Water Quality and Algal Diversity of Ten Lakes Along the Mountain Loop Highway, Washington

Water quality parameters, watershed characteristics and algal diversity and abundance were compared in ten lakes along the Mountain Loop Highway in Washington State. Water samples were collected in July and August 2014 and analyzed for temperature, dissolved oxygen, alkalinity, conductivity, pH, turbidity, chlorophyll, total phosphorous, total nitrogen, soluble reactive phosphorous, nitrate + nitrite, silica, chloride, sulfate, total organic carbon, dissolved organic carbon and total and dissolved metals (aluminum, antimony, arsenic, barium, beryllium, cadmium, calcium, chromium, cobalt, copper, iron, lead, magnesium, manganese, molybdenum, nickel, potassium, selenium, silver, sodium, thallium, thorium, uranium, vanadium and zinc). The watershed characteristics measured were elevation, lake surface area, watershed area, watershed slope, evergreen coverage and primary watershed geology. Live algae were collected and identified to the lowest practical taxonomic level to create a presence/absence species list. Additional algal samples were collected and preserved with Lugol's iodine and settled for enumeration and biovolume calculations. The lakes in this study had relatively warm temperatures (11-27 degreesC), high dissolved oxygen concentrations (7-11 mg/L), relatively low alkalinities (< 27 mg/L) and conductivities (< 58 μS/cm) and were at circumneutral pH or basic pH (6.1-7.9). Five lakes were oligotrophic, four lakes were mesotrophic and one lake was eutrophic. Many nutrient and metal concentrations were below detection levels. Dissolved organic carbon concentrations formed two distinct groups of lakes: relatively high dissolved organic carbon (>2.0 mg/L) and relatively low dissolved organic carbon (< 2.0 mg/L). A total of 405 different algal taxa were identified from the ten lakes, of which 256 taxa were unique to an individual lake. Desmids and diatoms represented the majority of the taxa (136 taxa and 101 taxa, respectively). Cyanobacteria dominated the numerical abundance of the ten lakes, representing 86% of the total cell counts. Algal biovolume was dominated by the 'other' category, which represented 77% of the total biovolume. Watershed slope was positively correlated with dissolved oxygen and negatively correlated with temperature, total phosphorous, total nitrogen, dissolved organic carbon and desmid counts. These correlations were a result of watershed morphology. Non-parametric cluster analysis created two clusters of lakes that corresponded to the high and low dissolved organic carbon groups. The two clusters of lakes had many differences in water quality, watershed characteristics and algal species richness and taxonomic diversity. The high dissolved organic carbon lakes had gradually sloped watersheds, well-developed shoreline vegetation, relatively high nutrient concentrations and high desmid diversity; the low dissolved organic carbon lakes had steep, rocky watershed slopes, little or no apparent littoral vegetation, relatively low nutrient concentrations and low desmid diversity.