ABSTRACT
This chapter presents a case study that illustrates an approach for watershed-wide causal assessment that has several advantages for making analysis efficient, consistent, and defensible. Models of common causes of adverse biological effects were developed using West Virginia’s monitoring data, so multiple streams could be easily assessed relative to regional expectations. The case study also illustrates the use of four causal characteristics, antecedence, co-occurrence, sufficiency, and alteration, in providing a useful framework for both reaching causal conclusions and communicating them. Because nutrients were not sampled regularly in the Clear Fork stream system, and phosphorus detection limits were too high to determine background or reference phosphorus concentration, nutrient levels could not be directly assessed within the causal pathway leading to habitat or food-base alteration. Evidence of antecedence was demonstrated by showing a causal pathway from sources through intermediate stressors that are known to increase the intensity of the candidate cause(s).
