are eutrophic (>0.02 mg/L), which despite the absence of an increasing trend of TP, suggests a high presence of this nutrient. NO3, by contrast, is increasing in French and Waushacum Brooks, both oligotrophic, indicating degrading water quality. Land use data suggests a pattern for altered drainage landscapes (those with greater percentage of imperviousness and cultivation) as potential sources of increased nutrient transport. Gates Brook had the highest concentration of TP, the second highest concentration of NO3, and has the largest percentage of imperviousness (21%). West Boylston had the highest concentration of NO3, classified as hypereutrophic (> 1.5 mg/L), and contained the second highest percentage of impervious land coverage (14.7%). All other subbasins have less than 8% imperviousness. Malagasco experienced the third highest concentrations of NO3, the second highest concentration of TP, and had the largest percentage of cultivated area (4.2%). All other subbasins contain less than 1.3% cultivated area. Potential further sources could relate to septic or sewer services, however, more investigation is needed.