Summary
In May 1980 Lago Calado was 9 meters deep, the water level was rising slowly, and below 4 meters the water was anoxic. Virtually all of the zooplankton was in the oxygenated layer. Adult and juvenile Daphnia gessneri, the most abundant crustacean species, occurred between 0.5 and 4.5 meters. Copepod nauplii tended to occur nearer to the surface, in the 0—2 meter stratum. No clear vertical migration was observed.
The epilimnion was undersaturated ( < 40% oxygen) and contained < 0.1 μ M phosphate, ammonium and nitrate. The hypolimnion contained substantial phosphate ( > 2 μ M) and ammonium ( > 5 μ M), but little nitrate ( < 0.1 μ. M). A peak in particulate carbon and nitrogen occurred between 4-5 meters, just below the thermocline, and was associated with a pigment maximum.