G. Dennis Cooke

Effectiveness and Longevity of Phosphorus Inactivation with Alum

ABSTRACT Effectiveness and longevity of alum treatments were evaluated in 21 lakes (or lake basins) across the United States; 9 were polymictic and 12 were dimictic. Effectiveness was judged from reductions in lake TP (total phosphorus) and internal loading rate, as well as chlorophyll a (chl a), both initially and over periods ranging from 4 to 20 years following treatment. Internal loading rate was reduced in six of nine polymictic lakes/basins by an average of two-thirds, and lake TP was reduced by about one-half, which persisted for 5–11 years. Internal loading rate in dimictic lakes (7 of 7 with adequate data) remained reduced by an average of 80% for 4 to 21 years (average 13 yrs). For the six polymictic lakes, in which treatment was effective, chl a decreased by an average of two-thirds initially, but was about 40% less than die pre-treatment level after 5 to 11 years. Chl a decreased in seven dimictic lakes by an average of 57% initially and 42% after 5–18 years. In some cases, response was indepe...

Internal Phosphorus Loading in Shallow Lakes: Importance and Control

Abstract Decreasing the algal biomass and increasing transparency in shallow, unstratified lakes is usually more difficult than for deep, stratified lakes. Eutrophic unstratified lakes (or shallow, stratified lakes susceptible to metalimnion erosion) have typically responded slowly to reduced external nutrient loading, usually because of longevity of internal loading. That is because sediment-released nutrients (especially phosphorus) readily enter the trophogenic zone of shallow lakes during the growing season and result in high lake concentrations. In stratified lakes, metalimnia may serve as barriers to phosphorus transport into the trophogenic zone. Although the whole water column in shallow lakes is usually aerobic, several mechanisms can combine to produce relatively high sediment phosphorus release rates in these lakes. These include: 1) wind resuspension and bioturbation, combined with high pH or low Fe/P ratio that maintains high P solubility, 2) periodic anoxia and reducing conditions promoted by calm, warm weather, and 3) macro-phyte senescence. Attempts to reduce algal biomass by controlling internal phosphorus loading have often been effective.

Effectiveness of Al, Ca, and Fe salts for control of internal phosphorus loading in shallow and deep lakes

Internal P loading can maintain high P concentrations and delay eutrophic lake recovery following abatement of external loading. Sediment P inactivation with Al salts has been shown to provide long-term (5–14 years) control of sediment P release; long-term effectiveness of Fe and Ca salts has not been reported. Al toxicity problems are possible unless pH is maintained in the 6–8 range. Vertical transport of hypolimnetic P is unlikely in small, deep, dimictic lakes (\-Z√A0 > 8), and effectiveness of P inactivation in lowering their mid-summer epilimnetic P has not been demonstrated. To date, P inactivation has been found to be most effective in improving trophic state in shallow, softwater, polymictic lakes where control of sediment P release affects the entire water column. Abatement of external loading, where necessary, is essential for a successful P inactivation treatment.

Potential Links Between Eutrophication and the Formation of Carcinogens in Drinking Water

ABSTRACT Eutrophication in lakes and reservoirs is a recreational problem and a drinking water quality problem. A major concern is trihalomethane (THM) formation from the reaction of chlorine, a disinfectant, with organic matter in natural water during drinking water treatment. Trihalomethanes, such as chloroform, are known or suspected carcinogens. Algae and allochthonous humic substances are known contributors to the THM precursor pool. Other in-reservoir precursor sources, macrophytes, and sediments, have not been investigated. The authors examined precursor generation in an Ohio water supply reservoir. A three-year input-output study demonstrated that 30 percent of the precursors entering the treatment plant were generated within the reservoir. Laboratory experiments revealed that macrophytes and sediments produce THM precursors. Estimated THM precursor contributions to the reservoir from macrophyte growth and sediment release were small, but algal productivity and macrophyte decomposition may contrib...

The occurrence of internal phosphorus loading in two small, eutrophic, glacial lakes in Northeastern Ohio

Internal loading of phosphorus for the summers of 1972–1974 in the eutrophic Twin Lakes, Ohio, USA was calculated from nutrient budgets, and was found to account for 65–100% of the increase in phosphorus content of the lakes during this period. Recovery of lakes of this type after nutrient diversion may be delayed by internal loading and chemical inactivation of phosphorus may be needed. A discussion of sources of this internal loading is presented.

Managing Drinking Water Supplies

ABSTRACT Efforts to provide safe drinking water cannot begin at the treatment plant. Processes occurring in the watershed can adversely influence drinking water reservoirs, and understanding linkages between these processes and reservoir water quality provides the basis for protecting or improving source water quality. Since the presence of molecules responsible for taste, odor and algal toxin problems, and for the formation of disinfection by-products (DBP) is often related to reservoir trophic conditions, sound and cost-effective water treatment approaches must include considerations for reservoir management. Source water management efforts should include both watershed management, as a means to reduce the loading of materials to the reservoirs, and in-reservoir treatments that ameliorate or minimize the symptoms of eutrophication. Discussed here are considerations for maintaining safe drinking water, water quality assessment approaches, and common methods for managing reservoir water quality.

Ceratophyllum demersum – phosphorus interactions in nutrient enriched aquaria

AbstractHigh macrophyte density in shallow lakes is often associated with clear water, especially when the non-rooted, submerged angiosperm Ceratophyllum demersum is dominant. Lack of true roots and high surface area:volume ratio suggest that nutrient uptake from the water column by C. demersum may be high. Therefore, possible competition for nutrients, including phosphorus (P), could contribute to phytoplankton inhibition. C. demersum ability to absorb and store P at four nutrient levels (unenriched + three enrichment treatments) was investigated in a 34-day laboratory experiment using agar-based nutrient diffusing substrates (NDSs). P uptake rates and abatement potential by C. demersum were assessed from total phosphorus concentration (TP) patterns in the water column. Changes in C. demersum biomass (wet weight) also were determined. C. demersum took up P quickly. Some P release occurred during the experiment, especially under high nutrient conditions. Initial net P uptake by C. demersum was high, but medium-term (five weeks) average uptake was relatively low. Projected long-term net P uptake approached zero. Plant biomass loss and production of macrodetritus (plant fragments >1 mm) were highest in unenriched aquaria. Biomass loss in the lower enriched treatments was equally divided between loss as macrodetritus and as dissolved organic matter (DOM), but loss as DOM was four times higher than loss as macrodetritus in the highest nutrient treatment. The results suggest that medium- and long-term low phytoplankton biomass in C. demersum-rich lakes is achieved via mechanisms other than direct competition for nutrients from the water column.

Evaluating the Restoration Potential of 19 Ohio Reservoirs

ABSTRACT Eighty-four percent of Ohios lakes and reservoirs are eutrophic. Significant reductions in nutrient loading are usually the object of lake restoration projects. However, variations in attainable nutrient concentrations, based on regional differences in watershed characteristics and land use, often are not considered. The purpose of this project was to evaluate the “ecoregion” concept for estimating which surveyed Ohio reservoirs might have the greatest potential for reduction in phosphorus concentrations. Ecoregional watershed characteristics dictate the practical lower or attainable limits of stream nutrient concentrations that can be reached. Attainable reservoir phosphorus concentrations were estimated from stream phosphorus concentration data that represent the best water quality in each Ohio ecoregion and by the use of a loading model. The reservoirs with actual summer 1989 phosphorus concentrations that exceeded predicted attainable concentrations by the greatest amounts were considered to...

Resource use and partitioning by two co-occurring freshwater gastropod species

Many trophic generalist gastropods exert predation-based control on their trophic resources. However, most grazing experiments have been carried out with single snail species, and little is known about snail effects on trophic resources by coexisting species. Substrate colonization and feeding behavior of Physa spp. (Physidae) and Helisoma trivolvis (Planorbidae) were observed in single- and two-species laboratory trials. Spatial overlap between Physa and H. trivolvis was derived from distributions of snail individuals on trophic (living macrophytes, periphyton, and leaf litter) and spatial resources (aquarium space divided into quadrats). Food consumption was determined as biomass changes with respect to snail-devoid controls. Snails reduced the degree of spatial overlap when coexisting, though Physa appeared to affect H. trivolvis distribution more than vice-versa regardless of snail density. Both species preferred leaf litter as a substrate, and both increased nutrient (phosphorus) concentration of water. Periphyton and leaf litter biomass loss was similar in all snail-present aquaria, with only inedible leaf veins left intact at the end of the 10-day experiment. Biomass of living macrophytes increased in all Physa-only aquaria, and in two-species, high density aquaria, suggesting that macrophyte enhancement may be possible in high-density, Physa-dominated snail assemblages.

A Test Of A Morphometric Index To Predict Vertical Phosphorus Transport in Lakes

ABSTRACT Osgood (1988) proposed a morphometric index, mean depth over square root of surface area ([zbar] / √ A0), to estimate the probability of partial or complete mixing of lakes during summer storms. Such mixing could introduce phosphorus (P)-rich waters to the entire water column (polymictic lakes) or to the epilimnion, and could delay lake recovery following abatement of allochthonous P loading. Cooke et al. (1993) hypothesized that aluminum sulfate (alum) applications to control internal P loading would be most effective in lakes with an Osgood Index less than 6 and significant diversion of external loading. We tested the hypothesis that vertical P transport is higher in lakes with the lowest Osgood Index numbers by estimating transport in four northeastern Ohio lakes with Osgood numbers of 2.9, 7.4, 9.7, and 26.3 during Summer 1992. The hypothesis was rejected. Although the lake with the lowest number most often had the highest vertical P transport rate, transport was not significantly different b...