Wetlands as a Local Scale Management Tool to Reduce Algal Growth Potential

Abstract

Recent land-use changes have led to a significant loss of natural wetlands worldwide resulting in increased amounts of organic and inorganic compounds reaching lakes and coastal areas. In turn, this has led to an increased algal growth, and subsequently the risk of algal blooms and deteriorated water quality. The capacity of wetlands to retain nutrients is well-known, suggesting that constructed wetlands may be a potential management strategy to mitigate algal blooms in downstream waters, although little is known about seasonal variation in reduction of algal growth potential. Therefore, in a long-term study, we experimentally evaluated the efficiency of seven wetlands to reduce the algal growth potential by comparing the growth in cultures containing 50:50 wetland water from the inlet or outlet and water from a eutrophic lake as a standard inoculum. We show that the majority of the wetlands have a considerable potential to reduce algal growth potential, with up to 89% for cyanobacteria and 73% for green algae. However, there were strong temporal variations in efficiency within, as well as between wetlands. Specifically, we show that the potential to reduce algal growth (standardized conditions) was generally higher in winter than in summer. In addition, the wetlands showed different efficiency in reducing the growth potential of cyanobacteria and green algae. Taken together, our results show that wetlands have a considerable potential to reduce algal growth potential, suggesting that they are an efficient local-scale tool in reducing the risk of algal blooms especially from a future climate change perspective.