Muddy Sediment

The Kathiawar Peninsula's coastal areas, crucial for Arabian Sea trade, face significant human impact from industries and fishing, potentially affecting intertidal life. The study explores the population dynamics of the mudskipper Scartelaos histophorus in the coastal area of Bhavnagar district, Gujarat, India, focusing on its ecological status along the muddy-rocky intertidal coastline. The research, using the quadrat method, categorized data into four seasons from 2022-23 to 2023-24. Hathab Coast showed the highest density and abundance of Scartelaos histophorus due to muddy habitats, while Ghogha had significant mangrove coverage. The mudskipper population characteristics were strongly correlated with the quantity and thickness of the mud layer, as it constructs burrows in the muddy substrate. Scartelaos histophorus was predominantly found in the upper intertidal zone during low tides.

The Vistula Lagoon is located in Europe and is the second largest lagoon in the Baltic Sea, after Curonian Lagoon. It is a transboundary water basin shared by Poland and Russia. The entire Polish part is a NATURA 2000 area. The whole lagoon area requires economic rehabilitation comprising integrated management involving ecological, social and economic interactions and couplings. Currently most of the actions and investments are devoted to development of local tourism and stimulation of local economy by construction of new marinas and small harbors. In Polish part this is enhanced by the Vistula Spit cross-cut construction. Such activities result in a need for expansion of navigational channels leading to their dredging and necessity of safe management of the dredged deposit. Investigations of sediment quality thus became indispensable. To assess its quality, sediment samples were collected in the Polish and Russian part of the Vistula Lagoon to evaluate and compare soil strength parameters and the concentrations of harmful substances in both parts. Due to the current political situation and interruption of scientific contacts between the Russian and Polish researchers only the results obtained for the Polish part are reported herein. The analysis revealed that the studied sediments are generally very weak in terms of strength parameters but safe as regards the presence of dangerous substances according to EU regulations. This allows for deposition in the form of artificial islands that will ultimately fulfill important ecosystem services and provide long term solution for the excess sediment management.

Methane (CH4) is the most abundant hydrocarbon and one of the most important greenhouse gases in the atmosphere. CH 4 bubble growth and migration within muddy aquatic sediments are closely associated with sediment fracturing. In this paper we present the modeling of buoyancy-driven CH 4 bubble growth in fine-grained muddy aquatic sediment prior to the beginning of its rise. We designed a coupled mechanical/reaction-transport numerical model that enables a differential fracturing over the bubble front (as it occurs in nature), when the fracturing increment stays constant at the bubble head and subsides towards bubble tail during bubble growth. We show that this differential fracturing over the bubble front controls the bubble shape and size temporal evolution, and is significantly affected by the critical stress intensity factor of the muddy sediment. The intercalated stages of elastic expansion and fracturing during the bubble growth shorten with time as the bubble approaches its terminal size (prior to its ascent). Our simulations reveal a high asymmetry in the bubble shape growing with time, with respect to its initial symmetric penny-shaped configuration. It was found that the bubble grows allometrically, while the importance of the bubble surface area growth with time. We also confirmed the earlier predictions about the "inverted tear-drop" bubble cross-section just prior to the beginning of its rise. Modeling of the terminal bubble characteristics will permit prediction of the delivery of gaseous methane from the sediment to the atmosphere via the water column.

The presence of free gas in sediments and ebullition events can enhance the pore water transport and solute exchange across the sediment−water interface. However, we experimentally and theoretically document that the presence of free gas in sediments can counteract this enhancement effect. The apparent diffusivities (D a ) of Rhodamine WT and bromide in sediments containing 8−18% gas (D a,YE ) were suppressed by 7−39% compared to the control (no gas) sediments (D a,C ). The measured ratios of D a,YE :D a,C were well within the range of ratios predicted by a theoretical soil model for gasbearing soils. Whereas gas voids in sediments reduce the D a for soluble species, they represent a shortcut for low-soluble species such as methane and oxygen. Therefore, the presence of even minor amounts of gas can increase the fluxes of low-soluble species (i.e., gases) by several factors, while simultaneously suppressing fluxes of dissolved species.

"Methane (CH4) is the most abundant hydrocarbon and one of the most important greenhouse gases in the atmosphere. CH4 bubble growth and migration within muddy aquatic sediments are closely associated with sediment fracturing. We present the finite element modelling results of buoyancy-driven CH4 bubble growth in fine-grained muddy aquatic sediment prior to the beginning of the bubble rise. The designed coupled mechanical/reaction transport numerical model enables a differential fracturing over the bubble front,
simulating the dynamics of the bubble growth observed in the nature. We show that this differential fracturing controls bubble shape and size temporal evolution. The intercalated stages of elastic expansion and fracturing during the bubble growth subside with time as bubble approaches its terminal size prior to
ascend. Our simulations reveal a high asymmetry in the bubble shape growing with time, with respect to its initial symmetric penny-shaped configuration. It is found that the bubble grows allometrically, while the importance of the surface area growth with time, making the bubble more sensitive to the ambient field of
concentrations. Modelling of the terminal parameters of the mature bubble emitted from the sediment permits predicting the delivery of gaseous methane to the atmosphere via the water column."

Methane (CH4) is the most abundant hydrocarbon and one of the most important greenhouse gases in the atmosphere. CH4 bubble growth and migration within muddy aquatic sediments are closely associated with sediment fracturing. In this paper we present the modeling of buoyancy-driven CH4 bubble growth in fine-grained muddy aquatic sediment prior to the beginning of its rise. We designed a coupled mechanical/reaction-transport numerical model that enables a differential fracturing over the bubble front (as it occurs in nature), when the fracturing increment stays constant at the bubble head and subsides towards bubble tail during bubble growth. We show that this differential fracturing over the bubble front controls the bubble shape and size temporal evolution, and is significantly affected by the critical stress intensity factor of the muddy sediment. The intercalated stages of elastic expansion and fracturing during the bubble growth shorten with time as the bubble approaches its terminal size (prior to its ascent). Our simulations reveal a high asymmetry in the bubble shape growing with time, with respect to its initial symmetric penny-shaped configuration. It was found that the bubble grows allometrically, while the importance of the bubble surface area growth with time. We also confirmed the earlier predictions about the ”inverted tear-drop” bubble cross-section just prior to the beginning of its rise. Modeling of the terminal bubble characteristics will permit prediction of the delivery of gaseous methane from the sediment to the atmosphere via the water column.