Anaerobic Metabolic Processes in Streams

Streams, though small relative to terrestrial systems, play a critical role in the movement and processing of energy, nutrients, and organic carbon. They are highly diverse and are dynamic in their response to disturbance and to shifts in drivers such as light regime, terrestrial carbon inputs and nutrient loads. Most streams are net heterotrophic – they process organic carbon from trees and plants and release carbon dioxide into the atmosphere. Some streams process reactive nitrate from terrestrial systems through denitrification, releasing it as N₂, which removes it from the biologically available N pool. The ability to measure and model these dynamics is paramount to understanding the global cycles of these elements. Traditional measurements of whole stream metabolism use daily rates of oxygen uptake and production measured at low resolution throughout the season. Snapshots like these are problematic as they cannot capture small-scale variation or response to and recovery from disturbance events. Oxygen measurements also completely overlook anaerobic components of metabolism, such as denitrification. As part of a larger macrosystems project (StreamPULSE), which is generating a database of continuous stream measurements of CO₂, O₂ and other parameters from a wide variety of streams across the USA, this research focuses on detecting and quantifying the hidden component of anaerobic metabolism. Diel CO₂ and O₂ curves contain more information than just photosynthesis and aerobic respiration. Through modeling and empirical measurements, we investigate the usefulness of offsets in the carbon and oxygen budgets along with measurements of nitrate and organic matter to predict timing and magnitude of anaerobic metabolism in streams.