Paper No. 11
Presentation Time: 4:15 PM
TRACING THE SOURCE OF THE SIGNAL - EXPLORING THE POTENTIAL FOR WATERSHED MONITORING TO EXPLAIN VARIATION IN SEDIMENTARY RECORDS
Three lakes in Iceland’s Westfjords contain records of mineral deposits with an apparent 80-110 yrs cyclicity (Doner, 2003). In 2011, a team of sedimentologists, geochemists and hydrologists began a 4–year monitoring project to identify the cause of these minerologic cycles by examining river, soil and lake reservoirs and fluxes under varying meteorology conditions. Here we present monitoring results of riverine, soil pore water and soil chemistry of the Vatnsdalsvatn catchment (65°36'N, 23°05'W; 102 km2). Analyses of isotopic and geochemical tracers from the feeder streams to the Vatnsdalur River show snowmelt is a major control on source water and that significant temporal chemical fluxes occurred in the river water. Despite high discharge, particulate load was minimal except during rain events. Runoff dominates solute fluxes of Na, Si, and K. but V and Rb are controlled by thaw and subsequent mobilization of porewater with snowmelt. Dissolved Al, Ti, Pb, Zn, Mo and Mn, weathering products of basalt, mobilize from the soils during rain events, creating solute peaks downstream. XRF analyses of continuous soil profile samples show generalized depletion of K, Mn, Y and Cl below the surface horizon and accumulation of Si, Al, Ti, Ca, Sr, V, Fe and P in discrete (but not coincident) soil layers. These results suggest that surface erosion of soil may be a source of some of the lake deposits, but that deeper erosion is needed to explain most of the lake sediment mineralogy. During wetter intervals, dissolved mineral yields are significantly higher than in drier intervals. Dissolved vanadium (at least) is stored by the lake, presumably in sediments. All year monitoring of lake thermal structure with themister chains indicates that, contrary to a commonly held scientific opinion, Iceland's deeper lakes do thermally stratify and so experience bottom anoxia in both winter and summer.