Nutrient removal processes in saltmarsh and adjacent habitats: overview and a preliminary study of denitrification in the Solent, UK

Perring, Michael P. ORCID: https://orcid.org/0000-0001-8553-4893; Aberg, Dan; Harley, Joanna ORCID: https://orcid.org/0000-0003-3861-9127; Dunn, Christian; Garbutt, Angus ORCID: https://orcid.org/0000-0002-9145-9786. 2025 Nutrient removal processes in saltmarsh and adjacent habitats: overview and a preliminary study of denitrification in the Solent, UK. Department for Environment, Food and Rural Affairs, 46pp.

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Abstract/Summary

•Saltmarsh and adjacent coastal habitats (e.g. mudflat, seagrass) can provide functions valued by people i.e. ecosystem services. As part of the marine Natural Capital and Ecosystem Assessment (mNCEA) program, the UK Centre for Ecology and Hydrology (UKCEH) and Bangor University, on behalf of the Environment Agency, conducted a pilot study to assess denitrification in coastal habitats, which can contribute to water quality improvement. •Denitrification can be provided by saltmarsh and adjacent habitat. It is one process from a broader suite of nutrient removal processes (e.g. sediment burial, plant uptake) provided by coastal habitats that together constitute the ecosystem service of water quality improvement. Complete denitrification permanently removes nitrate from the water column/sediment, transforming this compound to the environmentally benign nitrogen gas. Saltmarsh ecosystems, due to their position within the intertidal zone, are considered to have potential to provide high denitrification rates. •Previous studies highlight how environmental conditions, such as temperature, substrate supply and oxygen status, lead to high variation in denitrification rates across space and over time. However, limited evidence on denitrification rates is available from intact inter-tidal coastal systems in the UK. •The pilot study, conducted within Chichester Harbour Site of Special Scientific Interest, and using two laboratory handling methods, confirmed high variation across space and season (autumn vs winter) in potential denitrification rates. This high variation and the necessarily limited sampling precluded statements of statistical significance or the robust estimation of effect size. A tidal core method, where intact cores are subjected to realistic tidal cycles, showed trends for higher denitrification rates in the autumn than winter in upper and pioneer/low marsh zones, and a consistent estimate in the mid-marsh. A slurry method indicated that denitrification rates generally declined with depth, irrespective of season or saltmarsh zone, except for samples in the pioneer/low marsh zone in winter. Seagrass and mudflat habitats, that could only be sampled in autumn due to logistical constraints, had generally low denitrification rates, irrespective of method. •This study confirmed the utility of a tidal core method for estimating denitrification rates to compare among and within inter-tidal habitats and provides a first benchmark for denitrification rates in intact saltmarsh and adjacent inter-tidal habitat in the UK. Given the variability, and the expectation that such variation would be amplified when different estuaries are considered, scaling up understanding to the national level requires further work. •Short-term priorities include comparing among marshes within and across estuaries in different locations and with variation in underlying sediment; intensive seasonal sampling; and deriving benchmarks for sites undergoing managed realignment as well as sites that constitute intact coastal habitat. Results from such studies will provide foundational data for model development (e.g. Combined Phytoplankton Macroalgae model of CEFAS) and assist economic valuation assessments. •Longer-term efforts will help determine the absolute and relative role of denitrification as one process within a broader suite of nutrient removal processes in these coastal habitats; how to scale to nationwide estimates in a cost-effective manner (e.g. through eDNA and/or remote sensing approaches); and, the extent to which nutrient removal exhibits synergies or trade-offs with initiatives to tackle biodiversity and climate emergencies. Such research will need to include quantifying the potential of inter-tidal habitats to capture and remove other critical nutrients, such as phosphorus, as well as nitrogen. •Ultimately, this and allied work within the Land Sea Interface project, and elsewhere, will help achieve the UK Government's commitment to "secure clean, healthy, productive and biologically diverse seas and oceans".

Item Type:	Publication - Report (Project Report)
UKCEH and CEH Sections/Science Areas:	Environmental Pressures and Responses (2025-) Surface Atmosphere Interactions and Effects (2025-)
Funders/Sponsors:	Environment Agency
Additional Information. Not used in RCUK Gateway to Research.:	Open Access report - full text available via Official URL link.
NORA Subject Terms:	Ecology and Environment
Date made live:	20 Jan 2025 08:45 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/538761

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