Investigations into the occurrence and causes of diel changes in the chemistry of streams.

摘要

This study investigates the underlying causes of diel (24-h) concentration cycles of various chemical species in rivers. Major and trace element concentrations have been shown to undergo significant fluctuations over 24-h periods and these changes are linked to the biogeochemistry of the riverine environment.; Rivers are dynamic, "living" systems that are an integral component of the global hydrological network. There is a need for a better fundamental understanding of the science of how rivers and other hydrological systems function. One of the goals of this work is to gain insight into the processes controlling the mobility of metals and other contaminants within a river.; The concentrations of major and trace elements, dissolved CO2 , inorganic carbon, dissolved oxygen, as well as the stable isotope compositions delta13C-DIC and delta18O-DO were measured in the Big Hole River, MT; the Clark Fork River, MT; Fisher Creek, MT; and the Rio Agrio, Argentina. Results from the use of stable isotopes on the Big Hole River demonstrate the degree to which photosynthesis and respiration influence the daily stream chemistry. These daily changes in photosynthesis and respiration are shown to control the mobility of Mn, Zn, Cu, Al and Fe in the Clark Fork River. Evidence is presented suggesting that diel changes in redox conditions which alternately oxidize and reduce metals in biofilms affect the mobility of the metals.{09}Work in the Fisher Creek drainage shows that diel fluctuations in dissolved Cu and Zn in near-neutral pH waters are most likely controlled by upstream sorption of trace metals onto freshly formed hydrous Fe and Al oxides. The observed trends are consistent with thermodynamic and kinetic factors that predict increased precipitation of HFO during daytime, higher streams temperatures, coupled with more rapid sorption of dissolved cations. Results from the Rio Agrio, Argentina demonstrates that metals behavior and transport in a river receiving contamination from geogenic sources are similar to that observed in mining impacted streams of the Rocky Mountain West, USA.