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

这是一项初步研究，旨在评估森林对北极河流-洪泛平原生态系统的结构和功能的潜在影响。冰冰是许多北极河流常见的大量积冰，特别是在西伯利亚东北部和阿拉斯加北坡。在冻结期间，地表冰层和永久冻土层的变厚限制了河流的流量，导致河水溢出现有的冰层，从而形成河堤。上游地下水水源连续不断的溢出和冻结循环积累了大量的冰，一些河流的冬末积雪厚度达到3到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的潜热使下面的沉积物变暖，以及上面厚厚的绝缘层冰，整个冬天，aufeis都保持着不冻结的基础。虽然水文学家已经研究过森林，并且已知森林是当地重要鱼类过冬和产卵的栖息地，但对它们的生态学了解甚少。认识到这一点，这些研究人员将对阿拉斯加库帕鲁克河上一个单一的森林保护区的生态重要性进行有针对性的评估，作为发展假设驱动的研究计划的第一步。研究人员提出，森林可以被视为冬季绿洲，因为它们潮湿的基地可以为其他冰冻的栖息地提供水和热量。森林还可以作为夏季绿洲，为河床和下游栖息地提供稳定的水源。这项初步研究将侧重于评估：(1)河流流量和森林林地上面、里面和下面的营养化学成分；(2)森林林地下面全年不冻栖息地的潜力。调查人员将在农田上游和下游2.5公里的横断面上收集水样进行营养分析。他们将每小时收集河段、温度和每个样带的电导率数据。他们还将在1米和2米的深度安装一对压力计，以测量地下含水层和地表通道之间的垂直水力梯度，以及这些点上地下水的溶解氧、温度和电导率。垂直水力梯度的测量将决定河道一般是上涌还是下涌。为了估计水量和河流流量的潜在季节性贡献，他们将使用从低空垂直摄影测量中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端元混合分析提供数据，以确定融水在解冻季节流入河流的比例。在冻结和进入冬季期间，如果地下水流保持不变，这些记录将提供对河流下游泉水潜在下游影响的估计。为了评估气温的垂直影响，研究人员将用数字温度记录仪测量9个断面。他们预计，森林正下方的伐木者永远不会记录到低于冰点的温度，但森林足迹之外的伐木者会。调查人员还建议在8月和4月进行探地雷达调查，以确定融化深度。最后，在地表下一米深的聚氯乙烯井将被用来对生活在河流沉积物和地下的小型无脊椎动物进行取样。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实地助理在夏季实地考察。

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.