Three‐dimensional hydrodynamic and sediment transport modeling to test the sediment focusing hypothesis in upland lakes

Abstract

Palaeolimnological studies rely on assumptions regarding the distribution and completeness of lake deposits that are not always fully supported by observations. In particular, the assumption that "focusing" of suspended sediments leads to preferential deposition in the deepest part of a lake is not always justified, especially in upland lakes subject to energetic wind forcing. Few studies have investigated the hydrodynamic controls on lake sediment focusing, especially the importance of wind-driven currents in deep water. We combine a three-dimensional numerical hydrodynamic and suspended sediment model (FVCOM) with a semi-empirical wind wave model to investigate the potential mobility of bottom sediments in a small oligotrophic upland lake (Llyn Conwy, north Wales, UK). Exploratory simulations of wave-and current-generated bottom stress and suspended sediment dynamics confirm the expected importance of wave-generated bottom stresses in shallower waters (< 3 m depth) around the shore. Field survey shows that lake sediments are largely absent from this zone. This is consistent with peripheral wave action as a sediment focusing mechanism. In deeper water, wind-driven currents become the dominant contributor to bottom stress. Strong wind forcing events drive an energetic circulation with peak bottom stresses that intermittently exceed any realistic erosion threshold over a large proportion of the lake at depths far below those at which waves can be effective. The spatial distribution of lake sediments, and the completeness of the sediment record, is thus determined by a complex interaction between wind-driven circulation and bathymetry, rather than by bathymetry alone. Although our sediment dynamics simulations are purely exploratory, the results are consisted with survey results that show a patchy distribution of deep-water accumulation. Some implications of these results for the selection of sediment coring locations and the interpretation of sediment records are considered.

High‐turbidity events in Western Lake Erie during ice‐free cycles: Contributions of river‐loaded vs. resuspended sediments

“…(1) Fukuda and Lick (); (2) Lee et al (); (3) Lick et al (); (4) Lou et al (); (5) Cardenas et al (); (6) Hawley and Eadie (); (7) Harris et al (); (8) Hawley et al (); (9) Morales‐Marin et al (); and (10) Valipour et al ().…”

“…Given that suspended sediments from river loading and resuspension have distinct ecological functions and driving mechanisms, it is critical to understand their relative contributions to HTEs by tracking their origins explicitly. At present, however, this understanding cannot be fulfilled through field or satellite observations (e.g., Saldías et al 2012;Mendes et al 2017;Valipour et al 2017), nor has it been sufficiently investigated thoroughly in the modeling studies that have been conducted to date (e.g., Lou et al 2000;Liu and Wang 2014;Morales-Marin et al 2017;Yellen et al 2017).…”

A novel protocol for mapping the spatial distribution of storm derived sediment in lakes

“…In the context of reconstructing paleo-storm activity, however, one drawback of coring the z-max is that this area of a lake is often distal from catchment derived sediment sources. As flowing water erodes the catchment and enters a lake, the velocity of flow decreases with distance from the source, progressively reducing the water's ability to move coarser sediment [14]. Therefore, it is difficult for storm eroded sediment to consistently make it to the z-max, resulting in dampened paleo-storm signals that are difficult to differentiate from background sedimentation [14].…”

“…As flowing water erodes the catchment and enters a lake, the velocity of flow decreases with distance from the source, progressively reducing the water's ability to move coarser sediment [14]. Therefore, it is difficult for storm eroded sediment to consistently make it to the z-max, resulting in dampened paleo-storm signals that are difficult to differentiate from background sedimentation [14]. In addition, for steep sided basins, turbidity currents or slope instabilities on the edges of deep basins sometimes results in sediment age reversals and other disturbances that negatively impact the archived paleoenvironmental record [1,15].…”

A New Digital Lake Bathymetry Model Using the Step-Wise Water Recession Method to Generate 3D Lake Bathymetric Maps Based on DEMs

“…Wind agents and water agents are the two main types of geologic agent [34][35][36]. The natural ground surface is mainly influenced by wind agents, and the sediment layer surface is mainly influenced by water agents [33,37,38]. By applying assumption (1), the bathymetric map generated by our model is theoretically the natural surface, which means we can use the surrounding slopes as the initial condition to simulate the lake's bathymetry; subsequently applying assumption (2), the thickness of the sediment layer is directly proportional to the water depth due to the uniform deposition rate.…”