57. Strong-short-term effects of a volcanic eruption on the carbonate system of a highly stratified fjord in the Northern Chilean Patagonia

Maximiliano J. Vergara (1)*, Rodrigo Torres (2, 3), Emilio Alarcon (2), Cory Beatty (4), Michael DeGrandpre (4), L. Antonio Cuevas (5), José L. Iriarte (3, 6, 7)

1 Programa de Doctorado en Ciencias de la Acuicultura, Universidad Austral de Chile, Puerto Montt, 5501558, Chile
2 CIEP Research Center, Coyhaique, Chile.
3 IDEAL Research Center, Universidad Austral de Chile, Puerto Montt, Chile
4 Department of Chemistry & Biochemistry, University of Montana, Missoula, Montana, USA.
5 Department of Aquatic System, Faculty of Environmental Sciences & Environmental Sciences Center EULA Chile, Universidad de Concepción, Concepción, Chile
6 COPAS-Sur Austral, Universidad de Concepción, Concepción, Chile
7 Instituto de Acuicultura, Universidad Austral de Chile, Puerto Montt, 5501558, Chile

Background
Volcanic explosions can release large quantities of acidifying compounds, and can lead to significant environmental impacts in terrestrial and aquatic systems. From April to May of 2015 the Calbuco Volcano (north Patagonia) started an eruptive process releasing more than 0.21 km3 of ash. Previous studies have shown severe acidification effects from volcanoes and their impact to water chemistry. In this study, we investigated the dynamics of the carbonate system before and after the eruption (April-July) in surface waters of Reloncaví Fjord, a major shellfish farming area.

Methods
High temporal resolution data (every 1h) was collected from a buoy (3.5 m) in the middle section of the fjord (41ºS), for pH, pCO2, temperature, salinity and dissolved oxygen (SAMI-Sunburst; MicroCat-SeaBird). Samples were periodically collected for pH and total alkalinity. Hydro-meteorological data from a weather station (HOBO-U30) and river streamflow were measured at the study area.

Findings
The carbonate system of surface waters of the fjord before eruption showed natural pCO2 increases and pH decreases leading to an unsaturated aragonite state (Ω<1) during winter months (June-July). One month after the eruption (June), the carbonate system showed abrupt acidification at the top surface layer, related to recurrent heavy rain events, where waters reached pH values down to 7.2 (≈ 0.4 pH units lower than one day before). Additionally, aragonite saturation was almost near zero (Ω= 0.05) and abrupt changes in the pCO2 (≈1000 μatm variation) were observed, lasting for more than one week.

Conclusions
This study provides information on how the surface layer of an estuary responds to strong and rapid changes in the acid/base chemistry after a volcanic eruption. The findings suggest that the acidic event after the eruption could be due mainly to the transport of acidic runoff with volcanic materials via tributary rivers to the marine system of the fjord.