Human health, as well as the ecosystem’s natural equilibrium, may be jeopardized by the discharge of tetracycline into the aquatic environment. In order to effectively photocatalyzed the degradation of tetracycline in aqueous solution under visible light, this study used a two-step hydrothermal approach to produce composites of SrTiO₃/TiO₂ doped with two metal elements, lanthanum (La) and iron (Fe). The crystal structure, morphology, electronic structure, particle size, specific surface area and photocatalytic properties of the catalysts were assessed using a variety of methods, such as fluorescence spectroscopy, UV-Vis diffuse reflectance, X-ray diffraction, scanning electron microscopy, BET and particle size analysis. After 120 min of exposure to visible light, the co-doped catalyst showed a degradation rate of 99.1%, which was nine times greater than that of SrTiO₃/TiO₂ at catalyst dosing of 1.6 g/L and tetracycline concentration of 20 mg/L. The synthesized photocatalyst exhibited good tolerance to changes in pH, with the degradation efficiency of tetracycline remaining stable within the pH range of 4–10. The La-Sr (Ti-Fe) O₃/TiO₂ catalyst also demonstrated excellent photostability after recycling. The mechanism of tetracycline degradation is primarily attributed to the active oxidation by photogenerated holes and •O₂⁻. Furthermore, tetracycline degradation pathways were analyzed via HPLC-MS to identify intermediates.

The habitat and feeding environment of freshwater fish in freshwater lakes have been destroyed, with the problem of miniaturization and simplification of catches being serious. An artificial reef is an effective technical measure to protect and proliferate offshore fishery resources, but little research has been conducted on its application in freshwater lakes. A small artificial reef for freshwater lakes was designed according to the water depth of the lake and the habits of benthic fish. The artificial reef is composed of biomass modules, each of which is 900 × 120 mm. The community structure of phytoplankton around the artificial reef and its adjacent waters was studied. The results showed that 77 species from seven phyla were identified, with a high number of species from the Chlorophyceae. In terms of density composition, the density of cyanobacteria decreased month by month, while the phylum Chlorophyta and Cryptophyta increased first and then decreased. As for biomass composition, Chlorophyta and Cryptophyta increased first and then decreased. RDA analysis showed that water temperature, dissolved oxygen, and total phosphorus were the main influencing factors. To sum up, the artificial reef can improve the algae phase in the surrounding water column, inhibit the growth and reproduction of cyanobacteria to a certain extent, and have a significant enrichment and promotion effect on diatoms. Artificial fish reef affects the phytoplankton community structure of the surrounding water bodies mainly through the absorption of phosphorus nutrients. Artificial reefs can be popularized and applied in freshwater lakes to provide foraging and shelter for benthic fish in the lake.

Anaerobic ammonium oxidation (anammox) is a key biochemical process to reduce nitrogen pollution in aquaculture, especially in water recirculating pond aquaculture system (RPAS). We used 16S RNA and quantified PCR to study the distribution and environmental impacts of anammox bacteria in RPAS. The results show that the anammox bacterial community distributions and diversities that are apparently unit-specific and seasonal have significant (p < 0.05) difference variation in the RPAS. Most of the anaerobic ammonium oxidation bacteria sequences (77.72%) retrieved from the RPAS belong to the Brocadia cluster. The abundance of anammox bacterial in the RPAS ranged from 3.33 × 101 to 41.84 × 101 copies per ng of DNA. The environmental parameter of temperature and nitrogen composition in water could have impacted the anammox bacterial abundance. This study provides more information on our understanding of the anammox bacteria in the RPAS, and provides an important basis for RPAS improvement and regulation.

In this study, a group of large-scale biofloc shrimp culturing facilities were designed. The bioflocs were domesticated by continuously reducing the ratio of carbon to feed. The bacterial community diversity on the 20th, 40th, 60th, and 80th days was analyzed by high-throughput sequencing technology. The results showed that the biofloc content (0~16.8 ± 4.3) mL/L, TSS concentration (0~247.46 ± 27.3) mL/L, total ammonia nitrogen concentration (0~0.28 ± 0.052) mg/L, nitrite nitrogen concentration (0~4.13 ± 1.42) mg/L, nitrate nitrogen concentration (108.57 ± 19.6) mg/L were all within the safe concentration range of Litopenaeus vannamei. With the progress of reducing carbon input, the Chao1 index, the number of operational taxonomic units, and the Shannon index increased significantly. The number of OTUs of B80 (572.36 ± 13.26) was significantly higher than that of B60 (489.69 ± 12.97), B40 (423.35 ± 18.46) and B20 (407.67 ± 15.65) (p < 0.05). The Chao1 index of B80 (768.58 ± 36.96) was significantly higher than that of B60 (646.8 ± 52.53), B40 (569.7 ± 46.53) and B20 (516.3 ± 21.35) (p < 0.05). The Shannon index of B80 (5.63 ± 0.16) was higher than that of B60 (4.85 ± 0.13), B40 (4.68 ± 0.21) and B20 (3.65 ± 0.22), with significant difference (p < 0.05). At the end of the experiment, the domestication formed a micro-ecosystem with Proteobacteria as the carrier (46.98 ± 15.82%), Chloroflexi as the skeleton (2.2 ± 0.36%), Nitrospirae (1.35 ± 0.26%) as the main water treatment functional bacteria, and other bacteria as auxiliary nitrogen and phosphorus removal; At the genus level, unclassified_f_Rhodobacteracea (22.97 ± 3.82%), Ruegeria (10.35 ± 1.26%), Muricauda (5.73 ± 0.61%), Algoriphagus (3.75% ± 0.85%) and Nitrospira (1.56 ± 0.56%) are the dominant bacteria. Under the synergistic effect of the above bacteria, the biofloc system remains relatively stable. The survival rate and unit yield of shrimp were (65.32 ± 6.85)% and (4.15 ± 1.58) kg/m³, respectively.