The future of Blue Carbon science Macreadie, Peter I; Anton, Andrea; Raven, John A ...
Nature communications,
09/2019, Letnik:
10, Številka:
1
Journal Article
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The term Blue Carbon (BC) was first coined a decade ago to describe the disproportionately large contribution of coastal vegetated ecosystems to global carbon sequestration. The role of BC in climate ...change mitigation and adaptation has now reached international prominence. To help prioritise future research, we assembled leading experts in the field to agree upon the top-ten pending questions in BC science. Understanding how climate change affects carbon accumulation in mature BC ecosystems and during their restoration was a high priority. Controversial questions included the role of carbonate and macroalgae in BC cycling, and the degree to which greenhouse gases are released following disturbance of BC ecosystems. Scientists seek improved precision of the extent of BC ecosystems; techniques to determine BC provenance; understanding of the factors that influence sequestration in BC ecosystems, with the corresponding value of BC; and the management actions that are effective in enhancing this value. Overall this overview provides a comprehensive road map for the coming decades on future research in BC science.
Transformation of agricultural land to natural terrestrial vegetation has been suggested as a means to increase soil carbon storage. However, the capacity for carbon storage in terrestrial soils is ...limited as compared to soils of tidal salt marshes, the original vegetation of many coastal agricultural lands. In a number of countries, tidal salt marshes have been “reclaimed,” that is drained and diked to prevent tidal flooding and create suitable conditions for dry land agriculture. In this study we examine spatial and temporal patterns of carbon accumulation in tidal salt marshes of the Bay of Fundy and estimate the carbon storage potential of the bay's extensive area of reclaimed marsh. Rates of carbon accumulation vary from the upper to the outer Bay, over which there is a gradient of decreasing tidal range and suspended sediment supply. In the outer bay, high‐marsh densities are highest (0.042 ± 0.009 g C cm−3), but carbon accumulation rates over the past 30 years are lowest (76 g C m−2 yr−1). The reverse pattern occurs in the upper bay where carbon densities in the high‐marsh environment are lowest (0.036 ± 0.002 g C cm−3), but carbon accumulation rates over the past 30 years may be as high (184 g C m−2 yr−1). Compared to other ecosystems, the rates of carbon accumulation presented in this study were similar over timescales of years to centuries. Increases in relative sea level (over time) and suspended sediment supply (across the bay) positively affect the marsh soil accumulation rate and the rate of carbon sequestration. Parameters such as %C are not useful predictors of a marsh's potential for carbon sequestration. Soil carbon densities of functioning marshes and reclaimed marsh soils are similar, but marsh soils have a storage capacity that increases with rising sea level, while agricultural soils, such as those in reclaimed marshes, have a fixed (or possibly decreasing in reclaimed marshes) volume over time.
We show the first conclusive evidence that Melitasphaeridium choanophorum, a dinoflagellate cyst species until recently considered extinct, is still living in the northern Gulf of Mexico. This ...suggests the Gulf of Mexico may have acted as a refugium for some warm-water dinoflagellates during past glaciations. Melitasphaeridium choanophorum can be considered a living fossil because cysts with cell contents were found among 15 of the 39 surface sediment samples analyzed from the northern Gulf of Mexico, and from five of 12 samples from a dated core (1962–1997). Melitasphaeridium choanophorum comprises a minor component of the total dinoflagellate cyst assemblages, with a maximum of 1.4% or 15 cysts g-1. It was found in surface sediments with overlying sea-surface temperatures of 16.6 to 31.2 °C (winter and summer), and summer sea-surface salinities of 21.0 to 31.7 psu. The relationship of M. choanophorum with modern sea-surface conditions can be used to infer past oceanographic conditions.
Our study examined the relationship of microphytobenthos to greenhouse gas fluxes from sediments of a subtropical mangrove forest and adjacent mudflat in the Jiulong River Estuary, South China. The ...relationship between chlorophyll a concentration at the sediment surface and diatom density confirmed that these microalgae were the important component of the microphytobenthos, which produced an observable biofilm in cold seasons (winter and spring) on both the mangrove and mudflat sediment surfaces. Fluxes of methane and nitrous oxide were not affected by the microalgae film and were similar between the mangrove and mudflat. However, benthic microalgae affected the sediment to atmosphere carbon dioxide (CO₂) flux, and the effect was temporally variable with the seasonal change in microalgae abundance. In the cold seasons, the mangrove sediment was a CO₂ sink under light chambers but a source under dark chambers. In summer, when there was no visible microalgae film at the sediment surface, the intertidal sediments had CO₂ emissions and comparable fluxes between the two chambers. The negative daily CO₂ fluxes of the film-covered sediment (as the average of the dark and light fluxes) and positive flux of the sediment without visible biofilm indicated that the occurrence of microalgae film converted the mangrove sediment from a CO₂ source to a sink and that the photosynthesis of the microalgae film offset the sediment respiration during the cold seasons in this study. We also found similar effects of microalgae on CO₂ fluxes on the nonvegetated mudflat.
Beginning in the 17th century many Bay of Fundy marshes were diked and drained for agricultural use, but storm breaching of dikes and failure of tidal gates has returned tidal flooding to some ...marshes. We investigated two breached and undiked salt marsh pairs in the Bay of Fundy to assess the potential for recovery of these reclaimed lands and improve our knowledge about salt marsh restoration. We examined the distribution of major species with respect to elevation and compared plant cover and production of reference and recovering marshes. The vertical range of both Spartina alterniflora and Spartina patens increased with tidal range — a condition recognized for S. alterniflora, but not previously reported for S. patens. Our results reveal that S. alterniflora and S. patens are inundated less frequently than in microtidal marshes and tolerate a large variation in inundation frequency and depth. The upper portions of the S. patens zone may not be submerged by tidal waters in some years, so hydroperiod (and its associated stresses) may play less of a role in limiting the lower elevation of a species' distribution in the high marsh. Our comparisons of reference and recovering diked marshes inform not only restoration activities on the Bay of Fundy, but also give a perspective on recovery trajectories of reclaimed salt marshes in general. Regionally, the broad elevation range of S. alterniflora and high sediment deposition rates impart Bay of Fundy marshes with a high resilience and prospects for success of deliberate restoration efforts are promising, without the addition of fill required for marsh restoration in some regions. While marsh loss occurs in other areas the Bay of Fundy provides an opportunity to regain this resource.
As entomophilous plants, water lilies (
Nymphaea) and spatterdocks (
Nuphar) have low pollen production, thus can be under represented in the sediment record. These macrophytes produce distinctly ...shaped sclerenchyma tissue referred to as stone-cells, trichosclereids, astrosclereids or simply sclereids. This study examines the utility of using sclereids from two common species from the Nymphaeaceae Family as an alternative to their pollen. Histological studies of fresh tissues of
Nymphaea odorata and
Nuphar lutea show that each has distinct sclereids, but there has been confusion in the terminology used to designate their morphology. Some reports have referred to Nymphaeaceae sclereids as trichosclereids, but our histological studies show that the cells are more appropriately classified as polyramous, astrosclereids, librosclereids or rhizosclereids. Tissues from both species were treated using HCL, KOH, acetolysis and HF. We found that only the sclereids from
N. lutea survived chemical treatments in a detectable form, indicating that sclereids from
N. lutea can be a useful indicator of presence while the chance of observing sclereids from
N. odorata in pollen preparations is very low, severely limiting the utility of the latter as a paleoecological indicator. Another limitation to using sclereids as a proxy is that they originate from tissues that require extended acetolysis treatments for release from the matrix. Finally, we examined sclereid abundance in sediments from a slough in the Florida Everglades, USA to determine if abundance of Nymphaeaceae sclereids correlates with Nymphaeaceae pollen and we find no significant correlation. Additional analyses are required to determine if empirical relationships exist amongst plant populations, pollen, sclereids and environmental conditions. A clear report of chemical treatments used and processing times are critical to verify results of studies utilizing sclereids.
►
N. lutea and
N. odorata sclereids could be differentiated thin sections of tissues. ► Contrary to previous reports no "trichosclereids" were observed in either species. ► Acetolysis treatments degrade
N. odorata sclereids and make them unrecognizable. ►
N. lutea sclereids survive processing thus can be a useful proxy for plant presence. ► Release of sclereids from peat may require extended acetolysis.
We monitored salinity and temperature in pools at different elevations in two marshes on the Bay of Fundy to assess variability in pool environments and how climate change might affect these ...ecosystems. Water temperatures reached a maximum of 36.1°C, and ice covered pools in the winter. Ice lifting out of ponds in the spring scoured bottoms. Salinity ranged from 4 to 41. Environmental variability was mainly driven by weather. Variability in pool temperature declined with decreasing elevation. Regular tidal flooding at lower elevations moderated both temperatures and salinity. Variability in pool salinity was greatest in the middle marsh region, since proximity to groundwater also moderated salinity at high elevations. Projections of milder winters should reduce formation of ice in pools, resulting in decreased scour, and possibly shallowing of pools. This, accompanied by projected increases in extreme weather, will increase salinity variability, thus increasing stress to organisms in an already stressful environment.
We assess the status of channel networks and pools of two tidal salt marshes recovering from more than a century of agricultural reclamation on the Bay of Fundy, Canada. A process of largely ...unmanaged restoration occurred at these sites since abandonment of agricultural activities during the first half of the twentieth century. Each recovering marsh was compared to a reference marsh that was never drained or ditched. We field mapped channel networks at all marshes and used aerial photographs to map the pre-abandonment channel network at one of the sites.The recovering marshes have hybrid channel networks that feature highly variable channel morphologies, loss of original channels, and incorporation of drainage ditches. Although channel networks in recovering marshes integrate agricultural ditches, the recovering marsh networks may not be substantially increased in length or density. Our aerial photograph analysis shows that channel density at one of the recovering marshes is comparable to the pre-abandonment density, but with reduced sinuosity. Field mapping of permanent tidal pools on the lower Bay marshes revealed that pools cover 13% of the recovering marsh, compared to ~ 5% of the reference marsh. This study demonstrates that these essential marsh features can be regained through restoration or simple abandonment of drainage infrastructure.
We measured the amount of arsenic, chromium, copper, lead, nickel, vanadium, and zinc accumulated over a five-year period from 1997 to 2002 in surface sediments of seven salt marshes along the New ...Brunswick coast of the Bay of Fundy, Canada. Study sites extended from outer to inner Bay, spanning a gradient in tidal range (6-12 m) and mean sediment deposition rate (0.27-1.76 cm yr⁻¹). In each study site, metal concentrations were measured in low and high marsh areas. Concentrations of chromium, nickel, and zinc appear to be within their natural range, while arsenic, lead, and vanadium are enriched in some sites. Calculated sediment metal loadings rates showed variability among marsh sites that closely followed sediment deposition patterns, suggesting sediment deposition rate is the driving factor of short-term metal accumulation in Fundy marshes. The value of salt marshes as a sink for metals may be enhanced by high sedimentation rates.
Reports of shifts in rates of aggradation in a salt marsh deposit at Amherst Point, Nova Scotia have been linked with fluctuations in eustatic sea level, crustal subsidence and, possibly, changes in ...tidal amplitude. However, evidence for the most recent fluctuation is an artifact of early Acadian land reclamation that occurred in the seventeenth century at Amherst Point. Acadian settlers had constructed dikes to prevent regular tidal flooding, but probably allowed occasional flooding of the surface by tidal waters, thus maintaining the salt marsh signature of the deposit. Statistical analysis of the pollen assemblage from the uppermost deposit interpreted as a regressive sequence aligns critical depths with pollen assemblages retrieved from modern soils of diked and drained marshes. Inspection of historical aerial photographs confirms that the dikes persisted on the site until at least 1939. Interpretations of earlier fluctuations recorded in deposits below this regressive sequence remain valid. It is possible that the Bay of Fundy experienced a regressive period just prior to Acadian diking, but future research on unexamined salt marsh deposits here or elsewhere must include an exhaustive search of historical documents to avoid misinterpretation of anthropogenic modifications.
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