A falling rigid body through air, water, and sediment is investigated experimentally and theoretically. Two experiments were conducted to drop rigid cylinders with density ratio around 1.8 into shallow water (around 13 m deep) in the Monterey Bay (Exp-1) and into the Naval Postgraduate School’s swimming pool (Exp-2). During the experiments, we carefully observe cylinder track and burial depth w...

Gas hydrates, solid composites of biogenically derived gasses (mainly methane) combined with water ice, may be present in marine sediments, especially at continental margins, under the correct pressure and temperature conditions. Gas hydrates are detected by direct sampling, and inferred from seismic reSection data when a strong bottom-simulating reSector (BSR) is produced by the seismic veloci...

The severe incidences of Microcystis blooming in 1980s of the Sagami and Tsukui reservoirs, located in Sagami river, Japan were effectively controlled by the installation of 8 and 5 bubbling circulation systems, respectively. However, the blooming had started again in those reservoirs. It was found that those algal blooming occurred due to the formation of strong stratification following a temp...

Features extracted from echosounder bottom returns are compared with the ground truth in a North Sea survey area. The ground truth consists of 50 grab samples for which the grain size distribution, and the gravel and shell contents were determined. Echo envelopes are analysed for two single-beam echosounders, operated at frequencies of 66 and 150 kHz. It is shown that a set of six energetic, st...

Seasonal oxygen depletion (hypoxia) in coastal bottom waters can lead to the release and persistence of free sulfide (euxinia), which is highly detrimental to marine life. Although coastal hypoxia is relatively common, reports of euxinia are less frequent, which suggests that certain environmental controls can delay the onset of euxinia. However, these controls and their prevalence are poorly u...

The Conowingo Reservoir is situated on the Susquehanna River, immediately upstream of Chesapeake Bay, the largest estuary in the United States. Sedimentation in the reservoir provides an unintended benefit to the bay by preventing sediments, organic matter, and nutrients from entering the bay. The sediment storage capacity of the reservoir is nearly exhausted, however, and the resulting increas...

The aim of this study was to assess heavy metals mobility and toxicity in sediments collected from a dam reservoir in the conditions of intensive human impact by using chemical fractionation and a battery of bioassays. In the studies, the test organisms were exposed to substances dissolved in water (Microtox, Phytotestkit) as well to substances absorbed on the surface of solid particles (Phytot...

[1] Shallow coastal lagoons are environments where a dynamic equilibrium exists between water quality and seagrass cover. Dense seagrass canopies limit the resuspension of bed sediments thereby creating a clearer water column and a positive feedback for seagrass growth. Positive feedbacks are often associated with the existence of bistable dynamics in ecosystems. For example, a bare and a seagr...

Heavy metals are one of the most important factors among many others in biosphere pollution. Mobility and toxicity of metals associated with bottom sediments are generally affected by metal speciation and sediments compositions. The aims of this study were to investigated the distribution of metal speciation in sediment collected from Rybnik dam reservoir and to asses their toxicity for aquatic...

This study evaluated fluctuations in the output signal of a densimeter, an in situ suspended-sediment measurement device based on a very sensitive differential pressure transducer. Although the densimeter produced accurate less than 10% error results in the laboratory for concentrations of 10–1,000 mg/L, there was a much larger fluctuation in the field test output signal. These fluctuations wer...