Nitrogen and phosphorus loading from drained wetlands adjacent to Upper Klamath and Agency lakes, Oregon

Water-Resources Investigations Report 97-4059




Upper Klamath Lake and the connecting Agency Lake constitute a large, shallow lake in south-central Oregon that the historical record indicates has likely been eutrophic since its discovery by non-Native Americans. In recent decades, however, the lake has had annual occurrences of near-monoculture blooms of the blue-green alga Aphanizomenon flos-aquae that are thought to be a result of accelerated eutrophication. In 1988, two sucker species endemic to the lake, the Lost River sucker (Deltistes luxatus) and the shortnose sucker (Chasmistes brevirostris), were listed as endangered by the U.S. Fish and Wildlife Service, and it has been proposed that their decline is due to the poor water quality associated with extremely long and productive algal blooms. It has also been proposed that the effluent drained from wetlands has contributed to accelerated eutrophication.Since the turn of century, most of the wetlands adjacent to Upper Klamath Lake have been drained for agriculture--cultivation of crops and grazing of cattle. Wetland areas were reclaimed from the lake by building dikes to isolate them from the lake, constructing a series of drainage ditches, and installing pumps to drain the water and maintain a lowered water table. A consequence of lowering the water table is the increased ability of air and oxygenated water to move through the subsurface and facilitate the rapid aerobic decomposition of the peat soils. Nutrients, nitrogen and phosphorus, are then liberated, leach into adjacent ditches, and are subsequently pumped to the lake or its tributaries. The rate of peat decomposition may be related to the time since drainage and the type of agricultural land use. On lands cultivated for crops, farming practices, such as disking and furrowing, could enhance the movement of air and oxygenated water, resulting in a rapid rate of decomposition. In contrast, on grazed lands, the compaction of soils by cattle probably inhibits the movement of air and oxygenated water and results in a slower rate of decomposition relative to drained wetlands used for the cultivation of crops.This report presents the results of a cooperative study between the U.S. Geological Survey and the Bureau of Reclamation whose overall objective was to determine the nutrient loading to Upper Klamath Lake from adjacent drained wetlands. Nutrient loading from drained wetlands was estimated using two independent techniques. The first method involved the measurement of the quantity and quality of water discharged by pumps draining the wetlands. The second method was used to estimate the initial (before drainage) and present-day nutrient mass of the organic soils within the drained wetlands and to calculate the change (or loss) in nutrient mass.In an effort to estimate the nutrient contributions from the water pumped off selected drained wetlands adjacent to Upper Klamath Lake, annual loads and yields of total nitrogen and total phosphorus were estimated from concentration data and the volume of water pumped during the water year. In general, there was little variation among sites or among years in the annual total nitrogen (median load of about 18 tons per year and median yield of about 8 pounds per acre per year) or the annual total phosphorus (median load of about 3 tons per year and median yield of about 2 pounds per acre per year) contributions. The sum of the annual loads of nitrogen and phosphorus calculated for each of the pumping stations in 1995 was 80 tons per year and 15 tons per year, respectively.In 1995, soil-coring activities were undertaken to ascertain the nature and extent of the organic soils in the drained and undrained wetlands. The present-day nutrient mass was calculated for each drained wetland using the nutrient content (concentration) and the present-day peat mass. The initial nutrient mass prior to drainage was estimated for each drained wetland by using the initial nutrient content (assumed to be equal to the nutrient content of the undra

Additional Publication Details

Publication type:
Publication Subtype:
USGS Numbered Series
Nitrogen and phosphorus loading from drained wetlands adjacent to Upper Klamath and Agency lakes, Oregon
Series title:
Water-Resources Investigations Report
Series number:
Year Published:
U.S. Geological Survey : Denver, CO. : Branch of Information Services [distributor],
x, 67 p. :ill. (some col.), maps (some col.) ;28 cm.