Electron Transport System Activity: A Key Measurement in Ecosystem Monitoring

Abstract

The activity of the respiratory electron transport system (ETS) in a water, plankton, or sediment sample is arguably the most useful and informative biological variable to measure in the hydrosphere. This is especially true if hydrological background variables such as oxygen, nitrate, nitrite, temperature, light, sulphide, etc have been measured. Without knowing the hydrographic background of a sample the ETS measurement serves as a bio-index of living biomass, a detector of the level of life in the water (Packard, 1985). If the hydrographic background of a sample is known then ETS measurements can be used to calculate respiratory oxygen consumption and CO2 production, the metabolic organic carbon consumption rate, vertical carbon flux, nutrient retention efficiency (Osma et al., 2014), the ATP production rate, the rate of biological energy generation, the biological heat production rate (Pamatmat et al., 1981), the age and flow rates of deep and bottom waters (Packard, 1985). In anoxic waters, if the background chemistry (Richards, 1985; Pawlowicz et al, 2007) is known an ETS activity measurement can serve as a proxy rate measurement for denitrification (Packard, 1969; Codispoti and Packard, 1979), nitrite production, nitrous oxide production, and sulfide production (Packard et al., 1983), and even for iron and magnesium reduction rates. All are different forms or respiration controlled by the same basic respiratory ETS. Furthermore, because the energy generation of nitrification is based on a variation of this ETS it is likely the under the right chemical conditions the ETS can serve as a proxy for nitrification in water columns or sediments.