Effects of Nutrient Enrichment on Wetlands at Conboy National Wildlife Refuge

Conboy National Wildlife RefugeLocated at the base of Mount Adams in Washington, Conboy Lake National Wildlife Refuge (NWR) is a large seasonal marsh nestled within dense pine and fir forests.  The refuge supports large numbers of swans, geese, ducks, and sandhill cranes (Grus canadensis) during spring and fall migrations, as well as a wide variety of wetland-associated bird species, including black terns (Chlidonias niger), yellow-headed blackbirds (Xanthocephalus xanthocephalus), sora (Porzana carolina) and Virginia rails (Rallus limicola) and American bitterns (Botaurus lentiginosus).  Of the 17 pairs of greater sandhill cranes nesting in Washington, the refuge provides habitat for 14 of those pairs.  In addition, the refuge supports twelve species of reptiles and amphibians including the Oregon spotted frog (Rana pretiosa) which is a candidate species under the Endangered Species Act.  During early settlement of the area, the natural lake was altered to increase native pasture and hay production.  A series of channels were created to improve lake bed conditions for farming. Oregon Spotted FrogAgricultural activities including livestock grazing, haying, and crop farming continue to be major activities occurring in the valley. It is suspected these land use activities are resulting in increased levels of nutrients in the canal system and wetlands on the refuge.  Consequently, there is concern that nutrient enrichment of the wetlands may have the potential to impact the Oregon spotted frog.  Oregon spotted frogs are the most aquatic native frog in the Pacific Northwest (Owens 1999).  While larval stages of the spotted frog are restricted to the aquatic environment, adults remain dependent on aquatic habitats for reproduction, hibernation, and foraging.  With this close, almost constant contact with the aquatic environment, Oregon spotted frogs can be exposed to chemicals in the water through absorption through the skin and ingestion.

Methods: This study examined nutrient levels at various wetland sites at Conboy Lake NWR used by Oregon spotted frogs to determine if nutrient concentrations are such that they could impact the population.  Frog populations were surveyed to assess whether effects seen in controlled exposures to nutrients were being displayed in the wild.  Results of the study will be used to assist the refuge in formulating management strategies to improve seasonal water quality entering the refuge.

Lab TestingResults: There was no nitrite detected in any of the samples collected. Only two sites showed the presence of nitrate over above reporting levels.  Nitrate levels at Headquarters Spring ranged between 0.1 and 0.3 mg/L and concentrations at Willard Spring were 0.1 mg/L.  The only sample that contained ammonia was collected from the Headquarters eggmass site, and the concentration was 0.05 mg/L. Total nitrogen levels were measured between 0.2 and 4.9 mg/L, while dissolved nitrogen levels were between 0.2 and 1.3 mg/L.
Total phosphate ranged from 0.01 to 0.59 mg/L at sample sites on Conboy Lake NWR. Phosphorus was detected at every site with the highest values from Willard egg mass and Chapman egg mass sites. Orthophosphate was detected at levels less than 0.03 mg/L.  Orthophosphate was not detected at the Headquarters, C&H, or the Holmes Creek Inflow sites.  It was detected from only one of the sampling periods at Laurel West egg mass, Chapman egg mass, Chapman inflow, and Bird Creek Inflow sites. Headquarters Spring and Willard Spring had detectable orthophosphate during all sampling periods.

Learn More by Reading the Full Report:  Materna, E., Effects of Nutrient Enrichment on Wetlands at Conboy National Wildlife Refuge, Environmental Contaminants. USFWS, Olympia FWO. 2001.

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