ECOLOGICAL EFFECTS OF ANTHROPOGENIC NITROGEN ON ECOLOGICAL SYSTEMS

Mailea Miller-Pierce

Anthropogenic nitrogen (N) pollution has greatly increased the amount of inorganic N reaching ecosystems. Anthropogenic N adversely affects ecosystems, and these effects have received considerable research attention. Global biodiversity declines from N pollution have prompted scientists to estimate specific levels of N that cause significant ecological harm (i.e critical N loads). Critical N loads are widely used by policymakers to manage for individual species, habitats, and ecoregions. However, they are unstudied in the context of 1) plant-insect interactions; and 2) N-limited, early successional systems. This dissertation spans a wide range of investigations, all focused on the effects of anthropogenic N on natural ecosystems. First, we examined how nearshore water quality in Maui, Hawai`i is severely impaired from wastewater reclamation facilities, due to the injection of nutrient rich, partially treated wastewater. Our findings suggest that water quality impairments in Maui are a greater concern than previously acknowledged, and that policymakers should discourage the illegal discharge of human effluent into nearshore coral reef ecosystems. Second, we conducted a meta-analysis using field studies, on the effects of simulated N deposition on two leaf characteristics that affect insect herbivores, foliar N concentration and carbon-based chemical defenses, and on the abundance of associated insects. We found N deposition increases the abundance of insect herbivores and decreases the abundance of insect predators, regardless of the rate of N deposition. This suggests that insect herbivores and their natural enemies both have relatively low critical N loads. Lastly, across three years we investigated how two key agents of global change, N deposition and invasive species, alter early successional communities at Mount St. Helens (MSH) volcano. We simulated N deposition at 0x, 2x, and 4x ambient levels and included an exclusion treatment of the invasive insect herbivore, Cryptorhynchus lapathi. Both agents of global change altered foliar traits and growth patterns of an important woody plant pioneer at MSH, Salix sitchensis, resulting in decreased richness and diversity of the associated insect community. Primary successional habitats experienced more numerous and more significant ecological effects than secondary succession, suggesting different critical N thresholds for habitats with different successional starting points.

ECOLOGICAL EFFECTS OF ANTHROPOGENIC NITROGEN ON ECOLOGICAL SYSTEMS

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