Freshwater ecology in the Mato Grosso, Central Brazil I. The conductivity of some natural waters

Abstract

Streams and meander lakes in the Mato Grosso, between the Rio das Mortes and the Rio Suiá Missú, have low conductivities ranging from 12 to 50 μmho/cm/20°c, but exceptional isolated pools reach 800 μmho under the influence of evaporation. Rainfall at the beginning of the wet season had conductivities up to 110 μmho, but the general level of conductivity fell as the wet season progressed. Run-off water flowing over the ground during heavy rain generally had a higher conductivity than the rain. Short-term fluctuations in the conductivity of small streams showed increases with heavy rain accompanied by surface run-off. The rainfall had a high calcium to sodium ratio. It is estimated that during the period from 1 September to 30 November 1968 the rainfall supplied the area with at least 4 kg Ca per hectare.