Solute Dynamics In Streams

The workshop revealed that we have some exciting ideas about factors controlling nitrogen dynamics in streams—and it introduced powerful new tools for rigorously testing them

A Productive Intersite Workshop

While the rest of the country was sweltering in the summer heat wave, 26 stream researchers gathered for three days (July 16-18) in the cool Southern Appalachians at Coweeta Hydrologic Laboratory for a NSF-sponsored workshop entitled “Transport and Cycling of Biologically Important Solutes in Streams: A Cross-Biome Comparison.” Planning for the workshop began at the 1993 LTER All Scientists Meeting when a group discussing cycling of nitrogen in streams and another discussing stream channel hydraulics and solute dynamics coalesced to plan a comparative study of solute dynamics in streams. Donna D’Angelo and Judy Meyer, Coweeta LTER (CWT), joined with Bruce Peterson, Arctic Tundra, ARC), to lead the workshop and plan the study. Beth O’Grady (CWT) organized logistics.

Four features contributed to the success of the workshop:

• Using models to analyze existing data prior to the workshop
• Hands-on experience with the models during the workshop
• The availability of user-friendly versions of the models to take home and use at individual sites
• Demonstrations of conservative tracer and stable isotope field experiments and analytical methods

Workshop participants included graduate and undergraduate students, technicians, post-does, and principal investigators from 10 stream sites: H.J. Andrews, Arctic, Bonanza Creek, Coweeta, Hubbard Brook, Kellogg, Konza Prairie and Luquillo LTER sites, as well as Walker Branch and Sycamore Creek research sites. The first day, participants compared physical, chemical and biological features of the streams they had been studying. Jack Webster and Jen Tank, CWT, led an afternoon field trip to Hugh White Creek, where the group conducted a conservative tracer addition experiment to learn the field techniques involved and how to analyze the resultant data using a program developed by Donna D’Angelo and Les Howard to estimate hydraulic parameters. A copy of that user- friendly program was given to all participants.

Use of stable isotopes to assess nitrogen cycling and transport was the theme of the second day. Bruce Peterson discussed insights gained from use of stable isotope additions in the Kuparuk River, Alaska. Using a model developed by Bruce and David Jones, participants made predictions on the expected distribution of ¹⁵N added to the stream based on our current understanding of inputs, exports, and cycling of nitrogen in the ecosystem. This is an extremely powerful tool that permits development of testable hypotheses on factors controlling nitrogen cycling in streams. Participants learned how to use the model and will now be able to parameterize it with local data at their home sites.

Before the workshop, Will Wolheim (ARC) used data supplied by four sites to develop predictions of isotope distribution. Since at one of these sites, Hugh White Creek, Bob Hall (CWT) had run a pilot ¹⁵NH₄ addition the month before, participants were able to compare the predicted isotope distribution to what was observed. Using a sample analysis completed in just two days at the Woods Hole stable isotope facility, they found they had predicted labeling of the consumers fairly well, but had underestimated the size of some of the nitrogen pools with long turnover times. This pilot experiment was a compelling demonstration of the model’s usefulness in showing which components of the stream are most in need of further research. Despite several power failures, participants were also able to analyze some ¹⁵N samples in real time with the assistance of Brian Fry and three Europa Scientific staff, who brought one of their mass specs to the workshop.

The final day, participants learned new stream mapping methods and planned an intersite comparison of nitrogen retention and cycling in streams. Responsibilities for proposal development were assigned, and a timetable was established. Overall, the workshop revealed that we have some exciting ideas about factors controlling nitrogen dynamics in streams. Now we have the tools to rigorously test them.

For more information: Judy L. Meyer, 706/542-3363, jMeyer@LTERnet.edu