ON THE USE OF SEEPAGE METERS TO ESTIMATE GROUNDWATER NUTRIENT LOADING TO LAKES1

Data from a study on East Lake Tohopekaliga, Florida, indicate that the seepage meter measurement method may often overestimate nutrient contributions to lakes. Nutrient loading data from this method and a method employing lakeside piezometer nutrient data and seepage meter flows were not comparable. Seepage nutrient loading from the meter and piezometer methods comprised 39 and 18 percent of the nitrogen budget and 38 and 9 percent of the phosphorus budget, respectively, for East Lake Tohopekaliga. In terms of water, groundwater seepage accounted for only 14 percent of the total input to the lake. It is felt that some of the past studies using the seepage meter method to estimate nutrient loading may be in error due to reasons related to the enclosure of lake sediments by the meter and the accompanying anaerobic conditions which quickly result.     

Treatment of risk in environmental impact assessment

Risk assessment and environmental impact assessment have developed as separate traditions. While environmental impact assessment is a broad field that includes all activities that attempt to analyze and evaluate the effects of human and related actions on the environment, risk assessment has been concerned with the relatively well-defined regulatory problems and employs formal quantitative analysis of the probability of specific undesired events, such as cancer. Risk analytic approaches, particularly the explicit treatment of uncertainty, can significantly contribute to environmental assessments. This article discusses the type and sources of uncertainty in environmental assessments, techniques for their quantification, and ways to use uncertainty estimates to calculate probabilities of effects or probabilities of exceeding environmental standards and to determine the need for mitigation or additional research.This article was presented at the International Institute of Applied Systems Analysis, Task Force Meeting on Risk and Policy Analysis under Conditions of Uncertainty, Laxenburg, Austria, November 1985.     

Ecological effects of coastal marsh impoundments: A review

Many coastal resource managers believe estuarine marshes are critically important to estuarine fish and shellfish, not only because of the habitat present for juvenile stages, but also because of the export of detritus and plant nutrients that are consumed in the estuary. Concern has been widely expressed that diking and flooding marshes (impounding) for mosquito control and waterfowl management interferes with these values of marshes. Major changes caused by impoundment include an increase in water level, a decrease in salinity, and a decrease in the exchange of marsh water with estuarine water. Alteration of species composition is dramatic after impoundment. Changes in overall production and transport phenomena, however—and the consequences of these changes— may not be as great in some cases as the concern about these has implied. Although few data are available, a more important concern may be the reduction of access by estuarine fish and shellfish to the abundant foods and cover available in many natural, as well as impounded, marshes. Perhaps even more important is the occasional removal of free access to open water when conditions become unfavorable in impounded marsh that is periodically opened and closed. Collection of comparative data on the estuarine animal use of various configurations of natural and impounded marshes by estuarine animals should lead to improved management of both impounded and unimpounded marshes.     

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.     

CALCULATION OF NONLINEAR CONFIDENCE AND PREDICTION INTERVALS FOR GROUND-WATER FLOW MODELS1

ABSTRACT: A method is derived to efficiently compute nonlinear confidence and prediction intervals on any function of parameters derived as output from a mathematical model of a physical system. The method is applied to the problem of obtaining confidence and prediction intervals for manually-calibrated ground-water flow models. To obtain confidence and prediction intervals resulting from uncertainties in parameters, the calibrated model and information on extreme ranges and ordering of the model parameters within one or more independent groups are required. If random errors in the dependent variable are present in addition to uncertainties in parameters, then calculation of prediction intervals also requires information on the extreme range of error expected. A simple Monte Carlo method is used to compute the quantiles necessary to establish probability levels for the confidence and prediction intervals. Application of the method to a hypothetical example showed that includsion of random errors in the dependent variable in addition to uncertainties in parameters can considerably widen the prediction intervals.     

SOME GEOMORPHIC RELATIONSHIPS AND HYDROGRAPH ANALYSIS1

ABSTRACT: First order drainage channels originate when the tractive force exerted by flowing water is sufficient to move surface sediment. The amount of runoff available to move sediment is a function of geologic and climatic characteristics. An experimental analysis showed that soils derived from fine grained rocks had lower infiltration rates and higher runoff volume than soils derived from coarser grained rocks in a semi-arid climate. Root density and penetration increased in a more humid climate and increased infiltration rates. The number of first order channels was inversely proportional to the infiltration capacity of the soil. Each first order channel acts as a source area for surface runoff. The distribution of first order channel distances from the gage determines the timing of the delivery of water to the gage. A comparison of the frequency histogram of first order channel distances for drainage basins in Pennsylvania and their hydxographs of runoff from general storms showed marked similarity. This close correspondence indicated the shape of the surface runoff hydrograph and was largely controlled by the distribution of first order channel distances.     

Fuelwood Prices in India: Policy Implications

The price of fuelwood has been increasing at a rate higher than that of the consumer price index in most of the major urban centres of India. Today, in terms of cost per unit of energy delivered, fuelwood is more than twice as expensive as kerosene for cooking. This has immense public policy implications. A number of complementary policy interventions are needed so that forests can be saved and the stability of energy supplies can be achieved in developing countries.     

DRY STREAM REACHES IN CARBONATE TERRANES: SURFACE INDICATORS OF GROUND-WATER RESERVOIRS1

ABSTRACT: The method of identifying dry stream reaches in carbonate terrane as surface indicators of potential ground-water reservoirs offers a valuable exploration technique that is more rapid and less expensive than traditional exploration methods involving random test drilling. In areas where dry stream reaches occur, subsurface drainage successfully competes with surface drainage, and sheet-like dissolution openings have developed parallel to bedding creating the ground-water reservoir. The occurrence and hydraulic characteristics of such reservoirs are highly variable, as attested to by the wide range of well yields. Union Hollow in south-central Tennessee is the setting for a case study that illustrates the application of the dry stream reach technique. In this technique, dry stream reach identification is based on two types of readily acquired information: (1) remotely sensed black and white infrared aerial photography; and (2) surface reconnaissance of stream channel characteristics. Test drilling in Union Hollow subsequent to identification of the dry reach proved that a localized ground-water reservoir was present.