Experimental acidification of two biogeochemically-distinct neotropical streams: Buffering mechanisms and macroinvertebrate drift

CO2-driven experimental acidification effects on aquatic macroinvertebrates in a tropical stream

“…The macroinvertebrate drift measured in response to short-term acidification by HCl by Ard on et al (2013) showed significant results below the HCl injection site, where the macroinvertebrate drift was found to be higher than above the injection site. The drift results were significant not only at the station 10 m below the injection but also 100 m below in both the well-buffered and poorly-buffered streams (Ard on et al 2013). A possible reason for this is that unlike dissolved CO 2 , HCl has no way of leaving the stream once it is introduced, while CO 2 is able to dissolve back out of solution by passive diffusion when the atmospheric concentration becomes lower than the concentration in the stream.…”

“…Ard on et al (2013) observed increased macroinvertebrate drift in response to experimental acidification in tropical lowland streams; the drift was dominated by Ephemeroptera and Chironomidae. Some experimental studies have attempted to demonstrate the effects of acidification on stream macroinvertebrates using strong acids; some examples are the use of nitric acid by Dangles and Gu erold (2000), and hydrochloric acid in a study on tropical streams (Ard on et al 2013). Strong acids are good alternatives for the simulation of acid rain or the effects of mining, but not for the study of the effects of CO 2 pulses related to organic matter decomposition.…”

“…In order to model stream conditions resulting from increased dissolved CO 2 , gaseous CO 2 was added directly to the stream to cause an experimental decline in pH. It is well known that a major stream buffering system is the carbonate-bicarbonate system, in which gaseous CO 2 exchange at the water surface reacts with water molecules to form H 2 CO 3 , a weak acid which protonates easily to produce H C and HCO 3 -ions (Small et al 2012;Ard on et al 2013;Hasler et al 2016). With the addition of injected gaseous CO 2 , the equilibrium of this reaction may be driven to produce more H 2 CO 3 and cause the stream to become acidified.…”

Distribution and structure of lotic macroinvertebrate communities and the influence of environmental factors in a tropical cloud forest, Cusuco National Park, Honduras

“…Considering Cusuco's proximity to the large industrial hub of San Pedro Sula this could potentially include the kinds of industrial pollutants associated with acidification. However, the impacts of acidification on tropical, and in particular on neotropical streams has received little attention (Small et al, 2012;Ardón et al, 2013). In the tropics the warm, wet climate creates the potential for high rates of CO 2 production in the soil, subsurface water flows can dissolve this CO 2 and transport it to streams, thereby resulting in natural acidification in relatively pristine areas.…”

“…This can be exacerbated by more severe or prolonged dry seasons (Johnson et al, 2008;Small et al, 2012) which are predicted to occur in some tropical areas due to climate change (Milly et al, 2005). In La Selva research station, Costa Rica Ramírez et al (2006) detected decreases in insect density and biomass over the course of a year concurrent with declines in pH and Ardón et al (2013) observed an increase in invertebrate drift, especially Chironomidae and Ephemeroptera, in response to a decreases in pH. While in the present study Chironomidae were reasonably well represented in acidic (Group 1) sites the ephemeropteran fauna was distinctly depauperate with several taxa completely absent and those remaining represented by few or single individuals.…”