ABSTRACT: Five types of land use/land covers in the West Tiaoxi watershed of China were studied for nutrient losses in artificial rainstorm runoff. A self‐designed rainfall simulator was used. In situ rainfall simulations were used to: (1) compare the concentrations of nitrogen and phosphorous in different land use/land covers and (2) evaluate the flux of nitrogen and phosphorous export from runoff and sediment in various types of land use/land covers. Three duplicated experiments were carried out under rain intensity of 2 mm/min, each lasting 32 minutes on a 3 m2 plot. Characteristics of various species of nitrogen and phosphorous in runoff and sediment were investigated. The results showed that the concentrations of total nitrogen (TN) and total phosphorous (TP) were greatest in runoff from mulberry trees and smallest from pine forest. The TN and TP export was mainly from suspended particulate in runoff. TN and TP exports from the top 10 cm layer of five types of land use/land covers were estimated as high as 4.66 to 9.40 g/m2 and 2.57 to 4.89 g/m2, respectively, of which exports through sediment of runoff accounted for more than 90 percent and 97 percent. The rate of TN and TP exports ranged from 2.68 to approximately 14.48 and 0.45 to approximately 4.11 mg/m2/min in runoff; these rates were much lower than those of 100.01 to approximately 172.67 and 72.82 to approximately 135.96 mg/m2/min in the runoff sediment. 相似文献
ABSTRACT: In order to determine appropriate application rates and to ensure low pollutant levels in sewage sludge, knowing the chemical composition of sewage sludge is of great importance in a land application program. The objective of this study is to evaluate the variability of selected chemical characteristics of sewage sludge from New Jersey publicly owned treatment works (POTWs). Measurements of total Kjeldahl nitrogen (TKN), NH4+‐N, P, K+, Cd, Cu, Pb, and Zn reported by 98 facilities in the 1996 and 1997 New Jersey Sludge Quality Assurance Regulations (SQAR) reports were statistically analyzed. Sewage sludge from Category 5 POTWs (greater than 10 percent industrial input) showed higher Cd, Cu, and Pb concentrations than Category 3 and Category 4 facilities (less than 10 percent industrial input). Even though only two years of data were analyzed, there was an indication that Cd and Pb concentrations in sewage sludge are decreasing with time. The yearly mean of only a few facilities exceeded the federal pollution concentration limits (40 CFR Part 503, Table 3). Phosphorus and Cd values showed the highest variability within facilities based on the coefficient of variation. Due to the variability of sewage sludge constituents, the use of the yearly rolling mean of nutrient concentrations to determine application rates was considered inadequate. An actual analysis of the sewage sludge to be applied is more appropriate to determine application rates than historical data. 相似文献
ABSTRACT: A general framework is proposed for using precipitation estimates from NEXRAD weather radars in raingage network design. NEXRAD precipitation products are used to represent space time rainfall fields, which can be sampled by hypothetical raingage networks. A stochastic model is used to simulate gage observations based on the areal average precipitation for radar grid cells. The stochastic model accounts for subgrid variability of precipitation within the cell and gage measurement errors. The approach is ideally suited to raingage network design in regions with strong climatic variations in rainfall where conventional methods are sometimes lacking. A case study example involving the estimation of areal average precipitation for catchments in the Catskill Mountains illustrates the approach. The case study shows how the simulation approach can be used to quantify the effects of gage density, basin size, spatial variation of precipitation, and gage measurement error, on network estimates of areal average precipitation. Although the quality of NEXRAD precipitation products imposes limitations on their use in network design, weather radars can provide valuable information for empirical assessment of rain‐gage network estimation errors. Still, the biggest challenge in quantifying estimation errors is understanding subgrid spatial variability. The results from the case study show that the spatial correlation of precipitation at subgrid scales (4 km and less) is difficult to quantify, especially for short sampling durations. Network estimation errors for hourly precipitation are extremely sensitive to the uncertainty in subgrid spatial variability, although for storm total accumulation, they are much less sensitive. 相似文献
ABSTRACT: The use of transferable discharge permits in water pollution, what we will call water quality trading (WQT), is rapidly growing in the U.S. This paper reviews the current status of WQT nationally and discusses the structures of the markets that have been formed. Four main structures are observed in such markets: exchanges, bilateral negotiations, clearinghouses, and sole source offsets. The goals of a WQT program are environmental quality and cost effectiveness. In designing a WQT market, policy makers are constrained by legal restrictions and the physical characteristics of the pollution problem. The choices that must be made include how trading will be authorized, monitored and enforced. How these questions are answered will help determine both the extent to which these goals are achieved, and the market structures that can arise. After discussing the characteristics of different market structures, we evaluate how this framework applies in the case of California's Grassland Drainage Area Tradable Loads Program. 相似文献
ABSTRACT: Since 1989, the government of Pierce County, Washington, has prepared four watershed action plans. The watersheds cover almost 800,000 acres and include about 600,000 residents and diverse land uses, from the city of Tacoma to Mount Rainier National Park. The primary purpose of these plans was to address water quality impacts from nonpoint sources of pollution and to protect beneficial uses of water. Pierce County has experienced problems such as shellfish bed closures and the Federal Clean Water Act Section 303(d) listing of local water bodies as a result of declining water quality. Pierce County achieved improvements by engaging diverse groups of stakeholders in generating solutions to nonpoint sources of water pollution through our watershed planning process. Using participatory methods borrowed from private industry, Pierce County was able to reach consensus, build trust, maximize participation, facilitate learning, encourage creativity, develop partnerships, shorten time frames for the planning processes, and increase the level of commitment participants had to implementing the plans. As a result, the earliest plans have a high rate of voluntary implementation. This indicates that the process and methodology used to develop watershed plans has a significant, if not critical, impact on their success. 相似文献