Biocomplexity in the Environment:
Emergent Properties of Alluvial River Flood Plains
Principal Investigators:
Jack
Stanford, FLBS
Ragan Callaway, F.
Richard Hauer, John
Kimball, Mark
Lorang – FLBS and UM Division of Biological Sciences
Steven Sheriff, William Woessner – UM Geology
Geoff Poole – University of Georgia
Daniel Fagre – US Geological Survey
William Swaney – Salish and Kootenai College
The conceptual foundation
of this multi-disciplinary project is that river flood plains
are regional centers of ecological organization. This system
is dependent on interactions among dynamic, nonlinear physical
and biological processes linking water, heat and materials
(biota, sediment, plant-growth nutrients) flux and retention
to fluvial landscape change. Key processes driving biogeochemical
patterns and cycles include flood-caused scour and sedimentation
(cut and fill alluviation), routing of river water and nutrients
above and below ground, channel movement (avulsion) and production
and entrainment of large wood. Groundwater routing through
the flood plain and upwelling back to the surface involves
penetration of river water into zones of high hydraulic conductivity
(subsurface paleochannels) within the bed sediments that are
created by channel scour and subsequent filling with sorted
gravel and cobbles. Strong interactions between short-duration,
high stream-power floods, channel and sediment movement, increased
roughness due to presence of vegetation and dead wood and
upwelling of groundwater creates a complex, dynamic distribution
of resource patches, which we refer to as the shifting habitat
mosaic.
Floodplain springbrook
at Nyack
This mosaic promotes biodiversity and complex
food webs that sequester and transform energy and materials. Important
modifiers of system dynamics include floods, drought, wildfire,
human activities (e.g., dams and revetments) and invasions of nonnative
species.
An idealized view of the 3-D structure of alluvial river ecosystems, emphasizing dynamic longitudinal, lateral and vertical dimensions and the role of large wood eroded from the riparian zone. This landscape, produced by the legacy of cut and fill alluviation, is linked to the natural-cultural setting of the catchment. Hence, the size of the flood plain and extent of its alluvial aquifer (hyporheic and phreatic ground waters) can be substantially larger than indicated here, extending to the valley walls. We focus on the biogeochemistry of surface and ground water interactions on such flood plains, especially as mediated by complex interstitial flow paths (paleochannels) within the channel and riparian bed sediments.
Using this conceptual foundation and implications
of two decades of research on expansive gravel-cobble flood plains
in western USA rivers, we are investigating a set of working hypotheses
that address emergent properties of these and other similar flood
plains. We use a complex hydrologic model to route water through
the shifting habitat mosaic of our main study site, the Nyack Flood
Plain Research Natural Area of the Flathead River, Montana. This
model is novel because it is spatially explicit and 3-dimensional,
linking surface and subsurface features and processes. Guided by
our hypothesis-oriented field studies and experiments, we are improving
and integrating this hydrologic model with new channel change, heat
flux and nutrient cycling models in a dynamic flood plain biogeochemical
simulator that is initialized from remote sensing information. The
goal is spatially explicit quantification of heat and nutrient fluxes
in relation to the habitat dynamics. This computational framework
will be developed and validated at our Montana study site, and model
results compared to other sites in the USA, Europe and the Russian
Far East.
Conceptual model of
floodplain biocomplexity and system dynamics. Text size represents
relative spatial and temporal scales at which dynamics occur;
large text represents course spatial and/or long temporal
scales, small text notes fine spatial and/or short temporal
scales. Blue arrows represent predominantly physical interactions
while green arrows represent biogeochemical interactions.
Grey dashed circles represent cyclical interactions and feedback
mechanisms studied primarily by specific academic disciplines
on our team (shown in gray italic text).
The project includes an educational component
that proactively links the floodplain research with the summer
academic program at the Flathead Lake Biological Station,
the natural resources curriculum of our local Native American
college (Salish and Kootenai College) and an annual national
workshop for environmental professionals and high school teachers.
Classes collect data that compliment the research and present
the results in a public web site using contemporary informatics
and visualization tools. Support and guidance is provided
for 4 focused undergraduate research projects annually. Students
are recruited through a national competition. Also 2 M.S.
and 5 Ph.D. students in river ecology are being trained within
this multidisciplinary research environment.
This research portends to shift the science
toward a nonlinear, more dynamic view that emphasizes energy
dispersion and materials retention and cycling within large
flood plains as the primary organizing elements of regional
landscapes and ecosystems. Our education program cuts across
cultural and professional boundaries and adds significant
ecological literacy by providing hands-on demonstration of
the importance of river flood plains in maintaining regional
ecological organization.
Above: FLBS
graduate students discuss the Nyack floodplain with
Salish Kootenai College students
FLBS summer
session students learn ecology with hands-on techniques
and onsite lectures
Emergent Properties of Flood Plain
Rivers
The porous floodplain bed sediments
are laced with zones of preferential flow or paleochannels,
which appear to be the cobble-boulder beds of previous river
channels that have filled with upwardly-fining gravel after
avulsion events.
Subsurface paleochannels route river
water at high velocities (up to 10 cm/s) from localized
injection points (avulsion nodes) through the aquifer; spring
brooks, ponds and other distinctive alluvial wetlands occur
wherever saturated paleochannels intersect the surface.
Abundant, large-bodied invertebrates
are top consumers in species-rich food webs of the floodplain
ground waters and are substantially more abundant in paleochannels
than in the adjacent bed sediment matrix.
The groundwater food web is driven
by epilithic bacteria that metabolize dissolved organic
matter from the riparian zone and the river; C, N and P
transformations in the groundwater stimulate productivity
bursts in upwelling zones.
Entrainment of large wood is critical
for the initiation of the floodplain riparian forest over
the long-term.
Browsing animals shape the ultimate
characteristics of floodplain forests.
Regional biodiversity of plant and
animal assemblages maximizes on river flood plains because
of diverse environmental conditions and resource gradients
within the expansive 3-dimensional, shifting habitat mosaic.
Project Papers
Harner, M. J. and J. A. Stanford. 2003. Difference
in cottonwood growth between a losing and a gaining reach of an
alluvial flood plain. Ecology (in press)
Poole, G. C., J. A. Stanford, S. W. Running, C. A. Frissell and
B. K. Ellis. 2003. Floodplain Hydrologic
Complexity: Modeling Interactions between River Discharge, Geomorphology,
and Hyporheic Flow Dynamics. Ecological Applications
(submitted).
Pre-project Papers
Craft, J. A., J. A. Stanford and M. Pusch. 2002. Microbial
respiration within a floodplain aquifer of a large gravel-bed river.
Freshwater Biology 47(2):251-261.
Mouw, J. E. B. and P. B. Alaback. 2003. Putting
floodplain hyperdiversity in a regional context: An assessment of
terrestrial - floodplain connectivity in a montane environment.
Journal of Biogeography in press.
Mouw, J. E. B., J. A. Stanford and P. B. Alaback. 2003. Influences
of FluvialProcesses and Hyporheic Exchange on Floodplain Plant Diversity
and Productivity. Oikos (submitted)
Pepin, D. M. and F. R. Hauer. 2002. Benthic
responses to groundwater-surface water exchange in two alluvial
rivers in northwestern Montana. Journal of North
American Benthological Society 21(3):370-383.
Poole, G. C., J. A. Stanford, C. A. Frissell and S. W. Running.
2002. Three-dimensional mapping of geomorphic
controls on flood-plain hydrology and connectivity from aerial photos.
Geomorphology 48(4):329-347.
Whited, D. C., J. A. Stanford and J. S. Kimball. 2003. Application
of airborne multispectral digital imagery to characterize the riverine
habitat. Verh. Internat. Verein. Limnol.
28(3):1373-1380.
