RESEARCH ARTICLE OPEN ACCESSforest project, Desertification control program and the wind breaker belt project in the north, have been implemented in the past few decades (Li, 2004). Over the past 20 years in particular, comprehensive control of soil erosion has brought noticeable improvements, and soil erosion in North China has been effectively controlled by afforestation and construction of water conservancy projects (Wei et al., 2005).While the natural eco-environment of North China improves effectively, the water yield from the mountain areas, which are essential sources of freshwater supply for urban people,
AbstractAim of study: We studied effects of climatic variability and afforestation on water yield to make a quantitative assessment of the hydrological effects of afforestation on basin water yield in the Rocky Mountain Area of North China.Area of study: Seven typical forest sub-watersheds in Chaobai River watershed, located near Beijing's Miyun Reservoir, were selected as our study object.Material and methods: Annual water yield model and Separate evaluation method were applied to quantify the respective contributions of changes in climate and different vegetation types on variations in runoff.Main results: Statistical analysis indicated precipitation did not vary significantly whereas the annual runoff decreased significantly in the past decades. Although forest increased significantly in the late 20th century, climatic variations have the strongest contribution to the reductions in runoff, with the average contribution reaching 63.24%, while the remainder caused by human activities. Afforestation has a more positive impact on the reduction in runoff, with a contribution of 65.5%, which was more than the grassland of 17.6% and the farmland of 16.9%.Research highlights: Compared to the impact of climatic change, we believe the large-scale afforestation may not be the main reason for the reductions in basin water yield.
The diversity and abundance of ammonia-oxidizing bacteria was investigated in three different types of horizontal subsurface flow constructed wetlands, reed (Phragmites australis)/gravel bed (W1), hybrid vegetation {reed, cattail (Typha latifolia), bulrush (Scirpus validus)}/gravel bed (W2) and reed/hybrid substrates bed (gravel, zeolite, slag) (W3). The investigation of community structures of ammonia-oxidizing bacteria revealed that the types of macrophytes , substrate and space distributions had significant influence on the microbial community. The ammonia-oxidizing bacteria detected were all inculturable, and belonged to Nitrosomonas spp.
The removal of ammonia nitrogen from the polluted water was investigated in three different types of horizontal subsurface flow constructed wetlands, reed (Phragmites australis)/gravel bed (W1), hybrid vegetation {reed, cattail (Typha latifolia), bulrush (Scirpus validus)}/gravel bed (W2) and reed/hybrid substrates (gravel, zeolite, slag) bed (W3). At HRT of 28 d, NH3-N removal efficiencies of W1, W2 and W3 were-130%98%, -120%98% and 21%98% respectively throughout the whole year. The results showed that zeolite and slag contributed to higher NH3-N removal than gravel, especially in winter, and that cattail and bulrush did not show significant influences on NH3-N removal. The ranges of NH3-N removal rates were-2.332.14, -2.272.33 and 0.082.52 g·m-3·d-1 respectively under HRT of 2 d. NH3-N removal rates of W1 and W2 were much more affected by temperature than that of W3, which was due to the adsorption/desorption of zeolite.
Denitrification is strongly dependent on carbon quantity and quality in most constructed wetlands (CWs), and pH may be a key factor in determining the supply of available carbon source (ACS) in the pre-treatment of external plant biomass. In this study, three bath CWs were designed, and were fed with nitrate-dominated water to investigate nitrate removal affected by external cattail litter with different pH pre-treatment (pH = 7.0, 10.0, 12.0). During the experiment, higher nitrate removal was observed in the wetland using pH12.0 pre-treatment litter leachate as the carbon source. Strong alkaline fermentation at ambient temperature can be considered as a sustainable technology for wetland plant litter pre-treatment.
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