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The Alaska Section, American Water Resources Association
Annual Meeting Proceedings

April 4-6, 2001
Fairbanks, Alaska
Wednesday, April 4, 2001
Alaska Surface Water Session

Tidal Influences On Ground-Water and Surface-water Interactions in Contaminated Salmon Spawning Beds, Prince William Sound, Alaska

Michael R. Lilly
GW Scientific
Mark G. Carls, Stanley D. Rice
National Marine Fisheries Service, Auke Bay Laboratory

Because of the 1989 Exxon Valdez oil spill a mixture of oil and water was added on intertidal beach sediments. Although some streams crossed these oiled intertidal areas, salmon redds (gravel-covered egg nests) in stream channels were not directly oiled. However, exposure of eggs to oil was suspected, and recent studies detected polynuclear aromatic hydrocarbons in water within redds in tidal-influenced zones. Surrounding beach and stream-bank sediments provide a source area for migration of entrapped oil and dissolved-phase polynuclear aromatic hydrocarbons. Ground-water flow in this environment is very dynamic. Fluctuations occur in the stream-bed interface due to diurnal tide fluctuations, storm tides, snowmelt and precipitation stream-stage increases, and seasonal fluctuations in ground-water discharge.

We investigated two streams in Prince William Sound in the summer of 2000. Both stream outlets face north and were heavily oiled in 1989. Data indicated both streams interact with adjacent ground water. Water temperature and specific conductance indicated differences between streams and ground water. The Sleepy Bay stream entered the beach environment through a narrow break in bedrock sidewalls of the bay. There was less indication of ground-water inflow into the beach area than at Junction Creek. Tidal changes vary as much as five meters in Prince William Sound. The cyclic rise and fall of the water table in beach sediments, followed by inflow into the stream beds used for spawning provides a pathway for hydrocarbon migration into salmon redds.

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