基于LOADEST和数字滤波的水源地基流氮素输出定量方法应用实例

地表直接径流和基流均是流域非点源氮/磷养分输出的重要水文途径.科学认识和定量模拟基流氮/磷养分输出对于准确解析水源地水体非点源污染来源至关重要.基于Load Estimator模型和数字滤波算法,建立了定量水源地基流氮素输出的方法体系.以浙江省珊溪水源地的玉泉溪流域为例,利用玉泉溪2010-01—2013-12期间逐月总氮(TN)水质监测数据和逐日流量数据,展示了该方法的计算过程.结果表明,本文建立的水源地基流氮素输出定量方法结果合理,模拟精度高,决定系数和纳什系数分别为0.83和0.80;玉泉溪流域2010—2013年TN负荷量为141.21～274.68 t·a~(-1),平均208.63 t·a~(-1),年基流TN负荷量为84.39～168.68 t·a~(-1),平均127.69 t·a~(-1);基流对玉泉溪年均TN负荷量贡献率高达60%以上,流域基流养分输出对地表水体的污染应引起足够重视.     

CUMULATIVE IMPACTS OF LANDUSE ON WATER QUALITY IN A SOUTHERN APPALACHIAN WATERSHED1

ABSTRACT: Water quality variables were sampled over 109 weeks along Coweeta Creek, a fifth-order stream located in the Appalachian mountains of western North Carolina. The purpose of this study was to observe any changes in water quality, over a range of flow conditions, with concomitant downstream changes in the mix of landuses. Variables sampled include pH, HCO₃^2?, conductivity, NO₃^?_?-N, NH₄⁺-N, PO₄^3?-P, C1^?-, Na, K, Ca²⁺, Mg²⁺, SO₄^2?, 5iO₂, turbidity, temperature, dissolved oxygen, total and fecal coliform, and focal streptococcus. Landcover/landuse was interpreted from 1:20,000 aerial photographs and entered in a GIS, along with information on total and paved road length, building location and density, catchment boundaries, hydrography, and slope. Linear regressions were performed to relate basin and near-stream landscape variables to water quality. Consistent, cumulative, downstream changes in water quality variables were observed along Coweeta Creek, concomitant with downstream, human-caused changes in landuse. Furthermore, larger downstream changes in water quality variables were observed during stormflow when compared to baseflow, suggesting cumulative impacts due to landscape alteration under study conditions were much greater during storm events. Although most water quality regulations, legislation, and sampling are promulgated for baseflow conditions, this work indicates they should also consider the cumulative impacts of physical, chemical, and biological water quality during stormflow.     

THE ARMA MODELS APPLIED TO THE FLOW OF KARSTIC SPRINGS1

ABSTRACT: Autoregressive moving average (ABMA) models have been applied to study the flow series of the karstic springs of La Villa, Fuente Mayor (Spain), and Aliou (France). The theoretical meaning of the parameters involved in the model upon applying it to a simplified scheme of the emptying of a karstic aquifer is first analyzed. The types of transformations necessary to apply these models to the flow series that lack normality and have strong periodic components are also indicated, as are the advantages of this type of model and the physical significance of the parameters obtained, with respect to the standpoint of hydraulics, ranging from rather homogeneous aquifers (La Villa) to extremely karstic (Aliou), including aquifers with intermediate characteristics (Fuente Mayor).     

SENSITIVITY OF HIGH-ELEVATION STREAMS IN THE SOUTHERN BLUE RIDGE PROVINCE TO ACIDIC DEPOSITION1

ABSTRACT: The Southern Blue Ridge Province, which encompasses parts of northern Georgia, eastern Tennessee, and western North Carolina, has been predicted to be sensitive to impacts from acidic deposition, owing to the chemical composition of the bedrock geology and soils. This study confirms the predicted potential sensitivity, quantifies the level of total alkalinity and describes the chemical characteristics of 30 headwater streams of this area. Water chemistry was measured five times between April 1983 and June 1984 at first and third order reaches of each stream during baseflow conditions. Sensitivity based on total alkalinity and the Calcite Saturation Index indicates that the headwater streams of the Province are vulnerable to acidification. Total alkalinity and p11 were generally higher in third order reaches (mean, 72 μeq/θ and 6.7) than in first order reaches (64 μeq/θ and 6.4). Ionic concentrations were low, averaging 310 and 340 μeq/θ in first and third order reaches, respectively. A single sampling appears adequate for evaluating sensitivity based on total alkalinity, but large temporal variability requires multiple sampling for the detection of changes in pH and alkalinity over time. Monitoring of stream water should continue in order to detect any subtle effects of acidic deposition on these unique resource systems.     

RELATION OF NITRATE CONCENTRATIONS TO BASEFLOW IN THE RACCOON RIVER,IOWA1

ABSTRACT: Excessive nitrate‐nitrogen (nitrate) export from the Raccoon River in west central Iowa is an environmental concern to downstream receptors. The 1972 to 2000 record of daily streamflow and the results from 981 nitrate measurements were examined to describe the relation of nitrate to streamflow in the Raccoon River. No long term trends in streamflow and nitrate concentrations were noted in the 28‐year record. Strong seasonal patterns were evident in nitrate concentrations, with higher concentrations occurring in spring and fall. Nitrate concentrations were linearly related to streamflow at daily, monthly, seasonal, and annual time scales. At all time scales evaluated, the relation was improved when baseflow was used as the discharge variable instead of total streamflow. Nitrate concentrations were found to be highly stratified according to flow, but there was little relation of nitrate to streamflow within each flow range. Simple linear regression models developed to predict monthly mean nitrate concentrations explained as much as 76 percent of the variability in the monthly nitrate concentration data for 2001. Extrapolation of current nitrate baseflow relations to historical conditions in the Raccoon River revealed that increasing baseflow over the 20th century could account for a measurable increase in nitrate concentrations.     

A SIMPLE METHOD FOR ESTIMATING BASEFLOW AT UNGAGED LOCATIONS1

ABSTRACT: Baseflow, or water that enters a stream from slowly varying sources such as ground water, can be critical to humans and ecosystems. We evaluate a simple method for estimating base‐flow parameters at ungaged sites. The method uses one or more baseflow discharge measurements at the ungaged site and longterm streamflow data from a nearby gaged site. A given baseflow parameter, such as the median, is estimated as the product of the corresponding gage site parameter and the geometric mean of the ratios of the measured baseflow discharges and the concurrent discharges at the gage site. If baseflows at gaged and ungaged sites have a bivariate lognormal distribution with high correlation and nearly equal log variances, the estimated baseflow parameters are very accurate. We tested the proposed method using long‐term streamflow data from two watershed pairs in the Driftless Area of southwestern Wisconsin. For one watershed pair, the theoretical assumptions are well met; for the other the log‐variances are substantially different. In the first case, the method performs well for estimating both annual and long‐term baseflow parameters. In the second, the method performs remarkably well for estimating annual mean and annual median baseflow discharge, but less well for estimating the annual lower decile and the long‐term mean, median, and lower decile. In general, the use of four measurements in a year is not substantially better than the use of two.     

IMPACT OF IRRIGATION WELLS ON BASEFLOW OF THE BIG BLUE RWER,NEBRASKA1

ABSTRACT: The Kansas-Nebraska Big Blue River compact requires that the state of Nebraska insure a minimum flow of the Big Blue River across the state line. There are two options that the state of Nebraska may use to ensure minimum flows. The obvious option is to limit surface-water irrigators along the river. However, under the terms of the compact, a second option may be to regulate irrigation wells that are within one mile of the river and were installed after November 1, 1968. The objective of this study is to quantify the effects of 17 irrigation wells that may be regulated on baseflow of the Big Blue River. A finite-element model is used to study the hydrogeologic system between DeWitt and Beatrice, Nebraska. The 17 wells that may be regulated are located between these towns and are developed in sediments deposited in a cross-cutting paleovalley anchor alluvium associated with the Big Blue River. While there wore considerable existing data, additional data were gathered by drilling an additional nine test holes, conducting several aquifer tests, stream-stage measurements, and baseflow calculation through extensive stream-discharge measurements, establishment of a ground water-level monitoring network, determining the amount of water pumped for irrigation and municipal use in the area, and a short-term precipitation network. The model was calibrated using observed baseflow and ground water level data. The model clearly shows that regulating the 17 wells to maintain baseflow would have a minimal effect on the overall water budget. This is reasonable, especially considering that there are over 250 irrigation wells in the project area. The 17 wells considered pumped only 6 percent of the total pumpage within the modeled area during the irrigation season of 1984. The computer model provides the documentation needed to demonstrate this fact. Although much of the resources spent and a significant amount of hydrogeologic data are being collected over a period of three years on a relatively small area, the simulation model could be improved through further field testing of the aquifer and stream-bed sediment characteristics and quantification of ground water recharge, discharge, and evapotranspiration rates.     

IMPACT OF SURFACE COAL MINING ON THREE OHIO WATERSHEDS –PHYSICAL CONDITIONS AND GROUND-WATER HYDROLOGY1

ABSTRACT: A study was conducted over a six-year period in East-Central Ohio to determine the effects of surface mining and reclamation on physical watershed conditions and on ground-water hydrology in three ground-water zones in three small experimental watersheds. Mining disturbances in watersheds adjacent to the experimental sites affected ground-water levels in the undisturbed experimental watersheds prior to actual mining in the experimental sites. New subsurface flow paths, with different characteristics, formed during mining and reclamation. At all three sites mining dewatered the saturated zone above the underclay of the mined coal seam. Mining and reclamation affected ground-water levels below the mined coal seam in the middle and lower zones within at least two sites. Ground-water level recovery in the mined upper saturated zone was slow and irregular both temporally and spatially after reclamation. Hydraulic conductivities of postmining (Phase 3) spoil were generally greater than those of Phase 1 bedrock, but wide spatial variability was observed. Modelers need to be aware of the complexities of new flow paths and physical characteristics of subsurface flow media that are introduced by mining and reclamation, including destruction of the upper-zone clay.     

ESTIMATION OF THE HIEC1 LOSS PARAMETERS FOR ROUTING THE PROBABLE MAXIMUM FLOOD1

ABSTRACT: Twenty storm events were used to select design values of the HEC1 loss parameters STRTL and CNSTL in order to route the probable maximum flood, PMF, through the Englewood watershed, Ohio. The parameter STRTL represents the initial volume of water lost due to interception and incomplete saturation of the soil prior to the storm. The parameter CNSTL represents a continuous loss rate and depends only on the watershed. When optimized from each storm event, STRTL varied between 0.0 and 3.4 inches with an average of 1.0 inch; CNSTL varied between 0.02 and 0.26 inch/hour, and it followed a normal probability distribution with a mean of about 0.1 inch/hour. The absence of correlation between optimum CNSTL values and each of total rainfall, total loss, and runoff duration supported the selection of the mean CNSTL as a design value. PMF routing through the Englewood watershed revealed that the PMF at the outlet is not sensitive to STRTL, but highly affected by CNSTL variations. The insensitivity to STRTL was due to the presence of a dam at the outlet of the watershed that caused the buildup of water in the watershed, thereby masking the storage effect of STRTL. The peak PMF increased by about 27 percent when the design CNSTL was decreased to 0.05 inch! hour, and decreased by about 18 percent when the design CNSTL was increased to 0.15 inch/hour.     

STORM RUNOFF CHARACTERISTICS OF GRAZED WATERSHEDS IN EASTERN OREGON1

ABSTRACT: Rainfall and runoff data from 485 storms during the summers of 1979–84 were evaluated to characterize storm runoff volumes (SF) and peak flows (QP) for 13 small watersheds in the Blue Mountains of eastern Oregon and to determine differences among grazing intensities and vegetation types. Storm hydrographs were separated by using watershed-specific baseflow rise rates of 0.002–0.013 cfsm/hr. Median SF and QP were 0.0014 in and 0.43 cfsm, respectively, for all storms. Total storm rainfall (PPT) and initial flow (QI) were important stepwise regression variables in accounting for the variation in SF and peak flow above initial flow (QPI); 30- and 60-mm rainfall intensities and rainfall duration were relatively unimportant. Two classes of vegetation were evaluated: (1) western larch-Douglas-fir (nine watersheds), and (2) other (four watersheds representing fir-spruce, lodgepole pine, mountain meadow, and ponderosa pine). Mean SF and QP did not differ (P=0.05) among vegetation classes but significant differences were apparent in the relation of SF to PPT and QI, and QPI to PPT and QI. As PPT and QI increased, SF and QPI from larch-Douglas-fir watersheds increased at a slower rate than they did from the other watersheds. Four levels of grazing intensity had no effect on storm runoff.