Phosphate Budget and Mineralogy in Lake Ballard

1. Sedimentation Out Phosphate Budget and Mineralogy in Lake Ballard ` 5 Budget Amanda Antosh, Dan Christian, Rick Goshen, Jessi Strand, Regan Thomas Ocean, Earth and Atmospheric Science, Old Dominion University, Nofolk, VA Adsorption Out Introduction: Phosphate is often the limiting nutrient in freshwater bodies (EPA 2012). As phosphate cycles, it is used by plants and bacteria or can be incorporated into the sediments (Gunnars 1996). The amount of phosphate stored in the sediment is dependent on a variety of factors such as amount of oxygen in the water, percent organic matter, mineralogy, and salinity (Bostrom 1988, Wang 2006). If the sediment is a source of phosphate for the lake, it will be released into the water column. We are studying the total phosphate cycling at Lake Ballard (Portsmouth, VA). From that we will determine the phosphate budget for the lake. Methods (cont): Water Column (cont): -Darcy’s Law and well data used to calculate groundwater flow of the Lake Ballard area -Soluble phosphate concentration calculated in wells surrounding Lake Ballard -Mass balance equation was used to determine the movement of phosphate in and out of Lake Anoxic and Onxic Benthic sediments: -Took grabs; separated into two portions -first portion just organic surface layer -second portion organic layer and sediment -Dried and weighed -Strickland and Parsons (1965) total digestion -Samples were reacted with a modified molybdate solution (Cutter, 1985) -Read absorbency in a Milton Roy Spectronic 601 spectrophotometer at 885nm  -Converted absorbance numbers to phosphate concentrations (Clesceri et al. 1989) Mineralogy:-Samples sieved through 250um seive -1g of sediment mixed with 0.250g of corundum, ground to 0.03 mm with 4mL of ethanol in a McCronemicronizing mill for 5 mins -Mixture dried overnight at 80C -Sample placed in plastic scintillation vial with 3 10mm plastic balls and hexane (0.5mL), shaken for 10mins using Retsch MM2000 shaker -Resieved through 250um sieve and loaded in XRD -XRD data output ran through RockJock 11 excel workbook. Results: Binding Figure 3. Mineralogy of Lake Ballard benthic sediment. Insert shows minerals that bond to Phosphate. Figure 6. Total phosphate budget for Lake Ballard. Data collected between Jan 28 and Mar 20 of 2013. * Figure 1. Lake Ballard sampling sites and well locations. Figure 4. Total phosphate concentration in water column at “deep spot”. Figure 5. Standard addition curve used to convert absorbance values to phosphate concentrations. The * indicates the same absorbance values. Methods: Water Column: -Water samples collected at 1 meter intervals (0-12 m) -Samples filtered with hand pump and GF/F filters. -Strickland and Parsons (1985) method used to find the soluble phosphate concentration -Particulate phosphate obtained from filters was converted to soluble and tested for phosphate concentration Discussion and Conclusion: In the water column, there are low phosphate concentrations in the epilimnion because of photosynthetic uptake. In hypolimnionweobserved an increase in phosphate concentrations. After analyzing the benthic lake sediment, the phosphate in the shallow region was mainly bonded to the sediment; in the deep region, the phosphate was stored in the organic material that had not been decomposed. After testing mineralogy, over eighty percent of the phosphate binding was found in organic minerals and clays. By combining this information as well as phosphate information from other classmates, we created a phosphate budget for Lake Ballard. The source of phosphate was through the groundwater and was higher than the calculated phosphate sedimentation rate. Based on our calculations there is a larger sink of phosphate in the lake; we theorize the sediment is the most likely sink location. Figure 2. Collecting deep water samples. Acknowledgments: We would like to thank the professors Dr. Fred Dobbs, Dr. Rodger Harvey, Dr. Rich Whittecar and the T.A’s Patrick Tennis and Tanya Muniak as well as the staff of Hoffler Creek. We would also like to thank Dr. Cutter‘s Lab for their assistance and Tony Spicher, Ben Hiza, Robert Murray, Erik Hovland, and Matthew Kelley for the use of their samples and data. Sources: Bostrom, B., J. M. Andersen, S. Fleischer, and M. Jansson. 1988. Gunnars, A., and S. Blomqvist. 1996. Environmental Protection Agency (EPA). 2012. Water Monitoring: Phosphorus. Wang, S., X. Jin, H. Zhoa, X. Zhou, F. Wu. 2006.