Collaborative Research: Arctic Oases - How does the delayed release of winter discharge from aufeis affect the ecosystem structure and function of rivers?

合作研究：北极绿洲 - 冬季排放的延迟释放如何影响河流的生态系统结构和功能？

• 批准号: 1504453
• 负责人: Michael Gooseff
• 金额: $ 7.45万
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-03-15 至 2019-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1504453&HistoricalAwards=false
• 关键词: Collaborative; Research; Arctic; Oases; How

This is a preliminary study to assess the potential effects of aufeis on the structure and function of arctic river-floodplain ecosystems. Aufeis are massive accumulations of ice common to many arctic rivers, particularly in northeastern Siberia and the North Slope of Alaska. River aufeis form during freeze-up when thickening surface ice and permafrost restrict river discharge, causing water to overflow existing ice. Successive cycles of overflowing and freezing of water from upstream groundwater sources accumulate enormous quantities of ice, with late-winter aufeis on some rivers attaining thicknesses of 3 to 5 meters, covering up to 20 square kilometers in some Alaskan fields (even larger in Siberia), and storing as much as a third of the annual discharge of the river in the form of ice. In addition, aufeis maintain an unfrozen base throughout winter due to the release of latent heat as water is converted to ice, which warms the underlying sediments, and a thick insulating layer of ice above. Although aufeis have been studied by hydrologists and are known to be required for winter and spawning habitat for important local fish species, understanding of their ecology is poor. In recognition of this, these investigators will conduct a targeted assessment of the ecological importance of a single aufeis field on the Kuparuk River, Alaska as a first step toward developing a hypothesis-driven research program. The investigators propose that aufeis be viewed as winter oases due to their wet bases that supply water and heat to otherwise frozen habitats. Aufeis also function as summer oases by providing a stable supply of water to riverbed and downstream habitats. This preliminary study will focus on assessing 1) river flow and nutrient chemistry above, within, and below the aufeis field, and 2) the potential for year-round, unfrozen habitat beneath the aufeis field. The investigators will collect water samples for nutrient analysis in transects extending 2.5 km upstream and downstream from the aufeis field. They will collect hourly data on river stage, temperature, and electrical conductivity along each transect. They will also install pairs of piezometers to depths of 1 meter and 2 meters to measure the vertical hydraulic gradient between the underlying aquifer and the surface channel, and dissolved oxygen, temperature, and electrical conductivity of hyporheic waters at these points. Measurements of vertical hydraulic gradient will determine whether river reaches are generally upwelling or downwelling. To estimate volume and the potential seasonal contributions of the aufeis to river discharge they will use precise digital elevation models created from low-altitude vertical photogrammetry. Year-round temperature and electrical conductivity records will provide data for simple end-member mixing analyses to determine the proportion of aufeis meltwater to the river during the thaw season. During freeze-up and into the winter, these records will provide estimates of potential downstream influences of the spring-water downstream of the aufeis if subsurface flow is maintained. In order to assess the vertical influence of aufeis, the investigators will instrument nine transects with digital temperature loggers. They anticipate that loggers directly under the aufeis will never record temperatures below freezing but that those outside the aufeis footprint will. The investigators also propose August and April ground-penetrating radar surveys to determine thaw depths. Finally, PVC wells penetrating about one meter below the surface will be used to sample small invertebrate animals living in river sediments and below aufeis. The project will support two masters-level graduate students and will involve two undergraduate field assistants in the summer fieldwork.

这是一项初步研究，旨在评估奥菲斯对北极河流洪泛区生态系统结构和功能的潜在影响。奥菲斯是许多北极河流常见的大量冰堆积物，特别是在西伯利亚东北部和阿拉斯加北坡。河水在结冰过程中形成，当时表层冰增厚，永久冻土限制河流流量，导致水溢出现有冰。上游地下水源的水不断溢出和冻结，积聚了大量的冰，一些河流的冬末冰层厚度达到 3 至 5 米，在阿拉斯加的一些田地覆盖了 20 平方公里（西伯利亚的面积更大） ，并以冰的形式储存了河流每年排放量的三分之一。此外，由于水转化为冰时释放潜热，使下面的沉积物变暖，而上面有一层厚厚的冰绝缘层，因此奥菲在整个冬季都保持着不冻的底部。尽管水文学家已经对奥菲进行了研究，并知道它们是当地重要鱼类冬季和产卵栖息地所必需的，但对其生态的了解还很有限。认识到这一点，这些研究人员将对阿拉斯加库帕鲁克河上单个奥菲斯田地的生态重要性进行有针对性的评估，作为制定假设驱动的研究计划的第一步。研究人员建议，奥菲斯被视为冬季绿洲，因为它们的潮湿基地可以为原本冰冻的栖息地提供水和热量。奥菲斯还通过为河床和下游栖息地提供稳定的水源而发挥夏季绿洲的作用。这项初步研究将重点评估 1) 奥菲斯田地上方、内部和下方的河流流量和营养化学，以及 2) 奥菲斯田地下方全年不冻栖息地的潜力。研究人员将在aufeis油田上游和下游延伸2.5公里的样带中采集水样进行营养分析。他们将每小时收集每条横断面河流水位、温度和电导率的数据。他们还将在1米和2米的深度安装成对的测压计，以测量底层含水层和地表水道之间的垂直水力梯度，以及这些点的溶解氧、温度和潜流水的电导率。垂直水力梯度的测量将确定河段总体是上升流还是下降流。为了估计奥菲斯的流量和对河流流量的潜在季节性贡献，他们将使用低空垂直摄影​​测量创建的精确数字高程模型。全年温度和电导率记录将为简单的端元混合分析提供数据，以确定解冻季节奥菲斯融水进入河流的比例。在结冰期间和进入冬季，如果地下水流保持不变，这些记录将提供对奥菲斯下游泉水潜在下游影响的估计。为了评估奥菲斯的垂直影响，研究人员将使用数字温度记录仪对九个样带进行检测。他们预计，奥菲斯正下方的伐木者永远不会记录到冰点以下的温度，但奥菲斯足迹之外的伐木者却会。调查人员还建议在八月和四月进行探地雷达调查以确定解冻深度。最后，穿透地表以下约一米的 PVC 井将用于对生活在河流沉积物中和奥菲斯以下的小型无脊椎动物进行采样。该项目将支持两名硕士研究生，并邀请两名本科生现场助理进行夏季实地考察。