Mangrove forest stores large organic carbon stocks in a setting that is highly vulnerable to climate change and direct anthropogenic influences. As such there is a need to elucidate the causes and ...consequences of land use change on these ecosystems that have high value in terms of ecosystem services. We examine the areal pattern of land types in a coastal region located in southern Iran over a period of 14 years to predict future loss and gain in land types to the year 2025. We applied a CA–Markov model to simulate and predict mangrove forest change. Landsat satellite images from 2000 to 2014 were used to analyze the land cover changes between soil, open water and mangroves. Major changes during this period were observed in soil and water which could be attributed to rising sea level. Furthermore, the mangrove area in the more seaward position was converted to open water due to sea-level rise. A cellular automata model was then used to predict the land cover changes that would occur by the year 2025. Results demonstrated that approximately 21 ha of mangrove area will be converted to open water, while mangroves are projected to expand by approximately 28 ha in landward direction. These changes need to be delineated to better inform precise mitigation and adaptation measures.
Mangrove wetlands exist in the transition zone between terrestrial and marine environments and as such were historically overlooked in discussions of terrestrial and marine carbon cycling. In recent ...decades, mangroves have increasingly been credited with producing and burying large quantities of organic carbon (OC). The amount of available data regarding OC burial in mangrove soils has more than doubled since the last primary literature review (2003). This includes data from some of the largest, most developed mangrove forests in the world, providing an opportunity to strengthen the global estimate. First‐time representation is now included for mangroves in Brazil, Colombia, Malaysia, Indonesia, China, Japan, Vietnam, and Thailand, along with additional data from Mexico and the United States. Our objective is to recalculate the centennial‐scale burial rate of OC at both the local and global scales. Quantification of this rate enables better understanding of the current carbon sink capacity of mangroves as well as helps to quantify and/or validate the other aspects of the mangrove carbon budget such as import, export, and remineralization. Statistical analysis of the data supports use of the geometric mean as the most reliable central tendency measurement. Our estimate is that mangrove systems bury 163 (+40; −31) g OC m−2 yr−1 (95% C.I.). Globally, the 95% confidence interval for the annual burial rate is 26.1 (+6.3; −5.1) Tg OC. This equates to a burial fraction that is 42% larger than that of the most recent mangrove carbon budget (2008), and represents 10–15% of estimated annual mangrove production. This global rate supports previous conclusions that, on a centennial time scale, 8–15% of all OC burial in marine settings occurs in mangrove systems.
Key Points
Global mangrove sediments accumulate 26.1 Tg of organic carbon annually
This burial equates to twelve percent of annual mangrove primary production
The 95 percent confidence interval is from 131 to 203 g OC per square meter per year
In September 2017, Hurricane Irma made landfall in South Florida, causing a great deal of damage to mangrove forests along the southwest coast. A combination of hurricane strength winds and high ...storm surge across the area resulted in canopy defoliation, broken branches, and downed trees. Evaluating changes in mangrove forest structure is significant, as a loss or change in mangrove forest structure can lead to loss in the ecosystems services that they provide. In this study, we used lidar remote sensing technology and field data to assess damage to the South Florida mangrove forests from Hurricane Irma. Lidar data provided an opportunity to investigate changes in mangrove forests using 3D high-resolution data to assess hurricane-induced changes at different tree structure levels. Using lidar data in conjunction with field observations, we were able to model aboveground necromass (AGN; standing dead trees) on a regional scale across the Shark River and Harney River within Everglades National Park. AGN estimates were higher in the mouth and downstream section of Shark River and higher in the downstream section of the Harney River, with higher impact observed in Shark River. Mean AGN estimates were 46 Mg/ha in Shark River and 38 Mg/ha in Harney River and an average loss of 29% in biomass, showing a significant damage when compared to other areas impacted by Hurricane Irma and previous disturbances in our study region.
•Arid mangrove forest exists in an already extreme environment.•Climate change and anthropogenic activities are threatening mangrove health.•Threats include pollution, SLR, temperature increase, and ...precipitation decline.
Climate change is a major threat to mangrove ecosystems worldwide but particularly those in arid regions that exist near the limit of tolerance to extremes in temperature, precipitation, and salinity. Here we examine Persian Gulf arid mangrove ecosystems from the Nayband and Mond Protected Area in the south-west region of Iran to determine the ability of tidal mangrove forests to respond to rapid urban and industrial development, sea-level rise (SLR), and temperature and precipitation changes. Sea level has been rising by approximately 4 mm yr−1 in this region and might be intensified by subsidence on the order of 1–2 mm yr−1 due to natural phenomena as well as anthropogenic activities associated with fluid extraction. We use remote sensing along with statistical analysis to effectively monitor mangrove area changes over 60 years and infer responses to past environmental trends. Our spatiotemporal analysis demonstrates expansion in some areas and reduction in others. NDVI (Normalized Difference Vegetation Index) results indicate that Nayband mangroves are healthy and expanded between the years of 1990 and 2002 which could be in response to rising temperatures and above-average precipitation. However, NDVI changes after 2002 demonstrate the mangrove health and area have decreased which could be in response to industrial and urban development that occurred immediately after 1997. The natural stresses in this extreme system are been exacerbated by climate change and anthropogenic pressures as such it is essential to develop ways to reduce vulnerability through strategic management planning.
There is concern that accelerating sea-level rise will exceed the vertical growth capacity of coastal-wetland substrates in many regions by the end of this century. Vertical vulnerability estimates ...rely on measurements of accretion and/or surface-elevation-change derived from soil cores and/or surface elevation tables (SETs). To date there has not been a broad examination of whether the multiple timescales represented by the processes of accretion and elevation change are equally well-suited for quantifying the trajectories of wetland vertical change in coming decades and centuries. To examine the potential for timescale bias in assessments of vertical change, we compared rates of accretion and surface elevation change using data derived from a review of the literature. In the first approach, average rates of elevation change were compared with timescale-averaged accretion rates from six regions around the world where sub-decadal, decadal, centennial, and millennial timescales were represented. Second, to isolate spatial variability, temporal comparisons were made for regionally unique environmental categories within each region. Last, comparisons were made of records from sites where SET-MH stations and radiometric measurements were co-located in close proximity. We find that rates vary significantly as a function of measurement timescale and that the pattern and magnitude of variation between timescales are location-specific. Failure to identify and account for temporal variability in rates will produce biased assessments of the vertical change capacity of coastal wetlands. Robust vulnerability assessments should combine accretion rates from multiple timescales with the longest available SET record to provide long-term context for ongoing monitoring observations and projections.
Compared to other terrestrial environments, coastal "blue carbon" habitats such as salt marshes and mangrove forests sequester disproportionately large amounts of carbon as standing plant biomass and ...peat deposits. This study quantified organic carbon stocks in 16 salt marshes, salt barrens, and mangrove forests in Tampa Bay, Florida, USA. The sites included natural, restored, and created wetlands of varying ages and degrees of anthropogenic impacts. Peat deposits were generally less than 30-cm deep and organic content rapidly decreased with depth in all habitats. The top 15 cm of mangrove soil contained an average of 11.0% organic carbon by weight, salt marshes contained 6.6%, and salt barrens contained 1.0%. Total organic carbon stock in mangroves was 133.6 ± 12.8 Mg ha⁻¹, with 69.5% of that carbon stored belowground. Salt marshes contained 66.4 ± 25.0 Mg ha⁻¹ (93.5% belowground carbon), and salt barrens contained 26.6 ± 8.3 Mg ha⁻¹ (96.1% belowground carbon). These values were much lower than global averages for carbon stocks in mangroves and salt marshes, likely due to Tampa Bay's location near the northern limit of mangrove habitat, sandy soil, young age of the restored wetlands, presence of mosquito ditches, and recent habitat conversion from salt marshes to mangroves. In the late 1800s, Tampa Bay's coastal wetlands were dominated by salt marshes, but today they are dominated by mangroves. Based on the blue carbon values from the natural sites in this study, this habitat switching has led to the additional sequestration of 141,000 Mg of carbon in remaining wetlands in the Tampa Bay watershed.
The Qinghai-Tibetan plateau (QTP) stores a large amount of soil organic carbon and is the headwater region for several large rivers in Asia. Therefore, it is important to understand the influence of ...environmental factors on river water quality and the dissolved organic carbon (DOC) export in this region. We examined the water physico-chemical characteristics, DOC concentrations and export rates of 7 rivers under typical land cover types in the Three Rivers Headwater Region during August 2016. The results showed that the highest DOC concentrations were recorded in the rivers within the catchment of alpine wet meadow and meadow. These same rivers had the lowest total suspended solids (TSS) concentrations. The rivers within steppe and desert had the lowest DOC concentrations and highest TSS concentrations. The discharge rates and catchment areas were negatively correlated with DOC concentrations. The SUVA254 values were significantly negatively correlated with DOC concentrations. The results suggest that the vegetation degradation, which may represent permafrost degradation, can lead to a decrease in DOC concentration, but increasing DOC export and soil erosion. In addition, some of the exported DOC will rapidly decompose in the river, and therefore affect the regional carbon cycle, as well as the water quality in the source water of many large Asian rivers.
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•The riverine dissolved organic carbon on the Qinghai-Tibetan Plateau was examined.•Land cover type (i.e., meadow or steppe) controls DOC concentrations and exports.•Permafrost degradation may increase riverine organic carbon transport.
Hypersaline tidal flats (HTFs) are coastal ecosystems with freshwater deficits often occurring in arid or semi-arid regions near mangrove supratidal zones with no major fluvial contributions. Here, ...we estimate that organic carbon (OC), total nitrogen (TN) and total phosphorus (TP) were buried at rates averaging 21 (±6), 1.7 (±0.3) and 1.4 (±0.3) gm-2yr-1, respectively, during the previous century in three contrasting HTF systems, one in Brazil (eutrophic) and two in Australia (oligotrophic). Although these rates are lower than those from nearby mangrove, saltmarsh and seagrass systems, the importance of HTFs as sinks for OC, TN and TP may be significant given their extensive coverage. Despite the measured short-term variability between net air–saltpan CO2 influx and emission estimates found during the dry and wet season in the Brazilian HTF, the only site with seasonal CO2 flux measurements, the OC sedimentary profiles over several decades suggest efficient OC burial at all sites. Indeed, the stable isotopes of OC and TN (δ13C and δ15N) along with C:N ratios show that microphytobenthos are the major source of the buried OC in these HTFs. Our findings highlight a previously unquantified carbon as well as a nutrient sink and suggest that coastal HTF ecosystems could be included in the emerging blue carbon framework.
Blue carbon refers to the carbon accumulation capacity of vegetated coastal habitats, including salt marshes, mangroves forests and seagrass meadows. Here we present estimates of organic carbon ...(Corg) and calcium carbonate (CaCO₃) burial rates from 4 seagrass species (Halophila ovalis, Posidonia australis, Ruppia megacarpa, Zostera muelleri) in 3 temperate estuaries on the east coast of Australia. The Corg burial rates (mean ± SE) varied by an order of magnitude across the seagrass communities (16 ± 3 to 130 ± 40 g m−2 yr–1). The δ
13Corg and Corg:N ratios suggest that the seagrass communities buried variable mixtures of seagrass, algal and mangrove/terrestrial material. CaCO₃ burial rates ranged from 15 ± 11 to 188 ± 122 g m−2 yr−1, which, if precipitated by calcifying organisms in these or nearby habitats, may offset up to 89% of the Corg burial across the 8 seagrass communities. Our results highlight a large range in both Corg and CaCO₃ burial rates, and the provenance of the carbon sequestered in seagrasses, factors that need to be considered when assessing the role of seagrasses in blue carbon and climate change mitigation strategies.
The flux of total organic carbon (TOC) to depositional facies (intertidal mud flat, margin and forest) was quantified for a tropical mangrove forest in Brazil. Results indicate that these mangrove ...margins and intertidal mudflats are sites of large TOC accumulation, almost four times greater than the global averages for mangrove forests. The TOC burial rates were determined from organic carbon content in sediment cores which were dated using
210Pb. Burial rates were calculated to be 1129, 949, and 353 (g m
−2 yr
−1), for the mud flat, margin and forest, respectively. Sediment accumulation rates (SAR) were estimated to be 7.3, 5.0 and 2.8 mm yr
−1. Sediment characterization (δ
13C, δ
15N, TOC/TN and mud fraction) indicated a representative mangrove system with a record of consistent organic matter flux of up to 100 years. Because of substantial burial of organic carbon in mangrove ecosystems, their role in the global carbon budget must be considered. More importantly, as climate change influences temperature and sea level, mangrove ecosystems will respond to specific climatic conditions.
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