Sediment phosphorus fractionation and flux in a tropical shallow lake

Abstract

Aim The aim of the present study is to evaluate the potential phosphorus (P) release from the sediment to the water column of a tropical shallow lake in the northeast of Brazil, based on the sediment P fractions and on the flux of P between water and sediment. Methods We used a sequential extraction method to analyse the different P fractions of the sediment of Lake Extremoz. We also carried out a 40-day microcosm experiment to analyse the flux of P between water and sediment. We did so by flooding 200g of sediment from the lake with 800 mL of 1.2 µm filtered lake water in 1 L beakers. Every 5 days we analysed: soluble reactive phosphorus (SRP), total phosphorus (TP), organic phosphorus (Org-P), dissolved oxygen (DO), temperature, and pH of the water. Results The largest fraction of P in the sediment of Lake Extremoz is Refractory-P, which is non-mobile. The main mobile fraction of this lake’s sediment is composed of P bound to Fe and Mn oxides (BD-P) which is redox sensitive. During the P flux experiment, the water was always oxic and with nearly neutral pH, however the temperature increased by almost 4 °C due to the increase of the temperature of the air. SRP, TP and Org-P concentrations in the water had a general decrease in the first 20 days. But, on the second half of the experiment, those concentrations increased and the fluxes of P from sediment to water, mainly Org-P, were positive. Even with this increase in concentrations, indicating a period of P release, overall fluxes were negative. Conclusions The main mobile fraction of the sediment is redox sensitive, therefore it has the potential to be released in case of oxygen depletion. Under current conditions, most of the P released by the sediment is in organic forms, indicating that, in the presence of oxygen, the balance of P between water and sediment is controlled by the effects of organisms on P as well as temperature.

High Inter‐ and Intra‐Lake Variation in Sediment Phosphorus Pools in Shallow Lakes

“…Sediment P composition also varied among the study lakes; however, redox‐sensitive and organic P were consistently the most abundant fractions. Other eutrophic waterbodies also have high levels of redox‐sensitive P (Papera et al., 2021; Randall et al., 2019; Song & Burgin, 2017) and organic P forms (Frost et al., 2019; Nowlin et al., 2005). More generally, aquatic sediments tend to be enriched in redox‐sensitive, organic, loosely‐bound, and aluminum‐bound P because these forms are commonly associated with fine sediments, which are more easily eroded from the source material (i.e., terrestrial soils; Stone & English, 1993; Kerr et al., 2011).…”

Critical load of phosphorus in reservoirs of a tropical semi‐arid region

“…In some of the simulated scenarios, the critical load of phosphorus could not be estimated, which indicates that the reservoirs in those conditions are unable to receive additional external P loads and would probably require treatment to reduce the internal loads of phosphorus. Removal of phosphorus from the system can be achieved through, for example, the use of some phosphorus immobilization techniques in the sediment (Araújo et al, 2016(Araújo et al, , 2018Cooke et al, 2005;Papera et al, 2021;Van Oosterhout & Lürling, 2011) or by sediment reuse as soil fertilizer to increase productivity in small scale agriculture (Lira et al, 2020).…”