This action plan provides guidelines for preservation of the endangered plant Elatine hexandra (Six-stamened Waterwort) in Sweden. The action plan is a proposal, not a legally binding document.
Elatine hexandra is a small, aquatic or amphibious, vascular herb in the family Elatinaceae. In Sweden, it usually appears as a summer annual on the very edge of freshwater lakes or streams. Some populations have over-wintering individuals that occur at depths well below the ice-cover. Typically, the habitat is a moderately wave exposed littoral with inorganic, silty-sandy substrate, covered with a thin layer of mud. The lake habitats have clear water, a near neutral pH and may represent one of the two lake types that are included in the habitat directive, i.e. “Oligotrophic waters containing very few minerals of sandy plains” and “Oligotrophic to mesotrophic standing waters with vegetation of the Littorelletea uniflorae and/or of the Isoëto-Nanojuncetea”.
The species has been found in approx. 55 Swedish lakes or running waters since 1980. With a few exceptions, the occurrences are restricted to river basins of southwest Sweden with outlets in Skagerrak and Kattegat (County Administration Boards of Värmland, Västra Götaland, Jönköping, Halland and Kronoberg). In the Swedish red list Elatine hexandra is classified as Endangered (EN).
The main threats include deteriorating water quality. Eutrophication, acidification and brownification (increase in water color and dissolved organic matter) have adverse effects on growth and reproduction of the species. Other threats include exploitation of shorelines and water level regulations. The action plan proposes measures against deteriorating water quality in lakes with known occurrences of Elatine hexandra. Further, it points out the need for revision and ecological considerations of present water level regulations. Other suggestions aim to increase the conservation awareness among land owners, nature resource managers and municipality planners. These suggestions include production and spread of an information folder and implementation of conservation related information in the database WISS (Water Information System Sweden). WISS is an open information tool used in the planning cycle of river basin management. Finally, the action plan proposes additional investigations of the distribution in lakes and of the presence in seed-banks, as well as field studies on how growth and reproduction is affected by water regulations. With help of these results, lakes suitable for restoration measures can be selected. The action plan is valid for the period 2013-2018 and the costs are estimated to approx. 1 430 000 SEK.