Simulating Thermal Stress in Rhode Island Coldwater Fish Habitat Using SWAT

Abstract

Climate studies have suggested that inland stream temperatures and streamflow will increase over the next century in New England, thereby putting aquatic species sustained by coldwater habitats at risk. To effectively aid these ecosystems it has become ever more important to recognize historical water quality trends and anticipate the future impacts of climate change. This thesis uses the Soil and Water Assessment Tool (SWAT) to simulate historical and future streamflow and stream temperatures within three forested, baseflow driven watersheds in Rhode Island. The results provide a site-specific method to fisheries managers trying to protect or restore local coldwater habitats. The first manuscript evaluated two different approaches for modeling historical streamflow and stream temperature with the Soil and Water Assessment Tool (SWAT), using i) original SWAT and ii) SWAT plus a hydroclimatological model component that considers both hydrological inputs and air temperature effects on stream temperature (Ficklin et al., 2012). Model output was used to assess stressful events at the study site, Cork Brook, RI, between 1980-2009. Stressful events for this study are defined as any day where high or low flows occur simultaneously with stream temperatures exceeding 21˚C, the threshold at which brook trout (Salvelinus fontinalis), a coldwater fish species, begins to exhibit physiological stress. SWAT with the hydroclimatological component performed better during calibration (Nash-Sutcliffe Efficiency (NSE) of 0.93, R2 of 0.95) compared to original SWAT (NSE of 0.83, R2 of 0.93). Between 1980-2009, the number of stressful events increased by 55% and average streamflow increased by 60% at the study site. This chapter supports the application of the hydroclimatological SWAT component and provides an example method for assessing stream conditions in southern New England. The second manuscript uses the original SWAT model to simulate both historical and future climate change scenarios for Cork Brook and two other watersheds, the Queen River and Beaver River, in Rhode Island. These three sites were selected primarily due to their pristine aquatic habitat, data availability and existing interest in natural resource conservation by local non-profit and government groups. Similar to the first manuscript, this study analyzed model output to identify stressful events for brook trout. Results indicate that the Queen River has historically had the highest percent chance (6.4 %) that a stressful event would occur on any given day and Cork Brook had the lowest percent chance (4.4%). In future climate scenarios coldwater fish species such as brook trout will be increasingly