Chen Ye: Active revegetation does not impact nitrogen removal efficiency in a riparian zone

In this new post, Dr. Chen Ye—a Professor of Ecology at Wuhan Botanical Garden, Chinese Academy of Sciences, China—discusses her recently accepted paper, “Soil denitrification rates are more sensitive to hydrological changes than restoration approaches in a unique riparian zone”.

About the paper

The riparian zone is defined as the aquatic-terrestrial interface. This zone can improve water quality by removing nitrogen via denitrification processes. The riparian zone is also one of the most degraded and vulnerable ecosystems in the world. It has been reported that up to 90% of riparian ecosystems in Europe and North America have been degraded. Therefore, the natural regeneration approach (recovery without human intervention) and active revegetation approach (planting trees, shrubs, or herbs) have been put forward as methods for aiding the recovery of degraded riparian zones. The study was conceived because we were wondering how these two restoration approaches might impact denitrification processes, and we wanted to identify which restoration approach is better. In addition, riparian zones are subjected to hydrological change (i.e., changes in flooding density and frequency). Although some studies have reported on the impact of hydrological change on denitrification rates, few studies focus on riparian ecosystems, and the interactions between restoration approaches and hydrological change are not well known.

Riparian zone of the Three Gorge Reservoir, Chongqing, China (credit: Chen Ye)

We were excited to identify an ideal study site in the riparian zone of the Three Gorges Dam in central China. Due to the dam’s operation, vegetation diversity has been reduced by ~70%. In 2008, active revegetation was put forward to restore the riparian zone. These strategies included planting trees at high elevations (165–175 m), planting shrubs at middle elevations (155–165 m), and planting herbs at low elevations (145–155 m). In addition to this, flooding intensity varies among these three elevations, which provides an opportunity to investigate the impacts of flooding intensity on denitrification rates. In 2016, we also set up the hydrological change treatment to investigate the effects of flooding frequency. The water in the stream was pumped to the plots to simulate three different flooding frequencies, including continuous flooding (water level maintained at 5 cm above the soil surface), periodic flooding (6 days of submergence at 5 cm above the soil surface followed by a 6 days of well-drained condition), and no flooding (no water added to the plots).

This research should be of interest to a broad audience of ecologists—particularly for readers who are interested in the recovery of ecosystem functions. For policymakers, a take-home message is that active revegetation does not improve the efficiency of nitrogen removal in riparian zones.

About the research

Our research focuses on the varying impacts of restoration approaches and hydrological change (i.e., changes in flooding intensity and frequency) on denitrification rates in riparian zones. Active revegetation did not impact denitrification rates of the riparian zone. However, it is important to note that the active revegetation project in this study was only conducted for eight years. We speculate that this project might require a longer duration (more than a decade) to observe the different effects of restoration approaches on denitrification rates. This will be investigated in the future.

There were some challenges when setting up hydrological treatments to simulate different flooding frequencies. The flooding water was difficult to transfer from the nearby stream to the hydrological plots with a pump. Additionally, we needed to control the water level for hydrological plots and check the water level every day. Fortunately, the experiment went well.

About the author

Chen Ye standing in front of a river (credit: Wenjun Shi)

Dr. Chen Ye is a Professor of Ecology at Wuhan Botanical Garden, Chinese Academy of Sciences, China. After participating in the vegetation survey before and after the Three Gorges Dam operation, she became interested in ecosystem restoration and biogeochemical cycling. Her greatest inspiration was learning about effective ways to recover ecosystem functions, such as active revegetation. Her advice for other ecologists is to always be positive because she believes that solutions are always going to be more abundant than difficulties.

Enjoyed this blogpost? Read the research here.

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