Research Program Area: Ecosystem & Multimedia Effects
Changes in populations of stream algae and invertebrates have been associated with acid deposition in Europe, Canada and the northeastern United States. Alpine regions in the western United States have very limited capacity to neutralize acids and acidification of surface waters has been reported from nontane lakes and streams. It is not known, however, if these pulsed acidifications are having any effects on the aquatic biota of mountainous areas in western North America. In the summer of 1986: we performed a series of stream channel experiments to determine the effects of different levels of acid input on common invertebrates and algae found in High Sierra streams. Twelve small channels, each 2.4 m X 20 cm X 20 cm, were constructed next to the Marble Fork of the Kaweah River in Sequoia National Park. Water from the Marble Fork was diverted through these channels and channels were stocked with natural substrates, algae, and invertebrates. During acid pulses sufficient acid was added to one set of four channels to reduce pH to 4.6, another set of four channels received sufficient acid to reduce pH to 5.2, and a third set of four channels was. unmanipulated, acting 88 a control at pH 6.5. Every two weeks acid was added for eight hours in late morning and afternoon to simulate the magnitude and timing of acidic summer rain storms. Benthic densities of invertebrates and algae in each channel were measured before and after acid additions, and invertebrate drift was measured before, during, and after acidification. Four experiments were run through the summer and early autumn. The response of the stream periphyton community was measured during one of the experiments. Declines in total diatom abundance were noted in acidified channels relative to controls. one week after acid additions. Periphyton responses to acidification were species-specific. Achnanthes minutissina, Taxon 99396~3SN (Cymbella failaisencis or Gomphonema sp.), Gomphonema subclavatum, Achnanthes levanderi, and Pragilaria vaucheri were deleteriously affected by acid additions, whereas Eunotia spp. tended to be more abundant in acidified than control channels. Baetis was the most sensitive of the invertebrate taxa, drifting at significantly higher rates in treatment than control channels. The percentage of dead Baetis in the drift increased 2.5 to 8x during acidification. Similar responses were noted in other Ephemeroptera. Drift rates of Epeorus and Paraleptopblebia increased significantly in response to acid pulses in two experiments, pa.rticularPy when pD was reduced to 4.6. Drift rates of the stonefly Zapada increased In pH 4.6 channels relative to 5.2 and control channels during the acid pulse in one experiment. Other taxa, such as chironomid larvae, exhibited less consistent responses to acidification, although drift of chironomid larvae increased in pH 4.6 channels in one experiment. Benthic densities of Baetis declined to 10 to 16% of controls 2 days after acidification. Paraleptophlebia also declined in response to acid pulses in one experiment. Other taxa either exhibited no statistically significant responses or were present in too low densities for statistical analyses.
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
Stay involved, sign up with CARB's Research Email Distribution List