Trehörningen ( Swedish: "The Triangle"''Trehörningen'' literary translates to "The Three-Corner", a name most likely referring to the three "bays" of the laks.) is a small

lake A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from ...

located in the municipality

Huddinge Huddinge Municipality () is a municipalities of Sweden, municipality in Stockholm County, east central Sweden. Its seat is located in Huddinge (), which is a part of Stockholm urban area. The municipality is, with its approximately 110,000 inhabit ...

in southern

Stockholm Stockholm (; ) is the Capital city, capital and List of urban areas in Sweden by population, most populous city of Sweden, as well as the List of urban areas in the Nordic countries, largest urban area in the Nordic countries. Approximately ...

Sweden Sweden, formally the Kingdom of Sweden, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. It borders Norway to the west and north, and Finland to the east. At , Sweden is the largest Nordic count ...

. As part of the Tyresån Lake System, Trehörningen receives water from Lake Gömmaren and supplies water to Lake Ågesta.

History

The area surrounding Trehörningen,

Orlången Orlången is a lake in central Huddinge Municipality, just south of Stockholm, Sweden. Orlången, one of the lakes in the Tyresån Lake System, forms part of the Orlången Nature Reserve.Huddinge Municipality, ''Orlången'', site Catchment area ...

and

Ågestasjön Ågestasjön ( Swedish for "Lake of Ågesta") is a small lake in Huddinge Municipality south of Stockholm, Sweden. Ågestasjön forms part of the Tyresån Lake System and, with a biodiversity unique in the Stockholm region, is highly popular amo ...

, is a fine example of a historical landscape evolving from a prehistoric settlement into a traditional agricultural village discontinued in the 19th century, encompassing structures from all interjacent eras. It is one of the few areas in Stockholm which escaped the creation of the widespread 20th century suburbs around the historical city of Stockholm, and, consequently, the area is considered as having cultural and historical values of national interest. The landscape include open cultivated and grazed fields next to steep rocks, pine and deciduous forests. Several grave fields, hillforts, and other archaeological structures, reflects the area was connected to the

Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by the countries of Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden, and the North European Plain, North and Central European Plain regions. It is the ...

in prehistoric times. During medieval times, the area contained the only farmstead exempt from land dues (i.e. owned by a member of the

Swedish nobility The Swedish nobility (, or , ) has historically been a legally or socially privileged Social class, class in Sweden, and part of the so-called ''frälse'' (a derivation from Old Swedish meaning ''free neck''). The archaic term for nobility, ''fr ...

) in Huddinge. In the area traces from the

Stone Age The Stone Age was a broad prehistory, prehistoric period during which Rock (geology), stone was widely used to make stone tools with an edge, a point, or a percussion surface. The period lasted for roughly 3.4 million years and ended b ...

and some

cairn A cairn is a human-made pile (or stack) of stones raised for a purpose, usually as a marker or as a burial mound. The word ''cairn'' comes from the (plural ). Cairns have been and are used for a broad variety of purposes. In prehistory, t ...

s from the

Bronze Age The Bronze Age () was a historical period characterised principally by the use of bronze tools and the development of complex urban societies, as well as the adoption of writing in some areas. The Bronze Age is the middle principal period of ...

have been found, and parts of the present road network is left unaltered for thousands of years.

Stockholm County Museum Stockholm County Museum () is the regional museum of Stockholm County, Sweden. The museum strives to be the natural hub of knowledge for the cultural heritage of the county's residents and to create dialogue around history, present time, and the ...

Catchment area

Three-fourths of the catchment area is used for settlements, including the commercial centre of Huddinge (''Huddinge Centrum'') and half a dozen residential neighbourhoods. Nevertheless, the shores of the lakes are of significant recreational importance as they border the

Orlången Nature Reserve Orlången Nature Reserve (''Orlångens naturreservat'') is a nature reserve surrounding Lake Orlången in central Huddinge Municipality, south of Stockholm, Sweden. Description The reserve, founded in 1998, encompasses a total area of 15 square ...

and contain several cliffs popular for bathing and angling. Both major inflows, Fullerstaån and Solfagradiket, are guided through culverts under neighbouring settlements, but reaches the lake through open ditches. Today, motor-driven boats are not permitted on the lake and restrictions are imposed on angling.Huddinges sjöar (site)

Environmental influence

The lake used to receive waste water from both settlements and other neighbouring operations 1951–1971, but the inflow is today reduced to

stormwater Stormwater, also written 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 lan ...

- the old usage still echoing in

oxygen depletion Hypoxia (''hypo'': 'below', ''oxia'': 'oxygenated') refers to low oxygen conditions. Hypoxia is problematic for air-breathing organisms, yet it is essential for many anaerobic organisms. Hypoxia applies to many situations, but usually refers to ...

and

phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...

release at the lake bottom, and

algae bloom An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in fresh water or marine water systems. It is often recognized by the discoloration in the water from the algae's pigments. The term ''algae'' encompass ...

and limited water transparency. To restrict future influence to a minimum, reduction in incoming flows are given priority rather than any actions to the lake itself. The lake was dredged in 1975 and 1976, the product of which was pumped over to the lake's western bay where embankments prevent it from pouring back into the lake. Additionally,

reed bed A reedbed or reed bed is a natural habitat found in floodplains, waterlogged depressions and estuaries. Reedbeds are part of a succession from young reeds colonising open water or wet ground through a gradation of increasingly dry ground. As ...

s were removed and other measures were taken to clean the lake. Vegetation has been cleared annually since.

Flora and fauna

As a locale for birds, the lake was significantly deteriorated by the mid-1970s dredging which caused a colony of

black-headed gull The black-headed gull (''Chroicocephalus ridibundus'') is a small gull that breeds in much of the Palearctic in Europe and Asia, and also locally in smaller numbers in coastal eastern Canada. Most of the population is migratory and winters fu ...

to disappear. Today, the lake has a regular presence of

mallard The mallard () or wild duck (''Anas platyrhynchos'') is a dabbling duck that breeds throughout the temperate and subtropical Americas, Eurasia, and North Africa. It 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 ...

great crested grebe The great crested grebe (''Podiceps cristatus'') is a member of the grebe family of water birds. The bird is characterised by its distinctive appearance, featuring striking black, orange-brown, and white plumage, and elaborate courtship displa ...

common goldeneye The common goldeneye or simply goldeneye (''Bucephala clangula'') is a medium-sized sea duck of the genus ''Goldeneye (duck), Bucephala'', the goldeneyes. Its closest relative is the similar Barrow's goldeneye. The genus name is derived from th ...

; regular visits of

common gull The common gull (''Larus canus'') is a medium-sized gull that breeds in cool temperate regions of the Palearctic from Iceland and Scotland east to Kamchatka in the Russian Far East. Most common gulls bird migration, migrate further south in wint ...

heron Herons are long-legged, long-necked, freshwater and coastal birds in the family Ardeidae, with 75 recognised species, some of which are referred to as egrets or bitterns rather than herons. Members of the genus ''Botaurus'' are referred to as bi ...

common merganser The common merganser (North American) or goosander (Eurasian) (''Mergus merganser'') is a large sea duck 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 ...

osprey The osprey (; ''Pandion haliaetus''), historically known as sea hawk, river hawk, and fish hawk, is a diurnal, fish-eating bird of prey with a cosmopolitan range. It is a large raptor, reaching more than in length and a wingspan of . It ...

marsh warbler The marsh warbler (''Acrocephalus palustris'') is an Old World warbler currently classified in the family Acrocephalidae. It breeds in temperate Europe and the western Palearctic and winters mainly in southeast Africa. It is notable for incorpor ...

, great reed-warbler, and

grasshopper warbler The common grasshopper warbler or just grasshopper warbler (''Locustella naevia'') is a species of Old World warbler in the genus ''Locustella''. It breeds across much of temperate Europe and the western Palearctic. It is migratory, wintering ac ...

; and some uncommon guests such as

common kingfisher The common kingfisher (''Alcedo atthis''), also known as the Eurasian kingfisher and river kingfisher, is a small kingfisher with seven subspecies recognized within its wide distribution across Eurasia and North Africa. It is resident in much of ...

and

black-throated diver The black-throated loon (''Gavia arctica''), also known as the Arctic loon and the black-throated diver, is a migratory aquatic bird found in the northern hemisphere, primarily breeding in freshwater lakes in northern Europe and Asia. It winte ...

; the lake itself thus still being of

ornithological Ornithology, from Ancient Greek ὄρνις (''órnis''), meaning "bird", and -logy from λόγος (''lógos''), meaning "study", is a branch of zoology dedicated to the study of birds. Several aspects of ornithology differ from related discip ...

interest, while the forests surrounding the lake attracts

long-tailed tit The long-tailed tit (''Aegithalos caudatus''), also named long-tailed bushtit, is a common bird found throughout Europe and the Palearctic. The genus name ''Aegithalos'' was a term used by Aristotle for some European tits, including the long-tail ...

and

lesser spotted woodpecker The lesser spotted woodpecker (''Dryobates minor'') is a member of the woodpecker family Picidae. It was formerly assigned to the genus '' Dendrocopos'' (sometimes incorrectly spelt as ''Dendrocopus''). Some taxonomic authorities continue to list ...

Aquatic plant Aquatic plants, also referred to as hydrophytes, are vascular plants and Non-vascular plant, non-vascular plants that have adapted to live in aquatic ecosystem, aquatic environments (marine ecosystem, saltwater or freshwater ecosystem, freshwater ...

s, in addition to

reed Reed or Reeds may refer to: Science, technology, biology, and medicine * Reed bird (disambiguation) * Reed pen, writing implement in use since ancient times * Reed (plant), one of several tall, grass-like wetland plants of the order Poales * Re ...

and

club-rush ''Schoenoplectus'' (club-rush ld World species bulrush or tule ew World species is a genus of plants in the Cyperaceae, sedge family with a cosmopolitan distribution. Note that the name bulrush is also applied to species in the unrelated ...

, includes several species of

duckweed Lemnoideae is a subfamily of flowering aquatic plants, known as duckweeds, water lentils, or water lenses. They float on or just beneath the surface of still or slow-moving bodies of fresh water and wetlands. Also known as bayroot, they arose fr ...

and chickenwort. Along the shore are some 30 species of trees and plants, including

alder Alders are trees of the genus ''Alnus'' in the birch family Betulaceae. The genus includes about 35 species of monoecious trees and shrubs, a few reaching a large size, distributed throughout the north temperate zone with a few species ex ...

birch A birch is a thin-leaved deciduous hardwood tree of the genus ''Betula'' (), in the family Betulaceae, which also includes alders, hazels, and hornbeams. It is closely related to the beech- oak family Fagaceae. The genus ''Betula'' contains 3 ...

aspen Aspen is a common name for certain tree species in the Populus sect. Populus, of the ''Populus'' (poplar) genus. Species These species are called aspens: * ''Populus adenopoda'' – Chinese aspen (China, south of ''P. tremula'') * ''Populus da ...

spruce A spruce is a tree of the genus ''Picea'' ( ), a genus of about 40 species of coniferous evergreen trees in the family Pinaceae, found in the northern temperate and boreal ecosystem, boreal (taiga) regions of the Northern hemisphere. ''Picea'' ...

sedges The Cyperaceae () are a family of graminoid (grass-like), monocotyledonous flowering plants known as sedges. The family is large; botanists have described some 5,500 known species in about 90 generathe largest being the "true sedges" (genu ...

, loosestrife, forget-me-nots, cinquefoils, and water-pepper. The

common frog The common frog or grass frog (''Rana temporaria''), also known as the European common frog, European common brown frog, European grass frog, European Holarctic true frog, European pond frog or European brown frog or simply the frog, is a semi ...

and

common toad The common toad, European toad, or in Anglophone parts of Europe, simply the toad (''Bufo bufo'', from Latin ''bufo'' "toad"), is a toad found throughout most of Europe (with the exception of Ireland, Iceland, parts of Scandinavia, and some List ...

have been observed by the lake, as have

bat Bats are flying mammals of the order Chiroptera (). With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most birds, flying with their very long spread-out ...

s such as the

northern bat The northern bat (''Eptesicus nilssonii'') is the most abundant species of bat in northern Eurasia occurring from France to Hokkaidō and south to Kazakhstan. Description The northern bat is dark brown or black with some gold touched at the tip ...

and

Daubenton's bat Daubenton's bat or Daubenton's myotis (''Myotis daubentonii'') is a Eurasian bat with rather short ears. It occurs across Eurasia, from Ireland in the west to Hokkaido in the east, and is believed to be increasing its numbers in many areas of it ...

. No observations of

dragonflies A dragonfly is a flying insect belonging to the infraorder Anisoptera below the order Odonata. About 3,000 extant species of dragonflies are known. Most are tropical, with fewer species in temperate regions. Loss of wetland habitat threate ...

had been reported until July 2014, when two American visitors saw a small red dragonfly and a large black dragonfly.

Notes

References

* * *

External links

* {{DEFAULTSORT:Trehorningen (Sjodalen) Geography of Stockholm Lakes of Stockholm County