Spatial distributions of macronutrients, heavy metals and microplastics in surface sediments of the mainstem and lakes in the middle part of the Yellow River Basin

• Key environmental characteristics of sediments from the mainstem of the Yellow River and adjacent lakes show spatial differences. • The content of total nitrogen and heavy metals increased significantly after it flowed through concentrated agricultural cultivation areas. • Total nitrogen and heavy metal concentrations in lake sediments were highest in urban lake. • The variation of microplastics in river and lake sediments ranged from 233 to 3333 items kg −1 and 967 to 1556 items kg −1 , respectively. Nylon is the dominant polymer type. The Yellow River provides an important foundation for the sustainable development of Chinese civilization. Compared with the upper part (dominated by the Tibetan Plateau) and the lower part (represented by the Yellow River Delta), the central part of the Yellow River Basin (encompassing most of the Loess Plateau) is the most arid and exhibits the most complex relationship between humans and nature. The Chinese government is continuously promoting the protection and management of the ecological environment in the central part of the Yellow River Basin, as it is related to the country’s food security and people’s health, biodiversity conservation and sustainable socio-economic development. However, the distribution patterns and evolution of key ecological elements in the region, which are important determinants of ecosystem productivity and health, have yet to be revealed. This study focused on three key ecological elements, namely, macronutrients (sediment organic carbon, SOC, total nitrogen, TN and total phosphorous, TP), heavy metals (Cu, Ni, Pb, Zn, Cr, Cd, Hg, and As) and microplastics, and aimed to systematically elucidate the change patterns of their concentrations and compositions in sediments from the mainstem of the Yellow River and neighboring typical lakes. The results revealed that the TN content was mostly greater than the SOC content in the sediments from the mainstem of the Yellow River. Moreover, the TN, SOC and heavy metals concentrations increased significantly as a result of agricultural cultivation. Among the six typical lakes, the highest concentrations of both macronutrients and heavy metals were observed in sediment samples from Mingcui Lake (MC; an urban wetland), followed by those in sediment samples from Wuliangsuhai Lake (WLS; surrounded by agricultural fields). Among the heavy metals, the concentrations of Zn and Cr were highest. The abundance of microplastics in the sediments from the mainstream of the Yellow River ranged from 233 to 3333 items kg −1 , while the abundance of microplastics in lake sediments ranged from 967 to 1556 items kg −1 . The other characteristics of microplastics were consistent, including the concentration of microplastic particles within the 0.2–2 mm range. The main colors of the sampled microplastics were blue, transparent, and gray-black. In addition, rayon accounted for the highest proportion among all polymer types, followed by PET and PE + PP. In general, the amount of the above three environmental elements is closely correlated with the intensity of human activities such as agriculture and urbanization. Stronger correlations were obtained between the concentrations of macronutrients and heavy metals. This study systematically reveals the change patterns of key ecological elements in the study area and advances the understanding of environmental changes, ecosystem evolution and sustainable development in the Yellow River Basin.