In situ microscale distributions of O-2, H2S, pH and redox potential in sediments of Hongfeng Lake, SW China, were investigated using the powerful microsensor technique. Our results show that O-2 was depleted within the top 3.9 mm in surface sediments, and H2S was subsequently detected at similar to 6.0 mm depth, and reached its maximum concentrations at similar to 25 mm. The degradation of organic matter and reduction of sulfate might be the major pathways of producing H2S in sediments. pH rapidly reduced in surface layers mainly due to H+ release in the oxidation of organic matter. Eh also decreased sharply in surface sediments, probabl indicating the coexistence of Fe and Mn oxides with O-2 in aerobic region. Furthermore, the programme of PROFILE was applied to model the O-2 gradient, and good fit was obtained between the simulative values and the factual values both in sediments and in the diffusive boundary layer (DBL). The results indicate that the depth-integrated O-2 consumption rates within sediments were 0.083 and 0.134 nmol center dot m(-3)center dot s(-1) in site S1 and site S2, respectively. In addition, there were distinct DBL in two sediment profiles, with 1.2 mm thickness in S1 and 0.9 mm thickness in S2. The diffusive fluxes of O-2 within the DBL were 67.13 nmol center dot m(-2)center dot s(-1) in S1 and 88.54 nmol center dot m(-2)center dot s(-1) in S2.