Fate of Cd in agricultural soils: A stable isotope approach to anthropogenic impact, soil formation and soil-plant cycling

Supporting information

Martin Imseng1, Matthias Wiggenhauser2, Armin Keller3, Michael Müller3, Mark Rehkämper4, Katy Murphy4, Katharina Kreissig4, Emmanuel Frossard2, Wolfgang Wilcke5, Moritz Bigalke1*

1Institute of Geography, University of Bern, Hallerstrasse 12, CH-3012 Bern, Switzerland2Institute of Agricultural Sciences, ETH Zurich, Eschikon 33, CH-8315 Lindau, Switzerland 3Swiss Soil Monitoring Network (NABO), Agroscope, Reckenholzstrasse 191, CH-8046 Zürich, Switzerland 4Department of Earth Science & Engineering, Imperial College London, SW7 2AZ London, U.K. 5Institute of Geography and Geoecology, Karlsruhe Institute of Technology (KIT), Reinhard-Baumeister-Platz 1, 76131 Karlsruhe, Germany*Corresponding author: Moritz Bigalke, moritz.bigalke@giub.unibe.ch, tel. +41(0)316314055

Number of pages: 26Numbers of figures: 7Number of Tables: 4

S1

1. Materials and Methods (detailed information)

1.1. Soil sampling

At each site, samples were taken from a 10x10 m plot (Figure S2a). Soil samples from the 0-20 cm depth layer were sampled as four area-mixed replicates per site, each consisting of 25 subsamples. Further samples from deeper soil horizons were taken at six different locations per site and four depth intervals (0-20 cm, 20-50 cm, 50-75 cm, >75 cm), using an HUMAX® core sampler (HUMAX Bohrsonden, Martin Burch AG, Rothenburg, Switzerland).1 The depth of the deepest sample varied among sites (Table S1).

1.2. Sampling of seepage water and atmospheric deposition

To sample seepage water, three suction cups (SPE20®, UMS, Munich, Germany) with a nylon membrane (0.2 µm pore size) were installed at each 10x10 m plot at 50 cm depth. The suction cups were connected with acid-cleaned sampling bottles in a plastic box, located outside the field (at 5 m distance). The connection tubes were buried at 40 cm depth to allow for plowing (Figure S2b). Soil solutions were sampled by applying a vacuum of 50 kPa to the sampling bottles.

Next to the 10x10 m plot, 2 m above the ground, 5 acid-cleaned bulk precipitation samplers (volume: 2 L) were installed. The samplers consisted of a sampling bottle and a funnel on top. A polyester net (PES-1600/61, Franz-Eckert GmbH, Waldkirch, Germany) was used at the bottom of the funnels to prevent insects to fall into the samplers. Above the net, table tennis balls (PVDF, Semadeni, Ostermundigen, Switzerland) were used to reduce evaporation of the sampled water. Plastic thorns were put outside the funnels to prevent birds from sitting on the samplers. For the winter months, between week 52 in 2014 (2014.w52) and week 10 in 2015 (2015.w10), snow

S2

samplers were installed to sample atmospheric deposition. These consisted of 30 cm diameter buckets that were fitted with PE plastic bags. After each sampling, the full bags were taken back to the laboratory, where the snow and ice were thawed. All individual sampler components were acid-cleaned and tested for trace element leaching to exclude contamination of the sample (10% HNO3 leachate of the components was found to have Cd at <0.01 µg L-1).

Following collection, atmospheric deposition samples were passed through 0.45 µm filters to remove particles. Seepage water and atmospheric deposition samples were then acidified with 69% HNO3 (Suprapur) to give a 1% w/w HNO3 solution for subsequent measurement of metal concentrations and isotope compositions. The samples for isotopic analyses were stored at -20 °C.

Dielectric permittivity of the soils was measured with three TDR sensors (EC-5, Decagon Devices Inc., Pullman, WA, USA) at 50 cm depth in the plots at NE and WI, in 1-h resolution and the volumetric water content of the soil was calculated, using a sensor-specific calibration2 for mineral soils. In OE, data for soil water content were obtained from the Swiss Soil Moisture Experiment (SwissSMEX).3 This experiment was carried out on the same arable field, during the same time period and only ~70 m away from our plot.

1.3. Agricultural in- and outputs

Prior to liquid cattle manure sampling, the manure storage container was mixed for 30 minutes. A 5 m long tube was used to take a homogeneous sample over the whole depth of the storage container. The whole length of the tube was filled several times with liquid manure and poured into a 10-L bucket. The manure in the bucket was mixed again and two samples were taken with a 1-L beaker and stored in acid cleaned 1-L bottles. The samples

S3

were stored at -20 °C. In NE, dry horse manure was spread on the field in 2014. The manure was not sampled. For the mass balance calculations, formerly reported Cd concentrations were used.4

Different plant species were grown on the fields. During the first season, winter wheat was grown at OE (Triticum aestivum L. cv. Zinal) and NE (Triticum aestivum L. cv. Mulan) and summer wheat at WI (Triticum aestivum L. cv. Fiorina). During the second season, winter barley was grown at OE (Hordeum vulgare L. cv. Meridian), WI (Hordeum vulgare L. cv. Classic) and NE (Hordeum vulgare L. cv. Caravan).

1.4. τCd values

Gains and losses of Cd in soils relative to the parent material were calculated in the respective depth increments using the open-system mass balance (Equations S1 and S2).5,6,7 Positive and negative τCd values thereby indicate Cd gain and Cd loss, respectively. For example, τCd = 0.5 implies a Cd gain by 50% whereas τCd = -1.0 means a loss of 100%. The open-system mass balance also considers the change in density and volume during weathering by incorporation of strain εCd (Equation S1).5,6,7 Titanium was used as the immobile element.

For the calculation, Ti was used as the immobile element.

Equation S1 :εTi=ρ pm[Ti ]pmρsoil [Ti ]soil

−1

Equation S2 :τCd=ρsoil [Cd ]soilρpm[Cd ]pm

−(ε¿¿Ti , soil+1)−1 ¿

εTi: strain (>0 = dilation; <0 = collapse)ρ: bulk density [g cm-3]pm: parent material

S4

[Ti]: Titanium concentration [mg kg-1]τCd: mass fluxes (>0 = gain; <0 = loss)[Cd]: Cadmium concentration [mg kg-1]

1.5. Laboratory analysis

Soil samples were dried at 40 °C for 48 h and sieved to <2 mm. All plant and thawed manure samples were dried at 60 °C for 48 h. The six soil-core samples from locations A, B, C, D, E, and F (Figure S2a) from the same arable field were used to determine bulk density and coarse soil content (> 2 mm) and afterwards pooled to three samples (A&F, B&D, and C&E). Straw and manure samples were hackled with a knife mill (GM 200, Retsch, Haan, Germany). All samples (parent material, soil, plant, manure and mineral P fertilizers) were further ground with a planetary ball mill with agate beakers (PM 200, Retsch, Haan, Germany) and digested in a microwave oven (ETHOS, MLS, Leutkirch, Germany).

Water content of the soils was determined by weight loss after drying at 105°C, bulk density by drying and weighing a 100 cm3 soil core. Soil pH was measured with a pH electrode (soil:solution ratio 1:2.5 in 0.1 M CaCl2). Cation exchange capacity (CEC) was calculated with the charge equivalents of Al, Ca, K, Mg extracted with 1 M NH4NO3 (soil:solution ratio 1:20, 1 hour shaking). C, N, and S concentrations were determined by dry combustion and analysis of released gases with a CNS analyzer (Vario EL Cube, Elementar Analysensysteme, Langenselbold, Germany). The texture of the soils was measured with laser diffraction (Mastersizer 2000, Malvern Instruments GmbH, Herrenberg, Germany) after destruction of organic matter by boiling in H2O2 and dispersion of the sample.

1.6. Stable isotope measurements

S5

A detailed description of the methods that were applied for the Cd isotope analyses was previously provided by Wiggenhauser et al.,8 hence, only a brief summary is provided here and information on any techniques that are unique to the present investigation.

All samples were prepared to yield at least 100 ng of Cd for isotopic analysis, but some seepage water samples contained lower Cd contents. Between 1.1 and 9.1 L of seepage water and atmospheric deposition were collected and combined to acquire at least 10 ng Cd for isotopic analysis and evaporated prior to digestion. Because of the low Cd concentrations, wheat, barley and manure samples were pre-treated in the microwave oven. Depending on Cd concentrations, 0.5-3.0 g of a sample were thereby digested in 10 ml HNO3

(69%) at 200 °C for 0.5 h, transferred to Savillex® beakers (Savillex Corporation, Eden Prairie, MN, USA) and evaporated to dryness on the hot plate (120 °C). Evaporated water samples, pre-digested plant material and 0.1-0.3 g samples of parent material, soil and mineral P fertilizer were then fully digested on a hot plate (120 °C, 48 h) in 3 ml HNO3 (69%), 1 ml H2O2

(30%) and 2 ml HF (40%). The digests were dried and re-dissolved in 4 ml aqua regia (120 °C, 48 h) and dried again. After these initial digestion steps, samples were dissolved in 5 M HCl and Cd concentrations were determined on small solution aliquots by ICP-MS. All evaporation and sample preparation work was done in a clean lab facility.

An appropriate volume of the 111Cd/113Cd double-spike solution was equilibrated with the remaining sample solutions. Cadmium was then separated from the sample matrix using a three-stage column chemistry procedure that employs both anion exchange and extraction chromatography.9,10 This was followed by a liquid-liquid extraction step for further sample cleanup.9 The Cd isotope compositions were then determined on a Nu-Plasma HR multiple collector inductively-coupled plasma mass spectrometer (MC-ICP-MS, Nu Instruments Ltd, Wrexham, UK) at the Imperial College London MAGIC Laboratories. The added double-spike thereby

S6

ensured precise correction for the instrumental mass bias and any laboratory-induced mass fractionation.9,10 The final δ114/110Cd values were calculated relative to bracketing runs of the NIST 3108 Cd reference material11 and reported using a δ notation based on the 114Cd/110Cd ratio (Equation S3).

Equation S3 :δ 114 /110Cd=[ ( Cd114 / Cd110 )sample

( Cd114 / Cd110 )NIST 3108

−1] ∙1000

The ∆114/110Cd values, which denote the apparent isotopic fractionation between two reservoirs (e.g., between soil and seepage water) were calculated according Equation S4.

Equation S4 :∆114 /110Cdsoil−seepagewater=δ 114 /110Cd soil−δ 114 /110Cd seepagewater

1.7. Cd abundance mass balances

The Cd mass balances were set up for the upper soil horizons (0-50 cm). Cadmium inputs were provided by coarse soil weathering (weathering from the coarse rock fragments in the soil of > 2 mm), atmospheric deposition, mineral P fertilizers and manure. Cadmium outputs were from seepage water, and the wheat and barley harvests. The mass balance fluxes with the largest year to year variations were the Cd inputs from mineral P fertilizers and manure. Therefore, an average value of these inputs over the last 4 years (2012-2015 for OE and NE) or the last 6 years (2010-2015 for WI) were used to render the calculations more robust.

In a previous study, Albertsen et al.12 calculated the Cd inputs to soils from silicate weathering based on the reported Na release, the silicate content of the soil, and the Cd concentration in the silicates. This approach was modified here for WI: the silicate content was replaced by the coarse soil

S7

concentrations and the Cd content of the silicates was replaced by the Cd concentrations of the respective parent material. The Cd release by weathering calculated according this approach provides results that are of the same order of magnitude as calculations, which estimate the coarse soil weathering from silicate weathering rates per area.13,14 Soils at OE and NE formed on carbonate rocks. Because weathering rates of carbonate rocks were by three orders of magnitude higher15 than weathering rates of silicate rocks, we applied a factor of 1000 to calculate the weathering input at OE and NE.

Meteorological data (rainfall, temperature, atmospheric pressure, relative humidity, solar radiation and wind speed, one hour resolution) were provided by MeteoSwiss.16 For the water balances, data from the meteorological stations in Wynau (for OE and WI) and Basel/Binningen (for NE) were used (Figure S1). The FAO Penman-Monteith method was used to calculate the reference evapotranspiration ET0.17 Plant growth was monitored during biweekly sampling and used to calculate the crop evapotranspiration ETc with the dual crop coefficient method, using the growth stages and heights of the plants.17 The precipitation, crop evapotranspiration and changes in the soil water content allowed daily calculations of the seepage water flux (Equation S5), using a one box model from 0-50 cm depth.18 Precipitation and seepage water data were further used for the Cd abundance and isotope mass balances. Because of the distance between the meteorological stations and the arable land sites, uncertainties of 10% were assumed for the meteorological input data.

Equation S5 :SW=P−ET c−∆ S

SW: Seepage waterP: PrecipitationETc: Crop evapotranspiration∆S: Soil water content change (>0 = sink; <0 = source)

Agricultural data (amounts and kind of applied fertilizers, manure and harvest) were taken from the Swiss Soil Monitoring Network (NABO) database

S8

(OE and WI) and from the farmer’s logbook (NE). Such logbooks are mandatory for farmers in Switzerland if they receive direct payments from the state. Uncertainties of 10% were assumed for the agricultural data. The Cd concentration, meteorological, water balance and agricultural data were used to calculate Cd abundance mass balances for the three arable study sites for one hydrological year.

1.8. Stable isotope mass balances

No Cd isotope data are available for bulk atmospheric deposition for some periods of the year. For these periods, the mean of all available values for the relevant site was used for the isotope mass balance calculations. For the bulk atmospheric deposition of WI, Cd isotope data were not determined. But as the sites of OE and WI are near (~8.9 km, Figure S1), the values determined for OE were also used for WI calculations. Furthermore, Cd isotope results are not available for the manure of NE. The isotope balance calculations hence utilized the mean manure value determined for the samples from OE and WI.

1.9. Soil-plant cycling model

The parameters of the soil-plant cycling model are explained in the following.

The Cd surplus in the upper (0-35 cm) soil horizons compared to the deeper (35-75 cm) soil horizon: This Cd surplus was calculated with the help of the remaining Cd fractions (τCd values + 1). These remaining Cd fractions were higher in the upper soil horizons than in the deeper soil horizons, at all sites. In the calculations, the hypothetical Cd content (g ha-1) of the upper soil horizons was calculated, assuming to have the same remaining Cd fraction as the deeper soil horizons. Furthermore, the difference between the current Cd content and the hypothetical Cd

S9

content of the upper soil horizons represents the Cd surplus. This Cd surplus was 410, 193 and 1103 g a-1 at OE, WI and NE, respectively.

The Soil age: In central Europe, a so-called Upper Layer was formed during the Younger Dryas19 or the Oldest Dryas19,20 (i.e. 11700 to 13700 BP). The Upper layer was formed by cryoturbation and solifluction, which reworked the pre-existing superficial sediment and soil material.21 The lower boundary of the Upper Layer can be characterized by an abrupt increase of bulk density and a decrease in silt content.21

Both characteristics were not observed within our soil profiles and we can assume the whole soil columns of our sites to be within the Upper Layer, with an age of ~13700 years.

The annually cycled Cd: For this, the Cd surplus was divided by the soil age and resulted in 0.030, 0.014 and 0.081 g ha-1 yr-1 at OE, WI and NE, respectively. Former studies revealed higher amounts of deposed Cd with litter fall of 0.6-1.7 g ha-1 yr-1.22,23,24 This difference can be explained. Principally, the litter fall in the literature considers Cd which is taken up from the whole soil column. Thereby, plants take up more Cd from the upper than from the deeper soil horizon; our model only considers the Cd from the deeper soil horizons. Furthermore, only a part of the cycled Cd stayed in the soil, the other part was leached with seepage water; therefore, the amount of the total cycled Cd is bigger than the Cd surplus in the topsoil.

The Vegetation: Palynological reconstructions of the vegetation history revealed a tree-covered landscape in Switzerland since the Bølling period (ca. 13700 yr BP).21,25,26,27

The isotopic composition of the cycled Cd: To our knowledge, there is no study, which investigated the isotopic fractionation between soils and trees. However, the literature is consistent in predicting the Cd in plants to be isotopically heavier than the Cd in soils. Thus, we used

S10

different ∆114/110Cdsoil-trees values in the soil-plant cycling model. For each ∆114/110Cdsoil-trees value of the model, we plotted the remaining Cd fractions and the ∆114/110Cdsoil-parent material values and fitted a Raleigh fractionation model for soil formation. Thereby, the best results were achieved with ∆114/110Cdsoil-trees = -0.25‰ (Results of other values are shown in Figure 6). However, this value is smaller than the one for wheat and barley harvest in this study (∆114/110Cdsoil-wheat = 0.34 to 0.56‰; ∆114/110Cdsoil-barley = 0.71 to 0.83‰). This difference can be well explained because only a part of the cycled Cd stayed in the soil, the other part was leached with seepage water. Thus, the ∆114/110Cdsoil-trees

value does not only include the isotopic fractionation of the Cd uptake, but also the isotopic fractionation of the organic matter decomposition. Our data show, that the Cd in seepage water was isotopically heavier than the Cd in soils. Therefore, we can assume, that the part of the cycled Cd which was leached with seepage water was isotopically heavier than the part of the cycled Cd which stayed in the soil. This isotopic fractionation of the organic matter decomposition would lower the overall ∆114/110Cdsoil-trees value of the cycled Cd.

S11

1.10. Error propagation

For the calculation of τCd values, mass balances, isotope mass balances and ∆114/110Cd values, error propagations had to be performed. In the following, V is the result of an additive function (Equation S6) and ∆V the absolute error of this result (Equation S7).

Equation S6 :V=c1W 1+c2W 2+ .. .+cnW n

Equation S7 :∆V =√(c1∆W 1)2+(c2∆W 2 )2+ .. .+(cn∆W n)

2

V: additive function resultW1-n: additive function inputsc1-n: multiplicative factors∆V: absolute error of additive function result

Furthermore, Y is the result of a multiplicative function (Equation S8) and ∆Y the absolute error of this result (Equation S9).

Equation S8 :Y=X1m1∙ X2

m2 ∙+ .. . ∙ Xnmn

Equation S9 :∆Y=√(m1

∆ X1X1 )

2

+(m2

∆ X2X2 )

2

+ . ..+(mn

∆ Xn

X n)2

∙|Y|

Y: multiplicative function resultX1-n: multiplicative function inputsm1-n: exponents of function inputs|Y|̅: mean value of multiplicative function result∆Y: absolute error of function resultX1̅-n: mean value of multiplicative function inputs∆X1-n: absolute error of multiplicative function inputs

S12

2. Map with location of the study sites

Figure S1: Map of northwestern Switzerland with locations of the three arable study sites and the two meteorological stations.

S13

3. Sampling at the study sites

Figure S2: 10x10 m plot of the study sites. a: soil sampling. 1-4 area mixed samples from 0-20 cm depth, each consisting of 25 subsamples. A-F: HUMAX core samples, separated into 4 depths (0-20 cm, 20-50 cm, 50-75 cm, >75 cm), used to determine bulk soil density and coarse soil content (>2 mm). For further soil analysis, HUMAX core samples were pooled to three samples (A&F, B&D and C&E). b: Seepage water sampling, atmospheric deposition sampling and soil water content measurements. A-C: Suction cups with tubes and sampling bottles. 1-5: atmospheric

S14

deposition samplers. 6: snow sampler. I-III: EC-5 sensors to measure soil water contents in WI and NE. IV: HOBO® datalogger to record soil water measurement data.

S15

4. Cd abundance mass balances as a function of the Cd concentration in mineral P fertilizers

Figure S3: Relationship between Cd concentration in mineral P fertilizers and the Cd mass balance with (a) wheat and (b) barley production. We assumed that all the other fluxes were constant. Blue shows results for OE, red for WI and yellow for NE. The points indicate the mineral P concentrations at which the Cd mass balance of a site turns from a net loss to a net accumulation.

S16

5. Relationship between Cd surplus in the topsoils and Cd concentration in parent materials

Figure S4: Relationship between the Cd concentrations in the parent materials (OE: C horizon, 240-270 cm, WI: C horizon 110-130 cm, NE: limestone) and the Cd surplus in upper (0-35 cm) relative to the deeper (35-75 cm) soil horizons, calculated from τCd values. Error bars represent standard deviations, calculated with error propagation (Equations S4-S7).

S17

6. Rayleigh fractionation model for soil formation after removal of the soil-plant cycling effect with alternative ∆114/110Cdsoil-trees values

Figure S5: The remaining Cd fractions in the soils (τCd values + 1) and the 114/110Cdsoil-pm values in 2015 were plotted after reckoning back the plant pump effect. Thereby, the soil-plant cycling effect was calculated with 114/110Cdsoil-trees -0.10 (a) and -0.40 (b). With these calculations, the Rayleigh fractionation fit was worse than with 114/110Cdsoil-trees of -0.25, with ε = 0.16 (a) and 0.19 (b).

S18

7. Soil-plant cycling model results for WI and NE

Figure S6: Results of the soil-plant cycling model at Wiedlisbach. The remaining Cd fractions (τCd + 1) and the isotope compositions of the two soil boxes (0-35 and 35-75 cm) in grey indicate values in 2015 and include soil-plant cycling over the whole soil formation period. Input parameters for the soil-plant cycling model (in green) were the cycling time (i.e. age of the soil), ∆114/110Cdsoil-plant and total cycled Cd (calculated with the help of τCd values). The remaining Cd fractions and isotope compositions of the two soil boxes in red indicate values in 2015 if soil-plant cycling would not have occurred.

S19

Figure S7: Results of the soil-plant cycling model at Nenzlingen. The remaining Cd fractions (τCd + 1) and the isotope compositions of the two soil boxes (0-35 and 35-75 cm) in grey indicate values in 2015 and include soil-plant cycling over the whole soil formation period. Input parameters for the soil-plant cycling model (in green) were the cycling time (i.e. age of the soil), ∆114/110Cdsoil-plant and total cycled Cd (calculated with the help of τCd values). The remaining Cd fractions and isotope compositions of the two soil boxes in red indicate values in 2015 if soil-plant cycling would not have occurred

S20

8. Soil properties

Table S1: Soil properties of the three arable fields at the study sites OE, WI and NE. Number of replicates are indicated as superscripts. Errors represent standard deviations for all properties except δ114/110Cd values, where they represent 2 x standard deviations. τCd-values (Equations S1 and S2) were calculated with different numbers of replicates of Cd and Ti concentrations and bulk densities, the corresponding standard deviation was calculated with error propagation (Equations S4-S7). Texture abbreviations mean silt loam (si L), sandy loam (sa L) and loam (L). CECeff is the effective cation-exchange capacity.

Arablestudy site

Depth pH CECeff TextureOrganiccarbon

Bulk densityCoarse soil

(>2 mm)Cadmium

concentrationτCd δ114/110Cd

[cm] [- log H+] [mmolc kg-1] [-] [%] [g cm-3] [%] [mg kg-1] [-] [‰]

0-20 6.0 ±0.14 212 ±234 si L4 2.5 ±0.04 0.94 ±0.116 0.2 ±0.26 0.44 ±0.012 0.00 ±0.00* 0.06 ±0.082

20-50 7.2 ±0.03 457 ±243 si L3 1.5 ±0.03 1.17 ±0.156 0.4 ±0.46 0.31 ±0.042 -0.25 ±0.05* 0.14 ±0.062

50-73.5 7.2 ±0.03 284 ±53 si L3 1.1 ±0.03 1.41 ±0.136 0.1 ±0.16 0.30 ±0.012 -0.35 ±0.05* 0.09 ±0.032

73.5-77.5 7.0 ±0.23 258 ±153 si L3 1.0 ±0.03 1.51 ±0.704 0.2 ±0.14 0.20 ±0.012 -0.50 ±0.07* -0.01 ±0.242

C-horizon 240-270 - - - - - - 0.15 ±0.002 - 0.04 ±0.062

0-20 5.5 ±0.04 24 ±44 sa L4 1.4 ±0.14 1.15 ±0.086 6.5 ±2.66 0.17 ±0.022 -0.03 ±0.02* -0.15 ±0.162

20-50 5.1 ±0.13 50 ±23 sa L - L3 0.7 ±0.23 1.33 ±0.086 8.3 ±4.86 0.14 ±0.002 -0.29 ±0.08* -0.21 ±0.082

50-73.2 4.4 ±0.13 48 ±53 sa L - L3 0.2 ±0.03 1.42 ±0.346 11.3 ±13.06 0.13 ±0.012 -0.42 ±0.17* -0.15 ±0.092

73.2-77.0 4.3 ±0.13 47 ±103 sa L3 0.1 ±0.02 1.89 ±0.603 6.1 ±1.43 0.15 ±0.002 -0.38 ±0.18* -0.14 ±0.182

C-Horizon 110-130 - - - - - - 0.16 ±0.002 - -0.17 ±0.102

0-20 6.9 ±0.04 188 ±124 si L4 2.1 ±0.14 1.16 ±0.166 4.6 ±2.56 1.66 ±0.072 -0.76 ±0.05* 0.13 ±0.022

20-50 7.3 ±0.23 343 ±863 si L3 1.0 ±0.13 1.25 ±0.346 9.2 ±11.66 1.50 ±0.042 -0.79 ±0.07* 0.09 ±0.032

50-65.2 7.4 ±0.13 434 ±193 si L3 0.6 ±0.13 1.41 ±0.816 34.9 ±11.76 1.25 ±0.072 -0.82 ±0.07* 0.08 ±0.102

65.2-69.0 7.4 ±0.13 401 ±343 si L3 0.5 ±0.22 1.25 ±0.293 16.1 ±6.63 0.97 ±0.262 -0.86 ±0.23* 0.03 ±0.072

Limestone surface - - - - - - 0.45 ±0.002 -

NESoil

OESoil

WISoil

S21

9. Calculated Cd abundance and isotope mass balances

Table S2: Cd abundance and stable isotope mass balances of the three arable fields at the study sites OE, WI and NE for one hydrological year (May 2014 – May 2015). Mass balances were calculated for wheat (I) and barley cultivation (II). System inputs are highlighted in red, system losses in green and new bulk soil mass balance values represent Cd concentration changes after one hydrological year. New bulk soil δ114/110Cd values are calculated for 100 hydrological years, with current in- and outputs (*) and maximal Cd inputs (**) through atmospheric deposition, mineral P fertilizers and manure during the last century. Uncertainties in flux values represent standard deviations, uncertainties in isotope compositions 2 x standard deviations. Error propagation was calculated according to Equations S4-S7.

Cd input δ114/110Cd Cd input δ114/110Cd Cd input δ114/110Cd[g ha-1 yr-1] [‰] [g ha-1 yr-1] [‰] [g ha-1 yr-1] [‰]

Atmospheric depositionI,II 0.12 ±0.01 0.18 ±0.05 0.11 ±0.01 0.18 ±0.03 0.11 ±0.01 0.17 ±0.04

Mineral fertilizersI,II 0.75 ±0.05 -0.04 ±0.03 0.49 ±0.03 0.02 ±0.02 0.57 ±0.03 -0.05 ±0.01

ManureI,II 0.20 ±0.02 0.38 ±0.01 0.91 ±0.09 0.35 ±0.01 0.25 ±0.03 0.36 ±0.01

Coarse soil weatheringI,II 0.01 ±0.01 0.04 ±0.06 0.00 ±0.00 -0.17 ±0.05 0.39 ±0.27 0.36 ±0.02

Cd output δ114/110Cd Cd output δ114/110Cd Cd output δ114/110Cd[g ha-1 yr-1] [‰] [g ha-1 yr-1] [‰] [g ha-1 yr-1] [‰]

Seepage waterI,II 0.02 ±0.00 0.79 ±0.10 0.99 ±0.06 0.47 ±0.06 0.04 ±0.00 0.70 ±0.08

Wheat harvestI 1.47 ±0.11 0.44 ±0.07 0.52 ±0.04 0.38 ±0.10 1.77 ±0.13 0.57 ±0.08

Barley harvestII 0.33 ±0.02 0.81 ±0.09 0.33 ±0.02 0.57 ±0.06 0.73 ±0.05 0.94 ±0.12

Cd balance Cd balance Cd balance[g ha-1 yr-1] [g ha-1 yr-1] [g ha-1 yr-1]

Bulk soil 1928 ±217 1001 ±65 9159 ±1647

New bulk soil (1 yr) I -0.43 ±0.13 -0.01 ±0.12 -0.49 ±0.30

New bulk soil (1 yr) I I +0.71 ±0.06 +0.18 ±0.12 +0.55 ±0.28

δ114/110Cd δ114/110Cd δ114/110Cd[‰] [‰] [‰]

Bulk soil 0.10 ±0.03 -0.18 ±0.05 0.11 ±0.03

New bulk soil (100 yr) * 0.08 ±0.03 -0.21 ±0.05 0.10 ±0.04

New bulk soil (100 yr) ** 0.06 ±0.03 -0.14 ±0.05 0.10 ±0.04

Cd abundancemass balance

Stable isotopemass balance

OE WI NE

S22

10. Standard reference materials

Table S3: Cadmium isotope compositions and concentrations in standard reference materials (SRM’s)

SRM Type Applied methods δ114/110Cd ± 2SDa Reference Cd conc. ± SDe Reference n[‰] [‰] [ng g-1] [ng g-1]

NIST 2709a SoilDigestion, column chemistry,isotope measurement

-0.17 ±0.04a -0.22 ±0.02b 343.4 ±4.0e 371 ±2f

330 and 370g3

NIST 1567b Wheat flourDigestion, column chemistry,isotope measurement

0.89 ±0.00a 0.93 ±0.08b 22.3 ±1.6e 25.4 ±0.9h

22 to 27d2

NIST 3108 Isotope RM Column chemistry, isotope measurement 0.04 ±0.09a 0.00 ±0.09c - - 11

BAM-I012 Isotope RM Isotope measurement -1.31 ±0.10a -1.30 to -1.37d - - 36

a 2SD = 2 x standard deviation of n samplesb Mean value from Wiggenhauser et al.8 with uncertainty as 2 x standard deviationc Mean value from Gault-Ringold et al.28,29 and Abouchami et al.11

d Values summarized by GeoREM30

e SD = standard deviation of n samplesf Reported value from the National Institute of Standards & Technology31

g Mean values from Goix et al.32 and Wiseman et al. (2013)33

h Reported value from the National Institute of Standards & Technology34

S23

11. Measured isotope compositions

Table S4: Cadmium isotope compositions (as 114/110Cd values in ‰) of the bulk soils, inputs and outputs. The ratios are shown for the three arable fields at the study sites OE, WI and NE. Mineral fertilizers are not site-specific. Error bars represent 2 x standard deviations for sample replicates where n>1 and for measurement replicates where n=1. Isotope values of harvest and entire plants were calculated according to Equation 3, error propagation according to Equations S4-S7. wXX is calendar week.

Plant harvest OE WI NEWheat harvest 0.44 ±0.07 0.38 ±0.10 0.57 ±0.14

Barley harvest 0.81 ±0.09 0.57 ±0.06 0.94 ±0.11

Atmospheric deposition OE WI NE2014.w20-2014.w36 0.19 ±0.05 - 0.12 ±0.01

2014.w50-2015.w10 0.18 ±0.13 - 0.26 ±0.15

Manure OE WI NECow manure 0.38 ±0.00 0.35 ±0.01 -

Mineral fertilizersTSPLandorPhosphat-KaliProMixLinzerTipDAPMicrostarNovaphos

Bulk soil OE WI NE0-20 0.06 ±0.08 -0.15 ±0.16 0.13 ±0.02

20-50 0.14 ±0.06 -0.21 ±0.08 0.09 ±0.03

50-75 0.09 ±0.03 -0.15 ±0.09 0.08 ±0.10

>75 -0.01 ±0.24 -0.14 ±0.18 0.03 ±0.07

Seepage water OE WI NE2014.w20-2015.w20 0.79 ±0.09 - -2014.w20-2014.w36 - 0.39 ±0.01 0.57 ±0.14

2014.w36-2014.w50 - 0.46 ±0.07 0.71 ±0.01

2014.w50-2015.w10 - 0.53 ±0.09 0.66 ±0.08

2015.w10-2015.w20 - 0.47 ±0.12 0.69 ±0.09

Parent Material OE WI NEC-Horizon 240-270 cm 0.04 ±0.06 - -C-Horizon 110-130 cm - -0.17 ±0.10 -Limestone - - 0.36 ±0.04

0.01 ±0.09

-0.11 ±0.03

0.15 ±0.01

not site specific

0.00 ±0.05

0.12 ±0.08

-0.10 ±0.10

0.08 ±0.11

-0.15 ±0.08

S24

12. References

(1) Martin Burch AG. Bohrsonden zur Entnahme von Bodenproben: HUMAX Erdbohrgeräte. CH-6023 Rothenburg.

(2) Decagon Devices, I. EC-5 Soil Moisture Sensor: Operator’s Manual. Pullman.

(3) Swiss Soil Moisture Experiment. Institute for Atmospheric and Climate Science: ETH Zurich: Institut für Atmosphäre und Klima.

(4) Keller, A.; Rossier, N.; Desaules, A. Schwermetallbilanzen von Landwirtschaftsparzellen der nationalen Bodenbeobachtung: NABO - Nationales Bodenbeachtungsnetz der Schweiz; Schriftenreihe der FAL; FAL: Zürich, 2005; Vol. 54.

(5) Brimhall, G. H.; Dietrich, W. E. Constitutive mass balance relations between chemical composition, volume, density, porosity, and strain in metasomatic hydrochemical systems: Results on weathering and pedogenesis. Geochim. Cosmochim. Acta 1987, 51 (3), 567–587 DOI: 10.1016/0016-7037(87)90070-6.

(6) Chadwick, O. A.; Brimhall, G. H.; Hendricks, D. M. From a black to a gray box - a mass balance interpretation of pedogenesis. Geomorphology 1990, 3 (3–4), 369–390 DOI: 10.1016/0169-555X(90)90012-F.

(7) Brimhall, G. H.; Chadwick, O. A.; Lewis, C. J.; Compston, W.; Williams, I. S.; Danti, K. J.; Dietrich, W. E.; Power, M. E.; Hendricks, D.; Bratt, J. Deformational mass transport and invasive processes in soil evolution. Science 1992, 255 (5045), 695–702 DOI: 10.1126/science.255.5045.695.

(8) Wiggenhauser, M.; Bigalke, M.; Imseng, M.; Müller, M.; Keller, A.; Murphy, K.; Kreissig, K.; Rehkämper, M.; Wilcke, W.; Frossard, E. Cadmium isotope fractionation in soil-wheat systems. Environ. Sci.

S25

Technol. 2016, 50 (17), 9223–9231 DOI: 10.1021/acs.est.6b01568.

(9) Murphy, K.; Rehkamper, M.; Kreissig, K.; Coles, B.; van de Flierdt, T. Improvements in Cd stable isotope analysis achieved through use of liquid-liquid extraction to remove organic residues from Cd separates obtained by extraction chromatography. J. Anal. At. Spectrom. 2016, 31 (1), 319–327 DOI: 10.1039/c5ja00115c.

(10) Xue, Z.; Rehkamper, M.; Schonbachler, M.; Statham, P. J.; Coles, B. J. A new methodology for precise cadmium isotope analyses of seawater. Anal. Bioanal. Chem. 2012, 402 (2), 883–893 DOI: 10.1007/s00216-011-5487-0.

(11) Abouchami, W.; Galer, S. J. G.; Horner, T. J.; Rehkämper, M.; Wombacher, F.; Xue, Z.; Lambelet, M.; Gault-Ringold, M.; Stirling, C. H.; Schönbächler, M.; et al. A Common Reference Material for Cadmium Isotope Studies - NIST SRM 3108. Geostand. Geoanalytical Res. 2013, 37 (1), 5–17 DOI: 10.1111/j.1751-908X.2012.00175.x.

(12) Albertsen, M.; Mathess G.; Pekdeger A.; Schulz H. D. Quantifizierung von Verwitterungsvorgängen. Geol. Rundschau 1980, 69, 532–545.

(13) Buss, H. L.; Sak, P. B.; Webb, S. M.; Brantley, S. L. Weathering of the Rio Blanco quartz diorite, Luquillo Mountains, Puerto Rico: Coupling oxidation, dissolution, and fracturing. Geochim. Cosmochim. Acta 2008, 72 (18), 4488–4507 DOI: 10.1016/j.gca.2008.06.020.

(14) White, A. F.; Buss, H. L. Natural Weathering Rates of Silicate Minerals. In Treatise on Geochemistry; Elsevier, 2014; pp 115–155.

(15) Emmanuel, S.; Levenson, Y. Limestone weathering rates accelerated by micron-scale grain detachment. Geology 2014, 42 (9), 751–754 DOI: 10.1130/G35815.1.

(16) Schweizerische Eidgenossenschaft. Federal Office of Meteorology and

S26

Climatology MeteoSwiss.

(17) Allen, R. G. Crop evapotranspiration: Guidelines for computing crop water requirements; FAO irrigation and drainage paper; Rome, 1998; Vol. 56.

(18) Leimer, S.; Kreutziger, Y.; Rosenkranz, S.; Beßler, H.; Engels, C.; Hildebrandt, A.; Oelmann, Y.; Weisser, W. W.; Wirth, C.; Wilcke, W. Plant diversity effects on the water balance of an experimental grassland. Ecohydrology 2014, n/a-n/a DOI: 10.1002/eco.1464.

(19) Kösel, M. Der Einfluss von Relief und periglazialen Deckschichten auf die Bodenbildung im mittleren Rheingletschergebiet von Oberschwaben, 1996.

(20) Völkel, J.; Mahr, A. Neue Befunde zum Alter der periglazialen Deckschichten im Vorderen Bayerischen Wald. Zeitschrift für Geomorphol. 1997, 41 (1), 131–137.

(21) Mailänder, R.; Veit, H. Periglacial cover-beds on the Swiss Plateau: Indicators of soil, climate and landscape evolution during the Late Quaternary. CATENA 2001, 45 (4), 251–272 DOI: 10.1016/S0341-8162(01)00151-5.

(22) Huang, J. H.; Ilgen, G.; Matzner, E. Fluxes and budgets of Cd, Zn, Cu, Cr and Ni in a remote forested catchment in Germany. Biogeochemistry 2011, 103 (1), 59–70 DOI: 10.1007/s10533-010-9447-0.

(23) Sevel, L.; Hansen, H. C. B.; Raulund Rasmussen, K. Mass Balance of Cadmium in Two Contrasting Oak Forest Ecosystems. J. Environ. Qual. 2009, 38 (1), 93 102 DOI: Doi 10.2134/Jeq2007.0430.

(24) Landre, A. L.; Watmough, S. A.; Dillon, P. J. Metal pools, fluxes, and budgets in an acidified forested catchment on the precambrian shield, central Ontario, Canada. Water. Air. Soil Pollut. 2010, 209 (1–4), 209–

S27

228 DOI: 10.1007/s11270-009-0193-7.

(25) Burga, C. A.; Perret, R.; Vonarburg, C. Vegetation und Klima der Schweiz seit dem jüngeren Eiszeitalter: Vegetation and climate history in Switzerland during the later Pleistocene and Holocene; Ott: Thun, 1998.

(26) Ammann, B.; Lotter, A. F.; Eicher, U.; Gaillard, M.-J.; Wohlfarth, B.; Haeberli, W.; Lister, G.; Maisch, M.; Niessen, F.; Schlüchter, C. The Würmian Late-glacial in Iowland Switzerland. J. Quat. Sci. 1994, 9 (2), 119–125 DOI: 10.1002/jqs.3390090205.

(27) Lotter, A. F.; Eicher, U.; Siegenthaler, U.; Birks, H. J. B. Late-glacial climatic oscillations as recorded in Swiss lake sediments. J. Quat. Sci. 1992, 7 (3), 187–204 DOI: 10.1002/jqs.3390070302.

(28) Gault-Ringold, M.; Adu, T.; Stirling, C. H.; Frew, R. D.; Hunter, K. A. Anomalous biogeochemical behavior of cadmium in subantarctic surface waters: Mechanistic constraints from cadmium isotopes. Earth Planet. Sci. Lett. 2012, 341–344, 94–103 DOI: 10.1016/j.epsl.2012.06.005.

(29) Gault-Ringold, M.; Stirling, C. H. Anomalous isotopic shifts associated with organic resin residues during cadmium isotopic analysis by double spike MC-ICPMS. J. Anal. At. Spectrom. 2012, 27 (3), 449 DOI: 10.1039/c2ja10360e.

(30) Jochum, K. P.; Nohl, U.; Herwig, K.; Lammel, E.; Stoll, B.; Hofmann, A. W. GeoReM: A New Geochemical Database for Reference Materials and Isotopic Standards. Geostand. Geoanalytical Res. 2005, 29 (3), 333–338 DOI: 10.1111/j.1751-908X.2005.tb00904.x.

(31) NIST Standard Reference Material 2709a. San Joaquin Soil.

(32) Goix, S.; Point, D.; Oliva, P.; Polve, M.; Duprey, J. L.; Mazurek, H.; Guislain, L.; Huayta, C.; Barbieri, F. L.; Gardon, J. Influence of source distribution and geochemical composition of aerosols on children

S28

exposure in the large polymetallic mining region of the Bolivian Altiplano. Sci. Total Environ. 2011, 412–413, 170–184 DOI: 10.1016/j.scitotenv.2011.09.065.

(33) Wiseman, C. L. S.; Zereini, F.; Puttmann, W. Traffic-related trace element fate and uptake by plants cultivated in roadside soils in Toronto, Canada. Sci. Total Environ. 2013, 442, 86–95 DOI: 10.1016/j.scitotenv.2012.10.051.

(34) NIST standard reference material 1567b. Wheat Flour.

S29