A sampling of the water column and benthos was carried out at Mission Bay. Water column and plankton sampling was conducted biweekly while Sediment and benthic community samples were collected monthly. Particle size, porosity, and the initial phosphorus concentration in sediments are the main factors affecting phosphorus release flux through the sediment-water interface. Sediments can be physically divided to muddy and sandy matters, and the adsorption-desorption capacity of sediment with phosphorus depends on particle size.
Pollutants’ interaction with water and sediment allows sediment to become the main carrier of pollutants in rivers, lakes and other water columns, called the “sediment environmental effects”.
On the one hand, the transport of suspended sediment in water not only directly affects the pollutants in the distribution between the solid phase and liquid phase but also changes the spatial and temporal distribution in water columns. On the other hand, the deposition of sediment may be a potential important pollution “source” or “sink”, and certain hydrodynamic disturbances may result in the conversion between them.
(Andrieux-Loyer, F., & Aminot, A. 2001).
According to (D. M., & Warrick, J. A. 2010)Water of lakes and rivers, most of which comes from sediment, is regarded as a major component of the contaminant source. The release of phosphorus can be affected by many environmental factors such as temperature, pH value, red ox potential, etc. For phosphorus as active pollutant, its behavior of adsorption-desorption with the sediment particles plays a very important role in the diffusion process at the sediment-water interface. Phosphorus has a strong affinity with sediment particle.
During sediment particles settling and resuspension, some phosphorus adsorbed onto sediment particle surface can also suspend migrates with the sediment movement in water column.
Phosphorus stored in sediment can be released by two ways without disturbance. One is Molecular diffusion, which may be one of the most common reasons causing the sediment-water flux of contaminant though it has often been considered negligible. (Rubin, D. M., & Topping, D. J. 2008)The diffusion process is continuously and significantly modified by the rates of contaminants adsorption-desorption between the solid sedimentary particles and the surrounding pore waters. The other way is desorption from particle surface either from bottom sediment or suspended sediment. Contaminant-containing sediment has more changeable physical properties, which has an important influence on the pollutant mass transfer within the diffusion boundary layer. (Sanchez, A., & Ortiz, C. 2013)
Previous studies have not fully considered the effects of sediment physical properties with different grain-sized components on the diffusion and sorption processes of phosphorus. And it is significant to characterize the phosphorus adsorption/desorption behavior with respect to sediment size fractions. This paper mainly studied the role of sediment particle size and its distribution characteristics in the phosphorus transportation to the overlying water. Different characteristics of two release ways of phosphorus from sediment were also examined in different grain-sized sediments.
The natural sediments were collected from Mission bay. All sediment samples underwent a pretreatment process to remove a large number of inorganic, metal ions, polymer and humus, water algae and other microorganisms adhered on the surface of sediment particles. And then the sediments were restored at the state not contaminated and the main components of the sediment did not change a lot. (Sanchez, A., & Ortiz, C. 2013)
An instrument known as the test-bed aircraft multispectral scanner (TBAMS) was used in a research flight over the entrance to Mission Bay. Up welled radiances from the TBAMS data were correlated with the water parameters, particularly sediment and chlorophyll a. Several algorithms were demonstrated for monitoring sediment and chlorophyll, with a three-band ratio being the best. The primary advantage of the three-band ratio was found to be its apparent insensitivity to atmospheric and Sun-angle variations.
The abundance of macrofauna in sediment samples was determined by sorting through surface sediments from mission bay. Sediment sub cores were transported to the lab and placed upright in a freezer, where they remained for at least 24 hours. After the subcores had frozen, they were sectioned with a saw to remove the upper 2 cm of sediment. Each surface section was placed in a sample bottle to thaw, along with formalin (3.7% formaldehyde solution) buffered with seawater and borax. After the sample had thawed, it was agitated gently to mix the formaldehyde with the sediments. Samples were allowed to remain in formalin for at least 24 hours, after which the formaldehyde was decanted off and replaced by deionized water. After at least 24 hours the water was removed and replaced with fresh deionized water. At least 24 hours after this second transfer, the deionized water was removed and replaced with 70% ethyl alcohol and rose bengal, a stain used to enhance the visibility of biological material. (Lopez, G. R.1998).
Preserved samples were examined for organisms, which were removed from the sample and identified to lowest possible taxon. The volume of sediment examined was transferred to a graduated cylinder for quantification. A minimum of 3.0 ml of sediment was examined from each subsite for each sampling period.
Arcutula senhousia has become abundant in Mission Bay, San Diego, California. Here, the mussel exhibits many traits typical of opportunistic species. Although the maximum life span of senhousia is approximately 2 yr, mortality is high and most of the populations are only annuals. Overall. Senhousia appears to display similar life-history characteristics both in this invaded system and within its native range. (Warzocha, J., & Gostkowska, J. 1991)
Characteristics of the phosphorus interfacial diffusion from sediment with different particle grain sizes and porosities were investigated experimentally. Different particle diameters led to differences in phosphorus adsorption capacities. The smaller the particle size was, the greater the capacity of phosphorus adsorption-desorption were. These remarkable features directly affected not only the sediments phosphorus desorption release, but also the diffusion process through pore. (Sanchez, A., & Ortiz, C. 2013)
Water to the overlying water. For a given particle, there was a close correspondence between the maximum adsorption capacity and the sediment concentration, the sediment adsorption capacity increased at first and then decreased with the increase of particle sizes due to the early release of fine sediment particles themselves. The initial release of the coarse sediment was mainly from the sediment pore water caused by molecular diffusion.
In the static release process, sediments with different particle sizes and composition showed inconsistent relative trends during the initial release period. Fine particles had direct desorption ability, contribution to release flux to the overlying water was mainly reflected on the initial condition. (Warzocha, J., & Gostkowska, J. 1999)
The direct desorption capability of coarse particles were weaker than fine ones. But due to the large amount of pollutants stored in the sediment layer with larger porosity, the diffusion from pore water played a prominent role after initial desorption stage. At the same time, the initial concentration made greater impact on the adsorbed amount onto the sediment, the corresponding result lied indirect desorption of surface sediments and pore water diffusion release, both release mechanisms changed the relative contribution for different periods. In a certain depth of sediment, the decay time increased with the increasing particle size. Source of phosphorus in the overlying water came from desorption of the fine particles and diffusion from pore water in coarse sediment, indicating that the desorption process was faster than the diffusion of the molecules in pore water.
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