Introduction

Since about 1890, many marshlands have been drained in the upper Klamath River basin in southern Oregon, including 31,000 acres adjacent to Agency and Upper Klamath Lakes (Snyder and Morace, 1997). Although the undrained areas provide high quality habitat and food resources for diverse wildlife communities, 69 percent of the original within-lake wetlands have been drained. Effects of drainage include loss of marsh habitat and lake storage capacity, and altered soil biogeochemistry, including oxidation of peat soils, reduction in bulk mass, and release of carbon, nutrients, and minerals.

Wetlands in the upper Klamath River basin were drained for cattle grazing and crop cultivation including hay, barley, wheat, and potatoes. Draining lowered the water table and allowed oxygen to penetrate organic-rich peat soils, which promoted decomposition and release of nutrients and minerals that had accumulated over several thousand years (Snyder and Morace, 1997). The decreased nutrient content and greater bulk density of drained wetland soils manifested itself as land subsidence of as much as 13 ft in some wetlands adjacent to Upper Klamath Lake. Subsiding wetlands may release large quantities of carbon, nitrogen, and phosphorus when they are flooded. Subsequent pumping of standing water delivers great quantities of nutrients and carbon into Upper Klamath and Agency Lakes. Additional nutrient inputs from tributaries and internal loading fuel massive blooms of blue-green algae (Aphanizomenon flos-aquae) that cause periods of poor water quality. The annual growth and decomposition of dense algal blooms produce high pH (9–10 units), widely variable dissolved oxygen (anoxic to supersaturated), and high ammonia concentrations (nearly 0.3 mg-N/L, un-ionized) (Wood and others, 2006). Episodes of poor water quality have been associated with large kills of sucker fish species, including the Lost River sucker (Deltistes luxatus) and the shortnose sucker (Chasmistes brevirostris), which are protected under the Endangered Species Act (U.S. Fish and Wildlife Service, 1988).

Efforts to regain wetland function, increase water availability, decrease nutrient loading, and improve water quality and habitat have been initiated by several private landowners, organizations, and government agencies including the Klamath Basin Ecosystem Restoration Office (a division of the U.S. Fish and Wildlife Service), The Nature Conservancy, the Bureau of Land Management (BLM), and the Running Y Ranch Resort (MacLaren and Geiger, 2001). In 1994, the BLM completed acquisition of the Wood River Ranch, a 3,200-acre cattle ranch along the north shore of Agency Lake (fig. 1) that was drained and converted to pastureland in the 1950s and 1960s. Prior to 1994, this property was managed as irrigated pasture for beef production (Bureau of Land Management, 2006). This area is now referred to as the “Wood River Wetland” and currently is managed as an Area of Critical Environmental Concern to improve water quality, increase water availability, and provide wildlife and fish habitat (Bureau of Land Management, 1995, 1996, 2006). In 2003, the U.S. Geological Survey (USGS), in cooperation with BLM and with subsequent support from the U.S. Fish and Wildlife Service, began a study to characterize the hydrologic and water-quality conditions within the Wood River Wetland to help address questions regarding possible consequences of future management options.