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。太平洋西北地区的气候在仲夏和初秋几乎没有降雨，因此河流依靠冬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创历史新低，冬季积雪量严重减少，俄勒冈州、华盛顿州和加利福尼亚州的喀斯喀特山脉集水区的河流预计今年夏季流量将创历史新低。该项目将测量俄勒冈州一个大型森林流域的河流氮浓度变化，并确定在严重干旱条件下河流中的氮和生命是如何变化的。对太平洋西北地区的预报表明，与积雪减少相关的干旱将在未来更加普遍，并带来相关的生态、社会和经济后果，包括对在水源生态系统中繁殖的鱼类的影响。该项目将支持两名本科生实习生。由于它将与其他长期大学和美国林务局的研究项目联合开展，因此它将利用外联和更广泛的网络基础设施来推广成果，并与公众和森林管理者进行接触。由于地表水的稀释作用下降，预计极低流量条件将增加背景营养物浓度的可变性。在源流中，营养和光照都较高的地区初级产量较高，从而增强了生物地球化学活性。因此，确定氮可用性模式如何随着流量下降而变化，不仅对了解初级产量可能提高的地方，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的天气性采样工作，该工作将涵盖俄勒冈州喀斯喀特山脉12公里的四级流网络。在干旱年份工作将最大限度地确定养分有效性空间异质性的影响。

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.