Effects of flow diversion on downstream channel form in mountain streams

December 1993.Includes bibliographical references (pages 61-64).This paper reports on a study of regime, bedload transport, and channel morphology in diverted and free-flowing segments of mountain streams in Colorado where flow has been diverted, in some cases, for up to one hundred years. The goal of the project was to determine whether differences in channel form and processes could be detected and linked to changes in flow regime from diversion. The effect of diversion on flow fegime can very considerably between individual steams. Typically, the total annual water yield is drastically reduced by diversion, though, where storage is limited, occasional high flows, with a five-to-ten year return frequency, move thought the natural channel. These larger events have the potential to reset changes in morphology incurred during the intervening dry years, such as channel narrowing and fining of bed size distribution. In general, changes in channel capacity were quite subtle, and the most apparent change was a decrease in channel width due to vegetation and the development of low bank beneath a former cut bank. No change in morphology was apparent in constrained channels. The results here are preliminary as of December 1993. Final results will be presented in subsequent publications.Grant no. 14-08-0001-2008, Project no. 13; financed in part by the U.S. Dept. of the Interior, Geological Survey, through the Colorado Water Resources Research Institute

Sediment Movement at LTER Sites: Mechanics, Measurement and Integration with Hydrology

published or submitted for publicationis peer reviewedOpe

Spatial Variation among Lakes within Landscapes: Ecological Organization along Lake Chains

Although limnologists have long been interested in regional patterns in lake attributes, only recently have they considered lakes connected and organized across the landscape, rather than as spatially independent entities. Here we explore the spatial organization of lake districts through the concept of landscape position, a concept that considers lakes longitudinally along gradients of geomorphology and hydrology. We analyzed long-term chemical and biological data from nine lake chains (lakes in a series connected through surface or groundwater flow) from seven lake districts of diverse hydrologic and geomorphic settings across North America. Spatial patterns in lake variables driven by landscape position were surprisingly common across lake districts and across a wide range of variables. On the other hand, temporal patterns of lake variables, quantified using synchrony, the degree to which pairs of lakes exhibit similar dynamics through time, related to landscape position only for lake chains with lake water residence times that spanned a wide range and were generally long (close to or greater than 1 year). Highest synchrony of lakes within a lake chain occurred when lakes had short water residence times. Our results from both the spatial and temporal analyses suggest that certain features of the landscape position concept are robust enough to span a wide range of seemingly disparate lake types. The strong spatial patterns observed in this analysis, and some unexplained patterns, suggest the need to further study these scales and to continue to view lake ecosystems spatially, longitudinally, and broadly across the landscape.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42434/1/10021-2-5-395_2n5p395.pd

Mountain permafrost, a valid archive to study climate change? Examples from the Rocky Mountains

Abstract Mountain permafrost is highly sensitive to changing air temperatures because they affect the thawing depth of the annual active layer, as well as the time and speed of the refreezing process, mainly in the winter. The Long Term Ecological Research Site (LTER) Niwot Ridge and the Critical Zone Observatory Site (CZO) Green Lakes in Colorado, USA, with their high alpine tundra climate and vegetation, offer ideal conditions to study changes of mountain permafrost. The sites provide high quality climate data, together with studies on permafrost since the 1970's, which make these places rather unique in the US. We present data from our studies on permafrost distribution using different geophysical techniques to portray the shallow subsurface. The data on permafrost and soil temperature are compared with existing models of permafrost distribution and possible thermal degradation, as well as with older data on the existence and distribution of permafrost at these sites. At some locations, we find large differences when compared to the older data and the prognostic model. Sites formerly indicated as permafrost in the 1970's shifted towards sites with annual ice lenses today. We discuss the results and attempt to discern if the observed change is a direct consequence of the current rising air temperatures. Zusammenfassun