Lake Pohjalampi
Encyclopedia
Lake Pohjalampi is a lake
in eastern Finland
. The lake has a surface area of 61 hectare
s, and the mean and maximum depth are 3.2 meters and 5.3 meters, respectively.
The lake was used to study the effects of biomanipulation on a small, mesotrophic lake. From 1993 to 1997, over 200 kilograms of fish, mainly roach
(Rutilus rutilus) and bream (Abramis brama) were caught and removed. This resulted in a reduction of nearly 80% of fish biomass
. The effects on the benthic
invertebrates were investigated using biomass and density, during the years of fish removal and for the following three years. The decrease in benthivorous fish stock
led to higher biomass and density in all the major benthic invertebrate
groups.
Three years after fish removal had been discontinued, the fish stocks had recovered to almost its initial value. The biomasses of the benthic invertebrates in many groups was seen to drop in the years 1999-2000, apparently due to the increased predation. The relationship between the two trophic level
s is thought to be as a consequence of the open and sparsely vegetated bottom, which offers minimal shelter to invertebrate prey.
An additional factor in the reduced invertebrate biomasses was a fall in both phosphorus
and chlorophyll a
concentrations, which lead to a drop in primary production. The phosphorus and chlorophyll a decreases occurred after the three years of fishing and have remained low since. This could be related to the loss of waste products and detritus the fish would have produced over the years.
Lake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...
in eastern Finland
Finland
Finland , officially the Republic of Finland, is a Nordic country situated in the Fennoscandian region of Northern Europe. It is bordered by Sweden in the west, Norway in the north and Russia in the east, while Estonia lies to its south across the Gulf of Finland.Around 5.4 million people reside...
. The lake has a surface area of 61 hectare
Hectare
The hectare is a metric unit of area defined as 10,000 square metres , and primarily used in the measurement of land. In 1795, when the metric system was introduced, the are was defined as being 100 square metres and the hectare was thus 100 ares or 1/100 km2...
s, and the mean and maximum depth are 3.2 meters and 5.3 meters, respectively.
The lake was used to study the effects of biomanipulation on a small, mesotrophic lake. From 1993 to 1997, over 200 kilograms of fish, mainly roach
Rutilus
Rutilus is a genus of fishes in the family Cyprinidae, commonly called roaches. Locally, the name "roach" without any further qualifiers is also used for particular species, particularly the Common Roach Rutilus (Latin for "shining, red, golden, auburn") is a genus of fishes in the family...
(Rutilus rutilus) and bream (Abramis brama) were caught and removed. This resulted in a reduction of nearly 80% of fish biomass
Biomass (ecology)
Biomass, in ecology, is the mass of living biological organisms in a given area or ecosystem at a given time. Biomass can refer to species biomass, which is the mass of one or more species, or to community biomass, which is the mass of all species in the community. It can include microorganisms,...
. The effects on the benthic
Benthic zone
The benthic zone is the ecological region at the lowest level of a body of water such as an ocean or a lake, including the sediment surface and some sub-surface layers. Organisms living in this zone are called benthos. They generally live in close relationship with the substrate bottom; many such...
invertebrates were investigated using biomass and density, during the years of fish removal and for the following three years. The decrease in benthivorous fish stock
Fish stock
Fish stocks are subpopulations of a particular species of fish, for which intrinsic parameters are the only significant factors in determining population dynamics, while extrinsic factors are considered to be insignificant.-The stock concept:All species have geographic limits to their...
led to higher biomass and density in all the major benthic invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
groups.
Three years after fish removal had been discontinued, the fish stocks had recovered to almost its initial value. The biomasses of the benthic invertebrates in many groups was seen to drop in the years 1999-2000, apparently due to the increased predation. The relationship between the two trophic level
Trophic level
The trophic level of an organism is the position it occupies in a food chain. The word trophic derives from the Greek τροφή referring to food or feeding. A food chain represents a succession of organisms that eat another organism and are, in turn, eaten themselves. The number of steps an organism...
s is thought to be as a consequence of the open and sparsely vegetated bottom, which offers minimal shelter to invertebrate prey.
An additional factor in the reduced invertebrate biomasses was a fall in both phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
and chlorophyll a
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
concentrations, which lead to a drop in primary production. The phosphorus and chlorophyll a decreases occurred after the three years of fishing and have remained low since. This could be related to the loss of waste products and detritus the fish would have produced over the years.