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Mexico harbors more than 10% of the planet's endemic species. However, the integrity and biodiversity of many ecosystems is experiencing rapid transformation under the influence of a wide array of human and natural disturbances. In order to disentangle the effects of human and natural disturbance regimes at different spatial and temporal scales, we selected six terrestrial (temperate montane forests, montane cloud forests, tropical rain forests, tropical semi-deciduous forests, tropical dry forests, and deserts) and four aquatic (coral reefs, mangrove forests, kelp forests and saline lakes) ecosystems. We used semiquantitative statistical methods to assess (1) the most important agents of disturbance Electronic supplementary material The online version of this article (affecting the ecosystems, (2) the vulnerability of each ecosystem to anthropogenic and natural disturbance, and (3) the differences in ecosystem disturbance regimes and their resilience. Our analysis indicates a significant variation in ecological responses, recovery capacity, and resilience among ecosystems. The constant and widespread presence of human impacts on both terrestrial and aquatic ecosystems is reflected either in reduced area coverage for most systems, or reduced productivity and biodiversity, particularly in the case of fragile ecosystems (e.g., rain forests, coral reefs). In all cases, the interaction between historical human impacts and episodic high intensity natural disturbance (e.g., hurricanes, fires) has triggered a reduction in species diversity and induced significant changes in habitat distribution or species dominance. The lack of monitoring programs assessing before/after effects of major disturbances in Mexico is one of the major limitations to quantifying the commonalities and differences of disturbance effects on ecosystem properties.

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The salt content of soil and water in endorheic basins within arid areas greatly restrict agricultural activities. Despite this limitation, these lands are increasingly used to accommodate new settlements and/or agricultural practices. This study focuses on the Laguna El Cuervo closed basin of northern Mexico and its underlying aquifer, which has been found to contain high concentrations of arsenic (As) and fluoride (F). The spatial distribution of As and F, their variations with time, and the impact of drought conditions and land-use changes were investigated using well data collected from a total of 27 wells in 2007, 2010, and 2011 (As data also collected in 2005). Four of these wells were used as monitoring wells. Data also included the As content of 140 surface sediments. Results showed that 54.5 % of the wells surpassed the As limit for drinking water of 0.025 mg L(-1) and that 89.0 % surpassed he F limit of 1.5 mg L(-1). Spatial analyses identified the areas in the center of the basin with the highest content of contaminants. Principal component and correlation analyses showed a co-occurrence of As and F with r = 0.55 for the 2011 data and 0.59 for the combined data. In contrast, the relationship of As and F concentrations to droughts and changes in land use were not as clearly shown, possibly because of the short time this area has been monitored. The high As and F concentrations in the groundwater may be limiting the availability of water within this basin, especially considering the greater groundwater demand foreseen for the future. Water-conservation practices, such as drip irrigation and artificial groundwater recharge, should be considered to maintain groundwater levels supportive of agricultural practices.

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