Spatial Analysis of Metal Profiles in Sediments in a Tropical Estuary: A Geostatistical Approach

The spatial structure and distribution of heavy metals [cadmium (Cd), copper (Cu), iron (Fe), lead (Pb), and nickel (Ni)] in sediments were geostatistically analyzed along the estuarine ecosystem of Tigre River-San Andres Lagoon (Tamaulipas, Mexico). In most cases, heavy-metal concentrations exhibited a strong spatial autocorrelation along the estuary as indicated by variogram analysis. Heavy-metal concentrations were found to be higher in the middle estuary, close to the mouth of the Tigre River, and declined as distance from the mouth increased. Metal mean levels at the middle estuary were 2.41 mg/kg Cd, 4.80 mg/kg Cu, 172.36 mg/kg Fe, 5.22 mg/kg Pb, and 2.10 mg/kg Ni. The spatial distribution of heavy metals suggests the existence of a common heavy-metal source located in this area of the estuary. The importance of wastewater discharges and open dumping in the town of El Moron, adjacent to the mouth of the Tigre River, is highlighted; these are believed to be the anthropogenic sources for heavy metals in this estuarine ecosystem.