Carbon transfer along the land-river-ocean continuum is a key component of the global carbon cycle. Combined pressures from coastal development and land use change are dramatically altering carbon dynamics in tidal rivers. To explore the carbon patterns in subtropical tidal rivers, we collected 27 water samples from the mainstream and tributaries of the Tanjiang River in November 2019 (dry season) and July 2020 (wet season), and detected the concentrations of total organic carbon (TOC), total inorganic carbon (TIC) and general water quality indices. In addition, the characteristics of land use and landscape patterns in various regions and multiscale buffer zones (500, 1000, 1500, 2000 and 2500 m) were analyzed. Pearson correlation analysis, redundancy analysis (RDA) and other methods were used to quantify the impacts of land use change on the concentrations of carbon. The results showed that: (1) The overall mean concentrations of TOC and TIC were 3.5±0.92 mg/L and 2.61±2.10 mg/L, respectively, with significant spatial and temporal variability. Both TOC and TIC were significantly higher during the wet season than during the dry season. The high TOC was easily observed within the tidal reach of the core urban ecological area, which had a high proportion of urban land use and low proportion of forest land use. (2) The landscape pattern index of the buffer zone at different spatial scales had a good explanatory degree for water quality, and the landscape structure of the buffer zone at 1500 meters had the strongest explanatory ability for carbon concentration (20.03%). The sewage-dominated urban river network had more organic matter, while the rural branch had less organic matter due to plant interception and absorption. Surrounding ponds accounted for the high nutrient concentrations in rivers. (3) Meanwhile, water temperature, salinity and nutrients were related to carbon concentration. This research reveals that decreasing the carbon concentration in rivers and flux to estuaries can be achieved by strengthening management policies for land use patterns in buffer zones, especially those regarding pollution control for the surrounding ponds, and creating green belts between urban construction and rivers.