OXYGEN DEMAND OF LAKES: SEDIMENT AND WATER COLUMN BOD

Abstract

ABSTRACT The total biochemical oxygen demand (TBOD, g O2m−2) of two small, ≤ 5.0 ha, eutrophic lakes in central Iowa was estimated from measurements of the biochemical oxygen demand (BOD) from the top 25 mm of sediments (SBOD) and summation of the BOD values from each 1-meter strata of the water column (WBOD). Standard BOD procedures were used for both sediment and water column biochemical oxygen demand, although a special protocol was developed for the sediments. Continuous recording of the oxygen consumption of selected sediment samples during the five-day BOD procedure revealed a high initial oxygen demand which then declined exponentially over the five-day interval; the oxygen consumption in 20 minutes averaged 26 percent of the mean five-day SBOD value. The sediment and water column biochemical oxygen demand were measured for 28 months in both lakes. WBOD (9 O2m−2) values ranged from 2.0 to 13.1 and mean values were 5.1 and 6.5, respectively, in the two lakes. SBOD (g O2m−2) values ranged from 27.7 to 138.6 and averaged 79.6 and 80.3 in the two lakes. Monthly variation in water column and sediment biochemical oxygen demands were independent. Sediment values were greater than 90 percent (96.5 percent of the total demand in one lake and 94.0 percent in the other lake) of the total biochemical oxygen demand in 9 of 56 monthly samples in both lakes. During the winter ice-covered interval, sediment biochemical oxygen demand and the dissolved oxygen content of the water column were negatively correlated for the two 1-m strata nearest to the bottom.