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?”     

A CARLSON-TYPE TROPHIC STATE INDEX FOR NITROGEN IN FLORIDA LAKES1

: A data base consisting of predominantly nitrogen limited Florida lakes from the National Eutrophication Survey (NES) was used to develop a trophic state index based on total nitrogen concentration. This index was compared with Carlson's (1977) index based on total phosphorus concentration, and the lesser of the two values for each lake was averaged with indices based on Secchi disk transparency and chlorophyll a concentration to assess the trophic state of the 40 Florida NES lakes.     

The Contribution of Marsh Zones to Water Quality in Dutch Shallow Lakes: A Modeling Study

Many lakes have experienced a transition from a clear into a turbid state without macrophyte growth due to eutrophication. There are several measures by which nitrogen (N) and phosphorus (P) concentrations in the surface water can be reduced. We used the shallow lake model PCLake to evaluate the effects of three measures (reducing external nutrient loading, increasing relative marsh area, and increasing exchange rate between open water and marsh) on water quality improvement. Furthermore, the contribution of different retention processes was calculated. Settling and burial contributed more to nutrient retention than denitrification. The model runs for a typical shallow lake in The Netherlands showed that after increasing relative marsh area to 50%, total phosphorous (TP) concentration in the surface water was lower than the Maximum Admissible Risk (MAR, a Dutch government water quality standard) level, in contrast to total nitrogen (TN) concentration. The MAR levels could also be achieved by reducing N and P load. However, reduction of nutrient concentrations to MAR levels did not result in a clear lake state with submerged vegetation. Only a combination of a more drastic reduction of the present nutrient loading, in combination with a relatively large marsh cover (approximately 50%) would lead to such a clear state. We therefore concluded that littoral marsh areas can make a small but significant contribution to lake recovery.     

PREDICTION OF CHLOROPHYLL A CONCENTRATIONS IN FLORIDA LAKES: THE IMPORTANCE OF PHOSPHORUS AND NITROGEN1

ABSTRACT: Models for the prediction of chlorophyll a concentrations were developed and tested using data on 223 Florida lakes. A statistical analysis showed that the best model was log (Chl a) =?2.49 + 0.269 log (TP) + 1.06 log (TN) or log (Chl a) =?2.49 + 1.06 log (TN/TP) + 1.33 log (TP) where Chl a is the chlorophyll a concentration (mg m^-3), TP is the total phosphorus concentration (mg m^-3) and TN is the total nitrogen concentration (mg m^-3). The model yields unbiased estimates of chlorophyll a concentrations over a wide range of lake types and has a 95 percent confidence interval of 29–319 percent of the calculated chlorophyll a concentrations. Other models, especially the published Dillon-Rigler and Jones-Bachmann phosphorus-chlorophyll models, are less precise when applied to Florida lakes. The data support the hypothesis that nitrogen is an important limiting nutrient in hypereutrophic lakes.     

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.     

Source and Delivery of Nutrients to Receiving Waters in the Northeastern and Mid‐Atlantic Regions of the United States1

Moore, Richard B., Craig M. Johnston, Richard A. Smith, and Bryan Milstead, 2011. Source and Delivery of Nutrients to Receiving Waters in the Northeastern and Mid‐Atlantic Regions of the United States. Journal of the American Water Resources Association (JAWRA) 47(5):965‐990. DOI: 10.1111/j.1752‐1688.2011.00582.x Abstract: This study investigates nutrient sources and transport to receiving waters, in order to provide spatially detailed information to aid water‐resources managers concerned with eutrophication and nutrient management strategies. SPAtially Referenced Regressions On Watershed attributes (SPARROW) nutrient models were developed for the Northeastern and Mid‐Atlantic (NE US) regions of the United States to represent source conditions for the year 2002. The model developed to examine the source and delivery of nitrogen to the estuaries of nine large rivers along the NE US Seaboard indicated that agricultural sources contribute the largest percentage (37%) of the total nitrogen load delivered to the estuaries. Point sources account for 28% while atmospheric deposition accounts for 20%. A second SPARROW model was used to examine the sources and delivery of phosphorus to lakes and reservoirs throughout the NE US. The greatest attenuation of phosphorus occurred in lakes that were large relative to the size of their watershed. Model results show that, within the NE US, aquatic decay of nutrients is quite limited on an annual basis and that we especially cannot rely on natural attenuation to remove nutrients within the larger rivers nor within lakes with large watersheds relative to the size of the lake.     

EMPIRICAL MODELS FOR TROPHIC STATE IN SOUTHEASTERN U.S. LAKES AND RESERVOIRS1

ABSTRACT: A cross-sectional data set of 80 lakes and reservoirs in nine southeastern states was examined to specify and parameterize trophic state relationships. The relationships fitted are based on measurements of several limnological variables taken over the course of a growing season or year in each of the lakes. The trophic state models relate phosphorus and nitrogen loading to inlake phosphorus and nitrogen concentrations, which in turn are related to maximum chlorophyll level, Secchi disk depth, dominant algal species, and hypolimnetic dissolved oxygen status. Due to the empirical nature of the study, causal conclusions are limited; rather, the models are most useful for prediction of average growing season conditions related to trophic state.     

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.     

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.     

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.     

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.     

LONG-TERM EQUILIBRIUM PHOSPHORUS CONCENTRATIONS IN THE EVERGLADES AS PREDICTED BY A VOLLENWEIDER-TYPE MODEL1

ABSTRACT: Anthropogenic phosphorus loading, mainly from the Everglades Agricultural Area (EAA), is believed to be the primary cause of eutrophication in the Everglades. The state of Florida has adopted a plan for addressing Everglades eutrophication problems by reducing anthropogenic phosphorus loads through the implementation of Best Management Practices (BMPs) in agricultural watersheds and the construction of stormwater treatment areas (STAs). Optimizing the effectiveness of these STAs for reducing phosphorus concentrations from agricultural runoff is a critical component of the District's comprehensive Everglades protection effort. Therefore, the objective of this study was to develop a simple tool that can be used to estimate STAs’performance and evaluate management alternatives considered in the Everglades restoration efforts. The model was tested at two south Florida wetland sites and then was used to simulate several management alternatives and predict ecosystem responses to reduced external phosphorus (P) loadings. Good agreement between model predictions at the two wetland sites and actual observations indicated that the model can be used as a management tool to predict wetlands’response to reductions in external phosphorus load and long-term P levels in aquatic ecosystems. Model results showed that lowering P content of the Everglades Protection Area (EPA) depends on reducing P loads originating from EAA discharges, not from rainfall. Assuming no action is taken (e.g., no BMPs or STAs implemented), the steady state model predicted that the average concentration within the modeled area of the marsh would reach 20 μg L^?1 within five years. With an 85 percent reduction in P loading, the steady-state model predicted that Water Conservation Area 2A (WCA-2A) P concentration will equilibrate at approximately 10 μ L^?1, while elimination of all loadings is projected to further reduce marsh P to values less than 10 μg L^?1.     

Sediment-based investigation of naturally or historically eutrophic lakes -- implications for lake management

Implementation of the EU Water Framework Directive will call for new lake monitoring and management strategies. Therefore, different methods need to be tested in order to achieve reliable assessment of lake background conditions and water quality. Sediment-based techniques provide one such tool for lake management. In this work, 10 lakes, presumed to be naturally eutrophic, were investigated with a paleolimnological short core study. The aim of the study was to examine the composition of the diatom assemblages in their natural state, estimate their change over time and assess the background nutrient levels. One sediment profile from each lake was divided into six sub-samples that were analyzed for diatoms (60 samples). Diatom-based inference models were applied to reconstruct the past total phosphorus concentration and assess the eutrophication. The results indicated that all the lakes studied had already been nutrient-rich before the impact of modern agriculture. However, diatom assemblages have changed remarkably over time and total phosphorus concentrations have generally increased, so at present only two of the study lakes are close to their natural status. This suggests that naturally eutrophic lakes will probably require management actions to fulfill the new directive requirements in the future.     

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.     

NUTRIENT LOADS TO WISCONSIN LAKES: PART II. RELATIVE IMPORTANCE OF NUTRIENT SOURCES1

ABSTRACT: A comparison of municipal wastewater treatment plant (WWTP) and nonpoint source nutrient loads to Wisconsin's 14,927 inland lakes was performed. Only 65 of the 2,925 Wisconsin lakes having surface areas of at least eight ha and a maximum depth of at least 2.4 m had one or more WWTP's located within 40 km upstream; 99 of Wisconsin's 477 WWTP's were identified to be upstream of these 65 lakes. WWTP total nitrogen and total phosphorus loads to these 65 lakes were estimated using per capita influent loads and removal efficiencies based on wastewater treatment types. Nonpoint source nutrient loads were calculated utilizing nutrient export coefficients derived specifically for Wisconsin. Total nitrogen inputs to the lakes were dominated by nonpoint sources. The effectiveness of various phosphorus control programs to produce water quality improvements visible to the public was estimated to be as follows (going from most to least effective): municipal phosphorus removal and agricultural reductions, municipal phosphorus removal alone, agricultural reduction plus phosphate detergent ban, agricultural reductions alone, and phosphate detergent ban alone. The last option would not be expected to produce water quality improvement visible to the public in any Wisconsin lakes. The differences between the distributions in Wisconsin of population and inland lakes highlights the need to consider regional characteristics in any statewide water quality management plan.     

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.     

WATER QUALITY CHARACTERISTICS OF AGRICULTURAL PUMPAGE IN THE UPPER ST. JOHNS RIVER,FLORIDA1

Several large agricultural pumps, located in the upper St. Johns River Basin, Florida, and representative of the numerous pumps operating in the basin, were monitored during the spring and summer of 1982. These pumps have rated capacities ranging from 36 to 334 ft³/s and drain various quantities of improved pasture, row crop, and citrus land uses. The combined total pumping capacity of the pumps in this study is approximately equal to the average flow at US 192, near Melbourne (691 cfs). Results indicate high nutrient and suspended solids loading to the river, but the relative magnitude of each parameter varies with pump site and date. The row crop/Mary A pump (267 ft³/s capacity) exhibited the poorest water quality of the sampled pumps and appeared to have the greatest pollutional potential. The average suspended solids loading rate from the Mary A pump was high (37,900 Kg/day). The average total nitrogen (TN) and total phosphorus (TP) discharge concentrations at this pump were also high, with values of 3.96 mg/L and 0.79 mg/L, respectively. As expected, nutrient loading rates reflected discharge rates, to a large degree. Average TN loading rates for the pumping stations varied from 86 to 1935 Kg/day while TP loading ranged from 7 to 390 Kg/day. Nutrients from pumping are contributing factors to the increasing aquatic plant growth and algal blooms in the area. Poor quality discharge water, as well as rapid rises in water level from the cumulative discharges resulting in dead marsh vegetation and accompanying oxygen sags, have been suggested as causative factors for fish kills in the area.     

PREDICTIVE MODELS FOR THE BIOMASS OF BLUE-GREEN ALGAE IN LAKES1

In lakes which experience water quality problems due to the nuisance growth of blue-green algae, summer concentrations of chlorophyll a may not always be a meaningful measure of water quality for making management decisions. Models for the prediction of summer mean blue-green algal biomass were thus developed from data collected from five systems located in North America and Sweden. It is suggested that the model of choice is log BG =?0.142 + 0.596 log TP – 0.963 log Z, where BG is the biomass of blue-green algae (g m^?3), TP is the concentration of total phosphorus (mg m^?3), and Z is the mean depth of the lake (m). When coupled to current loading models, this model can potentially be used to assess the impacts of phosphorus loading reductions on threshold odor in water supplies.     

INPUT/OUTPUT MODELS AS DECISION AIDS FOR LAKE RESTORATION1

ABSTRACT: Over the past several years, input/output models have been used increasingly as decisionmaking aids in the design of lake restoration activities because they provide an approximation of the link between nutrient influx and lake trophic status. To evaluate the applicability of these models as design tools, a study was conducted in which “before” and “after” data were obtained for 25 lakes which experienced reductions in nutrient inflow, and comparisons were made of observed and predicted changes in lake conditions. Three input/output models were used as predictive tools to describe lake response: those reported by Dillon and Rigler (1974) and by Vollenweider (1975, 1976). Based on described trophic states of oligotrophic, mesotrophic, and eutrophic, it was found that all three models yielded accurate predictions for at least 70 percent of the study lakes. The model of Vollenweider (1976) performed slightly better than the other two (80 percent correct) on the data set studied.