Bioremediation of oil spills in mangrove and salt marsh habitats in tropical Australia

This three-year project (1995-1998) assessed short term effects of commonly transported oils and in situ bioremediation on tropical Australian mangrove and salt marsh habitats. Bioremediation strategies were developed from laboratory, mesocosm and preliminary field studies. Laboratory and mesocosm experiments were carried out at the Australian Institute of Marine Science, Cape Ferguson. Field studies were carried out at Fisherman's Landing, Port Curtis, near Gladstone, within mangrove and salt marsh areas approved for reclamation by the Gladstone Port Authority.A series of flask experiments were conducted in the laboratory to test for the presence of hydrocarbon degrading micro-organisms in representative wetland habitats. Also tested was the biodegradation of selected oils (Gippsland crude, Arabian Light crude and Bunker C fuel), that are transported along the Australian coast. Potential inhibition of biodegradation by natural organics in the mangrove pore waters was investigated and the ability of an oxygen release compound (ORC) to stimulate biodegradative processes was evaluated.Aeration experiments were conducted to determine whether forced aeration and/or magnesium peroxide (an oxygen release compound) might provide significant increases in molecular oxygen saturation in the surface aerobic layer of sediments collected from under the common tropical mangrove trees, Rhizophora stylosa. Anaerobic sediments collected from a mangrove forest were oxygenated in mesocosms using forced aeration and magnesium peroxide oxygen concentrations were measured. In field experiments, the bioremediation strategy in mangroves involved forced aeration and the addition of nutrients, while in salt marsh habitats only nutrients were added. Two types of oil were used, Gippsland Light crude oil and Bunker C fuel oil.The relative rates of weathering and biodegradation of oil in experimental plots was measured and the influence of the bioremediation strategies tested. Chemical analysis of sediment cores was used to determine whether bioremediation affected the rate of penetration, dissipation or long term retention of the medium range crude oils. Sediments were collected at day 2 (40 hours), then approximately at 1, 2, 6 and 12 months post spill for mangroves, and day 2, then 1, 3 and 9 months post spill for salt marshes. Samples were analysed for total hydrocarbons and for individual alkane markers.The effects of the bioremediation strategy on oiled mangrove and salt marsh vegetation and fauna was also monitored. Leaf loss from mangrove canopies, herbivory rates and mortality of plants within the plots were recorded. Dead macro fauna were collected from the sediment surface after oiling, to determine species diversity, density and biomass. The effects of the bioremediation strategy, in mangrove plots treated with Gippsland crude oil, on the indigenous populations of heterotrophic and hydrocarbon-degrading bacteria was investigated. Micro-organisms were isolated from the plots and described morphologically. The overall project objective was to develop an information base, draft policies and guidelines on the use of bioremediation in tropical Australian foreshore environments so that bioremediation can be incorporated into overall planning and response process for oil spills in tropical Australia. To achieve this objective five tasks were undertaken, which had the following objectives: 1. to determine the effectiveness of bioremediation across mangrove and saltmarsh habitats exposed to a range of common oil types transported in tropical Australian waters2. to determine the potential negative impacts which may result from the use of bioremediation within each of the tropical foreshore habitats studied 3. to undertake a critical review of existing methods and techniques to bioremediate oily waste and opportunities for their use in tropical Australia4. to provide draft policies and guidelines on the use of bioremediation within each of the habitats studied5. to appraise the usefulness and costs of bioremediation techniques in oil spill clean-up in comparison to conventional methods

本项目为期三年（1995年至1998年），旨在评估常用运输原油及原位生物修复技术对澳大利亚热带红树林与盐沼生境的短期影响。本项目的生物修复策略基于实验室、中宇宙（mesocosm）及初步野外研究制定。实验室及中宇宙实验于澳大利亚海洋科学研究所（Australian Institute of Marine Science）费格森角分部开展。野外研究于格拉德斯通附近的柯蒂斯港渔民登陆点开展，实验区域为格拉德斯通港务局获批用于围垦的红树林与盐沼地块。

实验室中开展了一系列摇瓶实验，以检测典型湿地生境中是否存在烃类降解微生物。同时还针对沿澳大利亚海岸运输的指定油品（吉普斯兰原油、阿拉伯轻质原油及C级船用燃料油）的生物降解性能进行了测试。研究了红树林孔隙水中天然有机物对生物降解的潜在抑制作用，并评估了释氧化合物（oxygen release compound, ORC）对生物降解过程的刺激能力。

通气实验旨在探究强制通气及/或过氧化镁（一种释氧化合物）能否显著提升取自常见热带红树林——红海榄（Rhizophora stylosa）——下方沉积物表层好氧层的分子氧饱和度。从红树林中采集的厌氧沉积物通过强制通气与过氧化镁在中宇宙系统中完成增氧，并对氧气浓度进行了测定。野外实验中，红树林生境的生物修复策略包含强制通气与营养盐添加，而盐沼生境仅添加营养盐。实验使用两种油品：吉普斯兰轻质原油与C级船用燃料油。

本研究测定了实验地块中石油的风化与生物降解相对速率，并评估了生物修复策略的影响效果。通过沉积物岩芯化学分析，探究生物修复是否会影响中质原油的渗透速率、消散速率及长期留存情况。沉积物采样节点设置如下：红树林生境为溢油后第2天（40小时）、约1个月、2个月、6个月及12个月；盐沼生境为溢油后第2天、约1个月、3个月及9个月。对采集的样品进行总烃及单体烷烃标志物分析。

同时监测了生物修复策略对受油污染的红树林与盐沼植被及动物群落的影响。记录了实验地块内红树林冠层落叶量、植食率及植物死亡率。溢油后从沉积物表面收集死亡大型动物，以测定其物种多样性、密度与生物量。针对经吉普斯兰原油污染的红树林地块，探究了生物修复策略对本土异养菌及烃类降解细菌种群的影响。从实验地块中分离微生物并进行形态学描述。

本项目的总体目标为构建信息数据库，并起草澳大利亚热带潮间带环境生物修复技术的相关政策与指南，以便将生物修复技术纳入澳大利亚热带地区溢油事故的整体规划与响应流程。为达成上述目标，项目开展了五项任务，具体目标如下：
1. 评估生物修复技术对暴露于澳大利亚热带水域常见多种油品污染的红树林与盐沼生境的修复效果；
2. 明确在所研究的各热带潮间带生境中使用生物修复技术可能带来的潜在负面影响；
3. 批判性评述现有含油废弃物生物修复技术方法，并探讨其在澳大利亚热带地区的应用潜力；
4. 为在所研究的各生境中应用生物修复技术起草相关政策与指南；
5. 对比传统溢油清理方法，评估生物修复技术在溢油清理中的实用性与成本效益。