Potential effects of anthropogenic induced sulphates (SO4) contaminating karst ecosystems contributing to oceanic decline globally.

Mike Buchanan, Karstologist 2024

 Increases in undesirable Acid Mine Drainage (AMD), associated with elevated sulphates (SO4) emanating from coal, heavy metals mining around the globe, are being allowed to escape into all globally important oceans. AMD is acidic water that flows from abandoned mines, often containing high levels of sulfuric acid, heavy metals, and other toxic pollutants.

 In most cases, AMD emanates via contaminated, resurgent groundwater ecosystems within carbonate karst hydrodynamic systems adjunct to catchments, or on the contact of heavy metal rich geology. AMD ultimately lands up flowing into terrestrial fluvial transport systems via subterranean hydrogeology en route to oceans around the globe.

Increasing SO4 concentrations in freshwater systems influence the biogeochemical processes of carbon, nitrogen, and phosphorus.

 Karst groundwater systems are unique carbonate-based fragile ecosystems that cover approximately 20–25% of the Earth's land surface. They are formed from carbonate sedimentary soluble rock like limestone, dolomite, chalk and gypsum which can be dissolved by acidic water. Acidification of karst systems is a significant geoethical water security concern globally. Anthropogenic induced AMD is one of the many primary causes.

 The acidification of karst systems can also have long-term consequences, such as:

• Permanent damage to the karst system's structure and function.
• Decreased water storage capacity, sedimentation affecting groundwater supplies. This includes increased risk of terrestrial flooding.
• Increased risk of contamination of adjacent water sources I.e. lower altitudes.

Globally, AMD is a significant problem, with many countries struggling to mitigate its effects. Some of the most affected regions include:

• The Appalachian region in the United States, where coal mining has led to widespread AMD.
• The Witwatersrand Basin in South Africa, where gold and coal mining has caused significant AMD.
• The coal-mining regions of Eastern Europe, such as Poland and the Czech Republic
• The karst systems of Australia, where AMD from coal and metal mines is a growing concern.

 

To address the issue of AMD in karst systems, it is essential to implement effective mitigation and remediation strategies, such as:

• Treating AMD before it enters any ecosystem or karst systems which are alkaline geological formations.
• Implementing passive treatment systems, such as confined wetlands, ponds and desalination.
• Conducting regular monitoring and maintenance of mines and adjunct karst systems.
• Promoting sustainable mining practices and appropriate rehabilitation of mined lands.

 

Overall, the acidification of karst systems due to AMD is a pressing global concern that requires immediate attention and action to protect these unique and fragile ecosystems, including onward flows to oceans.

 

When AMD enters karst systems, it can cause significant damage, including:

• Dissolution of rock formations, leading to the collapse of caves and sinkholes.
• Decreased water quality, affecting aquatic life and human consumption.
• Increased risk of flooding and erosion.
• Loss of biodiversity and ecosystem disruption.
• In mining regions where uranium is present, AMD can contribute to radionuclide mobilisation and potential atmospheric aerosolization.

 

In addition to these immediate effects, AMD can also lead to sedimentary deposition and chronic toxicity in karst systems. Sedimentary deposition occurs when the acidic water from AMD carries high levels of suspended solids, including heavy metals and other pollutants, which can settle out of the water column and accumulate on the karst system's subterranean floor or bedrock. This can lead to:

• Reduced water flow and increased risk of flooding.
• Decreased water quality and increased risk of contamination.
• Habitat disruption and irreversible loss of biodiversity services.
• Increased risk of chronic toxicity to important aquatic organisms.

 

Chronic toxicity in karst systems subjected to AMD can have long-term consequences, including:

• Bioaccumulation of heavy metals and other pollutants in aquatic organisms.
• Biomagnification of pollutants up the food chain.
• Decreased reproductive success and increased mortality rates in aquatic organisms and humans.
• Changes to the karst system's ecosystem structure and function. Exacerbation of carbonate karst dynamics(instability). Causing frequent sinkhole formation and disruption to naturally occurring vadose zones. Forcing the acceleration of groundwater tables downward. Potentially leading to soil desiccation or thus increasing the risk of desertification.

 

Some of the most common heavy metals associated with AMD and chronic toxicity in karst systems include:

• Iron: can cause changes to the karst system's ecosystem structure and function, as well as decreased water quality.
• Aluminium: can be toxic to aquatic organisms and cause changes to the karst system's ecosystem structure and function.
• Copper: can be toxic to aquatic organisms and cause changes to the karst system's ecosystem structure and function.
• Zinc: can be toxic to aquatic organisms and cause changes to the karst system's ecosystem structure and function.
• In some instances, Lead Pb, Molybdenum, Cobalt, Uranium and more.

 

Increased acidification of seawater.

While sulphate concentrations in AMD can be extremely high—sometimes reaching up to 20,000 mg/L—these inputs are often diluted significantly upon reaching the ocean. Natural seawater already contains high levels of sulphate, around 2,700 mg/L, making the global increase from AMD relatively minor. However, in localised areas such as estuaries and coastal zones, AMD can lower pH and mobilize toxic metals from sediments. These zones are more vulnerable due to weaker buffering capacity, and thus, AMD can cause considerable ecological disruption even if the overall impact on open ocean pH is limited. (Millero, 2006; Nordstrom, 2011; Zhang et al., 2012; Eyre et al., 2018; Johnson & Hallberg, 2005)

While sulphates contribute to acidification in freshwater systems, ocean acidification is predominantly driven by atmospheric CO₂, thereby lowering the pH of ocean water, amplifying oceanic acidity. This will impact the ability of marine organisms like corals, molluscs, and crustaceans to build shells and skeletal structures. (Doney et al. (2009), (Feely et al. (2004)

 

Toxic effects on marine life.

Higher sulphate levels can be toxic to some marine organisms and disrupt biological processes. It has been shown to negatively impact photosynthesis, development, and survival of some marine species. (Hansen (2002), (Vance et al. (2017). 

Release of metals from sediments.

As seawater becomes more acidic due to sulphate contamination, it can mobilise heavy metals like aluminium, iron and mercury that are normally bound in ocean sediments. This releases heavy metals and increases their concentrations in seawater, with potential toxic effects on marine ecosystems. (Breitbarth et al (2010), (Paulson & Hassett (1982).

 Disruption of biogeochemical cycles.

Sulphate entering oceans impacts natural biogeochemical cycles like those involving carbon, oxygen, nitrogen and sulphur. This can alter microbial communities and change the distribution and cycling of nutrients in the ocean. (Diaz & Rosenberg (2008), (Blackford & Gilbert (2007)

 Major sulphate (SO4)-producing countries whose rivers contribute significantly to ocean pollution.

 India

Coal-fired power plants and associated mining release sulphate into rivers in eastern India that flow into the Bay of Bengal, with levels up to 300 mg/L measured. (Patra et al. (2016), (Mohanty et al. (2014) 

 Russia

AMD is a significant issue in Russia, particularly in the Kola Peninsula and the Far Eastern region. The Kola River and the Amur River are among the affected waterways.

Sulphate from mining operations and fossil fuel extraction contaminates rivers in Siberia and the Russian Far East that discharge into the Arctic Ocean. SO4 concentrations over 200 mg/L were recorded. (Shirokova et al. (2013), (Pokrovsky et al. (2011). 

 Germany

Sulphate pollution from coal mining historically impacted rivers that drain to the North Sea. Acid mine drainage is an ongoing concern. (Küster et al. (2004), (Schippers et al. (2005).

 South Africa

South Africa being a major sulphate-producing country that contributes to ocean pollution via rivers. South Africa is a significant producer and has vast fluvial systems that drain to the two oceans.

Coal and heavy metals mining (gold, platinum, palladium etc) releases large amounts of sulphate into rivers through acid mine drainage, including other unchecked runoff. (Johnson et al. (2020).

AMD is a major issue in South Africa, particularly in the provinces of Gauteng and Mpumalanga. The Vaal River and the Olifants River are among the affected waterways.

Rivers like the Olifants River, which drains the mining areas of Mpumalanga Province, have unacceptably high sulphate levels, up to 3000 mg/L. (Oelofse et al. (2017), (McCarthy (2010). These rivers discharge into the Indian Ocean, increasing sulphate pollution in coastal waters off South Africa. Long-term monitoring shows rising sulphate trends. (Dabrowski et al. (2016), (Taljaard et al. (2009). South Africa is undoubtedly one of the largest global contributors to ocean sulphate pollution from industrial activities and riverine transport. A key sulphate producing country impacting sensitive marine ecosystems. Fossil fuel (coal) burning is a major “industry” in South Africa.

 Australia

Australia is another major sulphate-producing country contributing to ocean pollution.

Coal mining is a large industry in Australia, especially in eastern states like Queensland and New South Wales. (Australian Bureau of Statistics. Australian coal mining overview), (Geoscience Australia. Coal and coal seam gas resources of Australia). This mining activity releases sulphate into rivers through acid mine drainage and runoff. Rivers like the Hunter River show elevated sulphate levels of up to 800 mg/L. (Maher & O'Brien (2012), (Schulting et al. (2018). Australian rivers drain to the Tasman Sea, Coral Sea, Gulf of Carpentaria, and Southern Ocean - increasing sulphate pollution in coastal waters. (Eyre et al. (2018), (Talley (2008).

 United States

Acid mine drainage from coal mining operations, as well as agricultural and industrial runoff, cause elevated SO4 levels in rivers like the Ohio River basin draining to the Gulf of Mexico. Concentrations are often over 100 mg/L. (Ren et al. (2020), (Kaushal et al. (2018).

AMD is a concern in several states, including Pennsylvania, Ohio, and West Virginia. The Monongahela River and the Ohio River are among the affected waterways.

Note: This is not an exhaustive list, AMD is likely a concern in many other countries including coal producing countries within the EU and Balkan States. Below are further nations that experience uncontrolled AMD production.

 Brazil: The country's iron ore and coal mining activities have led to AMD contamination in several rivers, including the Rio Doce, which was severely impacted by a 2015 dam failure.

 Canada: AMD is a concern in several provinces, including British Columbia, Alberta, and Ontario. The Elk River in British Columbia and the Athabasca River in Alberta are among the affected waterways.

 Chile: Copper mining in Chile has led to AMD contamination in several rivers, including the Candelaria River and the Huasco River.

 Indonesia: AMD is a significant issue in Indonesia, particularly on the islands of Java and Sumatra. The Citarum River and the Musi River are among the affected waterways.

 Mexico: AMD is a concern in several states, including Chihuahua, Coahuila, and Sonora. The Rio Grande and the Yaqui River are among the affected waterways.

 Peru: AMD is a significant issue in Peru, particularly in the Andes Mountain region. The Mantaro River and the Apurimac River are among the affected waterways.

Philippines: AMD is a concern in several provinces, including Benguet and Palawan. The Agno River and the Palawan River are among the affected waterways.

China: Chinese rivers like the Yellow River discharge large amounts of SO4 into the Yellow Sea and East China Sea due to coal burning for energy production. SO4 levels in some rivers exceed 500 mg/L. (Zhang et al. (2012), ( Liu et al. (2015) 

 Conclusion/Discussion

 Increasing levels of Acid Mine Drainage (AMD) and sulphate (SO4) pollution in oceans worldwide is a pressing environmental concern. The main contributors to this issue are major coal and heavy metal mining operations in countries such as China, the United States, India, Russia, Germany, South Africa, and Australia. These countries' rivers, which drain into globally important oceans, are contaminated with high levels of sulphate, often exceeding 500 mg/L in some cases.

The consequences of sulphate pollution in oceans are far-reaching and devastating. Commencing from important major continental outflows and spreading via dilution. Increased acidification of seawater, toxic effects on marine life, release of metals from sediments, and disruption of biogeochemical cycles are some of the significant impacts of sulphate pollution. The ability of marine organisms to build shells and skeletal structures is compromised, and the mobilisation of heavy metals like aluminium, iron, and mercury can have toxic effects on marine ecosystems.

The countries mentioned above are significant contributors to ocean sulphate pollution, with South Africa and Australia being among the largest global contributors. The Olifants River in South Africa, for example, has unacceptably high sulphate levels of up to 3000 mg/L, while the Hunter River in Australia shows elevated sulphate levels of up to 800 mg/L.

 In conclusion, the increasing levels of sulphate pollution in oceans worldwide, primarily caused by coal and heavy metal mining operations, pose a significant threat to marine ecosystems and the environment as a whole. It is essential for these countries to take immediate action to mitigate the effects of sulphate pollution, including implementing stricter regulations on mining operations, improving wastewater treatment, and promoting sustainable practices.

 Some potential solutions to address this issue include:

• Implementing stricter regulations on mining operations to reduce acid mine drainage and sulphate pollution.

• Improving wastewater treatment and management practices to reduce sulphate levels in rivers and oceans.

• Promoting sustainable practices, such as renewable energy sources, to reduce the reliance on coal and heavy metal mining.

• Conducting regular monitoring and assessment of sulphate levels in rivers and oceans to track progress and identify areas for improvement.

• Encouraging international cooperation and collaboration to address the global issue of sulphate pollution in oceans.

 Ultimately, it is crucial for governments, industries, and individuals to work together applying geoethics to address the issue of sulphate pollution in oceans and protect the health of our planet.

  

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