Iron speciation and provenance during high flow events from catchments to receiving

Iron is an essential micronutrient that impacts phytoplankton biomass and productivity in both fresh and marine waters. Furthermore, solid, colloidal and dissolved iron species play significant roles in the cycling and bioavailability of carbon and phosphorus in aqueous systems via multiple mechanisms, suggesting widespread impact of Fe on other ecologically relevant biogeochemical cycles. Here, we integrate multiple studies describing Fe speciation and partitioning from catchment to receiving water during high flow events. River receiving water coninuums featured include glacial and forested headwater catchments of the Gulf of Alaska through their estuary, as well as forested and agricultural catchments in Vermont feeding a eutrophic bay in Lake Champlain. We find that during high flow events (peak glacial melt, snowmelt, summer and autumn storms, midwinter thaws), Fe speciation in riverine loads varies dramatically based on provenance, which is impacted by both landcover and seasonality. Iron species distribution and concentration in riverine sediment, colloidal and dissolved loads controls its association with C and P, which also varies by landcover and season. Ultimately, the role of Fe in receiving water ecology and biogeochemistry is driven by the form and concentration in which it is introduced from the watershed, as well as the ambient biogeochemical/hydrodynamic conditions of the receiving water column and sediment-water interface preceding the high flow event.