Largest Brackish Lake Research Articles

Distribution of microplastics in benthic sediments of Qinghai Lake on the Tibetan Plateau, China

Although several studies of microplastics (MPs) with size <5 mm in lake sediments focused on lakeshore areas, there have been no studies of distributions of MPs from lakeshores to the center of a lake. To test our hypothesis that MPs decrease from lakeshore to the center, a study was conducted on the largest brackish lake on the remote and high-altitude Tibetan Plateau, China. Abundances and characteristics of MPs in 14 samples of surface sediment collected from a river bay, a lake bay, and a lake central area were investigated. Distributions were influenced by river inflow, tourism, and minimal activity of humans, respectively around Qinghai Lake. The mean abundance of MPs in sediments of Qinghai Lake was 393 ± 457 items/kg, dry mass (dm). Based on the range of MP abundances in surface sediments of lakes worldwide, Qinghai Lake was classified as being moderately polluted with MPs. The dominant color, shape, size, and polymer type of MPs in sediments were transparent, fiber, 0.05–1 mm, and polypropylene, respectively. The river bay had a mean abundance of MPs two-fold greater than either the bay or central area of the lake. This indicates that the river catchment caused more pollution with MPs, while the central area of the lake was not a sink for MPs. Spatial trends of MPs in sediments from the shore to the center of the lake differed among areas, and were significantly related to wind, lake current, sedimentation rate, water- and sediment-properties, water depth, and proximity to land sources of MPs.

Ostracoda (Crustacea) as indicators of subaqueous mass movements: An example from the large brackish lake Tangra Yumco on the southern Tibetan Plateau, China

A conceptual model of subaquaeous mass movements and ostracod distribution in lacustrine sediment event layers was tested. Integrated methods (geophysical, sedimentological and microfossil analyses) were performed on a short sediment core retrieved from 220m water depth in the large brackish lake Tangra Yumco on the southern Tibetan Plateau, central Asia. The event layers of the core and their underlying and overlying sediments were investigated. Four major event layers composed of sandy silt with graded bedding are interpreted as turbidites. The fifth layer consisting of fine sand and silt and without graded bedding is characterized as a debrite.The ostracods, small bivalved aquatic crustaceans, identified are Leucocytherella sinensis Huang, 1982, Leucocythere? dorsotuberosa Huang, 1982, Limnocythere inopinata (Baird, 1843) and Fabaeformiscandona gyirongensis (Huang, 1982).Ostracod evidence is a good proxy for the evaluation of massive sediment event layers formed by subaqueous mass movements. Four assumptions of a conceptual model were confirmed: (i) fine grained sediments of event layers (turbidite deposits) contain very low numbers of ostracods compared to the underlying and overlying sediments; (ii) ostracods are sorted according to size and display high abundance and high proportion of adult valves of Leucocytherella sinensis at the base of event layers; (iii) a relatively low number of carapaces is present within the event layers; and (iv) the recolonization of newly event-generated habitats by pioneer assemblages transforming into pre-event association gradually.

STORM SURGE DEPOSITION BY HURRICANE IKE ON THE MCFADDIN NATIONAL WILDLIFE REFUGE, TEXAS: IMPLICATIONS FOR PALEOTEMPESTOLOGY STUDIES

Hurricane Ike made landfall at Galveston, Texas on September 13, 2008. A storm surge in excess of 3 m struck the upper Texas coast, situated in the northeast quadrant of the landfalling hurricane. The storm surge caused widespread flooding many tens of kilometers inland and transported large amounts of offshore and littoral sediments into nearshore subaerial environments. This study documents the character of storm surge sedimentation on the McFaddin National Wildlife Refuge, which includes extensive palustrine marshes and large brackish lakes. The storm surge deposit exhibits two distinct styles of sedimentation: a thick, sandy washover fan, extending about 150 m inland, deposited as traction load; and a thinner, finer, more organic-rich blanket of sediments extending more than 2.7 km inland, deposited from suspension. Cores collected from the bed of Clam Lake, a large brackish lake on the refuge, approximately four weeks before and 16 weeks after Hurricane Ike’s landfall, show that the storm surge deposited a 10-cm-thick sediment layer onto the lake bed. Lithologically, the deposit was similar to lake-bed sediments and did not form a distinct layer in cores, but it was distinguished by abundant offshore foraminifers. However, examination of a lake-bed core for earlier hurricane deposits revealed that foraminifers are not well preserved, and it was concluded that Clam Lake was unsuitable for paleotempestology studies based on lithologic and foraminiferal evidence of hurricane strikes. The study shows that storm surge sedimentation can extend a considerable distance inland, with the implication that paleotempestology studies could be conducted farther inland than in previous studies if sites suitable for long-term preservation of foraminifers are available.

Modeling of integrated marine ecosystem including the generation-tracing type scallop growth model

The new numerical marine ecosystem model has been developed to establish an optimum management plans for sustainable aquaculture in estuaries. This model was applied to Lake Saroma, which is the third largest brackish lake and one of the major sources of aquacultured scallops in Japan. In this study, the pelagic ecosystem model, the benthic ecosystem model and the scallop growth model were integrated comprehensively. This model is remarkable for two features. Firstly, the farming cycle in this area was considered in detail. This was achieved by dividing the aquacultured scallops into three compartments according to their age; each compartment having two state variables, biomass and number of individuals. This feature, called the Generation-tracing type model, made it possible to evaluate weight changes of scallops for each generation. Consequently, simulated results of scallop weights showed good accordance with the measurements. Secondly, the amount of released nutrients from the sediment was evaluated using a vertical diffusive equation with simultaneous mineralization processes in sediment. To evaluate the amount, the interaction between the pelagic and benthic systems, which is generally a very important factor in enclosed water, was modeled. This structure provided the model with an ability to predict future water quality and production of scallops with sediment changes. At the next stage of the study, we applied this model to compare scenarios for future management. Preliminary results showed that a larger number of cultured scallops would result in a smaller average scallop size and worse water quality because of sediment degradation due to the increased deposit of scallop feces.

WATER QUALITY IN LAKE OGAWARA RELATED TO THE HABITATION OF CORBICULA JAPONICA

In the regional development, a balance of development and preserving of natural resource should be considered. The precious natural environment has to be maintained. The Lake Ogawara in Aomori Prefecture is one of large brackish lake where the most dominant water organism for fishery is Corbicula japonica. And the water quality and the flow of the lake is very related to the habitation of the clams. The field observation of water quality was carried out for this lake in the period for three years from August 2002. From a viewpoint of water quality environment, egg-l aying and hatching of them are performed on the north side of the lake, and they diffuse throughout the lake by the flow.