Using Geospatial Methods to Quantify the Co-Dispersion of Mercury Sources and Exposures in River Otter (Lontra Canadensis) for Risk Prediction

Abstract

Mercury is an environmental contaminant of concern due to the established effects of methylated mercury (MeHg) on neurological functioning. Sentinel species such as the river otter (Lontra canadensis) are commonly used to monitor environmental mercury concentrations. Fur mercury has proven to be a reliable and cost-effective measure of exposure to MeHg in river otters and is a good proxy for assessing environmental mercury concentrations. A total of 311 geolocated fur samples were obtained from wildlife biomonitoring programs at Environment and Climate Change Canada and from the North American Fur Auction. These samples represent 131 unique locations throughout Canada collected between 2013 and 2016. Total mercury (THg) was measured on a MA-3000. Clustering of high THg was assessed using Getis and Ord’s Gi*. The association between fur THg and mercury sources was assessed using linear regression modelling alongside spatial regression methods such as geographically weighted regression. A cluster of low fur THg concentrations was observed in Alberta, and clusters of high fur THg concentrations were observed in northeastern Ontario, New Brunswick, and Nova Scotia. There is a statistically significant (p<0.05) negative relationship between fur THg and proximity to dam reservoir water, and pH of soil. There was also a statistically significant interaction between proximity to dam reservoir water and the pH of the soil. Otters that live closer to the reservoir water of dams have higher fur THg concentrations. This effect is enhanced if the soil pH surrounding the reservoir is also low. Using a geographically weighted regression these variables explain up to 35% of the variance. Results from this research are important for assessing the impact of future hydroelectric dam development on aquatic ecosystems. This research also further supports the use of river otter fur as a biomonitoring tool for environmental mercury exposure.