Spatial-Dynamic Modeling of Algal Biomass in Lake Erie: Relative Impacts of Dreissenid Mussels and Nutrient Loads

Over the past several decades, reductions in phytoplankton stocks and increased water clarity in Lake Erie have resulted from phosphorus load abatement and the introduction of zebra (Dreissena polymorpha) and quagga mussels (D. bugensis). The relative impacts of these developments and their implications for lake management have remained difficult to delineate. To address this issue, we numerically model the complex biophysical interactions occurring in Lake Erie using a two-dimensional hydrodynamic and water quality model that is extended to include dreissenid mussel and zooplankton algorithms. The model reasonably simulates longitudinal trends in water quality as well as the dynamics of central basin hypoxia. Phosphorus is the limiting nutrient through the euphotic zone and its control decreases the algal growth rate and biomass ( ～ 55–60%). Filter feeding by dreissenid mussels also decreases algal biomass ( ～ 25–30%), simultaneously stimulating increased net algae growth through enhanced algal consumption and subsequent phosphorus recycling. Effective recycling implies that algae stocks are ultimately regulated by external phosphorus loads. Returning phosphorus loads to pre-abatement 1960s levels, in the presence of dreissenid mussels, results in a western basin algae concentration of ～ 0.7?mg?dry?weight?L?1 with a potential for nuisance algae growth.     

Sediment Oxygen Demand and Nutrient Fluxes for a Tropical Reservoir in Singapore

Sediment oxygen demand (SOD) and nutrient flux studies were conducted for a tropical reservoir in Singapore in order to determine the approximate SOD and nutrient release rates from the sediments. SOD values obtained from laboratory experiments ranged from 1.4 to 3.3?g?O2/m2-day. Similar results were also obtained by calculating SOD values from in situ DO measurements taken in the field. The nutrient flux study was performed in the laboratory at a constant temperature of 25°C in oxic and anoxic columns. Except for nitrate+nitrite, higher nutrient release rates were generally observed under anoxic conditions. The ammonium release rate was 0.06?g?O2/m2-day under oxic conditions and 0.117?g?O2/m2-day under anoxic conditions. The nitrate flux rate was 0.17?g?O2/m2-day under oxic conditions but was negligible under anoxic conditions. Orthophosphate flux results were negative throughout the oxic incubation implying that sediments acted as a sink. The release rate of orthophosphate was 0.007?6?g?O2/m2-day under anoxic conditions.     

Development and Application of a Phosphorus Model for a Shallow Oxbow Lake

A three-dimensional numerical model was developed for simulating the phosphorus concentration in shallow lakes. In this model, the computational domain was divided into two parts: the water column and the bed sediment layer. The processes of mineralization, settling, adsorption, desorption, bed release (diffusion), growth, and death of phytoplankton were taken into account, and the concentration of organic phosphorus, phosphate, and related water quality constituents was simulated. The concentrations of adsorbed (particulate) and dissolved phosphate due to adsorption-desorption were calculated using two formulas derived based on the Langmuir equation. The release rate of phosphorus from the bed sediment layer was calculated by considering the effects of the concentration gradient across the water-sediment interface, pH, temperature, dissolved oxygen concentration, and flow conditions. The adsorption and desorption of phosphate from sediment particles, as well as its release from bed sediment, were verified using laboratory experimental data. The model was calibrated and applied to Deep Hollow Lake in the Mississippi alluvial plain. The simulated trends and magnitudes of phosphorus concentration were compared with field observations. The simulation results show that there are strong interactions between sediment-related processes and phosphorus concentration.     

Retention of Sediment and Nutrient Loads with Peak Runoff Control

The purpose of this research was to evaluate peak runoff control as a water protection method to reduce sediment and nutrient loads. Increased eutrophication of surface waters and risk of floods demands cost effective methods to reduce pollutant input and risks of flooding. With the peak runoff control it is possible to cut the main peaks and store the runoff water temporarily in ditches. The method decreases the suspended solids (SS) and nutrient loads by reducing flow velocities, and improving the settling of sediment particles. The method was tested in two heavily drained adjacent peat harvesting areas suffering considerable erosion. The peak flows were cut by 27–87%, the SS load by 61–94%, the total nitrogen (Ntot) by 45–91%, and the total phosphorus (Ptot) load by 47–88%. The peak runoff control method operated most effectively during extreme events when most of the SS load is transported. A detailed particle analysis of runoff water showed that water detention reduced the median particle size of SS load as the largest particles settle. The results clearly indicate that the peak runoff control is an effective method to control the sediment loads and peak flows from peatland drainage.     

Prediction of Nutrient Concentrations in Urban Storm Water

Excessive quantities of nutrients in urban storm-water runoff can lead to problems such as eutrophication in receiving water bodies. Accurate process based models are difficult to construct due to the vast array of complex phenomena affecting nutrient concentrations. Furthermore, it is often impossible to successfully apply process based models to catchments with limited or no sampling. This has created the need for simple models capable of predicting nutrient concentrations at unmonitored catchments. In this study, simple statistical models were constructed to predict six different types of nutrients present in urban storm-water runoff: ammonia (NH3), nitrogen oxides (NOx), total Kjeldahl nitrogen, total nitrogen, dissolved phosphorus, and total phosphorus. Models were constructed using data from the United States, collected as a part of the Nationwide Urban Stormwater Program more than two decades ago. Comparison between the models revealed that regression models were generally more applicable than the simple estimates of mean concentration from homogeneous subsets, separated based upon land use or the metropolitan area. Regression models were generally more accurate and provided valuable insight into the most important processes influencing nutrient concentrations in urban storm-water runoff.     

Development and Evaluation of a Copolymer for Removal of Taste and Odor Causing Compounds from Lake Michigan Water

In this study, a copolymer, cyclodextrin/epichlorohydrin was synthesized and used as an adsorbent to remove two taste and odor causing compounds, namely, MIB and geosmin from the Lake Michigan water. The removal efficiency of these compounds using the copolymer on average was 74.5% for MIB and 77.5% for geosmin as compared to the removal efficiency using powdered activated carbon that resulted in 52.9% and 67% removal, respectively, for the same compounds. The removal efficiencies were examined for an initial concentration range of 20 to 120?μg/L for both MIB and geosmin.     

Sediment Resuspension and Hydrodynamics in Lake Okeechobee during the Late Summer

In this study, in order to better understand the mechanisms affecting sediment resuspension, extensive data sets were collected in September and October of 2002 including wind velocity, wave, current velocity, water temperature, total suspended solid, suspended sediment concentration, and total phosphorus. Analyses of these data indicate that waves are the dominant factors in sediment resuspension while wind-induced currents are the primary forces to transport suspended sediments. Surface and bottom currents frequently flow in opposite directions, forming a stratified water column. A time lag exists between currents near lake bottom and wind forcing at the surface. The diurnal thermal stratification occurs in the deep region of the lake. A time lag is also found between suspended sediment concentration and wind speed. The study provides valuable storm-event data and mechanism analyses, which can improve our understanding of the lake circulation, wave dynamics, and their impact on sediment resuspension and vertical mixing in Lake Okeechobee. The data resulting from this study will be used to validate the Lake Okeechobee Environment Model which is used to predict the impacts of different management scenarios on lake activities.     

Resuspension of Mercury-Contaminated Sediments from an In-Lake Industrial Waste Deposit

The resuspension and transport of particulate mercury (HgP) from a nearshore industrial waste deposit to the pelagic zone of Onondaga Lake, N.Y., was investigated using an array of sediment traps radiating from the deposit, and quantified through application of a steady-state mass balance model. Time-averaged downward fluxes of suspended solids and HgP decreased in the offshore direction, indicating a nearshore source. Strong temporal variations in resuspension were documented and were linked to the dynamics of wind-driven wave action, as quantified by a validated surface wave model. A simple steady-state model of offshore transport from the resuspension zone, which assumes a balance between offshore transport and settling, was used to analyze sediment trap data. The resulting larger, and likely more accurate, estimate of HgP resuspension ( ～ 60?g?day?1) represents the dominant contemporary source to the water column. This result supports the planned remediation of this source as a part of a Superfund cleanup project.     

Spatial Variation of Sediment Sulfate Reduction Rates in a Saline Lake

Devils Lake in North Dakota is a terminal, multibasin, saline lake with an overall surface area that is currently approximately 44,520?ha (110,000?acres). Lake elevation has increased by more than 7?m within 10?years, and vast areas of prairie and cropland have been flooded. The lake is rich in sulfate, and water column sulfate concentrations are relatively uniform within each of the five major basins, but increase from 3.1?mM (300?mg/L) in West Bay to 31?mM (3,000?mg/L) in East Devils Lake. Sediment cores were collected from three of the basins at different water depths, and used in laboratory studies to evaluate the spatial distribution of sulfate-reducing bacteria (SRB) activity in the lake sediments. The high sulfate concentrations within the experimental sediment cores suggest that the activity of SRB is limited by the availability of suitable electron donors rather than by the availability of sulfate and that SRB activity can be defined by a zero-order volumetric rate constant (K0). Experimentally determined K0 values ranged from 11?to?88?mmol SO42? m?3?day?1. The water depths from which sediment cores were collected in Devils Lake are related to the elapsed time since inundation by the rising lake level. It was found that time since inundation influences the observed K0 value. Mean K0 values for cores from an average depth of 4.8?m (submergence time of about 5?years), and 9.4?m (submergence time of about 28?years) were 62 and 17?mmol SO42? m?3?day?1, respectively. The significant difference (two-tailed t-test, p<0.05) suggests that SRB activities in the Devils Lake sediments change with submergence times. A uniform sulfate reduction rate applied to all Devils Lake sediments is therefore only a crude approximation of reality.     

Dissolved Oxygen and pH Modeling of a Periphyton Dominated, Nutrient Enriched River

Nutrient enrichment of the South Umpqua River, Oregon was linked to periphyton growth and large diel fluctuations in dissolved oxygen and hydrogen ion (pH) concentrations using the water quality model QUAL2Kw. The available data provide a good case study for the relatively new water quality model. QUAL2Kw simulates a dynamic diel heat budget and water quality kinetics for a one-dimensional, steady-flow system and is part of a family of models meant to serve as an update to the widely used QUAL2E. The model was used to quantify nonpoint source loading, determine the pollutant of concern, estimate natural conditions, and calculate a phosphorus total maximum daily load during summer, low-flow conditions. Control of both nonpoint and point sources is required to achieve the low instream phosphorus concentrations necessary to meet water quality criteria. To our knowledge, this is the first paper that reports on the application of a model for computing the maximum allowable load necessary to manage the diel variation in pH.     

Depth-Dependent Dispersion Coefficient for Modeling of Vertical Solute Exchange in a Lake Bed under Surface Waves

Variable pressure at the sediment/water interface due to surface water waves can drive advective flows into or out of the lake bed, thereby enhancing solute transfer between lake water and pore water in the lake bed. To quantify this advective transfer, the two-dimensional (2D) advection-dispersion equation in a lake bed has been solved with spatially and temporally variable pressure at the bed surface. This problem scales with two dimensionless parameters: a “dimensionless wave speed” (W) and a “relative dispersivity” (λ). Solutions of the 2D problem were used to determine a depth-dependent “vertically enhanced dispersion coefficient” (DE) that can be used in a 1D pore-water quality model which in turn can be easily coupled with a lake water quality model. Results of this study include a relationship between DE and the depth below the bed surface for W>50 and λ ? 0.1. The computational results are compared and validated against a set of laboratory measurements. An application shows that surface waves may increase the sediment oxygen uptake rate in a lake by two orders of magnitude.     

PCB Volatilization from Sediments

The loss of polychlorinated biphenyls (PCBs) from sediment by volatilization is currently under scrutiny by polluters, regulators, and researchers. In this research, a one-dimensional mathematical model for the volatilization of PCBs from sediment was developed. The model considers a system with three phases: A water-saturated PCB contaminated sediment, the overlying water, and air above the water. A simple microcosm consisting of sediment, water and air that allows for (pseudo)-one-dimensional transport of PCB from the sediment to the gas phase was utilized to perform PCB transport studies using two PCB congeners: 4,4′-dichlorobiphenyl (DCB) and 2, 2′,4,4′,5,5′-hexachlorobiphenyl (HCB). The experimental data on DCB were used to calibrate and validate the mathematical model. The calibrated model was then used to simulate the effect of sediment layer thickness, depth of the overlying water, and the level of contamination on the rate of DCB volatilization.     

Case Study: Modeling of Sediment Transport and Wind-Wave Impact in Lake Okeechobee

There are increasing demands for reliable engineering tools for sediment modeling and water resources management. The Lake Okeechobee environmental model (LOEM), which was calibrated and verified to simulate sediment resuspension and transport in Lake Okeechobee, Florida, is a dependable tool to meet those demands. The LOEM contains 2,126 horizontal grid cells and 5 vertical layers. The primary hydrodynamic and sediment transport driving forces are wind waves, surface wind stresses, and inflows/outflows. The LOEM was calibrated and verified, using two sets of observed data from May 16 to June 13, 1989 and January 17 to March 3, 2000, respectively. The model results indicate that sediment solids are resuspended primarily by wind–wave action and transported by lake circulation. The strong relationship between significant wave height and suspended sediment concentration in the lake indicates that sediment resuspension is primarily driven by wind-induced waves. To simulate this sediment resuspension, the processes of wind–wave- and current-induced bottom shear stresses on the lake bed were added to the LOEM. Once resuspended, the suspended sediment is transported to different areas of the lake by wind-induced currents. The importance of wind-wave, currents, and their interactions to sediment transport is included and discussed. By using the comprehensive data set for model calibration and verification, the LOEM model is proven to be a useful tool to water sources management in the lake.     

Cost-Effective Approach for Continuous Major Ion and Nutrient Concentration Estimation in a River

Major ion and nutrient concentration monitoring and estimation are important factors in management and interpretations on river health, particularly in the context of total maximum daily load limits. Spatial and temporal (daily, seasonally, yearly, etc.) variations commonly complicate investigations and can produce unrepresentative results, particularly in systems with large seasonal or daily variation in river parameters or concentrations as a result of physical loading or biogeochemical activity (e.g., photosynthesis and respiration). This study combines an observed relationship between electrical conductivity and major ions, including nitrate, and continuous colorimetric estimation of ammonium and phosphate to permit cost-effective real-time estimation of river concentrations for major ions and nutrients for surface water quality monitoring. Data collected from sites both up- and downstream of a major city were used to evaluate the method. Constant total dissolved solids (TDS) to electrical conductivity (EC) relationships were observed at both the upgradient (TDS = 696EC; r2 = 0.93) and downgradient (TDS = 684EC; r2 = 0.90) sites. The resulting predicted estimations of major ion and nutrient concentrations for each site had average errors of less than 5%. Combining this method with a modified continuous colorimetric method for ammonia and phosphate allows for the continuous estimation of major ion and nutrient concentrations in a river system.     

Eutrophication Model for the Patuxent Estuary: Advances in Predictive Capabilities

A robust eutrophication and sediment diagenesis model has been developed for the Patuxent Estuary to study the impact of different nutrient loadings on phytoplankton biomass and dissolved oxygen (DO) levels. The modeling approach was to begin with an existing water quality model (CE-QUAL-W2) for the Patuxent Estuary (hereafter referred to as the Estuary). First, formulations for the water column kinetics were completely replaced with routines based on the WASP/EUTRO5 water quality model. Then, a sediment diagenesis component was added to simulate the accumulation and mineralization of organic matter in the sediment, the generation of sediment oxygen demand, and the flux of phosphate and ammonia from the sediment. Loadings from the tributaries for nutrients and flow were based on a combination of watershed modeling and sampling by scientists at the Smithsonian Environmental Research Center. The new model was able to reproduce the ambient water quality data from 1997 to 1999 by adequately simulating the high concentrations of phytoplankton and low DO levels in the Estuary. The model was then used to evaluate the response to various hypothetical nutrient loading scenarios. Model results show that phytoplankton growth in the upper Estuary is much more sensitive to nutrient loading from tributaries than in the lower estuary. Further, model results indicate that DO concentrations in the lower Estuary are largely influenced by levels of nutrients and organic carbon at the mouth of the Estuary.     

Enhancement of Aromatic Hydrocarbon Biodegradation by Toluene and Naphthalene Degrading Bacteria Obtained from Lake Sediment: The Effects of Cosubstrates and Cocultures

Toluene and naphthalene degrading (ND) bacteria, obtained from contaminated lake sediment, were used to degrade both monoaromatics and polycyclic aromatic hydrocarbons (PAHs) and the effects of cosubstrates and cocultures were examined. When toluene and naphthalene enrichments were used, the effect of the substrate interaction on their metabolism was found to be inhibitory and yet the cocultures were stimulatory, especially for toluene enrichment degradation of naphthalene (with toluene). Pseudomonas putida M2T14, a toluene degrading isolate, could efficiently degrade benzene and toluene but not naphthalene. Nonetheless, when toluene was present, this monoaromatic degrader became capable of degrading PAHs, among which the methyl substituted PAHs (mPAHs) were preferred to their corresponding unsubstituted PAHs (uPAHs). Pseudomonas azelaica ND isolate could degrade benzene, toluene, and all test PAHs. Although the uPAHs were preferred, the degradation rates of mPAHs were greatly increased via substrate interactions with naphthalene. The interaction modes of dual aromatic hydrocarbons (AHs) degraded by P. putida M2T14 and P. azelaica ND were cometabolism, synergism, no effect, inhibition, and antagonism. However, when a negative effect of biodegradation from the interaction of these AHs was found on one isolate, a positive effect would be found on the other. When benzene was present, it exhibited inhibitory effects on aromatic hydrocarbon biodegradation by M2T14 and ND isolates. A study of the biodegradation of the ternary mixture of benzene, toluene, and naphthalene by both isolates together illustrated that not only was inhibition relieved but that degradation of each compound was also greatly enhanced. Degradation by the toluene and the ND bacteria could be facilitated by complementary substrate interactions between monoaromatics and PAHs and by bacterial association. These model organisms may be very useful for the study of complex aromatic hydrocarbon degradation and for bioremediation purposes.     

Estimating Nutrient Outflow from Argicultural Watersheds to the River Kali in India

In India, fertilizers and chemicals are applied to different crops, which in turn, cause nonpoint source pollution of surface water and groundwater of the region. In the present work, extensive water quality surveys were done to estimate the nutrient outflow from three small agricultural watershed of the Kali Basin, Uttar Pradesh, India. A total of 576 field data sets have been collected during March 1999–February 2000 from four sampling stations. During the monsoon period the nutrient outflow from these agricultural watersheds were found to be orders of magnitude higher than during the nonmonsoon period. The percentage of nutrients outflow from each watershed was estimated on a monthly basis by obtaining periodical cropping patterns and the amounts of fertilizer applied for each watershed. A maximum of 85% of total nitrate and 70% of total orthophosphate applied in the field was found to be lost during the month of July from the third agricultural watershed having maximum slope and minimum watershed area. Using the data sets generated during field surveys, commonly used modeling approaches based on mass balance differential loading and decay fraction were tested for their applicability to estimate nonpoint source (NPS) pollution in the River Kali. The NPS concentration and load values computed from these approaches were compared with the NPS values measured in the field and the performances of different equations have been evaluated using error estimations such as standard error, normal mean error, mean multiplicative error, and correlation statistics. Further, a refined model based on reaction kinetics and mass balance differential loading has been proposed for the River Kali that minimizes error estimates and improves correlation between observed and computed nonpoint source loads.     

Dynamics of Large Polymictic Lake. I: Field Observations

The internal dynamics of Clear Lake, California—a large, multibasin and polymictic lake—under stratified conditions is described in this work. Particular attention is paid to one of the subbasins of Clear Lake (Oaks Arm). Several field experiments were conducted in the lake to obtain data of wind, currents, and water temperature using a wide range of devices. Based on field observations and previously published results on basin responses to wind stress, a conceptual model of the internal circulation of the Oaks Arm is proposed. Its internal dynamics are characterized by diurnal cycles of setup and relaxation of horizontal temperature gradients driven by the wind forcing. The setup and relaxation processes are modulated by the influence of the earth’s rotation and create a residual cyclonic circulation. This circulation mechanism is here referred to as baroclinic pumping. It is in all likelihood not exclusive to Clear Lake but probably exists in other large and relatively shallow lakes forced by strong and almost periodic wind events where basin-scale internal waves do not play a major role in the dynamics of the system.     

Surface Analysis of Chesapeake Bay Water Quality Response to Different Nutrient and Sediment Loads

Based on a set of Chesapeake Bay Estuarine Model (CBEM) scenarios, a three-dimensional response surface of a water quality index, such as chlorophyll concentration, versus a pair of loading constituents, e.g., nitrogen and phosphorus, is constructed. The responses of water quality, such as dissolved oxygen, chlorophyll, and water clarity, to nitrogen, phosphorus, and sediment loads are analyzed. From the response surface, a water quality response is estimated under loading conditions beyond that of a limited set of scenarios. Response surfaces may be used to determine the possible universe of nutrient and sediment load reductions needed to obtain a particular water quality standard and to examine the tradeoffs among nutrient and sediment load reductions that achieve the same water quality objective.     

Influence of Wind and Lake Morphometry on the Interaction between Two Rivers Entering a Stratified Lake

The interaction of two rivers flowing into Coeur d’Alene Lake (United States) was investigated with a field experiment and three-dimensional numerical simulations. The focus was on the influence of basin morphology, wind speed, and wind direction on the fate and transport of the inflowing water. Data from the field campaign showed that intrusions from the two rivers propagated into the lake at different depths, with the trace element polluted Coeur d’Alene River flowing into the lake above the trace element poor and nutrient rich St. Joe River inflow. The inflows initially intruded horizontally into the lake at their level of neutral buoyancy and later mixed vertically. Model results revealed that, as the intrusions entered the main lake basin, a forced horizontal mode-two basin-scale internal wave interacted with the intrusions to frequently siphon them into the lake proper and where rapid vertical mixing followed. The results serve to show how detailed transport and mixing patterns in a lake can have important consequences for the plankton ecology in the lake.