Mariculture Ponds Research Articles

The effect of Sesuvium portulacastrum for reducing inorganic nitrogen pollution in coastal mariculture wetland

Mariculture ponds are essential components of the coastal wetland, which are often criticized by eutrophication risk for the dissolved inorganic nitrogen (DIN) input to the coastal zone by the culture tailwater. However, the reduce of this DIN pollution was difficult because the tailwater is hard to collect and the treatment is inefficient and expensive. Sesuvium Portulacastrum is a coastal vegetation which has high efficiency in DIN absorption from the seawater and sediment. In this study, we use Sesuvium Portulacastrum as a tool species to study the control behavior of the DIN in mariculture ponds wetland. The change trend of DIN in pond water and benthic species in pond sediment was investigated. The results showed that Sesuvium Portulacastrum reduced NH4+, NO3-, and NO2- in the pond water by 83.21%, 95.22%, and 91.32%, respectively. The species number of benthic organisms was enhanced from 2 to 5 and the species structure was more optimized in Sesuvium Portulacastrum pond than control pond. At the end of the experiment, eutrophication indicator species (Capitella capitata) was disappeared in the Sesuvium Portulacastrum pond. Those suggest that the coastal vegetation (Sesuvium Portulacastrum) have great potential to eliminate DIN pollutants in mariculture pond wetland.

Effect of Low-Proportion Replacement of Dietary Fishmeal with Neanthes japonica Meal on Growth Performance, Body Composition, Muscle Texture, Serum Biochemistry, Digestive Enzymes and Gene Expression in Juvenile Tiger Puffer Takifugu rubripes

The polychaeta Neanthes japonica is a common by-product in mariculture ponds. It is rich in essential nutrients, but has not been well-explored. Therefore, this 56-day experiment investigated the effects of substituting N. japonica meal for dietary fishmeal on juvenile tiger puffer (15.49 ± 0.02 g, n = 450 fish). The control diet (CON) contained 40% fishmeal. Freeze-dried N. japonica meal (FNM) was supplemented into CON at the levels of 3% (FNM3), 6% (FNM6), and 9% (FNM9), replacing fishmeal. The fifth diet contained 6% oven-dried N. japonica meal (ONM6), replacing fishmeal. The results indicated that no significant difference was observed in growth, feed efficiency, and somatic index among all the treatment groups. The feed intake of the FNM6 group was significantly higher compared to CON. No significant difference was detected in fish proximate composition, as well as the fatty acid composition, amino acid composition, and muscle texture. The supplementation of N. japonica meal decreased the activities of intestinal lipase and α-amylase. The addition of freeze-dried N. japonica meal significantly up-regulated the expression of the intestinal amino-glycine transporter pat1. It was concluded that adding 9% N. japonica meal to the feed had no significant effect on the growth performance and body composition of juvenile tiger puffer.

Artificial wetlands providing space gain for the suitable habitat of coastal Pied Avocet

A large number of artificial wetlands have replaced natural wetlands along waterbird migration routes to supply breeding, resting and feeding grounds for waterbirds. Effective identification of potential artificial wetlands that could serve as suitable habitats for waterbirds can provide important reference for field investigation and waterbird conservation. In this study, the habitat suitability of the Pied Avocet in the Yellow River Delta (YRD), China was simulated with the optimized MaxEnt model based on its occurrence records and environmental variables. The results showed that the MaxEnt model could well predict the habitat suitability of the Pied Avocet (Recurvirostra avosetta) in the YRD. The suitable habitats were distributed in the specific areas of the coastal zone, and artificial wetlands such as salt pans and mariculture ponds were the main components in the high-suitability area. The top three environmental factors affecting habitat selection were the land use and land cover (LULC), distance to the coastline and normalized difference vegetation index (NDVI). This paper emphasizes the role of artificial wetlands in providing suitable habitat for waterbirds. In order to better protect the habitat of waterbirds and alleviate human-bird conflict in the YRD, some targeted suggestions were put forward for the management gap of artificial wetlands. This study has strong practical significance for the protection and habitat management of waterbirds in the YRD. The methodology we employed is transferable to other wetlands, where efficient management is inhibited due to a lack of comprehensive field investigations.

Influencing mechanism of farming clams on the CO2 flux from aquaculture ponds: Insights from ecosystem carbon metabolism

Aquaculture ponds have garnered increasing attention for their potential roles in the global carbon cycle within the context of global warming. As a significant co-culture species in mariculture ponds, clams exert a notable impact on CO2 flux across the water-air interface. However, the mechanism underlying this influence is as yet unclear. This study measured the CO2 flux as well as the ecosystem carbon metabolism and environmental physiochemical parameters from four marine polyculture ponds, i.e., the pond containing swimming crabs and kuruma shrimp was referred to as CS, and the other three ponds containing three varying densities of razor clams additionally based on CS were noted as CSB1, CSB2, and CSB3 in order of increasing clam density. All the bi-species and tri-species polyculture ponds acted as atmospheric CO2 sinks during the farming season, with the peak in CSB1 and the lowest in CSB3. Net ecosystem production was a dominant regulator of CO2 uptake, and sediment respiration significantly increased CO2 production and then affected the CO2 flux, contributing 16.7–20.0 % to the ecosystem respiration (ER). Water pH could function as a potentially reliable CO2 flux predictor in the polyculture ponds, while Chl a was an internal driving factor. The polyculture of clams at low density may have exerted a “bottom-up” effect, accelerating nutrient cycling and thus stimulating the planktonic community, gross primary production (GPP), and ER, whereas a high stocking density of clams can have a “top-down” effect that would have the opposite ecological effects through increased predation pressure from clams. Although GPP and ER were simultaneously promoted or inhibited by clams at different stocking densities, the effect on GPP was always greater than that on ER, resulting in the CO2 sink function that the polyculture ponds performed through the water-air interface being strengthened at low clam densities and weakened at high clam densities. Given the good predictive ability of water pH on CO2 flux, monitoring and management of water pH could be an effective way to regulate the CO2 sink function of mariculture ponds.

Mesopore-rich La-based metal organic framework derivatives for phosphorus removal from mariculture tailwater

Deep dephosphorization of mariculture tailwater, a typical high-salinity and weakly alkaline wastewater, is difficult but essential for meeting ever-stricter stringent emission standards. Herein, we developed an alkaline-conversion method to prepare lanthanum-based metal organic framework (La–MOF) derivatives for efficient phosphate removal from mariculture tailwater. During the templated alkaline-conversion process, the strong-alkaline regent gradually broke the coordination bonds of La–MOF while maintained its macrostructure, and the La nodes liberated from the framework were then crystallized into La(OH)3. The universality of this conversion method was verified on other La–MOF precursors with different benzoic multicarboxylate ligands. Importantly, numerous mesopores were formed in the derivative interior, increasing the number of exposed active La sites and accessible transfer channels. Therefore, the derivative exhibited superior phosphate-adsorption performance with a high adsorption capacity (Langmuir Q0: 155.7 mg P/g) and a rapid adsorption rate. The obtained La–MOF derivative with stable structure had broad neutral–alkaline pH range adaptability, which was demonstrated satisfactory dephosphorization selectivity and high cyclic performance under different seawater conditions (coexisting anions, cations, H3BO3 and natural organic matter). Finally, the obtained mesopore-rich La–MOF derivative exhibited an excellent deep dephosphorization capacity for actual mariculture tailwaters collected from seven mariculture ponds. The reactive phosphate level was quickly reduced to an ultra-low effluent concentration (<0.05 mg P/L), demonstrating the promising application potential of the La–MOF derivative.

Effects of salinity on the growth, physiological and biochemical components of microalga Euchlorocystis marina

Euchlorocystis marina, a new marine species of the genus Euchlorocystis discovered in 2022, has the potential to improve the water quality in mariculture ponds. However, the effects of salinity on the growth, physiology, and biochemical composition of these algae are not well understood. In this study, changes in physiological and biochemical indices such as cell density, photosynthetic pigment, polysaccharide, and lipid content of E. marina under different salinity treatments were analyzed. The results showed that the highest cell density was observed at a salinity of 15‰. The lowest photosynthetic pigment content was observed at a salinity of 60‰, and the highest polysaccharide and lipid content was observed at a salinity of 60‰. These results indicated that lower salinity was more conducive to E. marina reproduction and growth. E. marina can accumulate polysaccharides and lipids in high salinity environments. This study provides new information for understanding the salinity adaptation strategies of E. marina and has practical significance for its development and utilization.

Human-induced rapid siltation within a macro-tidal bay during past decades

Tidal bay evolution is the result of the comprehensive influence of multiple factors. It is crucial to analyze the primary factors to disassemble the comprehensive effects. In this study, remote sensing and bathymetric data were used to investigate anthropogenic activities and geomorphological changes in Puba Bay, China. From 1964 to 2020, the intertidal zone area decreased by 64.5% due to mariculture ponds and coastal reclamation, with the former accounting for 60.4% of the total area. Over five decades, the bay experienced significant silting, with a 61.5% decrease in underwater area, an 88.4% decrease in volume, and considerable reductions in maximum water depth, cross-sectional terrain depth, and width. Anthropogenic activities led to a reduction in tidal prism and tidal velocity, resulting in increased flood dominance and decreased ebb dominance in the main channel, leading to more siltation. Negative and positive feedback mechanisms were observed between anthropogenic activities, seaward expansion of intertidal flats, and bay siltation. The influence of mariculture ponds, as the major factor, on geomorphological changes was found to be similar to that of coastal reclamation. To maintain water depth and capacity for material exchange in the bay, preliminary suggestions for mariculture pond management are proposed.

Influence of wastewater discharge from dredging mariculture pond sediments on the food sources of two intertidal crab species

The present study δ13C, δ15N and fatty acid compositions of two dominant mangrove crabs, Tubuca arcuata and Parasesarma plicatum were compared between a mangrove site frequently receiving dredged wastewater from mariculture ponds and an adjacent reference site, to investigate the impact of wastewater discharge on their diets. A laboratory experiment was also conducted to further test how their diets changed with the wastewater input. The result showed no significant change in the δ13C while clear 15N enrichment of crabs in association with the wastewater discharge. Changes in 15N signature and fatty acid composition of the crabs due to the wastewater discharge indicated that the impact of wastewater discharge was related to crab species, being more apparent on the deposit feeder (T. arcuata) than the herbivorous P. plicatum. The results suggested that the discharge of dredged wastewater into mangroves resulted in the uptake of wastewater-derived materials and nutrients by mangrove crabs.

Identifying shorebird conservation hotspots and restoration gaps in stopover sites: A perspective of ‘ecologically linked’ habitats

Shorebird populations are declining around the world, which has prompted concerns regarding tidal flat protection during migration. The lack of high-tide roosts not only can limit the access of shorebirds to tidal flats but also means that they expend more energy when moving between tidal flats and roosting sites. This situation can negatively affect their body condition. This highlights the importance of maintaining a network of tidal flats and high-tide roosts “ecologically linked” by shorebirds. Using the Yellow River Delta (YRD), a key stopover site in the East Asian–Australasian Flyway (EAAF), as the case study area, we assessed how the availability of optimal high-tide roosts has changed over time and identified conservation hotspots and restoration gaps from the perspective of ecological connectivity for shorebirds. Based on a developed Geographic Information System (GIS) method, combined with knowledge of shorebird roost choices from the literature and remote sensing data, we evaluated the adequacy of high-tide roosts in the YRD over 20 years (2000–2020) and identified restoration areas by scenario analysis. The results showed that 1) the mean distance between potential intertidal habitats and the nearest optimal high-tide habitat increased from 1305 m in 2000 to 2931 m in 2020, with a 30 % decline in the area of intertidal habitats suitably covered by optimal high-tide habitats for shorebirds in Group 1 (body length ≦ 20 cm) in the YRD; 2) the scenario analysis suggested that this gap can be eliminated by seasonal management of mariculture ponds and salt pans in key areas. This approach is likely applicable to stopover sites throughout the EAAF.

Conversion of natural coastal wetlands to mariculture ponds dramatically decreased methane production by reducing substrate availability

Coastal wetlands are increasingly being converted into aquaculture ponds to meet growing global demand for fish protein. Coastal wetlands conversion has been predicted to result in significant carbon (C) emissions; however, a mechanistic understanding of the effects of coastal wetland conversion on soil’s capacity to produce greenhouse gases remains lacking. Here, integrated biogeochemical investigations on methanogenic substrates, community structures, and activities were conducted in a coastal Spartina alterniflora saltmarsh and three saltmarsh-converted mariculture ponds aged 6, 13, and 20 years. Saltmarsh conversion into mariculture ponds decreased CH4 production potential from 353 to 16.3–78.3 µg CH4 kg−1 d−1. The concentrations of dissolved organic C and non-competitive methanogenic substrate, trimethylamine, were reduced by 84.8% and 79.7%, respectively, whereas methanogens abundance decreased by 43.7%, probably due to the decreased C input following conversion. Among the ponds, CH4 production potential, methanogenic substrates (acetate and trimethylamine), and methanogen abundance decreased with conversion chronosequence. However, the dominant methanogen group did not shift after land conversion, and the potential methylamine-utilizing Methanosarcinaceae accounted for 86.5% and 85.3–89.7% of the total populations in the S. alterniflora saltmarsh and mariculture ponds, respectively, implying that methylotrophic methanogenesis was the predominant pathway of CH4 production in both ecosystems. The results indicated that the conversion of natural coastal saltmarsh to mariculture ponds decreased CH4 production by reducing substrate availability and methanogen abundance, and CH4 production potential in mariculture ponds was more efficiently suppressed with conversion chronosequence.

Water quality parameters retrieval of coastal mariculture ponds based on UAV multispectral remote sensing

The rapid expansion of aquaculture in coastal areas is typically associated with ecological negligence and low water quality owing to the economic exploitation of these areas. However, evaluation of these water bodies tends to be laborious, time-consuming, and costly. Therefore, to overcome the limitations of field surveys, in this study, we evaluated the water quality of the cultured water in the Beibu Gulf of Guangxi, obtained spectral reflectance by unmanned aerial vehicle with multispectral sensors, and constructed inverse models of 11 water quality parameters, namely, ammonia nitrogen (NH3-N), chemical oxygen demand (COD), active phosphate (PO4−), dissolved oxygen, nitrate nitrogen (NO3-N), nitrite nitrogen (NO2-N), inorganic nitrogen, total nitrogen, total phosphorus, suspended solids (SS), and chlorophyll a (chl-a), based on the partial least squares method to invert the water quality distribution of regional aquaculture. Furthermore, we compared the retrieval accuracy of different water quality parameters. The following results were obtained: 1) the constructed model’s results showed that the retrieval models for COD, NO3-N, SS, and chl-a had better accuracy compared with those of other parameters; 2) application of the model to the validation set data yielded a correlation coefficient of 0.93 between the measured and predicted SS values, with a mean absolute error of prediction of 4.65 mg L−1; this parameter constructed the best prediction model. According to the validation set results, the correlation coefficients of chl-a, COD and NO3-N are all greater than 0.8, which had better performance effects compared with the remaining models, which are 0.87, 0.86, and 0.81 respectively. This study provides a reference for remote sensing monitoring of water quality in mariculture in cloudy and rainy areas.

The Effect of Purified Attapulgite Addition on Migration and Transformation of Phosphorus in Mariculture Ponds Sediments Under Static and Disturbance Conditions

The Effect of Purified Attapulgite Addition on Migration and Transformation of Phosphorus in Mariculture Ponds Sediments Under Static and Disturbance Conditions

Enrichment of organic carbon increases the flux of phosphorus from sediment in mariculture ponds

Environmental pollution associated with aquaculture activities is one of the major bottlenecks encountered in the sustainable development of fisheries. Accumulating organic carbon (org-C) is an inevitable but undesirable consequence of aquaculture activities, and its degradation influences nutrient flux. However, neither the variations in org-C accumulation nor its impact on phosphorus (P) dynamic has been clearly untangled and reliably quantified so far. Therefore, we carried out a field survey to examine the influences of org-C accumulation on sediment P release in mariculture ponds. The results suggested that org-C contents varied considerably between ponds, being significantly lower in monoculture ponds with bivalve shellfish than in polyculture ponds with bivalve shellfish, shrimp, crab, and fish, likely due to the less-artificial-feeding practice and the function of bivalve shellfish as “environmental cleaners.”Sediment P in mariculture ponds mainly occurred in iron-bound P (44%) and organic-P (hot NaOH-extractable organic + acid-soluble organic P = 56%), while calcium-bound P (CaP) only contributed a tiny proportion of about 1%. The positive correlation between P-flux from sediment and org-C suggested that org-C enrichment can stimulate sediment P release. Further analysis of the linear mixed model combined with piecewise structural equation modeling indicated that the two main forces driving P release - enzymatic hydrolysis release and anoxic desorption - operate with sediment org-C being a significant factor (accounted for 75% of the variation in P-flux). At the same time, other factors such as alkaline phosphatase activity, pH, and CaP may play minor roles in affecting P release. Our findings indicated that org-C accumulated in the aquaculture ponds might trigger sediment P release, posing a potential risk of contaminating the downstream water bodies during tailwater discharge.

Benthic Habitat Quality Assessment in Estuarine Intertidal Flats Based on Long-Term Data with Focus on Responses to Eco-Restoration Activity

A long-term assessment of the benthic habitat quality of intertidal flats in Liaohe Estuary was conducted by three integrating ecological indices, AZTI’s Marine Biotic Index (AMBI), Multivariate-AMBI (M-AMBI), and Shannon–Wiener diversity index (H′) based on macrobenthos data from 2013 to 2020. The results showed that the macrobenthic communities were characterized by indifferent and sensitive species of AMBI ecological groups. The annual ranges of H′, AMBI, and M-AMBI were 0.77–1.56, 1.44–3.73 and 0.36–0.54, respectively. Noticeable differences were found among assessment obtained by these biotic indices. Approximately 100%, 24%, and 78% sampling sites had “moderate”, “poor”, and “bad” statuses as assessed by H′, AMBI, and M-AMBI, respectively. Compared with H′ and AMBI, M-AMBI may be more applicable to evaluate the benthic habitat quality of intertidal flats in Liaohe Estuary. Results suggest that the benthic habitat quality in the middle parts of intertidal flats still had an unacceptable status and has not improved radically to date after large-scale “mariculture ponds restored to intertidal flats”.

Adsorption and immobilization of phosphorus from eutrophic seawater and sediment using attapulgite - Behavior and mechanism

The adsorption behavior of phosphorus on raw sediment (RS), attapulgite (AT), purified attapulgite (PAT) and AT/PAT-amended sediments conforms to the Langmuir, pseudo first-order kinetics and liquid film diffusion model. The adsorption process is spontaneous and monolayer adsorption, and the adsorption rate is mainly controlled by liquid film diffusion. The addition of attapulgite improved the adsorption capacity of phosphorus in the sediments of mariculture ponds. The results of long-term sediment core incubation showed that the average reduction rates of total phosphorus (TP) and soluble reactive phosphorus (SRP) in overlying water and SRP in pore water by adding 20% purified attapulgite (S/PAT20) were 62.11%, 70.83% and 56.32% respectively, and the phosphorus flux in sediments decreased by 53.81%. The addition of attapulgite reduces the risk of phosphorus release in sediments, and changes sediments from “source” to “pool”. The specific surface area and pore volume of PAT increased to 203.254 cm2/g and 0.395 cm3/g respectively, but the phosphorus adsorption capacity was only increased by 2 times compared with AT (1431.3–2671.8 mg P/kg), indicating that the changes of mineral structure and chemical composition jointly determine the phosphorus adsorption effect. Adsorption mechanisms include physical adsorption, surface chemical precipitation, ligand effects, electrostatic attraction and ion exchange. Therefore, seeking modification methods with low energy consumption, low production cost, no damage to rod crystal, expansion of pore volume, increase of hydroxyl and other functional groups, and great retention of effective components are issues that need to be considered to improve the phosphorus adsorption capacity of attapulgite.

Effect of Sinonovacula constricta on sediment microbial numbers and easily degradable organics in shrimp-crab polyculture systems

To explore the influence of different densities of Sinonovacula constricta on the composition of easily degradable organic matter and related functional bacteria, four experimental ecosystems were established: three polyculture systems (PMB1, PMB2, and PMB3) of Portunus trituberculatus and Marsupenaeus japonicus with different stocking densities of S. constricta (11.6, 23.1, and 34.7×104 ind./hm2, respectively) and a polyculture system with only P. trituberculatus and M. japonicus (PM). Among the easily degradable organic components in all aquaculture systems, protein content was the highest (0.74%~0.86%), followed by carbohydrates (0.16%~0.21%) and lipids (0.06%~0.13%). In the high-density (34.7×104 ind./hm2) S. constricta mixed culture system, the contents of carbohydrates, lipids, and proteins in the sediment were significantly lower than those of the other polyculture systems. The number of cellulose-decomposing bacteria in PMB3 was 3.79×106 cfu/g, which was significantly higher than that in the other systems. The number of starch-degrading bacteria and glutin-degrading bacteria was the lowest in PMB3, 1.26×104 cfu/g, and 160.00 cfu/g, respectively. The number of lipid-degrading bacteria in PMB3 was 0.77×104 cfu/g, which was significantly lower than that in the other systems. The easily degradable organics content in sediment was significantly positively correlated with the corresponding functional bacteria. The results showed that mixed culture of S. constricta could reduce the content of easily degradable organics in the sediment of mariculture ponds and change the number of functional bacteria in the sediment and the availability of degradable organic sediments may determine the abundance of corresponding degradable bacteria.

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.

Groundwater salinization in a subtropical region, Beihai, southern China: Insights from hydrochemistry and multiple isotopes (H, O, S, Sr)

Groundwater salinization in coastal aquifers is frequently influenced by seawater intrusion, water-rock interaction, and human activities. We selected the Daguansha high productivity mariculture region and used hydrogeochemical, isotopic analysis methods, coupled with water level and quality monitoring, to identify the main groundwater recharging sources, salinization processes, and evolutionary mechanisms of groundwater in Beihai, China. Our conclusions are based on conventional groundwater chemical components and isotope data for hydrogen, oxygen, sulfur, and strontium. Groundwater levels display notable seasonal variations, and the intensity of anthropogenic exploitation is a major factor influencing fluctuations in groundwater level. The variations of total dissolved solids in groundwater correspond to patterns of spatiotemporal variation in deuterium, sulfur, and strontium isotopes. These results indicate groundwater salinization is influenced by a combination of seawater intrusion and infiltration of water from high-productivity mariculture ponds in the Daguansha area. Notably, interlayer leakage between various aquifers in this area was observed. Local anomalies in groundwater characteristics indicate that groundwater salinization is mainly influenced by water from high-productivity mariculture activities. Investigations of the sources and processes underlying groundwater salinization in the Beihai area can provide a scientific basis for groundwater resource management.

Carbon dioxide and methane fluxes from mariculture ponds: The potential of sediment improvers to reduce carbon emissions

The CO2 and CH4 fluxes across the water-air interface were determined in two groups of swimming crab (Portunus trituberculatus)-ridgetail white prawn (Exopalaemon carinicauda) polyculture ponds. One group of ponds with sediment improver application were referred to as SAPs, and the other group receiving no sediment improver were as NSPs. During the farming season, both the SAPs and NSPs acted as CO2 sinks and CH4 sources. The cumulative CO2-C fluxes from the SAPs and NSPs were −26.78 and −23.49 g m−2, respectively, and the cumulative CH4-C emissions from the SAPs and NSPs were 0.24 and 0.28 g m−2, respectively. CO2 fluxes were significantly related to net primary production and water pH, and CH4 fluxes were mainly regulated by water temperature during the farming season. The application of the oxidation-based sediment improver had a positive effect on reducing the CH4 emissions across the water-air interface but had no effect on CO2 fluxes. The sediment improver reduced the organic matter contents and improved the sediment pH and redox potential, which may have facilitated a decrease in CH4 production in the sediment. The CO2 produced through the oxidation of organic material in the sediment may have been absorbed by strong photosynthesis, resulting in a nonsignificant difference in CO2 fluxes between the SAPs and NSPs. The results indicated that the application of sediment improvers in coastal polyculture ponds can reduce carbon emissions, especially CH4 emissions, during the farming period and could help mitigate global warming with regard to the sustained-flux global warming potential (SGWP) and sustained-flux global cooling potential (SGCP) models over a 20-year time horizon. Future studies on the CO2 and CH4 production rates of the sediment and the related microbial community could improve our understanding of the effect mechanism of the application of sediment improvers on CO2 and CH4 emissions from mariculture ponds.

Characteristics and spatiotemporal distribution of microplastics in sediments from a typical mariculture pond area in Qingduizi Bay, North Yellow Sea, China

Microplastics (MPs) in mariculture environments may have an impact on mariculture and ecosystems. This study sampled the sediments in mariculture ponds and offshore areas in Qingduizi Bay during winter and summer. The abundance, characteristics, spatiotemporal distribution and pollution risk of microplastics were analyzed. The results showed that the abundance of MPs in the mariculture pond and offshore area was 49.2 ± 35.9 items·kg−1 d.w. and 17.1 ± 9.9 items·kg−1 d.w.; the MPs were mainly composed of transparent fibers of thickness 2000–5000 μm, with the main polymers being polyethylene terephthalate (PET) and cellophane (CP). The spatial distribution showed a downward trend from the inside to the outside, but the difference was not significant when comparing different seasons. The pollution load index (PLI) risk assessment showed that all sampling sites were at Hazard Level I. This study can provide valuable information for the risk assessment of microplastic pollution in mariculture areas.