The Gladstone field experiment, Queensland: Weathering and degradation of hydrocarbons in oiled mangrove and salt marsh sediments: Testing the effects of biomediation strategies

Experimental plots were established at three sites within mature stands of Rhizophora stylosa (FLNS1, FLNX8, FLNY9), in an area approved for reclamation by the Gladstone Port Authority. The sites were matched visually for tidal elevation, mangrove tree composition and condition, sediment composition and benthic invertebrate populations. Five plots ranging in area from 26 m² to 53 m² were constructed at each site, so that each plot enclosed at least 10 mangrove trees. Around each plot, prop roots were cut in a path about 0.5 m wide to allow installation of plastic retaining walls. The retaining walls were dug into the mud to a depth of 20 cm and supported to a height of 1 m. A gate was installed to allow tidal waters to move in and out while retaining the oil. Plots at three sites, located outside the reclamation area (FLNN, FLSS, CISS), which were established earlier for dispersant experiments were also used as undisturbed control plots for the mangrove bioremediation experiments. Five replicate plots were established at each of four sites (ABS-1, ABS-2, ABS-3 and ABS-4) in a Halosarcia sp. dominated salt marsh area, approved for reclamation by the Gladstone Port Authority. Enclosures consisted of circular walls of light weight plastic sheeting (Corflute), approximately 1.25 m in diameter, buried 7 cm into the sediment, and standing 33 cm above it. Regular tidal flushing in each plot, occurred through two plastic U tubes, each ~12 mm in diameter, and buried with their outlets on either side of the sheeting wall, within and outside the plot. The salt marsh plots did not have an undisturbed control plot.Before oiling, each mangrove plot was sampled to determine sediment grain size, hydrocarbon content and total organic carbon content. Replicate 7 cm diameter cores were collected from each plot, sliced and the 0-2, 10-12 and 20-22 cm sections from each replicate were pooled.One of five treatments was applied to each plot: Gippsland crude oil only; Gippsland crude oil and bioremediation; Bunker C fuel oil only; Bunker C fuel oil and bioremediation; and controls with no oil. The oils were preweathered prior to application and both oil types were applied at the rate of 5L/m² for for mangrove plots and 2L/m² for salt marsh plots. The average rate of dosing in each plot was calculated from four pooled surface sediment (0-2 cm) samples collected from each plot 40 hours after oiling. Bioremediation treatments were applied 40 hours after oiling. The bioremediation strategy used for the mangrove plots involved forced aeration of mangrove sediments and the addition of nutrients. For the salt marsh plots, only nutrients were applied. At 1, 2, 5 or 6 and 12 or 13 months, 4 replicate 7 cm diameter cores were collected from each mangrove plot, sliced and the 0-2, 10-12 and 20-22 cm sections from each replicate were pooled. For the salt marsh plots, cores were collected with 2 cm diameter plastic tubes after 1, 3 and 9 months. Four replicate 0-1 cm and the 9-10 cm core sections from each plot were combined for analysis. Observations, including the presence of roots, animals, burrows and oil were made before the samples were frozen for later analysis.The following analyses were conducted on the sediment samples: Water content of sediments; Total hydrocarbons determined by gas chromatography with flame ionisation detection (GC-FID); The percentage of unresolved hydrocarbons; Concentrations of individual isoprenoid and n-alkanes (µg/g dry weight); Ratios of isoprenoid to n-alkenes as biodegradation indices.At the end of the experiment (August, 1998), mangrove sediments were sampled for a range of nutrients, including total nitrogen, phosphorus and carbon. Sediment samples were taken from 0-5 cm deep cores using a plastic open mouth syringe, approximately 2 cm in diameter, placed in plastic screw top containers and kept on ice until returned to the AIMS laboratory at Townsville for analysis. Field trials were carried out to assess strategies developed to enhance in situ bioremediation of oil-contaminated sediments in mangrove and salt marsh habitats.

本研究于格拉德斯通港务局（Gladstone Port Authority）批准的填海区域内，于3处成熟柱果木榄（Rhizophora stylosa）林分样地（FLNS1、FLNX8、FLNY9）搭建实验样区。各样地在潮汐高程、红树植物组成与生长状况、沉积物组成及底栖无脊椎动物种群方面经目视匹配一致。每个样地设置5个面积介于26 m²至53 m²的样方，确保每个样方至少包含10株红树植物。围绕每个样方开挖宽约0.5 m的步道并剪除支柱根，以安装塑料挡墙；挡墙埋入泥层深度达20 cm，支撑高度达1 m，并安装闸门以允许潮汐水自由进出，同时阻隔油污。本研究同时采用此前为分散剂实验设立的3处填海区域外样地（FLNN、FLSS、CISS）作为红树生物修复实验的未受干扰对照样区。在格拉德斯通港务局批准的填海区域内的盐沼生境（以盐角草属（Halosarcia sp.）植物为优势种）中，于4处样地（ABS-1、ABS-2、ABS-3、ABS-4）各设置5个重复样方。围隔采用轻质塑料板（Corflute）搭建圆形挡墙，直径约1.25 m，埋入沉积物7 cm，露出沉积物表面33 cm；每个样方通过2根直径约12 mm的塑料U型管实现定期潮汐冲刷，U型管的管口分别埋设于挡墙内侧（样方内）与外侧（样方外）。盐沼样区未设置未受干扰的对照样方。投加油污前，对每个红树样方进行采样以测定沉积物粒度、烃类含量及总有机碳含量：采用直径7 cm的重复柱状采样器采集沉积物样，分层切割后合并每个重复样的0-2 cm、10-12 cm及20-22 cm层段样品。每个样方施加5种处理之一：仅施加吉普斯兰原油；施加吉普斯兰原油并进行生物修复；仅施加Bunker C燃料油；施加Bunker C燃料油并进行生物修复；以及无油对照组。所有油品在施加前均经预风化处理，红树样方与盐沼样方的油品施加量分别为5 L/m²与2 L/m²。投油40小时后，从每个样方采集4份混合的表层沉积物（0-2 cm）样品，以计算样方的平均投油量。生物修复处理于投油40小时后施加：红树样方采用的生物修复策略包括强制曝气红树沉积物及添加营养盐，盐沼样方仅施加营养盐。分别于投油后1、2、5或6个月以及12或13个月，从每个红树样方采集4份直径7 cm的柱状沉积物样，分层切割后合并每个重复样的0-2 cm、10-12 cm及20-22 cm层段样品；盐沼样方则分别于投油后1、3、9个月，采用直径2 cm的塑料采样管采集沉积物样，合并每个样方的4份重复0-1 cm层段与9-10 cm层段样品用于分析。在样品冷冻保存以待后续分析前，记录样方内根系、动物、洞穴及油污的存在情况等观测数据。对沉积物样品开展以下分析：沉积物含水率；采用气相色谱-火焰离子化检测器（GC-FID）测定总烃含量；未分辨烃类占比；单个类异戊二烯与正构烷烃的浓度（µg/g干重）；以及作为生物降解指标的类异戊二烯与正构烯烃比值。实验结束时（1998年8月），采集红树沉积物样品以测定一系列营养盐指标，包括总氮、总磷与总碳：采用直径约2 cm的塑料开口注射器采集0-5 cm深度的沉积物岩心，装入带螺旋盖的塑料容器中，置于冰上运输至汤斯维尔的AIMS实验室进行分析。本野外试验旨在评估用于强化红树与盐沼生境中石油污染沉积物原位生物修复的相关策略。