The association between watershed characteristics and mercury concentrations in fish of Northern Ontario lakes

Abstract

Many landscape, limnological, and ecological factors synergistically affect the mercury cycle and subsequently influence total mercury (THg) concentrations in fish. In Chapter 1, the associations between watershed and lake scale characteristics with THg in piscivorous fish are examined. ArcGIS was used to delineate the waterbody catchment area and extract waterbody catchment characteristics for 243 of northern Ontario’s lakes. Walleye (Sander vitreus, n= 121 lakes), lake trout (Salvelinus namaycush, n= 60 lakes), brook trout (Salvelinus fontinalis, n= 18 lakes), northern pike (Esox lucius, n =107 lakes), and smallmouth bass (Micropterus dolomieu, n = 37 lakes) were standardized to the mean length of the populations by using power-series regressions. Multivariate analysis (non-metric multidimensional scaling) and univariate analysis were used to determine the associations between total mercury concentrations in fish and watershed scale and lake scale variables. Watershed and lake chemistry characteristics poorly described the variability in THg concentrations. Forest harvesting and natural disturbance were not associated with fish mercury concentrations. In Chapter 2, the relationship between walleye (Sander vitreus) growth rates and mercury concentrations was evaluated. The von Bertalanffy growth model was used to standardize the age of walleye to the mean total length. Walleye populations with slower growth rates had higher THg concentrations (r2=0.333, p< 0.001), suggestive of growth efficiency. Moreover, abundance of walleyes was associated with the growth rate (r2 =0.136, p<0.0001). Concentrations of THg in piscivorous fish are attributed to physical, chemical, and ecological characteristics of lakes. It is likely that lake ecology exerts the strongest influence on high mercury concentrations in piscivorous species, masking the effect from from watershed disturbance.