Distribution and sources of sedimentary organic matter in different aquaculture areas of northeastern Zhanjiang Bay using stable carbon and nitrogen isotopes

Zhanjiang Bay is a major aquaculture area in China with many types of mariculture products(such as oysters,fish,and shrimp).The culture area and shrimp output in Zhanjiang Bay are ranked first in China.We investigated the total organic carbon(TOC),total nitrogen(TN),TOC/TN ratio,and stable isotopes(δ^(13)C and δ^(15)N) of the fish and shrimp feed,fish and shrimp feces,and sedimentary organic matter(SOM) in and around different aquaculture areas of northeastern Zhanjiang B ay to study the impact of aquaculture activities on SOM.The average TOC contents of fish and shrimp feed were 39.20%±0.91% and 39.29%±0.21%,respectively.The average TOC content in the surface sediments of the oyster culture area,the mixed(fish and shrimp) culture area,and the cage fish farm area were 0.66%,0.88%±0.10%,and 0.58%±0.19%,respectively,which may indicate that mixed culture had a greater impact on SOM.The relatively high TOC and TN contents and relatively low TOC/TN ratios,and δ^(15)N values in the upper layer of the core sediment in the mixed culture area could also support the significant influence of mixed culture.The average δ^(13)C and δ^(15)N values of fish and shrimp feed were -20.6‰±2.2‰ and 1.8‰±1.2‰,respectively,which were different from the isotopic values of SOM in the study area.δ^(13)C and δ^(15)N values for SOM in different aquaculture areas were different from those of nearby reference stations,probably reflecting the influence of aquaculture.The δ^(13)C and δ^(15)N values in the oyster culture area(-25.9‰ and6.0‰,respectively) seemed to have reduced δ^(13)C and enriched δ^(15)N relative to those of the reference station(-24.6‰ and 5.8‰,respectively).This may reflect the influence of organic matter on oyster culture.The δ^(15)N value of the station in the mixed culture area(7.1‰±0.4‰) seemed to be relatively enriched in δ^(15)N relative to that of the reference station(6.6‰).Sedimentation and the subsequent degradation of organic matter from mixed cultures may have contributed to this phenomenon.The surface sediment at the cage fish farm area seemed to be affected by fish feces and primary production based on the indication of δ^(13)C and δ^(15)N values.The sediment core at the mixed culture region(NS6) had lower TOC/TN ratios and more positive δ^(13)C and δ^(15)N values than the sediment core at the oyster culture area,suggesting a higher proportionate contribution of marine organic matter in the mixed culture area.In summary,oyster culture,mixed culture,and cage fish culture in northeastern Zhanjiang Bay had a certain degree of impact on SOM,and mixed culture had more significant influences on SOM based on the high TOC contents and the significant vertical variations of TOC/TN ratio and δ^(15)N value in the sediment of this area.This study provides new insights into the impact of aquaculture activities on SOM content.

Tumor microenvironment-responsive artesunate loaded Z-scheme heterostructures for synergistic photo-chemodynamic therapy of hypoxic tumor

Tumor microenvironment(TME)with the particular features of severe hypoxia,insufficient endogenous H2O2,and overexpression of glutathione(GSH)markedly reduced the antitumor efficacy of monotherapy.Herein,a TME-responsive multifunctional nanoplatform(Bi2S3@Bi@PDA-HA/Art NRs)was presented for synergistic photothermal therapy(PTT),chemodynamic therapy(CDT),and photodynamic therapy(PDT)to achieve better therapeutic outcomes.The Z-scheme heterostructured bismuth sulfide@bismuth nanorods(Bi2S3@Bi NRs)guaranteed excellent photothermal performance of the nanoplatform.Moreover,its ability to produce O2 and reactive oxygen species(ROS)synchronously could relieve tumor hypoxia and improve PDT outcomes.The densely coated polydopamine/ammonium bicarbonate(PDA/ABC)and hyaluronic acid(HA)layers on the surface of the nanoplatform enhanced the cancer-targeting capacity and induced the acidic TME-triggered in situ“bomb-like”release of Art.The CDT treatment was achieved by activating the released Art through intracellular Fe2+ions in an H2O2-independent manner.Furthermore,decreasing the glutathione peroxidase 4(GPX4)levels by Art could also increase the PDT efficiency of Bi2S3@Bi NRs.Owing to the synergistic effect,this nanoplatform displayed improved antitumor efficacy with minimal toxicity both in vitro and in vivo.Our design sheds light on the application of phototherapy combined with the traditional Chinese medicine monomer-artesunate in treating the hypoxic tumor.