Morphological evolution of creek networks in 10 restored coastal wetlands in the UK

Coastal wetlands provide crucial ecosystem services including flood protection and carbon storage, but are being lost rapidly worldwide to the combined effects of sea-level rise, erosion and coastal urbanisation. Managed Realignment (MR) aims to mitigate for these losses by restoring reclaimed land to tidal influence. Data of creek evolution is critical to assess the performance of design strategies and improve design and implementation practices. This data descriptor provides a dataset of the horizontal morphological evolution of creek systems from various initial conditions in 10 MR schemes across the UK. Using a semi-automated workflow, morphological creek parameters were extracted from 52 lidar datasets at 1 m horizontal resolution spanning 2 to 20 years post-breach. This constitutes the most comprehensive systematic monitoring of MR creek morphology to date. The dataset will assist future MR design and provide baseline morphological information for ecological and biogeochemical surveying

Rapid carbon accumulation at a saltmarsh restored by managed realignment exceeded carbon emitted in direct site construction

Increasing attention is being paid to the carbon sequestration and storage services provided by coastal blue carbon ecosystems such as saltmarshes. Sites restored by managed realignment, where existing sea walls are breached to reinstate tidal inundation to the land behind, have considerable potential to accumulate carbon through deposition of sediment brought in by the tide and burial of vegetation in the site. While this potential has been recognised, it is not yet a common motivating factor for saltmarsh restoration, partly due to uncertainties about the rate of carbon accumulation and how this balances against the greenhouse gases emitted during site construction. We use a combination of field measurements over four years and remote sensing to quantify carbon accumulation at a large managed realignment site, Steart Marshes, UK. Sediment accumulated rapidly at Steart Marshes (mean of 75 mm yr-1) and had a high carbon content (4.4% total carbon, 2.2% total organic carbon), resulting in carbon accumulation of 36.6 t ha-1 yr-1 total carbon (19.4 t ha-1 yr-1 total organic carbon). This rate of carbon accumulation is an order of magnitude higher than reported in many other restored saltmarshes, and is somewhat higher than values previously reported from another hypertidal system (Bay of Fundy, Canada). The estimated carbon emissions associated with the construction of the site were ~2–4% of the observed carbon accumulation during the study period, supporting the view that managed realignment projects in such settings may have significant carbon accumulation benefits. However, uncertainties such as the origin of carbon (allochthonous or autochthonous) and changes in gas fluxes need to be resolved to move towards a full carbon budget for saltmarsh restoration

Creek networks : natural evolution and design choices for intertidal habitat recreation

With the current rise in sea level jeopardising coastal biodiversity and the efficiency of traditional flood defence solutions, more sustainable coastal management options are being considered. The use of artificially restored intertidal habitats (mudflats and saltmarshes) as buffer zones for tidal and wave energy has been tested at numerous sites in the UK and around the world. Since the 1970s, the design of these habitats has significantly evolved along with our understanding of the natural processes involved. This paper reviews the state of the art in intertidal habitat recreation, focusing mainly on creek networks, for which no global systematic design method exists. The main parameters that control their initiation and development are investigated through the observation of natural creek networks and through the reproduction of this development in laboratory and numerical models. In areas like San Francisco Bay, such parameters have already been used in geometric relationships to provide guidelines for creek network implementation, but these empirical relationships are likely to be very site dependent. A series of steps is proposed to extend this implementation technique to other sites, thus making the design strategy more systematic and globally applicable. The sustainability of existing habitat recreation schemes remains a debated point, making the need for quantitatively defined objectives and better implementation guidelines all the more pressing.15 page(s

Parameterizing tidal creek morphology in mature saltmarshes using semi-automated extraction from lidar

Coastal saltmarshes provide a range of ecosystem services, such as flood protection and carbon sequestration, but face rapid global losses. Managed realignment (MR) is an increasingly popular method to artificially recreate these habitats by reinstating tidal regimes to reclaimed land. However, to improve MR design, better knowledge of the processes that control morphological evolution in natural saltmarshes is needed. In this paper, we develop tools to assist in the monitoring of creek network evolution towards dynamic morphological equilibrium, a state of landform stability under current physical forcings. Using lidar (Light Detection and Ranging) datasets, we combined a semi-automated creek extraction algorithm, based on elevation and slope thresholds, with a novel algorithm for morphometric creek analysis. A comprehensive suite of morphological creek characteristics was extracted for 13 natural British saltmarshes, including: amplitude, length, sinuosity ratio, junction angle, width, depth, cross-sectional area, creek order, bifurcation ratio, drainage density, and drainage efficiency. Results closely matched with field-validated manual digitization results, and were significantly faster and less subjective to produce. Morphological equilibrium relationships from the literature were found to be applicable to the new dataset, despite yielding high prediction errors due to the inherent variety of creek network shapes in saltmarshes. New equilibrium relationships were also defined relating the creek network drainage efficiency to the mouth cross-sectional area and the marsh elevation. To improve future scheme designs, these tools will be used in further studies to monitor rates of evolution towards equilibrium in MR sites depending on their initial conditions

Dataset: Morphological evolution of creek networks in 10 restored coastal wetlands in the UK

This dataset supports the publication: Chirol, C. et al (2022). Morphological evolution of creek networks in 10 restored coastal wetlands in the UK in Scientific Data.</span

Created coastal wetlands as carbon stores: potential challenges and opportunities

Intertidal habitats are widely created with the aim of benefiting biodiversity. The pressing need to mitigate greenhouse gas emissions and the increasing recognition that coastal wetlands can provide secondary benefits by storing carbon may provide additional incentives for their creation. However, there are a number of uncertainties in the carbon budget of these wetlands, including the magnitude of carbon accumulation and the relative scale of this compared with the carbon costs of site construction. Here, we explore the carbon accumulation potential of hypothetical intertidal wetland sites of different sizes and shapes created by managed realignment and made with construction material sourced from different locations. We combine different combinations of values of sedimentation and carbon content reported from created intertidal wetlands in the literature. We find that there is large variability in potential carbon accumulation rates, with sedimentation rates being the dominant control on carbon accumulation. When carbon accumulation rates are high, all hypothetical site designs paid off the carbon cost of embankment construction within a year, but when carbon accumulation rates were low and material for embankments was transported from off site, debts took about ten years to pay. Our analysis provides a broad indication of the balance between carbon accumulation and construction carbon costs in created intertidal wetlands, but further work is needed to develop a more complete carbon budget. We highlight five key research challenges that need to be addressed to better understand the potential for created intertidal wetlands to accumulate carbon

Saltmarsh Restoration Methods

This section describes the main factors controlling the development of vegetation on restored saltmarshes, and the management actions that may influence this. In addition to the predominantly abiotic (non-living) factors described below, secondary factors such as grazing or local species pool may influence vegetation. Assessments should therefore be site-specific using local reference conditions