Urbanization impacts on stream and lake water quality in a small watershed in central Massachusetts, USA

Urbanization of watersheds, including increased impervious surfaces, altered land use, and the introduction of anthropogenic pollutants, alters watershed hydrology and water quality. While the connection between land use and water quality is well established at regional scales, the inconsistent gains in water quality despite management efforts underscores the need to better understand how water quality in individual small watersheds responds to overlapping modern stressors and legacy effects. This study examines the influence of urbanization on the chemical characteristics of a small watershed in central Massachusetts. We used field measurements and laboratory analyses to assess how conductivity, nutrients (nitrate, ammonia, total phosphorus), and trace metals (Cu, Pb, Zn) varied across 13 stream, lake, and tributary sites during the 2022 field season. Land cover analysis of subwatersheds for each site revealed a gradient of urbanization from predominantly forested headwaters to densely developed downstream sites. Specific conductance was positively correlated with impervious surface area and road density; the highest values were observed downstream and during the winter and early spring, suggesting road salt as a key driver of stream salinization. Nitrates showed a strong correlation with impervious surface cover and lawn area, while phosphorus concentrations were more weakly correlated with urbanization metrics and may be more influenced by legacy (historical) sources. Following the single large precipitation event, phosphorus concentrations increased, consistent with a source of sediment-bound legacy phosphorus. Streambed metal concentrations showed no significant correlation with urbanization metrics across sites, but were markedly elevated at the most downstream main stem stream site, possibly indicating a localized point source from historical industrial activity. These findings underscore the complex and spatially variable impacts of urbanization on watershed health and emphasize the need for high-resolution, local monitoring to inform effective management and restoration strategies.