Mariculture Area Research Articles

Antibiotic resistance, virulence and genetic characteristics of Vibrio alginolyticus isolates from aquatic environment in costal mariculture areas in China.

Vibrio alginolyticus has been the second most common Vibrio species in the world and mainly grows in the ocean or estuary environment, which can induce epidemics outbreaks under marine organisms, and causing serious economic losses in aquaculture industry. In this study, the genetic populations and evolutionary relationship analysis of V. alginolyticus isolated from different geographical locations in China with typical interannual differences were exhibited originally genetic diversity. Then the virulence genes prevalence, antibiotic resistance phenotype, and antimicrobial resistance genes risk diversity of V. alginolyticus were analyzed by phenotypic and molecular typing methods. And they were complex correlations among antibiotic phenotypes, resistance and virulence genes under different genotype of V. alginolyticus. The results provide a theoretical foundation for further understanding the genetic and metabolic diversity among V. alginolyticus in China, and lay a theoretical foundation for the transmission risk assessment and regional diagnosis of Vibrio in aquatic animals.

Marine aquaculture mapping using GF-1 WFV satellite images and full resolution cascade convolutional neural network

ABSTRACT Growing demand for seafood and reduced fishery harvests have raised intensive farming of marine aquaculture in coastal regions, which may cause severe coastal water problems without adequate environmental management. Effective mapping of mariculture areas is essential for the protection of coastal environments. However, due to the limited spatial coverage and complex structures, it is still challenging for traditional methods to accurately extract mariculture areas from medium spatial resolution (MSR) images. To solve this problem, we propose to use the full resolution cascade convolutional neural network (FRCNet), which maintains effective features over the whole training process, to identify mariculture areas from MSR images. Specifically, the FRCNet uses a sequential full resolution neural network as the first-level subnetwork, and gradually aggregates higher-level subnetworks in a cascade way. Meanwhile, we perform a repeated fusion strategy so that features can receive information from different subnetworks simultaneously, leading to rich and representative features. As a result, FRCNet can effectively recognize different kinds of mariculture areas from MSR images. Results show that FRCNet obtained better performance than other classical and recently proposed methods. Our developed methods can provide valuable datasets for large-scale and intelligent modeling of the marine aquaculture management and coastal zone planning.

Spatiotemporal dynamics analysis of aquaculture zones and its impact on green tide disaster in Haizhou Bay, China

With the rapid marine economic development, the problem of the marine ecological environment has become progressively prominent. Mariculture monitoring plays an essential role in sustaining ecological stability, rational planning, and green economic development of sea areas. Using the Landsat image, the raft-mariculture area information of Haizhou Bay and its adjacent southern waters were extracted by the object-oriented classification method based on remote sensing techniques. Landscape pattern index and principal component analysis were used to analyze the spatiotemporal expansion and structural changes of mariculture areas, and to quantify the effects of natural, socio-economic factors on the spatiotemporal variations of mariculture areas. This study discusses the correlation between the mariculture area and the outbreak scale of Enteromorpha Enteromorpha green tide. Results show that the object-oriented classification method has the highest accuracy, with total classification accuracy and Kappa coefficient of more than 90% and 0.79, respectively. The total area, patch density, and landscape shape index of mariculture areas in Haizhou Bay increase yearly, which demonstrates that the heterogeneity and fragmentation increase with the expansion of the mariculture area. The landscape pattern changes in the mariculture area are predominantly impacted by annual mean sea surface temperature (SST), annual average wind speed, social development level, and population density, etc. The larger the area of raft-aquaculture, the wider the outbreak scale of the Enteromorpha prolifera disaster. Study results can provide scientific references for the further development of mariculture in Haizhou Bay and marine environmental protection.

Sea surface carbonate dynamics at reefs of Bolinao, Philippines: Seasonal variation and fish mariculture-induced forcing

Coral reefs are vulnerable to global ocean acidification (OA) and local human activities will continue to exacerbate coastal OA. In Bolinao, Philippines, intense unregulated fish mariculture has resulted in regional eutrophication. In order to examine the coastal acidification associated with this activity and the impact on nearby coral reefs, water quality and carbonate chemistry parameters were measured at three reef sites, a mariculture site and an offshore, minimally impacted control site during both the wet and dry season. Additionally, benthic community composition was characterized at reef sites, and both autonomous carbonate chemistry sampling and high-frequency pH measurements were used to characterize fine-scale (diel) temporal variability. Water quality was found to be poorer at all reefs during the wet season, when there was stronger outflow of waters from the mariculture area. Carbonate chemistry parameters differed significantly across the reef flat and between seasons, with more acidic conditions occurring during the dry season and increased primary production suppressing further acidification during the wet season. Significant relationships of both total alkalinity (TA) and dissolved inorganic carbon (DIC) with salinity across all stations may imply outflow of acidified water originating from the mariculture area where pH values as low as 7.78 were measured. This apparent mariculture-induced coastal acidification was likely due to organic matter respiration as sustained mariculture will continue to deliver organic matter. While TA-DIC vector diagrams indicate greater contribution of net primary production, net calcification potential in the nearest reef to mariculture area may already be diminished. The two farther reefs, characterized by higher coral cover, indicates healthier ecosystem functioning. Here we show that unregulated fish mariculture activities can lead to localized acidification and impact reef health. As these conditions at times approximate those projected to occur globally due to OA, our results may provide insight into reef persistence potential worldwide. These results also underscore the importance of coastal acidification and indicate that actions taken to mitigate OA on coral reefs should address not only global CO2 emissions but also local perturbations, in this case fish mariculture-induced eutrophication.

A two-year (2020–2021) observation of marine phycotoxins in phytoplankton in typical mariculture areas of East China Sea

A two-year (2020–2021) observation of marine phycotoxins in phytoplankton in typical mariculture areas of East China Sea

Relationship between toxic and harmful microalgae and environmental factors in typical mariculture areas of East China Sea

Relationship between toxic and harmful microalgae and environmental factors in typical mariculture areas of East China Sea

Exploring the variation of bacterial community and nitrogen transformation functional genes under the pressure of heavy metals in different coastal mariculture patterns

Equilibrium in microbial dynamics and nitrogen transformation in the sediment is critical for maintaining healthy mariculture environment. However, our understanding about the impact of heavy metals on the bacterial community and nitrogen transformation functional genes in different mariculture patterns is still limited. Here, we analyzed 30 sediment samples in the vertical distribution from three different mariculture patterns mainly include open mariculture zone (K), closed mariculture pond (F) and pristine marine area (Q). Illumina MiSeq Sequencing was applied to investigate the bacterial community and structure in the sediment. Quantitative polymerase chain reaction (qPCR) was used to determine the effect of heavy metals on nitrogen transformation functional genes. Results showed that bacterial community and structure varied greatly in different mariculture patterns. Chloroflexi, Proteobacteria and Desulfobacterota were predominant phyla in the coastal mariculture area. High concentrations of heavy metals mainly enriched in the up layer (5–40 cm) of the sediment in the mariculture zone. The abundance of functional genes in the closed mariculture pond was much higher than the open mariculture zone and pristine marine area. And the high abundance of nitrification and denitrification functional genes mainly accumulated at the depth from 5 cm to 40 cm. Heavy metals content such as Fe, Cr, Mn, Ni, As, Cd, Pb and nutrient content NH4+-N, NO3−-N and NO2−-N were highly associated with bacterial community and nitrogen transformation functional genes. This study comprehensively elaborated the effect of heavy metals on the bacterial community and nitrogen transformation functional genes in different coastal mariculture patterns, indicating the possible role of closed mariculture pond in reducing nitrogen transformation efficiency, which will provide useful information for preventing pollution risk in the mariculture area.

Ecological risks assessment of sulfur and heavy metals in sediments in a historic mariculture environment, North Yellow Sea.

The environment behaviors of sulfur and heavy metals in sediments are closely related to sediment aging in mariculture area. In this study, the distributions and ecological risks of reduced inorganic sulfur (RIS) and heavy metals were investigated, along with the relationships between different occurrences of RIS and heavy metals. The results indicated that the adequate organic matter in mariculture sediments significantly enhanced the accumulation of acid volatile sulfur (AVS) compared to the control area. In shellfish farming area, biological sedimentation contributed to accumulation of AVS. The chromium (II)-reducible sulfur (CRS) was the main component of RIS in mariculture area. The environmental risks of heavy metals in mariculture area presented low levels. Principal component analysis (PCA) showed that distribution of Cu closely related to mariculture activities compared to other heavy metals. For ecological risks of heavy metals, the ratio of ∑(acid-soluble fraction (F1)+reducible fraction (F2)+oxidizable fraction (F3))/AVS was the appropriate index rather than conventional simultaneous extraction of heavy metals (SEM)/AVS, because SEM/AVS would overestimate the toxicity of heavy metals. AVS/RIS ratios significantly positively correlated with Pb (F2/(F1+F2+F3+residual fraction (F4)), F2/∑F), Pb (F3/∑F), and Zn (F3/∑F), while significantly negatively correlated with Pb (F4/∑F) and Cu (F1/∑F). These results indicated that the accumulation of AVS during the mariculture process was conducive to the formation of F2 and F3 of Pb, and F3 of Zn, conversely to the formation for F4 of Pb and F1 of Cu, because it was opposite to the accumulation of CRS.

Submarine groundwater-derived inorganic and organic nutrients vs. mariculture discharge and river contributions in a typical mariculture bay

• Fresh SGD carries 7.4-80 % of the total SGD nutrients in a typical mariculture bay. • SGD contributes much more nutrients than river and rivals mariculture wastewater. • SGD-derived organic nutrients are dominant but were typically ignored previously. • China-wide upscaling shows significance of SGD in the whole mariculture areas. Submarine groundwater discharge (SGD) is recognized as one of the most significant pathways for terrestrial nutrient entry into coastal systems. However, SGD-derived nutrient fluxes, particularly organic nutrients, have not yet been considered in the management of mariculture areas. We quantified both saline (12.5 cm day −1 ) and fresh (1.8 cm day −1 ) SGD and related nutrient fluxes using the radium quartet and water mass balance model, respectively, and then reassessed nutrient budgets in a typical mariculture bay. Although fresh SGD accounts for 13 % of the total SGD, it carries 7.4–80.5 % of the total SGD nutrients, suggesting that fresh SGD was an important source of new nutrients with high nitrogen to phosphorus (N/P) ratios (585) into the coastal waters. Based on the rebuilt nutrient budgets, total SGD and mariculture discharge were the two major nutrient sources into the coastal water, providing 2.8–21.2 and 1.9–13.9 times more nutrients than local rivers, respectively. The nutrient speciation results revealed that SGD-derived organic nutrients, which are typically ignored, were dominant (i.e., dissolved inorganic nitrogen and dissolved organic phosphorus through SGD contributed about 22.9 % and 41.5 % of all nutrient resources). Furthermore, China-wide upscaling showed that SGD-derived nutrient fluxes in the mariculture area along the coast of China are comparable those of the rivers in China. Therefore, we suggest that SGD-derived inorganic and organic nutrient fluxes should be incorporated into the ecosystem management of mariculture areas.

Characteristics of microplastic pollution in golden pompano (Trachinotus ovatus) aquaculture areas and the relationship between colonized-microbiota on microplastics and intestinal microflora

Microplastic (MPs) pollution is a global marine environmental problem. The effects of MPs on the gut microbiota of aquatic organisms have received considerable attention. For example, microbes colonizing MPs in pond cultures alter the structure and function of the intestinal microbes of shrimp and fish. It was hypothesized that bacteria on MPs in natural mariculture areas also interact with the intestinal flora of golden pompano (Trachinotus ovatus) because biofilms can form on the surface of MPs during long-term floating in seawater. To our knowledge, this study is the first to investigate MPs pollution in T. ovatus aquaculture. DNA sequencing and bioinformatics analysis confirmed the effect of microbial colonization of MPs on the intestinal flora of T. ovatus. The MPs detected in the gut wet weight (w.w.) of golden pompano (546 ± 52 items/g) were mainly pellets and fragments of blue or green, whereas the sediment MPs dry weight (d.w.) (4765 ± 116 items/kg) were mainly black fibers. The MPs richness in the sediment gradually increased from the open-sea aquaculture area to the estuarine aquaculture area and was positively correlated with the MPs richness in the intestinal tract of golden pompano. MPs 20–200 μm were the most common in the gut and sediment. The intake of MPs increased the abundance of Proteobacteria and decreased that of Firmicutes in the intestinal flora. The functional compositions of MP-colonizing microbes and gut microbiota were similar, suggesting that the two communities influence each other. Network analysis further confirmed this and revealed that Vibrio plays a key role in the intestinal flora and surface microorganisms of MPs. Overall, the intake of MPs by aquatic animals not only affects the intestinal flora and intestinal microbial function, but also poses potential risks to aquaculture.

Atmospheric wet deposition serves as an important nutrient supply for coastal ecosystems and fishery resources: Insights from a mariculture area in North China

To determine the ecological effects of atmospheric wet deposition of dissolved nutrients on the coastal waters around the Yangma Island, rain and snow samples were collected and analyzed at a shore-based site for one year. The wet deposition fluxes of dissolved inorganic nitrogen and phosphorus (DIN and DIP) and dissolved organic nitrogen and phosphorus were 69.2, 0.136, 13.3 and 0.143 mmol m −2 a −1 , respectively. In summer, the new production fueled by wet deposition accounted for 19.3 % of that in seawater and 16.4 % of the amount of particulate organic carbon ingested by the scallops cultivated in the study area, indicating the potential contribution of wet deposition to fishery resources. Meanwhile, precipitation increased the seasonal average DIN/DIP ratios in surface seawater by 17.7 %, 16.3 %, 23.4 % and 6.5 % in spring, summer, autumn and winter, respectively, which could change the composition of ecological community and cause obvious negative impact on the ecosystem and mariculture. • The annual wet deposition flux of DIN contributed to 34.4 % of the DIN load. • Wet deposition may exacerbate the unbalance of DIN and DIP in coastal waters. • Wet deposition could support 19.3 % of the new production of the study area in summer. • Wet deposition could serve as an important source for fishery resources in summer. • Summer deoxygenation was partly related to excessive N input by wet deposition.

Environmental fate and effects of PAHs in tropical mariculture ponds near the northern South China Sea: Rainfall plays a key role

The behavior and fate of PAHs are affected by multiple meteorological factors, but the main factors driving PAHs in tropical mariculture areas are still not clearly understood. This study continuously monitored PAHs in a few tropical land-based mariculture ponds, discussed their dynamic change trend, migration among the multiple media, and the relevant affected factors. Results indicated that PAHs were widely distributed in these environmental media, and the PAHs' concentration showed an obvious attenuation trend in the mariculture cycle. Wet deposition brought overwhelming majority atmospheric PAHs (92 % ± 5.7 %) to the aqueous system, and >72 % of these PAHs came from oil combustion-related sources and biomass combustion. Compared with the natural sea areas in the same region, mariculture ponds sediment could be changed from a sink at the early stage to a secondary release source of PAHs at the late stage of the rainy season, which intensifies the bioaccumulation of PAHs and the risk of edible carcinogenesis of aquatic products. Our research revealed that rainfall drove the occurrence and environmental behavior of PAHs in the tropical mariculture areas, while land-based mariculture ponds ecosystem affected the regional environmental fate of PAHs and weakened their transmission to the marine environment from land.

Community Structure of Periphytic Diatoms in Early-stage Marine Biofilms in a Mariculture-impacted Area

Periphytic diatoms constitute a major part of complex unicellular aggregations called marine biofilm or periphyton, of which little is known about in tropical marine environments. The early-stage community structure of periphytic diatom genera on two artificial substrates – glass slide and polycarbonate sheets – was characterized. These artificial substrates were placed underwater for 6 d and examined on Days 1, 3, and 6 in four sites around Santiago Island, Bolinao, Pangasinan, Philippines, with different relative distances from the intensive milkfish mariculture area. Correlations of diatom community structures in these sites with physico-chemical factors were investigated. The five most abundant diatom genera – namely, Cylindrotheca, Nitzschia, Navicula, Amphora, and Pleurosigma – exhibited a weak correlation with nutrients. Less abundant genera Pseudonitzschia, Haslea, Bacillaria, Thalassionema, Rhizosolenia, Eucampia, Diploneis, Asterionellopsis, Chaetoceros, Bacteriastrum, Licmophora, Skeletonema, Lioloma, Thalassiosira, and Thalassiothrix showed a positive correlation with nutrients. Among sites, the highest benthic diatom cell densities (4.6 × 105 cells cm−2) after 6 d was found in Lucero. Generic richness and diversity varied among sites, with the highest diversity (H’ = 1.58) on Day 1 in Tomasa, the site nearest to the mariculture area, whereas the highest richness (D = 2.17–3.26) for all days and diversity (H’ = 1.38–1.52) for Days 3 and 6 were recorded in Silaqui, the most distal site. Generally, the highest diversity and richness were found on Day 1, which then decreased on succeeding days in all sites. The lack of a clear pattern in community structure among sites relative to the proximity of these sites to the mariculture area may in part be attributed to the presence of other nutrient sources. Results of the study provide baseline information on the variability of periphytic diatom community structure in a mariculture-impacted area, and insights on how benthic diatoms may be used in monitoring the impacts of nutrient pollution.

Biogeochemical properties and fate of dissolved organic matter in wet deposition: Insights from a mariculture area in North Yellow Sea

To address the potential roles of atmospheric wet deposition in carbon cycling in coastal waters, a comprehensive study of the biogeochemical properties of dissolved organic matter (DOM) in precipitation and the resulting implication in a mariculture area in North Yellow Sea was conducted. The annual mean concentrations of dissolved organic carbon (DOC), chromophoric and fluorescent dissolved organic matter (CDOM and FDOM) were 1.52 ± 1.52 mg C L−1, 0.36 ± 0.66 m−1 and 0.38 ± 0.35 QSU, respectively. The concentrations of most DOM proxies exhibited significant negative correlations with the corresponding precipitation amount (R2 = 0.15–0.40, P < 0.01), but the dilution effects became less significant when the precipitation amount exceeded 10.2, 10.7, 10.2 and 2.4 mm for DOC, CDOM, highly‑oxygenated and hypoxic structured humic-like substances, respectively. Seasonally, the dominant precipitation type in winter was snowfall, in which the DOM contained more high-molecular-weight compounds with higher aromaticity and humification degree, while the characteristics of DOM in intensive rainfall in summer were contrary to those in winter. The wet deposition flux of DOC to this region was estimated to be 6.31 × 108 g C a−1, which was 3.3 and 1.4 times that of the dry deposition and local riverine input, thereby contributing to 4.0 % of the DOC storage in the study area. In summer, the intensive input of DOC through wet deposition (0.43 g C m−2) to surface seawater could enrich its bioavailable DOC by 10.7 μmol L−1, the complete aerobic decomposition of which would cause an obvious dissolved oxygen depletion in the surface seawater by 21.4 μmol L−1, demonstrating the influence of wet deposition on summer deoxygenation in coastal waters.

Contaminant Characteristics and Influencing Factors of Heavy Metals in Seawater and Sediments in a Typical Mariculture Bay in South China

Heavy metal pollution in the mariculture areas is of considerable attention due to its potential ecological effects and public concern for seafood safety. A better understanding of the current contamination status and historical trend of heavy metals in the ecosystems of mariculture areas has an important implication for the sustainable development of marine ecosystems and for public health concerns. To assess the impact of human activities on heavy metal pollution in the mariculture area, seven metals (Cu, Pb, Zn, Cd, Hg, As, and Cr) and the environmental parameters were seasonally investigated in the surface seawater and sediments in Qinzhou Bay, a typical mariculture bay in South China. Seasonal variations in the concentration of heavy metals were found in both seawater and sediment, which are mainly influenced by seasonal hydrological change, biological activity, and human influence. The concentration of heavy metals in the seawater was at a relatively higher level than that of other mariculture areas in China, while a lower level was found in the sediment. The concentration of Cu increased in both seawater and sediment for the past decades (by nearly 2 times), which is mainly influenced by the mariculture and shipping activities. The concentration of Hg decreased significantly in the seawater for the past 40 years (decreased by 13 times) due to the decrease in production and usage of Hg. However, the concentrations of Pb, Zn, and Cd in seawater showed an increasing trend in the mariculture bay, while the concentrations of Pb, Zn, As, and Cr decreased in the sediment over the past decades. The decrease in pH value (decreasing by 4.7% for the past 20 years) was responsible for the different trend of those metals between seawater and sediment because the decrease in pH could re-release metals from sediments into the water column. Hg and As are the main ecological risk factors in the mariculture bay. This study suggests that environmental changes, such as ocean acidification, affect the distribution of metals in seawater and sediments, which we should be more vigilant and concerned about under the global climate change.

Carbon Sequestration in the Form of Recalcitrant Dissolved Organic Carbon in a Seaweed (Kelp) Farming Environment.

Under climate change scenarios, the contribution of macroalgae to carbon sequestration has attracted wide attention. As primary producers, macroalgae can release substantial amounts of dissolved organic carbon (DOC) in seawater. However, little is known about the molecular composition and chemical properties of DOC derived from macroalgae and which of them are recalcitrant DOC (RDOC) that can be sequestered for a long time in the ocean. In the most intensive seaweed (kelp) farming area (Sanggou Bay) in China, we found that kelp mariculture not only significantly increased DOC concentration, but also introduced a variety of new DOC molecular species, many of which were sulfur-containing molecules. A long-term DOC degradation experiment revealed that those DOC with strong resistance to microbial degradation, i.e., RDOC, account for approximately 58% of the DOC extracted from kelp mariculture area. About 85% (3587 out of 4224 with different chemical features) of the RDOC molecular species were steadily present throughout the long-term degradation process. 15% (637 out of 4224 with different chemical features) of the RDOC molecular species were likely newly generated by microorganisms after metabolizing macroalgae-derived labile DOC. All these stable RDOC should be included in the blue carbon budgets of seaweed.

Organophosphate esters in the mariculture ecosystem: Environmental occurrence and risk assessments

Most investigations on organophosphate esters (OPEs) are conducted predominantly in a separate biological or abiotic medium, and few joint analyses have been performed in the mariculture ecosystem based on yearly sampling. Herein, we investigated the occurrence, load estimation, phase distribution, source diagnostics, and risks of 20 OPEs in seawater, sediment, and aquaculture organisms from a typical mariculture area in China. The total of these OPEs (∑OPEs) ranged within 3.97–1068 ng/L, 0.39–65.5 ng/g (dw), and 4.09–16.3 ng/g (ww) in seawater, sediment and organisms, respectively. Chlorinated OPEs were the predominant congeners detected in seawater, whereas alkyl-OPEs were the leading contributors in sediment and biological samples. Seasonal variations of ∑OPEs in seawater were more distinct than those in sedimentary environments. Load estimation indicated that approximately 70% of the OPEs in the study area existed in the water bodies. Source identification performed using the U.S. EPA positive matrix factorization indicated that polyurethane foam/plastics and hydraulic oil made the greatest contributions in seawater, whereas chemical production was the predominant source in sediment. Indices of ecological and health risks of OPEs were lower than their risk threshold, indicating that the OPEs detected in this study posed a low risk to the aquatic environment and human health.

Interaction between live seaweed and various Vibrio species by co-culture: Antibacterial activity and seaweed microenvironment

The antibacterial activity of live seaweed (Ulva fasciata, Gracilaria blodgettii and Pelvetia siliguosa) were examined on the three Vibrio (V.) strains (V. parahaemolyticus J1 and V. alginolyticus R1 from maricultural areas, a standard strain of V. parahaemolyticus ATCC17802). Three seaweed species all showed strong inhibition on the culturability of Vibrio strains. Ulva (U.) fasciata as representative seaweed was further studied, which also exhibited inhibition on the swimming behavior, twitching behavior and biofilm formation of three strains. Much more up-regulated differentially expressed genes (DEGs) of U. fasciata occurred in response to V. alginolyticus (5213) than those to both two strains V. parahaemolyticus (3860, 4167), and more than 90% DEGs related to the biosynthesis of secondary metabolites (SMs) were all up-regulated (128–161 DEGs), the least of which and their related pathways occurred by the stress of the standard strain. The stress of two strains from mariculture areas caused richer and more similar profile of up-regulated DEGs in the 30–36 types of SMs biosynthesis pathways, especially for ubiquinone and other terpenoid-quinone biosynthesis with five more up-regulated DEGs than those by the stress of the standard strain. However, the most up-regulated DEGs in the pathways of biosynthesis of unsaturated fatty acids and steroid biosynthesis occurred under the stress of the standard strain and V. alginolyticus, respectively. In addition, Vibrio strains largely promoted the enrichment of endophytic bacteria (EB), mainly for phylum Proteobacteria and genera Alteromonas, Fretibacter, Ruegeria, etc., which favored the U. fasciata against Vibrio. The more significant variation of EB community was also caused by the Vibrio stress isolated from mariculture areas than that by standard strain.

Tidally driven submarine groundwater discharge to a marine aquaculture embayment: Insights from radium and dissolved silicon

For understanding the significance of tidal pumping for driving submarine groundwater discharge (SGD), two time series observations were conducted over tidal cycles in typical mariculture areas of Sanmen Bay, China. Based on 224Ra and dissolved silicon (DSi), the tide-driven SGD fluxes showed significant negative correlations with tidal height, and were 16.4 ± 5.6 cm d−1 and 21.7 ± 13.9 cm d−1 at two coastal sites of the Sanmen Bay, highlighting the potential of DSi in SGD calculation when coastal waters are on short time scales. Furthermore, nutrient fluxes through tidally influenced SGD were estimated to be 11.5–26.5 mmol m−2 d−1 for dissolved inorganic nitrogen, 0.06–0.34 mmol m−2 d−1 for dissolved inorganic phosphorus and 11.5–32.1 mmol m−2 d−1 for DSi, which were higher than those from surface loadings, revealing that tide-driven SGD with large amounts of nutrient and high N:P ratios may significantly contribute to the development of marine aquaculture.

Occurrence of microplastics in a pond-river-lake connection water system: How does the aquaculture process affect microplastics in natural water bodies

Aquaculture activities have been considered to be important sources of microplastics to the water. Microplastic contamination closely related to aquaculture activities has been found in mariculture areas as well as in there nearby natural water bodies. However, for freshwater bodies with complex connectivity, it remains to be revealed how aquaculture activities affect microplastics in neighboring natural water bodies. In this study, we investigated the occurrence of microplastics of a water system consisting of aquaculture ponds, rivers, and lakes in June and December, which represented different aquaculture stages. The average microplastic abundances in June were 167 (67–367) items/m3, 129 (67–233) items/m3, and 372 (100–1167) items/m3, respectively in the lake, river, and aquaculture ponds, while in December, those were 533 (200–933) items/m3, 311 (200–600) items/m3, and 429 (200–600) items/m3, respectively. Microplastic abundance in ponds was significantly higher than in the river in June, while there was no significant spatial difference of microplastic abundance in December. Microplastics abundances in both river and lake were significantly higher in December than in June. The characteristics of morphology, size, color, and polymer type of microplastics were also different among different water bodies in June. However, the differences became smaller in December. The results of this study implied that the drainage of aquaculture ponds might increase the microplastics abundances of natural water in the water system predominated by aquaculture ponds. Further studies of the environmental fate of microplastics in ponds would be beneficial for understanding and controlling microplastics in the whole water system.