FULL SUMMARY: This project addressed the impacts of climate change and melting glaciers on the fluxes of fresh water, and of the essential nutrients nitrate and iron, on the coastal ecosystem in the Copper River region of the Gulf of Alaska. The project included both terrestrial and marine components. The terrestrial part of this study focused on the Copper River and its tributaries, to examine how melting of glaciers is altering the magnitude and timing of freshwater supply from the Copper River, as well as the impact of glacier melting on the present and future supply of iron and nitrate from the river and from estuarine upwelling. The rates of glacier recession were assessed from remote sensing and physical observations of glaciers. The rate of discharge from the Copper River, and its contributions from precipitation, snowmelt, and glacier melting was inferred. A set of glaciated, deglaciated, and periglacial tributaries of the Copper River were sampled to examine present-day nutrient cycling in each of these settings, and to use a space-fortime substitution to make predictions about the future evolution of nutrients transported to the Gulf of Alaska from the Copper River. The flux and speciation of iron was examined, with the hypothesis that glaciated tributaries supply large amounts of reactive particulate iron that fuels a large dissolved iron pool in offshore waters, while deglaciated tributaries maintain wetlands that yield much lower particulate iron loads, yet promote dissolved oxygen carbon-rich waters with high dissolved iron concentrations. By contrast, glaciated tributaries were predicted to maintain low nitrate concentrations; however, immediately following deglaciation, alders and other nitrogen-fixing plants were predicted to establish themselves, leading to a much larger riverine nitrate load than occurred prior to the retreat of the glacier. As glaciers continue to recede, this invasion by nitrogen-fixing plants, and reduction in particulate iron load, has the potential to have a large impact on the present-day coastal, iron-rich, nitrogen-poor ecosystem. The marine component of this study built upon three research cruises per year to conduct transects from the Copper River mouth to beyond the shelf break. We studied the Copper River plume as a biological hotspot, examining both seasonal and interannnual change. The project tested the hypothesis that populations of fish, with critical lifestage requirements dependent on near-shore waters, are supported by phytoplankton and zooplankton populations, which are in turn controlled by nutrient inputs from glacier melt, riverine input, and the estuarine upwelling that results from freshwater inputs of these glacier-dominated rivers to the coast. Dissolved iron samples were collected using an underway pumping system, while underway measurements of nitrate, chl-a, turbidity, and zooplankton abundance were carried out using an undulating towed body. From a separate vessel, fish were enumerated with a surface trawl and their otoliths removed for later analysis. Data from these cruises were interpreted with the aid of physical oceanographic modeling and ecosystem modeling. The project resulted in several presentations and journal publications. The primary products that are useful to resource managers include the ecosystem model results that describe how the present-day coastal ecosystem responds to seasonal changes in snowmelt, glacier melt, precipitation, upwelling, and nutrient supply as well as the predictions about future ecosystem change in response to glacial recession in the coming decades.
