Soil & Water Conservation Society of Metro Halifax

Volunteer Co-ordinator: S.M. Mandaville E-mail Edited: 20 March 1997

Lake Restoration/Management

INDEX (listings are either shortcut links to relevant parts of this document or to other files written by us):

Introduction

Examples of common lake problems, impaired uses, and possible causes of the problem. (Olem & Flock. 1990)

Legend: XX= Problem shown definitely impairs use shown; X= Problem shown may impair use shown

Impaired Use- Aesthetics:

Impaired Use- Fishing: Impaired Use- Swimming: Impaired Use- Motor Boating: Impaired Use- Sailing: Impaired Use- Water Supply:

The importance of the lake and watershed relationship cannot be overemphasized

(Olem & Flock. 1990)

BEST MANAGEMENT PRACTICES (BMP)

Important Basic Assumptions in Lake Restoration

Any discussions of in-lake technique effectiveness, except where explicitly stated, always assume that loadings of nutrients, silt, and organic matter to the lake have already been controlled. Most in-lake procedures will be quickly overwhelmed by contin ued accumulation of these substances. In-lake programs can complement watershed efforts; however, such problems as algae, turbidity, and sedimentation may persist despite load reductions or diversion projects unless an in-lake procedure is also used.

Effectiveness, cost and chance of negative side effects associated with select watershed best management practices

Legend: E=Excellent; G=Good; F=Fair; P=Poor; U=Unknown

Hypothetical Lake In-Lake Management Evaluation Matrix

(Olem & Flock.1990)

Legend: E=Excellent G=Good F=Fair P=Poor

WETLANDS TREATMENT

(USEPA, 1988; Gersberg et al, 1983; Good et al, 1978; Hantzsche, 1985; Hickok et al, 1977; Kadlec, 1978; Reuter et al, 1992; Verry et al, 1982; Tennessee Valley Authority; Pope, 1981; Lakshman, 1978; Brown, 1985; Water Environment Federation, 1989)

One outgrowth of clean water legislation has been to promote interest in using natural and constructed wetlands. The scientific literature is replete with evidence that wetlands have the ability effectively to decrease levels of nutrients, suspended sedi ments, BOD, heavy metals and even viruses from stormwater, as well as domestic wastewater in warm as well as cold climates. Pollutant removal occurs through a combination of: (1) physical-chemical mechanisms, including entrapment, sedimentation, adsorpti on, precipitation and volatilization; and (2) biological transformations such as bacterial denitrification, bacterial and algal uptake and uptake by wetland vegetation.

Adsorption and precipitation reactions in the soil are reported to be the major mechanism of wastewater P removal by natural wetlands. In constructed wetlands, some P can be permanently removed by harvesting plants and sediment. Soluble inorganic P is r eadily immobilized in inorganic soils by reactions with aluminium, iron, calcium, clays and other minerals. Particulate P that flows into wetlands in association with sediments or organic matter is primarily removed by sedimentation. However, adsorption and precipitation do not represent a limitless sink for P, and under conditions of long-term, heavy loading, it is possible to saturate a wetland system and significantly reduce its efficiency as a natural filter. Indeed, it has been reported that many wetlands have a limited capacity to remove P relative to nitrogen. Nitrate removal in wetlands occurs almost exclusively via denitrification.

The use of wetlands for secondary and tertiary wastewater treatment has been extensively reported in the literature. Wetlands treatment of stormwater has also been reported (Reuter et al, 1992; Verry et al, 1982; Brown, 1985). Results from a newly const ructed wetland to treat stormwater in a cold climate region of California at Lake Tahoe (Reuter et al, 1992) were encouraging.

Gravel-filled constructed wetlands (Lake Tahoe) provide a much greater surface area for bacterial attachment than is possible in natural wetlands, thereby enhancing the substratum to water volume contact ratio, and hence need less land area than natural wetlands. Constructed Wetlands are most suitable as mitigation for small development projects where land is limited. These projects include golf courses that receive fertilizers, small commercial facilities, small housing developments, etc. They are gen erally limited in efficiency by the volume of water they can retain (4-8 day retention). It may be unrealistic to rely on small constructed wetlands to treat large urban areas.

Comparison of Lake Restoration and Management Techniques for Control of Nuisance Algae

(Olem & Flock. 1990)

Legend: E=Excellent; G=Good; H=High; F=Fair; P=Poor; L=Low; U=Unknown

Treatment (one application)

Comparison of Lake Restoration and Management Techniques for Control of Nuisance Aquatic Weeds

(Olem & Flock. 1990)

Legend: E=Excellent; F=Fair; G=Good; P=Poor; H=High; L=Low;
*The introduction of grass carp is prohibited by law in several states and provinces

Treatment (one application)

Lake Restoration by Biomanipulation

(Benndorf & Miersch 1991; Northcote 1988; DeMelo et al 1992; Shapiro et al 1984; Carpenter ed. 1988)

Lake biomanipulation theory is based on the prediction that increased piscivore abundance will result in decreased planktivore abundance, increased zooplankton abundance, and increased zooplankton grazing pressure leading to reductions in phytoplankton ab undance and improved water clarity. Water quality is dependent to a great extent on structure and function of food webs in aquatic ecosystems. Food webs are controlled by resource limitation ("bottom-up") and by predation ("top-down"). Undoubtedly, so lar energy and nutrient inputs and dynamics of an ecosystem set its overall level of production, so to that extent the control may be envisaged as bottom-up, but within those limits, some of the "coarse-tuning" and much of the "fine-tuning" of structure a nd function in the system results from the complexity of top-down processes. If the hypothesis of the "biomanipulation-efficiency threshold of the P-loading" should be confirmed by further investigations, important consequences for water quality management would emerge.

Comparison of top-down effects in 14 whole-lake biomanipulation studies (+ = effect observed; - = effect not observed; ? = no data). The results are presented in the following format:
[a = Effect explained by external P-load reduction
b = Shallow lakes with macrophytes
c = High flushing rate of the water]

Haugatjern:

L. Michigan: Stockelidsvatten: L. Trummen: Tuesday L.: Round Lake: Lago di Annone: Loch Loso: Grafenhain: Wirth Lake(b): L. of Isles(b): Broads Brundall: Elbe backwaters: Bautzen Reservoir: A high reliability of biomanipulation (i.e. top-down control of eutrophication) could then only be expected if the phosphorus loading a priori is below the threshold (oligotrophic and mesotrophic lakes), or if the phosphorus loading exceeding the thresho ld (eutrophic and hypertrophic lakes) will be reduced by other methods, or if the intensity of bottom-up mechanisms will be strongly controlled by light.

On the other hand, some investigators have pointed out that apparent biomanipulation successes may not have been caused by the cascading effects of zooplankton feeding on phytoplankton, but resulted from several of alternate food-web interactions. Are t hese examples merely atypical anomalies or rather do they reflect a systematic disharmony or incompetence in the biomanipulation theory to adequately address the majority of natural phenomena ? (DeMelo et al, 1992)

Sediment Removal as a Lake Restoration Technique

(Peterson 1981)

Freshwater lake sediment removal is usually undertaken to deepen a lake thereby increasing it's volume to enhance fish producion, to remove nutrient rich sediment, to remove toxic or hazardous material, or to reduce the abundance of rooted aquatic plants. Review of more than 60 projects and examination of 5 case histories (Lake Trummen, Sweden; Lake Herman, South Dakota; Wisconsin Spring Ponds; Steinmetz Lake, New York; and Lilly Lake, Wisconsin), reveals that the first three objectives are usually met t hrough sediment removal. The technique is recommended for deepening and for reducing phosphorus release from sediment. Sediment removal to control toxic materials is possible with minimal environmental impact when proper equipment is used, but it may be extremely expensive. Dredging will remove rooted aquatic plants, however, their re-encroachment rate will be depth, sediment texture, and sediment nutrient dependent.

Total phosphorus content of sediments in selected lakes in North America

Lake Restoration by Circular Canalisation

(OECD 1982)

Practically all phosphorus sources can be made to bypass a lake through a circular canal, and it was most effectively demonstrated in the now classic restoration case of Lake Washington.

Lake Restoration by Siphoning of Hypolimnetic Water

(OECD 1982)

A siphon called an Olszewski pipe is used to discharge nutrient rich water from the hypolimnium. This process reduces the thickness of the tropholytic layer and increases that of the trophogenic one, reduces the nutrient and toxic content of the hypolimnium and eliminates some of the water that is low in oxygen or lacking it completely. Considerable improvement in the reduction of the trophic response was obtained in several lakes such as Mauensee, Wilersee, and Piburgersee in Europe. This method is restricted to relatively small, deep lakes with a topography suitable for the application of a siphon.

Lake Restoration by Hypolimnetic Aeration

(Fast et al 1976; Fast & Lorenzen 1976; Fast 1973; Lorenzen & Fast 1977; Olem & Flock 1990)

Hypolimnetic aeration/oxygenation is an effective means of improving domestic and industrial water quality, satisfying downstream water release standards and creating suitable habitat for yearlong survival of cold water fish. It may be achieved by pure oxygen injection, or air injection. With air injection and downstream released, care must be taken not to supersaturate the water with nitrogen gas. Hypolimnetic aeration is the only known method of creating suitable cold water habitat in most warm eutro phic lakes. This system of aeration can result in adequate oxygen values throughout the lake without intolerable increases in hypolimnetic temperatures. Oxygen can be added to the hypolimnium without greatly heating it, or mixing it with epilimnetic or metalimnetic water.

Another use is to eliminate taste and color problems by precipitating iron and manganese. Hypolimnetic aeration may promote some control of algae by a type of phosphorus inactivation procedure under high oxygen, high iron conditions. A classic case history is the St. Paul water supply.

Hypolimnetic aerators need a large hypolimnium to work properly; consequently, any use of these aerators in shallow lakes and reservoirs should be done cautiously, if at all.

Dilution/Flushing Technique in Lake Restoration

(Welch 1981)

Dilution/flushing has been documented as an effective restoration technique for Moses and Green Lakes in Washington State. The dilution water added in both lakes was low in nitrogen and phosphorus content relative to the lake or normal input water. Flus hing rates were about ten times normal during the spring-summer periods in Moses Lake and three times normal on an annual basis in Green Lake. Improvement in quality (nutrients, algae, and transparency) was on the order of 50% in Moses Lake and even grea ter in Green Lake. Quality improvement may occur from physical effects of washout and instability if only high nutrient water is available.

Lake Restoration by Artificial Circulation

(Olem & Flock 1990; Lorenzen & Fast 1977; Vandermeulen 1992)

Artificial circulation eliminates thermal stratification or prevents its formation, through the injection of compressed air into lake water from a pipe or ceramic diffuser at the lake's bottom.

Algal blooms may be controlled, possibly through one or more of these processes:

Lake Restoration by Chemical Precipitation in the Lake

(OECD 1982; Olem & Flock 1990)

Iron, calcium and aluminum have salts that can combine with (or sorb) inorganic phosphorus or remove phosphorus-containing particulate matter from the water column as part of a floc. This method has been applied in the reservoirs in the Netherlands. Tot al phosphorus concentrations and algal biomass were successfully reduced in the Braakman and the Grote Rug Reservoirs. The disadvantage of this method is that some of the phosphorus precipitated is not bound permanently in the sediments and thus it could contribute to a later internal loading.

Aluminum is most often chosen because phosphorus binds tightly to its salts over a wide range of ecological conditions, including low or zero dissolved oxygen. In practice, aluminum sulfate (alum) or sodium aluminate (for soft water lakes) is added to t he water, and pinpoint, colloidal aggregates of aluminum hydroxide are formed. In addition, if enough alum is added, a layer of 1 to 2 inches of aluminum hydroxide will cover the sediments and significantly retard the release of phosphorus into the water column as an "internal load".

Phosphorus inactivation has been highly effective and long-lasting in thermally stratified natural lakes, especially where an adequate dose has been given to the sediments and where sufficient diversion of nutrient incomes has occurred. These treatments have been made to the more common smaller lakes and farm ponds as well.

Lime Treatment to Reduce Eutrophication

(Babin et al, 1989; Murphy & Pepas, 1990; Murphy et al, 1988; Murphy et al, 1991; Prepas et al, 1990)

While lime treatment has been extensively used to mitigate acidification effects, several studies of calcium carbonate precipitation led to the hypothesis that the addition of lime to lakes can also reduce eutrophication. Although biological reactions mu st influence phosphorus biogeochemistry, the effect of lime treatment on phosphorus biogeochemistry can be easily explained via apatite formation.

The generally accepted model for apatite formation is that phosphorus initially adsorbs to calcite and then a surface rearrangement produces phosphate heteronuclei that ultimately form the stable mineral apatite. If the surface application of calcium hy droxide was repeated for a number of years, the titration should exceed an end point, phosphorus and calcium should not redissolve, and phosphorus could be converted into apatite.

Lime has been added to several lakes and dugouts in Western Canada (Frisken, Figure Eight, Andorra, Beaumaris, Valencia, Halfmoon, Gour, Monnette, Desrosier, Frey, Fedora, Pederson, Sullivan, Schreger, Limno) to improve water quality. These hardwater la kes are eutrophic due to high natural, agricultural, or urban loadings of phosphorus. Source control of phosphorus loadings would be extremely difficult at all sites. Most of the lakes are primarily used for recreation but the dugouts have been used for human and agricultural water supplies. In two of the study sites, Figure Eight Lake and Frisken Lake, most of the sediment iron is converted into pyrite. These lakes have little reactive iron and presumably phosphorus biogeochemistry is not controlled by iron reactions.

Water Level Drawdown to reduce certain macrophytes

(Olem & Flock 1990)

Exposing sediments to prolonged freezing (2-4 weeks) and drying results in permanent damage to certain rooted plant species, but the technique is species-specific:

Shading and Sediment Covers

(Olem & Flock. 1990)

Sediment covering materials stop plant growth by the fact that rooted plants require light and cannot grow through physical barriers. These can be used in small areas such as dock spaces and swimming beaches only due to the high costs.

Phosphorus Control in Waste Water Treatment

(OECD 1982; Olem & Flock 1990)

Conventional waste water treatment is intended to reduce the organic matter in waste water and not to control phosphorus. The purely biological and mechanical process can remove 20-25% of phosphorus initially present, while modified, activated sludge pla nts can remove about 55% of phosphorus present in some special cases. Thus, phosphorus removal efficiency of conventional waste water treatment is very limited and usually not adequate to meet the requirements of a phosphorus program. In addition, durin g the summer, waste water discharges may dominate stream flow during dry periods when total flow is lower than usual, and water cannot hold as much dissolved oxygen as it does during the cooler periods of the year. Phosphorus removal efficiency in existi ng treatment plants can be improved by the application of a chemical precipitation process to the effluent.

Phosphorus from waste water can be effectively eliminated with a precipitation process. In this process aluminum or iron salts or lime are added to the waste water which form insoluble compounds with the phosphates. Different kinds of precipitation pro cesses may be employed, such as pre-precipitation, simultaneous precipitation and post-precipitation in combination with the biological process. The most comprehensive experience of phosphorus precipitation has been obtained in Sweden, and by early 1978, more than 600 municipal waste water treatment plants were operated with combined biological and chemical treatment.

It has been shown that where there is proper design and the use of suitable pH-values in the precipitation step, and no significant process disturbances, the following effluent concentrations of total phosphorus could be expected:

Case Studies (Listing) of Eutrophication Control Measures

(Ryding & Rast 1989)

Select Lake Restoration cases

cf. Lake Restoration (Summary of in-lake methodology for both culturally and naturally eutrophic lakes, the Canadian experience)

Lafayette Reservoir, California (Lorenzen et al In Corvallis Env. Res. Lab. 1979):

Stone Lake, Michigan (Theis & DePinto. 1976): Lake Aeration in several Wisconsin Lakes (Wirth. 1988): Lake Vikvatn, Norway (Biomanipulation) (Koksvik & Reinertsen. 1991): Lake Eola, Orlando, Florida (Wanielista et al. 1982): Mirror and Shadow Lakes, Waupaca, Wisconsin (Garrison & Knauer 1981): Lake Erie (OECD. 1982): (Estimated costs of phosphorus reduction alternatives, after PLUARG, 1978)

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