USING TURBIDITY TO DETERMINE TOTAL SUSPENDED SOLIDS IN URBANIZING STREAMS IN THE PUGET LOWLANDS

The replacement of forestland with impervious surfaces during urbanization can have significant effects on watershed hydrology and the quality of stormwater runoff. One component of water quality, total suspended solids (TSS), is both a significant part of physical and aesthetic degradation and a good indicator of other pollutants, particularly nutrients and metals that are carried on the surfaces of sediment in suspension. We investigated whether turbidity could produce a satisfactory estimate of TSS in urbanizing streams of the Puget Lowlands. A log-linear model showed strong positive correlation between TSS and turbidity (R2 = 0.96) with a regression equation of ln(TSS) = 1.32 ln(NTU) + C, with C not significantly different than 0 for 8 of the 9 sampled streams. These results strongly suggest that turbidity is a suitable monitoring parameter where water-quality conditions must be evaluated, however logistical and/or financial constraints make an intensive program of TSS sampling impractical.