## Quantile Regression: EPT Taxa Richness vs. Metals Toxicity Units for Colorado Streams

### Plot

- Analysis: Quantile regression
- Independent variable: Metal Toxicity Units
- Dependent variable: EPT Taxa Richness
- Key: dot=observation; line= 90
^{th}quantile - Sample size: n = 37

### Model

- EPT Taxa Richness = 22.565 - 8.708 (Metals-Toxicity Units)
- Date: 12 November, 2006

Variable | Estimate | lower CL | upper CL | Test Type | Statistic | p |
---|---|---|---|---|---|---|

Intercept | 22.565 | 17.087 | 28.043 | T value | 8.362 | |

Metal Toxicity Units | -8.708 | -16.112 | -1.303 | T value | -2.387 | 0.022 |

Wald | Chi^{2} |
5.700 | 0.017 | |||

Likelihood Ratio | Chi^{2} |
9.787 | 0.002 |

### Data Analysis

- Model generated using SAS Proc QUANTREG with the smoothing algorithm. The WALD and Likelihood test statistics were used to test the linear null hypothesis, H
_{0}: slope=0. - Analysis for sites classified as pH neutral, but with strong AMD input.
- Metal Toxicity Units (TU) were calculated as sum of the ratios of each measured metal concentration with the criterion for that metal.
- Replicate visits to a site were not excluded from the data set.

### Data Origin

- Agency: U.S. Environmental Protection Agency
- Program: Environmental Monitoring and Assessment Program (EMAP)
- Project: Colorado Metals Belt Stream Assessment (EPA Region 8)
- Filenames: Files benmet, fishmet and chem downloaded from the Surface Waters Information Management (S.W.I.M.S.) database web site.

### Sampling Design

- Data collected 1994 through 1995.
- Analyzed metals and metalloids: aluminum, arsenic, cadmium, chromium, copper, iron, manganese, nickel, lead, selenium, silver, zinc.
- A description of the sampling methods may be found in the EMAP West Methods Manual for Streams found on the S.W.I.M.S. database web site.

### Contact

Patricia Shaw-Allen, shaw-allen.patricia@epa.gov, (513) 569-7136