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漫滩生态系统结构和功能的潜在影响。奥菲斯是许多北极河流共同的巨大冰层堆积物，特别是在西伯利亚东北部和阿拉斯加的北坡。冰冻时，加厚的表面冰和永久冻土限制了河流的排放，导致水溢出现有的冰，从而形成了奥菲河。来自上游地下水来源的水连续溢出和冻结的循环积累了大量的冰，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野(西伯利亚更大)覆盖了多达20平方公里的面积，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变暖，以及上面厚厚的一层冰，奥菲斯在整个冬天都保持着一个未冻结的基地。尽管水文学家已经对奥菲鱼进行了研究，众所周知，奥菲鱼是当地重要鱼类越冬和产卵栖息地所必需的，但对其生态的了解很差。认识到这一点，这些研究人员将对阿拉斯加州库帕鲁克河上一块奥菲斯油田的生态重要性进行有针对性的评估，作为开发假设驱动的研究计划的第一步。研究人员提出，奥菲可以被视为冬季绿洲，因为它们潮湿的底部为原本冻结的栖息地提供水和热量。奥菲斯还起到夏季绿洲的作用，为河床和下游栖息地提供稳定的水源。这项初步研究将重点评估1)奥菲斯农田上方、内部和下方的河流流量和营养化学，以及2)奥菲斯农田下全年未冻结的栖息地的潜力。调查人员将在奥菲斯油田上下游2.5公里的横断面上收集水样进行营养分析。他们将每小时收集每条横断面的河水水位、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压力计，以测量地下含水层和地表水道之间的垂直水力梯度，以及这些点上潜水的溶解氧、温度和电导率。垂直水力坡度的测量将决定河段通常是上升流还是下升流。为了估计奥菲斯的流量和对河流流量的潜在季节性贡献，他们将使用由低海拔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为简单的终端成员混合分析提供数据，以确定融化季节期间奥菲斯融水到河流的比例。在冻结期间和进入冬季，这些记录将提供对奥菲斯下游泉水潜在下游影响的估计，如果地下水流保持不变的话。为了评估奥菲斯的垂直影响，调查人员将用数字温度记录仪测量9个断面。他们预计，直接在奥菲斯下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那些人会。调查人员还建议在8月和4月进行探地雷达测量，以确定融化深度。最后，钻入地表以下约一米的聚氯乙烯井将被用来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研究生，并将有两名本科生现场助理参加暑期实地考察。