7103

• UCREFRP Catalog Number: 7103
• Author: Grabowski, S. J. and S. D. Hiebert.
• Title: Green River Trophic Dynamics Study 1987
• USFW Year: 1988.
• USFW - Doc Type: Draft.
• Copyright Material: NO

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or quarterly schedule. Turbidity was measured using a Hach Chemical
Co. Model 16800 Turbidimeter, with backwater samples taken prior to
any other sampling disturbance. The calibrated turbidimeter provides
a readout in NTUs.

The light extinction coefficient is an index or measure of photic depth.
Light penetration in both main river and backwaters was calculated
from readings obtained from a Kahl Scientific Instrument Corp.
Model 268WA310 underwater irradiameter (limnophotometer). A photocell
in the underwater unit of the limnophotometer measured light intensity
at depth. A reading was obtained in air, just beneath the water surface
(0.01 m), then at 0.1 m depth increments to the bottom or to 1.0 m.
When clouds were present, corresponding air readings (ambient) were
taken to correct for changing solar radiation due to cloud cover, which
could influence light penetration through the water column. When ambient
values were required due to cloudy conditions, these values were used
to adjust underwater values and subsequently calculate the light extinction
coefficient. Secchi depth was also measured at each main river or
backwater site; there is some correspondence between light extinction
coefficient and Secchi depth, although Secchi depth is less precise
and subject to human judgment, whereas the light extinction coefficient
is calculated from light intensity measurements at discrete depths.

Water samples were collected and filtered on-site for chlorophyll ~
determination. Replicate 250 to 500 mL water samples from each site

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