ABSTRACT
One of the negative effects of monoculture is soil erosion and the loss of fertile soil surface. Fine sediment runoff from agricultural land enters the rivers with serious negative impacts on the aquatic environment. The settlement of fine sediments on or even into the river bed clogs the pore space and reduces the living space for juvenile fishes and macroinvertebrates. Furthermore, the natural exchange processes between surface water and groundwater can be disturbed. Nutrients and pesticides, which preferably bind to sediments are also transported to the rivers and may further reduce the water quality. The implementation of riparian buffer strips along river banks can attenuate the effects of fine sediment and nutrient input by retaining them. The aim of this study is to present a concept to reduce the introduction of fine sediments into river beds by implementing riparian buffer strips in a high monoculture dominated area. The riparian buffer strips are planned according to land use, slope as well as soil composition of the surrounded area. Therefore, different scenarios are developed to retain sediments by the buffer strips. An additional scenario is developed with different buffer widths and vegetation types to retain not only sediments but also nitrogen and phosphorous.
The study site is located in Jinghong County, Dai Autonomous Prefecture Xishuangbanna of Yunnan Province (South China). Xishuangbanna is one of Chinas most biodiverse regions and included in the Indo-Burma biodiversity hotspot (Li et al. 2007). With Chinas growing economy the demand of rubber has been increasing continuously in the last decades. Therefore, large areas with tropical seasonal rain forest have been transformed into rubber monocultures. This led to an increase in the cultivation of rubber of more than 20% between 1976 and 2003 and, also influenced by other changes, to a decrease of rain forest by 67% (Li et al. 2007).
Continuously measured turbidity data at the study site show a high increase in turbidity during rain events. Samples of suspended solids are used to correlate them with the turbidity data. Detailed sediment samples withdrawn from the river bed with the so-called freeze-core technique show a high amount of fine sediments within the river bed with a percentage of fines under 2 mm up to 26%.
To quantify the effectiveness of buffer strips, a GIS-based model is used that calculates the reduction of erosion risk when implementing buffer strips. This model is based on the well-known RUSLE approach, which calculates the annual runoff based on different parameters such as land use and soil properties (Chen et al. 2011). In a first step, the model estimates the current annual soil loss and allows for investigating the effect of the different scenarios with buffer strips.
The results show a significant retention of fine sediments within the buffer strips and a reduction of the erosion risk compared to the current state. It can be concluded that riparian buffer strips are an efficient and easy-to-implement measure to reduce the introduction of fine sediments into rivers.
