The unique landscape controls and meltwater contributions associated with glacial landcover along the coast of southeast Alaska were examined to better understand in-stream processing of dissolved organic matter (DOM) and nutrients during downstream transport. Specifically, this study paired glacial streams with nearby non-glacial streams and compared differences in landscape controls to: 1) evaluate the impact of glacial landcover and meltwater contributions on in-stream metabolism and uptake potential of proglacial streams; 2) quantify changes in DOM composition and concentration in glacial runoff during precipitation-driven flushing of a glaciated landscape; and 3) characterize the impact of glacial landcover and meltwater contributions on longitudinal trends in the physical and chemical signature of streamwater through changing watershed landscapes. Stream metabolism estimates suggested glacial streams receive little DOM from landscape sources and have the potential to function as net autotrophic systems under low flow regimes with unobstructed sunlight. Unlike most watersheds, shallow organic soils and low in-stream respiration rates associated with glacial systems resulted in near equilibrium dissolved CO₂ concentrations, with little flux to the atmosphere. Longitudinal stream analyses concluded low-elevation landscape discharge contributions had little influence on glacial streams compared to non-glacial streams. High specific discharge from glacial landscapes controlled streamwater chemistry throughout proglacial watersheds suggesting meltwater was delivered from the terminus of coastal glaciers downstream to the Gulf of Alaska (GOA) with little dilution or in-stream processing. Uniform concentrations of DOM and nutrients were found during increased discharge driven by precipitation on the glaciated watershed. This was in contrast to the non-glacial watershed, where streamwater DOM concentrations were largely controlled by connections to DOM-rich landscape sources during storm flows. Results from this study enhance the understanding of in-stream processes and landscape controls in watersheds that deliver freshwater to an ecologically productive marine zone and valuable commercial fishery. Furthermore, this study provides information about watersheds undergoing glacial recession to GOA basin-wide estimates of DOM export and future research initiatives focusing on in-stream DOM processing. / Ph. D.

Shrinking alpine glaciers alter the geochemistry of sensitive mountain streams by exposing reactive freshly-weathered bedrock and releasing decades of atmospherically-deposited trace elements from glacier ice. Changes in the timing and quantity of glacial melt also affect discharge and temperature of alpine streams. To investigate the effects of glacier ice melt on the geochemistry and hydrology of proglacial streams in the arid Intermountain West, we sampled supraglacial meltwaters and proglacial streams in the Dinwoody Creek watershed in the Wind River Range, Wyoming during late summer 2015, when the contributions of glacier meltwater were highest. Supraglacial meltwater was enriched in 8 trace elements (Cd, Co, Cu, MeHg, Mn, Pb, THg, Zn) relative to proglacial meltwaters. Concentrations of major ions (Mg2+, K+, Na+, Ca2+, SO42-) and the remaining 30+ analyzed trace elements were enriched in proglacial streams relative to supraglacial meltwater. To evaluate the diurnal effects of glacial meltwater on the chemistry and hydrology of proglacial streams, we collected hourly water samples of Dinwoody Creek and deployed loggers to monitor water depth, temperature, and specific conductance (SPC) at 15-min intervals over a 1-week period. The influx of glacial meltwater between 10:00 and 20:00 diluted solute concentrations and affected the relative enrichment/depletion of highly soluble elements (major ions, alkaline earth elements), less than REEs. Stable isotopes of H and O (δD, δ18O) in Dinwoody Creek were more depleted during peak runoff (10:00 – 20:00) than base flow, reflecting contributions from isotopically depleted glacial meltwaters. Looping hysteresis patterns were observed between water depth versus DO, pH, temperature and SPC in glaciated streams. Hysteresis patterns were affected by changes in weather and varied depending on the type of stream (glaciated versus non-glaciated) and the distance to glacier toe. Combination of multiple hydrologic tracers (solute concentrations, high frequency logger data, stable isotopes) shows strong potential to improve estimates of glacial meltwater contributions to Dinwoody Creek. Our results suggest that elevated concentrations of heavy metals in glacier ice melt across the Intermountain West may negatively impact sensitive alpine streams.