EPS mechanisms in aggregation and dispersion of oil: roller tank experiment using Thalassiosira pseudonana culture and natural bacterial inoculum

This is an experiment of a series investigating the mechanisms driving the incorporation of oil into diatom aggregates using a water accommodated fraction (WAF) of oil. The diatom Thalassiosira CCMP strain #1335 was used, and WAF was prepared from Macondo oil (Deepwater Horizon oil spill in the Gulf of Mexico April 2010) and from Refugio oil (pipeline oil spill off California May 2015). Roller tank experiments mimic in situ conditions of the ocean in that continuous sinking of particles is possible (infinity water column). Once aggregates>1mm (operationally defined) have formed, they are harvested separately from the surrounding seawater, which contains non-aggregates cells or small aggregates. Both fractions are analyzed separately, so that the fraction of material incorporated within aggregates may be calculated. Samples were analyzed for cell abundance, particulate organic carbon (POC) and nitrogen (PON), the isotopes Carbon-13 and Nitrogen-15, estimated oil equivalent (EOE), and transparent exopolymer particles (TEP). Sinking velocity of aggregates was determined.

本系列实验旨在探究石油被硅藻聚集体包裹的作用机制，实验采用石油水容馏分（Water Accommodated Fraction, WAF）作为油相底物。实验使用海链藻属（Thalassiosira）CCMP菌株#1335，其对应的WAF分别由马孔多原油（2010年4月墨西哥湾“深水地平线”漏油事件泄漏原油）和雷富希奥原油（2015年5月加州近海输油管道泄漏原油）制备得到。滚罐实验可模拟海洋原位环境，能够实现颗粒物的持续沉降（等效于无限水深水柱）；当形成粒径大于1mm的聚集体（按操作定义界定）后，将其与周围海水中的非聚集体细胞或小型聚集体分离并单独收获，对两个组分分别开展分析，由此可计算出被包裹在聚集体内的物质占比。对样品依次检测细胞丰度、颗粒有机碳（Particulate Organic Carbon, POC）与颗粒有机氮（Particulate Organic Nitrogen, PON）、碳-13与氮-15同位素组成、等效石油当量（Estimated Oil Equivalent, EOE）以及透明胞外聚合物颗粒（Transparent Exopolymer Particles, TEP），同时测定聚集体的沉降速率。