Effects of precipitation regime on neotropical streams
MetadataShow full item record
Climate change is predicted to cause acidification in both marine and freshwater systems. However, the vast majority of research on climate change and freshwater acidification has been conducted in the temperate zone, and little is known about how climate change might affect pH in tropical streams. Climate change in Central America is predicted to cause increased droughts, higher temperatures, and increased variability in precipitation in coming decades. Here we continue a longterm study on the physicochemistry of lowland Costa Rican streams; our overarching goal was to examine how climate change might impact physicochemistry and macroinvertebrates in lowland Neotropical streams of two groundwater types, low-solute local groundwater and high-solute regional groundwater entering the watershed via interbasin groundwater flow. The objectives of this dissertation were to (1) characterize stream temperature regimes in relationship to air temperatures, and determine whether climate change is more likely to affect streams via variability in precipitation vs. temperature; (2) determine the seasonal dynamics and relative impacts of CO2 influx vs. iron oxidation as drivers of stream pH; and (3) test the thresholds of pH effects of growth/survival of dominant stream macroinvertebrate taxa and compare those thresholds to longterm stream pH records. We determined that (1) stream temperatures were lower and more variable in local-groundwater than in regional-groundwater streams, but that changes in precipitation regime – a strong driver of pH – are in the short term more likely to affect streams than rising temperatures; (2) influx of soil CO2 drives typical seasonal stream pH regimes, but iron oxidation has the potential to drive extreme acidification events; and (3) dominant macroinvertebrate taxa are tolerant (in terms to survival) to pH values just below those recorded during an extreme climatic event (strong pH drop following a severe drought caused by an El Niño Southern Oscillation event). We suggest that, if the Neotropics become drier and experience increased precipitation variability as predicted, lowland Neotropical streams (especially those receiving only local groundwater) may be subject to increased pH declines, with potential risk to the macroinvertebrate communities.