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

Lead Research Organisation: University of Birmingham
Department Name: Sch of Geography, Earth & Env Sciences


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.

Planned Impact

Groups involved in catchment management and freshwater ecosystem conservation will benefit from new knowledge about the geomorphological and biotic response to different flooding regimes. This research will provide a key understanding of the effect of flooding variability in driving successional changes in aquatic communities and the recovery of these assemblages. The knowledge gained from our research into the dynamic evolution of these stream communities will help conservation managers to understand system shifts as they might occur due to environmental stresses and hence inform the development of future adaptation and mitigation strategies to climate change and increased incidence of extreme events like flooding. Despite the shortness of the project we will attempt to engage with the following groups:
a) Government agencies in the UK including the Environment Agency, Natural England and the Scottish Environmental Protection Agency.
b) Environmental Charities in the UK (e.g. Freshwater Biological Association) and Alaska (e.g. Alaska Conservation Foundation).
c) US Government agencies including the US National Park Service, the Biological Resources Division of the US Geological Survey, the US Environmental Protection Agency, the Alaska Department of Fish and Game and the Alaska Department of Conservation.
d) Researchers at the University of Alaska, Anchorage who have maintained long term records in a number of Alaskan streams (building on previous linkages with the University)
e) Using links developed as part of Milner, Brown and Klaar's work as part of a British Ecological Society special working group on the effects of extreme events on freshwater ecosystems (Jones et al., 2013), we will seek to communicate the findings to a broader group of UK policy makers and freshwater managers to explore possibilities for more general learning outcomes.
f) General public. There is a great desire for information on general topics about environmental change and flooding in the UK, Alaska, and further afield.

To maximise the utility and relevance of the research for the user community we have outlined a number of approaches of engagement and dissemination:
1. Workshops. We will organize one workshop with the National Park Service and other resource agencies in Alaska (e.g. US Geological Survey, Alaska Department of Conservation, EPA), which will be open to other regions of the Pacific Northwest. This will focus on the ecosystem effects of flooding regimes.
2. Direct discussions with existing contacts (in e.g. Natural England, Environment Agency) using, for example, the knowledge exchange capabilities of Klaar (who recently held a NERC/EA KE fellowship) and water@leeds core staff (e.g. Viki Hirst a recent NERC KE fellow).
3. Park Service Interpreters who deliver information to the 400,000 members of the public that visit Glacier Bay National Park annually. This will be through meetings with this group at the beginning of the 2015 field season to outline flooding regime in these streams or inviting them to join the fieldwork campaign (AM/LB/MK)
4. Visitors to Glacier Bay National Park. We will produce a flier that is available to explain the research to lay people - we have previously done this successfully in Denali National Park, Alaska.
5. Interested scientists in similar or related fields (AM/LB/MK) We will engage with other researchers, particularly those working in northern latitude river basins to better understand the implications of our results at a landscape/regional scale.
A range of reports, posters, presentations, fliers and press releases will be produced and disseminated to all interested parties.


10 25 50

publication icon
Milner AM (2018) River ecosystem resilience to extreme flood events. in Ecology and evolution

publication icon
Milner AM (2017) Glacier shrinkage driving global changes in downstream systems. in Proceedings of the National Academy of Sciences of the United States of America

publication icon
Woodward G (2016) The effects of climatic fluctuations and extreme events on running water ecosystems. in Philosophical transactions of the Royal Society of London. Series B, Biological sciences

Description Floods have a major influence in structuring river ecosystems. Considering projected increases in high- magnitude rainfall events with climate change, major flooding events are expected to increase in many regions of the world. However, there is un-certainty about the effect of different flooding regimes and the importance of flood timing in structuring riverine habitats and their associated biotic communities. In addition, our understanding of community response is hindered by a lack of long-term datasets to evaluate river ecosystem resilience to flooding. We showed that in a river ecosystem studied for 30 years, a major winter flood reset the invertebrate community to a community similar to one that existed 15 years earlier. The community had not recovered to the pre-flood state when recurrent summer flooding 9 years later reset the ecosystem back to an even earlier community. Total macroinvertebrate density was reduced in the winter flood by an order of magnitude more than the summer flood. Meiofaunal invertebrates were more resilient to the flooding than macroinvertebrates, possibly due to their smaller body size facilitating greater access to in-stream refugia. Pacific pink salmon escapement was markedly affected by the winter flood when eggs were developing in redds, compared to summer flooding, which occurred before the majority of eggs were laid. Our findings inform a proposed conceptual model of three possible responses to flooding by the invertebrate community in terms of switching to different states and effects on resilience to future flooding events. In a changing climate, understanding these responses is important for river managers to mitigate the biological impacts of extreme flooding effects.
Exploitation Route In many areas, the (re)-development of habitat complexity is increasingly advocated in river restoration efforts, but findings from this study appear to indicate that increased habitat complexity has the potential to effectively enhance the resilience of biotic communities and ecosystem functions to a 'new future' of extreme high flow events.
Sectors Environment