Why aquatic vegetation matters – and how evidence can help us conserve it
This blog post was written by Dr Nigel Taylor, a Research Associate at Conservation Evidence and lead author of the synopsis on Vegetation Conservation in Inland Aquatic Habitats
Inland aquatic habitats such as rivers, streams, lakes, ponds, reservoirs and canals occupy a tiny proportion of the Earth’s terrestrial surface – lakes are estimated to cover <4% [1] and rivers <1% [2]. But they support a disproportionate number of species and provide vital functions and services for both aquatic and terrestrial species, including humans [3][4].
Vegetation is arguably the unsung hero of inland aquatic ecosystems. Macrophytes, for example, stabilize sediments and improve water quality [5][6]. Aquatic vegetation also supports wider biodiversity as food and habitat for invertebrates, fish, birds and mammals. However, inland aquatic habitats – and the vegetation they contain – are under growing pressure from threats like pollution, invasive species, hydrological alteration and climate change [3][7].
In the face of such challenges, conservation action is urgently needed for inland aquatic habitats and their vegetation [3][8]. But which interventions really work? And how can practitioners be confident that their limited time and funding are being invested in the most effective strategies?
A new Conservation Evidence synopsis
This is where the latest Conservation Evidence synopsis comes in, focused on the conservation of vegetation in inland aquatic habitats. Drawing on hundreds of scientific studies from around the world, this comprehensive resource synthesises the best available evidence on what works — and what doesn’t — when managing, restoring and conserving aquatic vegetation.
The Aquatic Vegetation synopsis focuses on studies that test the effects of conservation actions, typically with some comparison in time or space, on desirable aquatic vegetation. It focuses on the conservation of vegetation overall, collating evidence on metrics such as community composition, diversity, abundance and structure. We interpret vegetation broadly, including macrophytes (large vegetation visible with the naked eye), phytoplankton (small algae floating in the water), and ‘periphyton’ (algae growing on the surface of rocks or plants). It includes evidence from all types of inland aquatic habitats – often called “freshwater” habitats, but they include salt lakes and other salty water bodies.
Importantly, this synopsis doesn’t include studies focused on individual species (e.g. rare or threatened species) or studies focused on the effectiveness of actions for managing problematic species (where only effects on the problematic species are reported; studies are included if they report the effects of controlling problematic species on desirable aquatic vegetation). These are, or will be, covered in other Conservation Evidence synopses.
>370 publications testing >200 actions
The new Aquatic Vegetation synopsis offers one of the most comprehensive syntheses ever assembled for this habitat type. It reviews the evidence for 204 different actions (two are further split into flowing and still waters) that could be done to conserve vegetation in inland aquatic habitats, organized around the threat they primarily address. This is intended to be a ‘longlist’, laying out possible options for any decision making process: the longlist should be narrowed down based on the supporting evidence, alongside considerations of cost, practicality, acceptability etc.
We identified studies testing these actions by systematic searches of over 1 million journal articles (in 18 different languages), and thousands of reports and other ‘grey literature’ on conservation organizations’ websites. Some studies were also identified by our international advisory board. In total, we summarized 538 distinct tests of actions from 374 publications.
The synopsis includes some well-studied actions, such as adding lime to restore acidified water bodies, and using herbicide to control problematic macrophytes. Both of these actions generally had desirable effects on vegetation (e.g. increasing diversity, shifting communities towards those characteristic of less disturbed conditions) but also caused harm in some circumstances. For example, liming was sometimes followed by massive dominance of bulbous rush Juncus bulbosus. Herbicide applications were often followed by a short-term decline in abundance or richness of native species – and sometimes long-term declines if high doses were used. In the future, we will publish expert assessments of the evidence that will categorize the overall effectiveness of each action. Interestingly, there was particularly strong geographic bias in tests of these actions: 38 of 39 studies testing herbicide use were in the USA, and 9 of 18 liming studies were in Scandinavia.
Some surprising actions, perhaps, include the use of artificial lights to stimulate growth of aquatic vegetation (potentially useful under structures such as bridges or culverts), deterring birds to reduce inputs of guano (which can otherwise lead to nutrient enrichment and algal blooms), promoting growth of bacteria that can control phytoplankton, and even adding fertilizer or other nutrient-rich materials (for example to compensate for reduced nutrient inputs to headwaters when dams restrict upstream migration).
We found no evidence for many of these actions, and a total of 90 actions in the synopsis. Future research effort could focus on these topics. Geographically, most evidence came from North America and Europe: further tests of actions in Africa, South America and Asia (outside of China and Japan) would ensure conservation decisions in those regions are based on evidence relevant to the local context.
From research to real-world impact
By providing an accessible and centralized synthesis of existing evidence, we hope the synopsis empowers users to make informed choices. Users will include anyone making decisions about conservation or management, from conservation practitioners and land managers, to NGOs, community conservation groups, and policy-makers. We do not prescribe solutions, and encourage use of local knowledge and experience alongside the synthesized evidence to develop effective and efficient management plans [9]. The synopsis is also a good starting point for researchers, students and funders to identify knowledge gaps and clusters, ensuring new research builds on the existing evidence.
By using the Aquatic Vegetation synopsis, practitioners can maximise the effectiveness of their interventions, reduce unintended harm, and contribute to healthier inland aquatic ecosystems worldwide. In a time of accelerating environmental change, evidence-based conservation has never been more important. The Aquatic Vegetation synopsis is a key tool to help the conservation community rise to the challenge.
We acknowledge funding from the MAVA Foundation and the Natural Environment Research Council (NERC) Changing the Environment Programme through their support for the Centre for Landscape Regeneration.
References
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[2] Allen G.H. & Pavelsky T.M. (2018) Global extent of rivers and streams. Science, 361, 585–588. https://doi.org/10.1126/science.aat0636
[3] Strayer D.L. & Dudgeon D. (2010) Freshwater biodiversity conservation: recent progress and future challenges. Journal of the North American Benthological Society, 29, 344–358. https://doi.org/10.1899/08-171.1
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[5] Thomaz S.M. (2021) Ecosystem services provided by freshwater macrophytes. Hydrobiologia, 1–21. https://doi.org/10.1007/s10750-021-04739-y
[6] Scheffer M., Hosper S.H., Meijer M.-L., Moss B. & Jeppesen E. (1993) Alternative equilibria in shallow lakes. Trends in Ecology & Evolution, 8, 275–279. https://doi.org/10.1016/0169-5347(93)90254-M
[7] Reid A.J. et al. (2019) Emerging threats and persistent conservation challenges for freshwater biodiversity. Biological Reviews of the Cambridge Philosophical Society, 94, 849–873. https://doi.org/10.1111/brv.12480
[8] Tickner D. et al. (2020) Bending the curve of global freshwater biodiversity loss: an Emergency Recovery Plan. BioScience, 70, 330–342. https://doi.org/10.1093/biosci/biaa002
[9] Sutherland W.J. et al. (2019) Building a tool to overcome barriers in research-implementation spaces: the Conservation Evidence database. Biological Conservation, 238, 108199. https://doi.org/10.1016/j.biocon.2019.108199
