ABSTRACT
Because stable isotopes of carbon and sulfur in pulp mill effluent (PME) can be incorporated through food sources into biological tissues, we hypothesized that stable isotopes may be used to quantify exposure of riverine biota to PME. We tested this hypothesis by assessing the C, N and S isotopic compositions of the waters and food web of the Thompson River and effluent samples from the Weyerhaeuser pulp mill in Kamloops, BC. Although the δ34S isotopic composition of the PME was distinct, it could not be used reliably to trace the fate of PME due to the mixing pattern of waters of the North and South Thompson River. In contrast, the food web had previously been thought to be supported by C fixed by riverine algae. However, an isotopic mass balance model suggested two C sources support this food web: (1) the algal biofilm which utilizes dissolved inorganic C from the river and (2) a source with an δ13C isotopic signature similar to terrestrial plants. Similarly, δ15N isotopic composition of the food web indicated a substantial input from terrestrial plants. This striking and unexpected input of terrestrial C and N is hypothesized to be from PME, suggesting that C and N loadings from PME may play an important role in supporting downstream food webs.
