Abstract:

In order to make clear that what kind of impacts the cascade reservoirs play on the nitrogen biogeochemistry circle in the river, we sampled water by different layers in front of the each dam and outflow water in the cascade reservoirs of Maotiao River, Guizhou Province, Southwest China. The water chemistry of the cascade reservoirs is discussed in terms of the physical and chemical parameters, together with N2O distribution in summer. The results indicate that discontinuity layers of temperature plays an important role in production and distribution of N2O in reservoirs of Maotiao River. The N2O distribution in the layer above the SDL (secondary discontinuity layer) in the four cascade reservoirs is dominated by nitrification, while between the SDL and PDL (primary discontinuity layer) is controlled by both of nitrification and denitrification. As two main processes that affect the production of the N2O, nitrification and denitrification change the distribution of N2O in cascade reservoirs. The contents of N2O in reservoirs are higher than that in the atmospheres. This suggests that high contents of the N2O in the reservoir are the N2O source of the atmosphere. However, N2O contents decrease at depth below 15 m with low contents of DO indicates that denitrification produced N2 by consuming a large part of N2O. The water discharge from bottom of cascade reservoirs along Maotiao River released large amount of N2O into atmosphere, which should be taken into account for improving environmental protection of waters in cascade reservoirs when hydroelectric power will be developed.

Key words: nitrous oxide/eutrophication/sourcesink effects/cascade reservoirs