Field observations suggest that surface water sulfate concentrations control the distribution of wild rice, an aquatic grass (Zizania palustris). However, hydroponic studies show that sulfate is not toxic to wild rice at even unrealistically high concentrations. To determine how sulfate might directly or indirectly affect wild rice, potential wild rice habitat was characterized for 64 chemical and physical variables in over 100 sites spanning a relatively steep climatic and geological gradient in Minnesota. Habitat suitability was assessed by comparing the occurrence of wild rice with the field variables, through binary logistic regression. This analysis demonstrated that sulfide in sediment pore water, generated by the microbial reduction of sulfate that diffuses or advects into the sediment, is the primary control of wild rice occurrence. Water temperature and water transparency independently control the suitability of habitat for wild rice. In addition to generating phytotoxic sulfide, sulfate reduction also supports anaerobic decomposition of organic matter, releasing nutrients that can compound the harm of direct sulfide toxicity. These results are important because they show that increases in sulfate loading to surface water can have multiple negative consequences for ecosystems, even though sulfate itself is relatively benign.
Bibliographical noteFunding Information:
This work was supported by the Clean Water Fund, created by the Clean Water, Land and Legacy Amendment to Minnesota’s constitution. LacCore was supported by NSF grant EAR-0949962 to Myrbo and others. LacCore field crew and lab staff: Kristina Brady, Aaron Fish, Cynthia Frickle, Lindsay Hastings, Jessica Heck, Aaron Lingwall, James Marty, Ailsa McCulloch, Emily Mellicant, Mark Neumeyer, Ryan O’Grady, Sean Rogers, June Sayers, Christopher Schodt, Alex Seeling, Valerie Stanley, Michelle Sutherland, Robert Thompson, Emily Whittaker, and Amanda Yourd. A partial data set is available in the EarthChem database: https://doi.org/ 10.1594/IEDA/100681. The full data set is available in the Data Repository for U of M (DRUM): https://doi.org/10.13020/ D6130R; http://conservancy.umn.edu/ handle/11299/185506.
- iron mining
- pore water