Field experiments on chemical and biological changes of thin-layer oyster shells capping sediments in dense aquaculture area.

Thin-layer oyster shell capping has been proposed as a method for improving contaminated coastal environments. Field experiments were conducted to investigate the effects of oyster shell capping on nutrient concentrations, microorganisms, and macrobenthic communities. The concentration of PO4-Pin the experimental area decreased by approximately 38% more than in the control, due to phosphorus fixation of oyster shells and the presence of Proteobacteria. Ammonia-oxidizing bacteria such as the order Pirellulales (phylum Planctomycetes) were related to the low ratio of NH3-N found in dissolved inorganic nitrogen in the experimental area, indicating nitrification promotion. The reduction in annular benthic organisms observed in the experimental area indicates a decline in sediment organic matter, which could potentially mitigate eutrophication. Oyster shell capping was confirmed to be an effective material for restoring coastal sediments by improving their chemical and biological properties.

Natural Variations in the Benthic Environment and Bacterial Communities of Coastal Sediments around Aquaculture Farms in South Korea.

The aim of this study was to examine the possible seasonal variations in the nutrients (dissolved inorganic nitrogen-DIN and phosphorus) and benthic bacterial communities in marine aquaculture surrounding sediments. The study areas were Geoje, Tongyeong, and Changwon bays in Korea, which are famous for oysters (Magallana gigas), Halocynthia roretzi, and warty sea squirt (Styela clava) farming, respectively. The study sites included semi-enclosed coastal areas with a low seawater exchange rate. Subtidal sediment samples were collected seasonally from the area surrounding the aquacultures between April and December 2020. Seasonal variations in nutrients were observed, with the highest concentration of DIN in August. For phosphorus, site-specific variations were also observed. To investigate the variations in benthic bacterial communities, the advanced technique of 16S rRNA gene amplicon sequencing was applied, and the results indicated a seasonal variation pattern and predominance of Proteobacteria (59.39-69.73%), followed by Bacteroidetes (6.55-12.85%) and Chloroflexi (2.04-4.50%). This study provides a reference for future studies on natural variations in the benthic environment and bacterial communities in the areas surrounding aquacultures. Supplementary Information: The online version contains supplementary material available at 10.1007/s12088-023-01067-8.

A microcosm study of microbial community profiles during sediment remediation using pyrolyzed oyster shells.

The accumulation of organic and inorganic components in sediments leads to a deterioration in the environment and an imbalance in the coastal ecosystem. Currently, capping is the most effective technology for remediating polluted sediment and restoring ecosystems. A microcosm experiment was designed using pyrolyzed oyster shell (POS). These were mixed in with coastal sediment or added as a capping layer. The results showed that POS effectively decreased pollutants, including PO4-P and NH4-N. Metagenomics analysis was performed using 16S rRNA gene sequencing and the most abundant phyla identified in the POS treated and untreated sediments were Proteobacteria, followed by Firmicutes, Bacteroidetes, Chloroflexi, Fusobacteria, Nitrospirae, and Spirochaetes. The relative abundance of Proteobacteria members of the Class Gammaproteobacteria significantly increased, but Deltaproteobacteria gradually decreased throughout the experiment in POS-covered sediment. This suggests that the POS effectively promoted a shift from anaerobic to facultative anaerobic or aerobic microbial communities in the sediment. Dominant species of facultative anaerobic or microaerophilic bacteria from the order Chromatiales and phylum Nitrospirae were observed in the POS-covered sediment. Based on these study results, it can be concluded that POS is an effective covering material for sediment remediation and restores the microbial communities in sediments.

Field study on short-term changes in benthic environment and benthic microbial communities using pyrolyzed oyster shells.

To evaluate the effect of pyrolyzed crushed oyster shells (PCOS) on the remediation of sediments and microbial diversity, a field study was conducted in Buksin Bay, Tongyeong City, Republic of Korea. It was observed that after treatment with PCOS, the concentration of H2S in the sediment of the control site was 287 mg/L. Furthermore, it decreased up to 0 mg/L and remained so until the end of the field study, that is for a period of six months. Moreover, the concentrations of NO2-N + NO3-N, NH4-N, and PO4-P decreased sharply, and the oxidation-reduction potential (ORP) increased after PCOS treatment in pore water and overlying water. Regarding the diversity of microbial communities, the predominance of bacteria from phylum Chlorobi was observed in highly reduced (-410 mV; ORP) sediment, which is well known for the production of H2S. After PCOS treatment, the relative abundance of Chlorobi was sharply suppressed. On the other hand, the predominance of bacteria from the phyla Proteobacteria and Bacteroidetes was observed, and their relative abundance in the PCOS-treated sediment increased throughout the experiment, based on 16S rRNA sequencing. The results demonstrate that the abundance of bacterial communities in the PCOS-treated sediments of Buksin Bay is important for marine ecological functioning, especially for pollutant transformation.

Diversity of Microbial Communities in Sediment from Yeosu Bay, Republic of Korea, as Determined by 16S rRNA Gene Amplicon Sequencing.

Monitoring natural variations in microbial diversity is crucial because microorganisms play a major role in the environmental processes in marine sediment. To evaluate the microbial diversity in Yeosu Bay sediment, 16S rRNA gene amplicon sequencing was performed. Proteobacteria, Chloroflexi, and Bacteroidetes were the predominant phyla in all sediment samples observed.

Effect of Bacillus subtilis Zeolite Used for Sediment Remediation on Sulfide, Phosphate, and Nitrogen Control in a Microcosm.

Eutrophication is an emerging worldwide issue concerning the excessive accumulation of various pollutants in sediments, owing to the release of industrial or household wastewaters to coastal areas. The coastal sediment of Goseong Bay in the Republic of Korea is organically enriched with pollutants, including heavy metals, sulfide, phosphate, and ammonia. Microbial remediation and capping techniques have been suggested as effective routes for sediment remediation. In this study, Bacillus subtilis zeolite (BZ) was used as a sediment capping material, and effective remediation of coastal sediment was observed in a 40-day laboratory microcosm experiment. A significant decrease in the sediment water content and reduced concentration of acid volatile sulfide were observed in the BZ-capped sediment. In the overlying water and pore water, significant decreases in phosphate and dissolved inorganic nitrogen (DIN; NO2-N + NO3-N and NH4-N) concentrations were observed in the BZ-treated experiment. Based on our findings, we conclude that BZ could be an effective capping material for coastal sediment remediation.

Seasonal Sampling of a Microbial Community in the Sediment of Geoje-Hansan Bay, Republic of Korea.

Several oyster farms are concentrated in Geoje-Hansan Bay, Republic of Korea, and there is concern about marine pollution. Hence, we monitored the sediment at this site for a year using 16S rRNA gene sequencing. The predominant phyla were Proteobacteria (69.9 to 79.1%) and Bacteroidetes (8.2 to 10.6%) in all seasons.

16S rRNA Gene Amplicon Sequencing of Contaminated Coastal Sediment Collected from the Taehwa River Estuary, South Korea.

The Taehwa River Estuary is one of the largest enclosed bays in east Korea. In order to understand the environment of the Taehwa River Estuary, the microbial diversity in the sediment of the estuary was investigated through 16S rRNA gene sequencing. The predominant phyla in all locations were Proteobacteria and Bacteroidetes.