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DRAFT Final Report ACWA-08-05

8 October 2008

At no time during our sampling did the water temperature exceed 12 degrees Celsius, and was therefore

within the acceptable limits set by the state of Alaska. The warmest temperatures were measured in

our August and September sampling events, with water temperatures of 10.8 to 11.4ºC near Koliganek,

and water temperatures of 11.3 to 11.8ºC near New Stuyahok. The coldest water temperatures were

measured in our May sampling event, where water temperatures near Koliganek ranged from 1.6 to

1.8ºC, and water temperatures near New Stuyahok ranged from 2.6 to 3.3ºC. Historic USGS water

temperature data ranged from 1.5 to 16.5ºC (May through September, 1956, and 1979 to 1986); data

from this study fall within this temperature range.

Dissolved oxygen

The dissolved oxygen content in a river is controlled by several factors, including water temperature,

atmospheric pressure, hydraulics, and rates of photosynthesis and respiration. All fish living in the

Nushagak River, and especially salmon, require well-oxygenated water throughout their entire life cycle.

Dissolved oxygen was measured as a concentration (mg/L) and as a percentage of its maximum value (%

saturation). Alaska state water quality standards set a lower limit of 7 mg/L of dissolved oxygen for

waters that support anadromous fish.

At no time during our sampling did the dissolved oxygen levels approach the lower limit of 7mg/L; in

fact, dissolved oxygen at no time was measured below 10 mg/L. With the exception of the May

sampling event, dissolved oxygen was measured near 100% saturation, indicating healthy levels of

dissolved oxygen for the river. During the May sampling event, dissolved oxygen measurements ranged

from 86 to 95% saturated. In August 2005, dissolved oxygen levels were detected at 115.2% saturated

(Zender, 2006). At no time during our sampling did percent saturation approach the upper limit as

defined by the Alaska State water quality standards of 110% saturated.

The pH of water is a measure of the hydrogen ion activity, or more commonly, the acidity or alkalinity of

the water. Neutral waters have a value of pH 7; pH values below 7 indicate acidic conditions, while

values above 7 indicate alkaline conditions. Natural waters typically have a pH between 6.5 and 8.5.

Alaska state water quality standards use this range as the acceptable pH range for natural waters, and

also state that they should not vary more than 0.5 pH units from their natural background condition.

Most of the pH values were below 7, indicating slightly acidic conditions in the lower Nushagak River.

Measured pH values were ranged from 6.2 to 7.3, within the typical range for healthy fish. Measured

pH values on the Nushagak tended to increase downriver from its confluence with the Mulchatna River.

Specific Conductance

Specific conductance is a measure of the water’s ability to conduct an electric current. Specific

conductance values increase with increasing concentrations of ions dissolved in the water. During low

flow conditions, the river’s specific conductance will typically be at its highest, indicating a larger

proportion of groundwater I the river’s makeup. Conversely, during high flow periods, specific

conductance values tend to be lower, indicating a higher proportion of runoff (from rainfall or

snowmelt) which typically has smaller ion concentrations. Specific conductance measured values

tended to follow this pattern, with values dropping from near 60µS/cm in the summer and fall months

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Draft Final Report Acwa-08-05 - Continuation Of Lower Nushagak River Fecal Coliform And Water Quality Assessment - Alaska Department Of Environmental Conservation - 2008 Page 9