Photosynthesis, respiration and reaeration in a stream with complex dissolved oxygen pattern and temperature dependence

Dissolved oxygen (DO) concentration and temperature were measured at high frequency over a five day period in Río Chiquito, a suburban shallow stream, in a protected area of environmental relevance in central western Mexico. The diel DO curve showed a complex pattern having two defined night sections deviating from the usual behavior described in the literature. Instead of using a single method, weighted averages for photosynthesis and respiration rates and the reaeration rate coefficient were estimated with selected approaches involving three DO mass balance diel curve methods. Results indicate that Río Chiquito is a heterotrophic system moderately affected by organic wastes from non-point sources, highly aerated and with high respiration and photosynthetic rates during winter. DO dynamics was modeled with good concordance to experimental data for the complete deployment period. Modeling results showed temperature dependence of the three key processes. However, the complex DO pattern could not be accurately described solely with temperature correction functions. In addition to temperature variation, topography, pulse loads, temperature coefficient issues and wind speed changes are discussed as possible factors of influence on DO dynamics.