Emmet M. Owens

Modeling fecal coliform bacteria—II. Model development and application

Abstract The episodic nature of their origin and the transience of the receiving water response make the modeling of fecal coliform bacteria contamination events particularly challenging. A two-layer mass balance model was developed to simulate spatial and temporal variability in fecal coliform bacteria concentrations in a polluted, urban lake. Independently validated submodels were used to estimate bacteria loads from tributary and point source discharges, to quantify mass transport and to determine losses due to sedimentation and death. The overall model was validated by successfully simulating spatial and temporal dynamics for dry weather conditions and two wet weather events. Sensitivity analyses indicate that the likelihood of violating public health standards is influenced by environmental conditions, e.g. light intensity and wind mixing. Model simulations are used to illustrate the impact of water quality management actions on bacteria levels at various locations in the lake. The general approach presented here and the techniques used to quantify model inputs may be of value in application to other systems.

Limnological and Loading Information and a Phosphorus Total Maximum Daily Load (TMDL) Analysis for Onondaga Lake

ABSTRACT The phosphorus (P) total maximum daily load (TMDL) analysis and associated management plan for culturally eutrophic Onondaga Lake, NY, are critically evaluated based on available input/discharge and limnological information for the system. The evaluation is based on: (1) results from a long-term monitoring program conducted on the lake, its tributaries, and the adjoining river that receives the lakes outflow, (2) algal bioassay experiments of the bioavailability of particulate P (PP) in inputs to the lake, (3) loading rate calculations for forms of P in these inputs, (4) calculations of water densities in inflows and the lake, (5) model analyses of plunging interflows and responses to seasonal material loading, and (6) mass balance calculations for a tracer conducted around the lake outlet and the receiving river to estimate inflow to the lake from the river. Several important system-specific characteristics were found not to be accommodated in the current TMDL analysis, including: (1) a P load from the river back into the lake, (2)seasonal plunging of tributaries to depths below the productive layers of the lake, (3) incomplete and different bioavailabilities of PP in the various inputs, (4) the different settling velocities of PP from these sources, (5) false high estimates of TP loading from tributaries associated with turbidity interferences in P analyses, and(6)the implications of the high flushing rate of the lake for strong seasonality in the relative impacts of externals loads. The TMDL analysis is demonstrated to understate the present role of the dominant point source and overstate the importance of non-point sources. Recommendations are made to upgrade the TMDL analysis through an integrated program of model development, testing and application, supporting process studies and monitoring, and re-evaluation of management options.

The Great Lakes Cladophora Model: Development, Testing, and Application to Lake Michigan

ABSTRACT A recent review of the Great Lakes Water Quality Agreement has concluded that while controls on phosphorus inputs to Lake Michigan achieved the desired effect in offshore waters, the nearshore region continues to suffer from elevated phosphorus levels. Failure to achieve trophic state goals in the nearshore is manifested in nuisance growth of Cladophora and attendant impacts on property owners, utilities, and the public health and welfare. This study focuses on a site in Lake Michigan near Milwaukee, Wisconsin, where nuisance growth of Cladophora and associated beach fouling occur regularly. A mechanistic model simulating Cladophora growth, suitable for guiding nutrient management in the Great Lakes nearshore, is presented. The model represents an update of the Canale and Auer framework, reflecting current understandings of Cladophora ecology and offering a user-friendly interface making the software more widely available to decision makers. This Great Lakes Cladophora Model (GLCM) is first validated for the Auer/Canale data set collected in 1979 at a site on Lake Huron and then for a data set developed in 2006 for a site on Lake Michigan. Model performance under the strikingly different forcing conditions (depth, light, phosphorus levels) characteristic of these two sites affirms the widespread applicability of the tool. The GLCM is then extended to examine the impacts of ecosystem perturbation (dreissenid colonization) on Cladophora growth and to future approaches to monitoring and management.

Calibration, Verification, and an Application of a Two-Dimensional Hydrothermal Model [CE-QUAL-W2(t)] for Cannonsville Reservoir

ABSTRACT The successful testing of a two-dimensional hydrothermal/hydrodynamic model, CE-QUAL-W2(t), for Cannonsville Reservoir is documented. The model is calibrated to the detailed temperature data collected in the reservoir (depth-profiles at six locations) over the April-November interval (weekly) of 1995, using comprehensive hydrologic and on-site meteorological forcing data. Further, the frequency of current oscillations predicted for the lower layers matched results of independent determinations made from thermistor chain deployments (two locations). The model is verified through the successful continuous simulation of the observed thermal stratification regime of the reservoir for the 1988–1994 interval, a period in which wide interannual differences were observed related to variations in meteorology and operations. The model performs well in simulating: 1) the timing of stratification and turnover, 2) the duration of stratification, 3) the dimensions of the epilimnion and hypolimnion, 4) the temp...

Phosphorus Bioavailability and P-Cycling in Cannonsville Reservoir

ABSTRACT Algal bioassays and chemical fractionation analyses were applied in determining the bioavailability of phosphorus (P) discharged to Cannonsville Reservoir from its major tributary, the West Branch of the Delaware River (WBDR) and in reservoir bottom sediment. Soluble phase (soluble reactive and dissolved organic) P discharged by WBDR was found to be 100% bioavailable, in a single, dry-weather sample. Tributary particulate-phase P bioavailability varied with hydrologic conditions: 48% for a dry-weather sample and 25% for a wet-weather sample. The P-bioavailability of reservoir bottom sediments (24%) was comparable to that for the wet-weather tributary sample. Phosphorus released over the course of the tributary bioassays came from the Fe/Al-P and extractable biogenic-P pools, while that generated in reservoir bottom sediment bioassays originated entirely from the Fe/Al-P pool (despite the presence of a significant extractable biogenic-P fraction). WBDR sediment had approximately two times more tot...

Development and Testing of One-Dimensional Hydrothermal Models of Cannonsville Reservoir

ABSTRACT Two one-dimensional (vertical) hydrothermal models of Cannonsville Reservoir, a water supply serving New York City, were developed and tested. A two-layer model, capable of hindcasting temperature dynamics for two (epilimnion, hypolimnion) completely-mixed, variable-volume layers, was calibrated by determining die seasonal variation of the vertical heat transfer coefficient. This model was used only to hindcast temperature for the spring-fall period of 1995. A multi-layer model (average layer thickness 1.5 m over 50 m maximum depth) was developed that has the capability of forecasting stratification and vertical transport conditions in the reservoir based on specified meteorologic, hydrologic, and reservoir operation conditions. As a part of calibration, the multi-layer model was used to hindcast stratification and vertical transport conditions for the continuous period 1988 through 1995. The model accurately reproduced observed temperature profiles and other observed features such as thermocline...

Turbidity Model for Ashokan Reservoir, New York: Case Study

Terrigenous inorganic particles delivered during runoff events cause problems of high turbidity in many lakes and reservoirs. A turbidity model, composed of a two-dimensional hydrothermal/transport submodel and a turbidity submodel, is developed and tested for Ashokan Reservoir, New York, that experiences elevated turbidity levels following runoff events. A robotic monitoring network, rapid profiling instrumentation, and individual particle analyses are used to support the modeling, by specifying turbidity loads and in-reservoir patterns and features of the particles that guided representation of settling. The turbidity-causing particles are clay minerals, 1–10 μm in diameter. The hydrothermal/transport submodel that serves as the physical framework for the overall model, was separately validated for a 13-year period. The turbidity submodel considered three particle-size/settling velocity classes of turbidity, consistent with the independent individual particle characterizations. Robust performance is dem...

Hydrologic Analysis and Model Development for Cannonsville Reservoir

ABSTRACT The hydrology of Cannonsville Reservoir, a water supply and flow augmentation reservoir for the City of New York, is analyzed. Measurements of components of the hydrologic budget of the reservoir over the entire 30 years of operation are reviewed. The largest tributary is gauged near its discharge to the reservoir; all others are ungauged. Water surface elevation and outflow, in the form of spillway flow, direct releases for flow augmentation, and drinking water withdrawal are monitored. Multiple uses of the reservoir and variations in runoff common to the region result in strong seasonal and interannual variations in hydrology. Spillway flow typically occurs in late winter and spring, and is rare in summer and early fall. Releases, to meet minimum flow requirements in the Delaware River downstream, generally occur only in summer and early fall. Drinking water withdrawal is relatively uniform throughout the year. On average, spill, dam releases, and withdrawal for the water supply have represente...

Development and Testing of a Nutrient-Phytoplankto Model for Cannonsville Reservoir

ABSTRACT A dynamic multi-layer one-dimensional mass balance nutrient-phytoplankton (eutrophication) model is developed and tested for the lacustrine zone of eutrophic Cannonsville Reservoir. The model simulates concentrations of chlorophyll (Chl), zooplankton biomass, various forms of phosphorus (P) and nitrogen (N), and dissolved oxygen (DO). Model development was integrated with, and supported by, limnological analysis of detailed monitoring data and findings of various system-specific process/kinetic studies. Model testing is supported by comprehensive monitoring data of in-reservoir concentrations and important environmental and operational forcing conditions. Model credibility is enhanced by the independent determination of a number of important model coefficients from the process/kinetic studies, which greatly constrains the role of calibration. The model performed well in simulating observations of seasonal average Chl concentration, the progressive depletions of nitrate plus nitrite from the epili...

Sediment Resuspension in Cannonsville Reservoir

ABSTRACT The operation of the sediment resuspension process in Cannonsville Reservoir, NY, a eutrophic flow-augmentation and water supply impoundment for New York City, during the major drawdown year of 1995 is documented. Methodologies used in the assessment included transmissometer profiling; electron microscopy-based physical and chemical characterization of individual particles from the water column, sediments and the principal tributary; analysis of sediment trap collections; and mass balance calculations for total suspended solids (TSS). The resuspension process had several pronounced manifestations. First was the development of a conspicuous benthic nepheloid layer (BNL) which, by mid-summer, extended nearly 10 m above the bottom at one location. Second was the increase in the concentration of inorganic particles in the upper waters as the reservoir was drawn down. These particles, ultimately derived from the watershed, caused increases in turbidity. Third was the measurement of higher downward flu...