Using Gas Exchange Estimates to Determine Net Production of CO₂ in Reservoirs and Lakes

Abstract

The net contributions to the atmosphere of GHG’s from reservoirs and lakes are made up of fluxes in inflows, outflows, and gas exchange. The rates of production, which are primarily due to bacteria and algae, and the transport coefficients due to hydrologic flows, wind velocity etc. can both vary considerably over time. Achieving accurate estimates of the net production requires an understanding of the variability of these various functions and requires sampling protocols adequate to define the parameters over the period of study. Several sampling protocols have been used each with strengths and weaknesses. This paper discusses the methods used for data collection and data interpretation for the gas exchange fluxes. Serious potential errors in estimates are identified for data based on infrequent sampling. Alternate protocols are recommended which use models of wind histories and estimates of diurnal changes due to photosynthesis. The recommended approach is to use high resolution measurements of parameters supplemented by models to understand the variability prior to designing programs to estimate fluxes.