Vivianite Formation and Its Contribution to Phosphorus Retention

Home , Goethite, Vivianite

Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1 , and M. Hupfer 1,* 1 discussions.cls. , A. Kleeberg 4 , M. Eder 3 X class copernicus E T A , T. Frederichs 1,2

M. Rothe

Leibniz-Institute of Freshwater Ecology andDepartment Inland of Fisheries, Geography, Berlin, Humboldt Germany UniversityDepartment of of Berlin, Geosciences, Berlin, University Germany ofDepartment Bremen, of Bremen, Biomaterials, Germany Max Planck Institute of Colloids andnow Interfaces, at: Potsdam, State Laboratory Berlin Brandenburg, Kleinmachnow, Germany

Correspondence to: M. Rothe ([email protected]) 1 2 3 4 Germany *

M. Rothe analytical approach retention in a recent lake sediment: a novel contribution to long-term phosphorus Evidence for vivianite formation and its

with version 4.1 of the L Manuscript prepared for Biogeosciences Discuss. Date: 29 July 2014 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | only. Thus, supersaturated pore water cm 2 of the sediment, the vivianite deposits were homogeneously aimed at restoring Lake Groß-Glienicke (Berlin, Germany). 3 cm , is a ferrous iron phosphate mineral which forms in waterlogged O 2 Fe(OH) 8H · 2 ) and 4 3 ) sediment fraction. Secondly, we assessed the contribution of vivianite to P 3 (PO − 3 FeCl Fe

3 gcm . 2

ρ > distributed within, and restricted to, the upper 23

than 20 years ago, significantly contributing to P retention in surface sediments. Glienicke, vivianite formation continues to be triggered by the artificial iron amendment more vianite throughout the upper 30 alone cannot serve as a reliable predictor for the in-situ formation of vivianite. In Lake Groß- shaped crystal aggregates. Although equilibrium calculations indicated supersaturation of vi- blue spherical vivianite nodules were 40–180 µm in diameter, and formed of platy- and needle from magnetic hysteresis measurements. Scanning electron microscopy revealed that the dark retention, combining results from chemical digestion with magnetic susceptibility data derived ( ments which allowed direct identification of vivianite by X-ray diffraction in the high-density In a novel approach, we firstly applied a heavy-liquid separation to the iron-rich surface sedi- plication of for P burial during early diagenesis we studied the consequences of a 1992/1993 in-lake ap- rect identification and quantification difficult. To identify vivianite and assess its significance remains unknown about vivianite in sediments, because technical challenges have rendered di- vivianite formation can make a major contribution to P retention during early diagenesis. Much Vivianite, mobilised because vivianite is stable under anoxic, reducing, sedimentary conditions. Thus, Abstract soils and sediments. The phosphorus (P) bound in its crystal lattice is considered to be im- Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 3 . The mineral is a regularly found deposit in sedimentary O 2 8H · 2 ) 4 (PO 3 Fe

One speciﬁc phosphate mineral which forms during sediment diagenesis is the ferrous phos- In natural systems, vivianite is stable under pH conditions from 6 to 9 (Nriagu, 1972) and can The burial of P depends on several processes (Ruttenberg, 1992; Søndergaard et al., 2001)

phate vivianite, conditions are still not fully understood (e.g., Stigebrandt et al., 2013). (see e.g., Jilbert and Slomp, 2013). However, the processes controlling the P burial under anoxic reactive P (SRP) often found in anoxic non-sulphidic environments (Nriagu, 1972; Nriagu and ble phosphate minerals which bind P in their crystal lattice and contribute to permanent P burial from pore water solution is favoured by high concentrations of ferrous iron (Fe(II)) and soluble Lehtoranta et al., 2009). Thus, during sediment diagenesis there may be the formation of sta- form in waterlogged soils and sediments (Berner, 1981). The precipitation of vivianite directly compounds, at least under non-sulphidic conditions (Hyacinthe and Van Cappellen, 2004; part of the inorganic sediment matrix (Lindsay et al., 1989). marine and estuarine sediments, indicating a resistance towards reductive dissolution of these While a large fraction of total P can be organic or sorbed P, vivianite may comprise only a small cite (Moosmann et al., 2006). P associated with Fe(III)-minerals have been found in anoxic Since P is only a minor constituent in sediments, the direct identification of vivianite is difficult. clude P sorbed onto the surface of iron(oxy)hydroxides, aluminium hydroxides, clays and cal- cores (e.g., Brauer et al., 1999; Fagel et al., 2005; Sapota et al., 2006; Minyuk et al., 2013). material which is refractory or not yet mineralised by microorganisms. Inorganic phases in- the internal nutrient cycle (Hupfer and Lewandowski, 2008). and fixation is of either organic or inorganic phases. Organic P originates from settled organic nism able to shield P from continuous (re)-cycling, and therefore represents an output of P from column have been studied intensively. Long-term burial of P in sediments is the only mecha- duction the cycling of P, and the role of the sediments in regulating P availability in the water among researchers for almost a century. Since P is an important nutrient limiting primary pro- Understanding phosphorus (P) dynamics in aquatic ecosystems has been of particular interest 1 Introduction Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | concentrations 2+ Fe and SRP, vivianite often occurs in the 2+ (Hush, 1967). As ferric iron (Fe(III))-phases Fe 2+ 4 Fe

is present in the culture medium (e.g., Borch and Fendorf, 2007; O’Loughlin et al., 2013).

−

3 4 To address this need, the aims of our present study were to: (1) identify vivianite crystal ag- Literature reported vivianite crystal aggregates to be needle-shaped or spherical with diame- All these ﬁndings indicate that the interplay between the availability of source materials

diffraction, elemental analyses and magnetic hysteresis measurements. ing heavy-liquid separation of surface sediments followed by mineral identification by X-ray formation. For these purposes we developed and applied a novel analytical approach, combin- (3) assess the impact of artificial addition of Fe during lake restoration as a trigger for vivianite (2) determine the significance of vivianite formation for P burial during early diagenesis, and early diagenesis. gregates from recent lake sediment showing favourable formation conditions in the pore water, limited knowledge about the quantitative importance of vivianite formation in P burial during tion. The difficulty in identifying vivianite in a sediment matrix might be a reason why there is calculations, sequential P extractions, or electron microprobe analysis lacking direct identifica- Often the claim of vivianite findings is solely based upon indirect measures, such as equilibrium et al., 1983; Manning et al., 1991; Taylor et al., 2008; Nanzyo et al., 2013) appears to be scarce. However, direct evidence of vivianite in recent sediments (e.g., Nembrini et al., 1983; Hearn tals turn vivid blue due to partial oxidation of ments, as well as the pore structure of the sediment matrix, are important in vivianite formation. is no equilibrium control by vivianite with respect to pore water SRP and ters ranging between a few micrometres to several centimetres. Upon exposure to air, the crys- PO (Fe(III)-phases, organic matter), the activity of DIRB and their cell-mediated microenviron- demonstrated that mineral formation is surface- rather than diffusion-controlled, and hence there phosphate solubility in an anoxic meadow soil. product following Fe(III) reduction by dissimilatory iron reducing bacteria (DIRB) if sufficient Dell, 1974; Roden and Edmonds, 1997). By flux calculations Emerson(Postma, and 1981). Widmer Recently, (1978) Walpersdorf et al. (2013) confirmed that vivianite does not control and organic matter servevicinity as of these source phases. material Laboratory for studies show that vivianite appears as a secondary mineral Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1 − gL membrane , and a sur- m m ) between Decem- 3 (1989–1992) (Klee- 1 − FeCl gL of the sediment, we used cm and 41 µ 1 − , a maximum depth of 11 m gL (Kleeberg et al., 2012). Due to the iron’s re- 5 dryweight ) and dissolved ferric chloride ( 3 1 − and subsequently deployed at the deepest site in the lake for h decreased reaching today’s mesotrophic levels of TP 20 µ mgg ) concentrations of 485 µ Fe(OH) a a E), with a mean depth of 6.8 00 (Chl and 2.6 . Until 1992 the lake was highly eutrophic, and had on average total P 39 a 2 0 . Sediment stratigraphs show a distinct increase in Fe and P content corre- 1 06 km ◦ − HT 200 tuffryn). To remove oxygen from the chamber water the samplers were ® gL N, 13 7 µ dryweight 00 1

a − . The samplers were ﬁlled with deionised water and covered by a 0.2 µ 57 0 . Both Fe and TP contents in the sediment almost doubled after the treatment, reaching

in September 2013 during thermal stratiﬁcation. cm 27

◦ d cm mgg

ﬁlter (Gelman degassed with nitrogen for20 24

of 4 two in-situ dialysis samplers (Hesslein, 1976) each with 14 chambers and a vertical resolution

To document the geochemical conditions within the upper 30 2.2.1 Porewater 2.2 Sample collection and preparation has accumulated since the in-lake treatment in 1992/93. dox sensitivity iron and TP contents are higher throughout the newly formed sediment which 23 33 sponding to the time of the in-lake treatment. Today, this shift is evident at a sediment depth of and Chl with solid ferric hydroxide ( P precipitation, TP and Chl berg et al., 2013). To reduce theber P 1992 concentration and February in 1993 (Wolter, the 2010). water Due to column, decreased the external P lake inputs and was the treated in-lake (52 Lake Groß-Glienicke is a dimictic lake located in the southwest of Berlin, Germany 2.1 Study site 2 Material and methods face area of 0.67 (TP) and chlorophyll Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , . , 3 O − 2 rcf H · 3 3 gcm . 2 at 9.050 9WO stainless steel · and the heavy 4 ρ > m min rcf WO 2 ) and placed in an ultra- 3Na and 63 µ 3 ) and processed analogous − 3 m − ) were homogenized by gentle was mixed in a centrifuge tube 9 gcm g 0 min at 9.050 . 1 3 gcm . slices, frozen, and freeze-dried for at = 1 ρ = 2 ρ ) were rinsed with deionised water until mm 3 gdryweight − ) was used and thereafter separated by density 6 m µ 9 gcm in diameter were taken in September 2012 and May . 80 1 , and then freeze-dried. In the following, sediment sam- ≥ 1 mm ρ < − ) were analysed and are refered to as “high-density” sam- 3 − and then centrifuged for , C: Scm 3 − min 3 gcm . long and 60 2 After sonication the mixture was centrifuged for 10 9 gcm . cm . ρ > 1 min > ρ > 3 of sodium polytungstate solution (density − . The freeze-dried sediment served as raw material for further analysis and is in the

h mL

3gcm .

2 Subsamples of freeze-dried sediment (about 1

conductivity dropped below 50 µ ples from fraction A ( ples. mixed with a sodium polytungstate solution (density tions of all three runs were pooled. In step II, the pooled heavy fractions from step I were fraction transfered to a new tube. This process was repeated a thirdto time step and I. the heavy Subsequently,B: frac- each of the three separated sediment fractions (A: were again sonicated for 10 with 10 sonic bath for 20 The heavy fraction was then transferred into a new tube. The light fraction and the supernatant ABCR). In step I, a sediment sample of approximately 0.3

following text refered to as “bulk” sediment. least 72

Sediment cores 35–40 cores were extruded, immediately sectioned into 20 2.2.2 Sediment 2013 by a gravity corer (UWITEC) at the deepest site in the lake. Two hours after sampling the pestling in an agatemeshes. mortar, Only and the subsequently largest sieved size throughusing fraction two 80 different µ ( concentrations of a sodium polytungstate solution ( Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , ++ 3100, Jena C / were determined N . Scanning electron + 4 s NH -radiation and a Sol-X α ), dissolved inorganic car- − 3 NO , − 2 4 ) in a high pressure microwave oven ). Temperature and pH were measured SO + 4 , was measured photometrically applying 1 : 3 − NH − Cl HS 7 and an integration time of 12 θ 2 ◦ ), 3 anions ( 2+ , volumetric ratio % Mn , 76 ), SRP, and ammonia ( 2+ 3 − Fe zinc acetate solution. , HS M HNO with a step of 0.05 2+ ). Cations were analysed by inductively coupled plasma atomic emission , θ 2 2+ % Mg ◦ , 36 Mn 2+ , Ca 2+ HCl ,

+ Fe

K ,

Quick sampling and ﬁxation with hypochloric acid prevented oxidation of redox sensitive

diately fixed with 0.2 Analytics). To prevent oxidation of free sulfides subsamples from each chamber were imme- sels and analysed on the day of collection using a carbon analyser (multi chromatography (Shimadzu). Subsamples for DIC were stored in nitrogen-flushed air-tight ves- spectrometry (ICP-OES, iCAP 7000series, Thermo Scientific). Anions were analysed by ion

digestion ( species ( The concentrations of Fe, Ca, Al, Mg, Mn, S and P were determined by ICP-OES after wet between 5 and 60 nol method (Bolleter et al., 1961) respectively, using segmented flow analysis (Skalar Scan 2.3.2 Sediment (XRD) with a Bruker AXS D8 diffractometerLohmann GmbH equipped KG) with served as Cu-K an internal XRD-standard. The XRD-patterns were measured bon (DIC), free sulfides ( in each chamber using a pH electrode (Mettler Toledo). the methylene blue methodphotometrically (Cline, by 1969). the Concentrations molybdenum of blue SRP method and (Murphy and Riley,Skalar 1962) Analytical and B.V.). All the determinations indophe- were performed in duplicate. (Gigatherm). Mineral composition of sediment was characterized by powdersolid X-ray diffraction state detector. Synthetic, slightly oxidised (blue appearance) vivianite powder (Dr. Paul micrographs of sediment concretions were obtained with a FEI Quanta 600FEG field emission ( Subsamples from each dialysis chamber were taken for the analysis of 13 parameters: 6 cations 2.3.1 Porewater 2.3 Analysis Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | metal-ligand complexes (e.g. Ca-, (Flanders, 1988). Diamagnetic matter, 1 : 1 ; sample mass ranging from about 1 to T 3 − ) for K 8 3 gcm . 2 ρ > acceleration voltage (Jeol-7500F scanning electron microscope) with kV

) were conducted on an Alternating Gradient Magnetometer (Princeton Measurement Cor-

The proportional factor between magnetisation and magnetic ﬁeld is named magnetic suscep- Magnetic hysteresis measurements (magnetisation vs. magnetic ﬁeld) of subsamples of bulk

mg carbon (DOC). The equilibrium constants (log database. The database was extended to include metal complexation with dissolved organic ing the computer program PhreeqC (version 2.18.5570) (Parkhurst et al., 1999) with minteq4 Geochemical equilibrium calculations were based on the results of the pore water analysis us- 2.4 Thermodynamic calculations minerals. paramagnetic susceptibility even in the presence of magnetically much stronger ferrimagnetic strong magnetic fields. Magnetic hysteresis measurements therefore allow the determination of poration) at room temperature in peak fields of 0.3 part of the hysteresis loop after magnetic saturation of ferrimagnetic minerals in sufficiently 5 be deduced from hysteresis measurements, by calculating the slope of the increasing linear and field-dependent in case of ferrimagnetic substances. Thus, paramagnetic susceptibility may tibility. This characteristic is field independent, i.e. linear, for dia- and paramagnetic substances, is called the hysteresis loop. magnetite exhibit a much stronger and non-linear field dependency. Their magnetisation curve of induced magnetisation on the ambient magnetic field. Finally, ferrimagnetic minerals such as as many Fe bearing minerals, including vivianite, show a strong and positive linear dependency duced magnetisation on the ambient magnetic field. In contrast, paramagnetic substances, such such as calcium carbonate and quartz, demonstrates a weak negative linear dependency of in-

sediment and high-density samples ( an EDX detector (X-Max, Oxford Instruments). ray spectroscopy at 15 coated with palladium prior to the analysis of elemental composition by energy dispersive X- environmental scanning electron microscope (FE-ESEM). Sediment concretions were sputter Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 1 1 1 − at 2 4 − − 2+ − 15 Fe . SO within 1 were not = 7 and − and mmolL mmolL mmolL − 3 + 4 2+ NO NH Fe mmolL and and 0.20 − 1 − , SRP, HS + 4 . Directly at the SWI, SRP NH cm mmolL 3 − at 1 and increased further downcore to reach − 1 − at the SWI, and decreased to pH 00 . 9 mmolL = 8 mmolL of the sediment (compared to their concentrations at the ) was taken from Nriagu (1972). to 0.25 to pH , respectively, and increased by a factor of two and ﬁve 36 concentration showed a decreasing sigmoidal trend across 1 ) (Fig. 1d). The concentrations of − cm 1 − cm − − cm 10 2 4 23 × 23 SO − − at mmolL = 1 at sediment depth (Fig. 1c). Concentration proﬁles of mmolL 1 and 2.7, respectively) and slightly decreased with sediment depth. For below the SWI and deeper, the concentration was so low to be close to viv − of the water body above the SWI, and increased to 6 9 60 . . cm K cm cm = 7 and 0.08 = 12 at 29 mmolL of the sediment and continuously increased down-core to reach 7.9 1 1 − − cm sediment depth (Fig. 1b). SRP concentration increased in the water body above the (Fig. 1c and d). The

sediment depth (Fig. 1a). The concentration of DIC was almost constant at 3.9 mmolL cm cm mmolL

cm The pore water of the sediment was supersaturated with respect to Fe(III) and mixed

constant of vivianite ( the SWI from pH Fe(II)-fulvic ligand complexes) were taken from Steinmann and Shotyk (1997). The solubility across the sediment–water interface (SWI) (Fig. 1). The pH increased in the water body above There were distinct gradients in pH and concentrations of DIC, 3.1 Chemical conditions in the pore water 3 Results 29 in the overlying 23 the upper 4 at 29 SWI from 0.15 had a local maximum concentration of 0.59

0.87 respectively within the uppermost 4 SWI). Further down-core the concentrations increased to 0.74

lepidocrocite (SI our equilibrium calculations, saturation indices (SI) were highest for magnetite and lowest for Fe(III)/Fe(II) phases, including magnetite, hematite, goethite and lepidocrocite. According to at 0.1 had a similar course: in the water body above the SWI concentrations were almost constant at 29 detectable.

the SWI, and from 4 the detection limit (0.001 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | − 3 4 ρ > PO above a cm of the pore . The results 1 cm − ), and 4 mgL cm against that of ) and supersaturation for 2+ 3 Fe a . As this threshold concentra- 1 − FeCO mgL through the formation of Fe(II)- organic 2+ Fe a 10 (see e.g., Reuter and Perdue, 1977), we performed of the sediment, but absent from subjacent sediment 2+ Fe a cm (Fig. 2). At the SWI, the supersaturation of vivianite was cm (Fig. 4a). h ) with sediment depth, as shown by plotting 2+ ). The heavy-liquid-separated, high-density sediment samples (fraction A, Fe for 24 ), saturation close to equilibrium for siderite ( a ( C 10 cm ◦ 2+ ≤ − Fe

To determine the effect of dissolved organic carbon (DOC) on the output of the equilib- Examination of sediment with a reﬂected-light microscope revealed that dark blue nodules

rium calculations, and in particular on phate (SI (Fig. 2). The thermodynamic calculations showed a strong subsaturationthe for calcium manganese phosphate phos- hydroxylapatite (SIwater ranged of from the 8 sediment. to 10) in the upper 28 layers (23–40 were present throughout the upper 23

heating at 60 its colour from dark blue to orange-brown and lost its characteristic diffraction pattern upon equilibrium calculations with DOC concentrations ranging from 10 to 500 data from the Crystallography Open Database (COD). The synthetic vivianite powder changed powder (blue appearance) was in coincidence with the vivianite reference pattern which use could not be identified from bulk sediment samples. The diffraction pattern of synthetic vivianite in Fig. 4a) to be present in the sediment. However, the XRD-reflexes characteristic for vivianite as well as several other minerals, e.g. dolomite, plagioklas and pyrite (for clarity not indicated The XRD-patterns from different sediment depths showed quartz and calcium carbonate phases 3.2 Structural and elemental composition of sediments tivity of Groß-Glienicke, we did not include DOC as input data for equilibrium modelling. the SWI the supersaturation was close to equilibrium. There was a sharp increase in the ac- showed that there isligand a complexes only significant at decrease DOC in tion concentrations above is 200 at least one order of magnitude higher than those found in the water column of Lake

of magnitude at depths of 4–28 vivianite, in the pore water of the sediment, there was continuousabout supersaturation of one four order orders of magnitude lower than in subjacent pore ﬂuids (4–28 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | . ) 1 x − kg FeS ) were 3 mol% m cm 6 − 10 ) as well as Mg × 05 . mol% = 1 , and L3: 21–30 ), S (2 cm vivianite in diameter) of platy- and needle- mol% m ]) in high-density samples was estimated , L2: 11–20 ), Ca (3 cm ). The Si content was high, reaching 8 (determined from peak area, Fig. 4b), which is 5 . 1 11 mol% . 0 ± 49 . 1 Fe : P = 1 values were calculated from the slope of the linear increas- weightas%of total [ sample ratio of vivianite ). c Fe : P ]) with the value given for vivianite, of MS 1 ratio of vivianite ( 5 mol% − . 1 kg 3 ≤ Fe : P m , from sediment depth layers L1: 0–10 [ 3 −

sample

Magnetic hysteresis measurements showed that in comparison to bulk sediment, the high- The vivianite content ( The SEM-EDX analysis on the aggregates revealed the major elemental constituents to be The XRD-patterns of high-density samples from sediment layers L1, L2 and L3 showed

3 gcm . Minor constituents of aggregates were Mn (4

density samples were enriched with paramagnetica such as vivianite and iron sulﬁdes ( and Al (both

(MS close to the by comparing the measured paramagnetic mass specific susceptibility of a high-density sample probably magnetite, recognized by the opening of the hysteresis loops. (Fig. 5a). Both bulk sediment and high-density samples contained ferrimagnetic material, most (Minyuk et al., 2013). The MS Fe and P, with a mean concentration. relative amount in samples from L1 and L2 was similar, whereas L3 had a significantly lower was more than four times higher, in samples from L3 than in samples from L1; for Mn, the L2 was similar, whereas the amount in L3 was significantly lower. For S, the relative amount significantly differ from that in L1 and L2. The relative amount of P of samples from L1 and much lower concentrations (Table 1). In L3, the relative amount of Fe, Ca, and Al did not elements in the high-density samples from layers L1 and L2 ; S, Al and Mn were present at but higher than in samples from L3 (Fig. 3a). Iron, P, and Ca were most abundant of the six (Fig. 4a). The abundance of blue nodules in samples from L1 and L2 was similar to each other reflexes characteristic for vivianite, and confirmed the existence of the mineral in the sediment nodules showed them to be spherical aggregates (40–180 µ diatom shells. 2 enriched with the dark blue nodules (Fig.shaped 3a). crystals Scanning (Fig. electron 3b). micrographs Occasionally of the these aggregates blue also included organic debris such as Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | P, for (1) (2) , of values FeS sample sample dryweight 1 lower than the − % ] in a high-density 16 mgg . 0 ± 96 . 0 weightas%of total P and [ FeS 12 , , which is equivalent to a relative vivianite content 1 dryweight − 1 100 − 100 kg × , we assumed all sulphur (Table 1) to be present as 3 x ) × m ) 7 FeS FeS c − 21 mgg . is the content of ] is the contribution of paramagnetic FeS to the measured mass × (Lide, 2004), equation (1) can be re-written as follows: . These values exceeded the maximum vivianite content based 0 10 1 1 − × ± FeS − FeS 6 . Assuming a paramagnetic mass specific susceptibility of . sample, FeS c . kg 95 3 . kg 3 MS 0 3 100 MS ( vivianite to m vivianite . These values were, except for sample H5, 1 to 15 [ m 7 × − − 7 − MS − MS 10 -corrected vivianite content in high-density samples ranged between 13 and 10 × sample sample sample 7 × vivianite . FeS sample, FeS 1 MS MS weightas%of total 54 MS ( ( . MS = = = = 1

in the high-density samples. Accordingly, high-density samples contained between 4 and

FeS weightas%of total FeS weightas%of total Relating the vivianite content in the high-density samples, calculated from chemical diges- This calculation is valid assuming that: (1) the contribution of diamagnetica, such as calcium where MS

vivianite vivianite c formation accounted for vivianite formation for the retention of P in the sediment. In samples from L1 and L2, vivianite tion, to the equivalent amount in bulk sediment, we were able to assess the signiﬁcance of

the contribution of paramagnetic FeS 21 MS sample. The 33 vivianite content derived from chemical digestion (Fig. 5b). of 22 to 48 upon the amount of P present in the high-density samples (Fig. 5b). To correct MS speciﬁc susceptibility and ranged from is the only paramagentic material present in the high-density samples. Our MS carbonate and quartz, to the overall measured magnetic susceptibility is small, and (2) vivianite c vivianite content in a high-density sample is then given as follows: ing part of the hysteresis loops after magnetic saturation of ferrimagnetic minerals. The relative Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | cm sediment cm ) (Fig. 6a and sediment depth, cm coincided with a peak dryweight 1 cm sediment depth). − cm mgg , P 5 of TP concentration in the upper 20 % dryweight supported that the vivianite nodules detected in 13 1 h − mgg ratio increased from 0.9 in the 25–30 for 24 C ◦ of the sediment, the Fe and P content were on average 2.4 and P). This lower concentration is because depth layer L3 included Fe : S cm of vivianite bearing sediment (Fig. 6b and d). cm dryweight 1 − 13 mgg . 0 sediment depth (Fig. 6b). Calcium content showed a reverse trend, and decreased on

cm 54 The vivianite-to-non-vivianite transition at a sediment depth of 23

0 reference pattern than with the metavivianite reference pattern (Fig. 4a). This finding confirms accounts for a partial oxidation of Fe(II)) there was even a higher conformity with the vivianite high-density sample with the reference diffraction pattern of vivianite and metavivianite (which tion pattern upon freeze-drying and exposure to air. Comparing the diffraction pattern of the the sediment were slightly surface-oxidised only and did not loose their characteristic diffrac- pearance) and after heating at 60 diffraction pattern of synthetic vivianite powder, both in its slightly oxidised form (blue ap- (Figs. 3a and 4a) and already are an alteration product of unoxidised, pristine vivianite. The successful, even though the vivianite nodules were partially oxidised due to contact with air the direct identification of vivianite by X-ray diffraction. In our study, X-ray diffraction was The heavy-liquid separation and the enrichment of vivianite aggregates are crucial steps for 4.1 Identification and quantification of vivianite in sedimentary Fe and P contentb). (Fe Above 80 this, in the upper 23 3.1 times higher than in the deeper, non-vivianite bearing sediment zone (24–30 to 1.6 in the upper 23 4 Discussion

zone (Fig. 6c). The mean molar average by a factor of 1.9 in the vivianite-bearing sediment zone compared to the non-vivianite 12 depth). The course of manganese resembled that of Fe but showed an increasing trend above sediment layers where no vivianite nodules were present (24–30

( respectively (Fig. 6a). The vivianiteof accounts the for sediment. 20 In contrast, there was signiﬁcantly less P in the high-density samples from L3 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | might have been ) there was a higher FeS cm ). These observations are and 2 cm FeS ) and L2 (11–20 cm ¨ arz et al. (2008). According to these studies, 14

In the high-density samples from layers L1 (0–10 The enrichment of high-density samples with vivianite nodules further allowed to assess EDX-analysis and scanning electron microscopy reveal fundamental characteristics of the

amount of vivianite nodules than in samples from layer L3 (21–30 et al., 2013). detected in paleolimnetic core records (e.g., Brauer et al., 1999; Sapota et al., 2006; Minyuk vivianite finding described here from Lake Groß-Glienicke from the vivianite deposits regularly occurrence of vivianite nodules in a recent and unlayered sediment horizon distinguishes the shells and other organic debris within the nodules confirms their authigenic origin (Fig. 3b). The Lake Groß-Glienicke shows that vivianite is currently forming. The incorporation of diatom The presence of vivianite within the first centimetre of the lacustrine sediment of freshwater 4.2 Contribution of vivianite to phosphorus retention of the heavy-liquid seperation of sediment samples and the paramagnetic nature of vivianite. vides a different, and independent approach to estimate the vivianite content taking advantage ods: (1) chemical digestion, and (2) magnetic hysteresis measurements. The latter method pro- density sediment samples, the vivianite content was calculated based upon two different meth- the amount of vivianite present in the sediment. To estimate the quantity of vivianite in high- saturation calculations. investigation of vivianite deposits in different sediment layers and comparison with results from vivianite nodules out of bulk sediments. Thus, a combination of techniques allowed a qualitative has been reported by Olsson et al. (1997) and M might have impacted the speciation of sulphur i.e. crystalline mineral aggregates, and a conventional reflected-light microscope allows identification of single mineral is detectable by X-ray diffraction even after contact with air; thishigh is sensitivity contrary towards to oxidation. what Aerobic handling of sediment and freeze-drying, however, that an aerobic handling of sediment does not lead to a significant oxidation of vivianite and the vivianite is not expected to be detectable by X-ray diffraction after contact withoxidised air and altered due to to amorphous its phases (Hjorth, 2004). Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | -corrected paramagnetic to the measured positive x value given by Lide (2004). FeS and chemical digestion data FeS 3 FeS − gcm are more than two orders of magnitude 3 -corrected vivianite contents were, except FeS CaCO 15 and 2 -corrected paramagnetic susceptibility methods match than vivianite, the correspondent weakening of the positive FeS SiO 3 CaCO and 2 SiO . For the susceptibility correction we used the MS

FeS -correction could account for the overestimation of the vivianite content derived from

FeS

Due to the high enrichment of vivianite nodules in the high-density samples, the P content we Provided that the the weakening of the measured positive magnetisation due to the pres-

were determined similarly by both the chemical digestion and the present as to note, that the relative changes in vivianite content between different high-density samples magnetisation of high-density samples was significant (Fig. 5b) when assuming all sulphur toThe be for one sample, lower than values derived from chemical digestion. However, it is important uncorrected magnetic susceptibility data. The more diamagnetic smaller than that of vivianite (Lide, 2004). Evenmagnetisation if was high-density negligible. samples The contained contribution of 3-5 paramagnetic times high-density samples as their density is higher than 2.3 associated P, or other Fe-phosphates. These compounds were expected to accumulate in the such as P sorbed onto the surface of Fe(III)-minerals which resisted reductive dissolution, Ca- netic mass specific susceptibility of of the P analysed in the high-density samples originated from compounds other than vivianite, from paramagnetic susceptibility. This assumption is valid, since the values of the diamag- determined, mainly represented the amount of P bound in vivianite. We cannot exclude that part analysed in the high-density samples could mainly be attributed to vivianite-boundence P. of diamagnetic Si and Ca compounds is small, the vivianite content can be determined both the chemical digestion and the P content was similar to each other, whereas samples from L3 contained significantly less P. results from magnetic susceptibility measurements support the assumption that the amount of P magnetic susceptibility of vivianite (Minyuk et al., 2013), the vivianite contents determined by reflected in the P content of the high-density sediment samples. In samples from L1 and L2 the confirmed the presence of Ca and high contents of Fe in these samples (Table 1). However, our susceptibility methods (Fig. 5). Considering the range of a factor of two foracceptably. the mass specific Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , cm P which is of the sediment. preventing further x of this increase. The cm dryweight % FeS 1 − mgg sediment depth (data not shown), cm of the sediment (Fig. 6). Assuming an cm 16 of the sediment in comparison to sediment layers deposited ) Si and Ca compounds at the same time. cm m 80 µ < of increase in total sedimentary P might be due to Fe(III)-phases which sorb in the upper 20 of the P content detected in high-density samples from L1 and L2. The good % 1 % − of the total sedimentary P in the upper 20

in diameter, the amount of vivianite present in the high-density samples serve as a reliable % mgg

m Although the sediment preparation method we used neglected vivianite nodules smaller than Our results suggest a homogeneous vivianite content in the upper 20 Furthermore, a high-density sediment sample from 35

amount of small sized ( 80 µ maximize the enrichment of vivianite nodules in high-density samples and minimize the relative proxy for the overall vivianite content in the sediment. The sieving step was applied in order to mainly represented vivianite-bound P. confirmed that the amount of P analysed in the high-density samples in sediment layers L1–L3 these compounds may explain the peak in P and Fe content at the sediment depth of 23 agreement between results from magnetic susceptibility measurements and chemical digestion sensitive Fe(III)-phases could be preserved by a protective coating of burial after the addition of Fe during lake restoration (Lalonde et al., 2012). The presence of for 20 of 2.5 anoxic sediment matrix (Hyacinthe and Van Cappellen, 2004; Lehtoranta et al., 2009). Redox- which co-precipitated during iron oxidation, could significantly contribute to the increase in P less than 6 Vivianite formation significantly contributed to P retention in Lake Groß-Glienicke, accounting increase in total sedimentary P due toprior the to artificial the in-lake application measure, of vivianiteremaining formation Fe 60 could during explain about lake 40 P, restoration and mixed Fe(III)/Fe(II) phosphate minerals, which resisted reductive dissolution within the reduction (De Vitre et al., 1988). Moreover, P originating from preserved organic material, even though no elevated vivianite contents could be detected at this depth. sample. The P content of this sample accounted only for 0.05 fields, indicative for a majority of diamagnetic material present in the high-density sediment containing no vivianite nodules, demonstrated a negative susceptibility at higher magnetic Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 2+ Fe of the cm ) and high 1 − increased with 2+ –4) throughout the Fe mmolL = 3 of the sediment. The present geo- cm concentrations (0.02 to 0.2 17 ), at neutral to slightly alkaline pH in the absence 2+ 1 − ) which potentially competes with vivianite for Fe 3 and SRP varied by a similar factor, the variation in pH has + FeCO mmolL . Assuming constant precipitation of vivianite from supersat- H cm there was moderate vivianite supersaturation (SI 2+ Fe

of the sediment (Fig. 2). The decrease in orthophosphate activity with sediment

According to these saturation calculations, and from a thermodynamic point of view the

and non-vivianite-bearing sediment layers. Vivianite was only present in the upper 23 omits consideration of a key feature, namely the sharp transition between the vivianite-bearing and Dell (1974). However, to rely upon these calculations to predict in-situ vivianite formation sediment depths of 24 and 28 chemical conditions, with relatively high SRP concentrations (0.04 to 0.09 of free sulﬁdes plot within the stability ﬁeld of vivianite proposed by Nriagu (1972) and Nriagu sediment, not in subjacent sediment layers even though the pore water was supersaturated at

precipitation of vivianite was favoured in the upper 30 using the XRD pattern. cate siderite precipitation. No crystalline siderite could be identiﬁed in the high-density samples is unlikely that the near-equilibrium conditions we now report for Lake Groß-Glienicke indi- is supposed to be controlled by very slow precipitation kinetics (Postma, 1981). Therefore, it

controlled. Formation of siderite ( ation of SRP and According to these studies crystal growth is driven by surface reactions and is not diffusion- organic and inorganic matter, and its subsequent microbial decomposition. Along with the liber- but rather by another process as proposed by Postma (1981) and Emerson and Widmer (1978). Changes in pH and dissolved substances across the SWI (Fig. 1) are due to the deposition of tion. Since simultaneous with the decrease in orthophosphate activity, the lines that mineral formation is slow, and not governed by the saturation state of the pore water 4.3 Prediction of vivianite formation by saturation calculations upper 30 a stronger inﬂuence on the saturation state of vivianite thandepth, does the the change degree in of SRP vivianite concentra- supersaturation persisted. The degree of supersaturation under-

with depth. While the activity of depth is due to the declining pH counteracting the concomitant increase of SRP concentration Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | − 3 4 PO but can react with of the sediment (Fig. 6), x cm FeS ¨ uller, 2003; Kleeberg et al., 2013). The , SRP from organic matter, and the liberation of 18 2+ ¨ achter and M Fe ¨ uller (2003) used a simple conceptual model to explain of the sediment, and emphasizes that supersaturated pore cm from iron(oxy)hydroxides. The presence of vivianite aggregates in ¨ achter and M − 3 4 PO

The Fe and Mn content is elevated throughout the upper 23 At the SWI, fresh organic matter is decomposed, and iron(oxy)hydroxides undergo reduc-

Groß-Glienicke. In 2003 G We consider that the Fe application in 1992/93 was the stimulus for vivianite formation in Lake 4.4 Processes influencing vivianite formation in-situ-formation of vivianite. As a consequence, not all reactive Fe(II) is precipitated as solid is therefore questionable whether supersaturated pore water alone is a reliable predictor of the Lake Groß-Glienicke. During restoration of Lake Groß-Glienicke Fe was provided in surplus. the iron addition. However, this was not the case for Lake Groß-Glienicke. From our findings, it in geochemical conditions which led to the favourable conditions for vivianite formation in have been supersaturated at longest time, for example in the sediment deposited shortly after through the formation of a solid ferrous iron phosphate, such as vivianite. It is exactly that shift why high-density samples from L1 and L2 contained less S than samples from L3 (Table 1). urated pore water, the highest concentrations of vivianite should be in sediment layers which that an increasing ratio of reactive Fe(II) to reactive P leads to an increased permanent P burial to form stable Fe(II)-phosphate minerals (G relative S content in the sediment decreased after the artificial application of iron and explains tive dissolution, leading to the release of

water alone is not sufﬁcient to cause vivianite formation. previously adsorbed vivianite content in the upper 20 vivianite is the uppermost sediment horizon close to the SWI. This explains the homogeneous of vivianite in freshly deposited sediments after the Fe application. The layer of formation of has become more oxidised. A high reactive Fe(II) concentration led in turn to the formation conditions in the hypolimnion and at the SWI after the Fe supplement, i.e. the sediment surface ticulate forms at the SWI after the Fe application. This feature reﬂects the change in redox because there has been a continuous cycling of both elements between their dissolved and par- Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | of total P % due to microbial activity, 2+ Fe ¨ urgen Exner and Elke Zwirnmann (IGB Berlin) 19

The authors are grateful to Hans-J

greatfully acknowledged. The study was funded by the German DFG project “RedoxPhos” HU 740/5-1. improvement of the text. The constructive comments by T. Jilbert and two anonymous reviewers are and Interfaces) are acknowledged for SEM and XRD assistance, and Sarah Poynton for the linguistic for ICP, DIC and IC analysis. Susann Weichold and Ingrid Zenke (Max Planck Institute for Colloids Acknowledgements. enabled the system to recover from its former eutrophic state to its current mesotrophic level. the formation of vivianite in particular, in the long-term retention of P in the sediment, which in sediment layers deposited after the in-lake measure. Our results emphasize the role of Fe, and formation of vivianite was triggered by an artiﬁcial Fe supplement, and explains 20 the in-situ precipitation and occurrence of vivianite. At our study site at Lake Groß-Glienicke, are supersaturated with pore water, constrains the validity of equilibrium calculations regarding ite for different sediment depths. However, the absence of vivianite from layers of sediment that digestion and magnetic hysteresis measurements, allow quantiﬁcation of the P bound in vivian- ment achieved after sediment preparation, and combining the results from standard chemical samples, and is key to demonstrating the presence of vivianite by X-ray diffraction. The enrich- Heavy-liquid separation of sediment leads to an enrichment of vivianite nodules in high-density 5 Conclusions

matter, in combination with an intensiﬁed release of SRP and sediment may thereby catalyse the growth of seed crystals (Zelibor et al., 1988). mation of crystal aggregates. The gel-like pore structure of a sediment matrix rich in organic Hydrophic, negatively charged, carbon-rich ﬁbres which build up a structure of walls within the 2005; Taylor et al., 2008), suggesting a crucial function of this organic material for the for- vivianite-supersaturation during crystal growth, even on a small scale (Cosmidis et al., 2014). (Mackereth, 1966; Kjensmo, 1968; Rosenqvist, 1970; Postma, 1981; Peretyazhko and Sposito, bacteria, cell-mediated microenvironments within the sediment matrix may evolve, sustaining association with organic matter or organic-rich deposits has been reported by numerous authors may serve as necessary prerequisite for vivianite formation in sediments. Through the activity of Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ´ e, L.: Vivianite ¨ el, V., Dublet, G., ´ equel, D., No ´ ez 20 ¨ unter, C., Litt, T., Stebich, M., and Negendank, J. F.: High resolution sediment ¨ uller, B.: Why the phosphorus retention of lakes does not necessarily depend on the /S(-II) transition layer in a eutrophic lake (Lake Bret, Switzerland): a multimethod approach, 2

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Søndergaard, M., Jensen, J., and Jeppesen, E.: Retention and internalSteinmann, P. loading and of Shotyk, phosphorus W.: Chemical in composition, shallow, pH, and redox state of sulfur and iron in complete Sapota, T., Aldahan, A., and Al-Aasm, I. S.: Sedimentary facies and climate control on formation of Ruttenberg, K. C.: Development of a sequential extraction method for different forms of phosphorus in Roden, E. E. and Edmonds, J. W.: Phosphate mobilizationRosenqvist, I.: in Formation iron-rich of anaerobic vivianite in sediments: Holocene microbial clay sediments, Lithos, 3, 327–334, 1970. Walpersdorf, E., Koch, C. B., Heiberg, L., O’Connell, D., Kjaergaard,Wolter, C., K.-D.: and Restoration Hansen, of eutrophic H. lakes B.: by Does phosphorus precipitation, with a case study on Lake

Reuter, J. H. and Perdue, E. M.: Importance of heavy metal-organic matter interactions in natural waters, Zelibor, J. J., Senftle, F., and Reinhardt, J.: A proposed mechanism for the formation of spherical vivianite Stigebrandt, A., Rahm, L., Viktorsson, L., Taylor, K. G., Hudson-Edwards, K. A., Bennett, A. J., and Vishnyakov, V.: Early diagenetic Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 3 4 6 . . . 0 0 0 ± ± ± 7 3 8 . . . 0 1 35 3 2 . . . 1 1 3 ± ± ± ) from three different 4 1 4 3 . . . − 5 7 51 3 5 . . . 2 3 gcm 1 2 . ± 2 ± ± 0 8 5 . . . ρ > 9 18 33 3 6 . . . 2 2 1 ± ± ± 5 0 9 . . . 24 0 23 5 13 5 23 . . . 4 2 11 ± ± ± 6 6 0 . . . ] of high-density samples ( ). 4 11 3 23 3 11 . . . = 5 6 2 mol% 11 n ± ± ± Fe Ca P S Al Mn 0 2 9 . . . = 5 55 = 5 51 = 5 43 n n n ); ); ); cm cm cm

Elemental composition [ standard deviation (SD,

Sediment depth L1 (0–10 L2 (11–20 L3 (21–30

Table 1.

mean sediment depth layers (L1–L3) of Lake Groß-Glienicke from September 2012 and May 2013. Data are Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (d) pH, ), + 4 (a)

5 5 2 7 . . ) ) 0 0 b d 8 ( ( 0 0 2 6 . . ] ] ] 1 0 0 - 1 1 - - L L

L 6 l

5 5 l l o 1 4 o o . . 0 0 m m m

m m [ m 0 0 - 4 [

[ - 2

1 3 2 4 + . . + 4 2 C 2 0 0 I O e e O S D F F

5 5

2 0 1 . . 0 0 0 indicates the sediment–water interface. 0 0 0 .

0 0 0 0 0 0 0 0 0 0 0 0

1 2 3 1 2 3 2 1 2 1

- - - - cm 25 ) ) 8

8 c a 0 . ( 0 . ( 0 0 0 . 8 ] ] 1 1 - - 6 6 L L 0 . 5

. l l 0 7 soluble reactive phosphorus (SRP) and ammonia ( 0 . o o 7 m m H

4 p m 4 m 0

5 ). A depth of 0 0

. + 0 + 4 P 7 4 P − H R H R 2 4 2 S N S N 5 2

0 . 2 . . 0 0 7 SO 0 0 . 0 0 . 0 7 0 0 0 0 0 0 0 0 0 0 0 0

1 2 3 1 2 3 2 1 2 1

- - - -

] m c [ h t p e D ] m c [ h t p e D ) and sulfate ( 2+

Vertical proﬁles of six parameters taken from an in-situ pore water sampler deployed at the

dissolved inorganic carbon (DIC),

deepest point of Lake Groß-Glienicke (positive downward sampling depth) (September 2013):

Fig. 1. (b) ferrous iron (

Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

5 . 3 h - t p e 2 6 0 4 8 d 4

0 4 8 1 1 2 2 2 ] t - n m e c [ I

A B C D E F G H I m

0 e

F S 4 - C D H 5 G E 4 5 . 4 - + 2 e 3 F a

B g o l 2 0 . 26 5 - 1 O 2 A H 8 5 0 2 - . ) 3 4 4 5 - O O P P (

3 + 1 e + - 2 F e given by Nriagu (1972). F 36 0 . − 6 - 10 5 0 0 5 5 0

2 0 5 7 2 0 × ...... 0 0 9 9 9 9 - - - -

1 1

- -

= 1

O P

a g o l - 3 viv K Degree of saturation of the pore water with repect to vivianite of Lake Groß-Glienicke in 9

constant (positive downward sampling depth). The thick line in the diagram represents the vivianite solubility different sediment depths (A to I) (September 2013). Letters next to data points indicate sampling depth Fig. 2. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (b) ) of Lake Groß-Glienicke. cm , L3: 21–30 cm 27 , L2: 11–20 cm

Reﬂected-light microscope images of heavy-liquid separated, high-density, samples from

three different sediment depth (L1: 0–10 Fig. 3. (a) Scanning electron micrographs of dark blue nodules enriched in high-density samples from L1–L3.

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for C

◦

K e F β

K e F α

K n M α 6 ] 5 V e k [

g K a C β r

K a C SEM-EDX elemental spectrum α n

L d P

β (b)

L d P α 3

K S α

K P α

K i S 2 α

K l A α

K g M α

K a N α

] s t i n u y r a r t i b r a [ s t n u o ) C

(

28 0 6 e z e t t t i i r z c n t c a r l a i u a a v q c q u i

- q - v

- - c q

q v 0 q q 5 c c ) C c ° q q 0 6 v 0

t c 4 a

h v 4 c 2 ] (

° [ n

o θ i t 2 a 0

v c d 3 i x v o q

q r t e n t f e a v

m v i e e t d q q i t 0

i e t n v 2 n s n a

i a v i e y v t i v i i m v s i v

n d c i c e e i t t v e e s d t l e i

- e p h n k h h t v l a t i e 0 g n m u t i v n i i y 1 a B y n v H

s S

a a

) i S t )

) v I

e i V ) I I

I I I I

V ( ( ( M (

XRD patterns of (I) synthetic vivianite, (II) synthetic vivianite after oxidation at 60

y t i s n e t n i e v i t a l e R ] s t i n u y r a r t i b r a [ ) a (

ratio is 1.49. Note that elemental peaks of carbon and oxygen were omitted.

, (III) high-density sample and (IV) bulk sediment. Characteristic reﬂexes of vivianite could only P h :

Fig. 4. (a) Crystallography Open Database (COD) REV 64680 (2012 edition). (blue, ﬁle number 96-901-2899) and metavivianite (black, ﬁle number 96-100-1784) use data from the be observed after heavy-liquid separation in the high-density sample (II). The line patterns of vivianite Fe 24 obtained from a dark blue sediment concretion from Lake Groß-Glienicke. The correspondent atomic

Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

of a high- y 6 t i l H i b i t 3 T p . e c s 5 u e l s H = 0

p c i t m e a B s n

t g n a 4 e H m y t m a i i l r i d a b

i e p t

p d y e e t 3 i t c n s c H s o n e i u t r e s r s

d o c e - i c t g h - i e g e d i n

2 d l i H g f a H l a c T], peak value u i m [ s

m a r n e a o h r B p i c

1 H

0 0 0 0 0 0

sediment depth. The positive slope of the high-

2 1 5 4 3

] l a t o t f o % s a t h g i e w [ t n e t n o c e t i n a i v i V ) b ( cm 29 e l p e l m p a 3 . s m

0 t a n s ]

e t T [ n

m ] vs. magnetic ﬁeld i e B 1 d

m e i s − d

e y t s i

kg s k l n u 2 e B d - h g i Am H [

m A ] g k 1 1

[

. ؓ .

1 - 0 2 0 - Variations in vivianite content (expressed as % weight of the sample) in each of (b)

Magnetization

3 ) . a 0 ( -

liquid separation. susceptibility and chemical digestion. density sample, and a bulkdensity sediment sample sample from at 10 higher magnetic ﬁelds indicates enrichmentsix with high-density paramagnetic samples, material after based heavy- upon paramagnetic susceptibility, iron sulﬁde-corrected paramagnetic Fig. 5. (a)

Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | calcium 0 3 ) (c) d ( represent the ] t 5 h 2 g i e (a) w 0

2 y r d

1 - 5 g

1 g m [

0 S 1

5 0 5 0 5 0 5 0 5 0 1 1 2 2 3 3 4 0 8 ) c ( ] t h g i e 0 w 6

y r d

1 - g

g 0 4 m [

a iron (Fe) and manganese (Mn), C

s (b) 2 e l 0 5 0 5 0 5 0 5 0 p 1 1 2 2 3 3 4 m 0 . a 2 ) s 30

b t 0 ( ] n 8 t ] t e h h g 5 m i g . i i e 1 d e 0 w e

w 6 s

y r y r t d i

0 d . 1

s - 1 1 - 0 n g

g 4 e

g d g - m h [ m n

[ 5 g e

. i n 0 M F 0 e h phosphorus (P), 2

M F

m o r

f 0

. t 0 (a) 0 n 0 0 5 0 5 0 5 0 5 e t 4 1 1 2 2 3 3 n o 6 ) c

a s ( u ] r 5 t o h h g i p e s 4 o w

h y p r

t d 3

n 1 - e l g

a . g v 2 L 1 : L 2 : i m u [ L 3 :

0 - 1 0 c m 1 1 - 2 0 c m q e P

1 2 1 - 3 0 c m = 5

n 0 sulphur (S) of Lake Groß-Glienicke from May 2013. Bar charts in graph

0 0 5 0 5 0 5 0 5

4 1 1 2 2 3 3

] m c [ h t p e d t n e m i d e S (d)

SD, Sediment stratigraphs of ±

denote (Ca) and equivalent P content analysed in the high-density samples from depth layers L1, L2 and L3. Error bars Fig. 6.