RELATIONSHIPS BETWEEN ORGANIC MATTER AND TRACE ELEMENTS IN AN OMBROTROPHIC BOG

Relationships between dissolved organic matter (DOM), trace elements, mercury, and major cations were examined in the S2 wetland of the Marcell Experimental Forest. DOM is known to bind trace metals and is a key component controlling trace metal transport from wetlands. However, the complex and largely unknown character of DOM prevents the construction of reliable models to predict delivery of toxic metals such as arsenic, lead, and mercury from wetlands. As several studies have reported increased DOM transport from multiple wetlands in recent decades, a better understanding of complex DOM-metal relationships is critical. In this study, we utilize the heavily instrumented and studied S2 wetland and an array of sampling locations within S2 to further understand the complex relationship between DOM and trace metals. Samples were collected from 2010-2012 from the outflow weir, lagg and bog porewaters, and in subsurface flow from the uplands. More frequent samples were collected from the S2 weir and one lagg location, while ~monthly samples were collected from multiple upland-to-lagg-to-bog transects. DOM was characterized by measuring total and dissolved organic carbon and by UV spectroscopy. Distinct differences were found between Hg and many of the other metals, helping us to better understand Hg dynamics in the S2 system. For example, Hg and several metals were found in significant quantities in the subsurface runoff. Metals that bind to soil organic carbon, such as Pb and As, and redox sensitive metals such as Mn and Fe, were low in the subsurface runoff, relative to the weir and lagg porewaters. Hg, which also has high affinity for soil carbon, had higher or similar concentrations in the subsurface runoff as the weir and lagg porewaters, demonstrating different binding affinities for soil and/or dissolved organic carbon. In general, Hg and other metals that were found at higher concentration in the subsurface flow (relative to the weir and lagg), were highest in concentration in the upland and lagg porewaters, and then decreased moving further towards the bog. Pb and As, on the other hand, both generally increased moving from upland to bog porewater. This study highlights the complex nature of metal/DOM interactions and insights that can be gained about the environmental system and Hg dynamics by also examining other metals.