Effects from log-yard stormwater runoff on the microalgae Scenedesmus subspicatus

Abstract

The effects posed by stormwater runoff from an industrial log-yard on the microalgae Scenedesmus subspicatus have been investigated. The effects of stormwater runoff sampled during two rain events on the microalgae were determined in different concentrations (% v:v). The test organisms were exposed to the stormwater runoff 96h and the percentage change in growth rates in relation to a control culture were measured at exposure times of 24h, 48h, 72 and 96h. Whereas the runoff from the first rain event posed in most cases growth stimulatory effects, the runoff from the second rain event inhibited algae growth. Differences in runoff physico-chemical characteristics combined with the hydrological factors of each rain event explained these opposite effects. The occurrence of the "first flush" phenomenon was studied and the results confirmed such occurrences in the second rain event. On the basis of normalized inhibitory effects and runoff volume, it was found that 42, 51 and 50% of the inhibitory effects during exposures of 24, 48 and 72h were associated with the initial 4% of the total discharged volume. To conclude it can be stated that since the stormwater runoff of only 2 rain events posed negative effects on the test organisms, the potential environmental threats posed by these waters during the entire hydrological year needs to be better understood in order to propose an adequate management program.