Spatial variation of the C: N ratio and its relationship with the carbon cycle in the middle reaches of the Yellow River during summer

Abstract

ABSTRACT Rivers are the critical link between soil, the atmosphere, and the ocean’s extensive carbon reservoirs, but the discharge of sewage into rivers has not only increased the content of organic matter but also significantly altered the geochemical cycles of carbon and nitrogen in the land, water, and atmosphere. However, few studies have been conducted to establish the relationship between the changes and distribution of river pollutants and the river carbon cycle. In this study, twenty water samples were collected from sixteen rivers in the middle reaches of the Yellow River (YR). The results showed that the concentrations of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) in the mainstream decreased from north to south, while DIC and DOC in tributaries showed the opposite trend in the middle reaches of YR during summer. The distribution of pCO2 and the C: N ratio had prominent regional distribution patterns in this study area, in which pCO2 tended to decrease from south to north, and the C: N ratio varied increasingly from south to north. The source or sink state of CO2 maybe can be judged by the variation of the C: N ratio in this study area during summer.