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Abstract Interior marsh pond formation has been commonly observed in tidal marshes affected by high rates of relative sea level rise (RSLR). However, it is difficult to conclude whether an accretion deficit (accretion which does not keep pace with RSLR) or natural ice and wrack disturbance has driven pond formation. We propose that marsh deterioration caused by accretion deficit can be differentiated from that caused by other disturbances based upon temporal vegetation changes and the spatial configuration of vegetation zones relative to tidal creeks and the marsh platform. We tested this hypothesis in six newly ponded sites within RSLR‐affected marshes in Deal Island, Chesapeake Bay. At each site, we used field surveys and remote sensing to study spatiotemporal dynamics of marsh vegetation, marsh topography, and tidal creek incision. We found flood tolerant plants displaced flood intolerant species over time in the landward direction, or upslope, of ponds. A reverse species transition was observed seaward of ponds because tidal creek incision alleviated interior marsh inundation. The landscape‐scale biogeographic pattern we have recognized sheds light on how plants adapt to chronically reshaped geomorphological configurations of the marsh platform, which differentiates ponding caused by accretion deficit from ponding caused by natural and artificial disturbances. Furthermore, our results point to vegetation patterns that can be used as early warning signals of interior marsh loss to ponding. As ponding has been a major driver of tidal marsh habitat loss in microtidal marshes around the world, early indicators of decline are sorely needed to direct conservation activities.
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The dynamics of marsh-channel slump blocks: an observational study using repeated drone imagery
Abstract. Slump blocks are widely distributed features along marsh shorelines that can disturb marsh edge habitats and affect marsh geomorphology and sediment dynamics. However, little is known about their spatial distribution patterns or their longevity and movement. We employed an unoccupied aerial vehicle (UAV) to track slump blocks in 11 monthly images (March 2020–March 2021) of Dean Creek, a tidal creek surrounded by salt marsh located on Sapelo Island (GA, USA). Slump blocks were observed along both convex and concave banks of the creek in all images, with sizes between 0.03 and 72.51 m2. Although the majority of blocks were categorized as persistent, there were also new blocks in each image. Most blocks were lost through submergence, and both decreased in area and moved towards the center of the channel over time. However, some blocks reconnected to the marsh platform, which has not been previously observed. These blocks were initially larger and located closer to the marsh edge than those that submerged, and they increased in area over time. Only 13 out of a cohort of 61 newly created blocks observed in May 2020 remained after 5 months, suggesting that most blocks persist for only a short time. When taken together, the total area of new slump blocks was 886 m2, and that of reconnected blocks was 652 m2. This resulted in a net expansion of the channel by 234 m2 over the study period, accounting for about 66 % of the overall increase in the channel area of Dean Creek, and this suggests that slump block processes play an important role in tidal creek channel widening. This study illustrates the power of repeated UAV surveys to monitor short-term geomorphological processes, such as slump block formation and loss, to provide new insights into marsh eco-geomorphological processes.
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- Award ID(s):
- 1832178
- PAR ID:
- 10561116
- Publisher / Repository:
- Biogeosciences
- Date Published:
- Journal Name:
- Biogeosciences
- Volume:
- 21
- Issue:
- 7
- ISSN:
- 1726-4189
- Page Range / eLocation ID:
- 1757 to 1772
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Consumer-mediated movement can couple food webs in distinct habitats and facilitate energy flow between them. In New England saltmarshes, mummichogs (Fundulus heteroclitus) connect the vegetated marsh and creek food webs by opportunistically foraging on the invertebrate communities of the marsh surface when access is permitted by tidal flooding and marsh-edge geomorphology. Via their movements, mummichog represent a critical food web node, as they can potentially transport energy from the marsh surface food web to creek food web and exert top-down control on the communities of the vegetated marsh surface. Here, I use gut content analysis, calorimetric analysis, and field surveys to demonstrate that access to the marsh surface (afforded by marsh-edge geomorphology) impacts the trophic relay of marsh production to creek food webs. Fish populations in creeks with greater connectivity had a higher total biomass of terrestrial invertebrates in their guts. However, bomb calorimetry showed no difference in the average caloric content of mummichog individuals from creeks with different creek edge geomorphology. Access also did not impact mummichog distribution across the marsh platform and exhibited no evidence of top-down control on their invertebrate prey. Thus, mummichogs function as initial nodes in the trophic relay, unidirectionally moving energy from the vegetated marsh to the creek food web. Reduced marsh surface access via altered marsh-edge geomorphology results in a 50 % to 66 % reduction in total energy available to aquatic predators via this route. Estuarine systems are intimately connected to coastal and offshore systems via consumer mediated flows of energy; thus, disruptions to the trophic relay from the marsh surface at the tidal creek scale can have far reaching impacts on secondary productivity in multiple disparate systems and must be accounted for in considerations of impacts to future food-web function.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/bg-21-1757-2024
