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It is recognized that there is some level of risk to aquatic organisms depending on the sediment levels discharged and the sensitivity of the organisms in the receiving stream. However, scientists have concluded that these impacts would be best assessed using the concentration of suspended sediment above background levels. The levels of risk and the corresponding concentrations of sediment follow:
Source: Birtwell 1999
It is concluded that elevated levels of sediment (typically over background) may be harmful to fish (i.e. acutely lethal, or elicit sublethal responses that compromise their well-being and jeopardize survival), and in addition, negatively impact their habitat. Criteria, guidelines and recommendations, though having been formulated by different agencies, all tend to be mutually supportive. At the same time they have application limitations, especially relating to the protection of aquatic organisms from the effects of sediment concentrations £ tens of mg- L-1. Application of the criteria must be done while recognizing potential impacts on aquatic organisms at both the lethal and the sublethal level. Particle size and nature of the sediment must be considered as well (Birtwell 1999).
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Works Cited:
Chapman, D., & Kimstach, V., (1992/1996). Selection of Water Quality Variables. In Water Quality Assessments - a Guide to Use of Biota, Sediments and Water In Environmental Monitoring (chap. 3). Retrieved November 20, 2007, from http://www.who.int/water_sanitation_health/resourcesquality/wqa/en/.
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