Trekanten ( en, The Triangle) is a small

lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...

in southern-central

Stockholm Stockholm () is the Capital city, capital and List of urban areas in Sweden by population, largest city of Sweden as well as the List of urban areas in the Nordic countries, largest urban area in Scandinavia. Approximately 980,000 people liv ...

Sweden Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...

. Trekanten is located in a park furnished with an artificial bathing beach and various planted-out fish species. It has a small drainage area with no major feeders. In the early 1980s, potable water was poured into the lake while water from the bottom of the lake was pumped out. These operations resulted in a significant reduction in levels of

phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...

but failed to affect levels of nutrients and oxygen depletion in the bottom layers. Levels of

lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...

and

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...

are among the highest documented in any lake in Stockholm.Trekanten Whilst the lake flora and fauna is roughly representative for Stockholm, the lake forms a natural link between the bays

Årstaviken Årstaviken is a bay in the Eastern parts of Lake Mälaren in Sweden. It is bordered by the Södermalm, Liljeholmen Liljeholmen is a district of the Hägersten-Liljeholmen borough in Söderort, the southern suburban part of Stockholm. Hist ...

and

Vinterviken Vinterviken ("Winter-cove") is a bay in the ''Mälaren'' lake in southern Stockholm, Sweden. Vinterviken is located in a valley surrounded by the Gröndal and Aspudden suburb areas. The origin of the name Vinterviken can be traced back to the 1 ...

Catchment area

Along the shores of the lake is a park created on a flat terrain. Leading up to Nybohov on the southern side of the lake is a fault bluff with pines and

deciduous In the fields of horticulture and Botany, the term ''deciduous'' () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, aft ...

trees, including

hazel The hazel (''Corylus'') is a genus of deciduous trees and large shrubs native to the temperate Northern Hemisphere. The genus is usually placed in the birch family Betulaceae,Germplasmgobills Information Network''Corylus''Rushforth, K. (1999). ...

. On the eastern shore is a bathe next to the

Liljeholmen Liljeholmen is a district of the Hägersten-Liljeholmen borough in Söderort, the southern suburban part of Stockholm. History In 1860 Liljeholmen became the first suburb outside Stockholm city limits. The district was then one of two self-gov ...

metro station, a bus terminal, the light rail

Tvärbanan Tvärbanan is a light-rail line in Stockholm, Sweden. Its name literally translates to ''The transverse line'', as it operates crosswise to the otherwise radial metro and commuter rail lines of Stockholm. It links together several transit li ...

, newly added flats, and some older buildings. Several residential areas surround the lake, including

Gröndal Gröndal (''Green Valley'') is a district of the Hägersten-Liljeholmen borough in Söderort, the southern suburban part of Stockholm. The name Gröndal means Green Dale or Green Valley. Gröndal developed as a working class and industrial subur ...

.Vattenprogram, p 14.3-14.4 About 30% of the catchment area is settled land and two major traffic routes passes through the area.

Environmental influence

In an old industrial area north of the lake is a timber trade, the only remaining polluting operation in the catchment area. About 60 kg of

is brought to the lake annually, of which more than half is released from lake sediments and the rest is derived from

surface runoff Surface runoff (also known as overland flow) is the flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. This can occur when th ...

, which also contributes some 260 kg of

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

. Historically, the lake was flanked by small scale industries such as

tanneries Tanning may refer to: *Tanning (leather), treating animal skins to produce leather *Sun tanning, using the sun to darken pale skin **Indoor tanning, the use of artificial light in place of the sun **Sunless tanning, application of a stain or dye t ...

dye A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution an ...

, and

creosote Creosote is a category of carbonaceous chemicals formed by the distillation of various tars and pyrolysis of plant-derived material, such as wood or fossil fuel. They are typically used as preservatives or antiseptics. Some creosote types were ...

works and until the early 1960s sewage and overflow water was guided into the lake. During the past 20 years, however, airing of bottom layers coupled with addition of potable water have improved the state of the lake. While the affected terrain has been restored since the operations were discontinued, in 1997 low levels of

arsenic Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, but ...

and increased levels of

DDT Dichlorodiphenyltrichloroethane, commonly known as DDT, is a colorless, tasteless, and almost odorless crystalline chemical compound, an organochloride. Originally developed as an insecticide, it became infamous for its environmental impacts. ...

were documented. Though

stormwater Stormwater, also spelled storm water, is water that originates from precipitation (storm), including heavy rain and meltwater from hail and snow. Stormwater can soak into the soil ( infiltrate) and become groundwater, be stored on depressed la ...

from parts of the traffic route

Essingeleden Essingeleden is a motorway that goes from Solna to Stockholm, Sweden, crossing the westmost parts of central Stockholm, by going over Kungsholmen, Lilla Essingen, and Stora Essingen. Essingeleden has three bridges – Fredhällsbron (270 m), Essin ...

has been redirected elsewhere, water from a 300 metres long viaduct is still brought into the lake via a water treatment plant lessening oil levels with some 10 per cent and

heavy metals upright=1.2, Crystals of osmium, a heavy metal nearly twice as dense as lead">lead.html" ;"title="osmium, a heavy metal nearly twice as dense as lead">osmium, a heavy metal nearly twice as dense as lead Heavy metals are generally defined as ...

with 9-14 per cent. Water from 200 metres of the Liljeholmsvägen traffic route (45,000 vehicles/day) is still led untreated into the lake. Thus, while surrounding blocks of flats are believed to contribute with most of the phosphorus and nitrogen, an estimated fourth of the

zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...

brought to the lake is believed to come from car tyres and about 18 per cent from settlements, while copper roofs, formerly abundant around the lake but mostly replaced by asphalt today, are thought to cause most of the copper.

Flora and fauna

In late summer,

phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'. Ph ...

stock is dominated by

green algae The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as ...

paired equal levels of

diatom A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...

, and a species of eutroph

carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...

flagellate A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word ''flagellate'' also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes and their ...

(

Ceratium hirundinella The genus ''Ceratium'' is restricted to a small number (about 7) of freshwater dinoflagellate species. Previously the genus contained also a large number of marine dinoflagellate species. However, these marine species have now been assigned to ...

). Several of the blue green algae present in the lake are potentially poisonous and, notwithstanding non-alarming levels, therefore carefully monitored near the bathe. Lacking soft and shallow bottom areas near the shore, the lake contains only commonplace vegetation, save for the population of

crack willow Crack frequently refers to: * Crack, a fracture in a body * Crack, a fracture (geology) in a rock * Crack, short for crack cocaine Crack may also refer to: Art, entertainment, and media * ''Cracks'' (film), a 2009 independent thriller * Crac ...

and the hybrid between

white willow ''Salix alba'', the white willow, is a species of willow native to Europe and western and central Asia.Meikle, R. D. (1984). ''Willows and Poplars of Great Britain and Ireland''. BSBI Handbook No. 4. .Rushforth, K. (1999). ''Trees of Britain an ...

and bay willow found on the southern shore.

Aquatic plant Aquatic plants are plants that have adapted to living in aquatic environments (saltwater or freshwater). They are also referred to as hydrophytes or macrophytes to distinguish them from algae and other microphytes. A macrophyte is a plant that ...

s are dominated by white waterlily, amphibious bistort, and occasional curled pondweed (uncommon to Stockholm).Vattenprogram, p 14.6 An inventory of lake bed fauna in 1997 produced a list of only 29 species/

taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

including most common species, mostly freshwater

gastropods The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. Ther ...

fireflies The Lampyridae are a family (biology), family of Elateroidea, elateroid beetles with more than 2,000 described species, many of which are bioluminescence, light-emitting. They are soft-bodied beetles commonly called fireflies, lightning bugs, ...

, and

leech Leeches are segmented parasitic or predatory worms that comprise the subclass Hirudinea within the phylum Annelida. They are closely related to the oligochaetes, which include the earthworm, and like them have soft, muscular segmented bodie ...

es but no

beetle Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...

s. A

rotenone Rotenone is an odorless, colorless, crystalline isoflavone used as a broad-spectrum insecticide, piscicide, and pesticide. It occurs naturally in the seeds and stems of several plants, such as the jicama vine plant, and the roots of several member ...

treatment in 1986 didn't affect the populations of

crucian carp The crucian carp (''Carassius carassius'') is a medium-sized member of the common carp family Cyprinidae. It occurs widely in northern European regions. Its name derives from the Low German ''karusse'' or ''karutze'', possibly from Medieval Lat ...

and

signal crayfish The signal crayfish (''Pacifastacus leniusculus'') is a North American species of crayfish. It was introduced to Europe in the 1960s to supplement the North European ''Astacus astacus'' fisheries, which were being damaged by crayfish plague, but ...

still dominating the fauna.

Perch Perch is a common name for fish of the genus ''Perca'', freshwater gamefish belonging to the family Percidae. The perch, of which three species occur in different geographical areas, lend their name to a large order of vertebrates: the Percif ...

was introduced shortly after the treatment, and

northern pike The northern pike (''Esox lucius'') is a species of carnivorous fish of the genus '' Esox'' (the pikes). They are typical of brackish and fresh waters of the Northern Hemisphere (''i.e.'' holarctic in distribution). They are known simply as a ...

and

roach Roach may refer to: Animals * Cockroach, various insect species of the order Blattodea * Common roach (''Rutilus rutilus''), a fresh and brackish water fish of the family Cyprinidae ** ''Rutilus'' or roaches, a genus of fishes * California roach ...

is believed to have found their way into the lake by themselves. Crucian carps are decimated by trawling annually and the population of roach has increased considerably since 2001. Carp,

rainbow trout The rainbow trout (''Oncorhynchus mykiss'') is a species of trout native to cold-water tributaries of the Pacific Ocean in Asia and North America. The steelhead (sometimes called "steelhead trout") is an anadromous (sea-run) form of the coasta ...

, and signal crayfish have been planted-out. In early summer the lake is home to a number of birds including

thrush nightingale The thrush nightingale (''Luscinia luscinia''), also known as the sprosser, is a small passerine bird that was formerly classed as a member of the thrush family Turdidae, but is now more generally considered to be an Old World flycatcher, Muscic ...

common chaffinch The common chaffinch or simply the chaffinch (''Fringilla coelebs'') is a common and widespread small passerine bird in the finch family. The male is brightly coloured with a blue-grey cap and rust-red underparts. The female is more subdued in ...

garden warbler The garden warbler (''Sylvia borin'') is a common and widespread small bird that breeds in most of Europe and in the Palearctic to western Siberia. It is a plain, long-winged and long-tailed typical warbler with brown upperparts and dull white ...

, and

blackcap The Eurasian blackcap (''Sylvia atricapilla''), usually known simply as the blackcap, is a common and widespread typical warbler. It has mainly olive-grey upperparts and pale grey underparts, and differences between the five subspecies are sma ...

. Other birds common to Stockholm, such as

mallard The mallard () or wild duck (''Anas platyrhynchos'') is a dabbling duck that breeds throughout the temperate and subtropical Americas, Eurasia, and North Africa, and has been introduced to New Zealand, Australia, Peru, Brazil, Uruguay, Arge ...

Eurasian coot The Eurasian coot (''Fulica atra''), also known as the common coot, or Australian coot, is a member of the rail and crake bird family, the Rallidae. It is found in Europe, Asia, Australia, New Zealand and parts of North Africa. It has a slaty-bla ...

tufted duck The tufted duck or tufted pochard (''Aythya fuligula'') is a small diving duck with a population of close to one million birds, found in northern Eurasia. The scientific name is derived from Ancient Greek '' aithuia'', an unidentified seabird ment ...

, and

great crested grebe The great crested grebe (''Podiceps cristatus'') is a member of the grebe family of water birds noted for its elaborate mating display. Taxonomy The great crested grebe was formally described by the Swedish naturalist Carl Linnaeus in 1758 in t ...

, are found by the lake, while

heron The herons are long-legged, long-necked, freshwater and coastal birds in the family Ardeidae, with 72 recognised species, some of which are referred to as egrets or bitterns rather than herons. Members of the genera ''Botaurus'' and ''Ixobrychus ...

visit the lake and

common merganser The common merganser (North American) or goosander (Eurasian) (''Mergus merganser'') is a large seaduck of rivers and lakes in forested areas of Europe, Asia, and North America. The common merganser eats mainly fish. It nests in holes in trees. ...

fish here during winters. No

amphibian Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terres ...

s have been documented by the lake.

Notes

References

* * {{cite web , url = http://www.stockholmvatten.se/Stockholmvatten/commondata/infomaterial/Sjo/14Trekant.pdf , title = Vattenprogram för Stockholm 2000 - Trekanten , publisher = Stockholm vatten , accessdate = 2007-06-03 , language = Swedish , format = PDF , archiveurl = https://web.archive.org/web/20070927014333/http://www.stockholmvatten.se/Stockholmvatten/commondata/infomaterial/Sjo/14Trekant.pdf , archivedate = 2007-09-27 Geography of Stockholm Lakes of Stockholm County

Catchment area

Environmental influence

Flora and fauna

See also

Notes

References