基于流域单元的营养盐输出与景观异质性影响研究

选择太湖上游西苕溪流域,利用GIS、RS及景观生态方法进行小流域划分和流域景观异质性分析,基于改进的输出系数模型估算小流域营养盐输出,并对流域单元主要景观类型空间异质性及多样性指数与营养盐输出的关系进行了分析.结果表明,西苕溪各小流域TN、TP输出强度变化范围分别为3.01～15.44 kg/(hm2.a)与0.049～0.355 kg/(hm2.a),营养盐输出水平空间差异性明显;小流域单元优势景观类型与营养盐输出关系明显,小流域林地面积增加10%,TN、TP输出强度分别降低0.203 1、0.015 2 kg/(hm2.a);小流域耕地面积增加10%,TN、TP输出强度分别增加0.572 6、0.027 3 kg/(hm2.a);西苕溪小流域景观多样性指数与氮磷输出水平关系呈二次多项式关系,营养盐输出强度随着SHDI增大而增大,当SHDI为1.5时,输出强度达到最大值,然后随着SHDI增大而降低.研究结果将为流域非点源污染治理提供参考.     

COMPARISON OF HSPF OUTPUTS USING FTABLES GENERATED WITH FIELD SURVEY AND DIGITAL DATA1

ABSTRACT: The Hydrological Simulation Program‐FORTRAN (HSPF) describes discharge from a stream reach based on function tables (FTABLES) that relate stream stage, surface area, volume, and discharge. For this study, five FTABLE scenarios were compared to assess their effect on daily discharge rates predicted using HSPF. Four “field‐based” FTABLE scenarios were developed using detailed cross section surveys collected at predefined intervals along 14 reaches in the study watershed. A fifth “digital‐based” scenario was developed using digital elevation models (DEMs) and Natural Resource Conservation Service (NRCS) Regional Hydraulic Geometry Curves. The Smirnov k‐sample test was used to compare average daily discharge rates simulated with HSPF using the five FTABLE scenarios. No significant difference in simulated stream discharge was found (p = 0.99) between the five FTABLE scenarios. Additional examination of the four field‐based scenarios revealed that the number of cross sections per stream reach used to generate FTABLES had little effect on the resulting stage discharge relationship. These findings suggest that FTABLES generated using digital data are a viable option when simulating stream discharge with HSPF and that if field data are used to generate FTABLES, using fewer cross sections will not adversely affect simulated discharge predictions.     

IMPERVIOUSNESS: A PERFORMANCE MEASURE OF A DELAWARE WATER RESOURCE PROTECTION AREA ORDINANCE1

ABSTRACT: The New Castle County Resource Protection Area Technical Advisory Committee (RPATAC) requested that the University of Delaware utilize impervious cover estimates to evaluate the performance of the Water Resource Protection Area (WRPA) ordinance. This 1991 ordinance was the first in Delaware to protect the quantity and quality of drinking water supplies by limiting new development in WRPAs ‐ such as areas of ground water recharge, wellhead protection, drainage above reservoirs (reservoir watersheds), and limestone aquifers ‐ to a maximum 20 percent impervious cover. The research used geographic information system (GIS) techniques to evaluate the effectiveness of the ordinance in attaining its objective. The analysis indicated that 138 new developments were proposed in WRPAs since the ordinance was approved in 1991. The composite impervious cover of the 231 square kilometers of WRPAs in New Castle County is 15 percent, less than the 20 percent code requirement, ranging from 7 percent in recharge areas to 41 percent in several wellhead protection areas. To further protect drinking water supplies, the study results indicate, New Castle County should discourage code variances for applications in the more developed WRPAs, those where impervious cover already exceeds 20 percent, and should acquire parks and open space to protect the healthier WRPAs where impervious cover is currently less than 20 percent.     

APPLICATION OF THE BASINS DATABASE AND NPSM MODEL ON A SMALL OHIO WATERSHED1

ABSTRACT: The purpose of this study was to evaluate the Better Assessment Science Integrating Point and Nonpoint Sources (BASINS) watershed management system. BASINS data were used with the NPSM model to predict discharge and sediment concentrations at the outlet of a 103 km² Ohio watershed. It was concluded that the NPSM model should always be calibrated but only a few of the parameters provided with BASINS needed to be calibrated. For a three‐year study period, there was a 2 percent underestimation of discharge using area weighted precipitation values and a 25 percent overestimation using the single station data in BASINS. A comparison of observed and predicted monthly discharge resulted in an r² of 0.86 with area‐weighted precipitation and an r² of 0.74 with the single station data. Calibrating the model to substantially improve sediment predictions was unsuccessful and we concluded that a calibration period of one year was too short. For the three‐year study period, the r² for sediment was 0.36 with a slope of 0.37 and an intercept of 18.8 mg/l. The mean observed and predicted sediment concentrations were 27.1 mg/l and 22.6 mg/l, respectively.     

WIDTH OF STREAMS AND RIVERS IN RESPONSE TO VEGETATION,BANK MATERIAL,AND OTHER FACTORS1

ABSTRACT: An extensive group of datasets was analyzed to examine factors affecting widths of streams and rivers. Results indicate that vegetative controls on channel size are scale dependent. In channels with watersheds greater than 10 to 100 km², widths are narrower in channels with thick woody bank vegetation than in grass lined or nonforested banks. The converse is true in smaller streams apparently due to interactions between woody debris, shading, understory vegetation, rooting characteristics, and channel size. A tree based statistical method (regression tree) is introduced and tested as a tool for identifying thresholds of response and interpreting interactions between variables. The implications of scale dependent controls on channel width are discussed in the context of stable channel design methods and development of regional hydraulic geometry curves.     

Groundwaters at Risk: Wetland Loss Changes Sources,Lengthens Pathways,and Decelerates Rejuvenation of Groundwater Resources

Wetland loss alters the hydrology of wetlandscapes in poorly understood ways. To quantify the effects of wetland loss on subsurface hydrology, a physically based hydrologic model that simulates the timing and pathways of subsurface hydrologic connections was coupled with wetland inventories over a 50‐year period during which substantial wetland loss occurred. The model revealed, based on vertical variations in saturated hydraulic conductivities, wetland loss of different degrees led to a contraction of catchment contributing areas to local surface waters but an expansion of contributing areas to the regional surface water body. This shift in groundwater contributing areas reflected (1) a decrease in baseflow contribution to the local surface water bodies, and (2) an increase in the transit time and length of subsurface hydrologic connections with an associated increase in the magnitude and age of baseflow discharging to the regional surface water body. The model also showed regions with thick permeable aquifers were particularly sensitive to the loss of wetlands. Our ability to predict these changes in hydrology of the watershed provides important support for designing science‐based policies to promote sustainable water resource management.     

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.     

黑土区小流域土壤氮素空间分布及主控因素研究

在经典统计学和地统计学的基础上,结合"3S"技术,对黑土区海沟河小流域土壤表层(0~20 cm)中全氮(TN)、碱解氮(AN)的空间变异、分布特征及主控因素进行深入探讨.结果表明:海沟河小流域土壤TN含量处于较高水平,AN含量为中等水平;TN和AN的变程分别为900 m和1282 m,其空间变异均受地形、成土母质等结构性要素影响较大,在东-西(E-W)方向的空间变异相对剧烈;TN含量与坡度等地形指标显著性相关,AN含量与高程等地形要素显著性相关;回归协同克里格插值结果显示,TN自东向西呈现"高-低"交替的带状格局,与土地利用方式在东西方向上的演替相近,AN的高值在东部山区,低值在中部旱地分布集中的区域,呈现"两边高,中间低"的特征;水系、居民点等环境要素对TN和AN的空间分布存在明显的作用距离,土地利用方式及坡位对TN和AN含量分布影响显著,且存在较大差异.     

信息约束条件下的流域农业面源污染控制优化

我国广大小流域迫切需要开展农业面源污染控制,但却面临着水质、水文、气象、土地等监测资料不足的信息约束条件。为了应对此问题,本文以具有冻融变化特征的东北地区为例,开发了一套信息约束条件下的流域农业面源污染控制优化系统。首先,提出了农业面源污染负荷的计算方法。其次,分析了流域水质的影响因素。接着,建立了面源污染输入与流域出水口水质之间的响应关系,经验证该系统输出数据与实际污染状况相吻合,能够很好地模拟流域污染状况。最后通过各种削减策略的运用,模拟出农业面源污染削减率和削减后的总氮浓度。通过采用本研究制定的控制优化方案,改变种植类型和面积以及改善施肥配施比,将污染源数据进行量化作为输入数据,经系统输出得到模拟污染输出数据,可得到较好的污染削减效果。研究结果为信息约束条件下治理流域农业面源污染提供了决策支持。     

三峡库区干流总磷浓度变化趋势分析研究

通过分析2000年-2015年的三峡库区长江、嘉陵江、乌江干流总磷浓度数据,掌握三峡库区总磷总体水平,长江干流总磷浓度为0.135±0.043 mg/1,为Ⅲ类水质;嘉陵江总磷浓度较低,为0.075±0.033 mg/1,为Ⅱ类水质;乌江干流总磷浓度较高,约为0.403±0.288 mg/1,为V类水质.长江重庆段入境朱沱断面的总磷浓度在枯、丰水期呈显著上升趋势,出境培石断面的总磷浓度在枯、平水期呈显著上升趋势.乌江干流入境万木断面和入库锣鹰断面总磷浓度变化趋势一致,都表现为先升高后降低.从2009年开始升高,在2011年或2012年达到峰值,最大浓度超过1.0 mg/1,然后开始逐年下降,到2015年浓度下降到0.2 mg/l.