Luo Y.,Xinjiang Institute of Ecology and Geography |
Luo Y.,CAS Beijing Institute of Geographic Sciences and Nature Resources Research |
Arnold J.,Grassland Soil and Water Research Laboratory |
Liu S.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute |
And 2 more authors.
Journal of Hydrology | Year: 2013
In this paper we proposed: (1) an algorithm of glacier melt, sublimation/evaporation, accumulation, mass balance and retreat; (2) a dynamic Hydrological Response Unit approach for incorporating the algorithm into the Soil and Water Assessment Tool (SWAT) model; and (3) simulated the transient glacier retreat and its impacts on streamflow at basin scale. Application of the enhanced SWAT model in the Manas River Basin (MRB) in the Tianshan Mountains in northwest China, shows that the approach is viable as evidenced by a Nash-Sutcliff efficiency of 0.65 and a percent bias of -3.7% for daily streamflow and water balance, respectively. The results indicate that the glacier area decreased by 11% during the simulation period from 1961 to 1999, which is within the range of records from other glaciers. On average, glacier melt contributed 25% to streamflow, although glacier area accounts for only 14% of the catchment drainage area in the MRB. Glacier melt was positively correlated to temperature change (R2=0.70, statistical significance P<0.001) and negatively correlated to precipitation (R2=0.20, statistical significance P<0.005). The results indicate that glacier melt was more sensitive to temperature change than to precipitation change, implying that modeling the effects of climate change with increasing temperatures and decreasing precipitation should be further studied. © 2012 Elsevier B.V.
PubMed | University of Colorado at Boulder, University of Zürich, Monash University, Queensland University of Technology and 25 more.
Type: Journal Article | Journal: Nature | Year: 2014
Studies of experimental grassland communities have demonstrated that plant diversity can stabilize productivity through species asynchrony, in which decreases in the biomass of some species are compensated for by increases in others. However, it remains unknown whether these findings are relevant to natural ecosystems, especially those for which species diversity is threatened by anthropogenic global change. Here we analyse diversity-stability relationships from 41 grasslands on five continents and examine how these relationships are affected by chronic fertilization, one of the strongest drivers of species loss globally. Unmanipulated communities with more species had greater species asynchrony, resulting in more stable biomass production, generalizing a result from biodiversity experiments to real-world grasslands. However, fertilization weakened the positive effect of diversity on stability. Contrary to expectations, this was not due to species loss after eutrophication but rather to an increase in the temporal variation of productivity in combination with a decrease in species asynchrony in diverse communities. Our results demonstrate separate and synergistic effects of diversity and eutrophication on stability, emphasizing the need to understand how drivers of global change interactively affect the reliable provisioning of ecosystem services in real-world systems.
Grace J.B.,U.S. Geological Survey |
Anderson T.M.,Wake forest University |
Seabloom E.W.,University of Minnesota |
Borer E.T.,University of Minnesota |
And 24 more authors.
Nature | Year: 2016
How ecosystem productivity and species richness are interrelated is one of the most debated subjects in the history of ecology. Decades of intensive study have yet to discern the actual mechanisms behind observed global patterns. Here, by integrating the predictions from multiple theories into a single model and using data from 1,126 grassland plots spanning five continents, we detect the clear signals of numerous underlying mechanisms linking productivity and richness. We find that an integrative model has substantially higher explanatory power than traditional bivariate analyses. In addition, the specific results unveil several surprising findings that conflict with classical models. These include the isolation of a strong and consistent enhancement of productivity by richness, an effect in striking contrast with superficial data patterns. Also revealed is a consistent importance of competition across the full range of productivity values, in direct conflict with some (but not all) proposed models. The promotion of local richness by macroecological gradients in climatic favourability, generally seen as a competing hypothesis, is also found to be important in our analysis. The results demonstrate that an integrative modelling approach leads to a major advance in our ability to discern the underlying processes operating in ecological systems. © 2016 Macmillan Publishers Limited.
Somura H.,The University of Shimane |
Takeda I.,The University of Shimane |
Arnold J.G.,Grassland Soil and Water Research Laboratory |
Mori Y.,Okayama University |
And 3 more authors.
Journal of Hydrology | Year: 2012
Lake Shinji lies in eastern Shimane Prefecture, and is typical of brackish lakes in Japan. Water quality of the lake does not meet the expected environmental standards for total nitrogen (TN) and total phosphorus (TP), even though the national and prefectural governments have tried to improve water quality by developing maintenance scenarios for sewage, plant effluent, agricultural activity, and forestry. Consequently, detailed data of nutrient loading to the lake from river inflows is crucial to support strategies for improving the lake water environment. The Hii River contributes approximately 80% of the discharge flowing into the lake. In this study, we examine the Hii River catchment with a focus on land uses such as paddy fields, upland fields, residential areas, and forestry. Average annual discharges of suspended sediment (SS), TN, and TP loads were determined at Otsu, near the outlet of the basin into Lake Shinji. We also determined average yield per unit area of SS, TN, and TP loads from each land use. Yields per unit area from upland areas were the greatest, whereas yields from forests were the lowest. Forests were the largest contributor of SS, TN, and TP in the basin, because of its dominant land area. Upland fields had the second largest impact on these loads in the basin, because fertilizer applied to the fields is a major source of nitrogen (N) and phosphorus (P). Large differences in yields per unit area between fine and rainy day conditions were also observed, especially for SS and TP loads. Furthermore, we determined that a major pathway of N to the river was through groundwater, regardless of land use, whereas P was transported to the river with sediments, especially in paddy and upland fields. Based on these analyses, it will be difficult to reduce the SS load discharge in the basin in the future, because forestry is the major source. In contrast, N and P load reductions are straightforward, because the primary source is agricultural, and appropriate management of fertilizer application will be a key factor in reducing loads. © 2012 Elsevier B.V.
Guo T.,Purdue University |
Engel B.A.,Purdue University |
Shao G.,Purdue University |
Arnold J.G.,Grassland Soil and Water Research Laboratory |
And 2 more authors.
Bioenergy Research | Year: 2015
Short-rotation woody crops (SRWCs) such as Populus have great potential as biofuel feedstocks. Biomass yields and yield stability at potential sites are important considerations when SRWCs are widely planted. The process-based, daily time-step simulation model Agricultural Land Management Alternative with Numerical Assessment Criteria (ALMANAC) offers promise as a useful tool to evaluate tree growth over large ranges of conditions. The objective of this study was to develop algorithms and growth parameters of hybrid poplar ‘Tristis #1’ (Populus balsamifera L. × Populus tristis Fisch) and eastern cottonwood (Populus deltoides Bartr.) in ALMANAC and to improve simulation of leaf area index (LAI) and plant biomass as well as biomass partitioning. ALMANAC with the improved algorithms for LAI and weight of falling leaves was applied to hybrid poplar plots in Wisconsin and cottonwood plots in Mississippi, and the modeled biomass yield and LAI were compared with measured data to modify and evaluate the location-specific ALMANAC models. Improved algorithms for LAI and biomass simulation and suggested values and potential parameter ranges for hybrid poplar and cottonwood were reasonable (Nash-Sutcliffe model efficiency (NSE) 0.81 ~ 0.99 and R2 0.76 ~ 0.99). ALMANAC with modified algorithms and parameters for Populus growth realistically simulated LAI, aboveground woody biomass, and root biomass of Populus. Thus, this model can be used for biofeedstock production modeling for Populus. The improved algorithms of LAI and biomass simulation for tree growth should also be useful for other process-based models, such as Soil and Water Assessment Tool (SWAT), Environmental Policy Integrated Climate (EPIC), and Agricultural Policy/Environmental eXtender (APEX). © 2015 Springer Science+Business Media New York
Joseph J.F.,University of Texas at San Antonio |
Sharif H.O.,University of Texas at San Antonio |
Arnold J.G.,Grassland Soil and Water Research Laboratory |
Bosch D.D.,Robert Bosch GmbH
Journal of the American Water Resources Association | Year: 2013
Abstract: The calibration of basin-scale hydrologic models consists of adjusting parameters such that simulated values closely match observed values. However, due to inevitable inaccuracies in models and model inputs, simulated response hydrographs for multiyear calibrations will not be perfectly synchronized with observed response hydrographs at the daily time step. An analytically derived formula suggests that when timing errors are significant, traditional calibration approaches may generally underestimate the total event-flow volume. An event-adaptive time series is developed and incorporated into the Nash-Sutcliffe Efficiency objective function to diagnose the potential impact of event-flow synchronization errors. Test sites are the 50km2 Subwatershed I of the Little River Experimental Watershed (LREWswI) in southeastern Georgia, and the 610km2 Little Washita River Experimental Watershed (LWREW) in southwestern Oklahoma, with the Soil and Water Assessment Tool used as the hydrologic model. Results suggest that simulated surface runoff generation is 55% less for LREWswI when the daily time series is used compared with when the event-adaptive technique is used. Event-flow generation may also be underestimated for LWREW, but to a lesser extent than it may be for LREWswI, due to a larger portion of the event flow being lateral flow. © 2012 American Water Resources Association.
Woli P.,Mississippi State University |
Paz J.O.,Mississippi State University |
Baldwin B.S.,Mississippi State University |
Lang D.J.,Mississippi State University |
Kiniry J.R.,Grassland Soil and Water Research Laboratory
American Society of Agricultural and Biological Engineers Annual International Meeting 2012, ASABE 2012 | Year: 2012
High biomass production potential, wide adaptability, low input requirement, and low environmental risk make switchgrass an economically and ecologically viable energy crop. The inherent variability in switchgrass productivity due to variations in soil and variety could affect the sustainability and eco-friendliness of switchgrass-based ethanol production. This study examined the soil and variety effects on these variables. Three locations in Mississippi were selected based on latitude and potential acreage. Using ALMANAC, switchgrass biomass yields were simulated for several scenarios of soils and varieties. The simulated yields were fed to IBSAL to compute energy use and CO2 emissions in various operations in the biomass supply chain. From the energy and emissions values, the sustainability and eco-friendliness of ethanol production were determined using net energy value (NEV) and carbon credit balance (CCB) as indicators, respectively. Soil and variety effects on NEV and CCB were analyzed using the Kruskal-Wallis test. Results showed significant differences in NEV and CCB across soils and varieties. Both NEV and CCB increased in the direction of heavier to lighter soils and on the order of north-upland, south-upland, north-lowland, and south-lowland varieties. Only north-upland and south-lowland varieties were significantly different because they were different in both cytotype and ecotype. Gaps between lowland and upland varieties were smaller in a dry year than in a wet year. The NEV and CCB increased in the direction of dry to wet year. From south to north, they decreased for lowland cytotypes but increased for upland cytotypes. Thus, the differences among varieties decreased northwards.
Rico C.,University of California at Santa Cruz |
Pittermann J.,University of California at Santa Cruz |
Polley H.W.,Grassland Soil and Water Research Laboratory |
Aspinwall M.J.,University of Western Sydney |
Fay P.A.,Grassland Soil and Water Research Laboratory
New Phytologist | Year: 2013
Plant gas exchange is regulated by stomata, which coordinate leaf-level water loss with xylem transport. Stomatal opening responds to internal concentrations of CO2 in the leaf, but changing CO2 can also lead to changes in stomatal density that influence transpiration. Given that stomatal conductance increases under subambient concentrations of CO2 and, conversely, that plants lose less water at elevated concentrations, can downstream effects of atmospheric CO2 be observed in xylem tissue? We approached this problem by evaluating leaf stomatal density, xylem transport, xylem anatomy and resistance to cavitation in Helianthus annuus plants grown under three CO2 regimes ranging from pre-industrial to elevated concentrations. Xylem transport, conduit size and stomatal density all increased at 290 ppm relative to ambient and elevated CO2 concentrations. The shoots of the 290-ppm-grown plants were most vulnerable to cavitation, whereas xylem cavitation resistance did not differ in 390- and 480-ppm-grown plants. Our data indicate that, even as an indirect driver of water loss, CO2 can affect xylem structure and water transport by coupling stomatal and xylem hydraulic functions during plant development. This plastic response has implications for plant water use under variable concentrations of CO2, as well as the evolution of efficient xylem transport. © 2013 The Authors © 2013 New Phytologist Trust.