Analysis of environmental proxies in recent sedimentary records from reservoirs in central Mexico

This study analyses and compares changes in environmental dynamics in Laguna de Yuriria (LY) and La Esperanza (PLE) reservoirs. For this purpose, short sediment cores were extracted, and a multi -proxy environmental analysis was performed together with the calculation of geo- chemical indices. Trace element concentrations were compared with international sediment quality guidelines for the protection of aquatic life. The sediments corresponding to the last decades of the LY indicated a progressive increase in primary productivity, evidenced by elevated contents of total organic carbon (TOC), chlorophyll deriv- atives (CD), total carotenoids (TC) and total phosphorus (TP) in the last years, which is likely related to increased urbanization, wastewater discharges and agricultural activities. While the northern and eastern zones of the LY have greater CD values indicating a high primary productivity linked to algal blooms, the western part of the LY has higher TC values reflecting a contribution of aquatic vascular plants (water hyacinth). The positive correlation between TOC and TIC (total inorganic carbon) in the LY record indicates that carbonate precipitation is caused by biological processes. Regarding trace elements, As showed elevated concentrations in the LY sediments, probably associated with the use of agrochemicals in the region, and with potential adverse effects on aquatic biota. On the other hand, the positive correlation found in the sediments of PLE between TOC and TP indicates the contribution of exoge- nous organic matter, most likely as a result of the hydrological basin's deforestation. Contamination by Cr and Zn was demonstrated in the PLE, which would be contributed by geogenic sources, while Cu and As would have an anthropogenic ori- gin (mining). Cu, Cr, As and Pb revealed potential negative effects on aquatic biota. This research allowed us to assess the status of contamination processes in both reservoirs and demonstrated that the sedimentary sequences serve to document the environmental dynamics at a spatial and vertical scale that can be used to improve the management and co -management of the reservoirs.