Biomanipulation

The biomanipulation is a biotechnology for control of food chains. It occurs mainly in the context of water quality management for the rehabilitation over-fertilized lakes used. The goal is a limitation of phytoplankton biomass over the construction of a well-developed predatory fish population. The technique of biomanipulation was developed and introduced by the American river ecologists Joseph Shapiro.

Method

The eutrophication of lakes usually leads by an oversupply of nutrients, especially phosphorus, at an inflated inventory of unicellular green algae or cyanobacteria from autotrophic ( formerly known as " blue-green algae ") is. This leads to a reduction of the depth of view. The " algae bloom " said mass propagation limits, eg given by toxins (toxins ) the usability of the water a. Through consumption of dissolved oxygen it can lead ( when the algae die ) for " upset " of the water.

Unicellular algae are harvested by predators in the open water of a watercourse. Particularly important are filtered small crabs, water fleas ( Daphnia ) and copepods ( Copepoda ). This can clear the waters again in principle. However: The filtering small crustaceans in turn have their predators. Importance are primarily planktivorous fish species, usually from the family of carp -like ( cyprinids ). These are referred to by anglers as " coarse fish " because they do not feed on other fish species. Also, this " coarse fish " now have turn predators, the " predators " such as the pike that 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 a plane with algae and small crustaceans there are two, etc. Each " full " level can control the underlying layer and effectively limit the density of organisms - but only as long as is not even higher by a level is regulated. So a high Fried fish stock indirectly promotes algae ( by harvesting the algivoren small crustaceans ). A high predator stock may limit the algae thus indirectly. In theory, the length of the food chain and thus the number of trophic levels by the productivity of the ecosystem is limited.

A modern version of these relationships in general has been proposed by the American ecologist SDFretwell as "food chain dynamics". In many larger bodies of water, the number of predators is not the naturally expected state. Predators are, for example, ( usually called " white fish " ) by anglers over the cyprinids preferred. The biomanipulation tried

By influencing the trophic levels in the waters of this an undesirable state ( algal blooms ) to lead to a desired state ( clear water ) without the conditions are changed. Frequently, it is e.g. impossible to reduce the nutrient content of a lake system without considerable effort. In these cases, the condition might be still improved over Biomanipulation.

The problem is, of course, influenced the waters always have a tendency to move towards a stable state, the ecological balance of a water body. If, for example, the number of predators increased in a lake on the viability addition, the surplus fish eventually perish from lack of food. Biomanipulation can therefore easily lead to dramatic short-term changes, but then are not permanent. But lasting success with the procedures appear quite possible. Promising are here especially waters that have two (at least meta- ) stable states.

In moderately eutrophic lakes, it is often observed that at slightly more elevated phosphorus contents disappear the previously lush developed " underwater meadows " from higher macrophytes, such as spawning herbs, Hornwort, Myriophyllum, Elodea and other species and are replaced by single-celled organisms that turn the water cloudy. Reason here is the macrophytes and unicellular algae are in competition for light and nutrients. Established macrophytes can "starve " the protozoa. Come this but once on, they can use the nutrients for themselves and additionally ausschatten the higher plants. These two states can be both relatively stable, but " flip" after a fault in each other in certain nutrient contents. In these cases Biomanipulation leads to the establishment rich macrophytes, which can then stabilize itself.

When Biomanipulation comes in either a top-down or a bottom-up process for the application:

• The top-down method influenced from the hierarchical pyramid of food their top level, are used in the top predators in the lake in addition as pike (down control). Consequently, the share zooplanktophager mass fish species is reduced, so that the small creatures of the zooplankton have less to suffer from their grazing pressure. You can then turn the primary producers, phytoplankton, better eat that which is not only the view depth increases, but also have a positive effect on water quality (see above). Occasionally, instead of this predatory fish stock and the pearling of Fried fish used.
• The bottom-up method affects the food pyramid in the lake ecosystem through the manipulation of the nutrient phosphorus from its lowest level of ( upward control): With a lower nutrient concentration, phytoplankton biomass decreases. The smaller food supply leads to lower quantities of zooplankton and thus zooplanktophager fish; the proportion of carnivorous fish increases. This in turn is ideally stabilizing the reverse mechanism of the top-down process in motion. Try is often a precipitation of phosphorus with soluble aluminum salts. Alternatively (or in parallel ) attempts abzubaggern cover or nutrient-rich mud. Pure nutrient management without altering the trophic interactions is, however, no Biomanipulation dar.

Application Examples

The method is used and tested worldwide. In mesotrophic eastern Finland Pohjalampi Lake roach and bream were fished between 1993 and 1997 200 kg, which resulted in a significant recovery of predators. The Indian Naini Lake in Nainital in Uttarakhand was filled in 2008 for biomanipulation with 35000 Mahseer fish (Tor putitora ), a native cyprinids, which can reach a length of 2.75 meters. In American Lake Mendota, which is considered by many limnological studies and research as one of the birthplaces of modern limnology, a significantly increased water transparency was achieved in a Biomanipulations project 1987-1998.

Among the experimental waters in Germany mainly include drinking water reservoirs like the Bautzen Reservoir or the Weidatalsperre, also the field Berger and Haussee the Plußsee. In the Seddiner chain of lakes, the Institute for Applied Aquatic Ecology used the biomanipulation between 2006 and 2009 with the stocking of pike in the context of a pilot project for the rehabilitation Northeast German shallow lakes under the EU Water Framework Directive ( WFD ).

Although biomanipulation is one of the many European countries most frequently used methods for the restoration of the lake water quality due to the low cost. Despite the initially entering successes but their long-term effect is critically evaluated.