PHYTOPLANKTON RESPONSES TO GROUND WATER ADDITION IN CENTRAL FLORIDA LAKES1

ABSTRACT: Phytoplankton were studied in lakes augmented with water from the Floridan aquifer and in control lakes. Augmented lakes exhibited enhanced phytoplankton diversity which was believed to be related to chemical changes in the lakes brought about as a result of ground water addition. In particular, elevated concentrations of inorganic carbon appeared to influence phytoplankton populations.     

UNCERTAINTIES IN ESTIMATING THE WATER BALANCE OF LAKES1

ABSTRACT: Evaluation of hydrologic methodology used in a number of water balance studies of lakes in the United States shows that most of these studies calculate one or more terms of the budget as the residual. A literature review was made of studies in which the primary purpose was error analysis of hydrologic measurement and interpretation. Estimates of precipitation can have a wide range of error, depending on the gage placement, gage spacing, and areal averaging technique. Errors in measurement of individual storms can be as high as 75 percent. Errors in short term averages are commonly in the 15-30 percent range, but decrease to about 5 percent or less for annual estimates. Errors in estimates of evaporation can also vary widely depending on instrumentation and methodology. The energy budget is the most accurate method of calculating evaporation; errors are in the 10–15 percent range. If pans are used that are located a distance from the lake of interest, errors can be considerable. Annual pan-to-lake coefficients should not be used for monthly estimates of evaporation because they differ from the commonly used coefficient of 0.7 by more than 100 percent. Errors in estimates of stream discharge are often considered to be within 5 percent. If the measuring section, type of flow profile, and other considerations, such as stage discharge relationship, are less than ideal errors in estimates of stream discharge can be considerably greater than 5 percent. Errors in estimating overland (nonchannelized) flow have not been evaluated, and in most lake studies this component is not mentioned. Comparison of several lake water balances in which the risdual consists solely of errors in measurement, shows that such a residual, if interpreted as ground water, can differ from an independent estimate of ground water by more than 100 percent.     

A CONCEPTUAL FRAMEWORK FOR EVALUATING AGRICULTURAL WATER CONSERVATION POTENTIALS1

ABSTRACT: This paper defines types of water losses in irrigated agriculture and outlines potentials for water conservation. Recoverable water “losses” (seepage, leakage, and spillage during storage and conveyance, and surface runoff and deep percolation during irrigation) and irrecoverable losses (evaporation from water and soil surfaces and transpiration from plants) are described and illustrated. Some conservation terms are defined, particularly the distinction between on-farm irrigation efficiency and areawide efficiency. Briefly reviewed are agricultural water conservation technologies and their applicability. The biggest untapped potential for water conservation may be a reduction in irrecoverable losses, especially evapotranspiration. The advantages and disadvantages of reducing recoverable and irrecoverable water losses are described, including possible effects on ground water, energy, salinity, crops, wildlife, and in-stream uses. Such information may be useful in several policy and management issues, e.g., ground water overdraft and possible constraints on crops and sites to be irrigated.     

CONTROLLING GROUND WATER DEGRADATION IN THE TULARE LAKE BASIN1

ABSTRACT This study examined the feasibility of extending the Accelerated Salt Transport (ASTRAN) method of groud water quality control to a complex, closed basin which is experiencing ground water quality degradation from irrigated agriculture (e.g., the Tulare Lake Basin in the Southern portion of the California Central Valley). A linear programming model was constructed and parametric analysis conducted which produced results with a “general appraisal” (or “level B”) degree of accuracy. The study concluded that a drainage water export drain is required in order to implement a long-term solution but that ground water degradation can be mitigated by a combination of the ASTRAN method and other measures even with existing entitlements and legal constraints.     

EXPERIMENTAL VERIFICATION OF MULTICOMPONENT GROUND WATER CONTAMINATION PREDICTIONS1

ABSTRACT: Recent advances in mass transport modeling have made possible computation of the theoretical consequences of intricate multicomponent species interactions during ground water contamination events. Predictions such as strong chromatographic effects and induced downstream precipitations may have considerable impact on environmental analysis and regulation. Results of laboratory attempts to verify theoretical multicomponent transport predictions are discussed. Evidence presented here indicates that natural variability of soil properties make such verifications difficult. Although species interactions are easily confirmed, dramatic effects often exist only within small mathematical windows in strongly variable coefficient sets. Currently, the ability to generate multicomponent predictions apparently exceeds the ability to quantify the necessary, presumably deterministic, information required for real soils.     

PRIVATIZING THE GROUND WATER RESOURCE: INDIVIDUAL USE AND ALTERNATIVE SPECIFICATIONS1

ABSTRACT: While most inquiries into improving the efficiency of ground water allocation have focused upon various schemes involving centralized management, recently the focus has shifted towards exploring private property solutions to these problems. However, most of these studies, when modeling ground water use, have equated behavior under private property to that under common property conditions. This leads to the possibly mistaken conclusion that private property rights do not promote more efficient ground water use, because these models assume that producers ignore the future effects of current pumping. This paper attempts to correct this deficiency by formally modeling ground water use under common property, central management, and private property scenarios. Moreover, there are many ways that property rights can be defined over ground water, some establishing more exclusivity over the resource than others. Four specifications of property rights are analyzed for their likely effects on allocative efficiency: full stock-flow, partial stock-flow, limited stock-flow, and pure flow rights.     

OPTIMIZING NONPOINT SOURCE CONTROLS IN WATER QUALITY REGULATION1

ABSTRACT: A stochastic programming framework is developed to evaluate the economic implications of reliability criteria and multiple effluent controls on nonpoint source pollution. An integrated watershed simulation model is used to generate probability distributions for agricultural effluents in surface and ground water resulting from agricultural practices. Results from the planning model indicate that reliability and multiple effluent constraints significantly increase the cost of nonpoint controls but the effects vary by control alternative. The analysis indicates that an evaluation of multiple water quality objectives can be an important planning tool for designing nonpoint source controls for innovative programs to promote cost-effective water quality regulation.     

BASINWIDE WATER-BALANCE MODELING WITH EMPHASIS ON SPATIAL DISTRIBUTION OF GROUND WATER RECHARGE1

ABSTRACT: A detailed but simple hydrologic budget for the entire Rattlesnake Creek basin (3,768 km²) in south-central Kansas was developed. With this budget, using minimal daily-weather input data and the soil-plant-water system-analysis methodology, we were able to characterize the spatial distribution of the hydrologic components of the water balance within the basin. A combination of classification and meteorological methods resulted in a basinwide integration methodology. Using this methodology, we found that, in addition to obvious climatic controls, soil, vegetation, and land-use factors also exert considerable influence on the water balance of the area. The available-water capacity (AWC) of soil profiles plays a dominant role in soil-water-deficit development and deep drainage. Vegetation and dryland or irrigated farming particularly affect the evapotranspiration (ET) components, with ET from irrigated corn and alfalfa being two to three times that from wheat. Deep drainage from irrigated wheat fields was found to be significantly higher than that from grassland and dryland wheat; deep drainage from alfalfa is practically nonexistent. We demonstrated how vegetation changes may affect components of the hydrologic cycle. We also showed that different portions of the watershed have different water-balance components and that use of single average values of hydrologic variables in management practices may not be realistic.     

THE BISCAYNE AQUIFER CONTAMINATION: CLEANUP AND PREVENTION1

ABSTRACT: The Biscayne Aquifer is the sole source of drinking water for approximately three million residents of southeast Florida. Nine hazardous waste sites on the EPA National Priority List overlie this aquifer. Extensive investigation of an 80 square-mile area in metropolitan Miami detected low to moderate levels of toxic contaminants in the ground water, with volatile organic chemicals the most prevalent. The Centers for Disease Control concluded that contamination of the aquifer within the study area poses a serious potential threat to public health. Recommendations for source control and cleanup have been partially carried out. The top few feet of soil at the Miami Drum site have been excavated and relocated; ground water encountered during excavation has been withdrawn and treated, and the Northwest 58th Street Landfill has been closed. Recovery and treatment of ground water from the contaminated area was the recommended cleanup measure and has been approved by EPA and state and local agencies. A preventive action program for the Biscayne Aquifer region was also recommended for implementation by local agencies. This program consists of regulations, waste management practices, construction and treatment guidelines, and public information activities and materials. Implementing this program will help keep the Biscayne Aquifer water drinkable far into the future.