A retrospective analysis on changes in sediment flux in the Mississippi River system: trends, driving forces, and implications

Abstract

PURPOSE: The Mississippi River is the largest river in the USA and one of the most regulated rivers in the world. Understanding fluvial sediment flux changes in the Mississippi River system has critical implications for future sustainable development and management strategies. MATERIALS AND METHODS: We obtained annual runoff and suspended sediment series from the United States Geological Survey (USGS) Data Series. Here, we investigated temporal trends and historical phases of fluvial sediment flux, while also quantifying the driving forces of changes in sediment loads in the Mississippi River system using a sediment identity approach and the sediment survey records. RESULTS AND DISCUSSION: Since the earliest estimates (initially 400–500 Mt year⁻¹), land-ocean sediment reduction in the Mississippi River system has displayed two temporal phases, decreasing from 350 Mt year⁻¹ during 1952–1962 to 200 Mt year⁻¹ during 1963–2009. The decline in land-ocean sediment flux was the result of an increase in precipitation and water yield capacity being outweighed by a decrease in sediment concentration. It is estimated that a total of 24 Gt of sediment was trapped by dams and reservoirs from 1985 to 2015, while the amount of sediment reduction by soil conservation is estimated to be 15 Gt in the USA. We can deduce that reservoir construction was the dominant driver (~ 62%) influencing land-ocean sediment flux from the Mississippi River system during 1985–2015. During 1950s–1960s, reservoirs played an overwhelmingly primary role in reducing riverine sediments. In the Missouri River basin, the largest contributor of sediment to the lower Mississippi River, we found a dominant role (> 53%) of reservoirs on tributaries in trapping sediments. The decrease in land-ocean sediment flux has caused degradation of the Mississippi River delta. CONCLUSIONS: Human activities are the main factors influencing changes in land-ocean sediment flux. Therefore, there is an urgent need of a basin-wide strategic plan to maximize the benefits and minimize the risks in order to achieve sustainable management of the drainage basin and river delta.