Abstract
Invasions of water bodies by floating vegetation, including water hyacinth (Eichhornia crassipes), are a huge global problem for fisheries, hydropower generation, and transportation. We analyzed floating plant coverage on 20 reservoirs across the world’s tropics and subtropics, using > 30 year time-series of LANDSAT remote-sensing imagery. Despite decades of costly weed control, floating invasion severity is increasing. Floating plant coverage correlates with expanding urban land cover in catchments, implicating urban nutrient sources as plausible drivers. Floating vegetation invasions have undeniable societal costs, but also provide benefits. Water hyacinths efficiently absorb nutrients from eutrophic waters, mitigating nutrient pollution problems. When washed up on shores, plants may become compost, increasing soil fertility. The biomass is increasingly used as a renewable biofuel. We propose a more nuanced perspective on these invasions moving away from futile eradication attempts towards an ecosystem management strategy that minimizes negative impacts while integrating potential social and environmental benefits.
Highlights
More than 50 years ago, Science published a landmark article, ‘‘Aquatic Weeds’’ (Holm et al 1969)
The Spanish government spent 20.9 million US$ over 4 years to use heavy machinery to physically remove floating vegetation along a 75 km stretch of the Guadiana river (EPPO 2009); two million US$ were spent on personnel costs to run a 3-year project on biological control of water hyacinths in Benin (De Groote et al 2003); and a single herbicide spraying campaign on Hartebeespoort dam in South Africa cost an equivalent of 200’000 US$ (Van Wyk and Van Wilgen 2002)
Our remote sensing analysis of plant coverage on 20 reservoirs indicates that floating vegetation invasions are getting worse (Fig. 2)
Summary
More than 50 years ago, Science published a landmark article, ‘‘Aquatic Weeds’’ (Holm et al 1969). The authors further suggested that such invasions are ‘‘the symptoms of our failure to manage our resources.’’ They argued that the management remedy to this global crisis is the stepping up of biological quarantines and physical, chemical and/or biological control interventions. Since Holm et al (1969) sounded the alarm, research on aquatic weed invasions has accelerated, while very substantial resources have been allocated to control measures (Villamagna and Murphy 2010; Hussner et al 2017). Local examples of successful control exist (Wainger et al 2018), aquatic weed invasions continue to persist in tropical and subtropical river systems to this day, and are even expanding to higher latitudes with warming climates (Kriticos and Brunel 2016)
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