Assessing the effects of EXtreme summer flooding on STREAM ecosystem successional processes (EXSTREAM).

影响河流生态系统的一个主要变量是干扰，特别是洪水造成的干扰。洪水维持了生态系统的多样性，并重新分配了河流中的能量、养分、沉积物和生物群。河流的生物群(如无脊椎动物和鱼类)可以通过抵抗干扰(抵抗)或迅速恢复(恢复能力)在洪水中幸存下来。虽然洪水对河流生态系统的干扰已经得到了较好的研究，但许多研究都有一个有限的干扰前系列数据来评估洪水的影响，很少有关于其演替发展的数据，也很少有研究比较不同的洪水情况。在阿拉斯加东南部的冰川湾国家公园，我们拥有长期连续的数据集(某些溪流长达35年)，详细描述了冰川消退后溪流群落的演变。这些数据为河流无脊椎动物和鱼类的初级演替(随时间变化)提供了独特的见解。对于其中一条溪流(Wolf Point Creek；WPC)，自1977年以来已经收集了一条非常详细的群落变化轨迹，表明这条溪流是如何从以少数摇蚊(不咬人的蚊子)为主的河流演变为最近包含无脊椎动物(昆虫/非昆虫)和幼年鲑鱼的多样化群落的河流。2014年夏天，冰川湾和阿拉斯加东南部普遍出现了创纪录的持续高降雨量，有记录以来最潮湿的6月(189毫米=231%，比正常高出231%)。此外，七月的降雨量为211毫米，较正常高180%，是有记录以来第二多雨的七月。7月12日，冰川湾的降雨量超过50毫米，4天内降雨量达到90毫米。八月持续有大雨，12日是有记录以来最多雨的八月。这在夏季造成了一系列大的、反复发生的和非典型的洪水事件(有些事件是中位数的8倍)，我们建议详细调查其影响。我们将从三个主要方面进行研究：(1)水浸对横跨不同年龄溪流的溪流栖息地和地貌的影响；(2)水浸对狼点溪基本演替结构(无脊椎动物、鱼类)的影响；(3)水浸对不同年龄溪流的影响，以提供不同演替发展阶段的溪流对水浸的反应资料。我们会将研究结果与2005年11月同一系统内一次受持续大雨(在少于72小时内超过650毫米)所驱动的大规模水浸的结果作比较。与920 MM的年平均降雨量相比，这次地震的规模是显而易见的。这项研究将提供一项独特的研究，比较一年中不同时间的不同洪涝状况对地貌和生物反应的影响。随着气候变化，这些极端洪水事件预计将在未来变得更加常见，因此我们的发现将为缓解战略提供参考，以管理洪水对生态系统完整性的影响。

A major variable influencing river ecosystems is disturbance, particularly that due to flooding. Floods maintain ecosystem diversity and redistribute energy, nutrients, sediment and biota in rivers. The biota of rivers (e.g. invertebrates and fish) may survive floods either by withstanding the disturbance (resistance) or recovering rapidly (resilience). Although disturbance to river ecosystems due to flooding has been relatively well studied, many studies have a restricted pre-disturbance series of data against which to evaluate flood effects and rarely in terms of their successional development and few have compared different flooding regimes. This in part reflects minimal continuous, year-on-year monitoring of stream communities against which to measure any disturbance effects.In Glacier Bay National Park in southeast Alaska, we hold long-term continuous data sets (up to 35 years for some streams) detailing stream community evolution following glacial retreat. These data have provided unique insights into primary succession (change over time) of stream invertebrates and fish. For one stream (Wolf Point Creek; WPC) a highly detailed trajectory of community change has been assembled since 1977, showing how the stream has evolved from one dominated by a few species of Chironomidae (non-biting midges) to one more recently containing a diverse community of invertebrates (insects/non-insects) and juvenile salmonids. The summer of 2014 has seen record-breaking prolonged high rainfall in Glacier Bay and southeast Alaska generally, with the wettest June on record (189mm = 231% higher than normal). Furthermore, in July precipitation was 180% greater than normal with 211mm, making it the second wettest July on record. Over 50 mm rain fell in Glacier Bay on July 12 and > 90 mm in a 4-day period. Heavy precipitation has continued into August with the 12th being the wettest August day on record. This has created a series of large, recurrent and atypical flood events during the summer (some events 8x median flow), the effects of which we propose to investigate in detail. Three major avenues of research will be followed: (1) the effect of the flooding on the stream habitat and morphology across streams of different ages, (2) an investigation of the effect of the flooding on the primary successional framework (invertebrates, fish) in Wolf Point Creek, and (3) an investigation into the effects of the flooding on streams of different ages to provide information on how streams at different stages of successional development respond to flooding.We will compare the results with those obtained from one massive flood disturbance in November 2005 in the same system but driven by continuous heavy rainfall (over 650mm in less than 72 hours). The size of this previous event is evident when compared against an average annual rainfall of 920mm. This research will provide a unique study in comparison of different flooding regimes at different times of the year with respect to geomorphological and biotic responses. These extreme flooding events are expected to become more common in the future with climate change, thus our findings will inform mitigation strategies to manage the effects of flooding on ecosystem integrity.