Valuing the Solent Marine Sites Habitats and Species: A Natural Capital Study of Benthic Ecosystem Services and how they Contribute to Water Quality Regulation: Environment Agency R&D Technical Report ENV6003066R

Excessive nutrient inputs (principally nitrogen [N] and phosphorous [P]) in the Solent Marine Sites (SEMS) are causing eutrophication, leading to a decline in water quality and an increase in the growth of green macroalgae on intertidal mudflats. These impacts can have adverse effects on the ecology and species within the UK nature conservation designation sites (e.g. overwintering birds) in and around the Solent, to which the Habitat Regulations apply. The impact on the condition of the sites is relevant in the context of meeting: legislative requirements (e.g. Water Framework Directive); protecting these habitats (e.g. Special Areas of Conservation, Special Protection Areas, Marine Conservation Zones); improving public health (e.g. reducing shellfish and bathing water contamination), but also for a viable and productive marine economy (e.g. sustainable aquaculture & fisheries and tourism). As such the University of Portsmouth in March 2019 was commissioned by the Environment Agency (EA) to provide this strategic update of the natural capital value of habitats and species in the context of water quality for the Solent and Isle of Wight area. The overall aim of this study is to provide evidence to help value the changes in the level of ecosystem service that could result from changes in the quality of benthic habitats as a result of increasing or reducing nutrients such as N and P. This critical evidence base will enable the EA and other decision-makers (at both a national government and local authority level) to ensure natural resources are given the appropriate level of protection, whilst supporting sustainable economic growth. Together they will support the delivery of the UK government’s 25-year plan for the environment, especially objectives set in Chapter 5: “Securing clean, healthy productive and biologically diverse seas and oceans”. The project was divided into three phases which are summarised below. Part A Mapping natural capital stocks and estimating their capacity to remove nutrients Following Office for National Statistics (ONS) guidance we assessed the extent of the SEMS marine natural capital stocks (habitats) defined using the European Nature Information System (EUNIS) habitat classification system. Baseline habitat assessments (in ha) have been made for: littoral sediments (including with green algal mats), coastal saltmarsh, seagrass beds, reedbed (Phragmites australis) and subtidal sediments from the Solent (Lymington Harbour to Pagham Harbour) and several inshore areas around the Isle of Wight (Yar estuary to Bembridge harbour). Due to the growing recognition of the ecosystem services provided by suspension-feeding bivalves (such as oysters) commercial Native Oyster (Ostrea edulis), shellfish beds in the SEMS were also mapped. The habitat map created for the SEMS represents the ‘best available evidence’ at the time of writing this report in September 2020. Using literature data from other temperate coastal systems we then assessed the N and P removal potential (via burial of N and P in underlying sediments and loss of N to the atmosphere [denitrification]) for each of the aforementioned habitats and species to determine annual ecosystem service flows. As N and P are also accumulated into biogenic material (e.g. the shell of bivalves), we have also incorporated this in to our calculations for native oyster beds. Results indicate that existing habitats in the SEMS could remove 3,590 tonnes of N yr−1 and 811 tonnes of P yr−1 based on each habitat’s current Water Framework Directive (WFD) condition status. To represent how the local condition of habitats may influence ecosystem service flows, we used the 2016 WFD (cycle 2) waterbody summary condition assessments, together with their qualifying sub-feature assessments, for each of the habitats in each region of the SEMS. The level of baseline ecosystem service and that 4 would be expected if all biotopes were adjusted based on their regional WFD condition classification data is presented in the ExSummary table 1 below.