Sediment Resuspension In Lakes Research Articles

Impact of Wind on the Spatio-Temporal Variation in Concentration of Suspended Solids in Tonle Sap Lake, Cambodia

Even though wind, water depth, and shear stress are important factors governing sediment resuspension in lakes, their actual relations to total suspended solids (TSS) distribution in natural environments have not been well elucidated. This study aims to elucidate the impact of the wind on the spatio-temporal variation of TSS in Tonle Sap Lake, Cambodia, during low-water (March and June, <1 m) and high-water (September and December, 8–10 m) seasons. To this end, wind and TSS data for December 2016 and March, June, and September 2017 were collected and analyzed. For spatial interpolation of wind speed, the inverse distance weighted method was found to be better (R2 = 0.49) than the vectorized average (R2 = 0.30) and inverse of the ratio of distance (R2 = 0.31). Spatial interpolation showed that the wind speed and direction on the lake were <5 m/s and southward during the low-water season and <7 m/s and westward during the high-water season. The TSS concentration in the low-water season was higher (>50 mg/L) than that in the high-water season. The TSS concentration during the low-water season was empirically described by wind speed (W), water depth (D), and shear stress (τ_wave) with a function of W3, W3/D, and exp(W/D) or exp(τ_wave), depending on the location in the lake. The critical shear stress due to wind-induced waves at most of the places in the lake was higher than the total shear stress indicated. Sedimentation was predominant in December and June, and erosion (siltation) was dominant in March. Most of the siltation in March was dominant in the southern part of the lake.

Features and impacts of currents and waves on sediment resuspension in a large shallow lake in China.

Wind-induced hydrodynamics are important forcing mechanisms of sediment resuspension in lakes. However, the relative contributions of wind-induced waves and currents on sediment resuspension during a wind event remain unclear. This study used high-frequency sensors to investigate the effects of wind waves, lake currents, and shear stress on sediment resuspension under different wind conditions (10 September to 17 October 2017) in Lake Taihu (China). Measurements showed that wind speed varied from 0.3 to 11.5m/s, wave height varied from 0.035 to 0.46m, lake current speed ranged from 0.001 to 0.39m/s, and turbidity changed from 36.5 to 158.7 NTU. Sediment resuspension resulted primarily from wave- and current-induced shear stresses. Calculation showed these quantities varied in the range 0.045-0.338 and 0.002-0.127N/m2, respectively. Total shear stress showed positive correlation with turbidity. Wave-induced shear stress contributed more than 60% of the total. Waves and currents have different responses to wind. During periods of increasing turbidity, the percentage of wave-induced shear stress was initially high (> 85%) before decreasing with the development of the current. During periods of decreasing turbidity, the percentage of wave-derived shear stress declined initially before increasing with the decrease of current speed. The results showed a clear process regarding the contributions of shear stress from waves and currents during different stages of hydrodynamic development, which could be used to describe sediment resuspension in large shallow lakes that would help in the development of high-efficiency sediment resuspension models.

Assessment of petroleum hydrocarbon in a tropical brackish water lagoon: Chilika, India

ABSTRACTAssessment of petroleum hydrocarbon (PHC) in the Chilika Lagoon, India, revealed a significant spatio-temporal variation in surface water (analysis of variance: n = 120, p < .01), whereas insignificant variation in sediment samples. The lagoon exhibited the highest PHC concentration during summer, attributed to higher boat activity and mixing of PHC from bottom sediment. For PHC in both the water of the lagoon and regions adjacent to jetties, the northern sector exhibited highest concentrations, followed by the southern, outer channels and central sectors, in order. The highest PHC level was due to the highest density of fishing boat operations and maintenance activities, as well as the resuspension of lake sediments across the shallowest region of the lagoon. The PHC found in the water and sediment in the jetty regions were relatively high in comparison to the rest of the lagoon, again attributed to the maintenance and operational activities of the motorised boats in the jetties. The sediment PHC concentration was ∼1000 times higher than the respective value for water, which could result from long-term deposition. The overall PHC concentration in the lagoon and jetties was found to be under the threshold limit and hence there is no risk to the existing biodiversity of the Chilika Lagoon.

Wind‐driven nearshore sediment resuspension in a deep lake during winter

AbstractOngoing public concern over declining water quality at Lake Tahoe, California‐Nevada (USA) led to an investigation of wind‐driven nearshore sediment resuspension that combined field measurements and modeling. Field data included: wind speed and direction, vertical profiles of water temperature and currents, nearbed velocity, lakebed sediment characteristics, and suspended sediment concentration and particle size distribution. Bottom shear stress was computed from ADV‐measured nearbed velocity data, adapting a turbulent kinetic energy method to lakes, and partitioned according to its contributions attributed to wind‐waves, mean currents, and random motions. When the total shear stress exceeded the critical shear stress, the contribution to overall shear stress was about 80% from wind‐waves and 10% each from mean currents and random motions. Therefore, wind‐waves were the dominant mechanism resulting in sediment resuspension as corroborated by simultaneous increases in shear stress and total measured sediment concentration. The wind‐wave model STWAVE was successfully modified to simulate wind‐wave‐induced sediment resuspension for viscous‐dominated flow typical in lakes. Previous lake applications of STWAVE have been limited to special instances of fully turbulent flow. To address the validity of expressions for sediment resuspension in lakes, sediment entrainment rates were found to be well represented by a modified 1991 García and Parker formula. Last, in situ measurements of suspended sediment concentration and particle size distribution revealed that the predominance of fine particles (by particle count) that most negatively impact clarity was unchanged by wind‐related sediment resuspension. Therefore, we cannot assume that wind‐driven sediment resuspension contributes to Lake Tahoe's declining nearshore clarity.

Seasonal and annual population dynamics of ciliates in a shallow eutrophic lake

Seasonal population dynamics and community composition of planktonic ciliates were studied for over a decade in a naturally eutrophic shallow lake, Lake Vortsjarv, which has a large open surface area (270 km 2 on average) and highly turbid water (Secchi depth 300 µm) gymnostomes. There was a positive correlation between ciliates and phyto- and bacterioplankton, implying that the ciliates were clearly bottom-up or food-controlled. This was further confi rmed by the positive correlation between ciliates and metazooplankton. As both bacteria and phytoplankton are coupled with resuspension of lake sediments, the large fl uctuations in water level infl uenced the ciliate community biomass annually.

Sediment resuspension in a shallow lake

Different mathematical formulations for the computation of the entrainment rate of sediment into suspension in lakes can produce widely disparate results under a given set of conditions, leading to problematic interpretation. In this paper, the results of a 4‐month field campaign on sediment resuspension in a large, shallow, hypereutrophic lake in southern California are presented. The field measurement program included the observation of currents and waves using a Nortek acoustic wave and current (AWAC) profiler, the observation of water temperatures using a thermistor chain, the use of optical backscatter sensors for the measurement of turbidity, a surrogate for suspended sediment concentration, and the use of meteorological data. The paper reports one of the first field experiments in lakes using the AWAC, whose signal strength has not been investigated in detail to date, and the correlation of a set of variables coming from different sources during a relatively long period of time. The contributions of different forcing mechanisms (waves, currents, and surface seiches) to the sediment resuspension in the lake are quantified, and the signal strength of the AWAC is used to address the vertical distribution of sediment in the water column. A novel relationship between the AWAC's backscatter intensity and turbidity is presented. Turbidity was found to be proportional to wK, where w is the wind speed measured at 2 m and K ranged from 4.5 to 6.5, depending on the water depth. Finally, the results of modeling the sediment entrainment into suspension in the Salton Sea are shown to be well represented by an extension of the García and Parker formula.

Horizontal and vertical variations in sedimentation and resuspension rates in a stratifying lake – effects of internal seiches

AbstractThe temporal and spatial variations in the rate of sedimentation and sediment resuspension in Lake Rehtijärvi (southern Finland) were studied by sediment traps deployed in the stratifying and non‐stratifying regions of the lake. Both the gross sedimentation rate and the resuspension rate recorded by near‐bottom traps were significantly higher in the stratifying region (&gt;20 m depth) than in the shallow part of the lake (2 m depth). These rate changes were caused by temporarily elevated hypolimnetic resuspension rates exceeding 40 g dry weight m−2 day−1 in July 2005, whereas in the shallow station no such peak was observed and the resuspension rate remained below 30 g dry weight m−2 day−1 throughout the study. The elevated resuspension rate in the hypolimnion could not be attributed to surface wave action or sediment disturbance by fish, but was due to the occurrence of internal seiches. The seiche amplitude was on average the highest in July, although the wind velocities were low; this was because winds temporarily were blowing along the longitudinal axis of the lake. Due to the steep slopes, the sediments of Lake Rehtijärvi are prone to redistribution and sediment focusing towards the accumulation areas also affected trap catches in the deep stations.

Lake restoration studies: Failures, bottlenecks and prospects of new ecotechnological measures

This paper critically reviews the published works on lake restoration in north-western Europe, with the aim to highlight the causes of failures of lake biomanipulation, and to identify the main bottlenecks that have impeded progress. More importantly, we explore the prospects of applying new ecotechnological measures to lakes with a focus on shallow lakes. These complementary measures are: (1) reduction of sediment resuspension; (2) water-level management; and (3) the use in shallow lakes of bivalves as effective grazers on lake seston, especially when cyanobacteria are dominant. If the sustainability of the positive effects of biomanipulation is considered over a decade, there are probably more cases of failures than successes. The failures can be ascribed to several bottlenecks that include: (1) inadequate reduction of allochthonous phosphorus (P) and an increase in autochthonous P inputs, i.e. release of P from the lake sediments following reductions of external P inputs; (2) poor edibility of filamentous and colonial cyanobacteria to daphnids; (3) inadequate coverage of the lake area by macrophytes partly due to foraging on the macrophytes by both fish and birds; (4) ineffective reduction of planktivorous fish biomass and our inability to maintain the fish mass to a ‘low level’ for longer periods; and (5) failure of northern pike ( Esox lucius) after its transplantation to the lakes to develop a population level that can control planktivorous fish to desired low levels. Three potentially complementary ecotechnological measures are discussed. The first such measure concerns prevention of sediment resuspension in lakes by creating islands in order to minimise the wind fetch to reduce the wave amplitude. The second measure involves allowing greater water-level fluctuations (WLF) in lakes as planned in lowland countries like the Netherlands; WLF are likely to allow more space for water , and may lead to improved water quality and higher biodiversity. The third ecotechnological measure relates to grazer populations that complement herbivorous zooplankton to regulate phytoplankton, particularly to control cyanobacterial blooms. For this, the bivalve Dreissena polymorpha appears to be a good potential candidate for grazing on phytoplankton, especially in shallow eutrophic lakes that are dominated by filamentous and toxic cyanobacteria (e.g. Planktothrix agardhii and Microcystis aeruginosa).

A temperate, tidal lake‐wetland complex 2. Water quality and implications for zooplankton community structure

Lakes Waihola and Waipori are shallow, coastal, tidal lakes that experience wind‐induced sediment resuspension, saline intrusions, and high inputs of nutrients. To determine the influence of externally‐driven, physical factors on spatial and temporal patterns of water quality in the two lakes, meteorological, hydrological, and water quality data were collected over 1 year. Multivariate analyses indicated that wind energy was driving the main water quality gradient in the lakes, which was primarily related to wind‐induced resuspension of lake sediments. The major, seasonally regulated, non‐tidal freshwater inflow was important in determining nutrient and salinity gradients in the lakes. The main nutrient inputs to the system were identified as the regulated, non‐tidal inflow (the upper Waipori River) and the tidal inflow (lower Waipori River). The impact of water quality gradients on zooplankton community structure in the lakes was assessed by canonical multivariate methods. Salinity gradients, caused by seasonal saltwater intrusions, were strongly related to zooplankton community structure in the lakes. Nutrient gradients (indicative of trophic state) were also related to zooplankton community structure. Although wind‐induced sediment resuspension had the largest impact on water quality in the lakes, it had little impact on the zooplankton community structure in either lake. The relationships between water quality and zooplankton community structure were confounded in Lake Waipori because of its very short hydraulic residence time (annual mean =1.9 days). Zooplankton community structure was resilient to short‐term changes in suspended particulate matter concentrations but not to seasonal changes in salinity. The results of this study support others which have shown impacts of even relatively small variations in salinity on the structure of zooplankton communities. This highlights the vulnerability of zooplankton communities in coastal lakes and wetlands to increasing salinity resulting from sea level rise and global climate change.

WIND GENERATED WAVES IN LAKE OKEECHOBEE1

ABSTRACT: The study of wind generated waves is important because waves affect sediment resuspension in lakes. Measurements of wind velocity and wave elevation were made at three different stations in Lake Okeechobee. Significant wave heights were computed using a direct count from the recorded data, and verified by the root‐mean‐square value approach. The correlation between wind stress and significant wave height also was analyzed. The data revealed a strong correlation. In addition to field measurements, a Boussinesq‐type wind‐wave model was developed to simulate wind‐generated, long‐propagating waves. This model included the effects of wind stress and bottom viscous dissipation. Wave elevation and velocity field were evaluated numerically. A six‐day simulation using 1996 wind data was conducted. Simulated significant wave heights were found to agree reasonably well with measured values. A predictive wind‐wave model provides information about wind generated waves, which is used to compute bottom shear stresses required for sediment resuspension studies.

Mechanisms, measurement and importance of sediment resuspension in lakes

The process of sediment resuspension in lakes influences lake metabolism by causing turbidity and cycling of particulate material. Wind, currents and morphometry of the lake basin are the most important causes of resuspension. So far, episodic resuspension events have been studied, rather than the impact on whole lakes. The bottom shear stress and the cohesion of sediments are the key mechanisms for sediment resuspension. Two zones of resuspension can be distinguished: the littoral zone, where wave action is significant; and the profundal zone, where seiche-induced currents are the most important factor governing resuspension. Repetitive sediment resuspension and redeposition over large areas are common in shallow lakes. Nearshore sediment resuspension, subsequent focusing and redeposition in the profundal zone are the main processes in large, deep lakes. The various methods of measuring sediment resuspension are reviewed, with special emphasis on the sediment trap method and the use of radionuclides.

Empirical evidence of the importance of sediment resuspension in lakes

This paper reviews the empirical evidence for bottom sediment resuspension, which has been documented in many aquatic systems, and attempts to put those observations into a predictive framework. The evidence suggests that resuspension is episodic in all systems with the spatial extent of resuspension being determined by the wind speed, duration of disturbance, effective lake fetch and lake morphometry. The rates of deposition of resuspended material vary greatly with measurements recorded between 0.5 and 50 g m−2 d−1. In many systems and at many times of year resuspended material comprises the majority of the flux of particles to lake bottoms. An order-of-magnitude estimate of the long-term contribution of resuspended material to the total flux of particulate matter is 85%.

Editorial: Sediment resuspension in lakes

Editorial: Sediment resuspension in lakes

Sediment resuspension in Lake St. Clair

Time‐series measurements of water transparency, wave conditions, and current speed were made at several different sites in Lake St. Clair during five different 1‐month periods in 1985 and 1986. Observed changes in suspended sediment concentration were modeled with a simple zero‐dimensional, spatially averaged, mass balance model in which local bottom erosion was expressed as a linear function of the bottom shear stress. Estimates of the three parameters required by the model (particle settling velocity, resuspension concentration, and background suspended material concentration) are reasonably consistent for the various data sets, suggesting that the properties of the lake bottom do not change significantly through either space or time. The modeled settling velocities agree with the observed suspended particle size data and the erosion rates are comparable to laboratory results for freshwater sediments. The results show that a simple mass flux model can be used to model local sediment resuspension events in Lake St. Clair with reasonable accuracy.