Phosphorus sorption and buffering mechanisms in suspended sediments from the Yangtze Estuary and Hangzhou Bay, China

Abstract

The adsorption isotherm and the mechanism of the buffering effect are important controls on phosphorus (P) behaviors in estuaries and are important for estimating phosphate concentrations in aquatic environments. In this paper, we derive phosphate adsorption isotherms in order to investigate sediment adsorption and buffering capacity for phosphorus discharged from sewage outfalls in the Yangtze Estuary and Hangzhou Bay near Shanghai, China. Experiments were also carried out at different temperatures in order to explore the buffering effects for phosphate. The results show that P sorption in sediments with low fine particle fractions was best described using exponential equations. Some P interactions between water and sediment may be caused by the precipitation of CaHPO₄ from Ca^2&plus; and HPO₄^2&minus; when the phosphate concentration in the liquid phase is high. Results from the buffering experiments suggest that the Zero Equilibrium Phosphate Concentrations (EPC₀) vary from 0.014 mg L⁻¹ to 0.061 mg L^&minus;1, which are consistent with measured phosphate concentrations in water samples collected at the same time as sediment sampling. Values of EPC₀ and linear sorption coefficients (<i>K</i>) in sediments with high fine particle and organic matter contents are relatively high, which implies that they have high buffering capacity. Both EPC₀ and <i>K</i> increase with increasing temperature, indicating a higher P buffering capacity at high temperatures

Hydrologic connectivity as a framework for understanding biogeochemical flux through watersheds and along fluvial networks

“…The POM contains varying stoichiometric ratios of C, N, and P and other biologically important elements, depending on its original source and degree of biological processing along its flowpath. In addition to POM deposition, sediment settling in lakes and reservoirs can deposit C, N, and P that can sorb to charged surfaces (Li et al, 2013;Tanoue and Handa, 1979). This physical retention process is particularly important in relation to P (Wodka et al, 1985) because phosphate (PO 4 ) readily sorbs to sediment particles (Walker and Syers, 1976), but sedimentation processes can also be important in watershed C and N dynamics (Teodoru et al, 2013).…”

Phosphorus export during storm events from a human perturbed watershed, southeast China: Implications for coastal ecology

“…In addition to the DOP & DRP changes, an important predicted climate change is an increase in the frequency and intensity of major storms (IPCC 5th report). The higher particleadsorbed P (high TPP and TSM concentrations) reaching the Jiulong River estuary might be released to ambient water in the form of DOP and/or DRP when mixed with saline water, due to the so-called P buffering effect (Froelich, 1988;Zwolsman, 1994;Conley et al, 1995;Li et al, 2013). Ultimately, dissolved P is likely to play an important role in changing species and ecosystem function in the Jiulong River estuary and adjacent coastal area.…”

Phosphorus Forms in Sediments of a River-Dominated Estuary

“…Combined with downstream transport in rivers, estuaries are vulnerable to nutrient pollution because dissolved inorganic P (orthophosphate) desorption from sediment surfaces occurs when anions in seawater compete with phosphate anions for binding sites, leading to P efflux (Fox et al, 1986;Froelich, 1988;House and Warwick, 1999;Monbet et al, 2010). Moreover, the reducing conditions associated with intense OM remineralization increase P desorption, setting up a positive feedback loop whereby eutrophic conditions contribute to P mobilization and limit nutrient sequestration (Howarth et al, 2011;Li et al, 2013). This impairs the critical function of estuaries and wetlands, which is to reduce nutrient loads before they reach coastal waters (Barbier et al, 2011).…”