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Eco-Hydrogeologic model

 

Conceptual model 

 

Streams are perennial (PENN) when they gain water from the aquifer (effluent) throughout the year, which occurs at the downstream sections and intermittent (INT) when they lose water to the aquifer (influent). The geographic location where the stream changes from influent to effluent, from upstream to downstream, changes throughout the year as the water table rises with the winter rains, and lowers as the aquifer loses water through its natural discharges or through pumping, attaining a minimum at the end of the dry season (end of September). This section is here identified as INT-PENN. 

 

 

Some species are better adapted to withstand water deficit than others. The best adapted ones should be found in sections where flow is intermittent, whereas temporary (TEMP) (opportunistic) species may be found when flow is the highest. Hence, the exclusive presence of permanent (PERM) species may be indicative of a stream section where flow is low or intermittence is too high for temporary species (INT section). The presence of both permanent and temporary in the wet season and only (or at least highly predominant) permanent species during the dry season is indicative of a INT-PENN section. When both permanent and temporary species are present throughout the year the section is PENN (in fact the temporary species may be permanent here). 

 

 

If measured, or estimated, stream flow is coupled with ecological data then the previous assumptions may be validated. Despite of its simplicity, the conceptual model has, nevertheless, some interesting applications, namely: i) one can use biological indicators to estimate groundwater levels in locations where direct measurements are not available; ii) given the possibility to model the impact of future water use and recharge rates on groundwater levels, the extent of stream length affected by these changes can be quantitatively estimated. 

 

 

A relative abundance index (RAI) is used in complement to the presence/absence of species, given by the quotien between count of individuals of all temporary or permanent species, and the total count of individuals of both temporary and permanent species. 

 

Several scenarious were built based on future climate changes. Estimates were made for stream length affected by these changes, as well as groundwater dependent ecosystems impated areas.

 

 

More detailed information may be found in the final report. 

 

 

 

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