RAPID: How does reduced snowpack in winter impact the availability and processing of stream nutrients in summer?

积雪减少是美国西部日益严重的环境、社会和经济问题。太平洋西北部的气候在仲夏和初秋期间降雨量很少，因此溪流依靠冬季积雪的遗产在春季和夏季保持较高的流量。2015年，喀斯喀特山脉的积雪量处于创纪录的低水平，冬季积雪量严重减少，预计今年俄勒冈州、华盛顿和加州的喀斯喀特山脉集水区的河流将经历创纪录的夏季流量。该项目将测量俄勒冈州一个大型森林流域溪流氮浓度的变化，并确定在这些严重干旱条件下溪流中的氮和生命如何变化。对太平洋西北部的预测表明，与积雪减少有关的干旱在未来将更加常见，并带来相关的生态、社会和经济后果，包括对在上游生态系统中饲养的鱼类的影响。该项目将支持两名本科实习生。由于它将与其他长期大学和美国林务局的研究项目联合进行，它将利用推广和更广泛的网络基础设施来扩展结果，并与公众和森林管理人员进行接触。随着地表水稀释作用的下降，极端低流量条件预计会增加背景营养物浓度的变化。在源头溪流中，营养物和光照都升高的地区具有较高的初级生产力，这反过来又增强了生物地球化学活动。因此，确定氮供应模式如何随着流量的下降而变化，不仅对了解初级生产力可能提高的地方，而且对了解生物地球化学热点可能发展的地方都很重要。这项工作将量化无机氮，光，和原位叶绿素a的天气采样工作，将包括12公里的四阶流网络在俄勒冈州的喀斯喀特山脉。在干旱年份开展工作将最大限度地发挥潜力，以确定养分供应的空间异质性的影响。

Declining snowpack is a growing environmental, social and economic concern across the western United States. The climate of the Pacific Northwest provides little rainfall during middle of summer and early fall, so that streams rely on the legacies of winter snow to maintain higher discharge during spring and into the summer. In 2015, the snowpack was at record low levels in the Cascade Mountains and with severely diminished snowpack in winter, streams that drain Cascade Mountain catchments across Oregon, Washington and California are expected to experience record low summer discharge this year. This project will measure the variation in stream nitrogen concentrations across a large forested watershed in Oregon and determine how nitrogen and life in streams change under these severe drought conditions. Forecasts for the Pacific Northwest suggest that droughts associated with reduced snowpack will be more common in the future, with associated ecological, social and economic consequences, including effects on fish species that rear in headwater ecosystems. This project will support two undergraduate interns. Because it will be conducted in association with other long-term university and U.S. Forest Service research projects, it will leverage the outreach and broader network infrastructure for extending results and engaging with the public and forest managers.Extreme low flow conditions are expected to increase variability in background nutrient concentrations as dilution by surface water declines. In headwater streams, areas with both elevated nutrients and elevated light have higher primary production which in-turn enhances biogeochemical activity. Determining how patterns of nitrogen availability change as flow declines is therefore important in understanding not only where primary production may be elevated but also where biogeochemical hotspots are likely to develop. This work will quantify inorganic nitrogen, light, and in situ chlorophyll a in a synoptic sampling effort that will encompass 12 km of a 4th-order stream network in the Cascade Mountains of Oregon. Working in a drought year will maximize the potential to identify the influences of spatial heterogeneity in nutrient availability.