Abstract
Turbidity is widely used as a water quality indicator and to infer the mass of suspended sediment transported through riverine systems. Equipment for monitoring turbidity is inexpensive, readily available, and can be easily deployed to record continuous measurements. However, using turbidity as a surrogate for suspended sediment concentration (SSC) is frequently confounded by the composition of riverine suspended material and the particle size and shape of sediments. Recent analysis of suspended material composition and turbidity response to organic matter and particle size in New Zealand rivers found that organic matter can be a dominant proportion of the total suspended particulate matter and that heterogenous sediment composition gives rise to noisy SSC-turbidity relationships. The composition and particle size of suspended particulate matter, and the sources of suspended materials within diverse catchments, must be accounted for when deriving SSC from turbidity for denudation and land disturbance geospatial datasets. The implications of troublesome SSC-turbidity relationships are particularly acute for regulatory frameworks within which limits on SSC or suspended sediment loads are imposed through thresholds of turbidity. This paper provides a critical reflection on the role of turbidity in environmental monitoring and regulatory frameworks and shows that, although pragmatic, its use in SSC monitoring in New Zealand is problematic.