Effect of Hydrological Regimes on Denitrification and Microbial Community Composition in Agriculturally Impacted Streams and Riparian Zones in Indiana, USA

• Main Author: Manis, Erin Evelyn
• Format: Publication
• Language: English
• Published: Kent State University / OhioLINK 24.07.2012
• Subjects: denitrification; Hydrology; microbial community composition

The landscape surrounding a particular stream or river has a complex relationship with the aquatic habitat, influencing ecological health on multiple scales. Alteration of the landscape through anthropogenic activity represents a primary threat to rivers and streams via a variety of mechanisms, including habitat loss, nutrient enrichment, pollution, riparian zone and canopy destruction, and alteration of hydrology. Nutrient enrichment in the form of nitrogen and phosphorus is associated with eutrophication, increased primary productivity, decreased biodiversity, and hypoxia in both freshwater and marine environments. Nitrate retention and loss can be controlled by several factors, including a variety of biological mechanisms by which nitrogen is temporarily or permanently removed from agriculturally impacted subsurface waterways. A dominant sink for nitrate is denitrification, carried out exclusively by denitrifying bacteria. Denitrifiers are able to reduce nitrate to nitrous oxide or di-nitrogen gas under anaerobic conditions, thus removing nitrate permanently from the system. Although the process of denitrification in streams is well studied, it is unclear how varying hydrologic regimes in agriculturally impacted streams and riparian buffer zones affect the denitrifying community’s structure. In this study, the effect of varying hydrologic regimes on microbial community composition and denitrification rates in agriculturally impacted streams was examined. The role of flooding in driving microbial community composition and denitrification rates of naturally formed riparian benches along a primary headwater agricultural stream was also examined via a simulated flooding experiment. Results suggest that hydrology plays a significant role in determining denitrification rate, likely due to changes in sediment and soil redox potentials. Results also suggest that bacterial community structure (i.e. 16S rRNA gene copy numbers, nosZ gene copy numbers, and relative denitrifier abundance) is not a good predictor of changes in denitrification rate and subsequent nitrate removal.