Pool of mobile and immobile phosphorus in sediments of the large, shallow Lake Peipsi over the last 100 years

Abstract

Temporal variations in sediment phosphorus (P) composition and mobility were estimated in surface sediments of accumulation (core PS509 44 cm) and erosion (core PS2009 30 cm) areas of the shallow, large Lake Peipsi sensu stricto (s.s.; 2611 km(2), unregulated water level). The P pool in sediments including buried and mobile P is evaluated for the first time, which will provide baseline data for the future modelling of internal loading in L. Peipsi. Five sedimentary P fractions (including inorganic and nonreactive P) were separately quantified: loosely adsorbed and pore-water P (NaCl-P); redox-sensitive fraction P (NaBD-P); P bound to oxides of non-reducible Fe and Al (NaOH-P); calcium-bound P, mainly from apatite minerals (HCl-P) and refractory, mainly organic P (Res-P). Concentrations of P fractions varied during the 100 years with the highest values around 2007-2008 and 1923-1935. The P in "active" layers that are available for bacteria and algae or those undergoing changes and diagenetic transformations in the sediment could follow sediments with the water content of ∼88%. Potentially mobile P is not decreased in the sediments deposited 50-100 years ago and makes up ca 63 mg m(-2) y(-1) (with range 8.3-23.7% of the total P (TP)) in the accumulation area, and ca 0.047 mg cm(-3) (with range 1.3-22.4% of TP) in the erosion area. The result shows that 13-60% of TP contained in the surface sediment (from 34 to 398 mg P m(-2) y(-1)) has been remobilised during accumulation and could be exported to the overlying water.

Strategic plan to restore a shallow overgrowing macrophyte lake

“…The reasons of the few failures were incomplete dredging and low P sorption capacity of the new sediment top layer (Sndergaard, 2007). The sum of P fractions in the sediment top layer of Lake Lahepera (2000 g P/g DW) is rather comparable with that in Lake Peipsi (Kapanen, 2011; Kisand et al, 2017), but exceeds substantially that measured in some other shallow lakes in Estonia, for example, eutrophic Lake Vrtsjrv (800 g P/g DW; Nges and Kisand, 1999) and macrophyte covered Lake Prossa (737 g P/g DW; Kisand and Nges, 2003). Lake Lahepera could benefit from sediment removal if it will result in greater water depth but as it could also enhance the suitable sediment surface for rooted macrophytes, the dredging should be accompanied by the removal of macrophytes to avoid overgrowth.…”

Spatio-temporal variability of surface sediment phosphorus fractions and water phosphorus concentration in Lake Peipsi (Estonia/Russia)

“…The TPsed concentrations in the investigated surficial sediments from Lake Peipsi (470-1400 mg kg"' DM) were similar to values measured by Nöges & Kisand (1999) in the surface sediments of Lake Vörtsjärv (900-1400 mg kg"' DM). Similarly, in a 44-cm sediment core from the central part of Lake Peipsi s.s. the average TPsed was 1036 mg kg ' DM (Kapanen 2012b). However, TPsed concentrations in sediments are not sufficient to predict the potential ecological danger (Kaiserli et al 2002).…”

“…The intensity and duration of intemal load may have a very significant impact on lake water P concentration and subsequently on lake water quality (Sondergaard et al 1999;Kelderman et al 2005). According to Punning & Kapanen (2009), there is a big storage of P in the sediments of Lake Peipsi .5..S. As much of 13-60% of TPsed contained in the surface sediment for over 100 years has been remobilized during accumulation and could be exported to the overlying water (Kapanen 2012b). The recycling of phosphorus from sediments enriched by years of high nutrient inputs can cause slow recovery, or nonrecovery of lakes from eutrophication (Carpenter 2005).…”