Regional meteorological drivers and long term trends of winter-spring nitrate dynamics across watersheds in northeastern North America
This study evaluated the contribution of winter rain-on-snow (ROS) events to annual and seasonal nitrate (N-NO3) export and identified the regional meteorological drivers of inter-annual variability in ROS N-NO3 export (ROS-N) at 9 headwater streams located across Ontario, Canada and the northeastern United States. Although on average only 3.3 % of annual precipitation fell as ROS during winter over the study period, these events contributed a significant proportion of annual and winter N-NO3 export at the majority of sites (average of 12 and 42 %, respectively); with the exception of the most northern catchment, where total winter precipitation was exceptionally low (average 77 mm). In years with a greater magnitude...
Atmospheric deposition and solute export in giant sequoia: mixed conifer watersheds in the Sierra Nevada, California
Atmospheric depostion and stream discharge and solutes were measured for three years (September 1984 - August 1987) in two mixed conifer watersheds in Sequoia National Park, in the southern Sierra Nevada of California. The Log Creek watershed (50 ha, 2067-2397 m elev.) is drained by a perennial stream, while Tharp's Creek watershed (13 ha, 2067-2255 m elev.) contains an intermittent stream. Dominant trees in the area include Abies concolor (white fir), Sequoiadendron giganteum (giant sequoia), A. magnifica (red fir), and Pinus lambertiana (sugar pine). Bedrock is predominantly granite and granodiorite, and the soils are mostly Pachic Xerumbrepts. Over the three year period, sulfate (SO42-), nitrate (NO3-), and chloride...
Warming prevents the elevated CO 2 -induced reduction in available soil nitrogen in a temperate, perennial grassland
Rising atmospheric carbon dioxide concentration ([CO2]) has the potential to stimulate ecosystem productivity and sink strength, reducing the effects of carbon (C) emissions on climate. In terrestrial ecosystems, increasing [CO2] can reduce soil nitrogen (N) availability to plants, preventing the stimulation of ecosystem C assimilation; a process known as progressive N limitation. Using ion exchange membranes to assess the availability of dissolved organic N, ammonium and nitrate, we found that CO2 enrichment in an Australian, temperate, perennial grassland did not increase plant productivity, but did reduce soil N availability, mostly by reducing nitrate availability. Importantly, the addition of 2 Â°C warming...
The trade-off between growth rate and yield in microbial communities and the consequences for under-snow soil respiration in a high elevation coniferous forest
Soil microbial respiration is a critical component of the global carbon cycle, but it is uncertain how properties of microbes affect this process. Previous studies have noted a thermodynamic trade-off between the rate and efficiency of growth in heterotrophic organisms. Growth rate and yield determine the biomass-specific respiration rate of growing microbial populations, but these traits have not previously been used to scale from microbial communities to ecosystems. Here we report seasonal variation in microbial growth kinetics and temperature responses (Q10) in a coniferous forest soil, relate these properties to cultured and uncultured soil microbes, and model the effects of shifting growth kinetics on soil...
Within the past few decades, humans have dramatically altered the earth?s nitrogen (N) cycle. Introduction of reactive nitrogen (N) into the biosphere by humans now exceeds the rate of biological N2-fixation in native terrestrial ecosystems (Galloway et al. 2004). This increased reactive N is due primarily to N fertilizer production and fossil fuel combustion used to support the food and energy demands of a rapidly expanding human population. The negative human and environment health effects of this increased N are many (Galloway et al. 2008; Howarth et al. 2005; UNEP and WHRC 2007). Denitrification is the main process that permanently removes fixed N from the environment. Denitrification, the microbial production...
Anthropogenic effects on New Hampshire surface water quality: Long term evidence from lake sediments
Chemical characterization and toxicological testing of windrow composts from explosives-contaminated sediments
Environmental influences on the super(137)Cs kinetics of the yellow-bellied turtle (Trachemys scripta)
Long term database as a tool for aquatic ecosystem stewardship: A study case in the southern Gulf of Mexico
Complementarity of light and water use in tropical agroforests I. Theoretical model outline, performance and sensitivity