SETTING AN EFFECTIVE TMDL: SEDIMENT LOADING AND EFFECTS OF SUSPENDED SEDIMENT ON FISR1

ABSTRACT: The Agricultural Drainage and Pesticide Transport model was used to examine the relationship between fish and suspended sediment in the context of a proposed total maximum daily load (TMDL) in two agricultural watersheds in Minnesota. During a 50‐year simulation, Wells Creek, a third‐order cold water stream, had an estimated 1,164 events (i.e., one or more consecutive days of estimated sediment loading) and the Chippewa River, a fourth‐order warm water stream, had 906 events of measurable suspended sediment. Sublethal thresholds were exceeded for 970 events and lethal levels for 194 events for brown trout in Wells Creek, whereas adult nonsalmonids would have experienced sublethal levels for 923 events and lethal levels for 241 events. Sublethal levels were exceeded for 756 events and lethal thresholds were exceeded for 150 events in the Chippewa River. Nonsalmonids would have experienced 15 events of mortality between 0 and 20 percent in Wells Creek. In the Chippewa River, there were 35 events of mortality between 0 and 20 percent and one event in which mortality could have exceeded 20 percent. The Minnesota Pollution Control Agency has proposed listing stream reaches as being impaired for turbidity at 25 NTU, which is approximately 46 mg suspended sediment/1. We estimated that 46 mg/1 would be exceeded approximately 30 days in a year (d/yr) in both systems. A TMDL of 46 mg SS/1 may be too high to ensure that stream fishes are not negatively affected by suspended sediment. We recommend that an indicator incorporating the duration of exposure be applied.     

MASS LOAD ESTIMATION ERRORS UTILIZING GRAB SAMPLING STRATEGIES IN A KARST WATERSHED1

ABSTRACT: Developing a mass load estimation method appropriate for a given stream and constituent is difficult due to inconsistencies in hydrologic and constituent characteristics. The difficulty may be increased in flashy flow conditions such as karst. Many projects undertaken are constrained by budget and manpower and do not have the luxury of sophisticated sampling strategies. The objectives of this study were to: (1) examine two grab sampling strategies with varying sampling intervals and determine the error in mass load estimates, and (2) determine the error that can be expected when a grab sample is collected at a time of day when the diurnal variation is most divergent from the daily mean. Results show grab sampling with continuous flow to be a viable data collection method for estimating mass load in the study watershed. Comparing weekly, biweekly, and monthly grab sampling, monthly sampling produces the best results with this method. However, the time of day the sample is collected is important. Failure to account for diurnal variability when collecting a grab sample may produce unacceptable error in mass load estimates. The best time to collect a sample is when the diurnal cycle is nearest the daily mean.     

STORM AND SEASONAL DISTRIBUTIONS OF FECAL COLIFORMS AND CRYPTOSPORIDIUM IN A SPRING1

ABSTRACT: The transmission of disease in ground water is a topic of great concern to government agencies, ground water specialists, and the general public. The purpose of this study was to compare the temporal variability in storm flow of fecal coliform bacteria densities and Cryptosporidium parvum oocyst densities in agriculturally impacted karst ground water. Cryptosporidium parvum oocyst densities ranged from 0 to 1,050 oocysts/1, and mean storm densities ranged from 3.5 to 156.8 oocysts/1. Fecal coliform densities ranged from less than 1 CFU/100ml to more than 40,000 CFU/100ml, and geometric mean storm densities ranged from 1.7 CFU/100ml to more than 7,000 CFU/100ml. Fecal coliform densities correlated well with flow during storms, but Cryptosporidium oocyst densities exhibited a great deal of sample to sample variability and were not correlated with flow. Fecal coliform densities did not correlate positively with Cryptosporidium oocyst densities. Fecal coliform densities were greatest at storm peaks, when sediment loads were also greatest. Multiple transport mechanisms for fecal coliform bacteria and C. parvum oocysts may necessitate various agricultural land management and livestock health maintenance practices to control movement of pathogens to karst ground water.     

Emission Models and Inventories for Local Greenhouse Gas Emissions Assessment: Experience in the East Midlands Region of the Uk

This paper considers how regional greenhouse gas emissioninventories can be determined. It presents a greenhousegas emissions inventory, by source, for the East Midlandsthat has been compiled as part of a regional study intoclimate change impacts in the United Kingdom. This hasused available local data, and national emissions datawith appropriate scaling factors. Total greenhouse gasemissions for the region are estimated to be 59 milliontonnes of carbon dioxide equivalent (CO₂ equivalent)for 1997. Of these emissions, approximately 86% werecarbon dioxide emissions, 7% methane emissions, and 5%were nitrous oxide, with emissions of hydrofluorocarbons(HFCs), perfluorocarbons (PFCs) and sulphur hexafluoride(SF₆) contributing less than 2% of total emissions.     

SAMPLING STRATEGIES FOR ESTIMATING ACUTE AND CHRONIC EXPOSURES OF PESTICIDES IN STREAMS1

ABSTRACT: The Food Quality Protection Act of 1996 requires that human exposure to pesticides through drinking water be considered when establishing pesticide tolerances in food. Several systematic and seasonally weighted systematic sampling strategies for estimating pesticide concentrations in surface water were evaluated through Monte Carlo simulation, using intensive datasets from four sites in northwestern Ohio. The number of samples for the strategies ranged from 4 to 120 per year. Sampling strategies with a minimal sampling frequency outside the growing season can be used for estimating time weighted mean and percentile concentrations of pesticides with little loss of accuracy and precision, compared to strategies with the same sampling frequency year round. Less frequent sampling strategies can be used at large sites. A sampling frequency of 10 times monthly during the pesticide runoff period at a 90 km² basin and four times monthly at a 16,400 km² basin provided estimates of the time weighted mean, 90^th, 95^th, and 99^th percentile concentrations that fell within 50 percent of the true value virtually all of the time. By taking into account basin size and the periodic nature of pesticide runoff, costs of obtaining estimates of time weighted mean and percentile pesticide concentrations can be minimized.     

CONTROLLING PHOSPHORUS IN RUNOFF FROM LONG TERM DAIRY WASTE APPLICATION FIELDS1

ABSTRACT: Phosphorus (P) in runoff from long term animal waste application fields can contribute to accelerated eutrophication of surface waters. Manure when applied at nitrogen (N) agronomic rates generally increases soil P concentrations, which can increase runoff of soluble P. Along the North Bosque River in central Texas, dairy waste application fields are identified as the most controllable nonpoint source of soluble P in a total maximum daily load. To evaluate P reduction practices for fields high in soil extractable P, edge‐of‐field runoff was measured from paired plots of Coastal bermudagrass (Cynodon dactylon) and sorghum (Sorghum bicolor)/ winter wheat (Triticum spp.). Plots (about 0.4 ha) received manure at P agronomic rates following Texas permit guidelines and commercial N during the pretreatment period. During the post‐treatment period, control plots continued to receive manure at P agronomic rates and commercial N. Treatment plots received only commercial N during the post‐treatment period. Use of only commercial N on soils with high extractable P levels significantly decreased P loadings in edge‐of‐field runoff by at least 40 percent, but runoff concentrations sometimes increased. No notable changes in extractable soil P concentrations were observed after five years of monitoring due to drought conditions limiting forage uptake and removal.     

加速开发宁夏南部山区农业资源

本文分析了宁南山区农业生产条件和存在的问题,认为宁南山区农业资源十分丰富,只要合理开发利用,宁南山区必将成为我区油料、大豆、畜产品的生产基地,并相应地提出了加速开发宁南山区农业资源的措施。     

EFFECTS OF AGRICULTURAL NUTRIENT MANAGEMENT ON NITROGEN FATE AND TRANSPORT IN LANCASTER COUNTY PENNSYLVANIA1

ABSTRACT: Nitrogen inputs to, and outputs from, a 55-acre site in Lancaster County, Pennsylvania, were estimated to determine the pathways and relative magnitude of loads of nitrogen entering and leaving the site, and to compare the loads of nitrogen before and after the implementation of nutrient management. Inputs of nitrogen to the site were manure fertilizer, commercial fertilizer, nitrogen in precipitation, and nitrogen in ground-water inflow; and these sources averaged 93, 4, 2, and 1 percent of average annual nitrogen additions, respectively. Outputs of nitrogen from the site were nitrogen in harvested crops, loads of nitrogen in surface runoff, volatilization of nitrogen, and loads of nitrogen in ground-water discharge, which averaged 37, less than 1, 25, and 38 percent of average annual nitrogen removals from the site, respectively. Virtually all of the nitrogen leaving the site that was not removed in harvested crops or by volatilization was discharged in the ground water. Applications of manure and fertilizer nitrogen to 47.5 acres of cropped fields decreased about 33 percent, from an average of 22,700 pounds per year (480 pounds per acre per year) before nutrient management to 15,175 pounds of nitrogen per year (320 pounds per acre per year) after the implementation of nutrient management practices. Nitrogen loads in ground-water discharged from the site decreased about 30 percent, from an average of 292 pounds of nitrogen per million gallons of ground water before nutrient management to an average of 203 pounds of nitrogen per million gallons as a result of the decreased manure and commercial fertilizer applications. Reductions in manure and commercial fertilizer applications caused a reduction of approximately 11,000 pounds (3,760 pounds per year; 70 pounds per acre per year) in the load of nitrogen discharged in ground water from the 55-acre site during the three-year period 1987–1990.     

INTEGRATION OF GEOGRAPHIC INFORMATION SYSTEMS AND A COMPUTER MODEL TO EVALUATE IMPACTS OF AGRICULTURAL RUNOFF ON WATER QUALITY1

ABSTRACT: This study integrates an Agricultural Non-Point Source Pollution Model (AGNPS), the Geographic Resource Analysis Support System (GRASS) (U.S. Army Corps of Engineers, 1987), and GRASS WATERWORKS (a hydrologic modeling tool box being developed at the Michigan State University Center for Remote Sensing) to evaluate the impact of agricultural runoff on water quality in the Cass River, a subwatershed of Saginaw Bay. AGNPS is used to estimate the amounts, origin, and distribution of sediment, nitrogen (N), and phosphorus (P) in the watershed. GRASS and GRASS WATERWORKS are used to generate parameters needed for AGNPS from digital maps, which include soil association, land use, watershed boundaries, water features, and digital elevation. Outputs of the model include spatially distributed estimates of volume and peak runoff, overland and channel erosion, sediment yields, and concentrations of nitrogen and phosphorus. Management scenarios are explored in the AGNPS model to minimize sedimentation and nutrient loading. Scenarios evaluated include variations in crop cover, tillage methods, and other agricultural management practices. In addition, areas vulnerable to erosion are identified for best management practices.     

The economic effects of stratospheric ozone depletion on U.S. agriculture: a preliminary assessment

The adverse effects of stratospheric ozone depletion on human health and welfare is a major environmental concern. One potential welfare effect is reduction in plant productivity, including agricultural crops, due to increased UV-B radiation and tropospheric ozone formation. This paper evaluates the economic effects of potential changes in crop yields due to hypothetical depletions in stratospheric ozone over regions of the U.S.A. Results suggest that increases in tropospheric ozone due to a 15 per cent stratospheric ozone depletion may cause economic losses of around 0·9 billion dollars. Combined effects of both tropospheric ozone and UV-B radiation range from 1·3 to 2·5 billion dollars. These estimates are preliminary, given the high degree of uncertainty in key plant science and aerometric data.