Shrinking and swelling soil cycles control a tropical wetland flooding through non-stationary infiltration effects

The Palo Verde National Park Ramsar wetland (NW Costa Rica) has witnessed a shift in vegetation from diverse vegetation and large open water areas to a near monotypic stand of cattail (Typha domingensis) with limited open water. This resulted in a sharp reduction in the bird population and biodiversity overall.

Climate and anthropogenic-driven changes in the hydrologic regime of the wetland are thought to be among the drivers of this shift.  Yet, the understanding of the drivers and processes controlling the hydroperiod of the wetland remains limited.

In this study, we aimed to characterize the hydrological dynamics of the Palo Verde wetland based on a combination of in situ monitoring stations of the groundwater and surface water levels and remote sensing satellite data. We hypothesized that the shrinking and swelling cycles of the wetland’s clay soils play a major role in controlling wetland flooding through non-stationary infiltration effects. This phenomenon might modify the flooding pattern by the tidal river bordering the wetland. First, we analyzed the trend of the hydrological time series and several hydrological indicators to interrogate and characterize the shift in the hydroperiod. Then, based on a conceptual mass balance, we estimated water infiltration at a weekly resolution, taking into account the river input by overbank flooding during high tide events. We observed that the shrinking-swelling clay soil of the wetland generated contrasted infiltration patterns at the shift between the wet and dry seasons.

This work showcases how the combination of remote sensing and ground data can help in understanding eco-hydrological dynamics and shifts in complex systems such as Palo Verde.