Geochemical Processes of Lake Averno

Kate Overmoe and Avery Cota

Background• Lake Averno is located in NW sector of the Campi Flegrei Volcanic

District.

• 15km west of Naples, Italy.

• Maximum depth of lake is 33m.

• Circumference of lake is 3.2km.

• No natural outlet.

S. Caliro et al., 2008. Geochemical and biochemical evidence of lake overturn and fish kill at Lake Averno, Italy. J. Volcanol. Geotherm. Res. 178 (305-316), 2.

Lake Averno• Lake Averno represents an outcropping of the water table that is feed

directly by meteoric water.

• Agricultural and illegal disposal of materials contribute to lake pollution.

• Previous studies suggest that an active magma source may still contribute to the heat and deep fluid release into the Campi Flegrei District.

http://faculty.uml.edu/nelson_eby/Field%20trip%20photo%20essays/IGC%202004/IGC%202004.htm

Fish Kill Event

• Fish kills recorded January 2002, February 2003, and February 2005.

• Likely to have occurred throughout history.

• Journal concentrates on two surveys conducted February and October 2005.

• Following fish kill event February 2005, the media linked the cause of the event to volcanic sources. These accusations triggered geochemical investigations of Lake Averno to identify conditions at which this overturn and fish kill event took place.

• The February 2005 survey was conducted 3 days following the event.

Methods

• Surveyed vertical profiles of the unstratified water column (Feb.) and the stratified water column (Oct.).

• A multiparameter probe (Hydrolab multiprobe) was used to collect temperature, Eh and pH data.

•Water samples were collected by pumping water to surface by means of a manual vacuum pump, keeping the pressure difference within 0.2 atm.

• Partial pressure of gases (CO2, N2, O2, Ar, CH4, He, H2S) were collected in pre-evacuated vials and analyzed by a gas chromatograph equipped with Thermal Conductivity Detector (TCD).

The ResultsFebruary 11, 2005 October 27,2005

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The ResultsOctober 27,2005

The Results

Sulfate reduction:

SO42- + organic matter → H2S + 2 HCO3

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The Results

Carbonate reduction:

CO2 + 4H2 → CH4 + 2H2OAcetate fermentation:

CH3COO- + H+ → CH4 + CO2

The Results

Fishkill caused by seasonal overturn

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Our Results

Initial Conditions Resulting Conditions

•Drop in Calcite to a nearly saturation level•Water becomes more dense than the bottom layers

•Allowing turnover to occur due to seasonal differences

Our ResultsInitial Conditions Resulting Conditions

•Increase in Calcite to slightly oversaturated•Water becomes less dense than surface waters

•Allowing a turnover to occur due to geothermic activity

Questions?