|Abstract or Summary
- Factors affecting physical, chemical, and biological characteristics of lakes
were investigated through the development of a lake-classification system for 162
lakes in North Cascades National Park Service Complex. A conceptual view of lake
development and its relationship to the expression of lake and watershed
characteristics was derived. Water quality and biological assemblages of these
primarily glacially formed high-mountain oligotrophic lakes were influenced by
elevation, lake morphology, and certain watershed characteristics: aspect, vegetation,
soils, hydrology, and degree of glacial influence. Lakes continually evolve relative to
changes in their watershed environments. A watershed-based, three-level hierarchical
classification was created to include 1) lake position relative to the hydrologic crest of
the North Cascade Mountain Range, 2) vegetation zone (alpine, subalpine, low
elevation forest, high elevation forest), and 3) basin origin. Hydrologic crest position
differentiated broad-scale climatic differences in precipitation and air temperature.
Vegetation zones reflected the localized geology (soil maturation) and climate
(precipitation, aspect). Morphogenetic class identified differences in lake morphology,
landscape position, and potential for persistence, and were unequally distributed
across vegetation zones with forest zones most diverse. Time of ice-out increased
from low-forest lakes to alpine lakes; eastslope lakes iced-out earlier. Epilimnetic
temperature was warmest in low-forest lakes and coolest in alpine lakes. Classification
did not clearly order lakes relative to chemical characteristics, though westslope low-forest
lakes differed significantly from other lake classes and were most productive.
Little seasonal or annual variation for most chemical characteristics were found.
However, chemical differences did mirror environmental and physical differences
between lakes. High phosphorus levels separated glacially influenced lakes. Total
Kjeldahl-N and total phosphorus concentrations decreased with increasing lake depth.
For a given flushing ratio, Kjeldahl-N decreased from low-forest to alpine zones. Depth
and vegetation class ordered the diversity and composition of phytoplankton,
zooplankton, and benthic macroinvertebrate assemblages. Nutrients, conductivity, pH,
alkalinity, and cations were correlated with phytoplankton and zooplankton
assemblages. Non-native trout presence was associated with large, deep [greater than or equal to] 3 m)