April 2011 (est.) article: “Surrogate Measures for Providing High Frequency Estimates of Total Suspended Solids and Total Phosphorus Concentrations,” by Amber Spackman Jones, David K. Stevens, Jeffery S. Horsburgh, and Nancy O. Mesner.
Surrogate measures like turbidity, which can be observed with high frequency in situ, have potential for generating high frequency estimates of total suspended solids (TSS) and total phosphorus (TP) concentrations. The principle is simple. TSS and TP are relatively costly to sample (e.g. grab samples and wet chemistry). Scattering of light by turbidity in water can be measured continuously with simple probes. Relate this to TSS and TP and you have a continuous estimate of the latter two.
The problem is the relationship between turbidity and TSS and TP varies with a lot of things, and differs for every stream. The authors considered other possible variables for two streams in Utah, including discharge, temperature, day of year, hour of day, and hydrologic categorical variables, before concluding, “turbidity was the only explanatory variable that was a significant predictor of TSS at both sites, suggesting that turbidity alone is sufficient to estimate TSS across hydrologic conditions at these locations. … For TP at both sites, only turbidity and the spring snowmelt/base flow categorical variable were significant.”
I thought this paper did a particularly thorough job of examining the relationship in two streams in Utah, coming up with regressions both simple and robust. While not exactly breaking any new ground on a theoretical basis, I hold this paper out as an example of a good way to conduct an investigation.
[Please note: I have quoted and paraphrased freely from the article, but the interpretation is my own!]