Do realignment sites restore microbial biodiversity-driven nutrient cycling and trace gas fluxes comparable to natural coastal ecosystems?

Realigned salt marshes (restored salt marshes on previously developed land) play a substantial and growing role in coastal management practices within the UK. These managed ecosystems have different above- and below-ground biodiversity and community structures, relative to their natural salt marsh counterparts, which leads to differences in ecosystem processes.

Saltmarshes play a large role in global climate, nutrient cycling and regional biodiversity, especially given their relatively small area (<0.1%of the planet's surface). They are purported to be significant carbon sinks, although upper marshes can be substantial sources of methane (CH4) and nitrous oxide (N2O). Saltmarshes may therefore have multiple, potentially conflicting, effects upon global warming through greenhouse gas fluxes. Saltmarsh communities also affect climate by producing significant amounts of halogenated, nitrogen- and sulphur-bearing compounds, which affect ozone in the lower atmosphere and the stratosphere as well as acting as aerosol precursors. The biological and abiotic drivers of these climate-influencing processes within natural saltmarshes remain poorly understood and/or quantified. This lack of knowledge reduces our capacity to effectively model future climate, nor can we accurately assess the implications of various feedback mechanisms (e.g. global warming on saltmarsh carbon storage potential) upon these processes.

All of the questions that arise regarding ecosystem services, biodiversity and connectivity in natural systems remain for modified-by-human systems and, at this time, are generally less quantified and more poorly understood. Our prior research has found plant and microbial community compositional differences between natural and realigned sites. A generally accepted, compelling explanation for these differences does not exist although recent evidence suggests that it is likely to be driven by physical and chemical differences in local sediments, which are in turn driven by physical processes. These changes in biodiversity are likely to lead to functional changes between natural and realigned sites; for instance below-ground biodiversity appears to be affected by nutrient (over)supply within inundation waters as well as aboveground plant community and root structure. Conversely, below-ground communities can directly and indirectly affect aboveground biodiversity by their effect on carbon storage, nutrient cycling rates, and their release of a number of climate affecting trace gases (CH4, N2O, halocarbons and sulfur-bearing compounds).

Quantifying ecosystem services for future climate projections will therefore be maximally effective only when combined with an understanding of the drivers of biodiversity, community composition, and succession in natural versus realigned saltmarshes. We therefore propose to quantify trace gas fluxes from a chronology of realigned saltmarshes, with comparisons to local, natural counterparts. Our connection to currently established BESS saltmarsh study sites means that we do not duplicate research priorities unnecessarily yet we expand the intent of the original proposal into an important sub-category of coastal communities that are, as of yet, poorly quantified or understood.

Our proposed research will identify connections between aboveground and below-ground biodiversity in restored saltmarshes and will correlate composition and activity within these communities to climate-impacting, biogenic trace gas fluxes and nutrient cycling. The proposal will quantify trace gas fluxes from a chronology of realigned saltmarshes, with comparisons to local, natural counterparts. The measured trace gas fluxes will be compared to and correlated with biodiversity (both microbial and aboveground) through meta-genomic and quadrat analyses. Comparisons of trace gas fluxes and biodiversity measures will be correlated with soil ecosystem function, as characterized through analysis of the sediment transcriptome. All of these ecosystem processes will be analysed in context of sediment physico-chemical properties. This combination of approaches will provide a unique resource through which various research, management and policy communities interested in salt marsh restoration and management, trace gas fluxes, ecosystem services and climate change will benefit.

We will engage with local and national UK management bodies, such as the Environment Agency, Associated British Ports, English Nature and regional counties throughout the research programme. These organizations are involved in the management decisions for all our UK study sites, and therefore have a vested interest in the observed outcomes. We will ensure rapid and thorough debriefings at the close of each sampling campaign, with an extended face-to-face meeting involving all stakeholders at the end of the grant. This meeting will reflect upon research conclusions and present the results from a meta-analysis of trace gas fluxes from natural and realigned saltmarshes. This workshop will, with input from the stakeholder community, develop and refine a white paper which will identify important research questions that engage with microbial biodiversity and trace gas fluxes in restored ecosystems for the next 5-10 years.

We intend to develop a summer training program for secondary school students which will incorporate human modifications of landscapes on microbial biodiversity and trace gas fluxes within the larger context of environmental complexity and climate change feedbacks. This outreach course will be offered at the University of York primarily, but will be constructed in such a way that it will be "portable" to any interested location. Training will be provided to secondary school teachers who wish to engage with this subject matter.