Response of Dissolved Nutrient Transport to “Source” and “Sink” Landscape Pattern in Typical Agricultural Small Watersheds in the Three Gorges Reservoir Area
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X522

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Supported by the Fundamental Research Funds of the Central Universities of China (No.XDJK2017B025)and the Innovation Training Program for College Students of Southwest University(No.S202110635130)

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    Abstract:

    【Objective】 The "source" and "sink" landscape pattern reflects the land use allocation and spatial element distribution. It equally controls the energy flow and water sediment process of the watershed, which is an important factor affecting nutrient loss in small watersheds. The purpose of this research was to investigate the effect of landscape patterns on the transport of dissolved nutrients in agricultural small watersheds under different rainfall types. 【Method】 The traditional agricultural catchments and agroforestry catchments in the Shipanqiu watershed of the Three Gorges Reservoir Area were selected as the research objects. The concentrations of dissolved nitrogen and phosphorus in the runoff at the outlet section of the catchments were monitored during different intensities of erosive rainfall events. Also, aerial survey data combined with the minimum cumulative resistance model were used to identify the "source" and "sink" landscape spatial pattern. The location-weighted landscape index(LWLI) was used to analyze the impact of the "source" and "sink" landscape pattern on dissolved nutrient transport in the small watershed. On this basis, the response mechanism of dissolved nutrient transport in the small watershed to the "source" and "sink" landscape pattern was further clarified. 【Result】 The results showed that:① In the traditional agricultural catchment area, the landscape area ratio of "source" and "sink" was 1.8:1, which was dominated by "source" landscape, and the vertical differentiation of landscape was obvious. In the agroforestry composite catchments, the landscape ratio of "source" and "sink" was about 1:1, which was evenly distributed, but the high and steep slope area accounted for a high proportion and the average slope was large. ② In the two catchments, the loss load of dissolved nitrogen and phosphorus was rainstorm > moderate rain > heavy rain. In different rainfall events, the nutrient output load and its coefficient of variation in the traditional agricultural catchments were higher than those in agroforestry catchments. The nutrient transport had strong volatility and was more vulnerable to the change in rainfall intensity. ③ Agricultural land was the main source of nutrient loss in both catchments, but due to the limitation of a slope, other woodlands may be important nutrient migration areas in the agroforestry composite catchments. The LWLI of the traditional agricultural catchment was as high as 0.75, which indicated the risk of high nitrogen and phosphorus loss in this catchment. Also, the LWLI of the agroforestry catchment area was 0.28 and with a low nutrient output. This was attributed to the joint action of reasonable landscape spatial patterns and the agroforestry management model. 【Conclusion】 The "source" and "sink" landscape patterns had a significant impact on nutrient loss in small watersheds. The risk of nutrient loss in small watersheds can be judged by the "source" and "sink" location-weighted landscape contrast index. Accordingly, it can provide a basis for the optimization of "source" and "sink" landscape pattern and the prevention and control of non-point source pollution in small watersheds.

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NI Ke, WANG Xiaoyan, YANG Lan, CUI Can, LI Jiaming, LONG Yi. Response of Dissolved Nutrient Transport to “Source” and “Sink” Landscape Pattern in Typical Agricultural Small Watersheds in the Three Gorges Reservoir Area[J]. Acta Pedologica Sinica,2024,61(2):408-423.

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History
  • Received:May 19,2022
  • Revised:November 11,2022
  • Adopted:May 30,2023
  • Online: July 17,2023
  • Published: March 15,2024