INTEGRATING LIMNOLOGICAL CHARACTERISTICS OF HIGH-MOUNTAIN LAKES INTO THE LANDSCAPE OF A NATURAL AREA

A general conceptual watershed-lake model of the complex interactions among climatic conditions, watershed location and characteristics, lak e morphology, and fish predation was used to evaluate limnological cha racteristics of high mountain lakes. Our main hypothesis was that decr easing elevation in mountainous terrain corresponds to an increase in diversity of watershed size and lake area, depth, temperature, nutrien t concentrations, and productivity, A second hypothesis was that water shed location and aspect relative to climatic gradients within mountai nous terrain influences the limnological characteristics of the lakes. We evaluated these hypotheses by examining watershed location, aspect and size; lake morphology; water quality; and phytoplankton and zoopl ankton community characteristics among high mountain forest and subalp ine lakes in Mount Rainier National Park. Although many of the compari sons between all forest and subalpine lakes were statistically insigni ficant, the results revealed trends that were consistent with our hypo theses. The forest lake group included more lakes with larger watershe ds, larger surface areas, greater depths, higher concentrations of nut rients, and higher algal biovolumes than did the group of subalpine la kes. Deep lakes, which were mostly of the forest lake type, exhibited thermal stratification and relatively high values of some of the water -quality variables near the lake bottoms. However, the highest near-su rface water temperatures and phytoplankton densities and the taxonomic structures of the phytoplankton and zooplankton assemblages were more closely related to geographical location, which corresponded to a wes t-east climate gradient in the park, than to lake type. Some crustacea n and rotifer taxa, however, were limited in distribution by lake type . Fish predation did not appear to play an important role in the struc ture of the crustacean zooplankton communities at the genus level with the exception of Mowich Lake, where crustacean taxa were absent from the zooplankton community. This was the only lake inhabited by a true zooplanktivourous species of fish.