Rivers provide fundamental ecosystem services to human societies and the environment, from delivery and purification of water supplies to eco-tourism. Successful environmental policies and effective management of freshwater resources require detailed and mechanistic knowledge of the biogeochemical processes occurring in rivers. However, understanding of the biogeochemistry of large rivers is far from complete, and there is a paucity of research on ecological processes in large rivers. Dissolved organic matter is a fundamental component of streams and rivers. In addition to being a source of nutrients for microorganisms, dissolved organic matter can influence acidity, light penetration and the concentration of oxygen and trace metals. The goal of this project is to fill knowledge gaps regarding the biogeochemistry of dissolved organic matter in large rivers, and the interactions between dissolved organic matter and microbial processes such as nutrient uptake and extracellular enzyme activity. The research will be conducted in seven large rivers in the western and midwestern United States.
This doctoral dissertation improvement project will contribute to a better understanding of large river ecology and river management in the U.S. The results will be presented at an international scientific meeting and published in peer-reviewed journal articles. An undergraduate student will work as a research assistant on the project and by doing so will gain valuable experience and training. Both the PI and co-PI will use the project as a demonstration or case study in the courses they teach at the graduate and undergraduate levels. Lastly, the co-PI will present results from this study at the Indiana University Women in Science Conference as a means of engaging undergraduate women who are interested in research but unsure about pursuing a career in science.
Rivers provide fundamental ecosystem services to human societies and the environment, from delivery and purification of water supplies to eco-tourism. Rivers are integrators of the landscape they drain: the biological, physical, and chemical characteristics of a river are largely the result of natural and human-impacted processes occurring within the watershed of the river. Dissolved organic matter is a fundamental component of streams and rivers. In addition to being a source of nutrients for microorganisms, dissolved organic matter can influence acidity, photochemical processes, and the concentration of oxygen and trace metals. Dissolved nutrients, particularly nitrogen and phosphorus, are important to healthy rivers – but when these nutrients occur in excess they can cause significant environmental and water quality problems. The field of study that addresses questions related to nutrients, dissolved organic matter, and the microorganisms that use these materials is called: biogeochemistry. Successful environmental policies and effective management of freshwater resources require detailed and mechanistic knowledge on the biogeochemistry of rivers. However, understanding of the biogeochemistry of large rivers is far from complete, and there is a lack of research on ecological processes in large rivers. The goal of this project was to fill knowledge gaps regarding the biogeochemistry of dissolved organic matter in large rivers, and the interactions between dissolved organic matter and microbial processes such as nutrient uptake and extracellular enzyme activity. During the summer of 2012, we sampled ten large river locations in two different biomes: the Western and Midwestern U.S. The Midwestern rivers included the Manistee, Muskegon, Tippecanoe, Saint Joseph, and White Rivers. The Western rivers included the North Platte, Bear, Colorado and two sites on the Green River. At each site, samples were collected for microbial enzyme activity, as well as nutrient and dissolved organic carbon concentrations, optical properties of the dissolved organic matter, and bacterial density. During late 2012 and early 2013, samples were analyzed in the laboratory at Indiana University. Enzymatic activities for carbon, nitrogen, and phosphorus acquisition were measureable in all rivers in both sediment and water samples, and values were comparable to those found in the literature from other river systems. We found that per unit of water volume, nitrogen- and carbon-acquiring enzyme activities were significantly lower in the Midwestern rivers. This could be the result of higher inorganic nutrient loads in this agriculturally-dominated landscape. Increased inorganic nutrients readily available for microbial utilization allow resources to be allocated into microbial functions other than production of enzymes. Regarding enzyme activity in the sediment, we found that carbon- nitrogen- and phosphorus-acquiring enzyme activities normalized per unit of organic matter were significantly higher in the Midwestern rivers. This contrasts with what we observed in the water column for carbon and nitrogen acquisition, and suggests that sediment properties, likely driven by geology and human land-use, exert a stronger control on sediment enzyme activity than do characteristics of the water column. Rivers play an important role in processing nutrients that enter waterways as a result of human activities, such as agriculture or urbanization. Our work has added to the body of knowledge on how this nutrient processing occurs and the factors that influence the bacteria and algae responsible for nutrient processing. The completion of this project has strengthened collaborations with research groups from various universities involved in the same field campaign. In addition, this project allowed one undergraduate and two graduate students to gain experience in a number of different laboratory techniques, as well as data organization and analysis. Results from this research have been presented at one international scientific meeting (Society for Freshwater Science, 2013) and to a large group of students and researchers of a variety of backgrounds during a seminar at Indiana University in May 2013.
