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.

本文是对北极河流洪泛区生态系统结构和功能的初步研究。奥菲斯是许多北极河流常见的大量冰堆积，特别是在西伯利亚东北部和阿拉斯加北坡。当地表冰层变厚，永久冻土层限制了河流的流量，导致水溢出现有的冰层时，河流就会结冰。上游地下水源的水连续不断地溢出和冻结，积累了大量的冰，一些河流的冬末冰厚达3至5米，在阿拉斯加的一些地区覆盖了20平方公里（在西伯利亚甚至更大），并以冰的形式储存了多达三分之一的河流年流量。此外，由于水转化为冰时释放出的潜热使下面的沉积物升温，以及上面厚厚的绝缘层，aufeis在整个冬季都保持着不冻的基础。虽然水文学家已经研究过奥菲鱼，并且知道它们是当地重要鱼类冬季和产卵栖息地所必需的，但对其生态的了解很少。认识到这一点，这些研究人员将对阿拉斯加Kuparuk河上一个单一的aufeis油田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。研究人员认为，奥菲被视为冬季绿洲，因为它们潮湿的基底为其他冰冻的栖息地提供了水和热量。奥菲斯还作为夏季绿洲，为河床和下游栖息地提供稳定的供水。这项初步研究将重点评估1）奥费斯油田上方、内部和下方的河流流量和营养化学，以及2）奥费斯油田下方全年不结冰栖息地的潜力。调查人员将从奥菲斯油田上游和下游2.5公里处收集水样进行营养分析。他们将每小时收集一次关于河流水位、温度和沿着电导率的数据。他们还将在1米和2米深的地方安装成对的压力计，以测量底层含水层和表面通道之间的垂直水力梯度，以及这些点的溶解氧、温度和潜流沃茨的电导率。垂直水力梯度的测量将确定河流河段通常是上升流还是下降流。为了估计水量和奥菲对河流流量的潜在季节性贡献，他们将使用由低空垂直摄影测量创建的精确数字高程模型。全年的温度和电导率记录将提供简单的端元混合分析的数据，以确定在解冻季节奥菲斯融水的比例到河流。在封冻和进入冬季期间，这些记录将提供估计的潜在下游影响的泉水下游的aufeis，如果地下水流保持。为了评估aufeis的垂直影响，研究人员将用数字温度记录仪对9个断面进行测量。他们预计，直接在奥菲斯下面的伐木工人永远不会记录到低于冰点的温度，但那些在奥菲斯足迹之外的人会。调查人员还建议在8月和4月进行探地雷达调查，以确定解冻深度。最后，将使用PVC威尔斯井穿透水面以下约一米，对生活在河流沉积物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水平的研究生，并将涉及两名本科生的实地助理在夏季实地考察。