Examining riverine community response to artificial nutrient enrichment in two Inner Bay of Fundy streams

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University of New Brunswick
Artificial fertilization of river systems is an environmental management strategy devised to subsidize for nutrient shortages in streams resulting in reduced or limited primary productivity. This has subsequent effects on primary consumers and the predators that feed on them. This method, most ubiquitously used in the Pacific Northwest of North America, was applied to Inner Bay of Fundy streams in order to analyze the applicability of this methodology to Atlantic stream communities. Multiple phosphorus concentrations of Multicote® (9-44-0) fertilizer were applied to two study streams. Subsequently, food web response to stream enrichment was monitored at the population and functional ecosystem level. Population-level changes were scrutinized through measuring water chemistry concentrations, benthic chlorophyll-a levels and benthic macroinvertebrate (BMI) biomass and densities. Functional ecosystem changes were measured through examining shifts in nutrient limitation and stable isotope analysis (i.e., ᵟ15N, ᵟ13C) of periphyton and benthic macroinvertebrates (i.e., grazers/collector-gatherers, predators). Results indicated a rapid response to nutrient enrichment in all trophic levels. Significant positive increases in chlorophyll-a, shifts away from phosphorus limitation, enhanced BMI abundance and biomass and notable stable isotope changes in biofilm and grazing BMIs were recorded by the first sampling period (21 days following enrichment). Total phosphorus concentration and predatory BMI stable isotopes also exhibited nutrient assimilation 42 days after initial fertilization. Improvements to future studies should include refining fertilizer dose calculations, more comprehensive analyses of each trophic level (e.g., periphyton composition) and increasing study length. Results of this current study, however, demonstrate great potential for applicative use of artificial nutrient fertilization to increase productivity within Inner Bay of Fundy river ecosystems.