Mark W. Williams

Learn More
Most terrestrial carbon sequestration at mid-latitudes in the Northern Hemisphere occurs in seasonal, montane forest ecosystems. Winter respiratory carbon dioxide losses from these ecosystems are high, and over half of the carbon assimilated by photosynthesis in the summer can be lost the following winter. The amount of winter carbon dioxide loss is(More)
Fluxes of CO2 and N2O were measured from both natural and experimentally augmented snowpacks during the winters of 1993 and 1994 on Niwot Ridge in the Colorado Front Range. Consistent snow cover insulated the soil surface from extreme air temperatures and allowed heterotrophic activity to continue through much of the winter. In contrast, soil remained(More)
Recent work in seasonally snow covered ecosystems has identified thawed soil and high levels of heterotrophic activity throughout the winter under consistent snow cover. We performed measurements during the winter of 1994 to determine how the depth and timing of seasonal snow cover affect soil microbial populations, surface water NO loss during snowmelt,(More)
Here we report measurements of organic and inorganic nitrogen (N) fluxes from the high-elevation Green Lakes Valley catchment in the Colorado Front Range for two snowmelt seasons (1998 and 1999). Surface water and soil samples were collected along an elevational gradient extending from the lightly vegetated alpine to the forested subalpine to assess how(More)
Fluxes of CO2 during the snow-covered season contribute to annual carbon budgets, but our understanding of the mechanisms controlling the seasonal pattern and magnitude of carbon emissions in seasonally snow-covered areas is still developing. In a subalpine meadow on Niwot Ridge, Colorado, soil CO2 fluxes were quantified with the gradient method through the(More)
We present spatial patterns of glacier fluctuations from the Cordillera Blanca, Peru, (glacier area, terminus elevations, median elevations and hypsography) at decadal timescales derived from 1970 aerial photography, 2003 SPOT5 satellite data, Geographic Information Systems (GIS) and statistical analyses. We derived new glacier outlines from the 2003 SPOT(More)
Here we provide an overview of current research activities on nitrogen (N) cycling in high-elevation catchments of the Colorado Front Range. We then use this information to develop a conceptual model of how snow cover controls subnivial (below snowpack) microbial processes and N leachate from the snow-soil interface to surface waters. This model is based on(More)
High elevation talus soils are extreme environments for life. They are pertinent to the hydrology and biochemical cycling of high elevation ecosystems that supply drinking water to major metropolitan areas, and are undergoing change as a result of N deposition. As biological systems, they are virtually unstudied. In order to gain a basic understanding of(More)
Dissolved organic matter (DOM) is an important vehicle for the movement of nutrients from terrestrial to aquatic systems. To investigate how the source and composition of aquatic DOM change in both space and time, we used chemical, spectroscopic, and isotopic analyses to characterize DOM in a headwater catchment in the Colorado Front Range. Streamwater(More)
[1] We investigated how the source and chemical character of aquatic dissolved organic carbon (DOC) change over the course of the runoff season (May–November, 1999) in Green Lakes Valley, a high-elevation ecosystem in the Front Range of the Colorado Rocky Mountains. Samples were collected on North Boulder Creek from four sites across an alpine/subalpine(More)