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Tropical salt pond ecosystem
Salt ponds are a natural feature of both temperate and tropical coastlines. These ponds form a vital buffer zone between terrestrial and marine ecosystems. Contaminants such as sediment, nitrates and phosphates are filtered out by salt ponds before they can reach the ocean. The depth, salinity and overall chemistry of these dynamic salt ponds fluctuate depending on temperature, rainfall, and anthropogenic influences such as nutrient runoff. The flora and fauna of tropical salt ponds differ markedly from those of temperate ponds. Mangrove trees are the dominant vegetation of tropical salt pond ecosystems, which also serve as vital feeding and breeding grounds for shore birds.
==Formation and cycle==
Tropical salt ponds form as bays are gradually closed off with berms of rubble from the reef. Mangroves grow atop the berms, which gradually close off the area to create a salt pond.〔Jarecki, L. 1999. A review of salt pond ecosystems. In Proceedings of the Nonpoint Source Pollution Symposium. University of the Virgin Islands, Eastern Caribbean Center, St. Thomas, U.S. Virgin Islands.〕 These typically form at the base of watersheds with steep slopes, as sediments transported during storm events begin to fill in and cover up the rubble berm. Mangroves may grow over the berm, also contributing to the isolation of the salt pond.〔 Typically, the ponds communicate with the open sea through ground seepage.
Evaporation and precipitation cycles in salt ponds create variable environments with wide ranges of salinity and depth.〔 Due to depth and temperature fluctuation salt pond could be classified as hyposaline 3-20 ppt, mesosaline 20-50 ppt, or hypersaline with ppt greater than 50.〔 Another important aspect of salt ponds is their permanence.〔Williams, W.D. 1998. Salinity as a determinant of the structure of biological communities in salt lakes. ‘’Hydrobiologica’’ 381: 191-201.〕 Salt ponds can eventually become filled in over time, and transition into an extension of the land.〔Gagemi, A. 2003. Ecological Assessment of Salt Ponds on St. John, USVI. Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering.〕 Some are intermittent ponds due to predictable dry and wet seasons while others are episodic (if the region has highly unpredictable weather).〔Hall, K. & K. KellerLynn. 2010. Virgin Islands National Park: geologic resources inventory report. Natural Resource Report NPS/NRPC/GRD/NRR—2010/226. National Park Service, Fort Collins, Colorado.〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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