A pump sampler study of microdistribution in Walker Lake, Arizona, U.S.A.: a senescent crater lake

SUMMARY. 1. The seasonal microdistribution of physico‐chemical features and plankton were examined at close intervals in a high elevation (2493m) senescent crateri lake (1m deep) in the arid southwestern U.S.A. 2. The protective volcanic rim and dense growth of provided highly stable thermal conditions throughout much of the year with the thermocline frequently in the top 30cm of the water column during the summer and dissolved oxygen typically <3.0mgl−1 in surface waters and <1.0mgl−1 below 50cm. 3. The microdistribution of both phytoplankton and zooplankton was examined at close intervals (10cm) throughout the water column with the aid of a peristaltic pump. 4. Aglaodiaptomus leptopus, along with Dinobryon sertularia and certain diatom species, were largely restricted to the top 30cm, while the colonial phytoflagellate, Pyrobotrys elongata and certain euglenoids were mostly located in the anaerobic lower strata. 5. Cryptomonas obovata demonstrated subsurface maxima at various locations within the water column depending upon season. 6. The distribution of plankton was also compared during daylight and darkness on one date.