SEDIMENT OXYGEN-DEMAND IN MAN-MADE LAKE TON-TON (URUGUAY)

A study on sediment metabolism was carried out during 1986 in Lake Ton-Ton, Uruguay. Sediment oxygen demand (SOD) from chemical and biological origin was measured in undisturbed sediment cores taken from the deepest part of the lake. Mean SOD rate for the study period (51.57 mgO2 m-2 h-1) corresponded well with the eutrophic state of the lake. During stratification, SOD from chemical origin accounted for 69-87% of total SOD, while SOD from biological origin was dominating for the rest of the year, except in July. Biological respiration was principally of microbial origin. Hypolimnetic temperature was the main factor controlling SOD rates (r = 0.771, p < 0.001). Nevertheless, freshly sedimented phytodetritus from an Anabaena bloom, together with a renewed input of oxygen to bottom water were responsible for the maximum SOD values, recorded at the beginning of a mixing period in April (72.51 mgO2 m-2 h-1).