Modeling Climate Change Impacts on Hydrology and Nutrient Loading in the Upper Assiniboine Catchment1

Shrestha, Rajesh R., Yonas B. Dibike, and Terry D. Prowse, 2011. Modeling Climate Change Impacts on Hydrology and Nutrient Loading in the Upper Assiniboine Catchment. Journal of the American Water Resources Association (JAWRA) 48(1): 74‐89. DOI: 10.1111/j.1752‐1688.2011.00592.x Abstract: This paper presents a modeling study on climate‐induced changes in hydrologic and nutrient fluxes in the Upper Assiniboine catchment, located in the Lake Winnipeg watershed. The hydrologic and agricultural chemical yield model, Soil and Water Assessment Tool (SWAT) was employed to model a 21‐year baseline (1980‐2000) and future (2042‐2062) periods with model forcings for future climates derived from three regional climate models (RCMs) and their ensemble means. The modeled future scenarios reveal that potential future changes in the climatic regime are likely to modify considerably hydrologic and nutrient fluxes. The effects of future changes in climatic variables, especially precipitation and temperature, are clearly evident in the resulting snowmelt and runoff regimes. The future hydrologic scenarios consistently show earlier onsets of spring snowmelt and discharge peaks, and higher total runoff volumes. The simulated nutrient loads closely match the dynamics of the future runoff for both nitrogen and phosphorus, in terms of earlier timing of peak loads and higher total loads. However, nutrient concentrations could decrease due to the higher rate of runoff increase. Overall, the effects of these changes on the nutrient transport regime need to be considered together with possible future changes in land use, crop type, fertilizer application, and transformation processes in the receiving water bodies.     

STREAM HEALTH RANKINGS PREDICTED BY SATELLITE DERIVED LAND COVER METRICS1

ABSTRACT: Land cover and land use change have long been known to influence the chemical, physical, and biological characteristics of streams. This study makes use of land cover maps derived from fine resolution satellite imagery and an extensive stream quality dataset to determine the relationship between small watershed health rankings and land cover composition and configuration. Landscape metrics were derived from digital impervious surface area (ISA), tree cover (percent), and agricultural crop maps within Montgomery County, Maryland. Watershed rankings were developed by state and county collaborators (MD‐DNR and MCDEP) using extensive biological and chemical measurements. In stepwise logistic regression models the factors accounting for the most variation in stream health ranking were the percent ISA, followed by the percent of tree cover. Riparian buffer zone tree cover was also a significant predictor. Of the metrics that considered the spatial configuration of the landscape, a contagion index and the percent of ISA in the flow path from the ISA to the stream were also found to be significant predictors of stream health. Despite limited ability to characterize landscape configuration or narrow riparian buffer zone vegetation with coarser resolution imagery (from Landsat), model results were not significantly different from those based on the use of fine‐resolution ISA information, suggesting that broader area applications of the approach are possible. The results indicate that management practices designed to improve stream water quality should focus on the amount of ISA and tree cover in both the watershed and within the buffer zone.     

杞麓湖流域环境规划工程效益分析

重点污染控制系统工程是杞麓湖流域环境规划的重要组成部分，本文通过对本规划中的重点污染控制系统工程的综合效益探讨分析，指出了该系统工程是杞麓湖流域环境综合治理的重要措施。工程有实施能有效改善湖泊水质，实现流域生态环境良性循环，同时可取得明显的社会效益和经济效益。     

基于GIS和L-THIA模型的深圳市观澜河流域非点源污染负荷变化分析

为探明深圳市观澜河流域在快速城市化过程中伴随土地利用变化的非点源污染负荷变化,基于GIS平台,运用L-THIA模型,通过校正其内设参数,模拟流域1996～2008年非点源污染负荷的空间分布及其变化.结果表明,1996～2008年的城市化过程中,TN、TP、COD这3种污染物的负荷总量都有大幅度的增长,其中TP变化最大,在13 a中增加了62.78%,TN和COD分别增加了59.73%和55.40%,TN、TP和COD等污染物高值区面积的空间分布变化在大趋势上基本一致,都是沿河道和主要交通干线向外围逐步扩张,最后连接成片;而SS的负荷总量却下降了7.59%.建设用地的扩张是非点源污染负荷及空间分布变化的主要因素,SS负荷输出最大的用地类型是水土流失严重的开发用地.以非点源污染负荷空间分布为依据,结合不同土地利用方式,可将观澜河分为4类非点源污染防治区,该结果可为流域非点源污染控制提供科学参考.     

Identification of Sediment Sources in Forested Watersheds With Surface Coal Mining Disturbance Using Carbon and Nitrogen Isotopes1

Abstract: Sediments and soils were analyzed using stable carbon and nitrogen isotope ratio mass spectrometry and carbon and nitrogen elemental analyses to evaluate the their ability to indicate land‐use and land management disturbance and pinpoint loading from sediment transport sources in forested watersheds disturbed by surface coal mining. Samples of transported sediment particulate organic matter were collected from four watersheds in the Southern Appalachian forest region of southeastern Kentucky. The four watersheds had different surface coal mining history that were classified as undisturbed, active mining, and reclaimed conditions. Soil samples were analyzed including reclaimed grassland soils, undisturbed forest soils, geogenic organic matter associated with coal fragments in mining spoil, and soil organic matter from un‐mined grassland soils. Statistically significant differences were found for all biogeochemical signatures when comparing transported sediments from undisturbed watersheds and surface coal mining disturbed watersheds, and the results were attributed to differences in erosion sources and the presence of geogenic organic matter. Sediment transport sources in the surface coal mining watersheds were analyzed using Monte Carlo mass balance un‐mixing and it was found that: δ¹⁵N showed the ability to differentiate streambank erosion and surface soil erosion; and δ¹³C showed the ability to differentiate soil organic matter and geogenic organic matter. Results from the analyses suggest that streambank erosion downstream of surface coal mining sites is an especially significant source of sediment in coal mining disturbed watersheds. Further, the results suggest that the sediment transport processes governing streambank erosion loads are taking longer to reach geomorphologic equilibrium in the watershed as compared with the surface erosion processes. The dual‐isotope technique provides a useful method for further investigation of the impact of surface coal mining in the uplands of the watershed upon the geomorphologic state of the channel and the source of organic matter in aquatic systems impacted by surface coal mining.     

Modeling Hydrologic Benefits of Low Impact Development: A Distributed Hydrologic Model of The Woodlands,Texas

Low Impact Development (LID) is alternative design approach to land development that conserves and utilizes natural resources to minimize the potential negative environmental impacts of development, such as flooding. The Woodlands near Houston, Texas is one of the premier master‐planned communities in the United States. Unlike in a typical urban development where riparian corridors are often replaced with concrete channels, pervious surfaces, vegetation, and natural drainage pathways were preserved as much as possible during development. In addition, a number of detention ponds were strategically located to manage runoff on site. This article uses a unique distributed hydrologic model, Vflo?, combined with historical (1974) and recent (2008 and 2009) rainfall events to evaluate the long‐term effectiveness of The Woodlands natural drainage design as a stormwater management technique. This study analyzed the influence of LID in The Woodlands by comparing the hydrologic response of the watershed under undeveloped, developed, and highly urbanized conditions. The results show that The Woodlands drainage design successfully reflects predeveloped hydrologic conditions and produces peak flows two to three times lower than highly urbanized development. Furthermore, results indicate that the LID practices employed in The Woodlands successfully attenuate the peak flow from a 100‐year design event, resulting in flows comparable to undeveloped hydrologic conditions.     

Associations between Water Physicochemistry and Prymnesium parvum Presence,Abundance, and Toxicity in West Texas Reservoirs

Toxic blooms of golden alga (Prymnesium parvum) have caused substantial ecological and economic harm in freshwater and marine systems throughout the world. In North America, toxic blooms have impacted freshwater systems including large reservoirs. Management of water chemistry is one proposed option for golden alga control in these systems. The main objective of this study was to assess physicochemical characteristics of water that influence golden alga presence, abundance, and toxicity in the Upper Colorado River basin (UCR) in Texas. The UCR contains reservoirs that have experienced repeated blooms and other reservoirs where golden alga is present but has not been toxic. We quantified golden alga abundance (hemocytometer counts), ichthyotoxicity (bioassay), and water chemistry (surface grab samples) at three impacted reservoirs on the Colorado River; two reference reservoirs on the Concho River; and three sites at the confluence of these rivers. Sampling occurred monthly from January 2010 to July 2011. Impacted sites were characterized by higher specific conductance, calcium and magnesium hardness, and fluoride than reference and confluence sites. At impacted sites, golden alga abundance and toxicity were positively associated with salinity‐related variables and blooms peaked at ~10°C and generally did not occur above 20°C. Overall, these findings suggest management of land and water use to reduce hardness or salinity could produce unfavorable conditions for golden alga.     

Reduced Soil Macropores and Forest Cover Reduce Warm‐Season Baseflow below Ecological Thresholds in the Upper Delaware River Basin

We examined the impacts of changes in land cover and soil conditions on the flow regime of the upper Delaware River Basin using the Water Availability Tool for Environmental Resources. We simulated flows for two periods, c. 1600 and 1940, at three sites using the same temperature and precipitation conditions: the East Branch, West Branch, and mainstem Delaware River at Callicoon, New York. The 1600 period represented pristine forest and soils. The 1940 period included reduced forest cover, increased agriculture, and degraded soils with reduced soil macropore fractions. A model‐sensitivity test examined the impact of soil macropore and land cover change separately. We assessed changes in flow regimes between the 1600 and 1940 periods using a variety of flow statistics, including established ecological limits of hydrologic alteration (ELOHA) thresholds. Reduced forest soil macropore fraction significantly reduced summer and fall baseflows. The 1940 period had significantly lower Q50 flows (50% exceedance) than the 1600 period, as well as summer and fall Q90 and Q75–Q90 flows below the ELOHA thresholds. The one‐ to seven‐day minimum flows were also lower for the 1940 period, by 17% on the mainstem. 1940 flows were 6% more likely than the 1600 period to fall below the low‐flow threshold for federally endangered dwarf wedgemussel (Alasmidonta heterodon) habitat. In contrast, the 1940 period had higher flows than the 1600 period from late fall to early winter.     

CHAPARRAL CONTROL IN MOSAIC PATTERN INCREASED STREAMFLOW AND MITIGATED NITRATE LOSS IN ARIZONA1

ABSTRACT: In a 16-year paired watershed study in Arizona, a 303-acre chaparral watershed was treated by helicopter in a mosaic pattern (55 percent of watershed) with tebuthiuron herbicide pellets to control the moderately dense, heavy water-using chaparral. The objective was to determine if annual stream discharge could be increased without degrading other resource values. An adjacent untreated chaparral watershed served as the control on which to base the water quantity and quality treatment effects. Annual streamflow was increased by 1.5 to 5 inches over a seven-year evaluation period. The streamflow increase was accompanied by a small but statistically significant increase in nitrate concentration. The relatively small nitrate response was attributed to the mosaic treatment. Nitrate released from the converted areas was diluted by streamflow from untreated areas, thereby reducing nitrate concentrations in streamflow at the watershed outlet.     

森林植被变化对流域水文影响的争论

针对“森林能否增雨、森林能否减少年径流量、调节枯水径流以及能否削减洪峰”等问题，综述了各种观点，分析了出现分歧的原因。作者认为森林对降水量的影响不大，森林植被的存在一般减少年径流量，而对调节枯水径流以及削减洪峰等的作用则因地带、因流域尺度而异。研究方法的局限性、研究对象的复杂性以及区域差异和尺度的影响，是导致争论的主要原因。正确评价森林的水文效应，应该注意地带性差异、尺度的影响以及不同森林的类型等。