Title page for ETD etd-06192011-172727

Type of Document Master's Thesis
Author Pinney, Jenae Elizabeth
Author's Email Address jpinney@vt.edu
URN etd-06192011-172727
Title Influence of light and algae on nutrient transformations at the sediment-water interface of an agricultural stream
Degree Master of Engineering
Department Biological Systems Engineering
Advisory Committee
Advisor Name Title
Scott, Durelle Committee Chair
Gallagher, Daniel L. Committee Member
Hession, William Cully Committee Member
  • DOM
  • Ammonium
  • Phosphorus
  • Nitrate
  • Nutrient Retention
Date of Defense 2011-05-27
Availability unrestricted
The sediment-water interface is an active biogeochemical zone within streams, where solutes come in contact with mineral surfaces, biota, and reducing conditions. Here, we sought to examine the influence of light, the sediment water interface, and algae on dissolved organic carbon (DOC), nitrogen, and phosphorus within Maple Creek, an agriculturally impacted stream located in Fremont, Nebraska. Simultaneous continuous injection experiments into replicate open- and closed-bottom chambers were used to control the hydrologic residence time. A bromide tracer was injected, and samples were taken for nutrient analysis in the surface and subsurface water at depths up to 8 cm. Dissolved oxygen (DO) and temperature were recorded in order to monitor biotic production. Experiments were conducted over 10 hours, encompassing both light and dark conditions. Results show a strong biotic influence at the sediment-water interface causing nutrient uptake and changes in carbon quality. Changes are especially pronounced during peak photosynthesis hours. The open-bottom mesocosms consistently showed removal of N and P from the surface water to the subsurface. An increase in DOC flux was observed in the open-bottom mesocosms and the organic matter pool exhibited evidence of microbial reduction. The closed-bottom mesocosm showed NH4+ increased likely due to photochemical oxidation. These results show the importance of promoting exchange through the subsurface and across the sediment-water interface due to the positive impact it has on nutrient retention.
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