NORTHERN ADRIATIC WATERSHEDS: CARBONATE GEOCHEMISTRY AND FLUXES WITHIN DIVERSE DRAINAGES OF W SLOVENIA AND NE ITALY

Carbonate mineral weathering within the terrestrial sphere offers a geologically rapid response to conditions within the critical zone. As CO₂ levels, land-use, and climatic conditions vary across landscapes, changes to the dissolution, precipitation, and export of carbonate mineral weathering products are observed. We are interested in how these carbonate mineral fluxes change over the course of a river system and if the headwater weathering products reach the shallow marine ecosystem. This study investigates the source of solutes into Northern Adriatic Sea from Southern Calcareous Alps in NE Italy (Adige, Brenta, Piave, and Tagliamento) and Julian Alps (Soča), dinaric karst (Reka/Timavo), and coastal plain in Slovenia. These rivers represent high gradient alpine headwater regions with MAP near 3000mm and lower gradient agriculturally impacted systems with MAP near 900mm. Each watershed is forested with narrow watershed boundaries in the agricultural plain. River length (<410km) offer a unique opportunity to investigate a relatively short run from the headwaters to their discharge points allowing for investigation of the potential influence river geochemical evolution might play into marine chemistry and ecosystem health.

Locations within the watersheds were sampled five times in fall and spring of 2007, 2008, and 2011. Ca²⁺, Mg²⁺, and HCO₃^- dominate the geochemistry with Ca²⁺ and Mg²⁺ accounting for 82.6% of cations and HCO₃^- accounting for 70.0% of anions. The solutes are controlled by the abundance of limestone and dolomite of Triassic and Mesozoic age. Localized anhydrite/gypsum account for Ca²⁺ in excess of carbonate weathering within Piave and Tagliamento watersheds. All streams show increasing Cl^- downstream as anthropogenic influence increases. Over 90% of samples are supersaturated for calcite at pCO₂ levels near atmosphere. Discharge data were obtained from ARSO for Slovenian rivers and ARPA-V, ARPA-ER and ARPA-FVG for Italian rivers. Variability of HCO₃^-, Ca, and Mg values does not appear to be dependent on specific runoff suggesting that carbonate dissolution is not limited by water volume. The study shows that the headwater chemistry dominates the entire length of the stream and may benefit the Northern Adriatic Sea by delivering water supersaturated with carbonate weathering products.