Abstract
Riparian buffers play an important role in intercepting nutrients entering lakes from non-point runoffs. In spite of its ecological significance, little is known regarding the underlying mechanisms of riparian buffers or their optimal width. In this study, we examined nutrient removal efficiency, including the quantity of nutrients and water quality, in the littoral zone of different types of riparian buffers in the watershed around eutrophic Lake Chaohu (China), and estimated the optimal width for different types of riparian buffers for effective nutrient removal. In general, a weak phosphorus (P) adsorption ability and nitrification-denitrification potential in soil resulted in a far greater riparian buffer demand than before in Lake Chaohu, which may be attributed to the soil degradation and simplification of cover vegetation. In detail, the width was at least 23 m (grass/forest) and 130 m (grass) for total P (TP) and total nitrogen (TN) to reach 50% removal efficiency, respectively, indicating a significantly greater demand for TN removal than that for TP. Additionally, wetland and grass/forest riparian buffers were more effective for TP removal, which was attributed to a high P sorption maximum (Qmax) and a low equilibrium P concentration (EPC0), respectively. The high potential nitrification rate (PNR) and potential denitrification rate (PDR) were responsible for the more effective TN removal efficiencies in grass riparian buffers. The nutrient removal efficiency of different types of riparian buffers was closely related with nutrient level in adjacent littoral zones around Lake Chaohu.
Highlights
Transport of nutrients to lakes and the resulting acceleration of eutrophication is a serious concern around the world
The relationships between riparian buffer width and nutrient removal efficiency are shown in Figure 3 (TP) and Figure 4 (TN), and exhibited log-normal distributions
The best total nitrogen (TN) removal efficiency was observed in the grass riparian buffer, which was 130 m, 749 m, and 2143 m in width for 50%, 75%, and 90% removal efficiency, respectively, followed by grass/forest and wetland riparian buffers
Summary
Transport of nutrients to lakes and the resulting acceleration of eutrophication is a serious concern around the world. Runoff from land surfaces such as grass, forest, farmland, and wetlands has been found to be an important nutrient source for aquatic ecosystems [1]. Riparian buffers have been considered as an effective and sustainable means of buffering aquatic ecosystems against nutrient stressors, such as N and P from runoff [2], and they have been considered as the last line of defense for nutrient removal. Riparian buffers attenuate nutrients through soil adsorption, microbial immobilization, plant uptake, and coupled nitrification-denitrification [3,4,5]. The determination of riparian buffer width range depends on the physiochemical and microbial properties of soil, slope, vegetation cover, the form and content of nutrients, and so on [6].
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