TA1 Developing Suspended and Bedded Sediments Criteria
256 Portland Ballroom
8:00 AM - 12:00 PM, Tuesday
() Assessing fisheries impacts of excessive cloudiness in clear water systems.
Newcombe, C. P. 1, 1 Ministry of Water, Land and Air Protection, Victoria, British Columbia, Canada
ABSTRACT- "An empirical model enables real time assessment of impacts caused by excessive water cloudiness as a function of reduced visual clarity (excessive cloudiness) and duration of exposure to cloudy conditions, in fisheries or fish life stages adapted to life in clear water ecosystems. This model has the form z = a + b(loge x) + c(loge y) where z is severity of ill effect (SEV); x is duration of exposure (h); y is black disk sighting range (yBD, m), a measure of water clarity; a is the intercept, and b and c are slope coefficients. Severity of ill effect is ranked on a 15-step scale that ranges from 0 to 14, where zero represents nil effect and 14 represents 100 percent mortality. This model identifies the threshold of ill effects among clear water fishes; projects the rate at which serious ill effects are likely to increase as a function of the amount of cloudiness and its persistence; (c) demonstrates changes in predator prey interactions at exposures greater than and less than the threshold of direct ill effects; (d) calibrates trout reactive distance as function of water clarity in the form y = a + bln(x) where y represents reactive distance (cm) and x represents visual clarity (black disk sighting range, cm), and where a and b are intercept and slope respectively, such that y = - 68.0546 + 30.8307 ln(x); (e) identifies black disk sighting range and its reciprocal (beam attenuation) as preferred monitoring variables; and (f) provides two additional optical quality variables (Secchi disk extinction distance, and turbidity) which expand the range of monitoring options in situations where the preferred technology is unavailable or impractical to use."
Key words: turbidity, visual clarity, fisheries impacts, Secchi disk depth