POTENTIAL PHOSPHORUS LOAD REDUCTIONS UNDER THE LAKE OKEECHOBEE REGULATORY PROGRAM1

ABSTRACT: Nutrient loading from beef pastures located within the northern Lake Okeechobee watershed in Florida, has been identified as a source of phosphorus contributing to the accelerated eutrophication of the lake. Since 1989 within the watershed, 557 agricultural drainage sites, mainly beef pasture, have been monitored for compliance under a regulatory program. Of those sites, 154 were actively monitored for phosphorus concentrations from October 1, 1998, to September 30, 1999. Of these 154 sites, 77 were considered to be out of compliance (OOC). An OOC site is defined as having runoff with a 12‐month average phosphorus concentration exceeding the permitted discharge limit. The average annual phosphorous load from the 77 OOC sites for an eight‐year study period from October 1, 1991, to September 30, 1999, was estimated using measured concentration values and simulated runoff obtained from an agricultural nonpoint source pollution model, CREAMS‐WT. The 77 OOC sites produced an estimated average annual 46 metric tonnes of phosphorus load, of which an estimated 22 tonnes of phosphorus reached Lake Okeechobee on an average annual basis. The remaining estimated average annual 24 tonnes of phosphorus load was retained by streams and wetlands in the discharge transport system between the sites and the lake. The estimated average annual load reaching Lake Okeechobee from the OOC sites represented 11 percent of the phosphorus load above a five‐year average annual target load for the lake. However, the OOC site drainage areas represented only 3 percent of the northern watershed that drains into the lake. Of the 77 OOC sites, 12 sites had an average annual phosphorus loading rate equal to or greater than 3.0 kg/ha and were placed on the priority list for the Critical Restoration Project in the Lake Okeechobee watershed. To estimate the possible phosphorus load reductions from the 77 sites, two scenarios were modeled. The first scenario reduced phosphorus concentrations in runoff to the permitted discharge limits under the Lake Okeechobee regulatory program. The second scenario changed current land uses to native rangeland with an estimated annual offsite total phosphorus areal loading rate of 0.114 kg/ha. These two scenarios are hypothetical with assumed concentration values and loading rate. Model results showed that the first management scenario reduced the average annual phosphorus load to the lake by an estimated 15 tonnes. The second scenario reduced the average annual phosphorus load to the lake by an estimated 21 tonnes.     

ANALYSIS OF LAKE-BOTTOM SEDIMENT TO ESTIMATE HISTORICAL NONPOINT-SOURCE PHOSPHORUS LOADS1

ABSTRACT Bottom sediment in Hillsdale Lake, Kansas, was analyzed to estimate the annual load of total phosphorus deposited in the lake from nonpoint sources. Topographic, bathymetric, and sediment-core data were used to estimate the total mass of phosphorus in the lake-bottom sediment. Available streamflow and water-quality data were used to compute the mean annual mass of phosphorus (dissolved plus suspended) exiting the lake. The mean annual load of phosphorus added to the lake from point sources was estimated from previous studies. A simple mass balance then was used to compute the mean annual load of phosphorus from non-point sources. The total mass of phosphorus in the lake-bottom sediment was estimated to be 924,000 kg, with a mean annual load of 62,000 kg. The mean annual mass of phosphorus exiting in the lake outflow was estimated to be about 8,000 kg. The mean annual loads of phosphorus added to the lake from point and nonpoint sources were estimated to be 5,000 and 65,000 kg, respectively. Thus, the contribution to the total mean annual phosphorus load in Hillsdale Lake is about 7 percent from point sources and about 93 percent from nonpoint sources.     

A STATISTICAL MODEL FOR SMALL LAKE WATER QUALITY MANAGEMENT1

ABSTRACT: Phosphorus loading tolerances of small lakes are analyzed by means of a statistical model of lake eutrophication based upon the work of Vollenweider and Dillon. Using a sample of 195 midwestern and eastern U. S. lakes, it was found that Vollenweider and Dillon's method of predicting the trophic status of relatively deep, slow-flushing lakes can be applied to shallower lakes with much shorter retention times. The statistical model used to replicate the results of Vollenweider and Dillon is stated in detail, for convenience of application to small lake water quality management problems. The model extends the Vollenweider and Dillon results by associating each alternative phosphorous loading with a probability that a given lake can achieve or maintain noneutrophis status. It is applicable to lakes for which only minimal data are available. The major policy conclusion is that the highly variable tolerance for phosphorus loading must be considered in legislating efficient effluent limitations. The paper concludes with a comparison to a recent contribution employing a similar approach.     

A FRAMEWORK FOR PHOSPHORUS TRANSPORT MODELING IN THE LAKE OKEECHOBEE WATERSHED1

ABSTRACT: A modeling framework was developed to determine phosphorus loadings to Lake Okeechobee from watersheds located north of the lake. This framework consists of the land-based model CREAMS-WT, the in-stream transport model QUAL2E, and an interface procedure to format the land-based model output for use by the in-stream model. QUAL2E hydraulics and water quality routines were modified to account for flow routing and phosphorus retention in both wetlands and stream channels. Phosphorus loadings obtained from previous applications of CREAMS-WT were used by QUAL2E, and calibration and verification showed that QUAL2E accurately simulated seasonal and annual phosphorus loadings from a watershed. Sensitivity and uncertainty analyses indicated that the accuracy of monthly loadings can be improved by using better estimates of in-stream phosphorus decay rates, ground water phosphorus concentrations, and runoff phosphorus concentrations as input to QUAL2E.     

AN ECONOMIC AND ENVIRONMENTAL EVALUATION OF ALTERNATIVE LAND DEVELOPMENT AROUND LAKES1

ABSTRACT: The objective of the study was to evaluate alternative land developments around New Hampshire lakes. Alternative development patterns, evaluated by their impacts on the lake area environment and area economy, included residential patterns, commercial patterns, and combinations of these two types. Phosphorus loading of the lake water was used as a proxy variable for changes in the lake water quality. Commercial developments yielded the highest revenues to the town and the local area. It also attracted the most lake users to the area as well as contributing the largest phosphorus loading in the lake waters. Residential developments, although contributing high revenues to the businessmen in the area, yielded less net income to the town. Phosphorus loading levels from residential developments were much lower than lake phosphorus loading by commercial developments.     

REVIEW OF A SEVENTEEN-YEAR CHLOROPHYLL RECORD AS IT PERTAINS TO THE TROPIIIC STATUS OF LAKE OKEECHOBEE,FLORIDA, USA1

ABSTRACT: A 17-year record of chlorophyll a at eight limnetic sampling stations was used to evaluate putative changes in the trophic status of Lake Okeechobee, a shallow polymictic lake located in the subtropical environment of South Florida. Significant spatial differences were observed in the temporal patterns and variability of chlorophyll a concentrations. The highest chlorophyll a values were found in the northern and northwestern regions of the lake. The center of the lake, subject to high levels of non-algal suspended solids, exhibited relatively low chlorophyll a values and coefficient of variation. The lowest chlorophyll a values were observed at the southernmost sampling station in the lake. This was also the station that showed a significant upward trend in annual mean chlorophyll a values over the 17-year period of record. Examination of the relationship between chlorophyll a and three key environmental variables (i.e., total phosphorus concentration, phosphorus loading, and lake stage) revealed significant correlations at two out of the eight stations. The overall results of this study indicate that spatial and temporal disparities in the distribution and dynamics of chlorophyll a in Lake Okeechobee mandate more temporally and spatially intense approaches to the evaluation of trophic state than used in previous studies.     

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.     

湖泊内源磷的释放与富营养化的植物修复

阐述了磷形态的不同分类方法及磷的形态、水生生物、温度、pH值、溶解氧和扰动等因素对湖泊沉积层磷释放的影响,并对植物修复富营养化湖泊的机理和影响植物修复的环境因素进行了探讨和分析,指出在加强控制外源污染的同时,因地制宜,选择适宜的水生植物种类,对湖泊进行植物修复,逐步恢复湖泊的自然净化能力,可有效抑制湖泊富营养化。     

THE DILUTION/FLUSHING TECHNIQUE IN LAKE RESTORATION1

ABSTRACT: Dilution/flushing has been documented as an effective restoration technique to restore eutrophic Moses and Green Lakes in Washington State. The dilution water added to both lakes was low in nitrogen and phosphorus content relative to the lake or normal input water. Consequently, lake nutrient content dropped predictably. Dilution or flushing rates were about ten times normal during the spring-summer periods in Moses Lake and three times normal on an annual basis in Green Lake. Improvement in quality (nutrients, algae, and transparency) was on the order of 50 percent in Moses Lake and even greater in Green Lake. The facilities for supplying dilution water were largely in place for the cited lakes; thus, costs for water transport were minimal. Available facilities, and therefore, costs, for water transport would usually vary greatly, however. Achieving maximum benefit from the technique may be more limited by availability of low nutrient water rather than facilities costs. Quality improvement may occur from physical effects of algal cell washout and water column instability if only high nutrient water is available.     

A Comparison of Alternative Strategies for Cost-Effective Water Quality Management in Lakes

Roughly 45% of the assessed lakes in the United States are impaired for one or more reasons. Eutrophication due to excess phosphorus loading is common in many impaired lakes. Various strategies are available to lake residents for addressing declining lake water quality, including septic system upgrades and establishing riparian buffers. This study examines 25 lakes to determine whether septic upgrades or riparian buffers are a more cost-effective strategy to meet a phosphorus reduction target. We find that riparian buffers are the more cost-effective strategy in every case but one. Large transaction costs associated with the negotiation and monitoring of riparian buffers, however, may be prohibiting lake residents from implementing the most cost-effective strategy. An erratum to this article is available at .     

ASSESSMENT OF NUTRIENT EFFECTS AND NUTRIENT LIMITATION IN LAKE OKEECHOBEE1

ABSTRACT: Lake Okeechobee, the third largest lake in the United States, is a shallow, mixing basin with annual total phosphorus concentrations ranging from 50–100 μg P/L. Data, mainly from unpublished agency reports, are analyzed to determine if nutrients limit phytoplankton, to describe spatial and temporal variability in trophic state parameters, and to evaluate conclusions obtained from empirical trophic state models. Algal bioassay experiments that have been used to assess nutrient limitation have produced equivocal results. However, seasonal minima in orthophosphorus and inorganic nitrogen indicate that both nutrients may be limiting seasonally. Strong, but reverse north-south gradients and large seasonal changes in phosphorus and nitrogen concentrations, show that empirical models based on annual phosphorus loadings or concentrations are not adequate to predict chlorophyll concentrations or other trophic state variables. Spatially-segmented, multi-class phytoplankton-nutrient models of seasonal phytoplankton responses that are coupled with hydrodynamic models may provide predictability in assessing effects of changing nutrient loads on phytoplankton composition and standing crop. Successful modeling efforts of responses to nutrients also must deal with resuspended and benthic algae, periphyton, and emergent and submergent aquatic plants that must play important trophic roles in some of the lake basin.     

CHANGE IN LAKE TROPHIC STATE AND INTERNAL PHOSPHORUS RELEASE AFTER ALUMINUM SULFATE APPLICATION1

ABSTRACT: Recovery of eutrophic lakes after nutrient diversion may be delayed if the lake experiences significant internal phosphorus (p) loading to the water column. A maximum dose of aluminum sulfate, defined herein, was applied to the anaerobic sediments of the hypolimnia of two dimictic Ohio lakes following septic tank diversion, with the objective of attaining long term control of the release of phosphorus to the water column from these sediments. The results were compared to a similar, downstream, untreated lake. Total phosphorus concentration declined sharply after treatment and has remained so through 1980 for both lakes, a period of 5 and 6 years of control, respectively. Internal P loading from anaerobic, hypolimnetic sediments was partially controlled by the treatment but there are other important sources, perhaps in the littoral zone, in these lakes. Algal biomass is Smaller and water transparency has increased. Both lakes became mesotrophic after treatment, as described by the Carlson (1977) trophic state index, and remain in that improved condition to date. No deleterious side effects were observed, although one lake experienced a significant decrease in diversity of planktonic microcrustacea and a lakeward extension of the macrophyte community. This method appears to be an effective and lasting means of accelerating the recovery of a eutrophic lake following nutrient diversion.     

Application of nutrient loading models to the analysis of trophic conditions in Lake Okeechobee,Florida

Lake Okeechobee (surface area = 1830 km², mean depth = 3.5 m), the largest lake in Florida, is eutrophic and has nitrogen and phosphorus loading rates in excess of nearly all established criteria. The lake is not homogeneous regarding trophic conditions, and spatial and temporal variations occur regarding nutrient limitation. Nonetheless, phosphorus loading rate and trophic state data fit reasonably well to various input-output models developed for temperate lakes. Modification of the models by regression analysis to fit data for Florida lakes resulted in improved predictions for most parameters. Analysis of nutrient management alternatives for the lake indicates that a 75% reduction of phosphorus loading from the largest source (the Taylor Creek-Nubbins Slough watershed) would reduce the average chlorophyll a concentration by less than 20%. Complete elimination of inputs from the largest nitrogen source (the Everglades Agricultural Area) would decrease the average nitrogen concentration in the lake by about 20%. Limitations of nutrient inputoutput models regarding analysis of trophic conditions and management alternatives for the lake are discussed.     

PRIORITIZING NONPOINT SOURCE PHOSPHORUS LOADING USING A GRASS-MODELING SYSTEM1

ABSTRACT: A UNIX-based windows application was developed to integrate a phosphorus transport model with the Geographic Resources Analysis Support System (GRASS). The system prioritizes potential phosphorus loading from fields or cells in a watershed and can evaluate the effects of alternate management practices on phosphorus yield. The model simulates phosphorus loading by using a daily mass balance on a unit-area basis and incorporates the effects from rainfall, topography, soil properties, fertilizer and animal waste application, and management. Model predictions include dissolved and sediment-bound phosphorus yield, runoff volume, and sediment yield. Within the integrated GRASS-modeling system, the user can obtain model input data, execute the model using various options, rank model input and out. put data, and display them as GRASS-based maps or data tables. All functions are menu driven, developed using C language and X-window tools to run on a SUN workstation platform. The system provides a powerful and efficient tool for prioritizing phosphorus loading from nonpoint sources.     

Dual Objective Control of Nutrient Loading into a Lake1

ABSTRACT: The control of nutrient loading into a water body is approached from a multiobjective viewpoint. The example of phosphorus (P) loading into Lake Balaton, Hungary, is used as a case study. The element P is chosen because it appears to be the limiting factor of eutrophication in the lake considered, as in many other lakes. About one-half of P loading originates from nonpoint sources; furthermore, the mechanism is poorly known and only few observation data are available. The objective of eutrophication control is to minimize P loading, while the objective of watershed management is to maximize agricultural revenue. These two objectives often appear to be in conflict. A discrete set of alternative control methods is defined, consisting in controlling a mix of the following elements: point sources, runoff, fertilizer type and application, cropping management, erosion, and sedimentation. The system dynamics is provided by a previously developed stochastic model, whose output is an empirical prohability density function (pdf) of P-loading reflecting the control policy. A compromise solution of “satisfactum” can then be chosen as a mix of the best ranked policies.     

Usefulness of natural regions for lake management: Analysis of variation among lakes in northwestern Wisconsin,USA

A map of summer total phosphorus in lakes was compiled recently for a three-state area of the upper Midwest for purposes of identifying regional patterns of total phosphorus in lakes and attainable lake trophic state. Spatial patterns in total phosphorus from approximately 3000 lakes were studied in conjunction with maps of geographic characteristics that tend to affect phosphorus balance in lakes to identify regions of similarity in phosphorus concentrations in lakes or similarity in the mosaic of values as compared to adjacent areas. While degrees of relative homogeneity are apparent at many scales, the map was designed at a scale that would yield regions with sufficient homogeneity to be useful for lake management throughout the area. In this study, data from 210 lakes in a 1560-mi² area in northwestern Wisconsin, sampled by the Wisconsin Department of Natural Resources in the spring of 1988 (subsequent to the compilation of the phosphorus map), were examined to: (1) substantiate the existence of the regions depicted on the map in northwest Wisconsin, (2) determine the nature and relative precision of the regional boundaries, (3) determine the relative importance of natural and anthropogenic watershed characteristics, lake types, lake area, and lake depth in explaining within-region differences in lake phosphorus, and (4) demonstrate how the regions might be used by local lake managers.     

DO WETLANDS BEHAVE LIKE SHALLOW LAKES IN TERMS OF PHOSPHORUS DYNAMICS?1

ABSTRACT: The applicability of empirical relationships governing phosphorus (P) retention and nutrient assimilation in lakes and reservoirs was extended to include free surface water wetland treatment systems. Mixed reactor models have been used in lakes to predict steady state P concentration, characterize trophic state, compare P‐dynamics, and predict permissible P‐loading rates. Applying lake models to free surface water wetlands treatment systems, it was found that: sedimentation rates, loading rates, and settling velocity in these wetlands, and their typology are comparable to their lake counterparts. The analyses also suggest that phosphorus removal efficiency in a free surface water wetland treatment system is independent of trophic status, and similar to lakes, these wetlands can be classified according to their trophic state. Oligo‐and eutrophic wetland treatment systems can be defined by low and high TP inflow concentrations, respectively. In this study, olig‐otrophic status is defined as systems receiving inflow P‐loading less than 0.10 g m^‐2 year‐¹, and their P inputs are mainly derived from agricultural and stormwater runoff. Eutrophic treatment systems, on the other hand, are defined as those receiving inflow P‐loading higher than 0.20 g m² year‐¹, and their inputs are mainly derived from industrial and municipal wastewater. The comparability found between lakes and free surface water wetlands treatment systems raises the question: should we consider these wetlands “shallow lakes?”     

PHOSPHORUS LOADING TO A MOUNTAIN RESERVOIR IN SOUTHERN CALIFORNIA1

Phosphorus loading from precipitation and more than a dozen tributaries of Big Beat Lake, Woman, was determined for the period from January to December 1978. Direct precipitation contributed 1120 kg·P·yr^-1 (0.096 g P·m^-2·yr^-1) while tributary runoff contributed 21,560 kg for a total P loading of 1.84 g P·m^-2 Rathbone creek, although accounting for only 4 percent of the hydro-logic input to Big Bear Lake, contributed >27 percent of the annual phosphorus load. Phosphorus loading increased with increased impervious geology and increased development. Nitrogen loading exhibited similar loading patterns. Big Beat Lake is currently eutrophic and is likely to remain eutrophic. Calculations based on Vollenweider's critical phosphorus loading concept indicated that tributary P-loading would have to be reduced by >95 percent to achieve mesotrophic conditions. The completion of Big Bear Dam created a “naturally” eutrophic re mix which dl require proper management to enhance its resource potential.     

WATER QUALITY TRENDS IN LAKE TOHOPEKALIGA,FLORIDA, USA: RESPONSES TO WATERSHED MANAGEMENT1

ABSTRACT: Water quality in eutrophic Lake Tohopekaliga, Florida, improved markedly from 1982 to 1992 as a result of reductions in phosphorus and nitrogen loading to the lake. Annual budgets of water, chloride, phosphorus and nitrogen were constructed for the lake, and indicate it is a sink for phosphorus and a source for nitrogen. Water column concentrations of total phosphorus, soluble reactive phosphorus, total nitrogen, dissolved inorganic nitrogen, and chlorophyll a all declined as external inputs of nutrients decreased. Water column nitrogen: phosphorus ratios have increased, suggesting a probable shift from nitrogen- to phosphorus-limitation. This apparent shift in nutrient limitation status also is supported by comparisons of the mean Trophic State Indices for phosphorus, nitrogen, and chlorophyll a. These improvements in water quality are attributed to the diversion of wastewater treatment plant effluent from the lake, and the increased use of wet retention ponds for stormwater runoff.     

Summer total phosphorus in lakes: A map of Minnesota,Wisconsin, and Michigan,USA

A map of summer total phosphorus in lakes has been compiled for Minnesota, Wisconsin, and Michigan to clarify regional patterns in attainable lake trophic state. Total phosphorus was used as a measure of lake trophic state because: (1) phosphorus plays a central role in controlling the overall fertility of most lakes, (2) total phosphorus values are available for a great number of lakes, and (3) phosphorus is measured in a consistent manner. The maps were compiled using patterns of total phosphorus data and observed associations between these data and geographic characteristics including physiography, land use, geology, and soils. Regions depicted on the map represent areas of similarity in phosphorus concentrations in lakes, or similarity in the mosaic of values, as compared to adjacent areas. Within each region, differences in total phosphorus can be compared to natural and anthropogenic factors to determine the types of lakes representative of each region, the factors associated with differences in quality, and the realistically attainable phosphorus levels for each type of lake.