Model Test of the Effect of River Sinuosity on Nitrogen Purification Efficiency

River pollution is a significant problem within the urbanization process in China. Nitrogen is one of the most important pollutants in rivers, and the nitrogen purification capacity of rivers can be affected by their sinuous morphology. In this study, a set of sandy circulating water test models was constructed, consisting of four river channel simulation models with sinuosities of 1.0, 1.4, 1.8, and 2.2. Each model was then infused with the same concentration of nitrogen-polluted water, which circulated for 52 h. The nitrogen reduction processes of rivers with different sinuosities were studied through water quality monitoring. The positive correlation between river sinuosity and nitrogen purification capacity was verified in physical laboratory test models. The effect of sinuosity on the spatiotemporal distribution of total nitrogen in pore water was confirmed. Additionally, the near-shore substrate was more involved in the process of river self-purification than the far-shore substrate. The concave bank of the sinuous rivers was more prone to pollutant accumulation and had a higher purification capacity than the convex bank. After the polluted water entered the sinuous channel systems, pollutant concentration differed within the convex bank between the more polluted upstream section and the less polluted downstream section. This study lays a foundation for studying the mechanism by which river sinuosity influences self-purification capacity.

Future Impacts of Climate Change and Land Use on Multiple Ecosystem Services in a Rapidly Urbanizing Agricultural Basin, China

Ecosystem services (ESs) in rapidly urbanizing agricultural basins are vulnerable to environmental changes. Adequately understanding the driving forces and the dynamics of ESs related to water quantity and quality can provide a basis for making sound management decisions on the development of basins. Here, we explored the impacts of future land use and climate changes on four ESs: nitrogen and phosphorous purification, water supply, and soil retention services in the Taihu Basin region of eastern China. Spatially explicit methods, a cellular automata-Markov (CA-Markov) model and the delta downscaling method were used to quantify the ESs, simulate land use changes, and project future climate changes, respectively. We built a business-as-usual land use scenario, representative concentration pathways (RCPs) scenarios for climate change, as well as a combined land use and climate change scenario to analyze the changes in the drivers and the responses of ESs. The results showed the following: (1) future land use changes would significantly enhance the nitrogen purification service while reducing the phosphorus purification service compared to other services; (2) climate change would have substantial effects on water supply and soil retention, but these impacts would vary with different RCPs scenarios during three future periods; and (3) the combined scenarios of both drivers would obviously influence all ESs and lead to a nitrogen purification service that was different from the other three services. Moreover, the policy implications of the results were discussed. The findings can help guide the creation of policies for land structure and patterns, climate change adaptation, and ecosystem-based management to promote the sustainable development of watersheds at the regional scale.

Urban River Water Purification Experiment by Strengthening Ecological Engineering Methods

Based on the biological purification technology combined with the engineering measures, the enhanced nitrogen purification biological experiment is implemented in Wenyu River in Beijing. The water in the river mainly is the outflow from the sewage treatment plant, in which the ammonium (NH4-N) has been effectively removed for the deeply nitrification, while treatment of the nitrate nitrogen (NO3-N) and total nitrogen (TN) is incomplete due to the denitrification. The water has low C/N value and has poor biodegradability. In this study, aiming at the water feature of low C/N and poor biodegradability, the effective way to strengthen denitrification by some enhanced techniques, such as increasing the microorganisms number and biodegradability (ie, improved nitrogen ratio), changing denitrification rates and so on, has been studied. The experimental results show that under the condition of water flow (Q) as 15 ~ 27L/hr, hydraulic detention time as (HRT) 10 ~ 18h, concentration of nitrate nitrogen (NO3-N) as 12.20 ~ 31.44mg / L, and total nitrogen (TN) as 14.50 ~ 34.71 mg / L, the removal rates of NO3-N and TN are over 30%.

Purifying Effects of Nitrogen in Wangyu River Water through Natural Wetlands

In order to study the purifying effects and influences on nitrogen caused by natural riparian wetlands in the river course, Cao Lake and Ezhen Lake in Wangyu River were selected as the main research regions. Samplings in the transfer period with a large flow in May, 2010 were taken in the sites over the whole wetland area and along the main river course, respectively. Observations on the physicochemical indexes such as water temperature, pH, dissolved oxygen(DO), turbidity, suspended solid(SS), total nitrogen (TN), total dissolved nitrogen(DTN), ammonia, nitrate and nitrite were performed to analyze the concentration and chemical forms variations, regional difference of nitrogen nutrient in the river water column. Results are showed as follows: (1) As the water flowed through Cao Lake and Ezhen Lake, the TN、DTN and nitrate showed a trend of descending (descending proportion: 10.45%, 17.85%, 7.62% in Ehen Lake, 9.09%, 7.17%, 7.60% in Cao Lake). The overall removal effects of nitrogen in Ezhen Lake was better than that in Cao Lake, but the retaining effect of ammonia in Cao Lake was better than that in Ezhen Lake. (2) The nitrogen existed in the water mainly in the forms of DTN and the rates on TN were 88.0% and 91.4%, respectively, higher than that of particle nitrogen, but the rates would decrease for the sedimentation of particle nitrogen in the vertical distribution.(3) Water temperature, pH and DO were the dominant factors that affected the purifying effects of nitrogen in the riparian areas. The research showed the obvious retaining effects of nitrogen and evident influences on the nutrients forms variations in the river water column. The results could provide theoretical foundation and technical support for nitrogen purification in the river course.