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Influence of Drought and Total Phosphorus on Diel pH in Wadeable Streams: Implications for Ecological Risk Assessment of Ionizable Contaminants
Citation:
VALENTI, T. W., J. M. TAYLOR, J. A. BACK, R. S. KING, AND B. W. BROOKS. Influence of Drought and Total Phosphorus on Diel pH in Wadeable Streams: Implications for Ecological Risk Assessment of Ionizable Contaminants. Integrated Environmental Assessment and Management. Allen Press, Inc., Lawrence, KS, 7(4):636-647, (2011).
Impact/Purpose:
Our study emphasizes the potential uncertainty that diel pH variability may introduce in site-specific assessments and provides recommendations for environmental assessment of ionizable contaminants.
Description:
Climatological influences on site-specific ecohydrology are particularly germane in semiarid regions where instream flows are strongly influenced by effluent discharges. Because many traditional and emerging aquatic contaminants, such as pharmaceuticals, are ionizable, we examined diel surface water pH patterns (i.e., change in pH over a 24-h period) at 23 wadeable streams in central Texas, USA, representing a gradient of nutrient enrichment during consecutive summers of 2006 and 007. The years of our study were characterized by decidedly different instream flows, which likely affected production:respiration dynamics and led to distinctions in diel pH patterns between 2006 and 2007. Site -specific ambient water quality criteria for NH3 and the aquatic toxicity of the model weak base pharmaceutical sertraline were predicted using continuous water quality monitoring data from the sites. Drought conditions of 2006 significantly increased (p<0.05)diel pH changes compared to high instream flows of 2007, and the magnitude of diel pH variability was most procounced at nutrient-enriched sites in 2006. Differences in diel pH change patterns between 2006 and 2007 affected predictions of the environmental fate and effects for model weak base pharmaceuticals and NH3. Overall, site-specifice diel pH was more variable at some sites than the difference in mean surface water pH between the 2 summers. Diel pH variability affected regulatory criteria, because 20% of the study sites in 2006 experienced greater than 5-fold differences in National Ambient Water Quality Criteria for NH3 over 24-h periods. Our study emphasizes the potential uncertainty that diel pH variability may introduce in site-specific assessments and provides recommendations for environmental assessment of ionizable contaminants.
