Science Serving Maryland's Coasts

Harold Manrique Hernandez, University of Puerto Rico Humacao

Class Year: 

Project Title: 

Effects of Temperature on Biochemical Oxygen Demand in Urbanizing Streams


Urbanization and climate change are occurring globally. These environmental changes can increase stream temperatures through rising air temperatures and urban heat island effects. We measured dissolved oxygen in streams draining a land-use gradient (forest, suburban, urban) in the Gwynns Falls watershed of the Baltimore Long-Term Ecological Research site in Baltimore, Maryland. In each stream, we exposed incubations to 4 different temperatures, 4°C, 20°C, 30°C, and 35°C. Incubations lasted 3 - 5 days with 2 experiments conducted during June and July of 2009. The experiment consisted of measuring biochemical oxygen demand, respiration and carbon consumption in a 3 day experiment on June and a 5 day experiment on July. For all sites, we observed significant increasing trends in respiration and carbon consumption with increasing temperature. Although urban streams showed higher biochemical oxygen demand during ambient temperatures before experiments, we did not observe significant differences in respiration rates across sites. The ratio of primary production to respiration decreased with increasing temperature as did net generation of dissolved and particulate organic carbon. The activation energy for respiration decreased with increasing temperature at all sites. Increases in stream temperatures due to urbanization and climate change may influence respiration dynamics and influence carbon cycling in small streams.