Understanding the natural variability of the carbonate system in a mytiliculture zone influenced by two environmental stressors: upwelling and rivers

Chair: Yuri Artioli

Luisa Saavedra L. (1), Cristian Vargas (2)

1 Department of Aquatic Systems, Faculty of Environmental Sciences, Universidad de Concepción, Chile. Center for the study of multiple-drivers on marine socio-ecological systems (MUSELS), Concepción, Chile.
2 Department of Aquatic Systems, Faculty of Environmental Sciences, Universidad de Concepción, Chile. Center for the study of multiple-drivers on marine socio-ecological systems (MUSELS). Millenium Institute of Oceanography (IMO), Concepción, Chile.

Background
The shellfish aquaculture developed in the coastal area of south-central Chile is exposed to two major environmental forcings: seasonal upwelling relevant in summer, and freshwater from rivers important in winter. Both stressors are acting on the natural variability of the carbonate system (lowering pH and CaCO 3 saturation state) wich has implications in the physiological adaptations of benthic organisms and their potential tolerance to the rapidly changing ocean conditions.

Methods
In the present study oceanographic parameters and water samples were obtained bimonthly, over a year, from two coastal stations located on a shelfish aquaculture. For each sample the pH were measured using a direct electrometric technique and alkalinity using an automated, closed-cell, potentiometric tritiation procedure. Chlorophyll and nutrients were also determined in each water sample. Parameters such as pCO2, Ωarag and DIC were obtained through the CO2SYS software.

Findings
The time series show pH values between 7.73 and 8.28, with lower and stable pH levels in winter (influenced by the river freshwater influence) and generally higher pH levels in summer. During the warmer season a higher pH fluctuation was observed, due to the occurrence of upwelling. The lower pH and Ω arag (1.13) levels were observed during upwelling events, associated with increased pCO2 levels (~900 µatm). A significant positive correlation was found between alkalinity and salinity, which is typical of a coastal environment. Oxygen was positively correlated with pH, potentially by the intrusion of upwelling waters with low oxygen concentration, which in turn have low pH and high nutrients.

Conclusions
The lower Ω arag levels during upwelling may be relevant to larval development and therefore to the shellfish aquaculture production. The knowledge of this natural variability in carbonate system is relevant for a optimal management of this developing shellfish aquaculture and for future scenarios of ocean acidification.