Hurricanes are recurring high-energy disturbances in coastal regions that change community structure and function of mangrove wetlands. However, most of the studies assessing hurricane impacts on mangroves have focused on negative effects without considering the positive influence of hurricane-induced sediment deposition and associated nutrient fertilization on mangrove productivity and resilience. Here, we quantified how Hurricane Irma influenced soil nutrient pools, vertical accretion, and plant phosphorus (P) uptake after its passage across the Florida Coastal Everglades in September 2017. Vertical accretion from Irma’s deposits was 6.7 to 14.4 times greater than the long-term (100 y) annual accretion rate (0.27 ± 0.04 cm y−1). Storm deposits extended up to 10-km inland from the Gulf of Mexico. Total P (TP) inputs were highest at the mouth of estuaries, with P concentration double that of underlying surface (top 10 cm) soils (0.19 ± 0.02 mg cm−3). This P deposition contributed 49 to 98% to the soil nutrient pool. As a result, all mangrove species showed a significant increase in litter foliar TP and soil porewater inorganic P concentrations in early 2018, 3 mo after Irma’s impact, thus underscoring the interspecies differences in nutrient uptake. Mean TP loading rates were five times greater in southwestern (94 ± 13 kg ha−1d−1) mangrove-dominated estuaries compared to the southeastern region, highlighting the positive role of hurricanes as a natural fertilization mechanism influencing forest productivity. P-rich, mineral sediments deposited by hurricanes create legacies that facilitate rapid forest recovery, stimulation of peat soil development, and resilience to sea-level rise.
Mangroves buffer inland ecosystems from hurricane winds and storm surge. However, their ability to withstand harsh cyclone conditions depends on plant resilience traits and geomorphology. Using airborne lidar and satellite imagery collected before and after Hurricane Irma, we estimated that 62% of mangroves in southwest Florida suffered canopy damage, with largest impacts in tall forests (>10 m). Mangroves on well-drained sites (83%) resprouted new leaves within one year after the storm. By contrast, in poorly-drained inland sites, we detected one of the largest mangrove diebacks on record (10,760 ha), triggered by Irma. We found evidence that the combination of low elevation (median = 9.4 cm asl), storm surge water levels (>1.4 m above the ground surface), and hydrologic isolation drove coastal forest vulnerability and were independent of tree height or wind exposure. Our results indicated that storm surge and ponding caused dieback, not wind. Tidal restoration and hydrologic management in these vulnerable, low-lying coastal areas can reduce mangrove mortality and improve resilience to future cyclones.
more » « less- NSF-PAR ID:
- 10253192
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 12
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Hurricane Irma (September 2017) was one of the most devastating hurricanes in recent times. In January 2018, a post‐hurricane field survey was conducted on Anegada (British Virgin Islands) to report on the erosional and depositional evidence caused by Hurricane Irma's storm surge and waves. We document the type and extent of hurricane‐induced geomorphological changes, allowing for an improved risk assessment of hurricane‐related inundation on low‐lying islands and carbonate platforms.
Anegada's north shore was most impacted by Hurricane Irma. The surge reached about 3.8 m above sea level and onshore flow depths ranged between 1.2 to 1.6 m. Storm wave action created 1 to 1.5 m high erosional scarps along the beaches, and the coastline locally retreated by 6 to 8 m.
Onshore sand sheets reached up to 40 m inland, overlie a sharp erosive contact and have thicknesses of 7 to 35 cm along the north shore. In contrast, lobate overwash fans in the south are 2 to 10 cm thick and reach 10 to 30 m inland.
Moreover, the hurricane reworked a pre‐existing coast‐parallel coral rubble ridge on the central north shore. The crest of the coral rubble ridge shifted up to 10 m inland due to the landward transport of cobbles and boulders (maximum size 0.5 m3) that were part of the pre‐hurricane ridge.
A re‐survey, 18 months after the event, assessed the degree of the natural coastal recovery. The sand along the northern shoreline of Anegada that was eroded during the hurricane and stored in the shallow water, acted as a nearshore source for beach reconstruction which set in only days after the event. Beach recovery peaked in February 2018, when beaches accreted within hours during a nor'easter‐like storm that transported large volumes of nearshore sand back onto the beach.
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The capacity of coastal wetlands to stabilize shorelines and reduce erosion is a critical ecosystem service, and it is uncertain how changes in dominant vegetation may affect coastal protection. As part of a long-term study (2012–present) comparing ecosystem functions of marsh and black mangrove vegetation, we have experimentally maintained marsh and black mangrove patches (3 m × 3 m) along a plot-level (24 m × 42 m) gradient of marsh and mangrove cover in coastal wetlands near Port Aransas, TX. In August 2017, this experiment was directly in the path of Hurricane Harvey, a category 4 storm. This extreme disturbance event provided an opportunity to quantify differences in resistance between mangrove and marsh vegetation and to assess which vegetation type provided better shoreline protection against storm-driven erosion. We compared changes in plant cover, shoreline erosion, and accreted soil depth to values measured prior to storm landfall. Relative mangrove cover decreased 25–40% after the storm, regardless of initial cover, largely due to damage on taller mangroves (> 2.5 m height) that were not fully inundated by storm surge and were therefore exposed to strong winds. Evidence of regrowth on damaged mangrove branches was apparent within 2 months of landfall. Hurricane-induced decreases in mangrove cover were partially ameliorated by the presence of neighboring mangroves, particularly closer to the shoreline. Marsh plants were generally resistant to hurricane effects. Shoreline erosion exceeded 5 m where mangroves were absent (100% marsh cover) but was relatively modest (< 0.5 m) in plots with mangroves present (11–100% mangrove cover). Storm-driven accreted soil depth was variable but more than 2× higher in marsh patches than in mangrove patches. In general, mangroves provided shoreline protection from erosion but were also more damaged by wind and surge, which may reduce their shoreline protection capacity over longer time scales.more » « less
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The capacity of coastal wetlands to stabilize shorelines and reduce erosion is a critical ecosystem service, and it is uncertain how changes in dominant vegetation may affect coastal protection. As part of a long-term study (2012–present) comparing ecosystem functions of marsh and black mangrove vegetation, we have experimentally maintained marsh and black mangrove patches (3 m × 3 m) along a plot-level (24 m × 42 m) gradient of marsh and mangrove cover in coastal wetlands near Port Aransas, TX. In August 2017, this experiment was directly in the path of Hurricane Harvey, a category 4 storm. This extreme disturbance event provided an opportunity to quantify differences in resistance between mangrove and marsh vegetation and to assess which vegetation type provided better shoreline protection against storm-driven erosion. We compared changes in plant cover, shoreline erosion, and accreted soil depth to values measured prior to storm landfall. Relative mangrove cover decreased 25–40% after the storm, regardless of initial cover, largely due to damage on taller mangroves (> 2.5 m height) that were not fully inundated by storm surge and were therefore exposed to strong winds. Evidence of regrowth on damaged mangrove branches was apparent within 2 months of landfall. Hurricane-induced decreases in mangrove cover were partially ameliorated by the presence of neighboring mangroves, particularly closer to the shoreline. Marsh plants were generally resistant to hurricane effects. Shoreline erosion exceeded 5 m where mangroves were absent (100% marsh cover) but was relatively modest (< 0.5 m) in plots with mangroves present (11–100% mangrove cover). Storm-driven accreted soil depth was variable but more than 2× higher in marsh patches than in mangrove patches. In general, mangroves provided shoreline protection from erosion but were also more damaged by wind and surge, which may reduce their shoreline protection capacity over longer time scales.more » « less
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Abstract Plant identity and cover in coastal wetlands is changing in worldwide, and many subtropical salt marshes dominated by low‐stature herbaceous species are becoming woody mangroves. Yet, how changes affect coastal soil biogeochemical processes and belowground biomass before and after storms is uncertain. We experimentally manipulated the percent mangrove cover (
Avicennia germinans ) in 3 × 3 m cells embedded in 10 plots (24 × 42 m) comprising a gradient of marsh (e.g.,Spartina alterniflora ,Batis maritima ) and mangrove cover in Texas, USA. Hurricane Harvey made direct landfall over our site on 25 August 2017, providing a unique opportunity to test how plant composition mitigates hurricane effects on surface sediment accretion, soil chemistry (carbon, C; nitrogen, N; phosphorus, P; and sulfur, S), and root biomass. Data were collected before (2013 and 2016), one‐month after (2017), and one‐year after (2018) Hurricane Harvey crossed the area, allowing us to measure stocks before and after the hurricane. The accretion depth was higher in fringe compared with interior cells of plots, more variable in cells dominated by marsh than mangrove, and declined with increasing plot‐scale mangrove cover. The concentrations of P and δ34S in storm‐driven accreted surface sediments, and the concentrations of N, P, S, and δ34S in underlying soils (0–30 cm), decreased post‐hurricane, whereas the C concentrations in both compartments were unchanged. Root biomass in both marsh and mangrove cells was reduced by 80% in 2017 compared with previous dates and remained reduced in 2018. Post‐hurricane loss of root biomass in plots correlated with enhanced nutrient limitation. Total sulfide accumulation as indicated by δ34S, increased nutrient limitation, and decreased root biomass of both marshes and mangroves after hurricanes may affect ecosystem function and increase vulnerability in coastal wetlands to subsequent disturbances. Understanding how changes in plant composition in coastal ecosystems affects responses to hurricane disturbances is needed to assess coastal vulnerability.
