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Potential for the Development of Submerged Macrophytes in Eutrophicated Shallow Peaty Lakes After Restoration Measures

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Potential for the Development of Submerged Macrophytes in Eutrophicated Shallow Peaty Lakes After Restoration Measures View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Springer - Publisher Connector Hydrobiologia (2007) 584:277–290 DOI 10.1007/s10750-007-0593-x SHALLOW LAKES Potential for the development of submerged macrophytes in eutrophicated shallow peaty lakes after restoration measures R. J. W. van de Haterd Æ G. N. J. Ter Heerdt Ó Springer Science+Business Media B.V. 2007 Abstract Biomanipulation of eutropicated peaty remained turbid and dense macrophyte stands did lakes has rarely been successful; clear water with not develop. The establishment of submerged dense macrophyte stands fails to develop in most macrophytes appeared not to be limited by a lack cases. It was unclear whether (1) high turbidity of propagules. Introduced plants grew poorly in due to resuspension by benthivorous fish or wind turbid water, but very well in clear water. Exclo- is the major cause of low macrophyte density or sures showed that bird grazing reduced the plant whether (2) the establishment of submerged biomass. In clear water grazing seemed to macrophyte stands is prevented by a lack of enhance the vegetation diversity. Periphyton propagules, low cohesive strength of the lake development did not prevent plant growth in sediment, high concentrations of phytotoxics, clear water. After the experiment, the fish stock grazing by waterfowl and/or shading by periphy- was greatly reduced in the whole lake (85 ha), to ton growth. These hypotheses were tested in an test if (3) in a large lake, submerged macrophyte experiment in a shallow peat lake in the Nether- stands will not develop after biomanipulation. In lands (Terra Nova). Removal of fish from a 0.5 ha the first season after fish reduction, transparency experimental site resulted in clear water and the increased and species-rich submerged macro- development of a dense (90% coverage) and phyte stands developed, covering 60% of the species-rich (10 species) submerged vegetation. shallow parts of the lake. Most of the species At a fish-stocked site and a control site the water known to have occurred in the past re-estab- lished. The results indicate that high turbidity caused by benthivorous fish in combination with bird grazing were the major causes of the absence Guest Editors: R. D. Gulati, E. Lammens, N. De Pauw & E. Van Donk of submerged macrophyte stands in this lake. Shallow lakes in a changing world Abiotic conditions after the clearing of the lake were suitable for the growth of macrophytes. We & R. J. W. van de Haterd ( ) infer that the restoration potential of submerged Bureau Waardenburg, P.O. Box 365, 4100 AJ Culemborg, The Netherlands macrophyte stands in eutrophicated peaty lakes e-mail: [email protected] can be high, and results can be obtained quickly. G. N. J. Ter Heerdt Keywords Shallow peaty lake Á Restoration Á Waternet, P.O. Box 8169, 1005 AD Amsterdam, The Netherlands Biomanipulation Á Macrophytes Á Herbivory Á e-mail: [email protected] Periphyton 123 278 Hydrobiologia (2007) 584:277–290 Introduction macrophyte cover (Jeppesen et al., 1997; Scheffer, 1998; Gulati & Van Donk, 2002). The process of Many of the freshwater lakes in the Netherlands colonisation by submerged macrophytes can be originate from peat digging and are very shallow hampered by factors like a lack of propagules, (<2 m). Once the water was oligotrophic and shading by abundant periphyton growth, insuffi- clear, but during the 20th century external cient light conditions in deeper water and grazing nitrogen (N) and phosphorus (P) loading caused by waterfowl (Jeppesen et al., 1997; Hansson et al., eutrophication. At first, this resulted in in- 1998; Scheffer, 1998; Van Donk & Otte, 1996). In creased macrophyte growth and increased bio- peaty lakes, the development of submerged mac- diversity. Since the 1950s, cyanobacterial blooms rophytes may also be limited by high turbidity, due have resulted in high turbidity, poor underwater to resuspension of sediment by wind and wave light climate and loss of submerged vegetation action (Meijer et al., 1999), low cohesive strength in most lakes. Restoration measures have been of the lake sediment in combination with wave employed to reduce the external loading, but action (Schutten & Davy, 2000; Schutten et al., the clear water and macrophyte-dominated state 2005) or high concentrations of phytotoxics such as generally did not return. For the history of the sulphide (Smolders & Roelofs, 1993; Lamers et al., eutrophication and restoration of shallow lakes, 1998). Hence, biomanipulation in peaty lakes may see Van Liere & Gulati (1992), Scheffer (1998) be less successful than in lakes with a mineral and Gulati & van Donk (2002). sediment. Meijer et al. (1999) showed that bioma- One of the reasons why nutrient reduction nipulation results for peaty lakes were indeed less does not result in the return of a clear water favourable than those for other lakes, but did not state is the presence of large numbers of clarify whether this was caused by insufficient fish planktivorous and benthivorous fish. Planktivo- removal or by the factors and conditions rous fish prevent zooplankton from becoming mentioned above. abundant and grazing down phytoplankton Waternet is the water quality manager of many blooms. Benthivorous fish stir up the sediment, shallow peaty lakes in the region south of resuspending large amounts of detritus. A dras- Amsterdam and restoration projects are going tic reduction of fish stocks, a form of bioma- on or planned for several of these turbid lakes to nipulation or biological control, often results in restore the clear-water and macrophyte-domi- a shift from a turbid state towards one with nated state. Before starting drastic and expensive clear water (Jeppesen et al., 1997; Scheffer, measures, we wanted to make sure that macro- 1998; Gulati & van Donk, 2002). However, phytes would be able to colonise peaty lakes unlike results obtained in lakes with mineral rapidly. As part of a large-scale biomanipulation sediment, biomanipulation in peaty lakes in the experiment, we started a pilot study of the Netherlands has rarely been successful (Van colonisation by submerged macrophytes in two Liere & Gulati, 1992; Meijer et al., 1999; Gulati small (0.5 ha) and shallow (0.7 m) experimental & Van Donk, 2002). sites. In this part of the experiment we tested the The failure of restoration measures might be following hypotheses: caused by poor colonisation of the lake sediment (1) High turbidity is the major cause of low by submerged macrophytes (Hansson et al., 1998; macrophyte density. Ko¨ rner, 2002). Macrophytes are able to absorb (2) The establishment of submerged macro- large quantities of nutrients, thereby suppressing phyte stands is prevented by a lack of algal blooms, and they stabilise the sediment propagules, low cohesive strength of the surface, reducing resuspension of detritus. lake sediment, high concentrations of Macrophytes also function as a refuge for zoo- phytotoxics, grazing by waterfowl and/or plankton and are the habitat of predatory fish shading by periphyton growth. (Scheffer, 1998; Hansson et al., 1998; Gulati & Van Donk, 2002). A sustainable clear water situation Even if the colonisation by macrophytes is not requires the development of a dense submerged inhibited in the enclosed sites, it would still not be 123 Hydrobiologia (2007) 584:277–290 279 certain that biomanipulation would work in larger were present in shallow parts of Lake Terra peaty lakes, where waves and poorer light condi- Nova. tions due to greater depth (1.75 m) might prevent macrophyte establishment. Therefore we also Experimental setup performed a whole-lake biomanipulation experi- ment in an 85 ha lake, testing the following Two experimental sites of 0.5 ha each were hypothesis: constructed by building dams between parallel banks in the western part of Lake Terra Nova (3) In a larger lake, submerged macrophyte stands (Fig. 1). Behind these dams, waves were greatly will not develop after biomanipulation. reduced, and water exchange and fish migration were no longer possible. Water depth at these sites ranged between 30 and 90 cm. The bottom Materials and methods was covered with a 0.9 m organic mud layer. At both sites, we greatly reduced the fish stock, using Study area fykes, seine nets, gill nets and electro fishery. Petersen’s mark and recapture method was used This study was performed at Lake Terra Nova, to estimate the fish population before and after also called Lake West Loenderveen (LWL). Lake fishing (Klinge et al., 2003). Fishing was repeated Terra Nova is an 85 ha shallow peaty lake in the until the stock was below 25 kg fresh weight (FW) centre of the Netherlands, originating from peat of benthivorous fish ha–1 and below 15 kg FW of excavation and subsequent erosion, and forming planktivorous fish ha–1. One site—referred to part of the Loosdrecht lake system (Hofstra & below as ‘‘fish-stocked’’—was restocked with Van Liere, 1992). In 1941, more than 50% of the 180 kg FW cyprinids ha–1 (the average density lake bottom was covered by submerged macro- in the lake) in April 2003. In December 2003, the phytes, dominated by Characeae. Water trans- fish population at the fish-stocked site had parency was 2–2.5 m Secchi depth (Leentvaar & increased to 320–400 kg FW of cyprinids ha–1. Mo¨ rzer Bruijns, 1962; Best et al., 1984). Between At the other site, which was not restocked— 1941 and 1980, several observations indicated that referred to as ‘‘fish-less’’, the fish stock had species-rich macrophyte stands were present in increased to 82.4 kg FW of cyprinids ha–1 in Lake Terra Nova. In 1980–1982, dense stands of December 2003. Next to the experimental sites, a Characeae, Elodea sp., Najas marina and Pota- third, morphologically identical but unenclosed mogeton spp.
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