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Impacts of mercury contamination in fishes and food webs of the Mazaruni River, Guyana. Dr. Carmen Montaña-Schalk Department of Biological Sciences

During this Spring break 2018, Dr. carmen Montaña-Schalk, Department of Biological Sciences, traveled to Guyana, specifically to the Mazaruni River, north Central Guyana, to continue her research documenting the effects of mercury contamination in freshwater fishes and food webs in the Mazaruni River and tributaries. The Mazaruni River houses one of the greatest concentration of freshwater biodiversity of the world and contains high levels of species endemism. However, a major problem facing the freshwater biodiversity in Guyana is habitat transformation via deforestation for gold mining operations and the release of mercury from alluvial-gold mining activities into water bodies. Mercury, which is used for gold amalgamation, is released into the environment, bioaccumulates in organisms and moves up the food chain to eventually affect people that rely on fish as a major food source. Mercury (Hg) contamination is pervasive in freshwater systems and is the leading cause of fish consumption in Guyana and other regions within the Guiana Shield (French Guiana, Suriname) and Amazon where gold mining activities represent the gross income for the national and local economic.

Photo 2. Gold dredges in the middle Mazaruni River. Dredges operate 24/7
Photo 2. Gold dredges in the middle Mazaruni River. Dredges operate 24/7

Although there are studies documenting the presence of mercury in freshwater fishes and alluvial sediments in rivers of Guyana. Still, very little is known about the synergic effects of gold mining on mercury contamination in all components of the aquatic food web and the pathways for inorganic mercury to be convert into organic methylmercury (MeHg), which is of the most concern form of Hg because MeHg. Preliminary results by Dr. Montaña-Schalk suggests a strong potential for bioaccumulation of mercury in the aquatic food web, for instance, large fish predators contain greater concentrations of mercury. Dr. Montaña-Schalk has also observed that several fishes important in local human diets had Hg levels higher (> 1 mg Hg/kg) than the threshold proposed by the World Health Organization (0.5 mg Hg /kg), therefore, local communities along the Mazaruni River are exposed to dangerous levels of mercury through consumption of fish as well as piscivorous wildlife.

Research Team in the Eping River. Eping River is a non-mined river with black water and high fish endemism. From left to right, back row: Dr. Carmen Montaña-Schalk (SHSU), Sherica Isaacs (Master Student University of Guyana), Clay Laughrey (undergraduate SHSU), Andre Lyttle (Technician University of Guyana); front row, left: Elford Liverpool (Professor at University of Guyana), right: Ravindra Mohandero (undergraduate University of Guyana),

For the last two years, Dr. Montaña-Schalk and colleagues from University of Guyana, (MSc. Elford Liverpool), in Georgetown (Guyana), have been surveying tributaries of the Mazaruni River and documenting fish diversity and mercury accumulation on fishes inhabiting these rivers. Every year, the effects of gold mining operations are greater. There are more gold dredges in the main channel operating 24/7, but also high inland deforestation to establish inland mining operations. Gold mining activities significantly alter local habitats and downstream waterbodies. The most noticeable effects in the ecosystem are high turbidity in the water and sediments accumulation. This is particularly concerning because some species endemic to the Mazaruni basin appear highly associated with the main channel habitats.

Research Team in the Eping River. Eping River is a non-mined river with black water and high fish endemism. From left to right, back row: Dr. Carmen Montaña-Schalk (SHSU), Sherica Isaacs (Master Student University of Guyana), Clay Laughrey (undergraduate SHSU), Andre Lyttle (Technician University of Guyana); front row, left: Elford Liverpool (Professor at University of Guyana), right: Ravindra Mohandero (undergraduate University of Guyana),

We understand that gold mining activities contribute significantly to Guyana’s GDP and the economy, but the post mining results are having adverse and detrimental effects on natural resources including biodiversity and the environment. We have observed severely degraded aquatic ecosystems, decline in fish diversity, and mercury accumulation in fishes used as food resources by locals. All of this is of great concern and requires immediate attention that involved conservation monitoring and restoration initiatives.

Dr. Carmen Montaña-Schalk (SHSU) holding two electric knife fishes collected in the Mazaruni River. Specimens will be deposited at the Sam Houston State Natural History Collections.

Dr. Montaña-Schalk and colleagues from University of Guyana will continue researching in the Mazaruni River in order to characterize the diversity and structure of the aquatic biota. We are interested in examining all components of the riverine food webs from microbial, macroinvertebrates, and fish communities, in tributaries along the Mazaruni River that are heavily impacted by gold and contrast sites with non-mined tributaries using novel techniques of stable isotope analysis and mercury analysis (Total Hg and MeHg). Currently, in collaboration with Dr. Choudhary, Madhusudan, Department of Biological Sciences at SHSU, we will investigate the pathways of mercury methylation and bioaccumulation from microbes.

This research conducted by Dr. Montaña-Schalk and colleagues from University of Guyana will have important implications for conservation and will serve as first-hand information for policy makers to address the threats on fish species in Mazaruni due to mercury contamination. It will also be the first comprehensive documentation of riverine aquatic communities and food webs in relation to gold mining threatens in the area.

Dr. Montaña-Schalk expects to involve both undergraduate and master students at SHSU in this ongoing research in Mazaruni River. This spring 2018, she was able to bring an undergraduate from Sam to experience research in mining impacts on local biodiversity and fisheries. She will deposit all fish specimens collected in Mazaruni River at the Sam Houston State Natural History Collections where they will become the basis for ongoing research and educational purposes.

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