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Accomplishments
In 2007, James Anthony completed his doctoral dissertation work on sediment-water exchanges of nitrogen and phosphorus in lakes. Dr. Anthony developed a turbulence control apparatus that allows undisturbed cores of lakes, along with their overlying water, to be treated experimentally in determining the relationship between turbulence, nutrient release, and sediment chemistry. One of Dr. Anthony's most important findings was a sharp increase in nutrient flux near the seasonal maximum epilimnetic temperature. This threshold for nutrient release indicates potential for large changes in nutrient flux associated with climate warming.
During 2007, the Center for Limnology continued its long-term study of biogeochemical and metabolic processes in the South Platte River below Denver. Center personnel completed a study of spatial and temporal patterns of denitrification in the South Platte River and found a strong relationship between dissolved organic carbon and denitrification during summer. These findings contribute to a mechanistic understanding of denitrification, specifically in the South Platte but also generally for running waters.
The Center benefited from collaboration with Tara Higgins, a Fulbright Scholar from Ireland. Dr. Higgins developed a portable chamber that simulates a hyporheic flow path and can be used to quantify rates of denitrification in river sediments. Dr. Higgins also completed a study of nitrogen ebullition (bubbling) in the South Platte River; ebullition is associated with biogeochemical "hot spots" within the river sediments and accounts for ~10% of total di-nitrogen flux from the river.
In addition to field studies, the Center for Limnology has continued the development of a detailed mechanistic system model of the South Platte River below Denver. The model focuses on biogeochemical processes that control nitrogen, carbon, and dissolved oxygen. This model incorporates physical processes such as gas exchange rates, travel time for water, and the relationships between river stage and river cross sections, as well as empirically determined rates of ammonification, nitrification, denitrification, photo-synthesis, and respiration. The model has been used in predicting future conditions in the South Platte River as the river undergoes chemical changes associated with increasing amounts of waste discharge and more intense management as cities withdraw more water for domestic use. The model also has been adapted to other running waters in Colorado, including Big Dry Creek and the St. Vrain basin (St. Coal Creek, Boulder Creek, and St. Vrain Creek).
The Center continues its historical involvement in tropical limnology through preparation of chapters for two books dealing with tropical aquatic environments. The first volume, which deals with streams, will contain a contribution from the Center for Limnology dealing with physical environmental gradients that figure importantly in the ecological transitions from temperate to tropical streams and rivers. The second volume focuses on tropical fish communities, and the Center's contribution to that volume focuses on the Center's previous studies of the Orinoco floodplain and its aquatic food webs.
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Impacts
Our research to understand the impacts of streamflows, hydrological manipulation, and cyanobacterial
blooms on inland water ecological systems, and therefore on productivity and water quality,
helps resource managers make better decisions and plan effective actions to steward these natural
resources.
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