EVALUATING THE NATURAL TRANSPORT PATHWAYS OF IODINE IN HEADWATER CATCHMENTS

Iodine is a biophilic halogen that is concentrated in organic rich rocks and soils, but very little is known about its export from forested headwater catchments. The purpose of our study is to assess the dynamics of terrestrial iodine fluxes by evaluating contributions of pathways of iodine under a variety of flow conditions, and to assess the spatial and temporal variability of those pathways. The Tioughnioga River is a major headwater to the Upper Susquehanna River Basin, the main watershed in central New York and Pennsylvania, and ultimately to a major contributor to the Chesapeake Bay. We collected weekly samples of surface waters downstream from a forested and an urban branch of the Tioughnioga River from 2012 to 2014, and again in 2016. We supplemented this dataset with high-resolution (2-hour interval) sampling during snowmelt and heavy rainfall events. We also sampled surface waters from 50 locations along the Tioughnioga River monthly in 2014 and 2016. Samples were analyzed for major ions using Ion Chromatography and for trace halogens (iodine and bromide) on ICP-MS.

Both linear discriminant analysis and mixing models suggest that the migration of groundwater may contribute iodine to surface waters during baseflow at downstream reaches. Elevated concentrations of iodine accompany high discharge. Iodine concentrations increase upstream in accordance with changes in lithology and proximity to wetlands, suggesting that controls on iodine may also be related to the flux of organic matter from soil pore waters. Our results indicate that the flux of terrestrial aquatic iodine is driven largely by climatic factors in combination with land use characteristics. This work provides the first assessment of the transport of iodine in the headwaters of the Chesapeake Bay watershed and suggests that with increasing precipitation, it is likely that the episodic flushing of iodine from the subsurface to streams and chemical weathering of exposed bedrock will intensify.