Does mechanically removing algal mats offer a suitable remediation method to improve coastal water quality and reduce nutrient pollution?

This was the topic Zoe Morrall – presented at the recent British Phycological Society (BPS) conference, during the session on “Phycology in a Changing World and Citizen Science”

Attendees were reminded of the global current situations where; increases in nutrients from agricultural runoff, sewage discharge and industry lead to widespread eutrophication, often resulting in extensive algal mat coverage in the coastal zone. These mats decrease light availability, increase siltation, accumulate organic matter and increase anoxic conditions impacting key coastal habitats (e.g. seagrass and saltmarsh) and species (wading birds, fish and shellfish).

Some of these coastal areas are designated as an SPA and SAC under the EU Birds and Habitats Directives as the area supports a number of important habitats and waterbird populations.

Although reducing the nutrient inputs is paramount, many studies have suggested direct mat removal as a cost effective and immediate solution to begin to achieve nutrient reduction. However, no studies have assessed the efficacy and impact of removing algal mats from intertidal mudflats. In summer of 2022 at four sites in the Channel region (2 UK and 2 French), our teams at RaNTrans assessed the success and ecological effects of removing approximately 400 m2 of algal mat using a floating boat platform.

Data on removal efficiency is being gathered at the times of removal. Subsequent repeated sampling of the sites over 6 months is being monitored to better understand both short and longer-term effects including: algal mat recovery, sediment changes, benthic community and wading bird behaviour (e.g. feeding).

Removal amounts will then be scaled at the regional level to calculate the potential bioremediation of mechanical removal for nitrogen and phosphorous, and also compared to other approaches (e.g. habitat restoration).
This novel scientific assessment at relevant temporal and spatial scales will enable European policymakers to make evidence-based decisions to achieve nutrient neutrality and Good Environmental Status, as well as assess the impact of physical removal as a way to combat smothering of key habitats such as saltmarsh and seagrass.

There is a growing interest in the uses of macroalgal seaweeds, and the production of inks might be an viable option to explore, as presented by Karen MacKechnie (from SAMs, CCAP) – “Algal inks, the future sustainable alternative for labelling”.

Stay tune for more updates…

Our work continues in 2023!

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