Alaska Section, American Water Resources Association

Richard Kemnitz, Alaska Section AWRA Northern-Region Director

I would like to invite you to the March 2001 Brown-Bag presentation by Scott Maclean, USGS, Alaska Biological Science Center. Please note this meeting is the second Wednesday in March. We look forward to seeing you, please feel free to bring a colleague to the meeting.

March 14, 2001
Alaska Section AWRA, Northern-Region Brown-Bag Presentation
Alaska Department of Natural Resources, Large Conference Room
Noon to 1300

"An evaluation of subsurface and upwelling groundwater flow patterns
on the survival of spawning chum salmon in the Tanana River drainage"
Scott Maclean, USGS, Alaska Biological Science Center

Scott H. Maclean | James E. Finn
USGS, Alaska Biological Science Center
1011 East Tudor Rd., Anchorage, AK 99503
Tel: (907) 456-0273; Fax: (907) 456-O454

Abstract

Little is known about factors influencing intergravel survival of chum salmon (Onchorhynchus keta) in the Tanana River drainage. During 1999 we installed arrays of piezometers to evaluate intergravel flow patterns and environmental conditions within two study sites (one fall-run and one summer-run). The summer-run site is located in a side channel of the Chena River (Hodgin's Slough) and the fall-run site within a side channel of the main-stem Tanana River near Delta Junction (Bluff Cabin Slough). Since 1997, we have been quantifying in-stream habitat, estimating the numbers of spawning fish, and mapping spawner distributions.

Piezometer measurements in Hodgin's Slough showed large variations in hydraulic variables, temperature, and dissolved oxygen (DO). Relatively distinct patterns were evident for temperature, DO and vertical hydraulic gradients (VHG) over small spatial scales (<5 m). In contrast, measurements taken in the Bluff Cabin Slough study site indicated a more homogenous environment, with the exception of VHG, which appeared patchy. In areas of high spawner densities, intergravel late July temperatures were higher (7 to 9.5° C) and D.O was slightly higher (4 to 5.5 mg/l) than in areas of little or no observed spawning where temperatures were 3 to 6° C and DO was <2 to 4 mg/l. In general, during winter the temperatures in the spawning areas were lower (0.0 to 1° C) than in non-spawning areas (1 to >2° C). However, DO was distinctly higher (>6 to 7.5 mg/l) in spawning areas than in non-spawning areas (>1 to 6 mg/l). In the Bluff Cabin Slough study site, temperatures varied little between September and January (3.1 - 4.4° C). Dissolved oxygen also showed little variation between fall (10.3 - 12.0 mg/l) and winter (9.5 - 11.0 mg/l) sample periods.

Survival of eggs and alevins was evaluated using in situ incubation baskets. At the Hodgin's Slough study site, survival was strongly related to intergravel dissolved oxygen levels. Survival at the Bluff Cabin study site was 87% (s.e. = 4%) up to the eyed egg stage but plummeted to 2.7% (s.e. = 2.3%) at the pre-emergence stage. Further investigation into the intrusion of fine sediments and gas entrapment is plausible.

It appears that spawning chum salmon use restricted and consistent habitat within the study sites, which appears to be primarily dependent on the delivery of intergravel temperatures and DO. Analysis of substrate composition in the fall-run site is currently in process. Two types of spawning sites are recognized, one influenced by subsurface stream flow (summer-run) and the other by upwelling ground water (fall-run). Our research is helping to define spawning habitat quality for Interior Alaska chum salmon and could reveal mechanisms and factors controlling freshwater production, thereby, assisting managers to assess rehabilitation strategies.