Changes in impervious surface area, flood frequency, and water chemistry within the Delaware River basin during the past 50 years: initial results

Proceedings of the Seventh International Conference on Hydroscience and Engineering, Philadelphia, PA, September 2006. http://hdl.handle.net/1860/732Housing development and total road mileage expansion, which result from the growing population and economic activity in the region, increased the total impervious surface area (ISA) within the Delaware River Basin (DRB) from either 3.19% or 3.69% of the total basin area in 1950 to either 5.41% or 6.44% of the total basin area in 2000, depending on which of two plausible scenarios are used for interpreting the available housing and road mileage data. Assuming an average area of 0.3 acre and 35% ISA for a single-unit detached house and 0.1 acre and 60% ISA for all other housing units, the projected ISA for the DRB is 5.66% in 2006. This result is comparable with the existing GIS data from the LandSat Thematic Mapper Imager for part of the DRB. Associated with the increasing ISA in the DRB, there also is an increase in flood events for recent years. Increased peak flows in July and August, which are the two months with the highest precipitation, also are noticeable. Concentrations of sodium and chloride in the Delaware River water increased between 2-4.6 times over the last 50 years at both upstream and downstream locations. Increased application of sodium chloride, in the form of deicing salt that is tied to the expansion of total road mileage in the basin, may be one of the main reasons for the increase of these ions in the waters of the Delaware River

Proceedings of the Thirteenth International Society of Sports Nutrition (ISSN) Conference and Expo

Meeting Abstracts: Proceedings of the Thirteenth International Society of Sports Nutrition (ISSN) Conference and Expo Clearwater Beach, FL, USA. 9-11 June 201

Soil-Litter Mixing Accelerates Decomposition in a Chihuahuan Desert Grassland

Decomposition models typically under-predict decomposition relative to observed rates in drylands. This discrepancy indicates a significant gap in our mechanistic understanding of carbon and nutrient cycling in these systems. Recent research suggests that certain drivers of decomposition that are often not explicitly incorporated into models (for example, photodegradation and soil–litter mixing; SLM) may be important in drylands, and their exclusion may, in part, be responsible for model under-predictions. To assess the role of SLM, litterbags were deployed in the Chihuahuan Desert and interrelationships between vegetation structure, SLM, and rates of decomposition were quantified. Vegetation structure was manipulated to simulate losses of grass cover from livestock grazing and shrub encroachment. We hypothesized that reductions in grass cover would promote SLM and accelerate mass loss by improving conditions for microbial decomposition. Litter mass decreased exponentially, with the greatest losses occurring in concert with summer monsoons. There were no differences in decay constants among grass cover treatments. A significant, positive relationship between mass loss and SLM was observed, but contrary to expectations SLM was independent of grass cover. This suggests that processes operating at finer spatial scales than those in our grass removal treatments were influencing SLM. Shifts in litter lipid composition suggest increased bacterial contribution to decomposition through time. SLM, which is seldom included as a variable controlling decomposition in statistical or mechanistic models, was a strong driver of decomposition. Results are discussed in the context of other known drivers of decomposition in drylands (for example, UV radiation and climate) and more mesic systems

Herbage Biomass and its Relationship to Soil Carbon Under Long-term Grazing in Northern Temperate Grasslands

While northern temperate grasslands are important for supporting beef production, it remains unclear how grassland above- and belowground biomass responds to long-term cattle grazing. Here, we use a comprehensive dataset from 73 grasslands distributed across a broad agro-climatic gradient to quantify grassland shoot, litter, and shallow (top 30 cm) root biomass in areas with and without grazing. Additionally, we relate biomass to soil carbon (C) concentrations. Forb biomass was greater (p  0.05). Forb crude protein concentrations were lower (p  0.05). Surface mineral soil C concentrations were positively related to peak grassland biomass, particularly total (above + belowground) biomass, and with increasing forb biomass in grazed areas. Finally, total aboveground shoot biomass and soil C concentrations in the top 15 cm of soil were both positively related to the proportion of introduced plant diversity in grazed and non-grazed grasslands. Overall, cattle grazing at moderate stocking rates had minimal impact on peak grassland biomass, including above- and belowground, and a positive contribution exists from introduced plant species to maintaining herbage productivity and soil C.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Soil Moisture and Soil-Litter Mixing Effects on Surface Litter Decomposition: A Controlled Environment Assessment

Recent studies suggest the long-standing discrepancy between measured and modeled leaf litter decomposition in drylands is, in part, the result of a unique combination of abiotic drivers that include high soil surface temperature and radiant energy levels and soil-litter mixing. Temperature and radiant energy effects on litter decomposition have been widely documented. However, under field conditions in drylands where soil-litter mixing occurs and accelerates decomposition, the mechanisms involved with soil-litter mixing effects are ambiguous. Potential mechanisms may include some combination of enhanced microbial colonization of litter, physical abrasion of litter surfaces, and buffering of litter and its associated decomposers from high temperatures and low moisture conditions. Here, we tested how soil-litter mixing and soil moisture interact to influence rates of litter decomposition in a controlled environment. Foliar litter of two plant species (a grass [Eragrostis lehmanniana] and a shrub [Prosopis velutina]) was incubated for 32 weeks in a factorial combination of soil-litter mixing (none, light, and complete) and soil water content (2, 4, 12% water-filled porosity) treatments. Phospholipid fatty acids (PLFAs) were quantified one week into the experiment to evaluate initial microbial colonization. A complementary incubation experiment with simulated rainfall pulses tested the buffering effects of soil-litter mixing on decomposition. Under the laboratory conditions of our experiments, the influence of soil-litter mixing was minimal and primarily confined to changes in PLFAs during the initial stages of decomposition in the constant soil moisture experiment and the oscillating soil moisture conditions of the rainfall pulse experiment. Soil-litter mixing effects on CO2 production, total phospholipid concentrations, and bacterial to total PLFA ratios were observed within the first week, but responses were fairly weak and varied with litter type and soil moisture treatment. Across the entire 32-week incubation experiment, soil moisture had a significant positive effect on mass loss, but soil-litter mixing did not. The lack of strong soil-litter mixing effects on decomposition under the moderate and relatively constant environmental conditions of this study is in contrast to results from field studies and suggests the importance of soil-litter mixing may be magnified when the fluctuations and extremes in temperature, radiant energy and moisture regimes common dryland field settings are in play

Herbage Biomass and its Relationship to Soil Carbon Under Long-term Grazing in Northern Temperate Grasslands

While northern temperate grasslands are important for supporting beef production, it remains unclear how grassland above- and belowground biomass responds to long-term cattle grazing. Here, we use a comprehensive dataset from 73 grasslands distributed across a broad agro-climatic gradient to quantify grassland shoot, litter, and shallow (top 30 cm) root biomass in areas with and without grazing. Additionally, we relate biomass to soil carbon (C) concentrations. Forb biomass was greater (p  0.05). Forb crude protein concentrations were lower (p  0.05). Surface mineral soil C concentrations were positively related to peak grassland biomass, particularly total (above + belowground) biomass, and with increasing forb biomass in grazed areas. Finally, total aboveground shoot biomass and soil C concentrations in the top 15 cm of soil were both positively related to the proportion of introduced plant diversity in grazed and non-grazed grasslands. Overall, cattle grazing at moderate stocking rates had minimal impact on peak grassland biomass, including above- and belowground, and a positive contribution exists from introduced plant species to maintaining herbage productivity and soil C.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author