Diurnal Biogeochemical Processes in Rivers, Lakes, and Shallow Groundwater

The U.S. Geological Survey (USGS) and Montana Tech of the University of Montana are co-sponsoring the Special Session "Diurnal Biogeochemical Processes in Rivers, Lakes, and Shallow Groundwater" at the 2009 Geological Society of America Annual Meeting—From Volcanoes to Vineyards: Living with Dynamic Landscapes—in Portland, Oregon, on October 18-21, 2009. The abstracts submission period will begin in April 2009.

Description of Meeting

Graph of diurnal variation of metals in Prickly Pear Creek, Montana (Larger version)

A growing body of literature has documented the importance of diurnal (24-h, or "diel") biogeochemical cycles in rivers and lakes. Diurnal changes in parameters such as temperature, pH, flow, and dissolved oxygen have been widely recognized but only recently have concentrations of other constituents, such as dissolved and particulate trace metals, rare earth elements, metalloids, dissolved organic carbon, and nutrients, been shown to vary diurnally. Similarly, the isotopic composition of dissolved oxygen and inorganic carbon as well as the redox speciation and isotopic composition of dissolved nitrogen in streams change diurnally due to microbial metabolism. Comparable changes in the concentration and isotopic composition of dissolved oxygen may even occur in shallow groundwater (i.e., through leakage of O2 from the roots of plants).

Despite a large body of recent literature, the mechanisms responsible for the 24-h fluctuations are widely debated, with a growing consensus that a combination of physical, chemical, and biological processes are involved. In addition, secondary effects that diurnal cycles might have on aquatic animals are poorly known. This session intends to bring together hydrologists, biologists, geochemists, and ecologists to discuss field studies, laboratory experiments, theoretical modeling, and field measurement techniques. With this cross-disciplinary synergy, a deeper understanding of the interrelationships between the diurnal processes being studied in different scientific disciplines will be developed.

Besides being important to studies of rivers and lakes, understanding diurnal processes is critical for regulatory agencies. What you measure from a particular stream depends on what time of day you sample it. For example, in certain streams in Montana, concentrations of dissolved zinc (a toxic substance) vary over 500% between day and night in a very robust, reproducible fashion. Given this observation, how should such streams be monitored for spatial (synoptic) or long-term trend analysis? How should diurnal processes in rivers factor into Total Maximum Daily Load (TMDL) guidelines? Questions like these underscore the relevance of the proposed Special Session to the greater scientific community.

Conveners

• Chris Gammons, Montana Tech of the University of Montana,
• David A. Nimick, USGS,

General Conference Information

• Conference Home Page

More Information

• Diel Cycling of Trace Metals in Streams
• Diurnal Metal Variations in Streams Photo Gallery
• Watershed Contamination from Hard-Rock Mining Investigation

Related Headlines

• Mercury Concentrations in Streams Found to Go Through Daily Cycles
• Importance and Causes of Daily Variation in Metal Concentrations in Streams
• Daily Variation of Metals in Streams Can Confound Scientific Studies

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