Sources and distributions of terrigenous organic matter in a mangrove fringed small tropical estuary in South China

The sources and distributions of terrigenous organic matter (OM) were investigated in a small tropical estuary in the Hainan Island, South China. Plants, suspended particulate matter (SPM), and surface sediments samples in the estuary and coast were collected. Bulk properties [organic carbon (OC%), total nitrogen (TN%), stable carbon isotope (δ13C) and grain size] and lignin phenol concentrations were measured. OC% of mangrove plants was (43.4 ± 2.1)%, which is similar to the values reported for mangrove plants in other regions. OC% of sediment samples ranged from 0.07% to 1.42%, and they were related to the sediment texture. Lignin phenols in the sediment ranged from 5.16 mg/100 mg OC in the uppermost station to 0.51mg/100mg OC in the coast. The molar ratio of organic carbon to total nitrogen (C/N) (～7) and δ 13 C (～-31.1×10-3 ) of riverine SPM revealed that the major OM sources of riverine SPM were aquatic OM (phytoplankton and/or bacteria). Moreover, the lower lignin concentration (Λ8) and higher (Ad/Al)v of lignin phenols suggest that terrestrial OM in riverine SPM were mainly from soil. Furthermore, C/N ratio, δ13C and lignin phenols reveal that mangrove plants were the predominant OM sources of mangrove surface sediment. Based on the δ13C and lignin phenols, it can be concluded that the major OM sources in estuarine and coastal surface sediments were marine phytoplankton, riverine SPM and mangrove surface sediment. In addition, the higher (Ad/Al)v of lignin phenols in those coastal sediments indicate that seagrass might be a potential OM source in coastal sediments, however, the lower (Ad/Al)v in the estuarine sediments in turn suggests that seagrass could not be transported to the mangrove fringed region. A three-end-member model which is based on lignin concentrations and δ13C was applied to evaluate the contribution of mangroves to the organic matter preserved in the surface sediments. Around the mangrove fringed region, mangrove could contribute more than 50% to the sedimentary OM, and this value is much higher than riverine OM. Nevertheless, mangrove OM could not be efficiently transported to the coastal region. Our study suggests that mangrove forest is an important OM source in this small estuary.     

Importance of seagrass as a carbon source for heterotrophic bacteria in a subtropical estuary (Florida Bay)

A stable carbon isotope approach was taken to identify potential organic matter sources incorporated into biomass by the heterotrophic bacterial community of Florida Bay, a subtropical estuary with a recent history of seagrass loss and phytoplankton blooms. To gain a more complete understanding of bacterial carbon cycling in seagrass estuaries, this study focused on the importance of seagrass-derived organic matter to pelagic, seagrass epiphytic, and sediment surface bacteria. Particulate organic matter (POM), seagrass epiphytic, seagrass (Thalassia testudinum) leaf, and sediment surface samples were collected from four Florida Bay locations with historically different organic matter inputs, macrophyte densities, and primary productivities. Bulk (observed and those reported previously) and compound-specific bacterial fatty acid δ¹³C values were used to determine important carbon sources to the estuary and benthic and pelagic heterotrophic bacteria. The δ¹³C values of T. testudinum green leaves with epiphytes removed ranged from −9.9 to −6.9‰. Thalassia testudinum δ¹³C values were significant more enriched in ¹³C than POM, epiphytic, and sediment samples, which ranged from −16.4 to −13.5, −16.2 to −9.6, and −16.7 to −11.0‰, respectively. Bacterial fatty acid δ¹³C values (measured for br14:0, 15:0, i15:0, a15:0, br17:0, and 17:0) ranged from −25.5 to −8.2‰. Assuming a −3‰ carbon source fractionation from fatty acid to whole bacteria, pelagic, epiphytic, and sediment bacterial δ¹³C values were generally more depleted in ¹³C than T. testudinum δ¹³C values, more enriched in ¹³C than reported δ¹³C values for mangroves, and similar to reported δ¹³C values for algae. IsoSource mixing model results indicated that organic matter derived from T. testudinum was incorporated by both benthic and pelagic bacterial communities, where 13–67% of bacterial δ¹³C values could arise from consumption of seagrass-derived organic matter. The IsoSource model, however, failed to discriminate clearly the fraction of algal (0–86%) and mangrove (0–42%) organic matter incorporated by bacterial communities. These results indicate that pelagic, epiphytic, and sediment surface bacteria consumed organic matter from a variety of sources. Bacterial communities incorporated consistently seagrass-derived organic matter, the dominant macrophyte in Florida Bay, but seagrass δ¹³C values alone could not account fully for bacterial δ¹³C values.     

The cycling and oxidation pathways of organic carbon in a shallow estuary along the Texas Gulf Coast

The cycling and oxidation pathways of organic carbon were investigated at a single shallow water estuarine site in Trinity Bay, Texas, the uppermost lobe of Galveston Bay, during November 2000. Radio-isotopes were used to estimate sediment mixing and accumulation rates, and benthic chamber and pore water measurements were used to determine sediment-water exchange fluxes of oxygen, nutrients and metals, and infer carbon oxidation rates. Using ⁷Be and ²³⁴Th_XS, the sediment-mixing coefficient (D_b) was 4.3 ± 1.8 cm² y⁻¹, a value that lies at the lower limit for marine environments, indicating that mixing was not important in these sediments at this time. Sediment accumulation rates (S_a), estimated using ¹³⁷Cs and ²¹⁰Pb_XS, were 0.16 ± 0.02 g cm⁻² y⁻¹. The supply rate of organic carbon to the sediment-water interface was 30 ± 3.9 mmol C m⁻² d⁻¹, of which ∼10% or 2.9 ± 0.44 mmol C m⁻² d⁻¹was lost from the system through burial below the 1-cm thick surface mixed layer. Measured fluxes of O₂ were 26 ± 3.8 mmol m⁻² d⁻¹ and equated to a carbon oxidation rate of 20 ± 3.3 mmol C m⁻² d⁻¹, which is an upper limit due to the potential for oxidation of additional reduced species. Using organic carbon gradients in the surface mixed layer, carbon oxidation was estimated at 2.6 ± 1.1 mmol C m⁻² d⁻¹. Independent estimates made using pore water concentration gradients of ammonium and C:N stoichiometry, equaled 2.8 ± 0.46 mmol C m⁻² d⁻¹. The flux of DOC out of the sediments (DOC_efflux) was 5.6 ± 1.3 mmol C m⁻² d⁻¹. In general, while mass balance was achieved indicating the sediments were at steady state during this time, changes in environmental conditions within the bay and the surrounding area, mean this conclusion might not always hold. These results show that the majority of carbon oxidation occurred at the sediment-water interface, via O₂ reduction. This likely results from the high frequency of sediment resuspension events combined with the shallow sediment mixing zone, leaving anaerobic oxidants responsible for only ∼10–15% of the carbon oxidized in these sediments.     

Correlation of the absorption coefficient with a reduction in mean mass for dissolved organic matter in southwest Florida river plumes

Results are presented from an investigation of the relationship between molecular mass distribution and optical properties for colored dissolved organic matter (CDOM); a complex assembly of organic macromolecules of marine and freshwater origin found throughout the surface ocean. Unique data are derived from the application of a new technique, a combination of a hydrophilic–lipophilic copolymer-based solid phase extraction (SPE) with electrospray ionization (ESI) continuous flowing ion trap mass spectrometry (cf-MS), for the direct determination of CDOM mass distribution. An evaluation of this copolymer-based extraction technique for the analysis of Suwannee River Natural Organic Matter (SRNOM) reference material revealed that the current method compares favorably with C₁₈ modified silica or XAD resin-based extraction methods reported in the literature when considering extraction efficiency or low extraction bias for CDOM. The mass distribution of CDOM in several freshwater to marine transition zones along coastal southwestern Florida has been determined with this technique. All rivers in the study region had a bimodal distribution of masses. A case study of the Caloosahatchee River outflow CDOM mass distribution data are presented as an example of the modification in mass distributions. The lower mass mode of the bimodal distribution was observed to have a relatively stable mean throughout the study region at 406±9 Da, while decreasing in concentration in a non-conservative manner with salinity. In contrast, the upper mass mode of the bimodal distribution was observed to have a variable mean, reaching 1408 Da in the least saline waters and decreasing by 174 Da through the transect toward higher salinity coastal waters. Coinciding with this reduction in mean mass for the upper distribution is a non-conservative reduction in concentration when compared with salinity. We define apparent organic carbon (AOC) as a function of the cf-MS determined total integrated area and use this value to determine concentration of the total extracted CDOM. Unique correlations between the CDOM fluorescence (350-nm excitation/450-nm emission) and the AOC for these coastal samples have been observed for each of three rivers in the study region. The steepest slope and highest correlation between optical and mass spectral properties are observed in rivers with strongly absorbing waters originating in the Florida Everglades and lowest in rivers draining clearer waters from widely variable and anthropogenic influenced regions. The trends in molecular mass distribution and corresponding optical properties support the theory that CDOM in coastal zones is environmentally processed material from terrestrial sources. Probable cause of the reduction in mean mass and suggestions for further investigation of sources and transformations of CDOM are discussed.     

Dissolved organic carbon in the freshwater tidal reaches of the Schelde estuary

To unravel the factors that regulate DOC dynamics in the freshwater tidal reaches of the Schelde estuary, DOC concentration and biodegradability were monitored in the upper Schelde estuary and its major tributaries. Although the Schelde estuary possesses a densely populated and industrialized catchment, our data suggest that the bulk of DOC in the freshwater tidal reaches is not derived from waste water. This was concluded from the low biodegradability of DOC (on average 9%), DOC concentrations that are close to the mean for European rivers (4.61 mg l⁻¹) and the absence of an inverse relationship between DOC and discharge. Most DOC originating from waste water being discharged in tributaries of the estuary appears to be remineralised before these tributaries reach the main estuary. Although dense phytoplankton blooms were observed in the upper estuary during summer (up to 700 μg chl a l⁻¹), these blooms did not appear to produce large quantities of DOC in the freshwater tidal reaches as DOC concentrations were low when phytoplankton biomass was high. The fact that DOC concentrations were high in winter and decreased in summer suggests a predominantly terrestrial source of DOC in the freshwater tidal reaches of the Schelde estuary.     

Studies of a mangrove basin,Tuff Crater,New Zealand: III. The flux of organic and inorganic particulate matter

Water samples were collected at 15 min intervals over 11 tidal cycles from a tidal creek draining the mangrove-covered basin of Tuff Crater, Auckland, New Zealand. The samples were filtered and total suspended sediment (TSS), inorganic suspended sediment (ISS) and organic suspended sediment (OSS) were determined. Variation in TSS was high, the concentration varied over a tidal cycle and during over-bank flows concentrations were lowest at or near slack high water. Covariance between TSS concentrations and velocity and discharge meant that the calculation of particulate matter flux over tidal hemicycles was particularly dependent on the method of estimating tidal flux. The hypsometrically-based volumetric method was found to be inappropriate, predicting a positive budget (import) more often than observed. Instead particulate matter budgets were calculated by means of the velocity-area method and indicate a net export of TSS, ISS and OSS. Floating macrodetritus was observed on both the flood and ebb tides, but a net export was found on the two tides monitored. It is considered that on an annual basis floating macrodetritus export accounts for less than 2% of the detrital production in the basin, and organic suspended sediment export from the basin is less than 3 kg C ha^?1 day^?1 and is below the rate of detrital production. It is implied that a proportion of the organic detritus produced in this basin is degraded and recycled in situ.     

Turbidity limits gas exchange in a large macrotidal estuary

In estuaries, the gas transfer velocity (k) is driven by a combination of two major physical drivers, wind and water current. The k values for CO₂ in the macrotidal Gironde Estuary were obtained from 159 simultaneous pCO₂ and floating chamber flux measurements. Values of k increased with wind speed and were significantly greater when water currents and wind were in opposing directions. At low wind speeds (<1 m s⁻¹), k increased with water current velocities (0–1.5 m s⁻¹) following an exponential trend. The latter was a good proxy for the Y-intercept in a generic equation for k versus wind speed in estuaries. We also found that, in this turbid estuary, k was significantly lower at high turbidity. The presence of suspended material in great concentrations (TSS > 0.2 g L⁻¹) had a significant role in attenuating turbulence and therefore gas exchange. This result has important consequences for modeling water oxygenation in estuarine turbidity maxima. For seven low turbidity estuaries previously described in the literature, the slope of the linear regression between k and wind speed correlates very well with the estuary surface area due to a fetch effect. In the Gironde Estuary, this slope follows the same trend at low turbidity (TSS < 0.2 g L⁻¹), but is on average significantly lower than in other large estuaries and decreases linearly with the TSS concentration. A new generic equation for estuaries is proposed that gives k as a function of water current velocity, wind speed, estuarine surface area and TSS concentration.     

Morphology, hydrography and sediment dynamics in a mangrove estuary: The Konkoure Estuary, Guinea

The Konkouré Estuary in the Republic of Guinea is a poorly understood atypical mangrove system. Sediment dynamics in tropical estuaries are controlled by a combination of processes including river discharge, morphology, salinity, erosion and deposition processes, the settling of mud, physico-chemical processes and mangrove swamps. Here we present a consistent set of data aimed at characterising the estuary and thus, increasing our understanding of tropical systems, as well as studying the impact of human intervention in the region. Water elevations, current measurements, salinity, suspended sediment concentrations, bathymetry and sediment cover are presented following a 3 year survey of the Konkouré Estuary. Here we provide conclusive evidence that the Lower Konkouré is a shallow, funnel shaped, mesotidal, mangrove-fringed, tide dominated estuary, well mixed during low river discharge. The estuary becomes stratified during high river flows and spring tides whereas a salt wedge appears during neap tides. The Konkouré Estuary has been described as hypersynchronous, and has three terminal outlets, two of which are landward-directed, attesting to a tidal pumping effect, while the third one is seaward-directed, and is controlled by the mangrove. The suspended matter is transported by the tidal effect within the middle estuary and is therefore trapped in the Turbidity Maximum zone (TMZ). The location of the TMZ is river-controlled and is correlated with residual currents but not with salinity front. A dam, constructed 130 km upstream, impacts on the hydrodynamics, and reduces the salinity intrusion by about 25%. It causes an increased low river discharge whereas its efficiency over high river flows is unclear.     

Transport of nutrients and organic matter in a mangrove swamp

Field observations of the tidal transport of nutrients and organic matter in a mangrove swamp on Ishigaki Island, Okinawa, Japan revealed that groundwater flow from the swamp plays a significant role in increasing concentration of dissolved inorganic phosphorous and organic matter in a major channel. In contrast, dissolved inorganic nitrogen is transported from the mangrove swamps via surface water flow in the small channels of the swamp.     

Sources and transport of particulate organic carbon in the Amazon River and its estuary

Stable carbon isotope ratios have been used to study the sources of particulate organic carbon(POC) in the Amazon River and its tributaries, and to examine the transport of the riverine POC intothe oceanic environment. POC in the upper reaches of the Amazon River has more positive δ ~(13)C values(--24.5‰ to -- 28.0‰) than that in the middle and lower reaches (--27.9‰ to -- 30.1‰). Theδ ~(13)C of POC from the tributaries is generally more negative than that observed in the Amazon mainchannel. This δ ~(13)C datum shows that the POC in the Amazon main channel is predominantly of terres-trial origin rather than a result of in situ production. A large range of δ ~(13)C values (--17.5‰ to -28.4‰) is observed in the Amazon Estuary and plume. and is considered as the result of the mixing     

Microscale gradients of planktonic microbial communities above the sediment surface in a mangrove estuary

The microscale (1 and 4 cm sampling resolution) distributions of chemical (O₂, NH₃, NO₃⁻, NO₂⁻, PO₄³⁻) and biological (Chl a, phytoplankton, bacterioplankton, viruses) parameters were measured in the 16 cm of water immediately overlaying the sediment-water interface (SWI) within a temperate mangrove estuary in South Australia during December 2003 and March 2004. Shear velocities (u_*) during the time of sampling were very low (<0.1 cm s⁻¹), and we consequently predict that resuspension of organisms and materials was negligible. In December 2003, profiles were often characterised by strong gradients in nutrients and organisms, with the highest concentrations often observed within 0.5 cm of the SWI. Microscale patterns in O₂, NH₃, NO₃⁻ and NO₂⁻ indicated that a variety of anaerobic and aerobic transformation processes probably occurred at the SWI and within profiles. Strong gradients in PO₄³⁻ were indicative of nutrient flux across the SWI as a consequence of degradation processes in the sediments. Pico- and nanophytoplankton concentrations were strongly correlated (p < 0.01) to PO₄³⁻, and exhibited 12- and 68-fold changes in abundance, respectively, with highest concentrations observed nearest to the SWI. Several bacterial subpopulations were discriminated using flow cytometry and significant shifts in the ‘cytometric structure’ of the bacterial community were observed within microscale profiles. Two populations of viruses were correlated to the phytoplankton and low DNA (LDNA) bacteria, and each exhibited elevated concentrations within 0.5 cm of the SWI. In March 2004, microscale distributions of O₂ and nutrients were more homogenous than in December 2003, and dissimilar microbial community structure and patterns were observed above the SWI. The patterns observed here support the prediction that benthic processes can strongly influence the ecology of planktonic communities in the overlaying water, and provide further evidence for the existence of microscale variability amongst communities of aquatic microorganisms.     

Modulation of the particulate organic carbon flux to the ocean by a macrotidal estuary: Evidence from measurements of carbon isotopes in organic matter from the Gironde system

The isotopic composition of the organic carbon of the suspended particulate matter in the Gironde estuary and the Biscay shelf has been measured on a seasonal basis from 1977 to 1982. The δ¹³C values show a progressive change along the estuary and permit an estimate of the proportion of terrestrial carbon in each sample. It is estimated from these data that up to 80% of the continental POC is mineralized in the estuary and 3–16% of the riverborne flux is exported to the shelf.     

The vertical attenuation of light in Charlotte Harbor, a shallow, subtropical estuary, south-western Florida

The relative contribution of different components to the attenuation of photosynthetically active radiation was determined in the Charlotte Harbor estuarine system based on laboratory and in situ measurements. Agreement between laboratory and in situ measurements of the attenuation coefficient (k_t) was good (r² = 0·92). For all in situ measurements (n = 100), suspended, non-chlorophyll matter accounted for an average of 72% of k_t, dissolved matter accounted for 21%, suspended chlorophyll for 4%, and water for the remaining 3%.For individual determinations, suspended non-chlorophyll matter, dissolved matter, suspended chlorophyll, and water, each accounted for as much as 99%, 79%, 21%, and 18% of k_t. Attenuation by suspended matter was greatest near the mouth of the northern tidal rivers and was variable over the rest of the estuarine system. Attenuation by dissolved matter was greatest in the brackish tidal rivers and decreased with increasing salinity. Attenuation due to dissolved matter was positively correlated with water color. The source of the color was basin runoff. Wavelength transmittance changed along the salinity gradient. Maximum transmittance shifted from 500 to 600 nm in gulf waters to 650 to 700 nm in colored, brackish waters. Dissolved matter was primarily responsible for the large attenuation at short wavelengths (400–500 nm).     

Sedimentation within and among mangrove forests along a gradient of geomorphological settings

Coastal wetlands provide important ecological services to the coastal zone, one of which is sediment retention. In this study we investigated sediment retention across a range of geomorphological settings and across vegetation zones comprising coastal wetlands. We selected six coastal wetlands dominated by mangroves over a gradient from riverine to tidal settings in Southeast Queensland, Australia. Each site was comprised of three distinct vegetation communities distributed as parallel zones to the coast line: seaward fringe mangroves, landward scrub mangroves and saltmarsh/ cyanobacteria mat of the high intertidal zone. We measured suspended sediment retention and sedimentation rates. Additionally, in order to assess the origin of sediment transported and deposited in the mangroves, glomalin, a novel terrestrial soil carbon tracer, was used. Our results show a mean average sedimentation of 0.64 ± 0.01 mg cm⁻² spring tide⁻¹, which was variable within sites, regardless of geomorphological setting. However, geomorphological setting influenced spatial patterns of sediment deposition. Riverine mangroves had a more homogeneous distribution of sediments across the intertidal zone than tidal mangroves, where most sedimentation occurred in the fringe zone. Overall, the fringe zone retained the majority of sediment entering the coastal wetland during a tidal cycle with 0.90 ± 0.22 mg cm⁻² spring tide⁻¹, accounting for 52.5 ± 12.5% of the total sedimentation. The presence of glomalin in suspended sediments, and thus the relative importance of terrigenous sediment, was strongly influenced by geomorphological setting, with riverine mangroves receiving more glomalin in suspended solids than tidal mangroves. Glomalin was also differentially deposited within the vegetation zones at different geomorphological settings: primarily at the fringe zone of tidal mangroves and within the scrub zone of riverine mangroves. The differences we observed in the spatial distribution of sedimentation and the difference in the origin of the sediment deposited in riverine and tidal mangroves are likely to have an impact on ecological processes.     

Utilization of carbon sources in a northern Brazilian mangrove ecosystem

Carbon and nitrogen stable isotope ratios (¹³C and ¹⁵N) and trophic level (TL) estimates based on stomach content analysis and published data were used to assess the contribution of autotrophic sources to 55 consumers in an intertidal mangrove creek of the Curuçá estuary, northern Brazil. Primary producers showed δ¹³C signatures ranging between −29.2 and −19.5‰ and δ¹⁵N from 3.0 to 6.3‰. The wide range of the isotopic composition of carbon of consumers (−28.6 to −17.1‰) indicated that different autotrophic sources are important in the intertidal mangrove food webs. Food web segregation structures the ecosystem into three relatively distinct food webs: (i) mangrove food web, where vascular plants contribute directly or indirectly via POM to the most ¹³C-depleted consumers (e.g. Ucides cordatus and zooplanktivorous food chains); (ii) algal food web, where benthic algae are eaten directly by consumers (e.g. Uca maracoani, mullets, polychaetes, several fishes); (iii) mixed food web where the consumers use the carbon from different primary sources (mainly benthivorous fishes). An IsoError mixing model was used to determine the contributions of primary sources to consumers, based on δ¹³C values. Model outputs were very sensitive to the magnitude of trophic isotope fractionation and to the variability in ¹³C data. Nevertheless, the simplification of the system by a priori aggregation of primary producers allowed interpretable results for several taxa, revealing the segregation into different food webs.     

Role of riverine mangrove forests in organic carbon export to the tropical coastal ocean: A preliminary mass balance for the Fly Delta (Papua New Guinea)

A preliminary mass balance for organic carbon in the Fly Delta was constructed to determine the quantity and source of organic matter exported to the adjacent Gulf of Papua and Coral Sea. Total organic carbon input from the river to the delta is 1.7 × 10¹² g C yr^–1, composed almost equally of DOC and POC. Benthic and pelagic respiration in the delta accounts for 1.0 × 10¹² g C yr^–1, being a major sink for riverine organic carbon. Benthic flux measurements indicate that one third of all DOC entering the delta is taken up by sediments there. Mangrove forests export >3.0 × 10¹¹ g C yr^–1 POC to delta waters, and it appears that this mangrove carbon is exported to the adjacent shelf and deep sea. These results imply that little of the riverine supply of organic carbon reaches the Gulf of Papua, but that mangrove forests in the Fly and other rivers lining the gulf play a major role in river-shelf carbon exchange.     

Benthic macro-invertebrate community composition within a mangrove/seagrass estuary in northern New Zealand

In the tropics and sub-tropics, estuarine environments with mangrove and seagrass habitats provide important structures and resources for diverse communities of benthic organisms. However, temperate estuarine habitats, especially in mangrove areas, may differ significantly in their community associations and interactions. The community composition of benthic macro-fauna was investigated within temperate Matapouri Estuary, northern New Zealand. The density and distribution of fauna were sampled within six distinctive habitats (mangrove stands, pneumatophore zones, Zostera beds, channels, banks, and sand flats), within four sampling events between December 2002 and September 2003. Each type of habitat was replicated seven times within different locations in the estuary. Counts of all infauna and epifauna within four replicate cores were recorded from each habitat and location. Multidimensional scaling plots were used to identify differences in structure and composition of assemblages among habitats and locations within each sampling event. Results from these benthic samples indicate that Matapouri Estuary has a high overall biodiversity, with distinctive faunal assemblages found within different habitats, and some seasonal variations also apparent. In terms of both number of individuals and taxa per unit area, seagrass beds had the highest numbers and mangrove areas had the lowest numbers, with all other habitats in between. Some locations were found to support a high diversity of organisms across habitats, while other locations had high densities of a few species only. Several physical and biological differences between tropical/sub-tropical and New Zealand's temperate mangrove habitats are put forth as potential reasons for the lower density and diversity of the benthic component observed herein. Further ongoing studies aim to elucidate the structure and interactions within food webs in this estuarine ecosystem.     

海南儋州湾红树林区沉积有机质来源及碳储量

本文测定了海南儋州湾南岸柱状沉积物的粒度、总有机质参数(TOC、C/N和 δ13C)和类脂生物标志物含量,并通过端元混合模型使用红树植物特征标志物蒲公英萜醇含量、长链正构烷烃含量和δ13C值半定量区分了海南儋州湾南岸沉积有机质来源,尤其是红树林的贡献.另外,通过估算沉积物的有机碳储量来评估儋州湾红树林区域的储碳能力.在...     

九龙江口秋茄红树林恢复对底质磷的影响

以光滩为对照,分别在白礁选取5、6、8a生秋茄(Kandelia candel)人工林以及天然秋茄林为样地,在草埔头选取20a生和44a生秋茄人工林为样地,比较分析了福建九龙江口秋茄红树林恢复对底质总磷和有效磷的影响.结果表明:白礁和草埔头秋茄人工红树林的总磷和有效磷含量随红树林恢复时间的增加而增高.白礁天然秋茄林和草埔头秋茄人工林的总磷随底质深度增加而减少,有效磷在中下层含量较高.潮位对草埔头总磷有显著影响,由外滩到内滩,其总磷含量逐渐增加.九龙江口秋茄红树林早期恢复阶段的底质总磷和有效磷缺乏,5a生秋茄人工林底质总磷和有效磷分别为0.68g/kg和2.99mg/kg.     

A cross-system analysis of sedimentary organic carbon in the mangrove ecosystems of Xuan Thuy National Park, Vietnam

A cross-system analysis of bulk sediment composition, total organic carbon (TOC), atomic C/N ratio, and carbon isotope composition (δ¹³C) in 82 surface sediment samples from natural and planted mangrove forests, bank and bottom of tidal creeks, tidal flat, and the subtidal habitat was conducted to examine the roles of mangroves in sedimentation and organic carbon (OC) accumulation processes, and to characterize sources of sedimentary OC of the mangrove ecosystem of Xuan Thuy National Park, Vietnam. Sediment grain sizes varied widely from 5.4 to 170.2 μm (mean 71.5 μm), with the fine sediment grain size fraction (< 63 μm) ranging from 11 to 99.3% (mean 72.5%). Bulk sediment composition suggested that mangroves play an important role in trapping fine sediments from river outflows and tidal water by the mechanisms of tidal current attenuation by vegetation and the ability of fine roots to bind sediments. The TOC content ranged from 0.08 to 2.18% (mean 0.78%), and was higher within mangrove forests compared to those of banks and bottoms of tidal creeks, tidal flat, and subtidal sediments. The sedimentary δ¹³C ranged from − 27.7 to − 20.4‰ (mean − 24.1‰), and mirrored the trend observed in TOC variation. The TOC and δ¹³C relationship showed that the factors of microbial remineralization and OC sources controlled the TOC pool of mangrove sediments. The comparison of δ¹³C and C/N ratio of sedimentary OC with those of mangrove and marine phytoplankton sources indicated that the sedimentary OC within mangrove forests and the subtidal habitat was mainly composed of mangrove and marine phytoplankton sources, respectively. The application of a simple mixing model showed that the mangrove contribution to sedimentary OC decreased as follows: natural mangrove forest > planted mangrove forest > tidal flat > creek bank > creek bottom > subtidal habitat.