The influence of mangrove biomass and production on biogeochemical processes in the Kimberley Region, Western Australia

The physiochemical and biogeochemical properties of mangrove forests in different macrotidal coastal settings were measured. The forests were: a dense Aegiceras corniculatum forest in a ria embayment of Strickland Bay (SB1); a mature Rhizophora stylosa forest in a ria delta of the Kammergoorh River (SB2); an immature Avicennia marina stand on the steep banks of Mary Island North, off the mouth of the Fitzroy River (KS3); and a mature Avicennia marina forest at a creek mouth in Roebuck Bay, a bay with sediments dominated by carbonate deposits (BR4).Rectangular plots were marked out in each forest and plot size was determined by the area occupied by 100 trees: 48.6 m² at SB1, 324.0 m² at SB2, 600.0 m² at KS3, and 399.6 m² at BR4. Above ground biomass was estimated using previously established allometric relationships for Rhizophora stylosa and Avicennia marina. The allometric equations derived for Avicennia marina were also used for Aegiceras corniculatum, for which allometric relationships were not known. Net primary production (mmol C/m²/day) was estimated using the light interception method. Below ground fine root biomass was estimated from 3 replicate cores (1 m long x 6 cm internal diameter) in each plot. Cores were subdivided at 2 cm intervals to 40 cm and 5 cm intervals to 1 m. Roots were washed and frozen until analysis, when live and dead roots were separated using the colloidal silica method. Sediment samples were collected from the forest floor within each plot. Duplicate samples for grain size and water content were taken every 10 cm to a depth of 50 cm using 50 cc syringes with the needle ends cut off. Temperature, redox potential, and pH were measured at 2 cm intervals from duplicate cores (1 m long x 6 cm internal diameter). Samples for interstitial water were taken using the same corer. Porewater samples were obtained by cutting cores under a N2 atmosphere and squeezing sediment cakes (cut at 2 cm intervals) in a Teflon porewater apparatus. Samples were analyzed for SO4 Cl, Fe, Mn, NH4, NO2 + NO3, PO4, DOC, and Total CO2. Separate samples were analyzed for CH4. The same squeezed cakes and live and dead roots were dried, ground, and analyzed for total organic carbon (TOC), total carbon (TC), and total nitrogen (TN). TOC was measured on a Beckman TOC Analyzer, and TC and TN on a Perkin Elmer 2400 CHNS/O Series II Analyzer.Rates of iron and manganese reduction were estimated, using a core incubation method, from two sets of duplicate cores (20 cm long x 7 cm internal diameter), which were subdivided into 4 cm long sections in a N2 saturated box. Rates of sulfate reduction were measured on triplicate 2.7 cm diameter cores taken from each plot using the core injection technique. Gas (O2, CO2, CH4) and solute (Total CO2, DOC, Mn, Fe, HS-, Ca, SiOH, PO4, DOP, DON, NH4, NO2 + NO3) fluxes were measured via the glass chambers placed in replicate box core (0.027 m²) samples taken from each plot. The samples were immediately incubated on board ship in a shaded water bath maintained at ambient seawater temperature. Water used in all experiments was taken from the mangrove waterways closest to each site.Gas exchange across the air-sediment interface was measured in clear and opaque chambers to estimate benthic respiration and gross primary production during air-exposed periods (12 hours/day). Benthic respiration from submerged sediments was estimated from the total CO2 flux. An estimate of daily benthic respiration (total carbon oxidation, TCOX) at each station, taking into account the effect on sediment of roughly one-half day exposure to air and one-half day submergence, was derived by averaging the CO2 (exposed condition) and total CO2 (submerged condition) flux rates. Field studies were undertaken to determine the influence on sediment biogeochemistry of various ages and types of mangroves, located in different coastal settings (ria, riverine delta and a carbonate dominated bay) in a high energy environment.

本数据集测定了不同强潮海岸生境下红树林的物理化学与生物地球化学特征。所涉及的红树林样地包括：斯特里克兰湾（Strickland Bay）溺湾湾道内的致密桐花树（Aegiceras corniculatum）林（SB1）；卡姆古尔河（Kammergoorh River）溺湾三角洲内的成熟红海榄（Rhizophora stylosa）林（SB2）；菲茨罗伊河河口外玛丽岛北岸陡峭岸堤上的幼龄白骨壤（Avicennia marina）林分（KS3）；以及以碳酸盐沉积为主的罗巴克湾（Roebuck Bay）河口处的成熟白骨壤林（BR4）。每个红树林样地内均划定矩形样地，样地面积以100株树木所占的区域面积为准：SB1为48.6 m²，SB2为324.0 m²，KS3为600.0 m²，BR4为399.6 m²。地上生物量通过已发表的异速生长关系（allometric relationships）估算，其中针对红海榄与白骨壤建立的异速方程已被广泛应用；由于尚未明确桐花树的异速生长关系，本研究采用针对白骨壤建立的异速方程对其地上生物量进行估算。净初级生产力（单位：毫摩尔碳每平方米每天）采用光拦截法估算。地下细根生物量通过每个样地内的3根重复柱状样（长1 m，内径6 cm）估算：柱状样以2 cm间隔分层至40 cm深度，之后以5 cm间隔分层至1 m深度。将根系冲洗干净后冷冻保存，后续采用胶体硅胶法区分活根与死根并开展分析。沉积物样品采集自每个样地内的林地表层：采用截去针头的50 cc注射器，以每10 cm为间隔采集两份平行样品，取样深度达50 cm，用于沉积物粒度与含水率分析。采用两根重复柱状样（长1 m，内径6 cm），以2 cm间隔测定沉积物温度、氧化还原电位与pH值；间隙水样品采用相同的柱状采集器获取。孔隙水样品的采集方法为：在氮气（N₂）气氛下切割柱状样，使用特氟龙（Teflon）孔隙水装置对2 cm间隔切割得到的沉积物饼进行挤压，获取孔隙水。样品分析指标包括硫酸根（SO₄²⁻）、氯离子（Cl⁻）、铁（Fe）、锰（Mn）、铵根（NH₄⁺）、亚硝酸根+硝酸根（NO₂⁻+NO₃⁻）、磷酸根（PO₄³⁻）、溶解性有机碳（DOC）与总二氧化碳（Total CO₂）；另有单独的样品用于甲烷（CH₄）含量分析。将挤压得到的沉积物饼以及区分后的活根、死根进行干燥、研磨，分别测定总有机碳（TOC）、总碳（TC）与总氮（TN）含量：总有机碳采用贝克曼（Beckman）总有机碳分析仪测定，总碳与总氮采用珀金埃尔默（Perkin Elmer）2400 CHNS/O Series II元素分析仪测定。铁与锰的还原速率采用柱状样培养法估算：采集两组重复柱状样（长20 cm，内径7 cm），在氮气饱和的密闭箱内将其以4 cm为间隔分层。硫酸盐还原速率采用柱状样注射法，通过每个样地内采集的3根直径2.7 cm的重复柱状样测定。气体（O₂、CO₂、CH₄）与溶质（总二氧化碳、溶解性有机碳、Mn、Fe、硫氢根（HS⁻）、钙（Ca）、羟基硅（SiOH）、PO₄³⁻、溶解性有机磷（DOP）、溶解性有机氮（DON）、NH₄⁺、NO₂⁻+NO₃⁻）的通量通过放置于重复箱式柱状样（面积0.027 m²）中的玻璃舱室测定，箱式柱状样采自每个样地。样品采集后立即在船上置于遮光水浴中培养，水浴温度维持为原位海水温度；所有实验用水均采自各研究位点附近的红树林水道。通过透明与不透明两种舱室测定气-沉积物界面的气体交换速率，以估算每日12小时空气暴露期的底栖呼吸与总初级生产力；沉水沉积物的底栖呼吸速率通过总二氧化碳通量估算。考虑到沉积物每日约有半天暴露于空气、半天处于淹没状态，通过将空气暴露条件下的CO₂通量与淹没条件下的总CO₂通量取平均值，得到各站位的每日底栖呼吸（总碳氧化，TCOX）估算值。本野外研究旨在探究高能量海岸环境中，不同海岸生境（溺湾、河流三角洲与碳酸盐主导海湾）内不同年龄与类型的红树林对沉积物生物地球化学特征的影响。