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Anthropogenic discharges into water environment can lead to destructive effects on marine ecosystems, like contaminations, habitat loss and loss of species. This is especially the case in urbanized and industrial harbors like Stavanger. Contaminants such as heavy metals and organic pollutants, no matter if discharges originate from air, rivers, urban runoff or effluent pipes, are usually picked up by suspended, fine-grained, mineral and organic particles in the marine environment, and are precipitated and “concentrated in hydrodynamically quiet basins where muddy sediments accumulate”.
Harbors represent and important links and borders between a marine ecosystem and industrial or populated areas and therefore are especially sensitive to contaminated sediment loadings (Lepland et al., 2010; Paetzel et al., 2003). The issue of toxic sediments has gained notable attention. Persistent contaminants are sorbed to sediments in the aquatic environment where they forming deposition layers in a chronological sequence (Chapman, 1990; Vaalgamaa, 2004), remaining over long time periods, and can affect organisms living in, or coming into contact with the sediments.
These contaminants can be heavy metals and chlorophenols that have a quick lethal impact or PCBs, PAH and dioxins that can have long-term harmful effects (reproductive, birth defects) (Chapman, 1990). The major concern about the reduction of benthic organisms is that they are the main food source for other trophic levels such as crabs, shrimp and fish. There have also been concerns about effects of toxic sediments on humans throughout food chain (seafood) from contaminated areas or engaging in water-contact activities (Black, 1984 in (Chapman, 1990)).
Therefore, it was extremely important to develop methods for assessing toxic sediments that are precise, efficient, comprehensive and reliable.
Such methods had to be based on the effects as contamination by itself is not an indication of toxicity. Sediment chemistry data only, have been used for assessment of sediment quality. But by using only chemical data we do not have a clear picture of the possible biological damage caused by contamination (Long and Chapman, 1985). So, essentially, such methods had to be related to the presence or absence of pollution-induced degradation because toxicity and contamination are, by themselves, of less consequence if there is no environmental effect (Chapman, 1990). 2 Sediment Quality Triad (SQT) The Sediment Quality Triad (SQT) is an integrative tool, very well established internationally, which was first published over 30 years ago (Long and Chapman, 1985) and which continues to develop (Chapman et al., 2006). SQT approach has been used as a sediment quality assessment tool to determine the existence and level of benthic ecosystem degradation, and also to determine the cause of that degradation (Chapman et al., 1997). It consists of three separate components: sediment chemistry analysis, which determines chemical contamination; sediment bioassays, laboratory toxicity tests which measure effects under standardized condition (experimentation), to determine toxicity; and assessments of resident community alteration which are most exposed to any sediment contaminants (generally the benthic infauna), measure of field conditions – in situ parameters (observation) (Chapman, 1990; Chapman et al., 2006; Chapman, 1996; Long and Chapman, 1985). The information provided by each category is unique and complementary.
Thus, combination of these three categories of measurements is necessary because no single component provides comprehensive information. Sediment chemistry provides no indication of biological damage, but it determines the degree and nature of contamination and provides clues about possible sources. Sediment bioassays can provide direct evidence of sediment toxicity related to contamination (chemistry data). However, these tests are usually conducted in a laboratory environment and may not accurately imitate conditions under which resident biota may be exposed to the toxic chemicals. Assessments of resident community alteration in situ can provide direct evidence of contamination related effects in the environment, but they can be misleading since benthic communities may be modified by non-pollution events and variation (e.g., competition, predation, sediment type, temperature) so they must be excluded (Chapman, 1990; Long and Chapman, 1985). Toxicity may vary depending on the concentration of the chemical substances and condition within specific sediment which may include grain size, organic content, pH, chemical form, the presence of other chemicals etc.
Because of that, as stated before, the importance of any particular chemical concentrations in sediments cannot be determined just from chemical measurements (Chapman, 1990). By using all three measures together we can determine quality of contaminated sediment and biological response on that contamination. Also, it provides a Weight of Evidence (WOE) framework for determining pollution-induced degradation based on multiple Lines of Evidence (LOE) (Chapman, 1990; Chapman et al., 2006). For example, if we have high levels of contamination, toxicity and alteration of resident community, the weight of evidence shows degradation. In the reverse case, low levels of contamination, toxicity and alteration of resident community indicate non-degraded conditions. Intermediate responses provide different levels of information, which is shown in Table 1 (Chapman, 1990).
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