Thomas C O'Keefe

ABSTRACT We examined denitrification potentials in six of the major landscape structure (riparian soils of both meandering and braided streams, peat lands, coniferous flats, alder slopes, and groundwater seeps) of the Lake Nerka catchment in southwest Alaska. We found significant potential denitrifying activity in all the soils of the main landscape patch types of the Lake Nerka catchment. The lowest potential denitrifying activity was measured in the peat lands. A highly significant relationship was found between soil organic matter and potential denitrification activity in three landforms - coniferous flats, groundwater seeps, and riparian soils of meandering streams. These three landscape structures also had the highest denitrifying potential. The finer soils of riparian zones along spawning streams, which corresponded to meandering streams, showed a significantly higher potential denitrification activity than the coarse riparian soils along nonspawning streams. These nonspawning streams corresponded to braided streams, where finer sediments were not as prevalent. Therefore, if this high potential denitrification measured in riparian soils of spawning streams is combined with large inputs of nitrate to anaerobic sites, it can result in 15N signatures that mimic that of the marine-derived nitrogen provided by Pacific salmon in these Alaskan ecosystems.

... Origins, Patterns, and Importance of Heterogeneity in Riparian Systems ROBERT J. NAIMAN, J. COTT BECHTOLD, DEANNE C. DRAKE, JOSHUA J ... Both iron and phosphorus are transported in microag-gregates of organic matter, silt and clay particles, and tend to concentrate ...

Evidence for the importance of marine-derived nutrient (MDN) inputs from spawning salmon to terrestrial and freshwater ecosystems is rapidly accumulating, but the mechanisms by which MDN inputs are transferred and stored within spawning streams and their catchments are poorly understood. Presumed marine isotope signals have been found in riparian vegetation, suggesting that marine nutrients may impact terrestrial plant communities. Studies have suggested that MDN increases stream productivity both im- mediately after spawning and during the following spring. The peak of many spawning runs occurs at the end of the summer growing season, suggesting that overwinter storage of MDN must be occurring. A potential location for lateral nutrient transfers and overwin- ter MDN storage is the hyporheic zone within stream channels or in adjacent riparian flood- plains. Within Lynx Creek, a sockeye-spawning stream in the Wood River Lake drainage in southwestern Alaska, extensive floodplain hypor...

... Thomas C.O'Keefe1, Matthew C.Brewer2 and Stanley I.Dodson Department of Zoology, Birge Hall, University of Wisconsin at Madison, 430 ... Since Daphnia are not sensitive to IR light (Smith and Macagno, 1990), we predicted that it would not affect their swimming behavior. ...