Phosphorus sorption–desorption behaviour of river bed sediments in the Abshineh river, Hamedan, Iran, related to their composition

Abstract

Phosphorus (P) sorption by sediments may play a vital role in buffering P concentration in the overlying water column. To characterize P sorption-desorption in the river bed sediments, 17 bed sediment samples collected from Abshineh river, in a semi arid region, Hamedan, western Iran were studied through a batch experiment and related to sediment composition. The sorbed fraction ranged from 4.4% to 5.4% and from 38.5% to 86.0% of sorption maxima when 20 and 1,500 mg P kg(-1), respectively, was added to the sediment samples. Phosphorus sorption curves were well fitted to the Langmuir model. Zero equilibrium P concentration ranged from 0.10 to 0.51 mg P l(-1) and varied with sediment characteristics. Phosphorus desorption differed strongly among the studied bed sediments and ranged from 10.8% to 80.2% when 1,500 mg P kg(-1) was added. The results of the geochemical modelling indicated that even under low P addition (2 mg l(-1)), the solutions are mainly saturated with respect to hydroxyapatite and ß-tricalcium phosphate minerals and undersaturated with respect to other Ca and Mg minerals, whereas under higher P addition (150 mg l(-1)), most Ca-P solid phases, except the most soluble mineral (brushite), will likely precipitate. A Langmuir sorption maximum was positively correlated with carbonate calcium. Estimated P retention capacity of the bed sediments are generally lower and zero equilibrium P concentration values higher in upstream sites than at the downstream sites, suggesting that sediments in upstream and downstream may act as source and sink of P, respectively.

Turkusowe Lake (Wolin Island, Poland) - Surface Waters Quality Changes in Years 1986-2010

“…The occurrence of well expressed eutrophication phenomena, specifically phytoplankton bloom in this case, may be treated as a consequence of intensified anthropogenic pressure, especially of increased discharge of municipal sewage directly to the lake in last years and draining the waste-waters to the ground in the alimentation zone of water sources feeding the Turkusowe Lake [7]. Obviously, the presence of CaCO 3 deposits at the bottom of the lake has been responsible for the sorption and binding of part of SRP as well as organic compounds from the reservoir of water [15][16][17]. Nevertheless, in the opinion of the authors of this paper, the presence of CaCO 3 at the bottom of lake basin does not automatically cause "by itself" the surface water to be resistant to eutrophication under conditions of permanent stratification of surface and near-bottom waters being maintained practically constantly.…”

Response to Referee 1

“…This caused a 15 % decrease in PHY con-centration when the water moved further downstream. Thus, SRP was most of the time fully assimilated by phytoplankton in summer, but phytoplankton was also subject to mortality and could partly be recycled to eventually constitute an autochthonous source of available P. Remineralization of autochthonous labile organic particulate P, known as part of the "microbial loop", is described in the literature of phytoplankton ecology (Reynolds, 2006;Li et al, 2014) and mostly identified in lakes, reservoirs or estuarine systems (Jossette et al, 1999;James and Larson, 2008;Song and Burgin, 2017) and rarely in rivers (Descy et al, 2002;Withers and Jarvie, 2008). On the one hand, bacteria compete with phytoplankton for SRP availability, and on the other hand, bacterial mineralization recycles P and supports phytoplankton growth.…”

Functions of Calcium-bound Phosphorus in Relation to Characteristics of Phosphorus Releasing Bacteria in Sediment of a Chinese Shallow Lake (Lake Wabu)

“…Higher EPC 0 means higher tendency of P release from sediment. For example, in the Abshineh river, EPC 0 values were higher in upstream sites than at the downstream ones, suggesting that sediments in upstream and downstream may act as source and sink of phosphorus, respectively (Jalali and Peikam 2013). The mean EPC 0 value in the rivers sediments was significantly higher than that in the lake sediments (P<0.01), in conjunction with the case of the CaCO 3~P content (P<0.01) (Table 1).…”