Sediment transport mechanisms influencing spatiotemporal resuspension patterns in a shallow, polymictic reservoir

Abstract

Although whole-lake sedimentation models have been developed for natural lakes, they may not apply to reservoirs due to differing physical, morphological, and hydrodynamic characteristics along a reservoir's longitudinal axis. We measured sedimentation rates immediately below the photic zone and near the sediment surface in a polymictic reservoir's riverine and lacustrine regions to identify transport mechanisms influencing sediment resuspension during an annual cycle. Lake-wide regression models revealed that wind-induced mixing depths explained <20% of sediment resuspension variability. However, site-specific mixing depth models explained 30% of sediment resuspension variability at a lacustrine station. Inverse relationships between mixing depth and sediment resuspension suggested that wind-induced mixing entrained deep-water advective river sediments into the photic zone rather than resuspending deposited sediments. Maximum mixing depths calculated from strong wind events never exceeded site depths, supporting this hypothesis. Lake-wide and site-specific mixing depth models were not improved by considering short-duration, strong wind events, suggesting that episodic winds did not generate enough momentum to effectively deepen mixing depths. Lake-wide regression models indicated that river discharge (r ²= 0.19) was a better predictor of sediment resuspension than mixing depth. Site specific discharge models explained 44% and 30% of sediment resuspension variability at 2 riverine stations, emphasizing the influence of horizontal advection in riverine regions. River discharge and wind-induced mixing influenced sediment resuspension at one sampling station only, indicating that the site may have been located in the transition region. Future reservoir sedimentation models should incorporate weighting factors to appropriately represent sediment transport mechanisms along a reservoir's longitudinal axis.

Key words:

• horizontal advection
• polymictic
• reservoir
• resuspension
• sedimentation
• wind mixing

Acknowledgments

We thank Lisa Vajdos, Bradley Christian, and Rodrigo Moncayo-Estrada for their efforts in the field and laboratory. We thank Dr. Joseph White, Jeffrey Back, and Jason Taylor for assistance with statistical analyses. We thank Tom Conry and the City of Waco (Texas) for project support. This research was funded by the Environmental Protection Agency through an ENSR, Inc. subcontract (#102200) to O. T. Lind. Partial funding was provided by the Folmar and Gardner Graduate Student Research Grants through Baylor University to C. T. Filstrup.

Notes

*Standard error.

**Standard error of the estimate.

*Standard error.

**Standard error of the estimate.

*Standard error.

**Standard error of the estimate.

†Variable not normally distributed (Shapiro-Wilk p= 0.045).

*Standard error.

**Standard error of the estimate.