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School of Geography

EXtreme summer flooding and STREAM ecosystem processes in Glacier Bay, Alaska (EXSTREAM)

Supervisors: Dr. Lee Brown (enquiries: l.brown(at)leeds.ac.uk) and Prof. Alexander Milner (University of Birmingham)

Project outline

The summer of 2014 has seen record-breaking prolonged high rainfall in Glacier Bay and southeast Alaska generally, with June being the wettest on record (189mm = 231% higher than normal) and July the second wettest. August 12th was the wettest August day on record and similar events occurred into September. These events have created a series of large, recurrent and atypical flood events (see Fig. 1) during the summer (some events at least 8x median flow).

 

 

 

These extreme rainfall events provide a clear opportunity to assess; (i) the short-term cumulative effects of a series of floods on stream geomorphology and biotic communities, (ii) the effect of the floods within a long-term (i.e. > three decades) successional framework, and (iii) how the stream ecosystems have responded to, and will subsequently recover from, these cumulative summer floods relative to the previous 2005 high-magnitude winter flood event1. These types of events are predicted to become more frequent with future climate change2, thus there is a pressing need to increase our understanding of their effects to inform the dynamics and management of river ecosystems. The role of floods has been controversial3, with much debate over the relative importance of an infrequent high magnitude flood versus the cumulative effects of frequent lower magnitude events. A major strength of this proposed project is our ability to address these issues in detail across replicated river catchments and for multiple groups of organisms. This PhD studentship will follow on from a NERC funded urgency application which has allowed Brown & Milner to resurvey impacted streams in the immediate aftermath of the flood. The studentship will have access to long-term pre-flood datasets whilst collecting additional data to monitor recovery.

Methodology

Channel cross section data will be collected within study reaches in five study streams using previous GPS fixes. Floodplain area, bankfull width, and channel bed measurements will be undertaken. Mesohabitats and the composition of channel geomorphic units will be quantified4. Tagged coarse woody debris with GPS locations will enable us to ascertain how it may have shifted following flooding. Long-term precipitation and temperature time series will be used to model discharge for the five study catchments. From the simulated discharge flood characteristics (i.e. magnitude, duration, frequency) will be extracted and the severity of the 2014 flood event will be evaluated against statistics for each catchment.

Macroinvertebrates will be collected using a coarser-mesh Surber sampler (ten replicates; 330-?m mesh, 0.1m2).  Juvenile coho salmon and Dolly Varden densities (CPUE) will be estimated with minnow traps baited with salmon eggs5. Changes in macroinvertebrate community trait composition will also be analysed following standard methods6

Benefits

The successful candidate will benefit from inter-disciplinary training in hydrology and aquatic ecology as part of the River Basin Processes and Management research cluster in the School of Geography, and as part of the wider water@leeds network (i.e. water@leeds: ecology group). Emergency field procedures, first aid in remote areas and small boat handling and Glacier Bay field protocols will also be covered in detail. Additional training delivered at Birmingham will include techniques in evaluating physical stream habitat, identifying macroinvertebrates, sampling juvenile fish and undertaking hydrological modelling. Statistical techniques will be acquired to integrate across this interdisciplinary project. The nature of the project means that the student will be trained in project specific research methods including river water quality analysis, macroinvertebrate/fish identification and applied statistics for analysing biological data, both internally and at external workshops. An additional important part of the training will be to attend national and international conferences to present results and gain feedback. The student will be encouraged to submit high quality papers for publication during the project.

Possible timeline:

Year 1:  Project development and DR training. Examine techniques for sampling and flood modelling. Learn techniques of identifying macroinvertebrates and fish.  Field season in Alaska in summer of 2016.

Year 2:  Laboratory analyses and work up data from first field season and make preparations for second field season in summer of 2017.

Year 3: Continue working on data collected and put in the context of the long term records and make comparison with previous flood effects. Paper and conference presentation and thesis preparation.

Further reading:

  1. Milner, A.M., A.E. Robertson, M. McDermott, M.J. Klaar and L.E. Brown (2013). Major flood disturbance alters river ecosystem evolution. Nature Climate Change. 3:137-141.
  2. Coumou, D., and S. Rahmstorf, 2012. A decade of weather extremes. Nature Climate Change 2, 491-496
  3. Stanley, E.H., S.M. Powers, and N.R. Lottig (2010). The evolving legacy of disturbance in stream ecology: concepts, contributions, and coming challenges. Journal of the North American Benthlogical Association. 29, 67-83.
  4. 4Klaar, M.J., I, Maddock, and A.M. Milner. (2009) The development of hydraulic and geomorphic complexity in recently formed streams in Glacier Bay National Park, Alaska. River Research and Applications. 25: 1331-1338
  5. Milner, A.M., E. Knudsen, C. Soiseth, A.L. Robertson,  D. Schell ,  I.T. Phillips, and K. Magnusson. (2000) Stream community development across a 200 year gradient in Glacier Bay National Park, Alaska, USA. Canadian Journal of Fisheries and Aquatic Sciences. 57:2319-2335.
  6. Brown, L.E. and A.M. Milner (2012) Rapid loss of glacial ice reveals stream community     assembly processes. Global Change Biology 18:1365-2486.

Informal enquiries should be directed to Lee Brown l.brown(at)leeds.ac.uk. Further details about postgraduate research degrees at the School of Geography, University of Leeds can be found here.