Introduction Classification of brackish waters Brackish waters comprise a range of exclusive habitats that can be subdivided into three major categories: transition zones between freshwater and marine habitats, transition zones between hyperhaline water and marine habitats, and inland waters without marine water exchange. Salinities of brackish-water habitats vary from relatively stable (e.g. some large saline lakes; see Fritz et al., this volume) to extremely instable in time and space (e.g. estuaries bordering tidal seas; see Trobajo & Sullivan, this volume). In the past, many efforts have been made to classify brackish waters according to salinity and the occurrence of biological species (Kolbe, 1932; Segerstråle, 1959; den Hartog, 1964). The more detailed such classifications are, the less well they appear to fit with all types of brackish waters. Based on salinity, defined as the total concentration of ionic components in g per kg water, generally accepted approximate limits are: limnetic (freshwater) <0.5 practical salinity units (psu) = parts per thousand (ppt), oligohaline 0.5–5 psu, mesohaline 5–18 psu, polyhaline 18–30 psu, euhaline 30–40 psu, hyperhaline 40 psu (known as the “Venice System”: Anonymous, 1959). Large brackish-water ecosystems Earth’s longest salinity gradient comprises the continental microtidal Baltic Sea (Leppäranta & Myrberg, 2009: surface area 377,000 km2, water volume 21,000 km3, mean depth 58 m, maximum depth 459 m) and its transition area to the North Sea.
|Undertitel||Applications for the environmental and Earth sciences, Second Edition|
|Redaktører||John P. Smol, Eugene F. Stoermer|
|Udgivelsessted||Cambridge, United Kingdom|
|Forlag||Cambridge University Press|
|Status||Udgivet - 1 jan. 2010|
- Programområde 5: Natur og klima