ECOSYSTEM METABOLISM AND OXYGEN DEFICIT IN LAKE MANINJAU: INSIGHT FROM HIGH-FREQUENCY MEASUREMENT

Abstract

High-frequency measurement provides a sophisticated insight in capturing environmental pattern. Compared to traditional discrete measurement, high-frequency sensors allow better understanding of any processes particularly those with temporal scale characteristics. Lake metabolism is one of the exemplars getting advantage of such better resolution measurement. The dynamics of dissolved oxygen concentration (DO) observed in hourly manner, even in minutes, may explain the balance of photosynthetic activity as expressed by gross primary production (GPP) and respiration (R), and atmospheric exchange. Using a coupled thermistor-chain and oxygen sensor, we computed lake metabolism of the eutrophic Lake Maninjau. Characterized by high phytoplankton productivity fueled by the abundance of nutrient availability, DO concentration in Lake Maninjau is likely to be supersaturated. On the other hand, floating cage aquaculture operated in the lake may have a consequence in increasing water column heterotrophy, oxygen demanding community. Through a simple mathematical model we revealed that water column respiration in Lake Maninjau is higher than gross primary production (R > GPP) with an average of 12.1 mg O 2 L -1 day -1 and 9.0 mg O 2 L -1 day -1 , respectively. Our findings highlight that as heterotrophy in eutrophic lakes may relatively be high, oxygen depletion in the water column may occur in any instance, especially in lakes where dense floating cage aquaculture is in place. Keywords: lake metabolism, dissolved oxygen, high-frequency monitoring, heterotrophy