Thin-layer sediment addition to an existing salt marsh to combat sea-level rise and improve endangered species habitat in California, USA

Thorne, Karen M.; Freeman, Chase M.; Rosencranz, Jordan A.; Ganju, Neil K.; Guntenspergen, Glenn R.

doi:10.1016/j.ecoleng.2019.05.011

Cited by 24 publications

(17 citation statements)

References 38 publications

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“…Urbanized estuaries with marshes around the world are at risk of submergence from SLR due to sediment starvation, human development, and the interaction of these complex processes [ 27 , 72 ]. Without management actions, many of these marshes may be converted to mudflat and subtidal habitats as SLR rates outpace accretion (e.g.…”

Section: Discussionmentioning

confidence: 99%

“…Without management actions, many of these marshes may be converted to mudflat and subtidal habitats as SLR rates outpace accretion (e.g. [ 27 ]). This study provided a unique, large-scale opportunity to explore the short-term impacts of sediment addition on important ecosystem features and processes.…”

Section: Discussionmentioning

confidence: 99%

“…Dredging was contracted by Orange County Public Works and was dredged from an adjacent subtidal area near SBNWR in Anaheim Bay ( Fig 1 ). The project goals were to spread a fairly uniform thin layer of sediment and maintain a minimum 7.62 cm increase in the marsh plain elevation within the project site two years after sediment addition [ 27 ]. Using sediment spray equipment sediment application began in late January 2016 and ended in early April 2016 over a 4.05-hectare area for 31,094 m 2 901 of dredge material [ 27 ]; depth of applied sediment varied across the site with an average of 25.4 cm [ 27 ].…”

Section: Methodsmentioning

confidence: 99%

“…Hay bales, straw wattles, sand bags, and geotextile fabric were placed along the perimeter of the sediment application site to minimize loss of sediment to nearby channels during the application process. While suspended sediment concentrations did increase immediately adjacent to the application area, these engineering interventions were successful in retaining sediment overall [ 27 ]. The goal of the USFWS for this sediment application project was intended to build elevation capital relative to SLR and enhance marsh plain elevations for Spartina foliosa , Ridgway’s Rail primary habitat requirement.…”

Section: Methodsmentioning

confidence: 99%

“…Fewer studies have been conducted in urbanized, sediment-limited salt marsh ecosystems. To date, only a few limited studies have analyzed a thin-layer sediment addition in salt marshes on the Pacific Coast of the United States [ 26 , 27 ], making this research timely. Our study highlights the plant and invertebrate community change under a deeper sediment application project with an elevation goal designed to offset high SLR risk and local subsidence.…”

Section: Introductionmentioning

confidence: 99%

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Short-term impact of sediment addition on plants and invertebrates in a southern California salt marsh

McAtee¹,

Thorne²,

Whitcraft³

2020

PLoS ONE

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The implementation and monitoring of management strategies is integral to protect coastal marshes from increased inundation and submergence under sea-level rise. Sediment addition is one such strategy in which sediment is added to marshes to raise relative elevations, decrease tidal inundation, and enhance ecosystem processes. This study looked at the plant and invertebrate community responses over 12 months following a sediment addition project on a salt marsh located in an urbanized estuary in southern California, USA. This salt marsh is experiencing local subsidence, is sediment-limited from landscape modifications, has resident protected species, and is at-risk of submergence from sea-level rise. Abiotic measurements, invertebrate cores, and plant parameters were analyzed before and after sediment application in a before-after-control-impact (BACI) design. Immediately following the sediment application, plant cover and invertebrate abundance decreased significantly, with smothering of existing vegetation communities without regrowth, presumably creating resulting harsh abiotic conditions. At six months after the sediment application treatment, Salicornia bigelovii minimally colonized the sediment application area, and Spartina foliosa spread vegetatively from the edges of the marsh; however, at 12 months following sediment application overall plant recovery was still minimal. Community composition of infaunal invertebrates shifted from a dominance of marsh-associated groups like oligochaetes and polychaetes to more terrestrial and more mobile dispersers like insect larvae. In contrast to other studies, such as those with high organic deposition, that showed vegetation and invertebrate community recovery within one year of sediment application, our results indicated a much slower recovery following a sediment addition of 32 cm which resulted in a supratidal elevation with an average of 1.62 m (NAVD88) at our sampling locations. Our results indicate that the site did not recover after one year and that recovery may take longer which illustrates the importance of long-term monitoring to fully understand restoration trajectories and inform adaptive management. Testing and monitoring sea-level rise adaptation strategies like sediment addition for salt marshes is important to prevent the loss of important coastal ecosystems.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Short-term impact of sediment addition on plants and invertebrates in a southern California salt marsh

McAtee¹,

Thorne²,

Whitcraft³

2020

PLoS ONE

Self Cite

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Sea otters in a California estuary: Detecting temporal and spatial dynamics with volunteer monitoring

et al. 2022

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Volunteer monitoring can support conservation of imperiled wildlife, by providing higher resolution data in space and time than those available from professional scientists. However, concerns have been raised that data collected by amateurs are inaccurate or inconsistent and thus do not allow for robust detection of spatial or temporal trends. We evaluated the rigor and value of volunteer monitoring data for one iconic wildlife species, the southern sea otter (Enhydra lutris nereis), in Elkhorn Slough estuary in central California, USA, and explored whether volunteer monitoring could provide added value to complement limited professional surveys. First, we compiled and analyzed sea otter counts taken on daily ecotourist boat trips along the estuary, and then compared temporal patterns to data collected by professional scientists tasked with monitoring this federally listed species. Second, we analyzed data on sea otter abundance, habitat use, and behavior collected by a team of trained volunteers, the Elkhorn Slough Reserve Otter Monitoring Program. Overall, we demonstrated the ability to detect important ecological patterns relevant to sea otter conservation and wetland habitat management using volunteer‐derived datasets. Long‐term trends and inter‐annual variability were similar between professional agency monitoring data and volunteer datasets. Moreover, the much higher frequency of volunteer observations allowed for seasonal and tidal dynamics to be detected that could not be revealed by less frequent professional monitoring. We found higher sea otter abundance in the estuary in spring–summer, indicating seasonality in use of the estuary. We detected differences in habitat use of the estuary between higher and lower tides, and greater frequency of foraging at low tide and in certain areas. Volunteer observations revealed fine‐scale differences in habitat use: eelgrass beds were used much more heavily than adjacent areas only a few meters away. Volunteer data can thus provide critical information about coastal habitat use and behavior that can improve conservation strategies for threatened wildlife species.

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Increasing Salt Marsh Elevation Using Sediment Augmentation: Critical Insights from Surface Sediments and Sediment Cores

Fard,

Brown,

Ambrose

et al. 2023

Environmental Management

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Sea-level rise is particularly concerning for tidal wetlands that reside within an area with steep topography or are constrained by human development and alteration of sedimentation. Sediment augmentation to increase wetland elevations has been considered as a potential strategy for such areas to prevent wetland loss over the coming decades. However, there is little information on the best approaches and whether adaptive management actions can mimic natural processes to build sea-level rise resilience. In addition, the lack of information on long-term marsh characteristics, processes, and variability can hamper development of effective augmentation strategies. Here, we assess a case study in a southern California marsh to determine the nature of the pre-existing sediments and variability of the site in relation to sediments applied during an augmentation experiment. Although sediment cores revealed natural variations in the grain size and organic content of sediments deposited at the site over the past 1500 years, the applied sediments were markedly coarser in grain size than prehistoric sediments at the site (100% maximum sand versus 76% maximum sand). The rate of the experimental sediment application (25.1 ± 1.09 cm in ~2 months) was also much more rapid than natural accretion rates measured for the site historically. In contrast, post-augmentation sediment accretion rates on the augmentation site have been markedly slower than pre-augmentation rates or current rates on a nearby control site. The mismatch between the characteristics of the applied sediment and thickness of application and the historic conditions are likely strong contributors to the slow initial recovery of vegetation. Sediment augmentation has been shown to be a useful strategy in some marshes, but this case study illustrates that vegetation recovery may be slow if applied sediments are not similar or at a thickness similar to historic conditions. However, testing adaptation strategies to build wetland elevations is important given the long-term risk of habitat loss with sea-level rise. Lessons learned in the case study could be applied elsewhere.

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Thin-layer sediment addition to an existing salt marsh to combat sea-level rise and improve endangered species habitat in California, USA

Cited by 24 publications

References 38 publications

Short-term impact of sediment addition on plants and invertebrates in a southern California salt marsh

Short-term impact of sediment addition on plants and invertebrates in a southern California salt marsh

Sea otters in a California estuary: Detecting temporal and spatial dynamics with volunteer monitoring

Increasing Salt Marsh Elevation Using Sediment Augmentation: Critical Insights from Surface Sediments and Sediment Cores

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