Tidal marshes maintain elevation relative to sea level through accumulation of mineral and organic matter, yet this dynamic accumulation feedback mechanism has not been modeled widely in the context of accelerated sea-level rise. Uncertainties exist about tidal marsh resiliency to accelerated sea-level rise, reduced sediment supply, reduced plant productivity under increased inundation, and limited upland habitat for marsh migration. We examined marsh resiliency under these uncertainties using the Marsh Equilibrium Model, a mechanistic, elevation-based soil cohort model, using a rich data set of plant productivity and physical properties from sites across the estuarine salinity gradient. Four tidal marshes were chosen along this gradient: two islands and two with adjacent uplands. Varying century sea-level rise (52, 100, 165, 180 cm) and suspended sediment concentrations (100%, 50%, and 25% of current concentrations), we simulated marsh accretion across vegetated elevations for 100 years, applying the results to high spatial resolution digital elevation models to quantify potential changes in marsh distributions. At low rates of sea-level rise and mid-high sediment concentrations, all marshes maintained vegetated elevations indicative of mid/high marsh habitat. With century sea-level rise at 100 and 165 cm, marshes shifted to low marsh elevations; mid/high marsh elevations were found only in former uplands. At the highest century sea-level rise and lowest sediment concentrations, the island marshes became dominated by mudflat elevations. Under the same sediment concentrations, low salinity brackish marshes containing highly productive vegetation had slower elevation loss compared to more saline sites with lower productivity. A similar trend was documented when comparing against a marsh accretion model that did not model vegetation feedbacks. Elevation predictions using the Marsh Equilibrium Model highlight the importance of including vegetation responses to sea-level rise. These results also emphasize the importance of adjacent uplands for long-term marsh survival and incorporating such areas in conservation planning efforts.

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Modeling Tidal Marsh Distribution with Sea-Level Rise: Evaluating the Role of Vegetation, Sediment, and Upland Habitat in Marsh Resiliency

In unmanned aerial vehicle (UAV) photogrammetric surveys, the cameracan be pre-calibrated or can be calibrated "on-the-job" using structure-from-motion anda self-calibrating bundle adjustment. This study investigates the impact on mapping accuracyof UAV photogrammetric survey blocks, the bundle adjustment and the 3D reconstructionprocess under a range of typical operating scenarios for centimetre-scale natural landformmapping (in this case, a coastal cliff). We demonstrate the sensitivity of the process tocalibration procedures and the need for careful accuracy assessment. For this investigation, vertical (nadir or near-nadir) and oblique photography were collected with 80%–90%overlap and with accurately-surveyed (σ ≤ 2 mm) and densely-distributed ground control.This allowed various scenarios to be tested and the impact on mapping accuracy to beassessed. This paper presents the results of that investigation and provides guidelines thatwill assist with operational decisions regarding camera calibration and ground control forUAV photogrammetry. The results indicate that the use of either a robust pre-calibration ora robust self-calibration results in accurate model creation from vertical-only photography,and additional oblique photography may improve the results. The results indicate thatif a dense array of high accuracy ground control points are deployed and the UAVphotography includes both vertical and oblique images, then either a pre-calibration or anon-the-job self-calibration will yield reliable models (pre-calibration RMSEXY = 7.1 mmand on-the-job self-calibration RMSEXY = 3.2 mm). When oblique photography was Remote Sens. 2015, 7 11934 excluded from the on-the-job self-calibration solution, the accuracy of the model deteriorated(by 3.3 mm horizontally and 4.7 mm vertically). When the accuracy of the ground controlwas then degraded to replicate typical operational practice (σ = 22 mm), the accuracyof the model further deteriorated (e.g., on-the-job self-calibration RMSEXY went from3.2–7.0 mm). Additionally, when the density of the ground control was reduced, the modelaccuracy also further deteriorated (e.g., on-the-job self-calibration RMSEXY went from7.0–7.3 mm). However, our results do indicate that loss of accuracy due to sparse groundcontrol can be mitigated by including oblique imagery.

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The Impact of the Calibration Method on the Accuracy of Point Clouds Derived Using Unmanned Aerial Vehicle Multi-View Stereopsis

Blue carbon ecosystems (BCEs), including mangrove forests, seagrass meadows and tidal marshes, store carbon and provide co-benefits such as coastal protection and fisheries enhancement. Blue carbon sequestration has therefore been suggested as a natural climate solution. In this Review, we examine the potential for BCEs to act as carbon sinks and the opportunities to protect or restore ecosystems for this function. Globally, BCEs are calculated to store >30,000 Tg C across ~185 million ha, with their conservation potentially avoiding emissions of 304 (141–466) Tg carbon dioxide equivalent (CO2e) per year. Potential BCE restoration has been estimated in the range of 0.2–3.2 million ha for tidal marshes, 8.3–25.4 million ha for seagrasses and 9–13 million ha for mangroves, which could draw down an additional 841 (621–1,064) Tg CO2e per year by 2030, collectively amounting to ~3% of global emissions (based on 2019 and 2020 global annual fossil fuel emissions). Mangrove protection and/or restoration could provide the greatest carbon-related benefits, but better understanding of other BCEs is needed. BCE destruction is unlikely to stop fully, and not all losses can be restored. However, engineering and planning for coastal protection offer opportunities for protection and restoration, especially through valuing co-benefits. BCE prioritization is potentially a cost-effective and scalable natural climate solution, but there are still barriers to overcome before blue carbon project adoption will become widespread. Mangroves, tidal marshes and seagrass meadows have historically been lost or degraded, threatening their ability to store carbon and provide ecosystem services. This Review details the global potential of blue carbon ecosystem protection and restoration in climate change mitigation, through carbon sequestration and co-benefit production.

Blue carbon as a natural climate solution

Australia’s tidal marshes have suffered significant losses but their recently recognised importance in CO2 sequestration is creating opportunities for their protection and restoration. We compiled all available data on soil organic carbon (OC) storage in Australia’s tidal marshes (323 cores). OC stocks in the surface 1 m averaged 165.41 (SE 6.96) Mg OC ha−1 (range 14–963 Mg OC ha−1). The mean OC accumulation rate was 0.55 ± 0.02 Mg OC ha−1 yr−1. Geomorphology was the most important predictor of OC stocks, with fluvial sites having twice the stock of OC as seaward sites. Australia’s 1.4 million hectares of tidal marshes contain an estimated 212 million tonnes of OC in the surface 1 m, with a potential CO2-equivalent value of $USD7.19 billion. Annual sequestration is 0.75 Tg OC yr−1, with a CO2-equivalent value of $USD28.02 million per annum. This study provides the most comprehensive estimates of tidal marsh blue carbon in Australia, and illustrates their importance in climate change mitigation and adaptation, acting as CO2 sinks and buffering the impacts of rising sea level. We outline potential further development of carbon offset schemes to restore the sequestration capacity and other ecosystem services provided by Australia tidal marshes.

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Carbon sequestration by Australian tidal marshes

It is increasingly common for scientists to engage in sharing science-related knowledge with diverse knowledge users—an activity called science communication. Given that many scientists now seek in...

/pdf/considerations-for-effective-science-communication-33f6zyjv8a.pdf

Considerations for effective science communication

Coastal saltmarshes are reputed to be one of the most vulnerable communities to global warming, with widespread evidence of retreat and movement of lower marsh vegetation into areas previously occupied by upper marsh vegetation in response to rising sea levels, and potential changes in community composition from changes in rainfall, temperature and wind. We undertook an investigation of decades scale change in the distributions of saltmarsh communities defined by dominant species, using historic vegetation maps, remote sensing imagery and extensive field data collection. Our study area in south-eastern Tasmania has suffered a marked increase in temperatures and wind speeds and a marked decrease in rainfall since 1975, with sea level rising at a rate of 0.8 mm per annum. We therefore tested the hypothesis that these changes would result in a shift in saltmarsh community composition towards more salt- and inundation-tolerant communities and salt scalds. Eighteen percent of the 1975 marsh was lost to direct human modification and a net 4% was lost to coastal retreat. One large marsh was cut off from the sea then burned, then reconnected with the sea. The vegetation change between 1975 and 2009 in other parts of the saltmarshes occurred in 21% of their 1975 area. Most of the community transitions were consistent with increasing aridity. Thus, our results indicate that global warming has already caused marked changes in community composition in saltmarsh in Tasmania.

Tasmanian coastal saltmarsh community transitions associated with climate change and relative sea level rise 1975–2009

Coastal saltmarshes of temperate Australia are in decline and have recently been listed as a threatened ecological community under Federal legislation. Further research is required to better understand both the extent and nature of their decline in order to plan their recovery. A case study is presented of the most extensive area of saltmarshes in Tasmania, on the north-west Circular Head coast. A mixture of aerial photographs and ground-truthing data were used to determine human impacts and saltmarsh loss between 1952 and 2006. There was an absolute loss of 219 ha since 1952, largely due to the effects of a 24.5 km network of levees. Of the 1 153 ha of saltmarshes that remained in 2006, a further 752 ha (65%) was associated with one or several of land-based human impacts. This left 401 ha (35%) of saltmarshes that had no recorded human impacts and a contiguous vegetative buffer zone of 50–100 m. These areas represent some of the least disturbed saltmarshes in Tasmania and warrant adequate conservation measures. Future planning for conservation and the use of land and marine resources should strive to promote both the extent and functional health of saltmarshes.

Human impacts and saltmarsh loss in the Circular Head coast, north-west Tasmania, 1952– 2006: implications for management.

Rising sea levels and changing wind climates are widely expected to be associated with receding coastlines, creating a planning need for coastal change prediction, especially for soft shores like those associated with saltmarsh. We ask whether it is possible use a simple cartographic wind-wave fetch method to estimate the spatial pattern of progradation and recession of soft shores in swell-sheltered situations in which there is little or no input of new sediment from terrestrial sources. For points on an extensive embayment shoreline of this type we mapped change over 54 years from aerial photographs, recorded current shoreline morphology and calculated a wave fetch index (WFI). Morphological indication of strong progradation was associated with low WFI, but there was no statistically significant effect of variation in WFI on the degree of shoreline retreat. Saltmarsh shorelines averaged 14 cm per annum retreat between 1952 and 2006, a rate that did not vary significantly between air photo periods. We conclude that our geographic information system approach utilising WFI is likely to be useful as a planning tool in identifying those parts of sediment-poor saltmarsh shores where erosion is most likely or least likely to occur, but not particularly useful for predicting finer-scale variation in rates of shoreline recession within the particular substrate types in our study area. In the context of relative sea-level rise and increasing wind speeds, such modelling can help identify coastlines which are likely to support saltmarshes into the future.

Is wind-wave fetch exposure related to soft shoreline change in swell-sheltered situations with low terrestrial sediment input?

Wetlands are extremely important ecosystems for biodiversity conservation and the wellbeing of humansThey contribute up to 40 percent of global annual renewable ecosystem services, yet cover less than three percent of the
globe Unfortunately, half of the world’s wetlands have been lost to human development and many lack sufficient conservation protection As a consequence, many policy initiatives have been initiated to foster the protection of
wetlands and wetland dependant species Several Multilateral Environmental Agreements (MEA) support global wetland conservation, the most well known being the intergovernmental Convention on Wetlands (Ramsar, Iran,
1971),commonly known as the Ramsar Convention

Implementation of the Ramsar Convention on Wetlands in Tasmania, Australia

This project is about the relationship of people, especially the local people, to the
natural environments of the extensive sheltered shores of the Circular Head region
including Duck Bay, Big Bay, Robbins Passage and Boullanger Bay.
This project is designed to focus on the benefits that flow to people from the
natural environments (or habitats) in the area and then broadly assess whether or
not they are vulnerable to sea level rise impacts.

V Prahalad

Papers

Tasmanian coastal saltmarsh community transitions associated with climate change and relative sea level rise 1975–2009

Human impacts and saltmarsh loss in the Circular Head coast, north-west Tasmania, 1952– 2006: implications for management.

Is wind-wave fetch exposure related to soft shoreline change in swell-sheltered situations with low terrestrial sediment input?

Implementation of the Ramsar Convention on Wetlands in Tasmania, Australia

Circular Head region coastal foreshore habitats: sea level rise vulnerability assessment. (Boullanger Bay - Robbins Passage - Big Bay - Duck Bay)