title: Development of a regression model to predict copper toxicity to Daphnia magna and site-specific copper criteria across multiple surface-water drainages in an arid landscape.
abstract: The water effect ratio (WER) procedure developed by the US Environmental Protection Agency is commonly used to derive site-specific criteria for point-source metal discharges into perennial waters. However, experience is limited with this method in the ephemeral and intermittent systems typical of arid climates. The present study presents a regression model to develop WER-based site-specific criteria for a network of ephemeral and intermittent streams influenced by nonpoint sources of Cu in the southwestern United States. Acute (48-h) Cu toxicity tests were performed concurrently with Daphnia magna in site water samples and hardness-matched laboratory waters. Median effect concentrations (EC50s) for Cu in site water samples (n=17) varied by more than 12-fold, and the range of calculated WER values was similar. Statistically significant (α=0.05) univariate predictors of site-specific Cu toxicity included (in sequence of decreasing significance) dissolved organic carbon (DOC), hardness/alkalinity ratio, alkalinity, K, and total dissolved solids. A multiple-regression model developed from a combination of DOC and alkalinity explained 85% of the toxicity variability in site water samples, providing a strong predictive tool that can be used in the WER framework when site-specific criteria values are derived. The biotic ligand model (BLM) underpredicted toxicity in site waters by more than 2-fold. Adjustments to the default BLM parameters improved the model's performance but did not provide a better predictive tool compared with the regression model developed from DOC and alkalinity.
authors.affiliation: ARCADIS US, Lakewood, Colorado, USA.
authors.forename: Barry A
authors.initials: BA
authors.lastname: Fulton
authors.forename: Joseph S
authors.initials: JS
authors.lastname: Meyer
mesh_terms: D000818:Animals; D002244:Carbon / Q000737:chemistry; D003300:Copper / Q000633:toxicity*; D003621:Daphnia / Q000187:drug effects*; D055864:Droughts; D054750:Ecotoxicology / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D015233:Models, Statistical; D012044:Regression Analysis; D014481:United States; D014867:Water / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D008024:Ligands; D014874:Water Pollutants, Chemical; D014867:Water; D002244:Carbon; D003300:Copper
keywords: Biotic ligand model; Multiple regression; Southwestern United States; Water chemistry; Water effect ratio