Modeling the Influence of Hyporheic Exchange in Dry Valley
I received my
Ph.D. while working as a research associate at the Institute of Arctic
and Alpine Research (INSTAAR).
My Ph.D. research was funded by the National Science Foundation (NSF), through the McMurdo Dry Valleys
Long Term Ecological Research Project (MCMLTER).
Project Duration: 1-Jun-1998 - 30-Nov-2002
Diane McKnight (University of Colorado)
Ken Bencala (U.S. Geological Survey)
Rob Runkel (U.S. Geological Survey)
Berry Lyons (The Ohio State University)
Overview: The polar desert of the Dry Valleys is the largest ice-free portion of Antarctica, located at 78o S, 161o E, on the western edge of the Ross Sea. The climate is very cold, with annual air temperatures of –20 oC, and very dry, with less than 10 cm water equivalent of precipitation annually. The landscape is dominated by glaciers, barren expanses of rock and exposed soils, ice-covered closed basin lakes, and glacial meltwater streams. There are no large indigenous terrestrial plants or animals, although soils are inhabited by nematodes, rotifers, and tardigrades, and some streams and lakes have extensive benthic algal communities.
Dry Valley streams flow for 6 to 10 weeks per year. Melt water is produced at the glaciers during the austral summer. Flow rates recorded at stream gauges may vary from periods of little or no flow to peak flows on the order of 500 L s-1. Early stream flow may only saturate the porous space of the streambed, which must be filled before consistent channel flow can be established. Streambeds are generally composed of very sandy porous alluvium (porosity of 0.3 is typical), except in areas where a stone pavement has developed. The stone pavement is developed by broad, flattened sides of large rocks being positioned right-side-up due to the legacy of geologic timescale freeze-thaw interactions. The stone pavement provides a stable substrate for benthic algal mats. Streams vary in length from hundreds of meters to several km, and vary in gradient, ranging from 0.02 to 0.55. The very porous streambed material allows for the development of an extensive zone of wetted sediment adjoining the stream. Because of the cold climate, there is no regional groundwater system that is in contact with the streams. Thus, all water in this wetted sediment comes from the streams. Permafrost is generally found at 0.5 to 0.7 m below the ground surface, acting as a lower boundary to the vertical extension of this wetted zone. Laterally, the wetted zone may extend several meters from the stream edge. This wetted zone makes up the hyporheic zone of a typical Dry Valley stream, as water that enters may later return to the stream.
Looking upstream at streamflow disappearing into the streambed (above), and re-emerging downstream (right).
research was broken up into a few specific studies. Together, the
results of these studies increased our understanding of hydrologic
processes in Dry Valley streams of Antarctica, and yielded intriguing
ideas about hydrologic-biogeochemical interactions that may be
occurring in any stream system.
reactions and hyporheic exchange controlling solute concentration in
Dry Valley streams, Antarctica.
simply focused on the hydrologic control that the hyporheic zone plays
on Dry Valley stream hydrology, and the chemical weathering reactions
that are occurring in the hyporheic zone. The alluvium that makes up
the hyporheic zone of these streams is unconsolidated and relatively
fresh, geologically speaking. Such a situation is very vulnerable to
rapid glacial meltwater exchange, and consequent rapid chemical
weathering of the alluvial substrate.
Using stable isotopes of D and 18O to determine hyporheic zone flow paths in Antarctic streams.
study, 9 piezometers were placed in and near Green Creek to sample
subsurface water. The results show that subsurface water is generally
more enriched in D and 18O than flowing stream water,
suggesting a long residence time in the subsurface, during which
fractionation can occur (possibly due to evaporation, chemical
weathering, or biological processes). Further discritization of the
data suggested that the lateral extents of the hyporheic zone exchange
on much slower timescales than the portion of the hyporheic zone that
is directly under the stream.
Denitrification in Antarctic streams.
was intended to address the various controls N transformation dependent
on hydrologic exchange between 1) the stream and the benthic algal
mats, and 2) the stream and the hyporheic zone. The benthic algal mats
of Antarctic streams are sparsely distributed on the stream beds.
Stream tracer/nutrient enrichment data suggested that nitrite was being
produced very quickly from injected nitrate, the first step in
denitrification. Previous modeling efforts suggested that hyporheic
exchange was rapid in Green Creek. Further modeling suggested that
nitrate conversion could not be accomplished in the hyporheic zone
alone. The final modeling effort in this study discritized the benthic
algal mat and the hyporheic zone as two seperate storage zones.
MN, DM McKnight, WB Lyons, and AE Blum. 2002. Weathering
reactions and hyporheic exchange controls on stream water chemistry in
a glacial meltwater stream in the McMurdo Dry Valleys. Water
Resources Research, 38(12): 1279, DOI 10.1029/2001WR000834.
PA, DM McKnight, L Leff, JE Fulghum, and M Gooseff. 2002. Direct
observations of aluminosilicate weathering in the hyporheic zone of an
Antarctic Dry Valley stream. Geochimica et Cosmochimica Acta,
MN, JE Barrett, P Doran, AG Fountain, WB Lyons, AN Parsons, DL
Porazinska, RA Virginia, and DH Wall. 2003. Snow
patch influence on soil biogeochemical processes and invertebrate
distribution in the McMurdo Dry Valleys, Antarctica. Arctic,
Antarctic, and Alpine Research, 35(1): 92-100.
MN, DM McKnight, RL Runkel and BH Vaughn. 2003. Determining
long time-scale hydrologic flow paths in Antarctic streams. Hydrological
MN, DM McKnight, RL Runkel, and JH Duff. 2004. Denitrification
and hydrologic transient storage in a glacial meltwater stream, McMurdo
Dry Valleys, Antarctica. Limnology and Oceanography, 49(5):
MN, DM McKnight, and RL Runkel. 2004. Reach-scale cation
exchange controls on major ion chemistry of an Antarctic glacial
meltwater stream. Aquatic Geochemistry, 10(3): 221-238.
MN, WB Lyons, DM McKnight, BH Vaughn, AG Fountain, and C Dowling. 2006.
stable isotopic investigation of a polar desert hydrologic system,
McMurdo Dry Valleys, Antarctica. Arctic,
Antarctic, and Alpine Research, 38(1): 60-71.
DM, RL Runkel, CM Tate, JH Duff, and DL Moorhead. 2004. Inorganic
N and P dynamics of Antarctic glacial meltwater streams as controlled
by hyporheic exchange and benthic autotrophic communities. Journal
of the North American Benthological Society, 23(2):171–188.
Runkel, RL, DM McKnight, ED Andrews. 1998. Analysis of transient storage subject to unsteady flow: diel flow variation in an Antarctic stream. Journal of the North American Benthological Society, 17(2):143-154.
MN, and DM McKnight. 1999. Ion exchange
reactions controlling Li transport in the hyporheic zone of a polar
desert stream (poster). American Geophysical Union Fall Meeting,
San Francisco, CA.
MN, and DM McKnight. 2000. Phosphorous
uptake by benthic algal communities in Antarctic streams (oral).
North American Benthological Society Annual Meeting, Keystone,CO.
MN, DM McKnight, and PA Conovitz. 2000. Subsurface water temperatures
in polar desert streams (oral). American Society of Limnology and
Oceanography, Copenhagen, Denmark.
MN, DM McKnight, E Chatfield, C Jaros. 2000. The McMurdo Dry Valleys
stream hydrology (poster). All Scientists Meeting, Snowbird, UT.
MN, JE Berret, and PT Doran. 2000. Snow pack coverage and influence on
soils of a polar desert (poster). Ecological Society of America Annual
Meeting, Snowbird, UT.
MN, WB Lyons, AE Blum, and DM McKnight. 2000. Modeling weathering
reactions in the hyporheic zone (poster). American Geophysical
Union Fall Meeting, San Francisco, CA
MN and DM McKnight. 2001. Flow path dependent weathering rate
calculation methods for streams and watersheds (oral). American
Geophysical Union Hydrology Days, Ft. Collins, CO
MN, DM McKnight, and B Vaughn. 2001. Using
stable isotopes to discern hyporheic flow paths in Antarctic streams
(oral). North American Benthological Society Meeting, La Crosse, WI
DM, WB Lyons, and M Gooseff. 2001. Glacial meltwater streams in the
McMurdo Dry Valleys: Hyporheic zone controls and climate responses .
Geological Society of America Annual Meeting, Boston, MA
MN and DM McKnight. 2001. Determining long
hyporheic flow paths in Antarctic streams using D and 18O
isotopes as tracers (poster). American Geophysical Union Fall
Meeting, San Francisco, CA.
MN, DM McKnight, RL Runkel, JH Duff. 2003. Denitrification
in a glacial meltwater stream, McMurdo Dry Valleys Antarctica.
American Society of Limnology and Oceanography Aquatic Sciences
Meeting, Salt Lake City, UT.
This project is funded through the National Science Foundation's Office of Polar Programs.