HR: 1340h
AN: H33D-1411    [Abstracts]
TI: The Role of Wind-driven Circulation in Severe Hypoxic Events in Upper Klamath Lake, OR
AU: * Wood, T M
EM: tmwood@usgs.gov
AF: US Geological Survey, Oregon Water Science Center 10615 SE Cherry Blossom Dr., Portland, OR 97005 United States
AU: Cheng, R T
EM: rtcheng@usgs.gov
AF: US Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Gartner, J W
EM: jgartner@usgs.gov
AF: US Geological Survey, Arizona Water Science Center 520 N. Park Avenue, Tuscon, AZ 85719 United States
AB: Upper Klamath Lake is a large (surface area about 300 square kilometers), shallow (mean depth about 2.5 m) lake in south central Oregon. The lake has been eutrophic for at least the last 1,000 years, but in recent decades it has become hypereutrophic and now experiences annual occurrences of cyanobacterial blooms. Several large die-offs of endangered Lost River and shortnose suckers in the lake have been documented over the last several decades, including three in the mid-1990's, and the evidence indicates that the primary cause of death during these die-offs is hypoxia that accompanies a crash in the cyanobacterial bloom. It is therefore of great interest to understand the mechanisms behind these periods of hypoxia. An array of water quality monitors deployed in the northern third of the lake in 2003 as part of a fish tracking project allowed a severe hypoxia event in July and August to be monitored with greater detail than was possible during previous events. The observations show that the hypoxia was spatially extensive (20 square kilometers), affected the entire water column, and persisted for a period of several weeks. Previously it was believed that hypoxia events detrimental to fish survival were brought on by an extended period of low wind stress that resulted in near-bottom oxygen depletion in a thermally stable water column, but that does not adequately explain the severe event observed in 2003. Instead, it appears that wind-driven circulation in the lake may have played an important role in this event. Wind-driven circulation during periods of northwesterly prevailing winds is clockwise around the lake, resulting in a broad and shallow southward flow through most of the lake and a narrow, deep northward flow along the western shoreline. The observations indicate that this northward flow in 2003 carried severely oxygen-depleted water into the northern portion of the lake that suckers occupy and where the monitoring was taking place. Thus, the hypoxic conditions did not develop in situ as previously believed. The observations have prompted the development of an hypothesis regarding how the interplay between wind-driven circulation and lake morphometry could be part of a convergence of events that brings on a crash in the cyanobacterial bloom as it moves along its flow path around the lake.
DE: 1845 Limnology (0458, 4239, 4942)
DE: 1847 Modeling
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: Fall Meeting 2005