Internal solitary waves (ISWs) of depression are common features of coastal environments and believed to resuspend sediments where they shoal. In this study, the sediment resupension process associated with ISWs propagating over a flat bed was investigated in the laboratory. The first‐ever profile measurements of the three‐dimensional instantaneous velocity field beneath the ISWs revealed that resuspension occurs during burst like vertical velocity events, which lift sediments into the water column, in the adverse pressure gradient region beneath the trailing part of the wave. Resuspension was not observed when the wave‐induced viscous bed stress was maximal directly beneath the ISW trough. Prediction of wave‐induced resuspension was, therefore, unsuccessful using a traditional viscous bed stress‐based Shields diagram. A parameterization for ISW‐induced resuspension is proposed as a function of the maximum instantaneous vertical velocity in the bursts . Here we have replaced the viscous bed stress with , where is the instantaneous resuspending bed stress and is the near‐bed fluid density. From these results, it is possible for field‐oceanographers to predict the occurrence of ISW‐induced resuspension from the bulk wave and stratifications characteristics in a two‐layer stratification. Further research is required to extend the parameterization to larger Reynolds numbers at field‐scale.

Near-inertial (Poincaré) waves with a period T_p ∼ 17 h are the dominant wind-induced internal wave motions in central Lake Erie and consequently have a substantial influence on lake circulation, mixing and biogeochemistry. However, due to the complex three-basin bathymetry in Lake Erie, the vertical and horizontal modal structure of these waves remain poorly understood. In this study, we analyze field data to show wind events energize frequent vertical mode-one Poincaré waves. The horizontal modal structure was also investigated, in a sensitivity analysis, using a calibrated three-dimensional hydrodynamic transport model forced with observed and idealized spatially uniform wind events. Strong horizontal mode-one Poincaré wave cells form in both the Central and Eastern Basins when wind events have a duration of 0.25 T_p to 0.5 T_p, are impulsive and periodic at T_p, or have anticyclonic rotation with a duration of T_p. Momentum transfer from longer wind events (> 0.5 T_p) will oppose the Coriolis-force rotated currents and damp Poincaré wave generation. In agreement with theory, the most efficient wind events are observed and computationally modeled to have a duration of 0.25 T_p; causing an excitation peak at ∼ 0.4 T_p and converting ∼ 0.8% of the wind energy input to Poincaré waves. The efficiency of wind work in generating Poincaré wave kinetic energy is given by (1-cos (2πf t)) t⁻¹, where f is the inertial frequency and t is the wind duration. Therefore, the efficiency peaks during each nT_p period, where n is a non-negative integer, and decreases significantly for longer wind events.

Breaking nonlinear internal waves (NLIWs) of depression on boundary slopes drives mixing in the coastal ocean. Of the different breaker types, fission is most commonly observed on mild slopes of continental margins. However, fission on mild slopes has rarely been investigated in the laboratory owing to limitations on flume length. In the present work, a train of NLIWs of depression is generated in an 18.2 m wave flume and shoaled upon a mild uniform slope. During fission, each NLIW of depression scatters into one or two NLIWs of elevation, which transforms into a bolus at the bolus birth point, where shear instability occurs through the pycnocline. The bolus propagates upslope, decreasing in size until it degenerates by shear and lobe-cleft instability, while losing volume to a return flow along the bed. The location of the bolus birth point, bolus propagation length scale, initial size and the number of boluses from each incident wave are parameterized from the wave half-width and the wave Froude number associated with the incident NLIW. These are compared with the characteristics of boluses generated by other breaking mechanisms on steeper slopes. Some bolus characteristics (height to length ratio, change in size and velocity field) are similar for boluses generated by fission, collapsing sinusoidal waves and internal solitary waves of elevation; however, the number of boluses, their birth point and initial height differ. The boluses formed by fission have more initial energy and no reflection. Further research is required to better quantify bolus-driven mixing on continental margins.

In dimictic lakes, the stable density stratification during summer and winter inhibits vertical mixing of nutrients and oxygen. This favors the development of hypolimnetic hypoxia, which degrades cool‐water fish habitat and enhances nutrient mineralization from the sediments. Fall and spring turnover events, therefore, provide a crucial biannual link between surface and bottom waters. However, the physical processes occurring to mix lakes during turnover events remain comparatively uninvestigated. In this study, long‐term field observations were supplemented with output from a three‐dimensional numerical model, to better understand turnover events within a small temperate lake during 2011–2017. Mid‐basin penetrative convection, sidearm convection, and wind‐induced mixing were identified, with mid‐basin convection likely contributing the most to turnover events; a typical side‐arm convective plume had 2% (spring) to 4% (fall) of the mass flux compared to those at mid‐basin. During fall turnover, wind shear only mixed the upper 35% of the surface mixed layer, with convection acting to deepen below. During spring turnover, ice‐cover sheltered the lake from wind, causing convection to be the only process occurring and lengthening the turnover duration (~ 51 d) compared to fall (~ 13 d).

During the 1970s, harmful cyanobacteria (HFCB) were common occurrences in western Lake Erie. Remediation strategies reduced total P loads and bloom frequency; however, HFCB have reoccurred since the mid-1990s under increased system stress from climate change. Given these concurrent changes in nutrient loading and climate forcing, there is a need to develop management tools to investigate historical changes in the lake and predict future water quality. Herein, we applied coupled one-dimensional hydrodynamic and biogeochemical models (GLM–AED) to reproduce water quality conditions of western Lake Erie from 1979 through 2015, thereby removing the obstacle of setting and scaling initial conditions in management scenarios. The physical forcing was derived from surface buoys, airports, and land-based stations. Nutrient loads were reconstructed from historical monitoring data. The root-mean-square errors between simulations and observations for water levels (0.36 m), surface water temperature (2.5 °C), and concentrations of total P (0.01 mg L⁻¹), PO₄ (0.01 mg L⁻¹), NH₄ (0.03 mg L⁻¹), NO₃ (0.68 mg L⁻¹), total chlorophyll a (18.74 μg L⁻¹), chlorophytes (3.94 μg L⁻¹), cyanobacteria (12.44 μg L⁻¹), diatoms (3.17 μg L⁻¹), and cryptophytes (3.18 μg L⁻¹) were minimized using model-independent parameter estimation, and were within literature ranges from single year three-dimensional simulations. A sensitivity analysis shows that 40% reductions of total P and dissolved reactive P loads would have been necessary to bring blooms under the mild threshold (9600 MTA cyanobacteria biomass) during recent years (2005–2015), consistent with the Annex 4 recommendation. However, these would not likely be achieved by applying best management practices in the Maumee River watershed.