Leonie, Esther Thomsen and Marie Seraphim had a recent outing to Aberlady Bay LNR where they had arranged to meet local resident Frank Neate. Marie and Esther are both seagrass experts and part of the Restoration Forth project which aims to reintroduce oysters to the Firth of Forth and to augment and create new seagrass meadows. Frank has been researching nutrient input to the Bay from sewage treatment outfalls and we were curious to hear more about Frank’s research and to visit the seagrass beds to check on their condition.
Aberlady Bay is an outstanding Local Nature Reserve, the first LNR in the UK to be designated in 1952 with sand dunes, salt marsh, intertidal sand and mud flats and of course seagrass beds. It has multiple designations being part of the Firth of Forth SSSI, the Firth of Forth Special Protection Area and is a Ramsar site. All in all a pretty special place.
Here are some images of the saltmarsh and seagrass beds on the intertidal mud:
Dwarf seagrass Zostera noltii growing on intertidal mud.
Algal mats on the intertidal mud
Algal mats swamping the saltmarsh habitat
Algal mats carpeting the intertidal area by the Combined sewage outfall
The combined sewage outfall indicating iron oxide precipitation and noxious froth
There is clearly an abundance of nutrients in the system resulting in algal growth which is smothering sensitive and critically important habitats including seagrass meadows and saltmarsh. Locally there has been quite a debate about sewage being pumped into the bay from combined sewage outfalls (CSOs). The idea behind CSOs is that under conditions of heavy rainfall the storm water and waste that would normally go to Scottish Water treatment centres is released into the sea or rivers. This is to stop sewage backing up into homes. SEPA’s Regulatory Method on Sewer Overflows (https://www.sepa.org.uk/media/152727/wat_rm_07.pdf) states that: The frequency of CSO overspill events per year should not exceed 3 for registered Bathing beaches and 10 for shell-fishing waters. ‘Shell fishing waters’ refers to the razor clam fishery west of Gullane Sands and Gullane Bay. Data obtained by Frank and the local community via Freedom Of Information requests indicate that since 2019, there have been over 1200 overspills from the Gullane Waste Water Treatment Works CSO outfall which is out of sight beyond the Bay’s Mean Low Water Spring level.
Seagrass meadows are critically important habitats improving water quality, capturing Carbon, reducing wave energy, enhancing biodiversity with meadows found to support 30 times as much biodiversity as bare mud and sand and providing nursery habitat for 9 commercially important species of fish. It is clearly vital that existing seagrass meadows are being well cared for while we try to expand this habitat around the Firth of Forth. Are seagrass meadows and saltmarsh habitats being impacted by sewage outfalls at Aberlady Bay? One way to establish where all these excess nutrients are coming from is to sample the seagrass, measure the Nitrogen content and identify the source of the Nitrogen as it is possible to distinguish between run-off from artificial fertiliser, sewage or enrichment from birds with thousands of geese and other birds visiting as passage migrants or overwintering. Project Seagrass for whom Esther works have a research programme to analyse seagrass leaves for carbon, nitrogen and phosphorus, the amounts of which show whether coastal environments are polluted with nutrients. Previous research has revealed that sewage and agricultural waste are responsible for nutrient pollution that harms seagrass. We are waiting for funding confirmation to progress this and will report back as soon as results are available.
LEONIE ALEXANDER
EDINBURGH SHORELINE PROJECT
June 2023