Glacial legacy effects on tundra stream processes and macroinvertebrate communities, North Slope, Alaska

Ecosystems are dynamic, with their structure and function changing through time. Often biological changes parallel changes in physical and chemical characteristics on the system. The Arctic tundra on the north slope of the Brooks Range, Alaska, has a complex landscape, with glacial terrains of different ages positioned in close proximity to each other. This study examined stream ecosystem structure and function across a range of landscapes, aged from 11.5-25 thousand years old to ca. 1.8 million years old. Effects of lakes on stream ecosystems, which are associated with young glacial terrains were also included, as the configuration of hydrologic networks changes through time. The overarching theme of this dissertation is to understand how the age of these glacial landscapes influences the structure and function of stream ecosystems.;The terrestrial ecosystems in the vicinity of the Toolik Lake Field Station, North Slope, Alaska, have different chemical and biological attributes associated with landscape age. There are also differences in the configuration of the hydrologic networks between these terrains. Using this information, I predicted that rates of stream ecosystem systems would be faster on younger aged glacial terrains and macroinvertebrate communities would be unique between landscape ages.;Contrary to my predictions, rates of ecosystem processes were not influenced by landscape age directly. Age of the landscape, however, did influence biotic characteristics of stream ecosystems indirectly, through the presence or absence of lakes in the hydrologic networks. Variability in those differences was explained by a gradients of physical attributes of the streams, mainly substratum stability and mean summer water temperature, although gradients in nutrient concentrations explained variability in some comparisons. Lakes altered the physical and chemical characteristics of outlet streams, and leaf litter breakdown rates decreased downstream of lakes and net chlorophyll-alpha accumulation rates increased downstream of lakes. Community production of the stream macroinvertebrates was similar in inlet streams, regardless of watershed. Community production in outlet streams, however, was different between watersheds. The presence of multiple lakes in a watershed had a cumulative effect on the rates of leaf litter breakdown and net chlorophyll-alpha accumulation in one watershed and was explained by a buffering effect of multiple lakes on temperature and hydrologic characteristics of the streams and the presence of specific invertebrate taxa. These results suggest that age of the glacial terrain does control stream ecosystem processes through the configuration of the lake-stream networks and the characteristics of the habitats associated with those configurations.