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Svoray T.,Geography and Environmental DevelopmentBen Gurion University of the NegevBeer Sheva Israel | Assouline S.,Soil
Water Resources Research | Year: 2015

Current literature provides large number of publications about ecohydrological processes and their effect on the biota in drylands. Given the limited laboratory and field experiments in such systems, many of these publications are based on mathematical models of varying complexity. The underlying implicit assumption is that the data set used to evaluate these models covers the parameter space of conditions that characterize drylands and that the models represent the actual processes with acceptable certainty. However, a question raised is to what extent these mathematical models are valid when confronted with observed ecosystem complexity? This Introduction reviews the 16 papers that comprise the Special Section on Eco-hydrology of Semiarid Environments: Confronting Mathematical Models with Ecosystem Complexity. The subjects studied in these papers include rainfall regime, infiltration and preferential flow, evaporation and evapotranspiration, annual net primary production, dispersal and invasion, and vegetation greening. The findings in the papers published in this Special Section show that innovative mathematical modeling approaches can represent actual field measurements. Hence, there are strong grounds for suggesting that mathematical models can contribute to greater understanding of ecosystem complexity through characterization of space-time dynamics of biomass and water storage as well as their multiscale interactions. However, the generality of the models and their low-dimensional representation of many processes may also be a "curse" that results in failures when particulars of an ecosystem are required. It is envisaged that the search for a unifying "general" model, while seductive, may remain elusive in the foreseeable future. It is for this reason that improving the merger between experiments and models of various degrees of complexity continues to shape the future research agenda. © 2015. American Geophysical Union.

Martin E.M.,University of Arkansas | Cousins S.L.,Soil | Clausen E.C.,University of Arkansas | Carrier D.J.,University of Arkansas
Transactions of the ASABE | Year: 2011

In order to establish the baseline quantities of key fermentable sugars, switchgrass (Panicum virgatum L., var. Alamo) stems and leaves were pretreated with dilute acid, and the release of sugars was compared to that reported in the U.S. DOE biomass feedstock composition and property database. Switchgrass was planted in the spring of 2008 and harvested in the spring of 2009. The feedstock was separated into leaves and stems and ground to particle sizes of 0.34 and 0.37 mm, respectively. Dilute acid pretreatment of the material (130°C in 0.98% H 2SO 4 for 25 min) yielded xylose recoveries of 76% and 61% for leaves and stems, respectively. Recoveries were calculated by dividing the recovered sugar by the values reported in the DOE feedstock database. Coupling a 2 h 85°C hot water presoaking step to the 25 min 130°C in 0.98% H 2SO 4 pretreatment increased the xylose recovery by 23% and 5% for leaves and stems, respectively. These results demonstrate that a presoaking step increases the sugar release without escalating the severity of the pretreatment. Moreover, the 85°C presoaking water contained the flavonoid quercetin, which is a documented antioxidant. The presoaking water from leaves and stems displayed yields of 0.14 and 0.12 mg of quercetin per g of dry switchgrass, respectively. Thus, the presoaking step not only increases monosacchride recovery, but provides a slipstream that could be processed into a value-added revenue-generating stream for the biorefinery. © 2011 American Society of Agricultural and Biological Engineers ISSN 2151-0032.

Monger G.R.,Soil | Monger G.R.,Haley and Aldrich | Duncan C.M.,Soil | Brusseau M.L.,Soil | Brusseau M.L.,University of Arizona
Water, Air, and Soil Pollution | Year: 2014

A gas-phase tracer test (GTT) was conducted at a landfill in Tucson, AZ, to help elucidate the impact of landfill gas generation on the transport and fate of chlorinated aliphatic volatile organic contaminants (VOCs). Sulfur hexafluoride (SF6) was used as the nonreactive gas tracer. Gas samples were collected from a multiport monitoring well located 15.2 m from the injection well and analyzed for SF6, CH4, CO2, and VOCs. The travel times determined for SF6 from the tracer test are approximately two to ten times smaller than estimated travel times that incorporate transport by only gas-phase diffusion. In addition, significant concentrations of CH4 and CO2 were measured, indicating production of landfill gas. Based on these results, it is hypothesized that the enhanced rates of transport observed for SF6 are caused by advective transport associated with landfill gas generation. The rates of transport varied vertically, which is attributed to multiple factors including spatial variability of water content, refuse mass, refuse permeability, and gas generation. © 2014 Springer International Publishing Switzerland.

Marble J.C.,Soil | Marble J.C.,University of Arizona | Marble J.C.,U.S. Department of Energy | Brusseau M.L.,Soil | And 5 more authors.
Water, Air, and Soil Pollution | Year: 2014

The purpose of this study is to examine the development and effectiveness of a persistent dissolved-phase treatment zone, created by injecting potassium permanganate solution, for mitigating discharge of contaminant from a source zone located in a relatively deep, low-permeability formation. A localized 1,1-dichloroethene (DCE) source zone comprising dissolved- and sorbed-phase mass is present in lower-permeability strata adjacent to sand/gravel units in a section of the Tucson International Airport Area (TIAA) Superfund Site. The results of bench-scale studies conducted using core material collected from boreholes drilled at the site indicated that natural oxidant demand was low, which would promote permanganate persistence. The reactive zone was created by injecting a permanganate solution into multiple wells screened across the interface between the lower-permeability and higher-permeability units. The site has been monitored for 9 years to characterize the spatial distribution of DCE and permanganate. Permanganate continues to persist at the site, and a substantial and sustained decrease in DCE concentrations in groundwater has occurred after the permanganate injection. These results demonstrate successful creation of a long-term, dissolved-phase reactive treatment zone that reduced mass discharge from the source. This project illustrates the application of in situ chemical oxidation as a persistent dissolved-phase reactive treatment system for lower-permeability source zones, which appears to effectively mitigate persistent mass discharge into groundwater. © 2014 Springer International Publishing Switzerland.

Zhang Q.,Zhejiang University | Wang J.,Soil | Wang G.,Zhejiang University | Shamsi I.H.,Zhejiang University | Wang X.,Zhejiang University
Agriculture, Ecosystems and Environment | Year: 2014

Site-specific nutrient management (SSNM) provides a field-specific approach for dynamically applying nutrients to crops on an as-needed basis. The demand for bamboo in China cannot be met despite increases in domestic production and yield in recent years. Further increases in bamboo yield and improve ecological environment, with good economic returns, are feasible in most favorable growth environments of China through relatively straightforward adjustments in crop and nutrient management. We created a SSNM system for bamboo forestry starting in 2009. The influence of SSNM on nutrient availability and characteristics of soil microorganisms in comparison to the current farmer fertilizer practice (FFP) in a bamboo (Phyllostachys pubescens) forest was investigated from January to December 2011. The results showed that SSNM, in comparison to FFP, increased the average bamboo yield by approximately 4.3%. Fertilizer N, P, and K levels, however, decreased by 55%, 8%, and 16%, respectively. Higher resin N, P, and K availability by using FFP compared to SSNM indicated an accumulation of inorganic nutrients during periods when the bamboo demand for nutrients is low. These nutrients were, therefore, prone to large losses via runoff. Resin nutrient availability was shown to be a good indicator of plant nutrient uptake but not yield. Moreover, the addition of chemical fertilizer altered the microbial biomass C and N, the total amount of PLFA was higher via SSNM (295. nmol/g) than those via FFP (262. nmol/g), indicating SSNM also increased soil microbial activity. Overall, the SSNM system was found to reduce nutrient release to the environment while maintaining bamboo yields and soil ecological environment. © 2014 Elsevier B.V.

Zhang Q.,Zhejiang University | Shamsi I.H.,Zhejiang University | Wang J.,Soil | Song Q.,Zhejiang University | And 4 more authors.
Environmental Science and Pollution Research | Year: 2013

Nitrogen (N) losses from agricultural fields have been extensively studied. In contrast, surface runoff and N losses have rarely been considered for bamboo forests that are widespread in regions such as southern China. The thriving of bamboo industries has led to increasing fertilizer use in bamboo forests. In this study, we evaluated surface runoff and N losses in runoff following different fertilization treatments under field conditions in a bamboo (Phyllostachys pubescens) forest in the catchment of Lake Taihu in Jiangsu, China. Under three different fertilization regimes, i.e., control, site-specific nutrient management (SSNM), and farmer's fertilization practice (FFP), the water runoff rate amounted to 356, 361, and 342 m3 ha-1 and accounted for 1.91, 1.98, and 1.85 % of the water input, respectively, from June 2009 to May 2010. The total N losses via surface runoff ranged from 1.2 to 1.8 kg ha-1. Compared with FFP, the SSNM treatment reduced total nitrogen (TN) and dissolved nitrogen (DN) losses by 31 and 34 %, respectively. The results also showed that variations in N losses depended mainly on runoff fluxes, not N concentrations. Runoff samples collected from all treatments throughout the year showed TN concentrations greater than 0.35 mg L-1, with the mean TN concentration in the runoff from the FFP treatment reaching 8.97 mg L-1. The loss of NO3 --N was greater than the loss of NH4 +-N. The total loss of dissolved organic nitrogen (DON) reached 23-41 % of the corresponding DN. Therefore, DON is likely the main N species in runoff from bamboo forests and should be emphasized in the assessment and management of N losses in bamboo forest. © 2012 Springer-Verlag Berlin Heidelberg.

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