Ten mountain lakes were analyzed in order that they be assigned a trophic status. The lakes which are located in the Mount Hood National Forest of Oregon are Anvil, Beaver Pond, Cripple Creek, Fish, Gifford, Monon, Ollalie, Rimrock, Round, and Sportsman. The purpose of this report is to determine the productivity of these waters. Data were collected for analyses of temperature, dissolved oxygen concentration, Secchi depth, major ion concentration, light intensity versus depth, alkalinity, phytoplanktcn species composition/total density, and zooplankton species composition/total density. Samples were collected in Van Darn sampling bottles and returned to the laboratory for chemical analyses and taxonomic identification of biological organisms. Field profiles were taken for light intensity, temperature, dissolved oxygen concentration, specific conductivity, and depth using portable electronic equipment. A Secchi disk was used in the field for obtaining light extinction data. The lakes were assigned a trophic status according to carlson's Trophic State Index (Carlson, 1977). Beaver Pond Lake which is the most productive lake of the 10 surveyed had an average Secchi depth of 1.7 meters, an average soluble reactive phosphorous concentration of 59.8 ug/L, and an average chlorophyll-a concentration of 29.3 ug/L for the dates sampled. These values are consistent with lakes which are eutrophic. Ollalie Lake had an average Secchi depth of 13.2 meters, an average soluble reactive phosphorous concentration of 1.64 ug/L, and an average chlorophyll-a concentration of 0.28 ugfL. This lake is ultraoligotrophic-to-oligotrophic according to the Carlson index. The other lakes of the study were assigned values for trophic state which are somewhere between those assigned to Beaver Pond and Ollalie lakes. The 10 lakes studied for this report were compared to lakes studied for the compilation of the Western Lake survey (Landers, et. al. 1987). It was noted that Beaver Pond, Round, and Sportsman lakes are nutrient rich while Monon, Ollalie, and Gifford, are nutrient poor when compared to other lakes located in the Pacific Northwest. Anvil, Cripple Creek, Fish, and Rimrock lakes have profiles consistent with the majority of mountain lakes located in the area.

Eutrophication is one of the primary factors causing harmful cyanobacteria blooms in freshwater lakes; climate change such as warmer temperature can potentially further increase both frequency and intensity of blooms. This study investigated the long-term changes in water quality and summer phytoplankton assemblages in Oswego Lake, OR, in relation to lake management practices (e.g., hypolimnetic aeration and alum treatments), as well as climatic and regional meteorological conditions. Both water quality and phytoplankton assemblages were sampled biweekly during summer seasons between 2001 and 2013. The concentrations of total phosphorus (TP), soluble reactive phosphorus (SRP) and total nitrogen (TN) decreased 66%, 93% and 31%, respectively, in response to the hypolimnetic aeration and alum treatments since 2005. The results of summer phytoplankton assemblages showed a 62% reduction of cyanobacteria biovolume and a switch from cyanobacteria dominance (2001-2005) to diatom and chlorophyte dominance (2006-2013). Cluster analysis identified four statistically different groups of summer phytoplankton assemblages (denoted Groups 1-4). Nonmetric multidimensional scaling analysis indicated that the four groups were associated with different water quality conditions. Group 1 occurred prior to hypolimnetic aeration and was primarily comprised of cyanobacteria, associated with water conditions of high nutrients and high primary production. Group 2, dominated by cyanobacteria and chlorophytes, occurred between hypolimnetic aeration and alum surface application. Group 2 was associated with turbid water conditions. Group 3 was dominated by diatoms, occurring after alum surface application. Group 4 included R-strategist phytoplankton that quickly respond to environmental changes, occurring in the years following alum injection, drawdown and inflow alum treatment. Both Group 3 and 4 were associated with reduced nutrients in the lake. The results demonstrated a strong temporal relationship between the long-term changes in water quality and summer phytoplankton assemblages and the lake management practices. The Pacific Decadal Oscillation (PDO) index, an El-Niño-like pattern of Pacific climate variability, showed a statistically significant correlation with the summer phytoplankton dynamics, while the multivariate ENSO index (MEI) and regional meteorological variables (air temperature, rainfall, wind speed, wind direction and solar radiation) were not significantly related to the changes of phytoplankton communities during the study period. In conclusion, the study results suggest that the lake management practices had strong effects on both production and community compositions of phytoplankton, and suggest the need for a future study on large-scale climate impacts on lake ecosystems and best management practice.

A study of phosphorus loading and water quality implications was conducted for the Oregon coastal lakes. The study was based on existing data for lake total phosphorus concentrations and for watershed land uses. A phosphorus mass-balance model was developed to predict lake total phosphorus concentrations from estimated phosphorus loading from land uses within the lake's watershed. Uncertainty in total phosphorus concentration estimates are included in the model, and model predictions are considered to be moderately to highly reliable. The Oregon coastal lake phosphorus mass-balance model was calibrated from data for 12 Oregon coastal lakes. Land use phosphorus loading coefficients for forestry, the coastal dunal aquifer, and precipitation were derived from data specific to the Oregon coastal region, while other phosphorus loading coefficients were estimated based on correlations between literature values and Oregon coastal conditions. The model may be used as an aid for land use management decisions by estimating water quality effects of projected land use changes. A case study of Mercer Lake was used to illustrate the model application. / Graduation date: 1994