Dynamics of oceanographic parameters in a coal mine impacted estuary

Abstract

The Araranguá River Estuary, in the south of Santa Catarina receives acidic waters with low pH from part of the hydrographic basin where coal mining activities have been taking place for more than 100 years, which impact the fishing activity, tourism, diversity and quantity of specimens of the local fauna and flora. This work aimed to relate the flow, salinity, suspended particulate material and pH in order to describe a qualitative model that can be recognized by varying the flow in this estuary impacted by coal mining activities. To this end, the results of previous work, historical surveys of pH values, as well as data collection between the years 2018 and 2019 were evaluated. The hydrodynamic behavior of the estuary explains the variations in particulate matter in suspension and pH, in an estuary that varies from partially well mixed to saline wedge, directly responding to flow variations. The presence of salt acts more strongly or less strongly neutralizing the pH, depending on the mixing pattern. Dependence on flow, and consequently rainfall, governs the processes of pH and particulate matter in suspension. The conditions for settling and exporting flakes formed as a result of the impact by Acid Mine Drainage on surface water resources to the adjacent coastal zone are demonstrated. The pH values tend to increase slightly as they move away from sources of acidity, due to: a) dilution with non-acidic water inputs, b) neutralization of acidic waters with the influence of the tide, and c) the action of chemical reactions in the estuary stretch, allowing the flocculation and decanting of more acidic components, removing acidity from the water column. Under normal conditions, the estuary plays a very important filtering role, receiving low pH waters through the Mãe Luzia river and delivering water with neutral pH to the adjacent coastal zone. This work encourages the discussion about the relationship between the impacts of the coal activity in the estuarine and coastal environment, hitherto little pointed out, subsidizing possible preventive actions to pollution in this environment.