Discipline: Ecology Environmental and Earth Sciences
Myrna N. Girald Perez - University of Puerto Rico - Aguadilla Campus
Co-Author(s): Nathan Johnson, University of Minnesota, Duluth, MN
The oxidation of the lower sulfidic layer in anoxic sediments can be responsible for the release of toxic metals into the water column and result in an alteration of nutrient cycles. Cyclical hydrological phenomena perturb redox interfaces in many different contexts and have been well studied, however sulfur cycling in anoxic sediments from riparian soils in response to seiche-induced activity – a crucial factor in sediment-water processes and nutrient transport – have not been examined. The objective of this research is to study the effect of oxygen intrusion in the redox reaction rate of sulfur in anoxic sediments subjected to periodic wetting and drying periods driven by a seiche (consistent with the Laurentian Great Lakes). A tank simulating an 8-hour, 8 cm seiche cycle and containing a sediment wedge, was constructed in the lab with sulfur-rich mud and coarse sand. It was divided into three different zones to compare: a dry zone, a splash zone exposed to periodic wetting and drying, and a saturated zone. The amount of reduced sulfur on the sediment was determined using the Brower Diffusion Method for acid volatile sulfides (AVS) and extract concentrations quantified with a sulfide ion-selective electrode. Sulfate concentrations in surface and pore water were measured in each of the zones with a Dionex ICS-1100 Basic Integrated IC System and used as an indication of the impact of oxygenation on sulfur cycling and movement. A one-way ANOVA was conducted to compare the average SO4-2 in the different zones and a pairwise differences in means were evaluated using a post hoc Tukey test. Results indicate a significant difference of SO4-2 in the upper part of the splash zone (F (3.22)=7.62, p < 0.00113), since it experiences longer periods of interaction with the atmosphere. In addition, a probable mobilization of SO4-2 into the saturated zone was observed. These finding suggest that anoxic sediments from riparian soils affected by the seiche can experience a faster oxidation rate of sulfides, potentially contributing to acceleration of other elemental-nutrient cycles and the release of metals into surface waters. References: Beck B, Johnson N. 2014. Geochemical factors influencing the production and transport of methylmercury in St. Louis River Estuary sediment. Applied Geochemistry 51: 44-54. Eckley C, Luxton T, Goetz J, McKernan J. 2017. Water-level fluctuations influence sediment porewater chemistry and methylmercury production in a flood-control reservoir. Environmental Pollution 222: 32-41. Korgen B. 2000. Bonanza for Lake Superior: Seiches Do More Than Move Water. Seagrant.umn.edu. Ostrovsky I, Yacobi Y, Walline P, Kalikhman I. 1996. Seiche-induced mixing: Its impact on lake productivity. Limnology and Oceanography 41: 323-332. Tabatabai M, Dick W. 1983. Simultaneous Determination of Nitrate, Chloride, Sulfate, and Phosphate in Natural Waters by Ion Chromatography1. Journal of Environment Quality 12: 209.
Funder Acknowledgement(s): I thank Dr. Nathan Johnson for serving as my mentor. I also thank L. Zuniga, S. LaFond-Hudson, A. White, B. Liscomb and M. Torrez for assisting in the laboratory analysis. Special thanks to the director of the program, REU on Sustainable Land and Water Resources, Diana Dalbotten and Co-director Antony Bertherlote. Finally, I appreciate the participation of all Native Americans tribes, especially Fond du Lac Reservation. Funding was provided by the National Science Foundation.
Faculty Advisor: Nathan Johnson, email@example.com
Role: The following are the parts of the research I did with the help of others: the collection of the rich sulfur mud and lake water, construction of the sediment wedge in the tank, monitor the simulated seiche, gather daily surface and pore water samples, prepared the samples for the ion chromatography analysis and took core samples of the sediment to be analyzed for acid volatile sulfides.