With the implement of  the Three Gorges project, the newly formed water level fluctuation zone results in various ecological problems such as loss of previous vegetation and soil erosion in an area of 350 km² in the Three Gorges Reservoir. To restore and protect the riparian ecosystem, revegetation has been carried out for recent years. A number of species (Cynodon dactylon, Hemathria sibirica, Hibiscus syriacus, Morus alba, Salix variegate, Salix chaenomeloides, and Taxodium distichum) with a high tolerance to summer exposure and winter inundation were transplanted to adapt to new conditions in the water level fluctuation zone of the Reservoir. However, very little information is available about the changes in soil N dynamics response to revegetation and flooding in the water level fluctuation zone.

Scientists at Wuhan Botanical Garden conducted a field experiment in the riparian ecosystem in the Three Gorges Reservoir to study nitrogen (N) dynamics under short-term revegetation and flooding during the period from 2008 to 2009. They found a significant decrease in inorganic N (NH₄+_N and NO₃-- _N) following the short-term revegetation and flooding, which was probably related to the interactions between surface flow, flooding, plant N uptake, and N transformation. Plants in conjunction with flooding increased the net mineralization potential rate (NMPR) and net nitrification potential rate (NNPR), and increased the denitrofication rate (DPR) only at the beginning of the revegetation and then decreased DPR after the flooding by regulating the concentration of soil organic carbon (SOC) and C:N ratios in soil, and decreasing the soil bulk density. Vegetation types affected N dynamics by changing SOC, soil N availability, and C:N ratios. The inorganic N, NMPR, and NNPR were higher in shrub soil than those in herb and tree soils due to higher SOC, whereas the DPR in tree soils was low compared shrub and herb soils because of lower C:N ratios together with the lower SOC. These results suggest that soil inorganic N declined following the revegetation and flooding, and the revegetation in the riparian zone could potentially improve water quality.

This study has been published in Ecological Engineering entitled "Soil nitrogen dynamics following short-term revegetation in the water level fluctuation zone of the Three Gorges Reservoir, China".

Article link: http://www.sciencedirect.com/science/article/pii/S0925857411003247 

Contact: CHENG Xiaoli

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Email: xlcheng@fudan.edu.cn