Plant soaking decomposition as well as nitrogen and phosphorous release in the water-level fluctuation zone of the Three Gorges Reservoir.
The operating scheme of the Three Gorges Reservoir results in a summer drought in the water-level fluctuation zone during which plants grow vigorously. In the winter inundation season, soaking plants may decompose and release nutrients resulting in water quality deterioration. This study quantifies the contributions of the underwater decomposition of nine dominant plant species in the water-level fluctuation zone to nutrient release. The in-situ litterbag technique was used to study for soaking decomposition over 200days. All soaking plant species decomposed rapidly at an average rate of 1.99±0.33%d-1in the early stage of soaking (0 to 30days) and at an average rate of only 0.07±0.04%d-1in the later stage (30 to 200days). After 200days of soaking, the nine plant species released an average of 312.40±39.97gkg-1organic carbon, 6.71±4.29gkg-1of nitrogen and 2.25±1.25gkg-1of phosphorus. A positive relationship was found between soaking plant decomposition rates and initial C/N ratios of 25 to 50, and a negative relationship where the C/N ratios were between 50 and 100. The amounts of total nitrogen or total phosphorus released were significantly negatively correlated with the initial C/N or C/P ratios of the plants. Among the studied plant species, Xanthium sibiricum Patr ex Widder showed high level of nutrient release via soaking decomposition. In contrast, Cynodon dactylon (Linn.) Pers. and Polygonum hydropiper exhibited low levels of nutrient release and are recommended as suitable species for the ecological restoration of the water-level fluctuation zone. Our results demonstrate that after 200days of soaking plant decomposition, the loadings of total organic carbon, nitrogen, and phosphorus in the water-level fluctuation zone of the Three Gorges Reservoir were 2942.1, 81.1, and 24.7kgha-1, respectively and therefore could potentially damage the aquatic environment of the reservoir.
Key Laboratory of Mountain Surface Processes and Ecological Regulation, Chinese Academy of Sciences, 610041 Chengdu, China; Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, 610041 Chengdu, China; University of Chinese Academy of Sciences, Beijing 100049, China.
Liwei
L
Xiao
Key Laboratory of Mountain Surface Processes and Ecological Regulation, Chinese Academy of Sciences, 610041 Chengdu, China; Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, 610041 Chengdu, China. Electronic address: bzhu@imde.ac.cn.
Bo
B
Zhu
Key Laboratory of Mountain Surface Processes and Ecological Regulation, Chinese Academy of Sciences, 610041 Chengdu, China; Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, 610041 Chengdu, China; University of Chinese Academy of Sciences, Beijing 100049, China.
Mathieu
M
Nsenga Kumwimba
Key Laboratory of Mountain Surface Processes and Ecological Regulation, Chinese Academy of Sciences, 610041 Chengdu, China; Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, 610041 Chengdu, China.
Shiwei
S
Jiang
D002681:China; D055868:Floods; D009584:Nitrogen / Q000032:analysis*; D010758:Phosphorus / Q000032:analysis*; D010944:Plants; D014867:Water
D014867:Water; D010758:Phosphorus; D009584:Nitrogen
Eutrophication; Litter-bag decomposition; Nutrient cycling; Plant species; Riparian zone; Three Gorges Reservoir