Variations of seasonal and spatial Hg, Pb, Cr and organic matter contents in Ayapel Flood Plain Lake sediments, Córdoba, northwest Colombia

Abstract

The Flood Plain Lakes of the Atlantic Colombian have been impacted by artisanal gold mining during last decades. However, the obtained results have been compared to action levels relevant to other latitudes and the investigations have not included other trace metals of sanitary interest. The present study contributed to understanding the spatial geochemical response controlled by hydrological pulse and organic matter (OM) composition within the Ayapel Flood Plain Lake influence area. We assessed the seasonal and spatial variations of mercury (Hg), lead (Pb), and chromium (Cr) content in recent Ayapel Flood Plain Lake sediments and then compared them with the determined local pollution level of Hg (0.032 μg g-1), Pb (2.39 μg g-1) and Cr (89.58 μg g-1) found in Betulia Formation. The ranges of metal content were 0.008-0.117 μg Hg g-1, 1.090-11.870 μg Pb g-1, and 5.350-93.430 μg Cr g-1. Hg showed the largest spatial variation (0.083 ± 0.064 μg g-1) and the highest values at the distributaries of the former gold mining fronts. About 91 % of samples displayed Pb enrichment (6.376 ± 4.048 μg g-1) and 66.6 % Hg enrichment when compared with the reference levels. In contrast, Cr content was relatively low (96.325 ± 29.868 μg g-1) and showed a decreasing trend from East towards West. The sediment was mainly inorganic (88.154 ± 3.822 %) with depleted OM levels (11.846 ± 3.822 %). The results suggested enhanced Hg motility owing to a high respiration rate of OM about the centre of the main water table. The sediment resuspension and migration was facilitated by thermal instability of the water column influenced by wind action.

Keywords

• lead
• chromium
• organic matter
• sediment
• gold mining
• heavy metal action level