Effects of irrigation canals on stream ecosystems in a tropical dry forest region of Costa Rica

The interaction between irrigation and stream systems near Palo Verde National Park, Costa Rica provided an opportunity to investigate critical concepts in stream ecology: ecohydrology, riparian patch ecology, and the river continuum concept, while addressing water management issues. This study integrated these components by exploring: (1) Effects of canals on stream community structure and function, and (2) Whether canals and streams have similar structure and function at the landscape level.;The ecohydrology investigation compared intermittent and perennial tropical dry forest streams. It provided details on their aquatic communities and demonstrated the strong influence of streamflow on the colonization, development, and succession of aquatic biota. Furthermore, this investigation increased knowledge of tropical dry forest stream ecosystems, which have been studied very little and exist within a threatened forest ecosystem. It also revealed that impacts of irrigation canals on tropical dry forest streams included increased habitat during the dry season, habitat fragmentation, channel scouring, and water quality changes.;The riparian patch investigation compared four distinct stream environments resulting from canal management at a site where an irrigation canal crossing is maintained without riparian vegetation and canal water is directly discharged into the stream. Some differences in physical-chemical characteristics and the biotic community were found between the deforested stretch and the adjacent upstream and downstream forested stretches, but that small-scale riparian deforestation (< 35 m) may not have severe detrimental effects on the stream community and may actually provide a greater diversity of habitats and resources that enhances biotic richness. In addition, perennial discharge from the canal into the stream may provide refugia in the dry season and a source of colonizers for the seasonal stream reach.;The canal continuum investigation analyzed the size classes of irrigation canals that diminish in size over their longitudinal gradient both to determine their structure and function and to examine whether canals follow predictions of the River Continuum Concept (RCC), but in reverse order. As a whole, the canals did support an aquatic community whose structure and function did change over their longitudinal gradient, and the canals did follow some RCC predictions. (Full text of this dissertation may be available via the University of Florida Libraries web site. Please check http://www.uflib.ufl.edu/etd.html).