Sunday, February 26, 2012

geochemical and microfaunal proxies to assess environmental quality conditions during the recovery process of a heavily polluted estuary: the bilbao estuary case (n. spain)

E. Leorri, A Cearreta, M.J. Irabien, I. Yusta
Elsevier. Science of the Total Environment 396 (2008) 12-27

There is a clear preference for focusing on benthic organisms as ecological indicators, given their inherent ability to integrate sediment quality (Quintino et al., 2006) and to respond to changing environmental conditions (Salas et al., 2006). The use of indicators is becoming an integral part of decision support systems for coastal zone management (Bortone, 2005). Among the characteristics that define a good ecological indicator are: (a) handling easiness, (b) sensitivity to small variations of environmental stress, and (c) applicability in extensive geographical areas and in the greatest possible number of communities or ecological environments (Salas et al., 2006).
Studies of pollution effects on benthic foraminifera (class Foraminifera, phylum Granuloreticulata) and of the possible use of these organisms as proxies were initiated in the 1960s. Since then, benthic foraminifera are increasingly used as environmental bioindicators, especially in polluted environments. These works study the relationship between foraminifera and the anthropogenic impact using surface sediment samples and short cores in shallow marine areas around the world (see Ernst et al., 2006 and Tsujimoto et al., 2006 for further references).
Shallow water benthic foraminifera are among the most abundant and conspicuous protozoa in marine and coastal environments (Ernst et al., 2006). As lower trophic level members, foraminifera are important to biological communities (Lipps, 1983) and can be valuable indicators of the overall faunal health of an area (Buzas-Stephens et al., 2003). Foraminifera are easy to collect and their analysis is most cost-effective. They are often found in high-density populations and provide an adequate statistical base (even in small volume samples). These characteristics make them ideal candidates for comprehensive environmental assessments (Buzas-Stephens et al., 2003). Because they have a short life cycle and specific habitats, they respond fast to environmental changes (Ernst et al., 2006)—as other meiobenthic organisms, they respond much faster than macrobenthic organisms (Salas et al., 2006)—and can be used as an early warning indicator (Kramer and Botterweg, 1991). Foraminifera respond not only to the natural environmental variability in such parameters as temperature and salinity but also to anthropogenic stresses such as pollution, eutrophication, and hypoxia (see Tsujimoto et al., 2006 and references therein). Recent studies have demonstrated that some benthic species seem extremely sensitive to heavy metals and/or organic compounds concentration levels (Ferraro
et al., 2006). Additionally, foraminifera present fossilizable tests, and when they die, those tests accumulate in the sediment (dead assemblage) providing a time-averaged picture of the environment (Murray, 1991). They have a particularly good fossil record and their taxonomic composition and general ecological distribution in coastal marine settings are the best known of all the microfossil groups, giving access to the pre-pollution background microfaunas (Hayward et al.,2004).
Foraminifera generally react to adverse environmental conditions by undergoing changes in abundance and diversity or by producing deformed tests. Environmental disturbances have various degrees of destructive impacts on benthic communities, and can lead to defaunation when a certain lethal threshold is reached (Buzas-Stephens et al., 2003; Alve, 1999). These benthic habitats severely disturbed by human activity can be recolonised by foraminifera after effective recovery has occurred (Alve, 1999). The recolonization
pattern will depend upon the hydraulic regime in, and the transit time from, the source area. Although species such as Ammonia tepida and Haynesina germanica are pollution tolerant and have been reported to dominate in both natural and polluted areas, substrate properties (e.g., recently reoxygenated or severely contaminated sediments) may delay colonization by months or even years (Alve, 1999).

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