9 Biomanipulation 9.1 INTRODUCTION Intensive research over many decades has developed an understanding of factors regulating distri- bution, abundance, productivity, and species composition of phytoplankton, especially in deep lakes (reviews by Pick and Lean, 1987; Hecky and Kilham, 1988; Kilham and Hecky, 1988; Seip, 1994, among many). The common approach for long-term control of nuisance algae is to lower nutrient concentrations, an approach supported by controlled experimental laboratory, field enclosure, and whole lake investigations demonstrating that phosphorus (P) and sometimes nitrogen (N) concen- trations are causally linked, especially on a long-term basis, to algal production (e.g., Schindler, 1977; Smith and Bennett, 1999). The link between P concentration and algal biomass is frequently illustrated with a log-log TP-chlorophyll regression indicating that most long-term changes in algal biomass are explained by changes in P concentration (Figure 9.1). However, when these data are plotted on a linear scale (Figure 9.2), especially on a short-term basis, variances are apparent, suggesting other factors in addition to nutrients can be important in determining algal biomass. For example, Schindler (1978) found a highly significant correlation (r = 0.69) between pelagic pro- ductivity and steady state lake P concentrations for 66 P-limited lakes (shallow and deep), ranging in latitude from 38° S to 75° N. The relationship, however, explained only about half of the variance, meaning that P concentration and chlorophyll are highly correlated, but that the relationship might be weak or non-existent for some lakes in some years or parts of years. Grazing, mixing, and/or allelopathic materials, might influence and/or control algal biomass in these lakes. An example is Square Lake, Minnesota (Osgood, 1984), a lake with a greater Secchi Disc (SD) transparency than expected from its TP concentration of about 20 μg P/L (mesotrophic). SD was more than 7 m during summer months, a depth typical of oligotrophic lakes, and apparently due to Daphnia grazing. One purpose of this chapter is to examine factors other than resources (e.g., nutrients, light) that can control algal biomass in deep lakes, and to discuss how lake managers might use this knowledge to address phytoplankton problems. Since most lakes are shallow and may be dominated by either phytoplankton or macrophytes, this chapter also examines factors determining which producer type dominates, and how this knowledge can be used to manage shallow lakes. 9.2 TROPHIC CASCADE As illustrated by the Square Lake, Minnesota case history, zooplankton grazing is a source of algal mortality, sometimes leading to lower algal biomass in the water column than expected for a given nutrient level. This might occur when planktivores are suppressed by piscivores. But in some lakes, zooplankton herbivory may be low during some periods of the summer, perhaps due to fish or insect planktivory, allowing phytoplankton to bloom. A set of hypotheses was developed to explain the roles of resources (nutrients, light) and trophic level interactions. The original organization of these ideas was directed at terrestrial communities (Hairston et al., 1960), and was later (Smith, 1969) proposed for lakes (see Hairston and Hairston, 1993). Hairston et al. (1960) predicted that in systems with three dominant trophic levels (producers, herbivores, primary carnivores), producers would be resource-controlled, whereas in four trophic Copyright © 2005 by Taylor & Francis level systems (top predator also), producers would be consumer (herbivore)-controlled and the first carnivore level would be controlled by predation. Observations of ponds by Hrbacek et al. (1961) supported the above ideas. Fish planktivory (no piscivory) reduced zooplankton grazing, leading to algal blooms. Further early evidence, from Brooks and Dodson (1965), found that planktivory by the alewife (Alosa pseudoharengus) in New England lakes led to elimination of the most efficient herbivores (large-bodied Daphnia) and to selection for smaller-sized zooplankton (e.g., Bosmina) that have lower grazing rates and choose smaller food (algae) particles. They proposed the “size–efficiency” hypothesis to explain grazing impacts of smaller and larger-bodied zooplankton on phytoplankton. The term “trophic cascade” was introduced by Paine (1980) to describe the roles of species that he termed “strong links” or “strong interactors” in intertidal communities. These are species whose removal (or introduction) produced dramatic changes in prey biomass. If the prey was a competitively superior species, the effects could “cascade” from predator to trophic levels one or two links away. Pace et al. (1999) defined “trophic cascades” as (p. 483): “reciprocal predator–prey effects that alter the abundance, biomass or productivity of a population, community or trophic level across more than one link of the food web.” The pelagic trophic cascade, with and without a dominant (“strong link”) top carnivore level, is illustrated in Figure 9.3. Carpenter et al. (1985) argued that trophic cascades could explain the large variances (Figure 9.2) in algal biomass or productivity between lakes with similar nutrient concentrations. They proposed that nutrient levels determined the long-term productivity or trophic state of a lake, but the year-to-year variances from expected trophic state were set by trophic-level interactions. Strong FIGURE 9.1 Relationship between summer chlorophyll and total phosphorus in a number of lakes. (From Shapiro, J. 1979. U.S. Environmental Protection Agency National Conference on Lake Restoration. USEPA 440/5-79-001.) Chlorophyll a µg/l 1000 100 10 1 0.1 1 10 100 1000 Total P µg/l Copyright © 2005 by Taylor & Francis piscivory suppressed planktivores, allowing zooplankton grazing to reduce algal biomass, a trophic cascade extending from piscivores to phytoplankton. DeMelo et al. (1992) suggested that evidence for trophic cascades in lakes is weak, except for strongly manipulated lakes, a conclusion contradicted by some experiments, but supported by others. Jeppesen et al. (2000) described trophic cascades in shallow Danish lakes. Brett and Goldman (1996) noted that there have been few whole-lake studies, but in 54 pond and enclosure experiments there was evidence of trophic cascades. Trophic cascades continued over a multi- year period in fertilized, dimictic lakes (Carpenter et al., 2001). In contrast, Drenner and Hambright (2002) found that 10 of 17 experiments, not confounded by other manipulations, failed to support the trophic cascade hypothesis. However, in most lakes dominated by planktivores (three trophic levels) the slope of the chlorophyll: TP regression (Figure 9.1) was three times that of four level (piscivore- dominated) lakes, indicating that piscivore control of planktivory may lead to enhanced zooplankton grazing and lower algal biomass than expected for a given nutrient level. There also may be a “behavioral cascade.” Planktivorous fish seek refuge in macrophyte beds in the presence of pisci- vores caged in open water, allowing longer open water feeding by Daphnia than when piscivores are absent (Romare and Hansson, 2003). FIGURE 9.2 Replotting of part of the data from Figure 9.1. (From Shapiro, J. 1979. U.S. Environmental Protection Agency National Conference on Lake Restoration. USEPA 440/5-79-001, pp. 161–167.) 200 150 100 50 0 0 50 100 Chlorophyll a µg/l 150 Total P µs/l Copyright © 2005 by Taylor & Francis The trophic cascade hypothesis of Carpenter et al. (1985) is one of the most significant in modern limnology. It stimulated new research and led to a paradigm about control of lake produc- tivity that included both biotic interactions and the role of resources. Readers are urged to examine the many books and review articles describing this concept (e.g., Kerfoot and Sih, 1987; Carpenter, 1988; Gulati et al., 1990; Elser and Goldman, 1991; Carpenter and Kitchell, 1992, 1993; Hansson, 1992; McQueen, 1998). FIGURE 9.3 Hypothetical scheme showing the connections involved in food-chain biomanipulation in lakes. Shaded area represents tentative connections. (From Benndorf, J. et al. 1984. Int. Rev. ges. Hydrobiol. 69: 407–428. With permission.) Low Possibly High (small species) (Large) (Colonies) Effects on water quality High secchi depth Normal or high pH Normal or extreme Low secchi depth High pH Extreme value of O 2 values of O 2 High Low Low High High Low High (Small species) (Small body size) (large body size) Zooplankton Predators Zoo- plankton feeders Phytoplankton Role of the carnivorous zooplankton Role of the nutrient load and of the hydrophysical conditions ? ? Biomass of Copyright © 2005 by Taylor & Francis 9.3 BASIC TROPHIC CASCADE RESEARCH Research on the trophic cascade hypothesis (Carpenter et al., 1985) generated a greater understand- ing of lakes, and many new questions about lake ecology. Trophic cascades may be more common in mesotrophic lakes than in oligotrophic or hypereutrophic lakes, leading to an “intermediate trophic state” hypothesis (Carney, 1990; Figure 9.4). In mesotrophic lakes, edible, nutritious algae dominate the plankton, and large-bodied zooplankton are abundant. In eutrophic lakes, especially hypereutrophic lakes, the phytoplankton community may be dominated by cyanobacteria that may be toxic, inedible, non-nutritious, and/or produce clogging of the filter-feeding mouthparts of zooplankton (Gliwicz, 1990; Lampert, 1982). These factors may explain the rarity of large-bodied zooplankton in eutrophic lakes, rather than planktivory (deBernardi and Giussani, 1990; Gliwicz, 1990; DeMott et al., 2001). The “intermediate trophic state” hypothesis was examined by comparing grazing in ultra- oligotrophic Lake Tahoe (California/Nevada), mesotrophic Castle Lake, California, and eutrophic Clear Lake, California, using enclosures with ambient or enhanced ambient zooplankton, and enclosures with added Daphnia pulex (Elser and Goldman, 1991). In the eutrophic lake, ambient zooplankton (even at eight times in-lake density) had no impact on phytoplankton biomass. D. pulex had a weak effect. It was believed that Anabaena circinalis, (42% of the phytoplankton) was either inedible or interfered with filter-feeding. In the mesotrophic lake there were large declines in phytoplankton but increases in primary productivity, suggesting grazing and nutrient recycling by zooplankton. In oligotrophic Lake Tahoe enclosures, copepods dominated with no grazing impact. The trophic cascade was strongest in the mesotrophic lake. McQueen et al. (1986, 1989, 1992) proposed a “top-down bottom-up” model to explain trophic level interactions, based on enclosure experiments and a multi-year study of eutrophic Lake St. George, Ontario. Regressions between TP, chlorophyll, and fish biomass (piscivore and planktivore) indicated that bottom-up forces (nutrients) were strongest at trophic levels nearest resources, while top-down forces were strongest near the piscivore level. They predicted that bottom-up control FIGURE 9.4 Schematic diagram of the strength of herbivore grazing and nutrient regeneraton in relation to trophic state. (From Carney, H.J. 1990. Verh. Int. Verein. Limnol. 24: 487–492. With permission.) Herbivore grazing pressure, nutrient regeneration High Low High Large, Oligo- trophic Lakes Mesotrophic Very Eutrophic Lakes, Ponds Cladocerans, esp. Daphnia, with higher filtering rates, nutrient regeneration Copepods dominate, lower grazer concen- trations, less nutrient regeneration Algae with greater defenses, less palatable and nutritious Trophic state Copyright © 2005 by Taylor & Francis becomes increasingly important relative to top-down control in enriched lakes. Therefore, piscivores are less likely to have a cascading effect on algal biomass in the most productive lakes. A 1982 fish winterkill in Lake George eliminated 72% of largemouth bass, allowing a test of the model, using a 6-year database. In 1983–1984, planktivore biomass increased rapidly, and then began to decrease in 1985 as the bass population recovered. As predicted, a strong top-down cascade from piscivores through planktivores to zooplankton was observed, though negative correlations between planktivore biomass and either total zooplankton or Daphnia biomass were not significant. Correlations of zooplankton or Daphnia biomass with chlorophyll and transparency also were not significant, but correlations between log chlorophyll and log TP were positive and significant. McQueen et al. (1989) argued that long-term processes determining trophic level biomass depend on resources and energy flow (“bottom-up”). In accordance with Carpenter et al. (1985), McQueen et al. (1989) concluded that short-term disturbances or cascades set “realized biomass” limits. Lakes are strongly influenced by year to year changes in precipitation and associated water and nutrient loading and by climate (mixing events, fish winterkill), and these stochastic events in turn affect both top and bottom trophic levels, including effects on fish biomass, reproduction, and mortality (Carpenter et al., 1985). These events may not be instantaneous effects of stochastic changes, but instead there will be lags or inertias that produce responses at other times. “Algal production today may depend on yesterday’s zooplankton, which depended on zooplanktivores during the past month, which depended on piscivore recruitment the previous year” (Carpenter et al., 1985, p. 637). The controls of algal biomass in shallow and deep lakes and at various levels of enrichment remain controversial. Empirical data from a large sample (n = 446) of shallow and deep lakes, from arctic to temperate zones and ranging from oligotrophic to hypereutrophic, did not support the hypothesis of McQueen et al. (1989) that the cascading effect might be greatest in oligotrophic lakes. Instead, the survey gave partial support to the “intermediate state hypothesis” (Elser and Goldman, 1991), and indicated that at high TP, the most probable condition (even with removal of planktivores) is high algal biomass and turbidity (Jeppesen et al., 2003a). Trophic cascades are an important determinant of biomass at planktivore, herbivore, and producer trophic levels, and explain some of the variance observed in regressions between resources and biomass. Exciting controversies remain about forces that organize ecosystems, and about the adaptations that species populations make to counter those forces. But lake managers want to know whether manipulations of trophic levels can produce clearer lakes, and if so, how long will the effect last? 9.4 BIOMANIPULATION Caird (1945) was the first to publish observations about phytoplankton responses to increased piscivorous fish biomass. Caird suspected that largemouth bass addition to a 15 ha lake in Con- necticut was associated, through food chain effects, with 4 years of reduced phytoplankton blooms, resulting in a termination of copper sulfate applications Shapiro et al. (1975) proposed the term “biomanipulation”, which he defined (Shapiro, 1990) as “a series of manipulations of the biota of lakes and of their habitats to facilitate certain interactions and results that we as lake users consider beneficial — namely reduction of algal biomass and, in particular, of blue-greens” (p. 13). Shapiro et al. (1975) included effects on algal biomass from “top-down” control of zooplanktivores by piscivores, and “bottom-up” effects on algae such as nutrient cycling by benthivorous fish. Many lake managers apply the term only to top-down control of planktivorous fish (see Drenner and Hambright, 2002). More recently, the term has referred to nearly all ecological manipulations to manage algae and aquatic plants. There have been many review articles and books about biomanipulation, including Shapiro (1979), Gulati et al. (1990), DeMelo et al. (1992), Carpenter and Kitchell (1992), Moss et al. Copyright © 2005 by Taylor & Francis (1996a), Hosper (1997), Jeppesen (1998), McQueen (1998), Bergman et al. (1999), and Drenner and Hambright (2002). Lazzaro (1997) is a particularly useful comparative summary. The following examines biomanipulation case histories, particularly their effectiveness and longevity. Several investigators (e.g., Jeppesen et al., 1997) indicated that resource control of algal biomass is weaker in shallow lakes, suggesting biomanipulation may be more successful in them. Therefore, the examination of shallow and deep lake case histories is separated. 9.5 SHALLOW LAKES Characteristics of deep and shallow lakes were described in Chapter 2. Briefly, shallow lakes have a mean depth less than 3 m, are usually polymictic, and often have significant nutrient recycling affecting the entire water column. Compared with deep lakes, fish biomass per volume is higher, the impacts of fish on turbidity and sediment nutrient release are greater, and the area colonized by macrophytes may be close to 100% (Cooke et al., 2001). These and other characteristics are summarized in Moss et al. (1996a) and Scheffer (1998). Shallow lakes are more common than deep ones. Unlike deep lakes, shallow lakes, at moderate (30–100 μg P/L) nutrient levels, appear to exist in alternative states: Either they are clear with rooted plant dominance, or turbid with algae dominance (Scheffer, 1998). At low nutrient concen- trations the clear-water vegetated state is most likely, whereas at higher (perhaps > 100 μg P/L) concentrations, the turbid state is more likely (Hosper, 1997). At concentrations between the extremes, either the clear or turbid state can occur. It is the forces determining lake state that are subject to manipulation, leading to the possibility of “switching” from one state to the other. Good examples of clear and turbid shallow lakes existing within a limited geographic area (Alberta) were presented by Jackson (2003). Macrophyte-dominated, clear-water lakes are resistant to development of algal dominance from increased external nutrient loading because plants reduce wind and boat-generated resuspension of sediments, provide daytime refuge to algae-grazing Daphnia, their periphyton may take up signif- icant amounts of nutrients, and some macrophytes release compounds inhibitory to algae. Piscivores may thrive in macrophyte-dominated lakes, controlling fish that prey on zooplankton and on periphyton-consuming snails (Bronmark and Weisner, 1996). This last effect of fish is important because, as discussed later, abundant periphyton may reduce rooted plant growth. Resistance of the clear water macrophyte-dominated lake to change is reduced by some plant management activities (e.g., harvesting, grass carp; Chapters 14 and 17), by increased fish produc- tion (young of the year (YOY) of most fish species are zooplanktivorous), and by introduction of toxins (e.g., copper sulfate, herbicides, insecticides) lethal to Daphnia and to plants. There is a nutrient-based stability threshold for the clear water, macrophyte-dominated state of about 50–100 μg P/L. Continued loss of stability as nutrient loading increases and/or plant removal occurs can produce an abrupt switch to the alternative, turbid, macrophyte-free state. Moss et al. (1996a) called these changes leading to the turbid state “forward switches.” Figure 9.5 illustrates this model of alternative states and the forces that promote a switch from one state to the other. Note that either the clear or turbid water state can occur without change in overall nutrient concentrations. Switching a turbid lake to a clear water lake may not occur, even when external loading is significantly reduced. This means that the common advice given to shallow lake owners to reduce external loading as a method to clear up the water may not produce expected results. Sediment re- suspension by wind, boat, and fish activity will attenuate light, preventing re-establishment of macrophytes. Extensive internal nutrient recycling may continue to sustain phytoplankton and reduce transparency, preventing re-establishment of clear water and macrophytes. Fish removals, followed by piscivore stocking and enclosures to protect plants from birds, are among the bioma- nipulation procedures that trigger the switch to a clear water state. Reduction of nutrient concen- trations through diversion (Chapter 4) or P inactivation (Chapter 8) increases the probability of the Copyright © 2005 by Taylor & Francis FIGURE 9.5 The alternative stable states model for dominance by aquatic plants or phytoplankton in shallow lakes, over the gradient of total phosphorus concentrations that includes both pristine values and those encountered in polluted conditions. (From Moss, B. et al. 1996. A Guide to the Restoration of Nutrient-Enriched Lakes. Broads Authority, Norwich, Norfolk, UK. With permission.) PLANT DOMINANCE (may operate at any nutrient concentration in the overlap range) Mechanical or boat damage, herbicides, exotic vertebrate grazers, pesticides, increased salinity, differential kills of piscivores. PHYTOPLANKTON DOMINANCE, TURBID WATER Controlled by low nutrient (P) availability to phytoplankton- clear water Tall plants. System stabilized by nitrogen competition with algae and possibly secretion of algal inhibitors, and grazing of periphyton by invertebrates such as snails. Tall plants. System increasingly stabilized by Cladoceran (Daphnia) grazing to maintain clear water. Sparser plants but clear water retained by grazing. PLANT DOMINANCE, CLEAR WATER System often with abundant blue-green algae, some of which may be poorly edible, but main buffer is the lack of zooplankton grazing due to lack of refuges for Cladocera. Green algae become more abundant at high nutrient levels, and are generally grazeable. System buffered by lack of grazers and heavy periphyton growth on any developing plants; possibly also by inhibiting conditions in sediments. 25 50 100 1000 Total phosphorus concentration (micrograms per litre) FORWARD SWITCHES (any nutrient concentration). Biomanipulation by removal of zooplanktivorous fish or addition of piscivores. REVERSE SWITCHES Copyright © 2005 by Taylor & Francis switch. Figure 9.6 illustrates the pattern of resistance of clear and turbid shallow lakes to increasing or decreasing external nutrient loading. Biomanipulation, especially top-down procedures, is more likely to be successful in shallow lakes, and in turn, shallow lakes are easier to biomanipulate because nearly all fish can be removed. The following case histories illustrate the outcomes of some efforts to restore turbid lakes to the clear, macrophyte-dominated state. Most examples are European because they prefer rooted plant- dominated, clear water conditions in their shallow lakes. In North America, with a high density of shallow lakes, ponds, and reservoirs, lake users appear to want an algae-free, non-turbid, macro- phyte-free lake, regardless of factors preventing this condition from being stable or even possible (e.g., high internal nutrient recycling, high external loading, and/or stocking of exotic herbivorous fish). This unrealistic goal is possible only with continual reliance on expensive mechanical and/or chemical controls. More realistic expectations about the trophic state of shallow lakes might be of value to North American lake users. For example, a common tactic is to attempt to manage a macrophyte-dominated lake toward an intermediate biomass of plants that may satisfy the lake users who want a macrophyte- free lake. This condition is unlikely where external and internal nutrient loads are high or increasing, and where plant removal (e.g., harvesting, stocking of grass carp) is extensive. These conditions may drive the lake to the turbid state. It could be more realistic, in some cases, to manage some shallow lakes in an area toward macrophyte-free water that may be compatible with boating and swimming, while managing other nearby lakes toward the clear water condition (Van Nes et al., 1999, 2002). For clear water lakes with high resilience (low probability of switching to the turbid state because nutrient loading and benthivorous fish biomass are low), some macrophyte removal could occur in high use areas. Management goals should be consistent with reality (Welch, 1992a). The following case histories were chosen from situations where the lake was intentionally manipulated rather than from instances of unplanned and drastic biological changes such as a winter fish kill or a drought. 9.6 BIOMANIPULATION: SHALLOW LAKES 9.6.1 C OCKSHOOT BROAD (UK) Cockshoot Broad (3.3 ha, mean depth 1.0 m) is one of several small, riverine, shallow lakes in eastern England. Originally they were macrophyte-dominated, but recently dense phytoplankton replaced macrophytes (Moss et al., 1996b). Aquatic plants in the UK are considered an asset, FIGURE 9.6 Eutrophication and oligotrophication in relation to algal biomass, showing a typical hysteresis curve. (From Hosper, H. 1997. Clearing Lakes. An Ecosystem Approach to the Restoration and Management of Shallow Lakes in The Netherlands. RIZA, Lelystad, The Netherlands. With permission.) Algal biomass Nutrient load Copyright © 2005 by Taylor & Francis providing high biodiversity, and efforts were made to rehabilitate some of these lakes, including Cockshoot Broad. Consistent with conventional wisdom of the time (early 1980s), P removal at municipal waste- water facilities was believed sufficient to rehabilitate Cockshoot Broad. However, high internal P recycling was a major P source, and the Broad was therefore isolated from the adjacent nutrient- rich river, and about one meter of P-rich sediment removed. TP fell, and aquatic plants returned. However, by 1984–1985, submersed plants declined and the phytoplankton-dominated state returned because Daphnia pulex, abundant following isolation and dredging, declined to small numbers by 1984 as planktivorous fish populations recovered (Moss et al., 1986b). Biomanipulation via nearly complete fish removal occurred in winter 1989 and 1990. Fish removal in winter is easier because fish tend to aggregate at this time, making electro-fishing and seining easier. Maintenance fish removal continued in subsequent winters. Daphnia returned, chlorophyll concentration declined, and submersed macrophytes recolonized the broad. High nutri- ent concentrations occurred in the macrophyte and phytoplankton-dominated conditions, indicating that these alternative states were influenced by biological interactions. When Daphnia were absent, chlorophyll concentrations were highly correlated with TP. There was no correlation in years of high Daphnia–low planktivore densities. Grazer control of phytoplankton appeared to be linked to macrophytes that served as physical refuges from planktivory (Timms and Moss, 1984; Moss et al., 1986b, 1994). Unlike deep lakes, where vertical migration can provide a daytime refuge for zooplankton from fish predation (Gliwicz, 1986), shallow lake zooplankton may employ diel horizontal migration (DHM) to and from the littoral zone to provide daytime refuge from planktivory. While Daphnia appear to be chemically repelled by some macrophytes (e.g., Myriophyllum exalbescens), they use other macrophytes to avoid fish (Lauridsen and Lodge, 1996; Burks et al., 2001). However, if littoral zones are dominated by planktivores (including YOY piscivores), Daphnia mortality may be high (Perrow et al., 1999). These authors suggested that if macrophytes comprise 30–40% of lake volume that is sufficient refuge from fish for zooplankton to maintain clear water. The clear-water stabilizing effect of DHM appears to be high when macrophytes are abundant and littoral-associated piscivores control plank- tivory (Burks et al., 2002). The clear water state may be possible, even at elevated nutrient concentrations, when Daphnia grazing is extensive. Additional studies on DHM are needed. An assessment of zooplankton grazing in increasing transparency may be difficult to determine using traditional sampling methods. Only nighttime sampling reveals the actual density of zooplankton in macrophyte-dominated shallow lakes. Daytime open water sampling fails to capture zooplankton in refuges (Meijer et al., 1999). Artificial refugia for large-bodied zooplankton in the English broads, including bundles of brush, strands of polypropylene rope, and mesh cages did not enhance zooplankton survival (Moss, 1990; Irvine et al., 1990). 9.6.2 LAKE ZWEMLUST (AND OTHER DUTCH LAKES) The Lake Zwemlust (1.5 ha, mean depth 1.5 m) case history is instructive because of its long-term data set, and because of problems in maintaining the clear water state after biomanipulation. In 1968, a broad-spectrum herbicide (diuron) was applied, eliminating macrophytes. There was a rapid shift to the turbid, algae-dominated state. A minimum transparency of 1.0 m in swimming lakes is required in The Netherlands, but blooms of Microcystis aeruginosa reduced transparency below this criterion. In winter, 1987, Lake Zwemlust was seined, electro-fished, and drained to eliminate planktivorous and benthivorous fish. It was then stocked with pike (Esox lucius) and rudd (Scar- dinius erythrophthalmus), willow twigs were added as shelter for pike fingerlings, yellow water lily (Nluphar lutea) and Chara were planted, and Daphnia magna and D. hyalina (1 kg wet weight) were introduced (Gulati, 1990; van Donk et al., 1990). Though external nutrient loading remained high (2.4 g P/m 2 per year; van Donk et al., 1993), the water became clear. In 1988–1989 Elodea nuttalli dominated, and phytoplankton became N- Copyright © 2005 by Taylor & Francis [...]... 197 7 with the stocking of pike-perch (Stizostedion lucioperca) and the imposition of fish catch restrictions Stocking, at rates of 20,000 to 80,000 pike-perch per year continued from 198 0– 198 2 and 198 4– 198 8 Changes in lake condition during the pre-biomanipulation years ( 197 7– 198 0) were compared with the biomanipulation period ( 198 0– 198 8) (Benndorf, 198 7, 198 8, 198 9, 199 0; Benndorf and Miersch, 199 1;... were low in 198 7, the first summer of the treatment, partly from intense Daphnia grazing By 199 1, small-bodied Daphnia became dominant after planktivory resumed, and grazing on algae declined Ceratophyllum demersum was the dominant macrophyte in 199 0– 199 1, but was nearly absent in 199 2– 199 4 Late summer algal blooms resumed in 199 2– 199 4 Potamogeton berchtholdii appeared in the spring of 199 2– 199 4, but became... Francis Start of biomanipulation 800 Edible algae Inedible algae Total P 50 600 40 30 400 −1 60 Total P (gL ) Phytoplankton biovolume (mm3 L−1) 1000 70 20 200 10 0 0 197 7 198 0 198 3 198 6 198 9 Year 199 2 199 5 199 8 FIGURE 9. 9 Biovolume of edible and inedible phytoplankton (summer averages, May–October) and concentration of total phosphorus (annual averages) in Bautzen Reservoir (Germany) before and after biomanipulation... Nutrients and lake productivity: Whole-lake experiments Ecol Monogr 71: 163–186 Cooke, G.D., P Lombardo and C Brant 2001 Shallow and deep lakes: Determining successful management options LakeLine 21: 42–46 Coops, H and S.H Hosper 2002 Water-level management as a tool for the restoration of shallow lakes in The Netherlands Lake and Reservoir Manage 18: 293 – 298 De Bernardi, R and G Giussanig 199 0 Are blue-green... Clearing Lakes An Ecosystem Approach to the Restoration and Management of Shallow Lakes in The Netherlands RIZA, Lelystad, The Netherlands Hosper, S.H and E Jagtman 199 0 Biomanipulation additional to nutrient control for restoration of shallow lakes in The Netherlands Hydrobiologia 200: 523–534 Hosper, S.H and M.-L Meijer 199 3 Biomanipulation, will it work for your lake? A simple test for the assessment of. .. nutrient-rich water sources with and without removal of sediment J Appl Ecol 23: 391 –414 Moss, B., S McGowan and L Carvalho 199 4 Determination of phytoplankton crops by top-down and bottomup mechanisms in a group of English lakes, the West Midland Meres Limnol Oceanogr 39: 1020–10 29 Moss, B., J Madgwick and G Phillips 199 6a A Guide to the Restoration of Nutrient-Enriched Lakes Broads Authority, Norwich, Norfolk,... of time scale, lake depth and trophic state Freshwater Biol 47: 2282–2 295 Bergman, E., L.-A Hansson and G Andersson 199 9 Biomanipulation in a theoretical and historical perspective Hydrobiologia 404: 53–58 Brett, M.T and C.R Goldman 199 6 A meta-analysis of the fresh water trophic cascade Proc Natl Acad Sci USA 93 : 7723–7726 Bronmark, C and S.E.B Weisner 199 2 Indirect effects of fish community structure... Engineering and biological approaches to the restoration from eutrophication of shallow lakes in which plant communities are important components Hydrobiologia 200: 367–377 Moss, B 199 8 Shallow lakes biomanipulation and eutrophication SCOPE Newsletter No 29 October, 199 8 Moss, B., H.R Balls, K Irvine and J Stansfield 198 6 Restoration of two lowland lakes by isolation from nutrient-rich water sources with and. .. Moss, 199 0, 199 8), and attempts to sharply reduce Canada Geese populations by addling eggs and by lakescaping (Chapter 5) Other low cost alternatives are described by McComas (2003) 9. 9 SUMMARY AND CONCLUSIONS Drenner and Hambright ( 199 9, 2000) reviewed methods and successes of biomanipulation experiments Most (80%) experiments were in Europe and on small (< 25 ha), shallow (< 3 m mean depth) lakes. .. following drastic fish-stock reduction in shallow, eutrophic lakes Ecol Eng 2: 63–72 Hrbacek, J., M Dvorakova, V Korinek and L Prochazkova 196 1 Demonstration of the effect of the fish stock on the species composition of zooplankton and the intensity of metabolism of the whole plankton assemblage Verh Int Verein Limnol 14: 192 – 195 Irvine, K., B Moss, and J Stansfield 199 0 The potential of artificial refugia . 199 0– 199 1, but was nearly absent in 199 2– 199 4. Late summer algal blooms resumed in 199 2– 199 4. Potamogeton berchtholdii appeared in the spring of 199 2– 199 4, but became covered with epiphytes and. period ( 198 0– 198 8) (Benndorf, 198 7, 198 8, 198 9, 199 0; Benndorf and Miersch, 199 1; Benndorf et al., 198 4, 198 8, 198 9, 2002). Planktivores (perch) were controlled but not eliminated by pike-perch and Goldman, 199 1; Carpenter and Kitchell, 199 2, 199 3; Hansson, 199 2; McQueen, 199 8). FIGURE 9. 3 Hypothetical scheme showing the connections involved in food-chain biomanipulation in lakes. Shaded