Loading in 2 Seconds...
Loading in 2 Seconds...
Evaluating the Extent and Relative Risk of Aquatic Stressors in Wadeable Streams throughout the U.S.A. John Van Sickle, John L. Stoddard, Steven G. Paulsen U.S. Environmental Protection Agency National Health and Environmental Effects Research Laboratory Western Ecology Division Corvallis, OR.
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Evaluating the Extent and Relative Risk of Aquatic Stressors in Wadeable Streams throughout the U.S.A.John Van Sickle, John L. Stoddard, Steven G. PaulsenU.S. Environmental Protection AgencyNational Health and Environmental Effects Research Laboratory Western Ecology Division Corvallis, OR
Problem:Which aquatic stressors are important in a region’s streams?
(“Stressors”-- Nutrients,excessfinesediment, degraded instream habitat, lack of ripariancover, toxicity, flow alteration, acidification, etc.)
Partial Answer:-- Compare the regional extents of stressors.
-- U.S. EPA’s Environmental Monitoring and Assessment
Program (EMAP) designs sample surveys to estimate
-- Stressor extent can be measured by the percent of
total regional stream length in “Poor” condition
for that stressor.
sampling locations, 2000-2004
Defining “Poor” (Most disturbed) and “Good” (Least disturbed) condition classes from stressor or response index scores at reference sites
-- We worry less about a widespread stressor,
if its occurrence has little effect on biota.
-- Need to also assess the size of a stressor’s effect on biota.
To assess stressor effects across a region:
-- Will use Index of Biotic Integrity (IBI) for stream macroinvertebrates
as an example measure of stream biota condition (Good or Poor).
-- If a stressor has a strong effect on stream macroinvertebrates,
then “Poor” IBI conditions will tend to occur wherever stressor
condition is also “Poor”.
-- Use relativerisk to measure co-occurrence of Poor IBI
and Poor stressor conditions.
Percent of stream length
(Risk of Poor IBI, given Poor ExSed) =
(Risk of Poor IBI, given Good ExSed) =
Result: The risk of Poor IBI when ExSed is Poor is higher than the risk when ExSed is Good.
( Note – “Risk” is just another word for “Probability” )
So: “The risk of Poor IBI is 3.6 times greater in streams
with Poor ExSed than in streams with Good ExSed.”
-- If stressor has no effect then RR = 1.
-- Use a confidence interval to express uncertainty in RR.
(EMAPsoftware for the R language calculates RR and
its confidence interval. Free, at www.epa.gov/nheerl/arm/ .
Also, see Van Sickle et al., Environmental Management, in press).
% of Stream Length
Relative Risk ratio
Challenges in using relative risk –
--- May not capture joint effects of correlated stressors.
--- Employs condition classes (‘Poor’ vs. ‘Good’).
Advantages of using relative risk –
-- Familiar language for general public.
-- Employs condition classes (‘Poor’ vs. ‘Good’).
-- Combines with stressor extent to assess the
relative importances of different stressors.