Human pressure on water quality and water yield in the upper Grijalva river basin in the Mexico-Guatemala border

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Forest ecosystems are major providers of high quality water and contribute to maintain a better distribution of base flows during the year. However, these environmental services have been adversely affected by human pressure due to the decline and deterioration of forested areas and the inadequate management of water resources. To better understand the relations between human population, forest area and water quality and yield, at a regional level, we studied six catchments located in the upper Grijalva river basin in the border between Guatemala and Mexico. Measurements of twelve water quality parameters and water yield from nine sampling periods during 2011-2013 were analyzed through PLS (partial least squares) regression, ANOVA and linear mixed models to assess the season effect on water quality and the forest cover effect on water yield. An ordination by PCA (principal components analysis) and Pearson's pair-wise correlations were used to identify association between hydrological and social catchment features (forest cover, protection of riparian buffer strips, population density and urban areas). Our results suggest that overall water quality is higher during the dry season (higher values of dissolved oxygen and lower levels of total dissolved solids, total suspended solids, total phosphorus, chemical oxygen demand and temperature were observed). Water yield is positively related to forest cover and riparian buffer strips, becoming essential in maintaining water security for local populations. Major threats to water flux and their quality are related to human pressures and untreated wastewater discharges, which reduce water quality of the receiving rivers. eng