Research Document - 1999/139
Effects of sediments on fish and their habitat.
By I.K. Birtwell
Abstract
This document provides information and comments on guidelines and criteria for the protection of aquatic resources from elevated levels of suspended and deposited sediment in fresh water.
Elevated levels of sediment and turbidities can reduce the productivity of aquatic systems. Both these correlated factors have the potential to decrease primary productivity that may have consequences to secondary productivity and the energy flow to higher trophic levels.
Examples of the lethal and sublethal effects of sediment on fish and their habitat, and factors such as temperature, particle size and angularity, and duration of exposure, that influence these effects, are presented. Levels of suspended sediment that have been determined to be acutely lethal to fish typically range from the hundreds to hundreds of thousands of mg·L-1 sediment, while sublethal effects are often manifest in the tens to hundreds of mg·L-1 sediment.
Guidelines that rely on gravimetric determinations of suspended sediment concentrations are recommended for use over those that rely solely on turbidity. However, if the relationship is known between these variables, then turbidity may be used as a surrogate for suspended sediment. The use of guidelines that incorporate the duration of exposure to sediments provide useful analytical information for predictive purposes, but caution is warranted when attempting to predict the effects of low (£ tens of mg L-1) levels of sediment over protracted periods of time. Guidelines that rely on the volumetric determination of "settleable solids" are not endorsed for use because of the difficulty of obtaining a meaningful and generally applicable relationship between this variable and suspended solids.
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 could compromise their well-being and jeopardize survival), and in addition, negatively impact on their habitat.
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