Water-air greenhouse gas flux calculations

This script calculates water-air fluxes of CO2, N2O, and CH4 based on inputs of dissolved gas concentrations, hydrology, and weather. Fluxes are computed based on calculating gas transfer velocity (k600) using four unique empirically-derived parameterisations. The exact parameterisations are selected based on whether the waterbody is tidal (bi-directional flow), lentic (no flow), or lotic (uni-directional flow). These distinctions are made based on a column that specifies waterbody type (estuary, tidal river, river, drain, feeder drain, or pond).