Long, A.; Xie, Q.; Yu, X.; Xiao, H., and Zhou, W., 2018. Nutrient exchange between sediments and overlying waters in the Modaomen estuary (China) over a complete semidiurnal tide cycle: Implications of saltwater intrusion.Spatial and temporal variations of inorganic nutrients (, , , , and ) and some relevant environmental parameters, including temperature, salinity, pH, Eh, dissolved oxygen (DO), in surface sediments and overlying waters were investigated during the cruise held on 16 to 19 April 2016 over a complete tidal cycle (a spring and neap tide together) in the Modaomen estuary, Pearl River, China. It was found that the dominant component of dissolved inorganic nitrogen (DIN, expressed as sum of , , and ) was in sediment interstitial waters and in overlying waters. Overlying waters contained higher concentration of and lower concentrations of and than interstitial waters. The exchange flux of inorganic nutrients between sediments and overlying waters was calculated using the Fick diffusion equation. Exchange flux calculations revealed that sediments were the sources of , , and but the sink of and . However, nutrimental exchange flux variations were not obvious during the present tidal cycle. Results of correlation analysis of single factor and principal component analysis revealed that nutrimental exchange fluxes mainly depend on the nutrient concentration gradient and overlying water chemical environment due to high stratification of waters, obvious homogeneity of sediments, and relative weakness of bioturbation in the Modaomen estuary.