Capacity of humic substances to complex with iron at different salinities in the Yangtze River estuary and East China Sea

Abstract

The iron binding capacities (IBC) of fulvic acid (FA) and humic acid (HA) were determined in the salinity range from 5 to 40. The results indicated that IBC decreased while salinity increased. In addition, dissolved iron (dFe), FA and HA were also determined along the Yangtze River estuary’s increasing salinity gradient from 0.14 to 33. The loss rates of dFe, FA and HA in the Yangtze River estuary were up to 96%, 74%, and 67%, respectively. The decreases in dFe, FA and HA, as well as the change in IBC of humic substances (HS) along the salinity gradient in the Yangtze River estuary were all well described by a first-order exponential attenuation model: y(dFe/FA/HA, S) = a0 × exp(kS) + y0. These results indicate that flocculation of FA and HA along the salinity gradient resulted in removal of dFe. Furthermore, the exponential attenuation model described in this paper can be applied in the major estuaries of the world where most of the removal of dFe and HS occurs where freshwater and seawater mix.

The Remobilization and Removal of Fe in Estuary—A Case Study in the Changjiang Estuary, China

“…The range and average of dFe concentration at XLJ were 15.0–111 nM and 52.8 ± 30.4 nM in 2013 and 16.7–159 nM and 58.2 ± 42.0 nM in 2014, respectively. This result was comparable to the data reported by Qu et al (), Koshikawa et al (), and Yang et al (), but was much lower than that reported by Edmond et al () and Wang and Liu (). However, the peak values over 100 nM in our study can possibly be resulted from particles leakage during filtration.…”

“…Significant removal of dFe from the water column was observed in this study, as shown by the relative low dFe in the saline water end‐member compared to that of S ≤ 1 water (Figures b and 4). This agrees with previous reports in the Changjiang Estuary and other estuaries worldwide (Bergquist & Boyle, ; Boyle et al, ; Dai & Martin, ; Sholkovitz et al, ; Yang et al, ). Our laboratory mixing experiment confirmed the high dFe removal (Figures c and d) as observed in the field, and was in accordance with the result of similar mixing experiment in Bergquist and Boyle ().…”

“…Our laboratory mixing experiment confirmed the high dFe removal (Figures c and d) as observed in the field, and was in accordance with the result of similar mixing experiment in Bergquist and Boyle (). The mechanism of dFe removal in estuaries was put forward in the 1970s (Boyle et al, ; Sholkovitz, ; Sholkovitz et al, ), and is still accepted to date (Oldham et al, ; Yang et al, ). Briefly speaking, when fresh water mixes with seawater, cations in the seawater neutralize the negatively charged colloids, giving rise to coagulation of colloids into large particles and settlement from solution.…”

“…The natural abundance of water and sediment, multistep bifurcations structure, and the extensive engineering works make the Changjiang Estuary an ideal site to carry out multidisciplinary studies. Research records on dFe in the Changjiang Estuary and the adjacent East China Sea published to date, to our best knowledge, mainly include Edmond et al (1985), Wang and Liu (2003), Koshikawa et al (2007), Jiann and Wen (2012), Huang et al (2015), Su et al (2015), and Yang et al (2017a), whereas the influence of the mouth bar area on dFe was not the focus of any study prior to this.…”

Iron oxide‐humic acid coprecipitates as iron source for cucumber plants

“…It has been observed that low molecular weight organic compounds (Cornell and Schwertmann, 1979) and/or HA (García-Mina et al, 2004;Angelico et al, 2014;Kleber and Johnson, 2015) may promote the precipitation of Fe in the form of poorly crystalline Fe hydroxides in soil. In addition, HAs might complex Fe 3+ , thus increasing Fe solubility and, as a result, the Fe fraction available for plant uptake (Pinton et al, 1998;Abadía et al, 2002;Chen et al, 2003;Fuentes et al, 2013;Yang et al, 2017).…”