Does Alumina-Refining Waste Increase the Nutrient Level in Tropical Mesotrophic Floodplain Lakes?

Several floodplain lakes of the Orinoco River have been impacted by alkaline alumina-refining waste including red mud, a by-product from the Bayer process. Some of these impacted lakes have undergone algal overgrowth, which has been detected due to the unusual green color of water and the dissolved oxygen oversaturation. Thus, we conducted sampling campaigns in impacted and non-impacted lakes to measure the concentration of nitrogen (N) and phosphorous (P) in water to detect any change in the nutrient levels. Despite the content of N and P in red mud is low, our findings suggest that N is released from red mud accumulated in bed sediments to the water column in the impacted lakes, increasing the content of total N. However, the total P concentrations in impacted lakes were not affected from their background values probably due to the strong adsorptive behavior of P onto red mud minerals.