Determinants of Stream Chemistry Across the State of Connecticut: Integrating Geological Properties and Hydrologic Processes

A healthy stream is an ecosystem that is sustainable, resilient, and that maintains its ecological structure and function over time while continuing to meet societal needs and expectations. Healthy streams provide habitats for aquatic animals, provide safe areas for public use, and reduce the cost of water treatment when stream water is used for water supply. In places like Connecticut (CT), urbanization, land-use practices, road coverage, and wastewater discharges affect water quality. This research project characterizes and analyzes anthropogenic and lithogenic chemical inputs to streams and identifies how these inputs respond to seasonal hydrologic variations. To address these issues, I conducted an in-depth study of a suburban stream in Danbury, CT, as well as a broad sampling campaign of 23 streams across the state of Connecticut. At the Danbury stream, I collected 54 water samples across two distinct periods: a preliminary spring period and an 11-week summer monitoring series. The samples were analyzed for major ions and nutrients to determine their chemical composition and to better understand the water quality and site hydrology. The samples were also analyzed for stable hydrogen and oxygen isotopes to identify the sources of water in the stream (i.e., surface runoff, groundwater, direct precipitation) and to determine seasonal variations in hydrologic processes. Identifying groundwater and surface water inputs allows for more accurate predictions of current stream chemistry and future water quality conditions. Ion concentrations varied seasonally, with the lowest values generally occurring in March and the highest values in the summer months. July was the most variable month for all measured parameters, including the ions, stable isotopes, pH, and conductivity. Stable water isotopes followed seasonal trends, with the most enriched values recorded in July. Measured water quality parameters consistently remained below the EPA regulations for drinking water and aquatic life, as well as CT drinking water standards. Examining the in-depth studied stream in Danbury, along with the 23 other streams sampled across CT, reveals distinct regional differences in water quality and allows us to characterize the role of geology and land-use on shaping water quality. These findings underscore the critical role of seasonal monitoring in capturing the complex interplay between anthropogenic stressors and natural hydrologic variability in urban stream ecosystems.