RESTORATION AND MANAGEMENT OF LAKES AND RESERVOIRS - CHAPTER 7 pps

7 Hypolimnetic Withdrawal 7.1 INTRODUCTION The hypolimnetic withdrawal technique involves changing the depth at which water leaves the lake from the surface to near the maximum depth, so that nutrient-rich, rather than low-nutrient surface water is discharged. Coincidentally, the hypolimnion detention time is shortened, the chance for anaerobic conditions to develop is decreased and the availability of nutrients to the epilimnion, through entrainment and diffusion, is reduced. The technique is accomplished by installing a pipe along the lake bottom from near the deepest point to the outlet, and possibly beyond. The outlet pipe is usually situated below lake level, so the device acts as a siphon. It was named an “Olszewski tube” after its original user (Olszewski, 1961), but the technique itself is more commonly referred to as hypolimnetic withdrawal. This technique is applicable to stratified lakes and small reservoirs in which anaerobic hypolimnia restrict the habitat for fish and promote the release of P, toxic metals, ammonia, and hydrogen sulfide from sediments. There are two important requirements for treatment success: (1) the lake level must remain relatively constant, and (2) thermal stability should not change. While stratification may be weak- ened because epilimnetic water tends to be drawn downward, destratification will not occur provided the removal rate of hypolimnetic water is relatively slow. Destratification should be avoided, because it increases the transport of hypolimnetic nutrients and anoxic water to the epilimnion. Polymictic lakes may not be good prospects for withdrawal. To lessen the chances of destratification, directing inlet water to the metalimnion or hypolimnion may be possible. This modification was installed in Lake Ballinger near Seattle (Figure 7.1). While the lake remained stratified with the inflow water directed to depth, the system was not tested without directed flow, for comparison. Destratification has not generally been a problem with the technique. Thermocline depth remained about the same in seven of nine cases examined by Nürnberg (1987). Lowered lake level and thus head loss, will hamper recovery by reducing hypolimnetic water and P export (Livingstone and Schanz, 1994; Dunalska et al., 2001). Preferentially removing hypolimnetic water, and therefore decreasing the residence time of the hypolimnion, should decrease the period of anoxia and increase the depth of the anoxic boundary resulting in a decrease in internal loading of P. In a large fraction of cases, this has occurred (Nürnberg, 1987). Continued P export should ultimately reduce the sediment P pool. Hypolimnetic withdrawal is an obvious and proven alternative, with relatively low cost, to accelerate recovery in stratified lakes where little improvement has followed wastewater diversion or wastewater P removal because of high internal loading. There have been few new cases reported since the second edition of this book, so most of the following remains relatively unchanged. The technique is employed inadvertently in reservoirs where hypolimnetic waters are normally discharged for power generation. However, that procedure has not been evaluated for benefits to water quality in the reservoir itself. Low DO content of discharged water has historically been a major problem with deep-discharge impoundments. Multiple and shallower outlets have been incorporated into reservoir design to counteract low DO discharge. Reducing discharge depth minimizes nutrient export. Some combination of deep and shallow outlets may optimize the two goals of sufficient DO and high-nutrient export, but there is little mention of such a practice in the literature. Copyright © 2005 by Taylor & Francis FIGURE 7.1 Inlet and outlet structures designed for hypolimnetic withdrawal in Lake Ballinger. (From KMC, 1981.) Hall Creek Lake Ballinger Control weir Pump Aerator McAleer Creek Intake structure Epiliminion Thermocline Metalimnion Hypolimnion Copyright © 2005 by Taylor & Francis 7.2 TEST CASES 7.2.1 G ENERAL TRENDS Hypolimnetic withdrawal installation is documented in 21 lakes and 15 of those are in Europe (Björk, 1974; Nürnberg, 1987). Results are reported from 17 lakes (Nürnberg, 1987; Nürnberg et al., 1987). Four of the 21 lakes, two from the U.S. and two from Canada, are either more recent or not included by Nürnberg. Morphometric and mixing characteristics of these lakes are shown in Table 7.1. There are three other European lakes (Laacher and Lützel in Germany and Rudnickii Wielkie in Poland) with withdrawal systems cited by Dunalska et al., 2001). Ten additional cases were reported from Finland (Keto et al., 2004). Internal loading from anoxic sediments during summer stratification occurred in all lakes prior to withdrawal and in most cases, external loading was reduced. Prior to withdrawal, Kleiner Montiggler See had been aerated with liquid oxygen and Reithersee was treated with iron chloride to precipitate P followed by dredging (Nürnberg, 1987). Withdrawal is initiated preferably after stratification, but before anoxic conditions occur. The siphon pipe is located usually 1 to 2 m above the bottom at the greatest depth to maximize P transport (see Tables 7.1 and 7.2). In meromictic lakes however, it may be most effective to position the pipe above the monomolimnion so that it continues to be a sink for P. If there are two basins, withdrawal from the shallowest basin may be more effective at reducing entrainment into the epilimnion (e.g., Lake Wononscopomuc, CT). Hypolimnetic water withdrawal rates and consequent TP export and duration are shown in Table 7.2. These values varied among the lakes. Years of withdrawal ranged from 1 to 10 for 20 of the listed lakes. Sufficient data were available to estimate TP export and duration in only 11 of the 20 lakes. The longest duration is for Kortowo, Poland, where the first withdrawal pipe was installed in 1956. Recent P budgets show 3.7 and 4.7 times more P exported from the lake than the inputs for 1999 and 2000 (Dunalaska et al., 2001). Hypolimnetic and epilimnetic data were available on 12 lakes, but data were available for both on only 10 lakes. Maximum hypolimnetic TP concentration decreased in all 11 of 12 lakes and epilimnetic TP decreased in 8 of 12 where data were available. The reduction in hypolimnetic TP is a direct effect, but epilimnetic reduction in TP is an indirect effect demonstrating that entrainment of P from hypolimnion to epilimnion was reduced. The effect of withdrawal on epilimnetic TP was most significant as a function of grand total TP exported over the project life rather than annual export, whether expressed as total mass or per area (Figure 7.2; Nürnberg, 1987). The lakes involved in this analysis were Burgaschi, Hecht, Kleiner Montiggler, Mauen, Meerfelder Maar, Piburger, Waramaug, and Wononscopomuc. Lake Ballinger showed no change in epilimnetic TP due to increased external loading so it was not included. The longer withdrawal operated the greater was the proportional change in epilimnetic TP (Figure 7.3; Nürnberg, 1987). More data were available for this analysis. The additional lakes besides those listed above for Figure 7.2 are Klopeiner, Kraiger and Wiler, although the latter was eliminated from the regression analysis due to high external P loading (Figure 7.3, open circle; Nürnberg, 1987). While substantial decrease in epilimnetic TP occurred in four lakes, on average, as long as 5 years may be necessary to see a significant decrease in epilimnetic TP (Figures 7.3). Recent data show a reduction of epilimnetic TP from 80 to 18 μg/L during 10 years of withdrawal in Lake Bled (Nürnberg and LaZerte, 2003). The depth of hypolimnetic anoxia also decreased in 12 of 13 cases with adequate data, but that effect decreased as volume increased, and the days of anoxia decreased in 8 of 10 cases. However, the reduction in anoxia could not be related to withdrawal rate or volume. Thus, the case for lessened anoxia with withdrawal is not strong. Thermocline position remained about the same in 8 of 10 cases and sank 2 to 3 m in 2 cases. Copyright © 2005 by Taylor & Francis TABLE 7.1 Morphometric Characteristics of Lakes Treated With Hypolimnetic Withdrawal Lake Watershed Area (10 3 m 2 ) Lake Area (10 3 m 2 ) Lake Volume (10 3 m 2 ) Water Res. Time (yr) Mean Depth (m) Max. Depth (m) Mixis Ballinger, Washington a 11,720 405 1,838 0.26 4.5 10.0 Monomictic Bled, Yugoslavia b NA 1438 25,690 3.6 17.9 30.2 Meromictic Burgäschi, Switzerland c 3,190 192 2,483 1.4 12.9 32.0 Meromictic Chain, British Columbia d — 460 2,760 0.5–3.0 6 9 Polymictic Devil’s, Wisconsin e 6,860 1,510 1,390 7.8* 9.2 14.3 Dimictic Germündener Maar, W. Germany f 430 75 1,330 8.0 17.7 39.0 Meromictic Hecht, Austria g 2,221 263 6,428 2.8 24.4 56.5 Meromictic Kleiner Montiggler, Italy h 1,252 52 518 NA 9.9 14.8 Meromictic Klopeiner, Austria i NA 1106 24,975 1.5 22.6 48.0 NA Kortowo, Poland j 1,020 901 5,293 NA 5.9 17.2 Dimictic Kraiger, Austria i NA 51 245 2.0 4.8 10.0 Dimictic Mauen, Switzerland k 4,300 510 1,989 0.6 3.9 6.8 Dimictic Meerfelder Maar, W. Germany l 1,270 248 2,270 4.5 9.2 18.0 Dimictic de Paladru, France m 48,000 3900 97,000 4.0 25.0 35.0 Dimictic Piburger, Austria g,k 2640 134 1,835 1.9 13.7 24.6 Meromictic Pine, Alberta n 157,070 4,125 24,088 9.0 5.3 13.2 Dimictic Reither, Austria g,o NA 15 67 0.3 4.5 8.2 Dimictic Stubenberg, Austria i NA 450 NA NA NA 8.0 Polymictic Waramaug, Connecticut p 37,000 2,866 24,758 0.8 8.6 12.8 Dimictic Wiler, Switzerland i,q 257 31 325 1.0 10.0 20.5 NA Wononscopomuc, Connecticut r 5994 1400 15,500 4.0 11.1 32.9 Dimictic Source: From Nürnberg, G.K. 1987. J. Environ. Eng. 113, with additions. With permission. Data sources: a KCM. 1981. Lake Ballinger Restoration Project Interim Monitoring Study Report; KCM. 1986. Restoration of Lake Ballinger: Phase III Final Report. Kramer, Chin, and Mayo, Seattle, WA. b Vrhovsek, D. et al. 1985. Hydrobiologia 127; Nürnberg, G.K. and B.D. LaZerte. 2003. Lake and Reservoir Manage. 19. c Ambühl, H., personal communication. d McDonald, R.H. et al. 2004. Lake and Reservoir Manage. 20. e Lathrop, R.C. personal communication. f Scharf, B.W. 1983. Beitrage Landespflege Reinland-Pfalz 9. g Pechlaner, R. 1978. Osterreichische Wasserwirtsch. 30. h Thaler, B. and D. Tait. 1981. Tatigkeitsbericht des Biologischen Landeslabors autonome Provinz Bozen 2. i Hamm, A. and V. Kucklentz. 1981. Materialien der Bayrischen Landesanstalt fur Wasserforschung, Munchen, FDR, 15. j Olszewski, P. 1961. Verh. Int. Verein. Limnol. 14; 1973. Verh. Int. Verein. Limnol. 18. k Gächter, R. 1976. Schweiz Z. Hydrol. 38. l Scharf, B.W. 1984. Natur und Landschaft 59. m Lascombe, C. and J. De Beneditis. 1984. Verh. Int. Verein. Limnol. 22. n Sosiak, A. 2002. Initial Results of the Pine Lake Restoration Program. Alberta Environment, Edmonton, Alberta. o Pechlaner, R. 1975. Verh. Int . Verein. Limnol. 19; 1979. Arch. Hydrobiol. Suppl. 13. p Nürnberg, G.K. 1987. J. Environ. Eng. 113. q Eschmann, K.H. 1969. Gesundheit- stechnik Zurich 3. r Kortmann, R.W. et al. 1983. In: Lake Restoration, Protection and Management. USEPA-440/5-83-001; Nürnberg, G.K. et al. 1987. Water Res. 21; NA, not available. Copyright © 2005 by Taylor & Francis TABLE 7.2 Specific Characteristics of Withdrawal Systems Lake Pipe Depth (m) Withdrawal Diameter b (cm) Pipe Outflow c (m) Annual TP Export (kg) Duration (yr) Volume (10 3 m 3 /yr) Rate (m 3 /min) Ballinger 9.0 ~480 3.4 30.5 NA NA 3.0 Bled NA 6307 12.0 NA NA NA 10.0 Burgäschi 15.0 1000 3.0 33.0 0.5 147.1 5.0 Chain 6.2 435 4.8 45 1.0 30 9.0 Devil’s 14.3 629 9.1 48 2.2 446 1.0 Gemündener Maar NA NA 0.1 NA NA NA NA Hecht 25.0 843 1.5 18.0 2.0 50.8 10.0 Kleiner Montiggler d 13.0 16 NA NA –0.5 16.0 1.0 Klopeiner 30.0 NA NA NA NA NA 3.0 Kortowo 13.0 NA NA NA 0.5 NA 45.0 Kraiger NA NA NA 20.0 NA NA 4.0 Mauen 6.5 1000 4.0 30.0 0.5 617.0 6.0 Meerfelder Maar 16.0 190 0.6 30.0 1.2 40.0 1.5 Paladru 31 NA 21.0 NA NA 416.0 5.0 Piburger 23.0 284 0.6 8.9 11.0 7.8 6.0 Pine 10.2 1140 5.3 53 2.0 153 2 Reither 8.0 126 0.24 10.0 1.0 NA NA Stubenberg NA NA NA NA NA NA NA Waramaug a 8.5 1330 6.3 31.8 0.0 131.9 3.0 Wiler 17.5 NA 0.6 11.0 NA NA 3.0 Wononscopomuc a 15.1 201 0.9 NA 0.0 21.0 5.0 a Active pumping. b Inner diameter. c Below lake level — or above for negative values. d Operation only during spring. Source: From Nürnberg, G.K. 1987. J. Environ. Eng. 113, with additions (with permission); NA, not available. FIGURE 7.2 Changes in epilimnetic TP concentrations (after – before) vs. grand total TP export via hypolim- netic withdrawal (calculated as annual export multiplied by years of operation): Regression line is shown, y = 46 − 30 log x, n = 8, r 2 = 0.75. (From Nürnberg, G.K. 1987. J. Environ. Eng. 113. With permission.) Change in epilimnetic TP (ug L −1 ) 0 −20 −40 −60 10 100 1000 Grand total TP export (kg) Copyright © 2005 by Taylor & Francis 7.2.1 SPECIFIC CASES 7.2.1.1 Mauen See This is one of the most successful cases of hypolimnetic withdrawal (Gächter, 1976). An Olszewski tube was installed in 1968 in this Swiss lake at a depth of 6.5 m (Table 7.1). Prior to installation, external P loading was reduced from about 700 to 300 mg/m 2 per yr (Nürnberg, 1987). The discharge of 4 m 3 /min provided a hypolimnetic (> 4 m) water residence time of 0.2 years. Marked improve- ment in lake quality followed installation. Hypolimnetic DO and Secchi visibility increased and hypolimnetic TP decreased by 1,500 μg/L, the most of any lake examined (Nürnberg, 1987). Epilimnetic TP decreased by 60 μg/L. Oscillatoria biomass decreased from a before-treatment summer maximum of 152 g/m 2 to 41 g/m 2 , 7 years after installation. Before installation, internal P loading from lake sediments during June and July was more than 200 times that of external loading. After installation, internal loading progressively decreased to only four times external loading. Sediment P release progressively declined for the 6 years of observation following installation. During that time, P export exceeded external loading (360 kg/yr) by a total of 3,700 kg, resulting in a decrease in P content of the surficial sediments. 7.2.1.2 Austrian Lakes Pechlaner (1978) reported on the response of three lakes following installation of Olszewski tubes; Piburger See, Reither See, and Hechtsee. Characteristics of the three lakes are given in Tables 7.1 and 7.2. All three lakes are relatively small but important to local populations and tourists for recreation, especially swimming. The Olszewski tubes were installed to accelerate the restoration process following sewage effluent divertion. The tube in Piburger See draws water from a depth of 23 m, which is nearly the maximum depth of the lake (24.6 m). Total length of the tube is 639 m, with a diameter of 8.9 cm. Hypolimnetic water is discharged at 0.6 m 3 /min at a point downstream that is 13.5 m below lake level. While oxygen content markedly increased, there was no recognizable oligotrophication. In 1970, the same year as the tube was installed, the DO content at the time of ice cover increased by 63% over pre-tube conditions in 1969. DO continued at the improved level or higher for the next 7 years. However, the lake’s trophic state did not change because epilimnetic TP declined by 5 μg/L (Pechlaner, 1979). Piburger See tends to be morphometrically meromictic. The lake mixed completely only twice during the 9 years of observation, even though the monomolimnion was effectively replaced about FIGURE 7.3 Proportional change - 0.116 (0.026) x, n = 10, r 2 = 0.72. (From Nürnberg, G.K. 1987. J. Environ. Eng. 113. With permission.) Proportional change of epilimnetic TP −.4 −.8 0 0369 Withdrawal duration (yr) Copyright © 2005 by Taylor & Francis three times per year by virtue of the tube discharge. Increased circulation of deep water across the bottom sediments, as well as the removal of P-rich water overlying the sediments, resulted in increased internal loading that tended to compensate for the increased losses of P via the tube (see effect of dilution on internal loading, Chapter 6). Phosphorus losses through the tube over 3 years were 79–192% more with the tube than would have occurred without it (Pechlaner, 1979). In contrast to Piburger See, Reither See improved markedly in quality following installation of a tube (Pechlaner, 1978). The tube was placed near the maximum depth (8.2 m) of the dimictic lake in 1972. Tube diameter was 10 cm and water discharged at 0.24 m 3 /min from the hypolimnion of the 1.5-ha lake. Epilimnetic TP decreased from annual means of 38 and 43 μg/L in 1974 and 1975 to 21 μg/L in 1977. Transparency nearly doubled over the 4-year period following installation. There was some uncertainty about change in phytoplankton biomass, due to interference with detritus. However, there were less blue-green algae after installation. A larger tube (18 cm) was placed in Hechtsee in 1973. The depth of placement, however was not near the maximum depth as in the other two lakes. Because of meromixis, odors from the monomolimnion were quite strong. Therefore, the tube was placed at 25 m, considerably less than the 56.6 m maximum depth, in order to protect the recreational environment around the lake from nuisance odors. Tube discharge from the 26.3 ha lake varied from 1.2 to 1.8 m 3 /min. Because monomolimnetic water was not withdrawn, DO remained at zero from 25 m to the bottom. DO increased significantly above 25 m after installation of the tube and P transport from the lake increased markedly even though the tube was placed above the monomolimnion. During the first four years following installation, P output (203 kg) exceeded input (93 kg) by 110 kg, which was the actual decrease in lake TP content. TP above 25 m declined by 70–80% from 1973 to 1977, while, as expected, TP below 25 m changed little and actually showed some increase (Pechlaner, 1978). 7.2.1.3 U.S. Lakes Withdrawal systems were installed in the shallower of two basins of Lake Wononscopomuc, Connecticut, in 1980. Hypolimnetic water was discharged from the shallow basin’s maximum depth of 15.1 m at 0.9 m 3 /min (Table 7.2), which was sufficient to replace the hypolimnetic volume in 5.6 months (Kortmann et al., 1983; Nürnberg et al., 1987). Lake quality improved substantially. Hypolimnetic TP decreased from about 400 μg/L before to less than 100 to 50 μg/L over 5 years and epilimnetic TP decreased from 24–30 μg/L to 10–14 μg/L following the start of withdrawal. The decreased TP was apparently due to reductions in internal loading, which was verified by a 79% decrease in measured sediment release in the shallow basin after 2 years of withdrawal (Nürnberg et al., 1987). DO in the hypolimnion also increased and the anoxic factor (days of anoxia) decreased from 50–65 before to less than 30 after withdrawal. Transparency remained high and unchanged (> 5 m), but metalimnetic blooms of O. rubescens were eliminated by the treatment. Two systems were installed in Lake Waramaug, Connecticut, in 1983. One withdrew water from 8.5 m in one end of the long, S-shaped lake (12.8 m maximum depth) and discharged it at 6.3 m 3 /min (Table 7.2). The other system withdrew water from the hypolimnion at the other end of the lake, returning it aerated. There were no significant trends in TP, either in the hypolimnion or epilimnion, during the first 3 years following withdrawal. However, the anoxic factor decreased from 76–89 to 75 days. Reasons for no significant response in TP were: (1) insignificant magnitude of TP removal or duration of removal, or (2) excessive external loading (Nürnberg et al., 1987). The other U.S. lake treated with withdrawal is Lake Ballinger, north of Seattle. The device was installed in 1982 and allows the lake inlet stream to be directed to the hypolimnion through a 276 m, 30.5 cm diameter pipe. The option also exists to allow all or some fraction to enter the epilimnion if inflow temperature exceeds 16°C and there is a tendency to destratify the water column. A control Copyright © 2005 by Taylor & Francis weir exists at the outlet to adjust the fraction of hypolimnetic and epilimnetic water discharged. The mean flow through the 381 m, 30.5 cm outflow pipe was 3.4 m 3 /min, which resulted in a replacement time for the hypolimnion of about 3 months (KMC, 1986). Anoxia occurred for only 2 weeks in 1983, the year after installation, and the hypolimnion remained oxic with at least 3 to 4 mg/L DO during the stratification period in 1984, which was thought to be due to reduced ammonia in the inflow. Hypolimnetic DO remained above 2 mg/L during 1985. Maximum hypolimnetic TP decreased from about 450 to 900 μg/L during 1979–1981, before installation, to about 100 to 150 during 1982 to 1985, after installation. TP at overturn in 1984 was 15 μg/L, the lowest level ever observed. More recent data are unavailable. Operation of the system has been intermittent in recent years due to odors from the discharge stream that borders a golf course. The lake was treated with alum in 1993. Internal loading was reduced from a high pre-installation value of 227 kg in 1979 to only 17 kg in 1984. The overall decrease in internal loading was 70%. Unfortunately, a substantial increase in external loading during the late 1970s and early 1980s prevented much reduction in epilimnetic TP and consequent improvement in lake quality (KCM, 1986). A 1,677-m hypolimnetic withdrawal pipe was installed in Devil’s Lake, Wisconsin, in 2002 at the maximum depth, which varies from 13.5 to 15.7 m (Table 7.1,2). The outflow rate is controlled to vary from 6.8 to 10.3 m 3 /min, depending on lake level. The outflow P concentration averaged 725 μg/L for 48 days of operation in 2002, discharging 446 kg of hypolimnetic TP (Lathrop, personal communication; Lathrop et al., 2004). Data were not yet available to assess lake quality improvement. The project was initiated because high internal P loading from deep-water sediments caused excessive amounts of planktonic and periphytic algae, even though external inputs from cultural sources were eliminated in prior decades. Potential indirect benefits of reduced productivity included reduction in swimmer’s itch by decreasing parasite–host snail densities feeding on periphyton, and reduced fish mercury concentrations by shortening the extent and duration of hypolimnetic anoxia, which is necessary for sulfate-reducing bacteria to convert inorganic Hg to methyl Hg. Hypolimnetic withdrawal was chosen as the only suitable technique to restore the lake to its original pristine condition because field and laboratory results confirmed that internal P loading could be significantly reduced after multiple withdrawals. Other techniques to reduce internal P loading were rejected due to: (1) high cost, e.g., aeration, hypolimnetic water treatment, (2) opposition to adding chemicals, e.g., alum, to one of the state’s high use, “outstanding resource waters,” and (3) long-term ineffectiveness of other techniques, e.g., aeration, alum, without continual or periodic retreatment. The siphon withdrawal system has the important advantage of no operation cost. An additional benefit was alleviation of recently recurring flooding problems in the State Park from high lake levels (Lathrop, personal communication; Lathrop et al., 2004). 7.2.1.4 Canada The restoration of Pine Lake, near Red Deer, Alberta, began in 1991 to improve water quality to a mesotrophic state that existed prior to European settlement (Sosiak, 2002). Epilimnetic TP concentrations reached medians around 100 μg/L during the mid 1990s with chlorophyll (chl) a medians of 20–50 μg/L. Most (61%) of the lake TP originated from internal loading. Controls on external loads from surface sources (36%) took place during 1996–1998 and a 1,400-m hypolimnetic withdrawal pipe was installed in 1998 to reduce internal loading (Table 7.1). The withdrawal system produced high rates of P loss (Table 7.2), and along with external controls, has reduced lake TP and improved water quality (Sosiak, 2002). TP concentration decreased by 44–47% and chl a by 76–81% during 1996–2000. Median TP concentrations of 53–61 μg/L equaled those expected from recovery, while chl a (7.5–11.1 μg/L) and transparency (2.7–3.4 m) exceeded expectations. Since 2000, TP and chl concentrations have remained relatively low Copyright © 2005 by Taylor & Francis (Sosiak, personal communication). However, there have been blooms of Gloeotrichia, which was apparently absent before treatment. While external controls probably contributed to the recovery, most of the reduction in lake TP (29%) occurred during, and was attributed to, hypolimnetic withdrawal. Some of the improvement, however, was probably due to lower year-to-year surface runoff, which was positively related to lake TP over the 15 year period of data. Nevertheless, monitoring of other Alberta lakes did not show a widespread decline in lake TP that could be attributed to regional climatic conditions (Sosiak, 2002). There have been no significant adverse water quality effects in the outlet stream, although temperature and DO were lower immediately downstream. Odors have not been a problem. Such a complete, long-term data set for a project is unusual and is continuing. Such thorough monitoring has allowed a definitive assessment of the recovery and project cost-effectiveness. Chain Lake is small, shallow and polymictic in British Columbia (Table 7.1). Raising the lake level 1.3 m in 1951 created eutrophic conditions (McDonald et al., 2004). Low nutrient dilution water was diverted to the lake in the 1960s and a small area to 9 m was dredged to enhance stability. Summer TP and chl a reached concentrations of 300 and 100 μg/L, respectively, with blue-green algal blooms. Withdrawal has consistently exported water and TP over the 9 years of operation (Table 7.2). Transparency has increased significantly (∼ 1 m) over that time period. Downstream adverse effects from degraded water quality were partially mitigated by a fountain aerator. 7.3 COSTS Installation costs (in 2002 U.S. dollars) for the three systems in the U.S. lakes were as follows: Lake Ballinger (41 ha, 3.4 m 3 /min flow) — $420,000; Lake Waramaug (287 ha, 6.3 m 3 /min) — $62,000 (Davis, personal communication; KMC, 1981); Devil’s Lake (151 ha, 9.1 m 3 /min) — $310,000 (Lathrop, personal communication); Pine Lake (412 ha, 5.3 m 3 /min) — $282,000, not including contributed labor and equipment. Relatively low cost and low annual maintenance are definite advantages of hypolimnetic withdrawal. 7.4 ADVERSE EFFECTS Discharge of hypolimnetic water containing high concentrations of P, ammonia, hydrogen sulfide and reduced metals and no oxygen may cause a water quality problem downstream. If the outflow stream contains an important fishery and is otherwise used for recreation or water supply, then special precautions are necessary to minimize adverse effects. Withdrawal water from Lakes Wononscopomuc and Waramaug is aerated and mechanically cleaned before being discharged downstream and the intake pipe end in Lake Waramaug is elevated to avoid high concentrations and fertilization effects downstream (Nürnberg et al., 1987). Discharge from Lake Ballinger must be interrupted at times due to odors (2 of the 6 months of stratification) and high nutrient content is apparently responsible for extensive periphyton growth downstream from the outlet. Odors are a nuisance to users of the adjacent golf course. The discharges from Hect, Klopeiner, and Kraiger See contained high concentrations of toxic substances so they were stopped during the late summer. Mixing of discharge hypolimnetic water with epilimnetic water would minimize adverse downstream effects. 7.5 SUMMARY The advantages of hypolimnetic withdrawal are threefold: (1) relatively low capital and operational costs, (2) evidence of effectiveness in a large fraction of cases, and (3) potentially long-term and even permanent effectiveness. In most cases hypolimnetic DO increased, resulting in a decrease in Copyright © 2005 by Taylor & Francis the anoxic volume and the days of anoxia. Internal P loading usually decreased and if there was not an offsetting high external loading, epilimnetic TP also decreased. The effectiveness of withdrawal apparently depends on magnitude and duration of TP transport from the hypolimnion. Thus, it is important to exchange the hypolimnion volume as frequently as possible. A low rate of replacement may limit the effectiveness of this technique. A desirable exchange rate is severalfold during the stratification period and the desired magnitude can be determined by comparing the oxygen deficit rate with the rate of oxygen transport. For example, the flow directed to the hypolimnion in Lake Ballinger was established based on the desire to add oxygen at double the oxygen demand rate in the hypolimnion. As a result, hypolimnetic water was exchanged about every 3 months. In Mauensee, it was exchanged every 2.4 months. Therefore, an exchange rate of at least once in 2 to 3 months is recommended to assure the effectiveness of withdrawal. In addition, results indicate that at least a 3 and possibly a 5 year duration of TP export may be necessary to see improvement in lake (epilimnetic) quality. There is a possibility of negative effects on downstream water quality due to low DO, high nutrient content and reduced substances. If the outflow stream contains an important fishery and is otherwise used for recreation or water supply, then special precautions may be necessary to maintain water quality. The extent to which DO in the outflow water will be reduced can be estimated by comparing the existing DO deficit in the lake with the input load of DO (Pechlaner, 1979). If low DO is expected in the outlet, then aeration equipment should be installed. Whether the high P content will cause nuisance attached algal and secondary BOD problems downstream will depend upon the extent to which periphyton growth is limited by nutrients compared with other factors. REFERENCES Björk, S. 1974. European Lake Rehabilitation Activities. Rep. Inst. Limnol. University Lund, Sweden. Davis, E.R. 1983. Personal communication. The Hotchkiss School, Lakeville, CT. Dunalska, J., G. Wisniewski and C. Mientki. 2001. Water balance as a factor determining the Lake Kortowskie restoration. Limnol. Rev. 1: 65–72. Eschmann, K.H. 1969. Die sanierung des wiler Sees durch albeitung des Tiefenwassers. Gesundheitstechnik Zurich 3: 125–129. Gächter, R. 1976. Die Tiefenwasserableitung, ein Weg zur Sanierung von Seen. Schweiz Z. Hydrol. 38: 1–28. Hamm, A., and V. Kucklentz. 1981. Moglichkeiten und Erfolgsaussichten der Seenrestaurierung. Materialien der Bayrischen Landesanstalt fur Wasserforschung, Munchen, FDR, 15: 1–221. Keto, A., A. Lehtinen, A. Mäkelä and I. Sammalkorpi. 2004. Lake Restoration. In: P. Eloranta, Ed., Inland and Coastal Waters of Finland, University of Helsinki and Palmina Centre for Continuing Education. KMC. 1981. Lake Ballinger Restoration Project Interim Monitoring Study Report. Kramer, Chin and Mayo, Seattle, WA. KMC. 1986. Restoration of Lake Ballinger: Phase III Final Report. Kramer, Chin, and Mayo, Seattle, WA. Kortmann, R.W., E.R. Davis, C.R. Frink and D.D. Henry. 1983. Hypolimnetic withdrawal: Restoration of Lake Wonoscopomuc, Connecticut. In: Lake Restoration, Protection and Management. USEPA-440/5- 83-001. pp. 46–55. Lascombe, C., and J. De Beneditis. 1984. Une expérience de soutirage des eaux hypolimniques au Lac de Paladru (lsère-France): Bilan des cing premières années de fonctionnement. Verh. Int . Verein. Limnol. 22: 1035. Lathrop, R.C. Personal communication. Wisconsin Dept. Nat. Res., Madison. Lathrop, R.C., T.J. Astfalk, J.C. Panuska and D.W. Marshall. 2004. Restoring Devil’s Lake from the bottom up. Wisc. Nat. Resour. 28: 4-9. Livingstone, D.M. and F. Shanz. 1994. The effects of deep-water siphoning on small, shallow lake. Arch. Hydrobiol. 32: 15-44. McDonald, R.H., G.A. Lawrence and T.P. Murphy. 2004. Operation and evaluation of hypolimnetic withdrawal in a shallow eutrophic lake. Lake and Reservoir Manage. 20: 39–53. Copyright © 2005 by Taylor & Francis [...]... Olszewski, P 1 973 Funfzehn Jahre Experiment auf den kortowo-See Verh Int Verein Limnol 18: 179 2– 179 7 Pechlaner, R 1 975 Eutrophication and restoration of lakes receiving nutrients from diffuse sources only Verh Int Verein Limnol 19: 1 272 –1 278 Pechlaner, R 1 978 Erfahrungen mit Restaurierungsmassnahmen an eutrophen Badeseen Tirols Osterreichische Wasserwirtsch 30: 112–119 Pechlaner, R 1 979 Response to...Nürnberg, G.K 19 87 Hypolimnetic withdrawal as lake restoration technique J Environ Eng 113: 1006–1016 Nürnberg, G.K and B.D LaZerte 2003 An artificially induced Planktothrix rubescens surface bloom in a small kettle lake in southern Ontario compared to blooms worldwide Lake and Reservoir Manage 19: 3 07 322 Nürnberg, G.K., R Hartley and E Davis 19 87 Hypolimnetic withdrawal in two North American lakes with... See to reduced external loading and removal of monomoliminic water Arch Hydrobiol Suppl 13: 293–305 Scharf, B.W 1983 Hydrographie und morphometric einiger Eifelmaare Beitrage Landespflege Reinland-Pfalz 9: 54–65 Scharf, B.W 1984 Errichtung und Sicherung Schutzwürdige Teile von Natur und Landschaft mit gesamtstaatlich Repräsentativer Bedeutung Natur und Landschaft 59: 21– 27 Sosiak, A Personal communication... Initial Results of the Pine Lake Restoration Program Alberta Environment, Edmonton Thaler, B and D Tait 1981 Kleiner Montiggler See Die auswirkungen von Belüftung und Tiefenwasserableitung auf die physikalischen und chemischen Parameter in den Jahren 1 979 und 1980 Tatigkeitsbericht des Biologischen Landeslabors autonome Provinz Bozen 2: 132–193 Vrhovsek, D., G Kosi, M Karalj, M Bricelj and M Zupar 1985... Tatigkeitsbericht des Biologischen Landeslabors autonome Provinz Bozen 2: 132–193 Vrhovsek, D., G Kosi, M Karalj, M Bricelj and M Zupar 1985 The effect of lake restoration measures on the physical, chemical, and phytoplankton variables of Lake Bled Hydrobiologia 1 27: 219–228 Copyright © 2005 by Taylor & Francis . from the hypolimnion of the 1.5-ha lake. Epilimnetic TP decreased from annual means of 38 and 43 μg/L in 1 974 and 1 975 to 21 μg/L in 1 977 . Transparency nearly doubled over the 4-year period following. 855–861. Olszewski, P. 1 973 . Funfzehn Jahre Experiment auf den kortowo-See. Verh. Int. Vere in. Limnol. 18: 179 2– 179 7. Pechlaner, R. 1 975 . Eutrophication and restoration of lakes receiving nutrients. Francis 7. 2 TEST CASES 7. 2.1 G ENERAL TRENDS Hypolimnetic withdrawal installation is documented in 21 lakes and 15 of those are in Europe (Björk, 1 974 ; Nürnberg, 19 87) . Results are reported from 17 lakes