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During the last decades, many places around the world have been facing major changes in land use due to the implementation of engineered water systems. These systems aim to answer the ever growing need for food, energy, and water by withdrawing, storing, conveying and/or transferring the resource. Most often, those systems have been planned and managed to address a limited set of objectives, which often results in unintended consequences on the ecosystem. This study focuses on the 5404 km2 Tempisque watershed in NW Cost Rica that faced drastic transformations with the late 70’s implementation of a large-scale water transfer project for hydroelectric power and irrigation. Today, it is largely recognised that the basin suffers from severe ecological degradation. Amongst others, the Palo Verde coastal wetland, situated in the lower part of the watershed and internationally recognized as a Ramsar site, has shown major degradation with a dense cattail invasion and decrease in the bird population. There is no clear evidence regarding causal factors but understanding these is critical from a management and restoration perspective.
In this study, we hypothesize that ecological degradations are linked with transformations in the upper watershed, and consequent impacts in the dynamic of water quantity and quality. The complexity of the water system makes the establishment of a direct causal-relationship difficult. High resolution time series data of rainfall, discharge and water level in the wetland were analysed with explanatory, dimension-reduction time-series analysis tools (Single Spectral Analysis (SSA), phase-space reconstruction, Dynamic Factor Analysis (DFA)) in order to (i) infer the emerging patterns in the water flow and wetland hydroperiod; (ii) identify the drivers; and (iii) identify hydrological relationship between the upper watershed and the lower wetland.
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