Investigating Stream Metabolism and Nutrient Dynamics in Contrasting Ecosystems: The Role of Hydrologic Compartments

Abstract:

The interactions between mobile and less mobile hydrologic compartments affect the quality and quantity of water in streams and aquifers, and the cycling of dissolved carbon and nutrients. As new laboratory and field techniques become available, new questions and challenges emerge, including: What do we measure, where, and for how long to fully characterize a system? and, What is the ideal cost-maintenance-benefit relationship that we should strive for to maximize knowledge gained in different field settings? We recently performed a series of field experiments to measure aquatic metabolism and nutrient dynamics in two highly contrasting hydrologic systems, i.e., 1) a wetland-stream alpine, tropical system in Colombia (South America) and 2) a dryland river continuum (1^st – 5^th stream orders) in New Mexico. In this presentation we discuss how multiple lines of evidence can support the analysis of key aquatic processes and how co-interpretation provides a more complete picture of stream complexity. For this analysis, we deployed YSI EXO2 and 6920 sondes, Turner Designs C-sense and C6 sensors, and Onset HOBO water quality data loggers. Parameters measured by these instruments include conductivity, temperature, dissolved oxygen, pH, turbidity, pCO₂, chlorophyll-a, phycocyanin, fluorescein, CDOM, brighteners and water depth. We also injected conservative tracers (i.e., NaCl and NaBr) and the bioreactive tracer resazurin in both experimental sites, and NO₃ in the dryland river continuum. NO₃ was measured in-situ with Satlantic Submersible Ultraviolet Nitrate Analyzers (SUNA) sensors and in the laboratory using Ion Chromatograph techniques using stream grab samples. Our results highlight the role of both residence times and chemical fluxes in regulating the effective processing of carbon and nutrients. Our results also demonstrate that stream stimuli from controlled experiments are ideal for maximizing the information content derived from short (hours to days) and mid-term (weeks) sensor deployment campaigns.