Streams 101

January 6, 2010 by susanrwhitehead 36 Comments

We have spent the last couple of days helping out the “stream team”, a group of scientists working on stream ecology in Taylor Valley, Antarctica.  The stream team is headed by Dr. Diane McKnight, a limnologist at the University of Colorado, who has been working in Antarctica for over 20 years.  Stream ecology is an important topic here.  Streams flow only during the summer, when glaciers melt in the 24-hour sun and feed the lakes that are dispersed throughout the valleys.  As streams flow, they transport reactive chemical elements away from the glaciers, providing a critical source of nutrients to the lakes and stream basins.  The phrase “where water exists, life exists” is well illustrated here—the streams are the only places where we can actually SEE anything living at all (although there are microscopic organisms in soils and other places!).  As we walk down to the stream’s edge, we are careful not to tread on the delicate algal mats that grow along the margins of the water.  Despite the harsh conditions of the dry valleys, there are at least 30 taxa of cyanobacteria and green algae and 38 species of diatoms that have been found living in the streams here.

A beautiful view of Aiken Creek, which flows into Lake Fryxell

An algal mat near the Commonwealth Glacier

The stream team’s annual research efforts focus on measuring long-term changes in stream flow.  The flow of the streams is strongly tied to climate, since sunlight and temperature are what causes melting of the glaciers.   We can even see the changes in flow throughout the day as the sun circles the sky and moves across the faces of the 12 glaciers that surround the Fryxell Lake Basin where we are staying.  Stream flow is measured at 16 gauging stations throughout Taylor Valley and several more in other nearby valleys.  Each of these permanent stations is equipped with a big box full of equipment that continuously monitors streams throughout the Antarctic summer.  Inside the box there are data loggers that measure water temperature, conductivity, and stream stage.  Stream stage is essentially a measure of the depth of the water above a reference point.  This is measured by forcing pressurized nitrogen gas from a tank inside the box, through a length of tubing, and out an orifice that is installed at a particular height in the water.  The pressure in the tubing is a function of the height of the water above the orifice, so pressure in the tubing is recorded and converted into a measure of the stage of the stream.  This is called a pressure transducer system, ingenious!

Stream guaging station along Aiken Creek

Lee showing us the stream monitoring equipment inside the gauging box

In addition to these continuous measurements of stream stage, the stream team visits each station once per week to check the gauges, collect water samples, and take a manual measurement of stream velocity and area.  To measure stream velocity, a long measuring tape is stretched across the stream, and velocity is measured at regular intervals across the stream using a current meter, which consists of a propeller that is rotated by the action of the flowing water.  With knowledge of the velocity of water and the width of the stream, the stream team can calculate a mathematical relationship between the stream stage and the discharge, which is the total amount of water that is flowing through the stream at any particular point.  Stream discharge is what the stream team ultimately wants to know to help them understand the stream ecology, but as you can see sometimes in science we have to do multiple measurements and calculations to arrive at the variable we are most interested in!

Mike from the stream team measuring water velocity along the Onyx River in Wright Valley. He wears hip waders to stay dry while wading across the river, but it is still pretty cold in the 1.5º C water!

We have assisted the stream team with their measurements here in Taylor Valley over the last couple of days, and yesterday I was very lucky to get to join them on a trip to Wright Valley, the next valley over.  There we measured stream flow on the Onyx River, the longest river on the whole continent!  To get there, a helicopter picked us up at our field camp and we flew across the Asgard mountain range.  The views from the helicopter were unreal.

View from the helicopter on our way over the Asgard Range

Our helicopter landing site in the Wright Valley.

On the way home we couldn’t fly back the way we came, since the weather conditions had changed and the winds were too strong to make it over the tall peaks in the helicopter.  Instead we flew out over the Lower Wright Glacier to the entrance of Wright Valley, past Marble Point, along the edge of McMurdo Sound, and back up Taylor Valley to Lake Fryxell.  I was lucky to have the best seat in the helicopter (other than the pilot’s of course!) on the way home, and from the window I marveled at the landscape at the edge of the continent.  Most impressive was where the Wright Lower Glacier pushed into the McMurdo Sound.  Jagged pressure ridges form out of ice where the glacier meets the frozen sea and for me these images were an impressive reminder of the fact that these huge masses of ice are actually moving.  Hard to fathom.

Pressure ridges where the Wright Lower Glacier meets the sea ice of McMurdo Sound

We are now back at F6, our field camp on Lake Fryxell.  F6, by the way, is named after the stream gauging station that is located nearby.  There are 10 gauging stations around Lake Fryxell, numbered F1-10.  Streams that flow into other lakes are numbered with a different letter—B1-3 flow into Lake Bonney, H1-2 flow into Lake Hoare, etc.  Interesting to think that the stream gauging station was here before the field camp!

View of F6 from the helicopter as we returned from Wright Valley

Tomorrow we hopefully start with another project, looking at the effects of snowpack on soil chemistry and respiration.  After all the training and logistical challenges we had to get through just to get out to the field, we are so excited to finally be working full speed on science!

More soon…