Modeling of spatio-temporal dynamics of methane, carbon dioxide and nitrogen oxide effluxes emitted from natural lake-land ecotones along the wet-to-dry soil gradient

Globally, many lakes are facing the threat of drying up due to water withdrawal, land use and climate change. During the drying process, lake sediments exposed to air can be become hot spots for carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) fluxes. Measurement of CO2, CH4 and N2O fluxes emiited from the air-exposed dry lake sediments has been largely neglected to date, resulting in significant uncertainties in the accurate calculation of global carbon (C) and nitrogen (N) budgets. In this study, CO2, CH4 and N2O sediment external flux dynamics along a wet-dry gradient (variation), daily time gradient (morning-afternoon) and ecological geographic gradient (latitude-longitude; 5 different geographic regions) in 20 lakes located in western part Turkey were measured and both linear and non-linear environmental drivers controlling the fluxes nonlinearly identified. The mean daily fluxes of CO2, CH4 and N2O were 3,79 ± 6,71, 0,54 ± 1,30 and 0,006 ± 0,007 from wet sediments and 24,22 ± 74,94, 0,04 ± 0,06 and 0,004 ± 0,008 mmol m-2 h-1 from dry sediments, respectively. The relative effects of sediment physicochemical properties on sediment CO2, CH4 and N2O fluxes are explained by evaluating them together with the wet-dry gradient, diurnal time gradient and spatial categorical variables. With the model approach based on ANN and Monte Carlo resampling method, the importance levels of the drivers of CO2, CH4 and N2O fluxes are explained together with their physicochemical properties, temporal and spatial parameters and the effects of their interactions. Accordingly, the explanatory variables of SPI3, wet-dry gradient, PO43--P (mg L-1), latitude and RP (mV) stand out as the most important factors in explaining the formation mechanisms of CH4 and CO2 fluxes in drying freshwater sediments. For the N2O fluxes, the most important drivers are SPI3, SHC (%), latitude and PO43--P (mg L-1).