Abstract
Pressure on the biodiversity of ecosystems along many rivers is growing continuously due to the increasing number of hydropower facilities regulating downstream flow and sediment regimes. Despite a thorough understanding of the short-term processes and interactions at this hydro-biosphere interface, long-term analyses of the impacts on floodplain dynamics are lacking. We used interannual Landsat 4, 5, 7, and 8 time series to analyze the effects of hydrological events on floodplain vegetation in four mountainous floodplains in the Swiss Alps. Using a spectral mixture analysis approach, we demonstrate that the floodplain vegetation dynamics of mountainous rivers can be recovered at a spatial resolution of 30 m. Our results suggest that interactions between floods and floodplain vegetation are complex and not exclusively related to flood magnitude. Of the four reaches analyzed, only data gathered along the submountainous reach with a quasi-natural flow regime show a clear link between remotely sensed vegetation indices and floods. In addition, our 29-year time series shows a continuous upward trend in vegetation indices along the floodplains, strongest in the reaches affected by hydropower facilities. The approach presented in this study can be easily replicated in other mountain ranges by providing available flow data to verify the impact of hydropower on floodplain vegetation dynamics.
Highlights
R IVERS and their floodplains provide essential ecosystem services worldwide while under pressure from hydropower production, agricultural expansion, and climate change [1]–[3]
Our observations confirm that satellite time series can support the study of floodplain ecosystems in mountainous and submountainous river floodplains under the influence of flood events
The results suggest that it is important to take into account the sequence of flood events and their magnitude to contextualize the impact of a single flood on floodplain vegetation
Summary
R IVERS and their floodplains provide essential ecosystem services worldwide while under pressure from hydropower production, agricultural expansion, and climate change [1]–[3]. The changes imposed on the flow regime largely impact the floodplain vegetation through the modification of natural hydrogeomorphic processes [4], since the forms of floodplain vegetation are largely related to flood and sediment characteristics [5], [6]. Alterations of the flow regime, as well as alterations of the sediment transport, result in changes in the floodplain ecosystem, such as vegetation encroachment or increase in nonwoody vegetative cover, but prediction of Manuscript received October 30, 2019; revised January 16, 2020 and February 20, 2020; accepted March 7, 2020. Observation and monitoring of floodplain vegetation development and recovery are crucial to assess flow regime management needs and the achievements of restoration projects along river systems globally [9]
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