We explored nutrient distribution in water and heavy metal contamination in sediments after rice harvest in a rice-shrimp co-cropping system. Additionally, we assessed aquatic ecological risks by evaluating molecular ammonia toxicity and heavy metal levels in rice-shrimp fields and systematically analyzed the ecotoxicity of nutrients and heavy metals in water in the co-cropping system by monitoring physicochemical indices in water during the late cultivation period in four rice and shrimp co-cultivation fields. After rice harvesting, the water showed high pH (9.25) and the total nitrogen concentration, ammonia nitrogen, and COD reached 14.15, 11.49, and 92.01 mg/L, respectively. In perennial rice-shrimp co-cropping systems, elevated levels of ωAs (16.21 mg·kg–1) and ωCd (0.20 mg·kg–1) were found in sediments, exceeding natural baseline levels by 2.35 and 1.72 fold, respectively. Levels of other heavy metals were lower, in addition, the concentration of heavy metal was lower than the baseline levels of the sediments. The potential ecological risk index and our potential biological toxicity evaluation revealed low ecological risks posed by heavy metals in rice-shrimp co-cropping system sediments, which can be attributed to mineral elements required for Procambarus clarkii culture. In conclusion, co-cultivating rice with shrimp can potentially mitigate soil heavy metal pollution.
This study investigated the heavy metal distribution characteristics, assess the pollution status, and identify potential pollution sources. A total of 514 topsoil samples were collected in the public area of the industrial park, and 11 element concentrations were tested. The concentration distribution of heavy metals was characterized on the plane using Geographic Information Systems (GIS). Our research involved the application of various analytical methods, including single factor index analysis, potential ecological risk index assessment, and principal component analysis-absolute principal component scores-multiple linear regression (PCA-APCS-MLR). The results revealed that all 10 heavy metals, except for Cr (Ⅵ) which was below the detection limit, were detected in concentrations surpassing the background values. The regional proportion were Cu (86%) > Cd (71%) > Co (53%) > Ni (50%) > Be (45%) > As (42%) > Sb (40%) > Pb (23%) > V (16%) > Hg (4%), and the concentrations of all major elements were relatively high. Moreover, there were areas with extremely strong (Cd element proportion was 1.7%, Sb element proportion was 1.5%) and very strong (Cd element proportion is 1.0%, Sb element proportion is 0.2%) ecological risk levels. They were all located near large chemical enterprises on the northwest side of the park. The composite ecological risk index of heavy metals in surface soil belonged to moderate ecological hazards, and there was a certain degree of ecological hazard risk. The main heavy metal pollution sources in the surface soil of the study area included chemical and combustion sources, natural sources, and transportation sources, accounting for 27.2%, 17.0%, and 11.0% of the pollution load, respectively.
The impact of rapid development of coastal aquaculture on aquatic environments is an important topic in environmental science. Quantitative assessment of the impact of aquaculture on sediment heavy metal pollution has been challenging because of the complex conservative-nonconservative behavior of heavy metals in coastal brackish waters. In this study, Sansha Bay, Fujian Province, the world’s largest yellow croaker cage culture area, was used as a research area for offshore aquaculture. Using aquaculture data recorded by remote sensing images combined with the relationships between sedimentary heavy metals and salinity, this study sought to analyze the effects of aquaculture on sediment heavy metal pollution. The results showed that over the past 15 years, the area of cage culture in Sansha bay has increased from 9.1 km2 to 33.4 km2, and the maximum intensity of cage culture per square kilometer has increased from 3% to 22%. As a result, the average values of Cu, Zn, Cd, and Pb levels in the cuprophilic elements in the culture area increased by 44%, 11%, 15%, and 17%, respectively, compared to non-farmed areas, and the slope of the conservative regression line with an increase in salinity decreased by 27%, 35%, 18%, and 2%, respectively. The average values of the siderophile elements Cr, Mn, and Ni in the breeding area increased by 16%, 15%, and 29%, respectively, compared to those in non-farmed areas. The results of potential ecological risk evaluation showed that Cd is a potential environmental pollutant in the surface sediments of Sansha Bay, and Sansha Bay as a whole is at a medium ecological risk level.
中国综合性科技类核心期刊(北大核心)
