Carbon dioxide uptake overrides methane emission at the air-water interface of algae-shellfish mariculture ponds: Evidence from eddy covariance observations

Greenhouse gases emissions from aquaculture ponds: Different emission patterns and key microbial processes affected by increased nitrogen loading

Global aquaculture production is expected to rise to meet the growing demand for food worldwide, potentially leading to increased anthropogenic greenhouse gases (GHG) emissions. As the demand for fish protein increases, so will stocking density, feeding amounts, and nitrogen loading in aquaculture ponds. However, the impact of GHG emissions and the underlying microbial processes remain poorly understood. This study investigated the GHG emission characteristics, key microbial processes, and environmental drivers underlying GHG emissions in low and high nitrogen loading aquaculture ponds (LNP and HNP). The N2O flux in HNP (43.1 ± 11.3 μmol m-2 d-1) was significantly higher than in LNP (-11.3 ± 25.1 μmol m-2 d-1), while the dissolved N2O concentration in HNP (52.8 ± 7.1 nmol L-1) was 150 % higher than in LNP (p < 0.01). However, the methane (CH4) and carbon dioxide (CO2) fluxes and concentrations showed no significant differences (p > 0.05). N2O replaced CH4 as the main source of Global Warming Potential in HNP. Pond sediments acted as a sink for N2O but a source for CH4 and CO2. The △N2O/(△N2O + △N2) in HNP (0.015 ± 0.007 %) was 7.7-fold higher than in LNP (0.002 ± 0.001 %) (p < 0.05). The chemical oxygen demand to NO2-N ratio was the most important environmental factor explaining the variability of N2O fluxes. Ammonia-oxidizing bacteria driven nitrification in water was the predominant N2O source, while comammox-driven nitrification and nosZII-driven N2O reduction in water were key processes for reducing N2O emission in LNP but decreased in HNP. The strong CH4 oxidization by Methylocystis and CO2 assimilation by algae resulted in low CH4 emissions and CO2 sink in the aquaculture pond. The Mantel test indicated that HNP increased N2O fluxes mainly through altering functional genes composition in water and sediment. Our findings suggest that there is a significant underestimation of N2O emissions without considering the significantly increased △N2O/(△N2O + △N2) caused by increased nitrogen loading.

Carbon fluxes of China's coastal wetlands and impacts of reclamation and restoration

Coastal wetlands play an important role in regulating atmospheric carbon dioxide (CO2) concentrations and contribute significantly to climate change mitigation. However, climate change, reclamation, and restoration have been causing substantial changes in coastal wetland areas and carbon exchange in China during recent decades. Here we compiled a carbon flux database consisting of 15 coastal wetland sites to assess the magnitude, patterns, and drivers of carbon fluxes and to compare fluxes among contrasting natural, disturbed, and restored wetlands. The natural coastal wetlands have the average net ecosystem exchange of CO2 (NEE) of -577 g C m-2 year-1, with -821 g C m-2 year-1 for mangrove forests and -430 g C m-2 year-1 for salt marshes. There are pronounced latitudinal patterns for carbon dioxide exchange of natural coastal wetlands: NEE increased whereas gross primary production (GPP) and respiration of ecosystem decreased with increasing latitude. Distinct environmental factors drive annual variations of GPP between mangroves and salt marshes; temperature was the dominant controlling factor in salt marshes, while temperature, precipitation, and solar radiation were co-dominant in mangroves. Meanwhile, both anthropogenic reclamation and restoration had substantial effects on coastal wetland carbon fluxes, and the effect of the anthropogenic perturbation in mangroves was more extensive than that in salt marshes. Furthermore, from 1980 to 2020, anthropogenic reclamation of China's coastal wetlands caused a carbon loss of ~3720 Gg C, while the mangrove restoration project during the period of 2021-2025 may switch restored coastal wetlands from a carbon source to carbon sink with a net carbon gain of 73 Gg C. The comparison of carbon fluxes among these coastal wetlands can improve our understanding of how anthropogenic perturbation can affect the potentials of coastal blue carbon in China, which has implications for informing conservation and restoration strategies and efforts of coastal wetlands.

Prediction and assessment of marine fisheries carbon sink in China based on a novel nonlinear grey Bernoulli model with multiple optimizations

The vigorous development of marine fisheries carbon sinks (MFCS) has become a momentous pathway to mitigate global warming and effectively cope with the climate crisis. Deservedly, based on clarifying mechanism of carbon sequestration, this paper designs a research paradigm for predicting and evaluating the potential of MFCS. Specifically, a novel nonlinear grey Bernoulli model, namely MFCSNGBM(1,1), is proposed by innovatively mining the original data law through adaptive cumulative series and introducing the compound Simpson formula to optimize background values. More precisely, we utilize a heuristic Grey Wolf Optimization algorithm to find the best power index, which enhances the adaptability. To prove usefulness and robustness of MFCSNGBM(1,1) model, yields of seven common shellfishes (oyster, clam, mussel, scallop, razor clam, bloody clam, and snail) and three main algae (kelp, pinnatifid undaria, and laver) are predicted and compared with six competing models. Based on prediction results, new model has the most accurate predictions, with all prediction errors being <10 %, and thus can achieve effective prediction of shellfish and algae production from 2022 to 2025. Further, the capacity and potential of MFCS in China are scientifically evaluated using a removable carbon sink model, considering various yield levels and biological parameters of shellfish and algae. The assessment results show that during the sample period, China's marine fisheries carbon sinks steadily increased with an annual growth rate of 57,000 tons. From 2022 to 2025, with support of policy of MFCS and improvement of disaster prevention and mitigation capacity, the potential of MFCS will be further released. The growth rate of MFCS will be increased to 94,000 tons per year, and its overall scale is expected to reach 2,198,245 tons by 2025, equivalent to fixing 8.06 million tons of CO2. The carbon sink's economic value is significantly estimated to be over 400 billion yuan.

Significant inter-annual fluctuation in CO2 and CH4 diffusive fluxes from subtropical aquaculture ponds: Implications for climate change and carbon emission evaluations

Aquaculture ponds are potential hotspots for carbon cycling and emission of greenhouse gases (GHGs) like CO2 and CH4, but they are often poorly assessed in the global GHG budget. This study determined the temporal variations of CO2 and CH4 concentrations and diffusive fluxes and their environmental drivers in coastal aquaculture ponds in southeastern China over a five-year period (2017-2021). The findings indicated that CH4 flux from aquaculture ponds fluctuated markedly year-to-year, and CO2 flux varied between positive and negative between years. The coefficient of inter-annual variation of CO2 and CH4 diffusive fluxes was 168% and 127%, respectively, highlighting the importance of long-term observations to improve GHG assessment from aquaculture ponds. In addition to chlorophyll-a and dissolved oxygen as the common environmental drivers, CO2 was further regulated by total dissolved phosphorus and CH4 by dissolved organic carbon. Feed conversion ratio correlated positively with both CO2 and CH4 concentrations and fluxes, showing that unconsumed feeds fueled microbial GHG production. A linear regression based on binned (averaged) monthly CO2 diffusive flux data, calculated from CO2 concentrations, can be used to estimate CH4 diffusive flux with a fair degree of confidence (r2 = 0.66; p < 0.001). This algorithm provides a simple and practical way to assess the total carbon diffusive flux from aquaculture ponds. Overall, this study provides new insights into mitigating the carbon footprint of aquaculture production and assessing the impact of aquaculture ponds on the regional and global scales.

Unveiling CRESS DNA Virus Diversity in Oysters by Virome

Oysters that filter feed can accumulate numerous pathogens, including viruses, which can serve as a valuable viral repository. As oyster farming becomes more prevalent, concerns are mounting about diseases that can harm both cultivated and wild oysters. Unfortunately, there is a lack of research on the viruses and other factors that can cause illness in shellfish. This means that it is harder to find ways to prevent these diseases and protect the oysters. This is part of a previously started project, the Dataset of Oyster Virome, in which we further study 30 almost complete genomes of oyster-associated CRESS DNA viruses. The replication-associated proteins and capsid proteins found in CRESS DNA viruses display varying evolutionary rates and frequently undergo recombination. Additionally, some CRESS DNA viruses have the capability for cross-species transmission. A plethora of unclassified CRESS DNA viruses are detectable in transcriptome libraries, exhibiting higher levels of transcriptional activity than those found in metagenome libraries. The study significantly enhances our understanding of the diversity of oyster-associated CRESS DNA viruses, emphasizing the widespread presence of CRESS DNA viruses in the natural environment and the substantial portion of CRESS DNA viruses that remain unidentified. This study's findings provide a basis for further research on the biological and ecological roles of viruses in oysters and their environment.

Higher Food Yields and Lower Greenhouse Gas Emissions from Aquaculture Ponds with High-Stalk Rice Planted

Aquaculture ponds are an important artificial aquatic system for global food fish production but also are a hot spot of greenhouse gas (GHG) emissions. The GHG mitigation strategy and the underlying mechanism for aquaculture ponds are still poorly understood. In this study, we conducted a 2 year field experiment to determine the effects of planting high-stalk rice (an artificially bred emergent plant for ponds) on GHG emissions from aquaculture ponds. Our results showed that planting high-stalk rice reduced CH4 emission by 64.4% and N2O emission by 76.2% over 2 years. Planting high-stalk rice significantly increased the content of O2 and the abundance of pmoA in the sediment, thus prompting CH4 oxidation in the ponds. The reduction of N2O emission from ponds was attributed to the decreased inorganic nitrogen, amoA-B and nirS in the sediment induced by rice. Furthermore, high-stalk rice culture in the pond increased shrimp yields and gained rice yields, resulting in a significant reduction of yield-scaled global warming potential. Our findings suggest that breeding appropriate emergent aquatic plants is a potential pathway to mitigate GHG emission from aquaculture ponds with more food yields and economic benefits.

Shellfish-algal systems as important components of fisheries carbon sinks: Their contribution and response to climate change

In the context of global climate change, ocean acidification and warming are becoming increasingly serious. Adding carbon sinks in the ocean is an important part of efforts to mitigate climate change. Many researchers have proposed the concept of a fisheries carbon sink. Shellfish-algal systems are among the most important components of fisheries carbon sinks, but there has been limited research on the impact of climate change on shellfish-algal carbon sequestration systems. This review assesses the impact of global climate change on shellfish-algal carbon sequestration systems and provides a rough estimate of the global shellfish-algal carbon sink capacity. This review evaluates the impact of global climate change on shellfish-algal carbon sequestration systems. We review relevant studies that have examined the effects of climate change on such systems from multiple levels, perspectives, and species. There is an urgent need for more realistic and comprehensive studies given expectations about the future climate. Such studies should provide a better understanding of the mechanisms by which the carbon cycle function of marine biological carbon pumps may be affected in realistic future environmental conditions and the patterns of interaction between climate change and ocean carbon sinks.