Dissolved iron (dFe) delivered by rivers plays a vital role in supporting primary productivity in coastal ecosystems. River‐borne Fe is generally removed in estuaries due to the salt‐induced flocculation. However, effects of the river mouth bar area on the variations of dFe concentration are frequently overlooked. Here we show the results of quasi‐synchronous observation conducted in three water channels in the mouth bar area of the Changjiang Estuary during both spring and neap tides in July 2014. dFe showed high spatial variation, from 2.63 to 690 nM, with higher values commonly found in the inner study area. An episode of significant Fe remobilization was observed in the inner mouth bar before the removal in the subsequent fresh‐saline water mixing process. Averaged dFe concentration increased from 45.2 ± 22.9 nM at Xuliujing to 188 ± 185 nM in the inner salinity (S) ≤ 1 water, then decreased to 10.3 ± 9.53 nM in the outer S > 1 water. Budget calculations revealed that the Changjiang input was the largest terrestrial source for dFe, while desorption from particles was the main reason for dFe enhancement in the study area. The entire mouth bar area was identified as a net sink for dFe, whereas, its S ≤ 1 and S > 1 zones were a source and a sink, respectively. We suggest that the mouth bar area diversifies the biogeochemical behavior of Fe in the estuary and enhances Fe output flux. Our study offers a new insight for better understanding the behavior of Fe and other particle‐reactive elements in large dynamic estuaries.
Flooding is one of the most destructive natural disasters globally, having caused $1 trillion of economic damages and 220,000 deaths between 1980 and 2013 (Winsemius et al., 2016). Coastal regions are exposed to both fluvial and oceanic flood drivers, which, when combined, usually lead to compound flooding events (Moftakhari et al., 2017). The number of compound events in major coastal cities of the United States has significantly
We adapted the WRF‐Hydro modelling system to Hurricane Florence (2018) and performed a series of diagnostic experiments to assess the influence of initial soil moisture and precipitation magnitude on flood simulation over the Cape Fear River basin in the United States. Model results suggest that: (1) The modulation effect of initial soil moisture on the flood peak is non‐linear and weakens as precipitation magnitude increases. There is a threshold value of the soil saturation, below and above which the sensitivity of flood peak to the soil moisture differentiates substantially; (2) For model spin‐up, streamflow needs longer time to reach the ‘practical’ equilibrium (10%) than the soil moisture and latent heat flux. The model uncertainty from spin‐up can propagate through the hydrometeorological modelling chain and get amplified into the flood peak; (3) For ensemble flood modelling with a hydrometeorological system, modelling uncertainty is dominated by the precipitation forecast. Spin‐up induced uncertainty can be minimized once the model reaches the ‘practical’ equilibrium.
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