The influence of cascade reservoir construction on sediment biogenic substance cycle in Lancang River from the perspective of phosphorus fractions

Abstract The impact of the development of cascade reservoirs on the biogenic substance cycle is an important scientific issue for the future sustainable development of the Lancang-Mekong River. The vertical distribution of phosphorus (P) fractions of Xiaowan (XW) and Nuozhadu (NZD) Reservoir sediment in Lancang River were studied to better understand the environment influence of cascade deep reservoir for the first time. The results showed that the P concentration in the overlying water and the P content in sediment of the upstream XW Reservoir was higher than that of the downstream NZD Reservoir, but the P bio-availability (BAP) in sediment were lower than that of the NZD Reservoir. The sediment of the XW Reservoir showed low BAP content and high inert P content. In the contrast, the sediment of the NZD Reservoir showed high BAP content and low inert P content. The P in the sediment of the two reservoirs has totally different control factors, which indicates that the biogenic substance cycles mechanisms of two reservoirs are significantly different under the influence of the cascade reservoir. The less sediment source of downstream reservoir highlights the role of regional sediment in turn. The biogenic substance of the regional sediment plays an important role in the downstream reservoir sediment.