Biomanipulation

The biomanipulation is a biotechnology for control of the food chain . It is mainly used in the context of water quality management for the rehabilitation of over-fertilized lakes. The aim is to limit the phytoplankton biomass by building up a well-developed predatory fish population . The technique of biomanipulation was developed and introduced by the American aquatic ecologist Joseph Shapiro.

Procedure

The eutrophication of lakes usually leads to an excessive supply of unicellular green algae or autotrophic cyanobacteria (formerly also known as "blue algae") due to an oversupply of nutrients , especially phosphorus. This leads to a reduction in the depth of view. The "algae bloom" called mass reproduction limits, z. B. through released toxins (toxins) the usability of the water. When the dissolved oxygen is consumed, it can cause the water to "overturn" (when the algae die).

Single-cell algae are harvested by predators in the free water of a body of water. Filtering small crabs, water fleas (daphnia) and hippopotamuses (copepods) are particularly important. As a result, the water can in principle become clear again. However, the filtering small crustaceans also have their predators. Planktivorous fish species are particularly important, mostly from the carp-like family (cyprinids). Anglers refer to these as "coarse fish" because they do not feed on other fish species. These "non-predatory fish" also have predators, the "predatory fish" such. B. the pike, which feed on other fish species. The process of biomanipulation is now based on an application of the principle of "trophic levels". A system with only algae has one level, with algae and small crustaceans there are two, etc. Each "complete" level can control the level below and effectively limit the density of organisms - but only as long as it does not move itself from a higher level is regulated. A high population of coarse fish therefore indirectly promotes the algae (by harvesting the algivorous small crustaceans). A high population of predatory fish can thus indirectly limit the algae. According to the theory, the length of the food chain and thus the number of trophic levels is limited by the productivity of the ecosystem.

Food web section of a European lake, without destructors (for water fleas ( Daphnia ), ciliates ( Paramecium ), rotifers ( Brachionus ), small crabs ( Mysis ), yellow beetle larvae ( Dytiscus ), pearlfish ( Leuciscus ) and pike ( Esox ) see there)

A modern version of these relationships in general was proposed by the American ecologist SDFretwell as "food chain dynamics". In many larger bodies of water the number of predatory fish does not correspond to the naturally expected state. Predatory fish are z. B. preferred by anglers over cyprinids (usually called "white fish"). Biomanipulation tries to change the trophic levels in the water from an undesirable state (algal blooms) to a desired state (clear water) without changing the framework conditions. Often it is z. B. impossible to reduce the nutrient content of a lake system without considerable effort. In these cases, biomanipulation could still improve the condition.

Naturally, it is problematic that the affected bodies of water always have a tendency to move towards a stable state, towards the ecological balance of a body of water. Is z. If, for example, the number of predatory fish in a lake increases beyond its carrying capacity, the excess fish will eventually perish due to a lack of food. Biomanipulation can therefore easily lead to dramatic short-term changes that are then not permanent. However, lasting successes with the process appear quite possible. Waters with two (at least meta-) stable states are particularly promising here.

In moderately eutrophic lakes, it can often be observed that with slightly increased phosphorus levels, the previously lushly developed "underwater meadows" made up of higher macrophytes, such as spawning herbs, horn leaf, milfoil, waterweed and other species, disappear and are replaced by unicellular organisms that make the water cloudy . The reason is that macrophytes and unicellular algae compete for light and nutrients. Established macrophyte populations can "starve" the unicellular organisms. But if these do arise, they can use the nutrients for themselves and also shade the higher plants. These two states can both be relatively stable with certain nutrient contents, but "tilt" into the other after disturbance. In these cases, biomanipulation leads to the establishment of rich macrophyte populations, which can then stabilize themselves.

Either a top-down or a bottom-up approach is used for biomanipulation :

• The top-down procedure influences the hierarchically structured food pyramid from its top level, in which top predators such as pike (downward control) are also used in the lake . This reduces the proportion of zooplanktophagous mass fish species, so that the small organisms of the zooplankton suffer less from their feeding pressure. In this way, they can better graze the primary producers , the phytoplankton , which not only increases the depth of view , but also has a positive effect on the water quality (see above). Occasionally, fishing from non-predatory fish is used instead of this predatory fish stock.
• The bottom-up process influences the food pyramid in the lake ecosystem by manipulating the nutrient phosphorus from its lowest level (upward control): If the nutrient concentration is lower, the biomass of the phytoplankton decreases . The smaller food supply leads to smaller quantities of zooplankton and thus zooplanktophagous fish; the proportion of carnivorous fish is increasing. In the ideal case, this in turn triggers the reverse mechanism of the top-down process to stabilize. It is often attempted to precipitate the phosphorus with soluble aluminum salts. As an alternative (or parallel to this) attempts are being made to dredge or cover nutrient-rich mud. Pure nutrient management without changing the trophic interactions does not, however, constitute biomanipulation.

Application examples

The process is used and tested worldwide. In the mesotrophic Pohjalampi Lake in eastern Finland, 200 kg of roach and bream were fished between 1993 and 1997 , which led to a significant recovery of the predators . The Indian Naini Lake near Nainital in Uttarakhand was populated in 2008 for biomanipulation with 35,000 Mahseer fish ( Tor putitora ), a native cyprinid that can reach a length of 2.75 meters. In the American Lake Mendota , which is one of the birthplaces of modern limnology due to numerous limnological investigations and research, a significantly increased water transparency was achieved in a biomanipulation project between 1987 and 1998.

The experimental waters in Germany primarily include drinking water reservoirs such as the Bautzen reservoir or the Weidatalsperre , as well as the Feldberger Haussee and the Plußsee . In the Seddin chain of lakes , the Institute for Applied Aquatic Ecology used biomanipulation between 2006 and 2009 to stock pike as part of a pilot project for the rehabilitation of northeast German shallow lakes in accordance with the EU Water Framework Directive (WFD).

Due to its low cost, biomanipulation is one of the most frequently used methods for restoring the quality of seawater in many European countries. Despite the initial successes, however, their long-term effect is assessed critically.

literature

• E. Jeppesen, M. Søndergaard, N. Mazzeo et al. a .: Lake restoration and biomanipulation in temperate lakes: relevance for subtropical and tropical lakes. In: Tropical eutrophic lakes: their restoration and management. Ed. Mallapureddi Vikram Reddy, Science Publishers, Enfield (NH) 2005, Chapter 11, pp. 331-359, ISBN 978-1-57808-370-1 .
• Ranka Junge, Andreas Graber: Biomanipulation of waters: Findings for swimming pond management . Department of Environment and Natural Resources, University of Wädenswil online pdf .
• Peter Kasprzak, Jürgen Benndorf u. a .: Reduction of nutrient loading and biomanipulation as tools in water quality management: Long-term observations on Bautzen Reservoir and Feldberger Haussee (Germany) . In: Lake and Reservoir Management , Volume 23 Issue 4, 2007, pp 410-427. Ed .: North American Lake Management Society ISSN  1040-2381 (electronic) ISSN  0743-8141 (paper) abstract .
• Winfried Lampert : Biomanipulation - a new opportunity for lake restoration? In: Biology in Our Time . Volume 13 Number 3, 2005, pp. 79-86. Wiley-VCH Verlag , Wiesbaden, ISSN  0045-205X .
• M. Leppa, H. Hamalainen, J. Karjalainen: The response of benthic macroinvertebrates to whole-lake biomanipulation . In: Hydrobiologia, Volume 498, 2003, pp. 97-105.
• Hartmut Willmitzer: Restoration of drinking water reservoirs through biomanipulation. In: Wasser & Abwasser Praxis, 2/1996, Gütersloh, 16–23. on-line

Individual evidence

1. ↑ ^{a b} Ranka Junge, Andreas Graber: Biomanipulation von Gewässern .
2. ^ Fretwell, SD (1987): Food chain dynamics - the central theory of Ecology? Oikos 50: 291-301. (Copenhagen)
3. ↑ Olaf Mietz: Deeper insights into the Kähnsdorfer See . In: Land in Sicht , No. 9, 2006. Ed .: Landschafts-Förderverein Nuthe-Nieplitz-Niederung eV, pieces and nature park administration Nuthe-Nieplitz, Dobbrikow. P. 17. ISSN  0946-6762 .
4. ↑ M. Leppa, H. Hamalainen, J. Karjalainen: The response… .
5. ^ Rainwater Harvesting, Naini Lake
6. ^ University of Wisconsin Regents, Center for Limnology
7. ↑ See Hartmut Willmitzer: Restoration of drinking water reservoirs through biomanipulation. Water & wastewater practice, 2/96.
8. ^ Institute for Applied Aquatic Ecology GmbH (IaG) . In: Research for rural areas. Ed .: Land Brandenburg, Ministry for Rural Development, Environment and Consumer Protection. Potsdam 2009, p. 169 PDF ( Memento of the original from December 20, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . 
9. ↑ Stefan Zerbe, Gerhard Wiegleb Renaturation of Ecosystems in Central Europe Heidelberg 2008, p. 141