Spatial Variation in Fine Sediment and Microbial Transport along Stream Cross Sections: Implications to Modeling and Monitoring

Spatial variations in suspended concentrations of fine sediment and indicator bacteria in streams is noted as a source of uncertainty in various applications of water quality datasets. Without proper analysis of the persistence and reasoning for this variance in natural systems, a finer resolution of model calibration is necessary to account for spatial variation in stream cross sections. This level of calibration has become of utmost importance due to technological advancements presenting the ability for water quality modeling frameworks to generate a much finer resolution of outputs. While the importance of model calibration has been noted for remediating levels of uncertainty in output datasets, single point sampling along a stream cross section is still predominately utilized for input data acquisition within the field. In order to test the level of variation which might be accounted for by implementing higher resolution sampling strategies, five evenly distributed positions were sampled simultaneously along stream cross sections. Along with lateral variation, vertical variation was addressed by sampling at 20% and 80% of the respective stage. These sample sets were analyzed for: 1) spatial variation in suspended sediment concentrations, 2) spatial variation in microbial concentrations, and 3) association between the variations of these constituents. Results showed spatial and temporal variations clearly existed within both datasets. Due to the sporadic nature of these variations both within and between events on any given site, it is recommended spatial variation be accounted for by higher resolution input calibration steps rather than purely empirical framework improvements. Spearman correlations showed little evidence of particulate to microbial associations within this study, but it is recommended particle size distributions be evaluated in consideration to attempting correlations between total suspended solids and fecal indicator bacteria in future studies.