790 research outputs found

    Linking land to ocean: Flux and fate of water and sediment from the Yangtze River to the East China Sea

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    Although precipitation and runoff for the entire Yangtze River watershed have changed little since 1950, the increase of runoff in Yangtze southern sub-basin has been much larger than that of precipitation, reflecting decreased temperatures and evapotranspiration, In contrast, the marked decreases in runoff in northern Yangtze have been due mainly to increased water consumption. Since the 1980s, the Yangtze sediment load has declined dramatically, and 2004 loads at Yichang (just below the Three Gorges Dam - TGD) and Datong (lower stream) were only 12% and 33% of those in the 1950s and 60s, reflecting precipitation decline, landuse change, and most importantly, construction of \u3e50,000 dams. Following the impoundment of the TGD, annual sediment load at Yichang dropped by 164 million tons (mt), but in the preceding 16 years it had decreased by ∼300 mt/yr. Future dams and diversions will decrease the load to \u3c100 mt/yr, thereby endangering the Yangtze coasts. Sediments on the inner shelf of the East China Sea reflect illite-dominated mud from the Yangtze River in the north as well as sandy silt and fine sand (low feldspar/quartz and low K-feldspar/plagioclase) from small mountainous rivers draining Taiwan to the south. Both sediments are significantly different from muds derived from the Yellow (smectite-rich) and Min (kaolinite-dominated) rivers. Grain-size distribution further confirms that ∼25% of coarse sediments in northern Taiwan Strait (south of 26??N) are Taiwan-derived. Along the inner shelf, an elongated (800 km) mud wedge, ∼40 m thick at the 30-m isobath, overlies a transgressive sand layer; the mud wedge thins offshore to \u3c2 m at 80-m isobath. Four acoustic facies can be delineated: late-Pleistocene, Transgressive System Tract (TST), and early and late High-Stand System Tracts (HST). The thin (\u3c3m) and acoustically transparent TST is only located between 40- and 90-m isobaths south of 30??N. In contrast, early (2-11 ka BP) and late (0-2 ka BP, more opaque) sigmoidal HSTs are widely distributed shallower than 70- and 50-m isobaths, respectively. The average Yangtze sediment flux between 2 and 11 ka BP was 215 mt/yr, but increased to 330 mt/yr after 2 ka BP, primarily reflecting increased deforestation and agriculture

    Arkansas Bulletin of Water Research - Issue 2018

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    The Arkansas Bulletin of Water Research is a publication of the Arkansas Water Resources Center (AWRC). This bulletin is produced in an effort to share water research relevant to Arkansas water stakeholders in an easily searchable and aesthetically engaging way. This is the second publication of the bulletin and will be published annually. The submission of a paper to this bulletin is appropriate for topics at all related to water resources, by anyone conducting water research or investigations. This includes but is not limited to university researchers, consulting firms, watershed groups, and other agencies. Prospective authors should read the “Introduction to the Arkanasas Bulletin of Water Research” contained within this publication and should refer to the AWRC website for additional infromation. https://arkansas-water-center.uark.edu

    Moisture origin as a driver of temporal variabilities of the water vapour isotopic composition in the Lena River Delta, Siberia

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    In the context of the Arctic amplification of climate change affecting the regional atmospheric hydrological cycle, it is crucial to characterize the present-day moisture sources of the Arctic. The isotopic composition is an important tool to enhance our understanding of the drivers of the hydrological cycle due to the different molecular characteristics of water stable isotopes during phase change. This study introduces 2 years of continuous in situ water vapour and precipitation isotopic observations conducted since July 2015 in the eastern Siberian Lena delta at the research station on Samoylov Island. The vapour isotopic signals are dominated by variations at seasonal and synoptic timescales. Diurnal variations of the vapour isotopic signals are masked by synoptic variations, indicating low variations of the amplitude of local sources at the diurnal scale in winter, summer and autumn. Low-amplitude diurnal variations in spring may indicate exchange of moisture between the atmosphere and the snow-covered surface. Moisture source diagnostics based on semi-Lagrangian backward trajectories reveal that different air mass origins have contrasting contributions to the moisture budget of the Lena delta region. At the seasonal scale, the distance from the net moisture sources to the arrival site strongly varies. During the coldest months, no contribution from local secondary evaporation is observed. Variations of the vapour isotopic composition during the cold season on the synoptic timescale are strongly related to moisture source regions and variations in atmospheric transport: warm and isotopically enriched moist air is linked to fast transport from the Atlantic sector, while dry and cold air with isotopically depleted moisture is generally associated with air masses moving slowly over northern Eurasia

    Global land surface temperature influenced by vegetation cover and PM2.5 from 2001 to 2016

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    Land surface temperature (LST) is an important parameter to evaluate environmental changes. In this paper, time series analysis was conducted to estimate the interannual variations in global LST from 2001 to 2016 based on moderate resolution imaging spectroradiometer (MODIS) LST, and normalized difference vegetation index (NDVI) products and fine particulate matter (PM2.5) data from the Atmospheric Composition Analysis Group. The results showed that LST, seasonally integrated normalized difference vegetation index (SINDVI), and PM2.5 increased by 0.17 K, 0.04, and 1.02 �g/m3 in the period of 2001–2016, respectively. During the past 16 years, LST showed an increasing trend in most areas, with two peaks of 1.58 K and 1.85 K at 72�N and 48�S, respectively. Marked warming also appeared in the Arctic. On the contrary, remarkable decrease in LST occurred in Antarctic. In most parts of the world, LST was affected by the variation in vegetation cover and air pollutant, which can be detected by the satellite. In the Northern Hemisphere, positive relations between SINDVI and LST were found; however, in the Southern Hemisphere, negative correlations were detected. The impact of PM2.5 on LST was more complex. On the whole, LST increased with a small increase in PM2.5 concentrations but decreased with a marked increase in PM2.5. The study provides insights on the complex relationship between vegetation cover, air pollution, and land surface temperature

    Multi-scale modeling of water resources in a tropical inland valley and a tropical floodplain catchment in East Africa

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    This study investigated the dynamics of hydrological processes at the wetland-catchment scale through field scale-based analysis, point scale modeling using Hydrus-1D model along a floodplain transect in Tanzania and wetland-catchment modeling with SWAT model in an inland valley in Uganda. The impact of different land use management options and the projected climate change on the water resources of the inland valley were also evaluated using a hydrological response unit (HRU)-based (ArcSWAT2012) and a grid-based setup (SWATgrid) of the SWAT model. The inland valley is located in Namulonge, central Uganda, and it is one of the headwater catchments of Lake Kyoga basin. The inland valley catchment covers an area of 31 km2 with a wetland area of 4.5 km2. The floodplain is located in Kilombero district, Southern Tanzania and the catchment area is 40,240 km2 and the study area in a wetland is 96 km2. Both sites reflect the prevailing diversity of wetland attributes and uses. Monitoring of hydro-meteorological data for both sites was conducted for two hydrological consecutive years of 2015 and 2016. The cross–section of the wetland transect was subdivided into three major hydrological positions defined as riparian zone, middle, and fringe. Hydrological instrumentation and data collection for soil moisture, soil properties, depth to shallow groundwater was conducted along these hydrological positions for both wetland systems. In addition, there was data mining from other sources. Following the field-based analysis at a wetland scale in the inland valley, the spatial and temporal variability in soil moisture increased significantly (p In the Kilombero floodplain, Hydrus-1D model was successfully calibrated (R2 = 0.54–0.92, RMSE = 0.02–0.11 cm3/cm3) using measured soil moisture content. Satisfying statistical measures (R2 = 0.36–0.89, RMSE = 0.03–0.13 cm3/cm3) were obtained when calibrations for one plot were validated with measured soil moisture for another plot within the same hydrological zone, indicating the transferability of the calibrated Hydrus-1D. The hydrological regimes correlated with the hydrological positions in the floodplain. Soil moisture dynamics is controlled by overbank flow, precipitation, and groundwater control at the riparian and middle zone, while it is controlled by rainfall and lateral flow from mountains at the fringe during the long rainy seasons. In the dry and short rainy seasons, rainfall, soil properties, and atmospheric demands control soil moisture dynamics at the riparian and middle zone. For the wetland-catchment scale hydrological modeling in the inland valley, good model performance was achieved from the calibration and validation of daily discharge (R2 and NSE > 0.7) for both model setups (ArcSWAT2012 and SWATgrid). The annual water balance indicates that 849.5 mm representing 65% of precipitation is lost via evapotranspiration. Surface runoff (77.9 mm) and lateral flow (86.5 mm) are the highest contributors to stream flow. Four land use management options were developed in addition to the current land use system, with different water resources conservation levels (Conservation, Slope conservation, Protection of the headwater catchment, and Exploitation). There is a strong relationship between the first three management options with decreasing surface runoff, annual discharge and water yield while the fourth option will increase annual discharge and total water yield. The future climate change in the inland valley was analyzed using climate scenarios RCP4.5 and 8.5 of six GCM-RCM models from the CORDEX-Africa project. Compared to the reference period of 1976-2005, a general increase in temperature of +0.9 0C to +1.9 0C over the period of 2021-2050 is projected by the model ensemble. A mixed change signal in annual precipitation (-30 to 43.9%) is projected among the six climatic models. However, on average, the models show an increase in annual precipitation of +7.4% and +21.8% under RCP4.5 and 8.5, respectively. The application of the climate model ensembles in SWAT showed future discharge change similar to the projected precipitation change. The six climate models showed uncertainty in the annual discharge change ranging from -44 to 149% although on average, the climate models project an increase of +16% and +29% under RCP4.5 and 8.5, respectively. Wet and dry seasons are expected to get wetter and drier, respectively in the future. Compared to land use management options, climate change will have a dominant impact on the water resources in inland valleys. Adoption of Conservation, Slope conservation and protection of the headwater catchment options will significantly reduce the impacts of climate change on the total water yield and surface runoff and increase evapotranspiration and water availability in the inland valley

    Sustainable Use of Soils and Water: The Role of Environmental Land Use Conflicts

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    This book on the sustainable use of soils and water addressed a variety of issues related to the utopian desire for environmental sustainability and the deviations from this scene observed in the real world. Competing interests for land are frequently a factor in land degradation, especially where the adopted land uses do not conform with the land capability (the natural use of soil). The concerns of researchers about these matters are presented in the articles comprising this Special Issue book. Various approaches were used to assess the (im)balance between economic profit and environmental conservation in various regions, in addition to potential routes to bring landscapes back to a sustainable status being disclosed

    Annual Report: 2009

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    I submit herewith the annual report from the Agricultural and Forestry Experiment Station, School of Natural Resources and Agricultural Sciences, University of Alaska Fairbanks, for the period ending December 31, 2009. This is done in accordance with an act of Congress, approved March 2, 1887, entitled, “An act to establish agricultural experiment stations, in connection with the agricultural college established in the several states under the provisions of an act approved July 2, 1862, and under the acts supplementary thereto,” and also of the act of the Alaska Territorial Legislature, approved March 12, 1935, accepting the provisions of the act of Congress. The research reports are organized according to our strategic plan, which focuses on high-latitude soils, high-latitude agriculture, natural resources use and allocation, ecosystems management, and geographic information. These areas cross department and unit lines, linking them and unifying the research. We have also included in our financial statement information on the special grants we receive. These special grants allow us to provide research and outreach that is targeted toward economic development in Alaska. Research conducted by our graduate and undergraduate students plays an important role in these grants and the impact they make on Alaska.Financial statement -- Grants -- Students -- Research Reports: Partners, Facilities, and Programs; Geography; High-Latitude Agriculture; High-Latitude Soils; Management of Ecosystems; Natural Resources Use and Allocation; Index to Reports -- Publications -- Facult
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