The effects of weather and dispersion on lethal and sublethal toxicity of oil to Gulf killifish across a range of salinities

Aim 1: Characterize the effects of weather and dispersion on lethal and sublethal toxicity of oil across a range of salinities. Thirty mesocosms were established with ~80L of oxic water overlaying ~15L of sediment with an oxic surface layer and an anoxic subsurface similar to conditions seen along the LA coast. Ten mesocosms each were prepared at 4, 12 and 18 ppt. Additional mesocosms were prepared as extra and/or pilot systems. Shading was prepared to equalize the light exposure and temperature between top and bottom row tanks. Following advice from scientists from EPA, it was decided that oil will be pre-weathered prior to addition to mesocosms. This pre-weathering is to mimic oil during a spill event. Volatile components are removed prior to exposure as they would in a spill. During pre-weathering oil (~1:5 oil:water; ~220mL per tank), corexit (~1:50 corexit:water), and oil/corexit mixture was weathered overnight in 4, 12, or 18 ppt water. Water and oil fractions were separated and equally divided into 3 aliquots (1, 4, and 16 week tanks). Aliquots were stored refrigerated in amber glass bottles with Teflon lids until addition to mesocosms. Weathering has been completed at 4 and 12 ppt and 18 ppt.研究目标1：表征不同盐度梯度下，风化与扩散过程对原油致死性与亚致死性毒性的影响。共设置30个中型实验生态系统（mesocosm），每个体系以约80升含氧水覆盖约15升沉积物，沉积物具备含氧表层与缺氧底层，与洛杉矶沿岸的自然环境一致。分别在盐度4、12、18ppt的条件下设置3组重复，每组10个中型实验生态系统；另设置若干中型实验生态系统作为备用体系与预实验体系。通过安装遮光装置，平衡顶层与底层排水槽的光照时长与温度。参考美国环境保护署（Environmental Protection Agency, EPA）科研人员的建议，我们决定在将原油投加至中型实验生态系统前，对其进行预风化处理。该预风化流程旨在模拟溢油事故发生后的原油状态：如实际溢油事故中发生的那样，在暴露实验前将移除原油中的挥发性组分。预风化阶段，将原油与水按1:5比例混合（每个水槽约220毫升）、科瑞克斯（Corexit）消油剂与水按1:50比例混合的制剂，以及原油-科瑞克斯混合物，分别置于盐度4、12、18ppt的水中过夜风化。随后将水相与油相分离，均分为3份等分试样，分别对应1周、4周与16周实验组水槽。将等分试样储存在带有特氟龙（Teflon）密封盖的棕色玻璃瓶中，冷藏保存直至投加至中型实验生态系统。目前盐度4、12、18ppt组的风化处理均已完成。