Abstract
The “ecological ditch” (eco-ditch) is an effective measure used to alleviate agricultural non-point-source pollution. However, information is lacking about the continuous transport characteristics of internal and external nitrogen and phosphorus in the interstitial water of the bottom mud of these ditches and overlying water under dynamic continuous inflow conditions. Understanding of the effect of matrix dams and microbial communities inside eco-ditches on the continuous transport characteristics of the N and P therein needs to be improved. To determine the interception effects of eco-ditches on the transfer of endogenous and exogenous N and P, an eco-ditch combining plants and a matrix dam was built to explore the transport distribution characteristics of N and P in the intermittent water and overlying water in the bottom of the eco-ditch and in the bottom of the soil ditch. We compared and analyzed the composition characteristics of the microbiological communities along the ecological and soil ditches. The research results showed that: (1) The concentration gradient between the interstitial water and the overlying water in the soil ditch is the main reason for the transport and diffusion of pollutants. However, in eco-ditches, the absorption function of plant roots and the differences between the structures of the microbial communities destroy the correlation of this concentration gradient diffusion, especially the effect on ammonium N; (2) a large number of mycelia adhere to the surface of the matrix dam in an eco-ditch, and are conducive to the adsorption and purification of pollutants in the water; (3) Proteobacteria, Chloroflexi, Actinomycetes, and Acidobacteria were the main bacterial groups in the ditches. The aquatic plants in the eco-ditch changed the microenvironment of the sediment, and both the microbial diversity and abundance along the eco-ditch were higher than in the soil ditch.
Highlights
With the improved management of point-source pollution, agricultural non-point-source pollution, characterized by nitrogen and phosphorus, has become the primary source of pollution of water environments [1]
In the interstitial water were higher than in the overlying water (Figure 5), which indicated that the endogenous N and P in the sediment were released fast at first, entering the interstitial water, and were released into the overlying water along the concentration gradient between the interstitial and overlying water
Comparing the changes between the concentrations of pollutants in the interstitial and overlying waters in the ecological and soil ditches, and the microbial community structure in the sediment, waters in the ecological and soil ditches, and the microbial community structure in the sediment, we we found that the main that the eco-ditch more effectively therelease endogenous release of found that reason the main reason that the eco-ditch more effectively inhibitedinhibited the endogenous of pollutants compared to the soil ditch was that the root system of plants played a major role
Summary
With the improved management of point-source pollution, agricultural non-point-source pollution, characterized by nitrogen and phosphorus, has become the primary source of pollution of water environments [1]. Even though external N and P contents may be under control, eutrophication in farmland drainage ditches continues to occur [6] This is mainly caused by the continuous release of N and P in the sediment, which is termed endogenous release, for which inhibiting the release of endogenous N and P to the bottom of farmland ditches is important for reducing agricultural non-point-source pollution [7]. The farmland drainage ditch, as a typical linear wetland, provides an exchange function between the N and P in the interstitial water of the sediment and the overlying water [8,9]. Stevo L. et al [10] conducted relevant research on the concentrations of N and P pollutants in sediments, interstitial water, and overlying water in farmland drainage ditches based on static tests or single-sample monitoring results over a large time span.
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