资源环境科技发展态势分析平台

We present a scientific replication of a benthic algae nuisance threshold study originally conducted in Montana, but we do so using a different sampling methodology in a different state. Respondents are asked to rate eight photographs that depict varying algae conditions. Our initial results show that Utah resident preferences for benthic algae levels are quite similar to those of Montana residents, thus replicating the Montana study. For the full Utah sample, though, Cronbach's a indicated poor internal consistency in rating the photographs, so a "monotonicity rule'' was used to identify respondents providing monotonic preferences with respect to chlorophyll a densities. Simple graphical analyses are combined with ordered probit analysis to determine the maximum desirable density of chlorophyll a (Chl a). Our analysis indicates that Chl a levels in excess of 150 mg Chl a/m(2) are undesirable, but the regression model suggests that those with strictly monotonic preferences were far more likely favor a more stringent standard.

Plain Language Summary Excess nutrients in water can cause eutrophication, a potentially undesirable condition that fosters the growth of nuisance algae. Unlike many other water quality problems, excess algae are easily discerned by those who recreate at streams, rivers, and lakes. EPA has recently tasked state water quality agencies with establishing a numeric criterion for excess nutrients. Some agencies have used public opinion surveys to gauge aesthetic preferences for algae when developing a chlorophyll a-based criterion. This approach implicitly assumes that (1) chlorophyll a densities closely correspond to the quantity and type of benthic algae and (2) preferences for algae are strictly monotonic, i.e., less algae are preferred to more algae. We scientifically replicate a Montana study and find that preferences of Utah residents demonstrate a remarkable similarity to those of Montana residents. However, responses for a significant proportion of the sample were not monotonic. Hence, the water quality criterion implied by survey data may be sensitive to the assumption of monotonicity. Multiple preferred criteria may emerge, each differing according to how researchers treat the monotonicity assumption. We find that respondents whose preferences for chlorophyll a are strongly monotonic are more likely to favor a more stringent criterion.