Hydrologic and Water-Quality Conditions During Restoration of the Wood River Wetland, Upper Klamath River Basin, Oregon, 2003–05

Restoring previously drained wetlands is a strategy currently being used to improve water quality and decrease nutrient loading into Upper Klamath Lake, Oregon. In this 2003–05 study, ground- and surface-water quality and hydrologic conditions were characterized in the Wood River Wetland. Nitrogen and phosphorus levels, primarily as dissolved organic nitrogen and ammonium (NH4) and soluble reactive phosphorus (SRP), were high in surface waters. Dissolved organic carbon concentrations also were elevated in surface water, with median concentrations of 44 and 99 milligrams of carbon per liter (mg-C/L) in the North and South Units of the Wood River Wetland, respectively, reaching a maximum of 270 mg-C/L in the South Unit in late autumn. Artesian well water produced NH4 and SRP concentrations of about 6,000 micrograms per liter (μg/L), and concentrations of 36,500 μg-N/L NH4 and 4,110 μg-P/L SRP in one 26–28 ft deep piezometer well. Despite the high ammonium concentrations, the nitrate levels were moderate to low in wetland surface and ground waters. The surface-water concentrations of NH4 and SRP increased in spring and summer, outpacing those for chloride (a conservative tracer), indicative of evapoconcentration. In-situ chamber experiments conducted in June and August 2005 indicated a positive flux of NH4 and SRP from the wetland sediments. Potential sources of NH4 and SRP include diffusion of nutrients from decomposed peat, decomposing aquatic vegetation, or upwelling ground water. In addition to these inputs, evapoconcentration raised surface-water solute concentrations to exceedingly high values by the end of summer. The increase was most pronounced in the South Unit, where specific conductance reached 2,500 μS/cm and median concentrations of total nitrogen and total phosphorus reached 18,000–36,500 μg-N/L and about 18,000–26,000 μg-P/L, respectively.