The distribution of CH4, ΣCO2, and NH3-N below the thermocline of Lake 227 can be reproduced using a simple numerical model. The model uses a constant vertical eddy diffusion coefficient and assumes the sediments to be the sole source of the chemical species. Analogs dependent on oxygen concentration can effectively represent conditions at the interface of the modeled region and the shallower depths in the lake. The best tit value for the vertical eddy diffusion coefficient is 3.1 × 10−3 cm2∙s−1. This is in good agreement with other independent measurements of this phenomena. The best fit fluxes of CH4, dissolved inorganic carbon and NH3-N are respectively: 13 × 10−3 mol∙m−2∙d−1, 7.5 × 10−3 mol∙m−2∙d−1, and 1.65 × 10−3 mol∙m−2∙d−1. The flux of methane is similar to that found in other small productive northern lakes and the ratio of CH4:ΣCO2 production of 1.73 falls in the range of values established for fermentation of mixed organic materials and sediments. The flux of ΣCO2 is 50–75% of the bicarbonate flux (10–15 × 10−3 mol∙m−2∙d−1) found previously in Linsley Pond, Connecticut.Key words: sediment–water interactions, methane, CO2, and ammonia fluxes, diffusion from sediments, Experimental Lakes Area