Environmental determinants of invertebrate community structure and nutrient storage in aquatic invertebrate larvae
University of New Brunswick
Aquatic invertebrates play a key ecological role in riverine biogeochemical cycles, transferring nutrients incorporated from diverse food sources (e.g.algae or terrestrial detritus) to resident and migratory predators within aquatic and riparian ecosystems. Agricultural land use affects stream aquatic invertebrate communities, generally reducing their diversity and the prevalence of sensitive taxa as a result of the introduction of agro-chemicals (nutrients and pesticides) and other environmental stressors (fine sedimentsand flow). This thesis aims to understand how agricultural land use affects aquatic invertebrate communities and the role these communities play in the storage and transfer of nutrients within stream food webs. To accomplish this, streams in northwestern New Brunswick were sampled over a three-year period (2010 –2012) for water nutrient concentrations, site characteristics, and aquatic invertebrate biomass and nutrient content. The first study established associations between agricultural land use and stream water nutrient concentrations (positive), aquatic invertebrate community diversity and sensitivity (negative), and total community biomass (negative).The second study determined that the nitrogen and phosphorus content within aquatic invertebrate communities decreased and increased, respectively, as aquatic invertebrate communities lost diversity and sensitive taxa. Using data from a subset of these sites and additional ones sampled in 2012, the final study validated the results of the previous studies and showed similar effects of agricultural land use on aqueous nutrient concentrations, aquatic invertebrate communities, and community nutrient content. Further, this study showed that the quantity of nitrogen stored within the aquatic invertebrate community decreased with increasing agricultural land use while the quantity of phosphorus was unaffected. Together these results demonstrate that as aquatic invertebrate communities change their composition in response to increasing agricultural land cover in the catchment, the amount of nutrients stored by the community decreases. This reduction in nutrient storage capacity likely results from shifts in life history strategies in the aquatic invertebrate community. More broadly, these findings suggest that agriculture affects how aquatic invertebrates cycle nutrients in riverine food webs, which may in turn impact aquatic and terrestrial predators that rely on these communities.