Of growing interest in the control of sediment phosphorus (P) release in lakes is the use of solid phase P-sorbing products (PSPs) including industrial by-products and naturally occurring or modified ...mineral complexes. However, there is a need to report on novel PSPs proposed by suppliers for use in lake remediation projects at the national scale. We comparatively assessed the elemental composition and P sorption properties of six industrial waste-products (waste-products from treatment of abandoned mine waters — ‘red ochre’ and ‘black ochre’; waste products from building practices: ‘gypsum’, ‘sander dust’, ‘mag dust’ and ‘vermiculite’) and one commercially available modified lanthanum (La) bentonite product (Phoslock®), all of which have been proposed for use in remediation projects in UK lakes. P sorption was well described (r2>0.70) by Langmuir isotherms for all products with the exception of ‘gypsum’ for which no significant P sorption was reported. P sorption capacities ranged from 4mgPg−1 dry weight (d.w.) PSP (‘black ochre’) to 63mgg−1 d.w. (‘sander dust’), with products composed mainly of calcium oxide (CaO) and silicon dioxide (SiO2) (i.e. ‘vermiculite’, ‘mag dust’ and ‘sander dust’ PSPs) having significantly higher sorption capacities than all other PSPs. Estimates of the equilibrium P concentration (EPC0) from Langmuir isotherms indicated that all PSPs, with the exception of ‘gypsum’, were capable of reducing soluble reactive P (SRP) concentrations to <5.1μgL−1. Further research and development required to underpin regulatory policy decisions regarding the use of PSPs is discussed. Dose estimates for each PSP required to treat a eutrophic shallow loch (40.6ha) with persistent internal loading issues are reported.
► Seven phosphorus (P) sorbing products (PSPs) proposed for eutrophication management in lakes were comparatively assessed. ► P sorption capacities of six PSPs ranged from 4mgPg−1 dry weight PSP to 63mgg−1 d.w. ► Six PSPs were capable of reducing P concentrations to levels likely to limit phytoplankton growth in lakes. ► Dose estimate procedures must be improved and used to underpin the selection of PSPs for use in lakes.
Phoslock® is a lanthanum (La) modified bentonite clay that is being increasingly used as a geo-engineering tool for the control of legacy phosphorus (P) release from lake bed sediments to overlying ...waters. This study investigates the potential for negative ecological impacts from elevated La concentrations associated with the use of Phoslock® across 16 case study lakes. Impact-recovery trajectories associated with total lanthanum (TLa) and filterable La (FLa) concentrations in surface and bottom waters were quantified over a period of up to 60 months following Phoslock® application. Both surface and bottom water TLa and FLa concentrations were <0.001 mg L−1 in all lakes prior to the application of Phoslock®. The effects of Phoslock® application were evident in the post-application maximum TLa and FLa concentrations reported for surface waters between 0.026 mg L−1–2.30 mg L−1 and 0.002 mg L−1 to 0.14 mg L−1, respectively. Results of generalised additive modelling indicated that recovery trajectories for TLa and FLa in surface and bottom waters in lakes were represented by 2nd order decay relationships, with time, and that recovery reached an end-point between 3 and 12 months post-application. Recovery in bottom water was slower (11–12 months) than surface waters (3–8 months), most probably as a result of variation in physicochemical conditions of the receiving waters and associated effects on product settling rates and processes relating to the disturbance of bed sediments. CHEAQS PRO modelling was also undertaken on 11 of the treated lakes in order to predict concentrations of La3+ ions and the potential for negative ecological impacts. This modelling indicated that the concentrations of La3+ ions will be very low (<0.0004 mg L−1) in lakes of moderately low to high alkalinity (>0.8 mEq L−1), but higher (up to 0.12 mg L−1) in lakes characterised by very low alkalinity. The effects of elevated La3+ concentrations following Phoslock® applications in lakes of very low alkalinity requires further evaluation. The implications for the use of Phoslock® in eutrophication management are discussed.
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•Lanthanum (La) concentrations were investigated following Phoslock® treatment in 16 lakes.•La recovery reached an end-point between 3 and 12 months post-application.•La3+ ions were unlikely to cause ecotoxicological effects in moderate-high alkalinity lakes.•Ecological effects of La3+ should be assessed prior to applications in very low alkalinity lakes.
Phoslock® is increasingly used worldwide to control sediment phosphorus (P) release and cyanobacterial blooms despite the fact that little is known about its mode of action in lake bed sediments. ...This study quantified the effects of Phoslock® on sediment elemental composition and P fractionation (one year pre- and post-application of 170 g Phoslock® m−2) in an attempt to address these knowledge gaps. Post-application, sediment La content was significantly higher in the top 10 cm of the sediment compared to pre-application conditions. Mass balance calculations indicated that the applied mass of La had the potential to bind 25% of potentially release-sensitive P (Pmobile; sum ‘labile P’, ‘reductant-soluble P’ and ‘organic P’ fraction) present in the top 4 cm or 10% of Pmobile present in the top 10 cm of the sediment. Assessing variation in sediment P partitioning indicated that the application caused a significant increase in the mass of P present in the more refractory ‘apatite bound P’ fraction between post-application month 4 and 7 compared to Pmobile. This suggests that Phoslock® controls sediment P release by increasing the mass of P permanently bound in the sediment. To address uncertainty in estimating product dose required to control sediment P release we conducted laboratory assays using intact sediment cores to which we added serial additions of Phoslock® under either aerobic or anaerobic conditions. The laboratory experiment indicated that the original dose to Loch Flemington was sufficient to control sediment P release under aerobic conditions but that significant P release will occur should prolonged anaerobic conditions persist. However, Phoslock® may be a viable option to control sediment P-release under anaerobic conditions which would require an estimated additional application of up to 510 g Phoslock® m−2. A conceptual model is proposed for the use of P-capping agents in lake remediation projects which is likely to increase cost-effectiveness and reduce non-target effects by applying multiple smaller doses compared to a single high dose.
•Ecosystem scale experiment investigating mode of action of P capping agent.•Phoslock® increases mass of P in more refractory ‘apatite bound P’ fraction.•P partitioning processes occurred following a lag time of 4–7 months.•Phoslock® is likely to permanently reduce the magnitude of sediment P release.•New conceptual model suggesting application of multiple smaller doses.
Lanthanum (La) modified bentonite is being increasingly used as a geo-engineering tool for the control of phosphorus (P) release from lake bed sediments to overlying waters. However, little is known ...about its effectiveness in controlling P across a wide range of lake conditions or of its potential to promote rapid ecological recovery. We combined data from 18 treated lakes to examine the lake population responses in the 24 months following La-bentonite application (range of La-bentonite loads: 1.4–6.7 tonnes ha−1) in concentrations of surface water total phosphorus (TP; data available from 15 lakes), soluble reactive phosphorus (SRP; 14 lakes), and chlorophyll a (15 lakes), and in Secchi disk depths (15 lakes), aquatic macrophyte species numbers (6 lakes) and aquatic macrophyte maximum colonisation depths (4 lakes) across the treated lakes. Data availability varied across the lakes and variables, and in general monitoring was more frequent closer to the application dates. Median annual TP concentrations decreased significantly across the lakes, following the La-bentonite applications (from 0.08 mg L−1 in the 24 months pre-application to 0.03 mg L−1 in the 24 months post-application), particularly in autumn (0.08 mg L−1 to 0.03 mg L−1) and winter (0.08 mg L−1 to 0.02 mg L−1). Significant decreases in SRP concentrations over annual (0.019 mg L−1 to 0.005 mg L−1), summer (0.018 mg L−1 to 0.004 mg L−1), autumn (0.019 mg L−1 to 0.005 mg L−1) and winter (0.033 mg L−1 to 0.005 mg L−1) periods were also reported. P concentrations following La-bentonite application varied across the lakes and were correlated positively with dissolved organic carbon concentrations. Relatively weak, but significant responses were reported for summer chlorophyll a concentrations and Secchi disk depths following La-bentonite applications, the 75th percentile values decreasing from 119 μg L−1 to 74 μg L−1 and increasing from 398 cm to 506 cm, respectively. Aquatic macrophyte species numbers and maximum colonisation depths increased following La-bentonite application from a median of 5.5 species to 7.0 species and a median of 1.8 m to 2.5 m, respectively. The aquatic macrophyte responses varied significantly between lakes. La-bentonite application resulted in a general improvement in water quality leading to an improvement in the aquatic macrophyte community within 24 months. However, because, the responses were highly site-specific, we stress the need for comprehensive pre- and post-application assessments of processes driving ecological structure and function in candidate lakes to inform future use of this and similar products.
•Water quality and macrophyte community responses were assessed following Phoslock treatments.•Phosphorus concentration and phytoplankton biomass decreased and water clarity increased.•Macrophyte species richness and extent increased.•Responses were highly site specific and decreased with increasing DOC concentrations.
Lanthanum-modified bentonite clay (Phoslock
®) is a lake remediation tool designed to strip dissolved phosphorus (P) from the water column and increase the sediment P-sorption capacity. This study ...investigated short term alterations in sediment elemental composition and sediment P-fractions based on sediment cores taken 2 days before and 28 days following the application of 24
t of Phoslock
® to a 9
ha, man-made reservoir. Following the application, sediment lanthanum (La) content increased significantly (
p
<
0.05;
n
=
4) in the top 8
cm of the sediment, thereby theoretically increasing sediment P-binding capacity on the whole reservoir scale by 250
kg. Mass balance calculations were used to estimate the theoretical binding of release-sensitive P (
P
mobile; sum of ‘
labile P’, ‘
reductant-soluble P’ and ‘
organic P’ fraction) by La across the top 4
cm and 10
cm depth of sediment. The amended mass of La in the sediment had the potential to bind 42% of
P
mobile present in the top 4
cm or 17% of
P
mobile present in the top 10
cm. However, with the exception of a significant increase (
p
<
0.05;
n
=
4) in the ‘
residual P’ fraction in the top 2
cm, sediment P-fractions, including
P
mobile, did not differ significantly following the Phoslock
® application. Experimental P-adsorption studies indicated P-saturation values for Phoslock
® of 21,670
mg
P
kg
−1 Phoslock
®. Sequential extraction of P from saturated Phoslock
® under laboratory conditions indicated that around 21% of P bound by Phoslock
® was release-sensitive, while around 79% of bound P was unlikely to be released under reducing or common pH (5–9) conditions in shallow lakes. Applying Phoslock
® is, therefore, likely to increase the P-sorption capacity of sediments under reducing conditions.
► Whole lake application of La-modified bentonite for internal P load management. ► Post-application sediment La content significantly higher in top 8 cm. ► Post-application mobile sediment P fractions not significantly lower. ► High experimental P binding capacity of 21,670 mg P kg
−1Phoslock
®. ► Phoslock
® increases refractory sediment P fractions.
Loch Flemington is a shallow lake of international conservation and scientific importance. In recent decades, its status has declined as a result of eutrophication and the establishment of non-native ...invasive aquatic macrophytes. As previous research had identified the lake bed sediments as an important source of phosphorus (P), the P-capping material Phoslock® was applied to improve water quality. This article documents the responses of the aquatic macrophyte community by comparing data collected between 1988 and 2011. Summer water-column total P concentrations decreased significantly and water clarity increased following treatment. Aquatic plant colonisation depth increased and plant coverage of the lake bed extended. However, the submerged vegetation remained dominated by the non-native Elodea canadensis Michx. Aquatic macrophyte community metrics indicated no significant change in trophic status. Species richness and the number of ‘natural’ eutrophic characteristic species remained broadly similar with no records of rare species of conservation interest. Loch Flemington is still classified as being in ‘unfavourable no change’ condition based on its aquatic macrophytes despite the water quality improvements. The implications of these results are discussed in relation to the future management of Loch Flemington and in the wider context of trying to improve our understanding of lake restoration processes.
The use of geoengineering techniques for phosphorus management offers the promise of greater and quicker chemical and ecological recovery. It can be attractive when used with other restoration ...measures but should not be considered a panacea. The range of materials being proposed for use as well as the in-lake processes targeted for manipulation continues to grow. With increasing political imperatives to meet regulatory goals for water quality, we recommend a coordinated approach to the scientific understanding, costs, and integration of geoengineering with other approaches to lake management.
We explored spatial and temporal relationships between contemporary aquatic vegetation and surface sediment macrofossil remains in a small, shallow, English lake (Green Plantation Pond). The aquatic ...vegetation of Green Plantation Pond underwent a marked compositional change after 2005 with a shift from Elodea spp.-Potamogeton pusillus-Chara spp. to Ceratophyllum spp.-Chara spp.-Potamogeton crispus dominance. By comparing macrophyte and plant macrofossil distributions at multiple, closely spaced points in Green Plantation Pond for 2000 and 2008–2009, we studied the ability of macrofossils to track this major aquatic vegetation change. Representation of macrophytes by macrofossils was high with 63 and 76 % of extant plant species recorded by macro-remains in the 2000 and 2009 sediment surveys respectively. Nevertheless, plants were both over-represented (Nitella flexilis, Chara spp. and Zannichellia palustris) and under-represented (Ranunculus sect. Batrachium, Potamogeton spp.) in the sediment record in terms of relative macrofossil abundances and the number of occupied sample points. The study also revealed a lack of preservation of Elodea spp. leaf remains in the second (2009) survey compared to the first (2000) probably due to a longer time interval (5 vs. 10 months) between macrophyte and sediment sampling. Nevertheless, the macrofossils reliably recorded both the main shift in the contemporary vegetation (e.g. especially increases in Ceratophyllum spp. and P. crispus abundance) and other more subtle floristic changes (e.g. increases in Myriophyllum spicatum and Lemna spp.) exceptionally well. This study highlights the huge potential of macrofossils for tracking sub-decadal changes in the aquatic vegetation of small, shallow lakes.
Lanthanum-modified bentonite clay (Phoslock registered ) is a lake remediation tool designed to strip dissolved phosphorus (P) from the water column and increase the sediment P-sorption capacity. ...This study investigated short term alterations in sediment elemental composition and sediment P-fractions based on sediment cores taken 2 days before and 28 days following the application of 24t of Phoslock registered to a 9ha, man-made reservoir. Following the application, sediment lanthanum (La) content increased significantly (p<0.05; n=4) in the top 8cm of the sediment, thereby theoretically increasing sediment P-binding capacity on the whole reservoir scale by 250kg. Mass balance calculations were used to estimate the theoretical binding of release-sensitive P (Pmobile; sum of 'labile P', 'reductant-soluble P' and 'organic P'fraction) by La across the top 4cm and 10cm depth of sediment. The amended mass of La in the sediment had the potential to bind 42% of P|>mobile present in the top 4cm or 17% of Pmobile present in the top 10cm. However, with the exception of a significant increase (p<0.05; n=4) in the 'residual P' fraction in the top 2cm, sediment P-fractions, including P|>mobile, did not differ significantly following the Phoslock registered application. Experimental P-adsorption studies indicated P-saturation values for Phoslock registered of 21,670mgPkg-1 Phoslock registered . Sequential extraction of P from saturated Phoslock registered under laboratory conditions indicated that around 21% of P bound by Phoslock registered was release-sensitive, while around 79% of bound P was unlikely to be released under reducing or common pH (5-9) conditions in shallow lakes. Applying Phoslock registered is, therefore, likely to increase the P-sorption capacity of sediments under reducing conditions.
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