MERCURY DYNAMICS IN SOUTHERN APPALACHIAN MOUNTAIN AQUATIC AND RIPARIAN FOOD WEBS

Abstract

The understanding of how community level trophic ecology affects the bioaccumulation/biomagnification of contaminants, and more specifically Hg in streams, remains largely unstudied. The current paradigm was built largely on the backs of studies that investigated lowland lakes and wetlands with an industrial point source. Growing evidence suggests that in river and stream systems, where the source of Hg is atmospheric, the old paradigm must be reevaluated. The chapters of this dissertation examined the biomagnification potential of mercury (Hg) and the role of community level trophic ecology (CLTE) in six southern Appalachian Mountain headwater aquatic and riparian food webs. Utilizing ecological tracers like naturally abundant stable isotopes of carbon (δ13C) and nitrogen (δ15N), this research determined that the community standard ellipse area (SEAc) influenced THg biomagnification, and that carbon normalized to the trout baseline (δ13CE) was the primary driver of total mercury (THg) bioaccumulation in trout. Although the SEAc of each respective reach’s neighboring aquatic and riparian communities had a high degree of trophic overlap in δ13C and δ15N biplot space, when the trophic level of riparian taxa was used to test the predictive function of aquatic THg biomagnification, the aquatic biomagnification model consistently underestimated concentrations in tetragnathids, araneids, and striders. These high Hg concentrations in spiders could cause harm to adult and nestling passerine birds inhabiting the southern Appalachian Mountains. This research sought to understand how riparian spiders can be better utilized with applied research (e,g,, ecological risk assessments) and the assumptions that researchers make when sampling. This research demonstrated that the selection of which spider to use as a surrogate for “all spiders” can influence the characterization of risk to passerine birds, and that tetragnathids provide a more conservative estimation of risk than araneids. Additionally, this research sought to understand the assumptions of field collected tetragnathids. The research suggests that spiders could be sampled without regard for sex: female tetragnathids were significantly larger than male spiders and represented a larger proportion of spiders collected at all sites; however, no differences in growth dynamics, isotopic signature (δ13C and δ15N), or THg concentrations were observed. Additionally, this research demonstrated that the leg of a tetragnathid can accurately represent the stable isotope signature of an entire spider.