Whitehorse Pond – 4.0 DISCUSSION

Crater Lake National Park Whitehorse Pond Limnological and Vascular Plant Study, 1993



4.1 Physical Characteristics

The Whitehorse Ponds were visited several times in 1993. Compared to Crater Lake itself, these ponds experience great physical extremes. In winter they are covered with several feet of snow and in spring the fast melting snow flushes each pond and fills it with seasonal water. The quality of the ponds depends completely on the quality of the precipitation.

This study included physical, chemical, phytoplankton, zooplankton, and floral studies. Observations were included on each pond visited. The ponds were visited between July 14 and September 10, 1993. In this brief period the water temperatures varied from 13 to 240 C, the acid concentration or pH varied from 5.55 to 6.20, dissolved oxygen levels were low and varied from 4.5 to 6.7 mg/L and the conductivity of the pond water varied from 7.6 to 16.6 ,MHO/L.

Comparing pond chemical concentrations with a bulk deposition study (precipitation and dryfall) completed in 1988, a caldera spring study 1984/89 and chemical species in the Lake itself 1982/90, interesting relationships are revealed (Table 3). Chemical concentrations paralleled the concentrations of a bulk deposition study completed in September 1988 (Larson, 1993). All chemical species determined were of similar concentration except nitrate and sulfate ions. Nitrate ion was found to be 18 times less concentrated in the ponds than in Crater Lake precipitation. Nitrate ion, an important nutrient, was probably being taken up by plants in and around the ponds. Sulfate ion was also found in very small concentrations in the ponds about 100 times less than in Park precipitation. Total phosphate, sodium, potassium, calcium, magnesium, and chloride were all similar in concentration when compared to precipitation.

When Crater Lake water chemical specie concentrations were compared to pond water concentrations, they ranged from similar, as in total phosphate, to 50 times greater for alkalinity. All the other chemical species were in the 8 to 20 times range greater in the Lake. The ponds are probably fed by precipitation alone. Changes in the quality of the precipitation would certainly affect the ponds.

4.2 Plankton Discussion

With only three phytoplankton samples, it is difficult to interpret much. However, with six of the eight freshwater algal divisions represented, the population data suggest the possibility of more eutrophic, than oligotrophic, systems. It is also known that euglenoids require particular organic inputs (i.e. B-12) and therefore, further leads towards more organically rich systems. The greater diversity of taxa, during the August samples, as opposed to the much reduced taxonomic number, but thirty fold increase in cell densities of the September sample, suggests a reduction in nutrients (i.e. available nutrients bound up), higher water temperatures (the dominance of cyanobacteria and the Cholorella sp.), and light intensity. The herbivory by the zooplankton is surely of some effect upon the phytoplankton also.