『Abstract
This review summarizes biogeochemical processes that operate
on diel, or 24-h, time scales in streams and the changes in aqueous
chemistry that are associated with these processes. Some biogeochemical
processes, such as those producing diel cycles of dissolved O2 and pH, were the first to be studied, whereas
processes producing diel concentration cycles of a broader spectrum
of chemical species including dissolved gases, dissolved inorganic
and organic carbon, trace elements, nutrients, stable isotopes,
and suspended particles have received attention only recently.
Diel biogeochemical cycles are interrelated because the cyclical
variations produced by one biogeochemical process commonly affect
another. Thus, understanding biogeochemical cycling is essential
nit only for guiding collection and interpretation of water-quality
data but also for geochemical and ecological studies of streams.
Expanded knowledge of diel biogeochemical cycling will improve
understanding of how natural aquatic environments function and
thus lead to better predictions of how stream ecosystems might
react to changing conditions of contaminant loading, eutrophication,
climate change, drought, industrialization, development, and other
factors.
Keywords: Diurnal: Geochemistry; Trace elements; Nutrients; Carbon;
Isotopes』
1. Introduction
2. Biogeochemistry of physical and chemical characteristics that
exhibit diel cycles in streams
2.1. Water temperature
2.2. Streamflow
2.3. Dissolved gases
2.4. pH
2.5. Dissolved inorganic carbon
2.6. Dissolved organic matter
2.7. Nutrients
2.8. Stable isotopes
2.9. Trace elements
2.9.1. Iron speciation and concentration
2.9.2. Arsenic
2.9.3. Zinc, cadmium, manganese, and other cationic trace elements
2.9.4. Causes of diel cycles of cationic trace elements and
arsenic
2.9.5. Mercury
2.9.6. Diel trace-element cycles related to cyanide photodissociation
2.9.7. Total suspended solids and particulate trace elements
3. Role of biofilm
4. Measurement methods
5. Implications
Acknowledgments
References