Martin T. Auer

Modeling fecal coliform bacteria—I. Field and laboratory determination of loss kinetics

Abstract Contamination of surface waters through the discharge of fecal material in surface run-off, combined sewer overflows and point source discharges is an important water quality problem in many urban environments. Field and laboratory studies were conducted to develop and verify the kinetic expressions and attendant coefficients required to simulate the loss of fecal coliform bacteria in lakes due to death [as mediated by irradiance (light) and temperature] and sedimentation. The dark death rate coefficient at 20°C ( k d = 0.73 d −1 ) was established in laboratory experiments utilizing raw sewage diluted with filtered lake water. No consistent relationship was observed between the dark death rate coefficient and temperature ( θ = 1). The irradiance-mediated death rate ( k i ) was shown to be proportional to irradiance ( I ) in water column incubations of raw sewage using a dialysis tube technique: k i = αI ; α = 0.00824 cm 2 cal −1 . The settling loss rate (1.38 m d −1 ) was quantified by determining the association of fecal coliform bacteria with particles of various size classes and measuring the sedimentation rate for those particle classes using sediment traps. Individual loss terms are combined into a single predictive expression which may be used to simulate fecal coliform bacteria dynamics in lakes.

Great Lakes Cladophora in the 21st Century: Same Algae-Different Ecosystem

ABSTRACT Nuisance growth of the attached, green alga Cladophora was considered to have been abated by phosphorus management programs mandated under the Great Lakes Water Quality Agreement. The apparent resurgence of nuisance growth in Lakes Erie, Michigan and Ontario has been linked conceptually to ecosystem alterations engineered by invasive dreissenid mussels (Dreissena polymorpha and Dreissena bugensis). Here, we apply contemporary modeling tools and historical water quality data sets in quantifying the impact of long-term changes in phosphorus loading and dreissenid-mediated changes in water clarity on the distribution and production of Cladophora. It is concluded that reductions in phosphorus loading in the predreissenid period achieved the desired effect, as model simulations were consistent with the biomass declines reported from the early 1970s to the early 1980s. These declines were, however, largely offset by dreissenid-driven changes in water clarity that extended the depth of colonization by Cladophora, increasing total production. We were not able to isolate and quantify the significance of dreissenid mediation of phosphorus cycling using the historical database. Phosphorus management remains the appropriate mechanism for reducing nuisance levels of Cladophora growth. The development of action plans will require an improved understanding of nearshore phosphorus dynamics such as might be obtained through regular monitoring of soluble reactive phosphorus levels, internal phosphorus content and Cladophora biomass in impacted nearshore regions of the Great Lakes.

Ecological Studies and Mathematical Modeling of Cladophora in Lake Huron: 3. The Dependence of Growth Rates on Internal Phosphorus Pool Size

The relationship between growth rate and internal phosphorus pool size was examined using field populations of Cladophora glomerata from Lake Huron. Algal samples, representing a range of internal phosphorus concentrations, were harvested from the lake and used for laboratory measurements of growth. Rates of net photosynthesis and respiration were measured under controlled conditions of light and temperature using a dissolved oxygen (light/dark bottle) technique. The net specific growth rate and respiration rate were calculated from photosynthesis and respiration measurements using a fixed stoichiometric relationship and the measured carbon content of the algae. The maximum rates for net specific growth rate, gross specific growth rate, and specific respiration rate were 0.77, 1.08, and 0.44 day−1, respectively. Management decisions may be importantly influenced by the relationships derived from these data. A non-linear response by growth to reductions in phosphorus loading is suggested from the results of these experiments. The internal nutrient status of algal populations (e.g. Cladophora) must be considered in predictions of the impact of phosphorus management strategies on aquatic systems.

Nitrification in the water column and sediment of a hypereutrophic lake and adjoining river system

Abstract Nitrification in lakes and rivers is usually modeled using first-order water column kinetics. Over the years, a number of scientists have, however, recognized the importance of sediment nitrification, especially in shallow systems. The aim of this study is to determine the extent of nitrification in the water column and sediments of a eutrophic system and to propose simple kinetic equations to describe the process. An intensive experimental study was performed (summer and fall 1992, fall 1993) on Onondaga Lake and the adjoining Seneca River, a hypereutrophic system with high ammonia concentrations (2–10 mgN l−1). Water samples and sediment cores were collected and laboratory nitrification studies performed. The results clearly demonstrate that there is rapid nitrification in the sediments of both Onondaga Lake (0.37 gN m−2 d−1) and the Seneca River (0.32 gN m−2 d−1). In contrast, no apparent nitrification was observed in the water column of the lake or river, despite high ammonia concentrations. The findings of the Most Probable Number (MPN) test provide a likely reason for this phenomenon, showing that the lack of nitrification in the water column is probably due to low nitrifier densities (∼101 cells ml−1), whereas the rate is rapid in the sediments due to high nitrifier populations (∼105 cells ml−1). It is therefore believed that nitrification in this relatively deep system is localized to the sediments and simple zero order kinetics is proposed as a first approach to model the process. It also stimulates the question of whether nitrification in most freshwater systems is principally a sediment process and should be modeled accordingly.

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.

Ecological Studies and Mathematical Modeling of Cladophora in Lake Huron: 2. Phosphorus Uptake Kinetics

Laboratory experiments were conducted with field populations of Cladophora glomerata to examine the phosphorus uptake process. Results from 35 experiments conducted over two field seasons emphasize the importance of two factors in regulating phosphorus uptake: dissolved phosphorus concentration and internal phosphorus pool size. The phosphorus uptake rate increases as dissolved phosphorus availability increases. Negative feedback on uptake rate by internal phosphorus pool size reduces the maximum phosphorus uptake rate as internal pools approach saturation. The absolute maximum phosphorus uptake rate for Cladophora was 4.5%P/day. Values for the half-saturation constant for uptake varied with internal phosphorus pool size and ranged between 30 and 250 μgP/L. The data were fit to published mathematical expressions which describe uptake as a function of internal and external phosphorus levels. The expressions may be used in mathematical models simulating the growth of Cladophora.

Ecological Studies and Mathematical Modeling of Cladophora in Lake Huron: 1. Program Description and Field Monitoring of Growth Dynamics

A 3-year program was conducted to examine the ecology of Cladophora glomerata and to develop a mathematical model useful in evaluating various management strategies for the control of this nuisance alga. This manuscript provides a detailed description of the field program and study site in support of subsequent papers dealing with the results of field monitoring, autecological studies, calibration and verification of the model, and the impact of a demonstration phosphorus removal program on Cladophora growth. A municipal wastewater treatment plant discharge at Harbor Beach, Michigan, on Lake Huron has resulted in severe nuisance conditions associated with the presence of Cladophora. An intensive field monitoring program was established at the site to record weather conditions daily, and levels of dissolved and stored phosphorus and standing crop of Cladophora on a weekly basis. The distribution of Cladophora was shown to be essentially symmetrical about the nutrient source. Seasonal variation in biomass followed a pattern of early spring growth, stabilization, and midsummer senescence. The high degree of spatial and temporal heterogeneity in the nearshore environment was clearly evident from the results of the monitoring program. Wind direction and velocity importantly affect dissolved phosphorus distribution. Internal phosphorus levels reflect long term trends in wind and current regimes. The growth of Cladophora is importantly influenced by internal phosphorus levels while the loss of algal material through sloughing is closely correlated with wind-storm events. The observations of nearshore dynamics point to the need for high sampling frequency in such systems.

Chloride model for polluted onondaga lake

Abstract The validation of a mass balance chloride (Cl) model for enriched Onondaga Lake is documented for the period 1973–1991. The history of loading of Cl to the lake, extending from the mining of NaCl brines adjoining the lake in the late 1700s, through the 102 year period of operation and discharges of an adjoining soda ash/chlor-alkali facility, is reviewed. Loads are estimated for the 1973–1991 interval based on a program of continuous flow measurements and bi-weekly monitoring of Cl concentration for the major inflows. The model performs well in matching the substantial seasonal variations in lake Cl concentration and the major reduction in concentration observed since closure of the facility in 1986 (from about 1585 to 430 mg l −1 ). Projections with the validated model demonstrate the Cl concentration in the lake would be about 230 mg l −1 , nearly 50% lower than the present concentration, without the continuing waste input from the soda ash/chlor-alkali facility.

Supply of phosphorus to the water column of a productive hardwater lake: controlling mechanisms and management considerations

Onondaga Lake is a hypereutrophic, industrially polluted lake located in Syracuse, NY. High hypolimnetic concentrations of H2S that develop after anoxia restrict the accumulation of total Fe2+ due to the formation of FeS, and may limit Fe-PO4 interactions. High water column concentrations of Ca2+ and high rates of CaCO3 deposition occur due to inputs of Ca2+ from an adjacent soda ash manufacturing facility. Patterns of P concentration and other water chemistry parameters in the lower waters, and results from chemical equilibrium calculations, suggest that Ca-PO4 minerals may regulate the supply of P from sediments to the water column in Onondaga Lake. These findings have important management implications for Onondaga Lake. First, declines in water column Ca2+ concentrations due to reductions in industrial CaCl2 input may result in conditions of undersaturation with respect to Ca-PO4 mineral solubility and increases in the release of P from sediments to the water column. Second, introduction of O2 from hypolimnetic oxygenation, as a lake remediation initiative, may enhance P supply from sediments, because of increased solubility of Ca-PO4 minerals at lower pH.

LIGHT AND TEMPERATURE AS FACTORS REGULATING SEASONAL GROWTH AND DISTRIBUTION OF ULOTHRIX ZONATA (ULVOPHYCEAE)1

Ulothrix zonata (Weber and Mohr) Kütz. is an unbranched filamentous green alga found in rocky littoral areas of many northern lakes. Field observations of its seasonal and spatial distribution indicated that it should have a low temperature and a high irradiance optimum for net photosynthesis, and at temperatures above 10°C it should show an increasingly unfavorable energy balance. Measurements of net photosynthesis and respiration were made at 56 combinations of light and temperature. Optimum conditions were 5°C and 1100 μE·m−2·s−1 at which net photosynthesis was 16.8 mg O2·g−1·h−1. As temperature increased above 5° C optimum irradiance decreased to 125 μE·m−2·s−1 at 30°C. Respiration rates increased with both temperature and prior irradiance. Light‐enhanced respiration rates were significantly greater than dark respiration rates following irradiance exposures of 125 μE·m−2·s−1 or greater. Polynomials were fitted to the data to generate response surfaces. Polynomial equations represent statistical models which can accurately predict photosynthesis and respiration for inclusion in ecosystem models.