Oxycline formation induced by Fe(II) oxidation in a water reservoir affected by acid mine drainage modeled using a 2D hydrodynamic and water quality model - CE-QUAL-W2.
The Sancho reservoir is an acid mine drainage (AMD)-contaminated reservoir located in the Huelva province (SW Spain) with a pH close to 3.5. The water is only used for a refrigeration system of a paper mill. The Sancho reservoir is holomictic with one mixing period per year in the winter. During this mixing period, oxygenated water reaches the sediment, while under stratified conditions (the rest of the year) hypoxic conditions develop at the hypolimnion. A CE-QUAL-W2 model was calibrated for the Sancho Reservoir to predict the thermocline and oxycline formation, as well as the salinity, ammonium, nitrate, phosphorous, algal, chlorophyll-a, and iron concentrations. The version 3.7 of the model does not allow simulating the oxidation of Fe(II) in the water column, which limits the oxygen consumption of the organic matter oxidation. However, to evaluate the impact of Fe(II) oxidation on the oxycline formation, Fe(II) has been introduced into the model based on its relationship with labile dissolved organic matter (LDOM). The results show that Fe oxidation is the main factor responsible for the oxygen depletion in the hypolimnion of the Sancho Reservoir. The limiting factors for green algal growth have also been studied. The model predicted that ammonium, nitrate, and phosphate were not limiting factors for green algal growth. Light appeared to be one of the limiting factors for algal growth, while chlorophyll-a and dissolved oxygen concentrations could not be fully described. We hypothesize that dissolved CO2 is one of the limiting nutrients due to losses by the high acidity of the water column. The sensitivity tests carried out support this hypothesis. Two different remediation scenarios have been tested with the calibrated model: 1) an AMD passive treatment plant installed at the river, which removes completely Fe, and 2) different depth water extractions. If no Fe was introduced into the reservoir, water quality would significantly improve in only two years. Deeper extractions (3m above the bottom) would also improve the water quality by decreasing the hypoxic zone. However, extractions at the epilimnion would increase the amount of hypoxic water in the reservoir.
Institute of Environment Assessment and Water Research (IDAEA), CSIC, C/Jordi Girona 18-26, 08034 Barcelona, Spain. Electronic address: ester.torres@idaea.csic.es.
Ester
E
Torres
University of Huelva, Department of Geodynamics and Paleontology, Faculty of Experimental Sciences, 21071 Huelva, Spain.
Laura
L
Galván
University of Huelva, Department of Geodynamics and Paleontology, Faculty of Experimental Sciences, 21071 Huelva, Spain.
Carlos Ruiz
CR
Cánovas
Departamento Biología, Facultad de Ciencias del Mar y Ambientales, Universidad de Cádiz, Pol. Río San Pedro s/n, 11510 Puerto Real, Cádiz, Spain.
Sara
S
Soria-Píriz
Instituto Flumen UPC-CIMNE, Escuela Técnica de Caminos, Canales y Puertos de Barcelona, Universitat Politècnica de Catalunya, BarcelonaTech, C/Jordi Girona, 1-3, Módulo D1, Despacho 206, 08034 Barcelona, Spain.
Marina
M
Arbat-Bofill
Barcelona Science, Carrer llacuna 162, 08018 Barcelona, Spain.
Albert
A
Nardi
Departamento Biología, Facultad de Ciencias del Mar y Ambientales, Universidad de Cádiz, Pol. Río San Pedro s/n, 11510 Puerto Real, Cádiz, Spain.
Sokratis
S
Papaspyrou
Institute of Environment Assessment and Water Research (IDAEA), CSIC, C/Jordi Girona 18-26, 08034 Barcelona, Spain.
Carlos
C
Ayora
D002734:Chlorophyll; D000077194:Chlorophyll A; D005068:Eutrophication; D057446:Hydrodynamics; D007501:Iron / Q000737:chemistry*; D008906:Mining; D008956:Models, Chemical; D010758:Phosphorus; D013030:Spain; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry*; D060753:Water Quality
D014874:Water Pollutants, Chemical; D002734:Chlorophyll; D010758:Phosphorus; D007501:Iron; D000077194:Chlorophyll A
Acid mine drainage; CE-QUAL-W2; Holomictic reservoir; Iron oxidation; Nutrient cycling