Anthropogenic drivers of increasing sediment accumulation in contrasting Mexican mangrove ecosystems

Abstract

Mangrove sediments are valuable records to reconstruct the impacts of human-induced changes on the coastal zone. Seven lead-210 dated sediment cores were used to evaluate temporal trends of sedimentation rates over the past century in Mexican mangrove areas at Términos Lagoon (TL; southern Gulf of Mexico) and El Verde Camacho Lagoon (EV; northern Mexican Pacific coast). We hypothesized that the contrasting characteristics (e.g., meteorological, demographic, and land-use change) would lead to significant differences in sedimentation rates between the study sites. Sediment accumulation rates (SAR) in both sites (TL 0.03–2.1 cm yr−1; EV 0.04–4 cm yr−1) were comparable to the global SAR range for mangrove forests. Mass accumulation rates (MAR) in the TL cores (0.03–0.47 g cm−2 yr−1) were consistent with previous studies of the region. Excluding conspicuous MAR maxima, attributed to meteorological events, MAR values in the EV cores (0.04–0.9 g cm−2 yr−1) were higher than in other mangrove areas of the Mexican Pacific coast, but comparable to other sites in the world. Similar exponentially increasing MAR values towards present in both sites were attributed to general factors driving sediment accumulation in mangroves, mainly continental erosion promoted by land-use changes, which has accelerated since the 1950s, associated with (i) population growth and the consequent expansion of human activities and (ii) sea-level rise, similar in the studied regions and from which mangrove ecosystems seem to adapt. Intensifying population growth and land-use change are already reducing the extent of mangrove coverage in some parts of the study areas. Adaptation to an accelerating sea-level rise depends on maintaining conditions that allow mangroves to accrete vertically. However, both global change pressures may pose future threats to these ecosystems. Efforts to monitor sediment accretion and adapt the management of mangrove conservation areas are required to understand better mangrove response to global change impacts.