Lake Powell, Hite UT 2014-2016 gas analysis

In 1963, the Glen Canyon Dam, in Hite Utah was completed, creating the Lake Powell reservoir along the Colorado River. The water levels of Lake Powell peaked in 1983 and have declined since, releasing over-pressure on the underlying sediment. This release in over-pressure created mud volcanoes, structures along the shoreline made of cavities that allow fluid and gases to rise to the surface and escape. Green house gases including methane are released from these structures, and to better understand how development of natural wetlands can result in unintended increased levels of greenhouse gas emissions, we asked 1) how much of each gas is generated or and whether the amount of each gas is changing through time and 2) how are these gases forming in the subsurface? We first measured the amounts of carbon dioxide (CO2), methane (CH4), and air (N) in volcano gas samples collected in 2014, 2015, and 2016. We found that from 2014 through 2016, methane levels from these volcanoes fluctuated significantly. In 2016, we looked at the amounts of carbon and hydrogen isotopes in the methane, which told us the gas is generated from microorganisms feeding on organic matter and is released during water-level fluctuations. We looked at mud volcanoes only located along the Lake Powell marina delta in Hite, Utah. The data spans geological structures restricted to one marina delta.

1963年，位于犹他州海特（Hite）的格伦峡谷大坝（Glen Canyon Dam）竣工，沿科罗拉多河形成了鲍威尔湖（Lake Powell）水库。鲍威尔湖水位于1983年达到峰值，此后持续下降，解除了下伏沉积物所承受的超压。该超压释放作用形成了泥火山（mud volcanoes）——沿湖岸线分布的孔洞构造，可使流体与气体上升至地表并逸散。此类构造会释放包括甲烷在内的温室气体。为深入理解天然湿地开发可能意外导致温室气体排放水平上升的机制，我们提出了两个研究问题：其一，各类气体的生成量如何，且各气体的排放量是否随时间发生变化；其二，这些气体在地下是如何形成的。我们首先测定了2014、2015及2016年采集的泥火山气体样本中的二氧化碳（CO₂）、甲烷（CH₄）及空气（N）含量。研究发现，2014至2016年间，这些泥火山的甲烷浓度出现了显著波动。2016年，我们对甲烷中的碳、氢同位素进行了分析，结果表明该气体源自以有机质为食的微生物代谢产物，并在水位波动过程中逸出。本次研究仅聚焦于犹他州海特鲍威尔湖码头三角洲沿岸的泥火山，本数据集所覆盖的地质构造仅局限于单个码头三角洲区域。