Supplementary Material for

Phosphorus (P) Release Risk in Lake Sediment Evaluated by

DIFS Model and Sediment Properties: A New Sediment P

Release Risk Index (SPRRI)

Zhihao Wu a,b,c, Shengrui Wang a,b,c *, Ningning Ji a,b

a. National Engineering Laboratory for Lake Pollution Control and Ecological Restoration, Institute of Lake

Environment, Chinese Research Academy of Environmental Sciences (CRAES), Beijing 100012, China.

b. College of Water Sciences, Beijing Normal University, Beijing, 100875, China.

c. Yunnan Key Laboratory of Pollution Process and Management of Plateau Lake-Watershed, Kunming, Yunnan

Province, 650034, China.

* Correspondence should be addressed to E-mail: wangsr@bnu.edu.cn(S. R. Wang)

The number of pages: 35

The number of the parts for information: 5 (SM A~E)

The number of figures: 6

1

The number of tables: 11

2

Fig. S1 S1-1: The classification of land use in Dianchi river basin based on GIS.

(Reprinted from Wang, X.X., 2014; Optimization of land use and dynamic simulation for Dianchi river basin based

on CA-Markov model. Master thesis, Yunnan University of Finance and Economics, PRC (in Chinese); with the

permission from Yunnan University of Finance and Economics).

S1-2: (1) The emission intensity of TP and (2) the key pollution source of TP in sub-watersheds in

Dianchi river basin (Reprinted from Acta Scientiae Circumstantiae, published online

(DOI:10.13671/j.hjkxxb.2013.01.035), Gao, W., 2013; High-resolution nitrogen and phosphorus emission

inventories of Lake Dianchi Watershed (in Chinese); with the permission from Science Press in China).

Fig. S1-1

water area

unused land

construction land

grassland

arable land

garden

conifer forest

mixed forest

broad-leaved forest

3

Fig. S1-2

4

Fig. S2 The schematic diagraph for Fig. S2-1: the sorption-desorption-diffusion

processes of labile P in sediment porewater induced by the DGT piston. Csolu is

sediment porewater concentration, Cs is the initial concentration of labile phosphorus

in solid phase, Ci is the interfacial concentration of labile P species in sediment

porewater, the k1 is the sorption constant, k-1 is the desorption constant, Δg is the

thickness of diffusion layer; Fig. S2-2: Representation of the concentration of SRP in

a DGT piston and adjacent porewater during deployment is: fully sustained (case a);

partially sustained (case c); or diffusion only (case b) by resupply from the solid phase

in sediment.

Fig.S2-1

Fig.S2-2

5

Fig. S3 Fig. S3-1: The distribution map of 100 sampling sites for SRPPI classification

in Lake Dianchi; and Fig. S3-2: Gaussian distribution curve for SPRRI indexes.

Fig. S3-1

6

Fig. S3-2

Freq

uenc

y

5.0 15.00.0 10.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 55.0 60.0

SPRRI index [lg (nmol cm-3 d-1)]

Average value: 23.80 Standard deviation:13.917N=100

SPRRI=4.87N=8

SPRRI=14.97N=32

SPRRI=29.96N=68

SPRRI=44.78N=68

SPRRI rank 0-5light

15-30

relative high30-45

high very high

>455-15moderate

8% 24% 36% 24% 8%

7

Fig. S4 DIFS curves of Fig. S4-1: r value against t (deployment time) and Fig. S4-2:

Csolu(P) against distance from DGT surface at 24h for sites 2 and 10 in Lake Dianchi.

0.0

0.2

0.4

0.6

0.8

1.0

0 4 8 12 16 20 24

r val

ue

Time (h)

site 2

site 10

Trmax=0.28 h; rmax=0.408

Trmax=2.77 h; rmax=0.882 ↓

Fig. S4-1

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

-1.0 0.0 1.0 2.0 3.0 4.0 5.0

Cso

lu(n

mol

l-1)

Distance (cm)

site 10

Xsolu=1.294 cm ↓

0.0

4.0

8.0

12.0

16.0

20.0

-0.20 -0.10 0.00 0.10 0.20 0.30 0.40 0.50 0.60

Cso

lu(n

mol

l-1)

Distance (cm)

site 2

Xsolu=0.061 cm ↓

Fig. S4-2

8

Fig.S5 The inner relationship between SPRRI and sub-indexes.

SPRRI

lg (1000×LAP/TP) r×lg(Dspt rate) BD(Fe)/Al[NaOH25]

The relative reactive P pool size in solid phase

P exchange between porewater and sediment solid

The effect of Al on P release

Different P pool

NH4Cl-P+BD-P NH4Cl-P

Biogeochemical reactions for P release

Resupply ability of solid phase

The desorption rate constant

P sequestration by aluminum (Al) hydroxide

Sub-indexes

9

Fig.S6 P adsorption-desorption equilibrium concentrations of the sediment (EPC0) and soluble reactive P in overlying water (SRP) in Lake

Dianchi. (Reprinted from Acta Scientiae Circumstantiae, published online (DOI:10.13671/j.hjkxxb.2014.07.09), Chen, C.Y., Characteristics of phosphorus adsorption on surface

sediment of Dianchi Lake (in Chinese); with the permission from Science Press in China).

10

Table S1 The longitudes and latitudes for sampling sites in Lake Dianchi. Five regions

of Caohai (I), middle-north (II), east (III), middle-south (IV), west (V) and south (VI) with the

occupied areas of 10, 49.5, 65, 78, 42.8 and 61 km2, in turn.

Region Site longitude (E) latitude (N)Caohai (I) 1 102.6564 25.0136

2 102.6419 25.0048

3 102.6394 24.9917

　 4 102.6402 24.9798Middle-North(II) 5 102.6522 24.9521

6 102.6585 24.9396

7 102.6638 24.9220

　 8 102.6803 24.9065

East (III) 9 102.7212 24.898310 102.7512 24.8741

11 102.7550 24.8283

12 102.7341 24.7803

13 102.6969 24.7603Middle-South

(IV) 14 102.7079 24.8851

15 102.7229 24.8506

16 102.7139 24.8022

17 102.6714 24.7733

West (V) 18 102.6679 24.881419 102.6700 24.8350

20 102.6633 24.7924

21 102.6160 24.7609

South (VI) 22 102.6173 24.727123 102.6452 24.7287

24 102.6730 24.7295

25 102.6257 24.6921

　 26 102.6581 24.6914

11

Table S2 The parameters in input file for DIFS software including: r, Tc, Kd, Pc, D, , Co, T, g, times, domsize, rtol and atol and the description

of them.

Parameter Units Line # in input file

Description

r - 1 The ratio of initial dissolved to DGT measured concentrationTc s 2 Exchange process response timeKd cm3 g-1 3 Distribution coefficientPc g cm-3 4 Particle concentrationD cm2 s-1 5 Diffusion coefficient(s) - 6 porosity (porosities)Co mol cm-3 7 Initial dissolved concentrationT hours 8 DGT device deployment timeg cm 9 Diffusion layer thicknesstimes - 10 No. of solution times, or listdomsize cm 11 Initial domain sizertol - 12 Relative tolerance for ODE solveratol - 13 Absolute tolerance for ODE solver

12

Table S3 SPRRI indexes for the classification of release risk rank.

(SPRRI indexes are arranged in accordance with the value from low to large value)

SPRRI range Site SPRRI SPRRI

range Site SPRRI SPRRI range Site SPRRI

　 　 [lg (nmol cm-3 d-

1)] 　 　 [lg (nmol cm-3 d-

1)] 　 　 [lg (nmol cm-3 d-

1)]

0～5 1 0.07 15～30 33 15.09 30～45 69 30.27

light 2 0.57 relative high 34 15.77 high 70 30.77

3 1.54 35 16.35 71 31.574 1.95 36 16.85 72 32.425 2.54 37 17.14 73 32.566 3.67 38 17.65 74 33.787 4.25 39 18.22 75 34.12

　 8 4.87 40 18.77 76 34.65

5～15 9 5.21 41 19.33 77 34.77moderate 10 5.78 42 19.78 78 35.37

11 6.07 43 20.16 79 36.2412 6.45 44 20.85 80 36.7313 6.99 45 21.33 81 37.2714 7.21 46 21.84 82 37.3515 7.43 47 22.43 83 38.5616 7.87 48 22.87 84 39.2117 8.11 49 23.66 85 39.5718 8.55 50 23.79 86 40.0619 8.83 51 24.11 87 40.6520 9.22 52 24.51 88 41.3321 9.48 53 24.67 89 42.6722 10.33 54 25.33 90 43.3223 10.65 55 25.42 91 43.6724 11.43 56 25.74 92 44.7825 11.66 57 26.18 >45 93 45.0426 12.43 58 26.43 very high 94 46.7627 12.77 59 26.77 95 47.8928 13.14 60 27.12 96 48.5629 13.44 61 27.47 97 49.3330 14.58 62 27.54 98 50.7531 14.71 63 28.22 99 52.48

　 32 14.97 64 28.63 　 100 53.45

　 65 28.8966 29.1867 29.6468 29.96

13

Table S4 Quality control summary for the analysis of porewater, DGT elution solution, overlying water and sediment. Reference materials: sediments

(GBW07311 for P；GSD9 for Fe2O3，Al2O3，CaO；GBW07455 for TOC); the standard solution made from GBW07311 for P or GSD9 for Fe.

Standard reference material Recovery Reproducibility Standard value

Limits of detection Repeatability

Sediment (%) (%) (mg kg-1) (mg kg-1) (%)　 n=5 n=9 n=5　 　 　 　 　 　 　 　 　

GSD9 Fe2O3 93.2±4.1 4.9±1.5 43900 0.15 4.5±1.2Al2O3 94.1±3.2 3.7±1.8 103700 0.54 3.2±1.6CaO 94.7±3.8 4.1±2.0 4700 0.77 3.7±1.8

GBW07311 TP 93.7±5.1 4.3±0.9 271 1.26 4.0±0.5GBW07435 TOC 93.7±5.4 8.3±3.8 14300 1.05 7.8±3.2

Standard reference material Recovery Reproducibility Standard value

Limits of detection Repeatability

Standard solution (%) (%) (μg L-1) (μg L-1) (%)　 　 n=5 n=9 n=5

Standard P solutionGBW07311 　 　 　 　 　

DGT 103.0±2.3 4.3±0.4 100 0.09 3.2±0.2water and porewater 102.4±2.7 4.5±0.6 50 2.6 3.9±0.4Standard Fe solution

GSD9DGT 104.2±4.7 4.6±0.7 50 0.07 4.3±1.2

water and porewater 103.0±3.3 4.0±3.3 50 0.24 3.7±1.8

14

Table S5 The physicochemical properties for sediment and overlying water in Lake Dianchi.

Table S5-1

Region Sampling site Water Sediment

DTPpH DO

(mg L-1)

ConductivitypH

Eh TOC TFe TAl TCa TP

(μg L-1) (μs cm−1) (mv) (mg kg-1) (mg kg−1 dw) (mg kg−1 dw) (mg kg−1 dw) (mg kg-1)

Caohai(I) 1 756 8.23 5.97 1126 8.37 -87 295 22815 7865 8013 3110

2 589 8.18 5.45 1109 8.21 -89 264 23457 7654 8458 30523 378 8.01 6.02 1099 8.03 -76 201 18765 6533 8754 1764

4 301 7.92 6.31 1023 7.96 -71 198 19754 7126 8883 1678Middle-North

(II) 5 277 7.89 6.45 1011 7.92 -67 178 18754 5567 8959 1778

6 345 8.11 5.92 1105 8.12 -83 268 20836 6421 8786 20437 213 7.93 6.43 1043 7.94 -54 211 20985 6874 9654 1497

8 256 7.95 6.46 1006 7.92 -59 238 20896 7085 9548 1783East(III) 9 73 7.82 7.32 976 7.80 117 167 18754 5543 9897 748

10 49 7.78 7.27 969 7.82 98 199 18432 5752 9965 67411 275 8.02 6.1 1043 8.01 -69 221 18996 6676 8906 175612 286 7.91 6.36 1021 7.99 -67 208 20963 7123 8932 1967

　 13 312 8.03 6.12 1052 8.04 -70 242 22352 5876 8809 1729Middle-South

(IV) 14 273 7.95 6.21 1102 7.98 72 226 17432 6762 8908 1798

15 321 7.96 6.26 1108 8.01 76 254 19743 6986 8896 203116 295 7.82 7.34 982 7.83 -56 228 20853 8642 8965 1887

17 256 7.96 6.25 1064 7.95 -58 236 21245 6674 9032 1632West(V) 18 223 8.02 6.33 1075 7.99 -55 258 22356 6876 9125 1576

19 253 7.84 7.36 988 7.84 -66 255 26743 6764 9668 166120 62 7.81 7.33 976 7.88 85 184 19864 6043 9789 801

21 47 7.84 7.41 981 7.91 64 237 17753 6127 12041 778

15

South(VI) 22 432 7.99 6.4 1066 8.06 -93 264 28742 7643 8871 2347

23 375 8.05 6.22 1063 8.25 -108 273 23252 6437 8856 211824 354 8.14 5.99 1054 8.23 -113 247 24574 6256 8675 195425 453 8.11 6.32 1076 8.22 -102 254 26313 6654 8689 2099

　 26 488 8.18 5.93 1064 8.32 -137 275 27653 6468 8568 2575

Table S5-2

16

Region Sampling site

NH4Cl-P+BD-P NH4Cl-P BD-P NaOH(25)-P HCl-P NaOH(85)-P TP NH4Cl(Fe)+BD(Fe) BD(Fe) Al[NaOH25]

　 　 (mg kg-1) (mg kg-1) (mg kg-1) (mg kg-1) (mg kg-1) (mg kg-1) (mg kg-1) (mg kg-1) (mg kg-1) (mg kg-1)

Caohai 1 295 31 264 1147 778 890 3110 6712 4331 5136(I) 2 324 50 274 1065 935 728 3052 7259 4249 5311

3 89 13 77 639 528 508 1764 2076 1264 1740　 4 62 9 53 853 215 548 1678 1508 1034 1301Middle-North 5 44 7 37 875 467 392 1778 1105 837 1016

(II) 6 154 22 132 1086 339 464 2043 3258 3071 28317 57 8 49 1126 158 156 1497 1424 867 1125　 8 62 6 56 1235 174 312 1783 1660 1038 1625

East 9 20 6 13 214 246 269 748 563 259 646(III) 10 42 5 38 267 228 137 674 1110 603 1386

11 52 5 47 876 453 375 1756 1322 1232 115712 49 6 43 654 478 786 1967 1326 1083 1109　 13 119 19 100 629 575 406 1729 2637 1741 2156

Middle-South 14 96 43 54 543 753 406 1798 1345 979 1809(IV) 15 62 32 31 897 697 375 2031 1556 601 881

16 61 8 53 987 543 296 1887 1385 1047 1729　 17 55 5 50 886 543 148 1632 1453 1083 1306West 18 58 9 50 764 567 187 1576 1272 1113 1666(V) 19 74 8 66 908 364 315 1661 1503 1338 2078

20 26 8 18 135 216 424 1062 801 335 786　 21 31 5 26 276 225 246 778 1311 495 657South 22 164 17 147 957 765 461 2347 3908 3636 3861(VI) 23 76 8 67 987 876 179 2118 2066 1918 1782

24 130 11 119 897 744 184 1954 3244 3127 219425 173 27 146 877 875 175 2100 3832 3623 3734

　 26 226 34 192 897 787 665 2575 4886 4094 3404

17

18

Table S6 The linear correlation coefficient (R2) for CDGT(P) (FDGT(P)), r or Dspt rate against sediment properties or DIFS parameters at twenty or

six sites with NH4Cl-P+BD-P or NH4Cl-P pool, in turn. For all linear correlation relationships, p<0.01.

R2 (twenty sites) R2 (six sites)

　 CDGT(P)/FDGT(P) r Dspt rate 　 CDGT(P)/FDGT(P) r Dspt rate

NH4Cl-P+BD-P 0.86 0.45 0.40 NH4Cl-P 0.94 0.57 0.79BD-P 0.86 0.44 0.43 BD-P 0.08 0.03 0.16

NH4Cl(Fe)+BD(Fe) 0.86 0.44 0.41 NH4Cl(Fe)+BD(Fe) 0.53 0.54 0.08BD(Fe) 0.75 0.40 0.28 BD(Fe) 0.32 0.49 0.18

OM 0.34 0.11 0.25 OM 0.50 0.65 0.13Pc 0.26 0.21 0.13 Pc 0.00 0.09 0.15

porsed 0.27 0.22 0.13 porsed 0.00 0.09 0.14CDGT(P)/FDGT(P) 1.00 0.66 0.56 CDGT(P)/FDGT(P) 1.00 0.65 0.59

C0(P) 0.81 0.37 0.56 C0(P) 0.98 0.53 0.49CDGT(Fe)/FDGT(Fe) 0.71 0.45 0.49 CDGT(Fe)/FDGT(Fe) 0.60 0.29 0.90

r 0.66 1.00 0.19 r 0.65 1.00 0.44kd 0.63 0.60 0.16 kd 0.42 0.34 0.92

rmax 0.68 0.97 0.24 rmax 0.79 0.80 0.74Trmax 0.08 0.07 0.12 Trmax 0.32 0.76 0.08

Tc 0.31 0.61 0.06 Tc 0.36 0.85 0.17k-1 0.58 0.23 0.99 k-1 0.57 0.51 0.99k1 0.62 0.28 0.97 k1 0.55 0.47 0.99

Dspt rate 0.56 0.19 1.00 Dspt rate 0.59 0.45 1.00

19

Table S7 The R2 for the linear correlation relationships between FDGT(P), C0(P), FDGT(Fe), DIFS parameters and sediment solid properties for

twenty sites with NH4Cl-P+BD-P pool. (p<0.01) Twenty

sites FDGT(P) C0(P) FDGT(Fe) r kd rmax Trmax Tc k-1 k1 Dspt rate

NH4Cl-P+BD-P 0.86 0.84 0.58 0.45 0.77 0.46 0.06 0.13 0.39 0.43 0.40BD-P 0.86 0.86 0.59 0.44 0.75 0.45 0.06 0.13 0.42 0.46 0.43TOC 0.34 0.40 0.18 0.11 0.32 0.11 0.01 0.00 0.23 0.26 0.25Pc 0.26 0.19 0.07 0.21 0.12 0.26 0.13 0.05 0.15 0.13 0.13

porsed 0.27 0.20 0.07 0.22 0.13 0.27 0.14 0.05 0.15 0.13 0.13FDGT(P) 1.00 0.81 0.71 0.66 0.63 0.69 0.08 0.31 0.58 0.62 0.56C0(P) 0.81 1.00 0.65 0.37 0.46 0.39 0.03 0.16 0.55 0.57 0.56

FDGT(Fe) 0.71 0.65 1.00 0.45 0.45 0.44 0.05 0.27 0.49 0.53 0.49r 0.66 0.66 0.45 1.00 0.60 0.97 0.07 0.61 0.23 0.28 0.19kd 0.63 0.63 0.45 0.60 1.00 0.55 0.03 0.31 0.17 0.22 0.16

rmax 0.68 0.39 0.44 0.97 0.55 1.00 0.16 0.48 0.29 0.34 0.24Trmax 0.08 0.03 0.05 0.07 0.03 0.16 1.00 0.06 0.14 0.16 0.12

Tc 0.31 0.16 0.27 0.61 0.31 0.48 0.06 1.00 0.07 0.09 0.06k-1 0.58 0.55 0.49 0.23 0.17 0.29 0.14 0.07 1.00 0.99 0.99k1 0.62 0.57 0.53 0.28 0.22 0.34 0.16 0.09 0.99 1.00 0.97

Dspt rate 0.56 0.56 0.49 0.19 0.16 0.24 0.12 0.06 0.99 0.97 1.00

Table S8 The R2 for the linear correlation relationships between FDGT(P), C0(P), FDGT(Fe), DIFS parameters and sediment solid properties for the

20

six sites with NH4Cl-P pool. (p<0.01)

Six sites FDGT(P) C0(P) FDGT(Fe) r kd rmax Trmax Tc k-1 k1 Dspt rateNH4Cl-P 0.94 0.90 0.82 0.58 0.64 0.80 0.19 0.28 0.76 0.75 0.80

TOC 0.50 0.45 0.04 0.65 0.03 0.58 0.77 0.48 0.17 0.14 0.13Pc 0.00 0.00 0.11 0.09 0.13 0.01 0.25 0.33 0.12 0.14 0.15

porsed 0.00 0.00 0.10 0.09 0.13 0.01 0.25 0.32 0.12 0.14 0.14FDGT(P) 1.00 0.98 0.60 0.65 0.42 0.79 0.32 0.36 0.57 0.55 0.59C0(P) 0.98 1.00 0.55 0.53 0.33 0.68 0.25 0.28 0.46 0.44 0.49

FDGT(Fe) 0.60 0.55 1.00 0.30 0.89 0.54 0.01 0.10 0.84 0.85 0.90r 0.65 0.53 0.30 1.00 0.34 0.80 0.76 0.85 0.51 0.47 0.44kd 0.42 0.33 0.89 0.34 1.00 0.51 0.02 0.17 0.90 0.92 0.92

rmax 0.79 0.68 0.54 0.80 0.51 1.00 0.49 0.42 0.78 0.75 0.74Trmax 0.32 0.25 0.01 0.76 0.02 0.49 1.00 0.71 0.13 0.10 0.08

Tc 0.36 0.28 0.10 0.85 0.17 0.42 0.71 1.00 0.22 0.20 0.18k-1 0.57 0.46 0.84 0.51 0.90 0.78 0.13 0.22 1.00 1.00 0.99k1 0.55 0.44 0.85 0.47 0.92 0.75 0.10 0.20 1.00 1.00 0.99

Dspt rate 0.59 0.49 0.90 0.45 0.92 0.74 0.08 0.18 0.99 0.99 1.00

Table S9 The linear correlation equations (multivariable regression) for (1) twenty sites with NH4Cl-P+BD-P pool: FDGT(P) against (i) r and TOC

21

in sediment solid; (ii) NH4Cl(Fe)+BD(Fe) and TCa; and (iii) NH4Cl(Fe)+BD(Fe), Al[NaOH25] and TCa in sediment solid; and (2) six sites with

NH4Cl-P pool: FDGT(P) against (iv) NH4Cl-P and TOC; (v) NH4Cl-P and TCa and (vi) NH4Cl-P and Al[NaOH25].

Twenty sites FDGT(P)/10000 　 r TOC 　 　 NH4Cl(Fe)+BD(Fe) TCa 　 　ng/(cm2 s) 　 　 (mg kg-1) 　 　 (mg kg-1) (mg kg-1) 　 　

FDGT(P)/10000=329.9×r+0.85×TOC-268.8 FDGT(P)/10000=0.026×[NH4Cl(Fe)+BD(Fe)]-0.077×TCa+738

(R2=0.77; p<0.0001) (R2=0.94; p<0.0001)FDGT(P)/10000 　 NH4Cl(Fe)+BD(Fe) Al[NaOH25] TCa 　 　 　 　 　

ng/(cm2 s) 　 (mg kg-1) (mg kg-1) (mg kg-1) 　 　 　 　 　FDGT(P)/10000=0.045×[NH4Cl(Fe)+BD(Fe)]-0.028×Al[NaOH25]-0.068×TCa+662　 　 (R2=0.96; p<0.0001) 　 　 　 　

six sites FDGT(P)/10000 　 NH4Cl-P TOC 　 　 NH4Cl-P TCa 　 　ng/(cm2 s) 　 (mg kg-1) (mg kg-1) 　 　 (mg kg-1) (mg kg-1) 　 　

FDGT(P)/10000=2.28×NH4Cl-P+0.25×TOC-48.2 FDGT(P)/10000=0.089×NH4Cl-P-0.083×TCa+828.7

(R2=0.97; p<0.006) (R2=0.99; p<0.0005)

FDGT(P)/10000 NH4Cl-P Al[NaOH25]

ng/(cm2 s) 　 (mg kg-1) (mg kg-1) 　 　 　 　 　 　FDGT(P)/10000=2.91×NH4Cl-P-0.02×Al[NaOH25]+13.06　 　 (R2=0.97; p<0.005) 　 　 　 　 　

Table S10 The sequences for SPRRI index [lg (nmol cm-3 d-1)], lg(1000×LAP/TP), r×lg(Dspt rate) [lg (nmol cm-3 d-1)] or BD(Fe)/Al[NaOH25] at

22

26 sites in Lake Dianchi.

Sequence Site SPRRI Site lg(1000×LAP/TP) Site r×lg(Dspt rate) Site BD(Fe)/Al[NaOH25]

↓ 26 49.73 2 2.03 1 4.47 24 0.7424 46.52 1 1.98 26 4.11 26 0.62

Decrease 1 38.62 26 1.94 2 3.82 6 0.562 32.03 25 1.92 13 3.76 23 0.566 31.97 6 1.88 24 3.46 11 0.55

13 28.90 13 1.84 6 3.03 12 0.5125 18.79 22 1.84 3 2.86 25 0.503 18.35 24 1.82 14 2.69 22 0.49

11 15.58 3 1.70 4 2.24 1 0.4423 15.26 19 1.65 15 1.99 17 0.434 14.46 7 1.58 25 1.95 5 0.43

22 11.57 18 1.57 11 1.92 13 0.4214 10.37 4 1.57 23 1.76 2 0.4112 8.72 23 1.55 18 1.46 4 0.4115 8.36 8 1.54 5 1.37 7 0.405 8.12 17 1.53 21 1.30 21 0.39

18 7.89 16 1.51 22 1.29 3 0.3817 7.29 11 1.47 12 1.24 15 0.357 6.58 5 1.39 17 1.11 18 0.358 5.07 12 1.39 7 1.04 8 0.33

16 4.84 14 1.38 16 1.02 19 0.3321 4.18 15 1.19 8 0.99 16 0.3119 3.20 20 0.97 20 0.71 14 0.2820 1.53 9 0.93 19 0.58 10 0.239 0.20 10 0.85 9 0.10 20 0.22

　 10 0.18 21 0.82 10 0.09 9 0.21

23

Table S11 The linear correlation coefficient (R2) of SPRRI index against LAP/TP, BD(Fe)/Al[NaOH25], r, lg(Dspt rate) or CDGT(P) (p<0.001)

and (ii) the multivariable regression equations of SPRRI index against BD(Fe) and Al[NaOH25] for twenty or six sites with NH4Cl-P+BD-P or

NH4Cl-P pool, in turn.

Sediment 　 lg(1000×LAP/TP) Fe：Al r lg（Dspt rate） CDGT(P)

Twenty sites SPRRI 0.584 0.46 0.813 0.843 0.7

Six sites SPRRI 0.758 0.341 0.852 0.947 0.909

Sediment 　 Al[NaOH25] BD(Fe)

Twenty sites SPRRI SPRRI = -0.011×Al[NaOH25]+0.018×BD(Fe)+4.51 (R2=0.708, p<0.0001)

Six sites SPRRI SPRRI = -0.01×Al[NaOH25]+0.029×BD(Fe)-1.96 (R2=0.855, p<0.05)

24

SM A (1) The introduction to the deployment of DGT in sediment; (2) The

calculation method for the mass of solute (M) accumulated on the binding gel,

induced DGT-flux (F) and DGT concentration (CDGT).

(1)

After the sediment core was pulled from water surface, a rubber plug was used to

block up the opening of the sediment core at once. The sediment cores were brought

into the lab in bank in one hour; then, they were immediately kept in incubators

(MIR-262, Panasonic Company) at the same temperature (T) (21 OC) as in-situ sites.

A scale for length was adhered to the outer wall of each sediment core. Then, one

ferrihydrite and one chelex-100 DGT pistons back-to-back, were fixed to the end of a

plastic ruler. With the aid of the ruler and the scale on the outer wall of sediment core,

these two DGT pistons were inserted into sediment layer until the lower edge of each

DGT piston was 4.0 cm away from SWI. The ruler is put in the sediment layer as the

initial status. After 24h, the ruler and two pistons were pull out from sediment for

subsequent measurement. During DGT test, Eh, pH and T in surface sediment were

measured by Orion 4-star meter (Thermo, USA) for five times at 0, 6, 12, 18 and 24 h.

The incubation for sediment cores and the deployment method for DGT pistons

ensure the minimum disturbance of sediment. It has been verified by “the relative

standard deviations (RSDs) for Eh, pH or T (n=8) for the in-situ sites and the

incubators were less than 8.8%, 7.1% or 6.2%”. Eh, pH and T in each sediment core

were measured five times during DGT deployment time (24 h); while, for the in-situ

sites, they were determined three times. It reflected sediment microenvironment for

surface sediment in the incubators was similar to the in-situ sites. The redox status in

surface sediment in the incubators standed for that at in-situ sites .to a great extent.

Moreover, the disturbance of sediment core during DGT deployment was kept to

25

minimum.

(2)

DGT-concentration and flux were calculated according to the standard method

and theory (Zhang et al., 2002; User’guide to DGT technique, 2003). The mass of

solute (M) accumulated on the binding gel can be calculated from the concentration of

solute in the elution solution (Ce) using SM Eq. (1):

M= Ce(Vgel+Vacid)/fe SM Eq. (1)

Vgel is the volume of the gel strip, Vacid is the acid for elution and fe is the elution

factor (1.0 for P and 0.80 for Fe).

The fluxes (F) induced by DGT can be calculated using SM Eq. (2):

F=M/(tA) SM Eq. (2)

Where t is deployment time (in second) and A is the area of the gel strip (in cm2).

The concentration of solute measured by DGT (CDGT) can be calculated using SM

Eq. (3):

CDGT=F g/D SM △ Eq. (3)

g is the thickness of the diffusive gel plus the thickness of the filter membrane,△

and D is the diffusion coefficient of solute in the gel (5.42 or 5.47 ×10-6 cm-2 s-1 for P

or Fe, respectively) (T=21 ). ℃

26

SM B The introduction to DIFS parameters.

The parameters needed to run DIFS are passed to the program using an input file.

The parameters in input file for DIFS software including: r, Tc, Kd, Pc, D, , Co, T, g,

times, domsize, rtol and atol and the description of them were indicated in Table S9.

Two of the three parameters kd, Tc and r are determined as inputs, and DIFS calculates

the other parameter. Distributions of porewater/sediment-solid concentrations through

the DGT-sediment system are calculated for any chosen time. Two of the three

parameters Kd, Tc and r are determined as inputs, and DIFS calculates the other

parameter. Distributions of porewater/sediment-solid concentrations through the

DGT-sediment system are calculated for any chosen time. DIFS runs in one of two

modes, simulation or parameter estimation, determined by the format of the input file.

DIFS runs in the former, if the colon in the 1st (‘r’) parameter line is followed by a ‘?’.

Then DIFS calculates the response based on the parameters given. If a ‘?’ follows the

colon in either the 2nd or 3rd parameter lines, then DIFS runs in parameter estimation

mode. DIFS varies Tc or kd respectively such that the difference between the modelled

R and the experimental R given in the input file is minimised. Four figures are

displayed: plotting dissolved and sorbed concentrations against distance and time, and

r values and DGT accumulated mass against time. The text output file contains all the

information to reproduce any of the plots, and can be opened with any text editor or

word processor.

The input file (Table S2) contains all the information needed by the software. r,

Kd, Pc, D, and C0, which are measured according to the method introduced in Sect.

“2.4 DGT calculation and DIFS simulation” and SM C. T is 24 h for DGT deployment

and g is diffusion layer thickness of 0.92 mm; Times, domsize, rtol and atol are

defaults as 40, 0.01, 10-3 and 10-6.

27

Input files can be generated most easily by modifying the sample file included

(example.dat) using any text editor or word processor (e.g. WordPad or Word). When

modified, it can be saved with a different filename (but remember to use the .dat

extension). If using a word processor, ensure the file is saved as ‘text only’ rather

than in the default document style.

The text output file contains all the information to reproduce any of the plots, and

can be opened with any text editor or word processor. After 24 hours deployment,

DIFS outputs parameters and files, which include: Time, r, Conc (Dissolved

Concentration and Sorbed Concentration), Mass, Flux, Av. Flux. Moreover, DIFS

curves for r, Dissolved Concentration, Sorbed Concentration and Mass vs. time or the

distance from DGT surface can also be output.

28

SM C (1) The calculation methods for DIFS parameters (Ds, k1,k-1, Dspt rate, Xsol,

rmax and Trmax); (2) The kd distribution in each lake region, the distribution

of“external P-loading” in Lake Dianchi, and the effect of OM on P release.

(1)

The depletion extent of Csolu at DGT/sediment interface can be reflected by R,

which can be classified into three cases, including (a) Fully sustained (R>0.95); (b)

Diffusion only (R<0.10); or (c) Partially sustained (0.10<R<0.95). TC (the response

time) is the characteristic time for the perturbed system to attain 63% of the

equilibrium state. The calculation method for kd and TC is indicated in SM Eq. s (4~5):

kd= C s

C0=

k1

PC× K−1 SM Eq. (4)

TC = 1

k1+k−1 SM Eq. (5)

Where, kd (cm3 g-1) is the distribution ratio; Cs (nmol g-1) is the concentration of

labile P adsorbed on solid phase; C0 (nmol ml-1) is the initial porewater concentration;

TC is the response time (s); k1 is the sorption constant (s-1); k-1 is the desorption

constant (s-1).

k1 (sorption rate constant, d-1) and k-1(desorption rate constant, d-1) are calculated

according to SM Eq. s (6~7).

k-1=1

Tc×(1+kd× Pc) SM Eq. (6)

k1= kd×Pc×k-1 SM Eq. (7)

where, kd is the distribution coefficient between solid and solution phase (cm3 g-

1); Pc is ratio between dry weight and volume of soil solution (g cm-3).

Effective diffusion coefficient in the sediment (Ds) is calculated in SM Eq. (8):

29

Ds=Do

1−2 ln s SM Eq. (8)

Where s is the sediment porosity, D0 is the diffusion coefficients of labile

elements in porewater (21 )℃ .

The desorption rate constant (Dspt rate) (nmol ml-1 d-1) can be calculated using

SM Eq. (9) according to the modified method proposed by Menezes-Blackburn, et al.

(2016).

Dspt rate= (the labile P pool size)×Pc×k-1 SM Eq. (9)

where, NH4Cl-P+BD-P or NH4Cl-P (nmol g-1) is the contents of loosely sorbed

P and iron associated P (anoxic site) or loosely sorbed P (oxic site) in solid phase; Pc

(g cm-3) is particle concentration; k-1 (d-1) is desorption parameter.

The distance from the DGT device to which the sediment solution (Xsol) is

depleted after 24 h are also estimated by DIFS derived data. The limit to depletion is

arbitrarily set on reduction of at least 5% of solution concentration (Xsol) based on the

resolution of the outcome data from the DIFS model, as a standard limit that could be

used to compare all the studied sediments. The method for Xsol is based on the method

by Menezes-Blackburn, et al. (2016). According to the method by Menezes-

Blackburn, et al. (2016), the dependency of the output r values on time is used to

calculate the maximum r (rmax) and the time at which rmax was reached (T(rmax)).

(2)

The average kd was in the sequence of Caohai(I)>south(VI)>middle-

north(II)>west(V)>east(III)>middle-south(IV). The labile P pool sizes in sediments

were corresponded to municipal effluent in Caohai (I) and middle-north (II),

agriculture non-point effluent with the moderate intensity and phosphate ore mining in

south (VI) and the relative light agriculture non-point effluent in the other regions 30

(Fig. S1-2). The average kd values for all sites in Caohai(I), south(VI) and middle-

north(II) with NH4Cl-P+BD-P pool in sediment solid were distinctly larger than the

other regions (III, IV and V) with NH4Cl-P pool. TOC range of 178～295 mg kg-1

with average value (240.7 mg kg-1) at twenty sites with NH4Cl-P+BD-P pool in

sediment solid was distinctly larger than 167～254 mg kg-1 with average value of

210.5 mg kg-1 at six sediment sites with NH4Cl-P pool. The oxidation of OM is

normally accompanied by the reduction of electron acceptors such as O2, NO3-,

Mn( IV), Fe( III), and SO42- (Tessier, 1992). OM can increase P solubility by its

competition with P for sorption sites in Fe(OH)3 (Bulleid, 1984; Easterwood and

Sartain, 1990). So, the more abundant OM also contributed to the large FDGT (P) in

anoxic sites.

SM D The classification method for five ranks of P release risk 31

The P release risk is classified to five ranks according to the distribution

characteristics of 100 SPRRI indexes in Lake Dianchi (Fig. S3-2). SPRRI values are

calculated by LAP/TP, r×lg(Dspt rate), BD(Fe)/Al[NaOH25] in 100 sediment sites.

The SPRRI data range accords to five release risk ranks of light, moderate,

relative high, high or very high release risk. Based on the data base (n=100) of labile P

pool size, kinetic P exchange or the effect of Al in references (Chinese Research

Academy of Environmental Sciences, 2014; Wu et al., 2015, 2017), each data group

for the sub-indexes of (1) LAP/TP, (2) r×lg(Dspt rate) and (3) BD(Fe)/Al[NaOH25] is

calculated. Then, all SPRRI data are classified to five data sets according to the

sequence from low to large value; the number of each data set accords with 8%, 24%,

36%, 24% or 8% of the total number of SPRRI indexes (n=100).

Gaussian distribution curve for SPRRI indexes (n=100) is indicated in Fig. S3-2.

The SPRRI indexes for 100 sampling sites in Lake Dianchi are listed in Table S3. The

eighth, thirty-second, sixty-eighth and ninety-second values from low to high in all

SPRRI values (n=100), are checked out and these four data are rounded off to the

nearest whole number. These boundary SPRRI indexes are the boundary values for

five release risk ranks, which are indicated as SPRRI-5, SPRRI-15, SPRRI-30 and

SPRRI-45. The five ranks are 0～5 (light), moderate (5～15), relative high (15～30),

high(30～45) and very high (>45) (Table 1-1).

SM E The detailed inform for the character of SPRRI and each sub-index at 26 sites32

For example, (1) SPRRI of “relative high” at site 11 was corresponded to

lg(1000×LAP/TP) (1.47) and BD(Fe)/Al[NaOH25] (0.55) lower and larger than the

average values for all sites (1.53 and 0.42), respectively; it led to the high SPRRI of

15.58 at site 11; SPRRI of “moderate” at site 22 was corresponded with

lg(1000×LAP/TP) (1.84) and r×lg(Dspt rate) (1.29 [lg (nmol cm-3 d-1)]) higher and

lower than the average values for all sites (1.53 and 1.94 [lg (nmol cm -3 d-1)]),

respectively; the low kinetic exchange in sediment led to “moderate” P release risk at

site 22; (2) SPRRI of “moderate” at site 14 was corresponded with r×lg(Dspt rate)

(2.69 [lg (nmol cm-3 d-1)]) larger than the average value for all sites; the “moderate”

risk at this site was due to lg(1000×LAP/TP) (1.38) and BD(Fe)/Al[NaOH25] (0.28)

lower than the average sub-indexes for all sites; r×lg(Dspt rate) (1.76 [lg (nmol cm -3 d-

1)]) at site 23 with “relative high” risk was lower than the average sub-index for all

sites; it was due to the effect of high BD(Fe)/Al[NaOH25] (0.56) on P release risk at

this site; (3) BD(Fe)/Al[NaOH25] is the reciprocal of Al[NaOH25]/BD(Fe) for the

effect of Al-P on P release (Kopáček et al., 2005; Norton et al., 2008). The sequence

of the average BD(Fe)/Al[NaOH25] for five SPRRI risk grades in Lake Dianchi was

0.68(“very high”)>0.48(“relative

high”)>0.47(“high”)>0.40(“moderate”)>0.28(“light”); the average

BD(Fe)/Al[NaOH25] for “relative high” was slightly larger than that of “high” risk;

moreover, BD(Fe)/Al[NaOH25] (0.38) for “relative high” at site 3 was lower than

sites (11, 23 and 25) with the same SPRRI grade (Table 1-2); it was mainly due to

r×lg(Dspt rate) (2.86 [lg (nmol cm-3 d-1)]) at site 3 higher than that of sites (11, 23 and

25) and the average value for all sites; on the contrary, the very high

BD(Fe)/Al[NaOH25] of 0.51 at site 12 accorded with “moderate” risk, which was due

33

to r×lg(Dspt rate) (1.24 [lg (nmol cm-3 d-1)]) lower than the average value for all sites.

The sequences of SPRRI and lg(1000×LAP/TP) in six regions were North(1.82)

> South(1.81)>Middle-North(1.60)>Middle-South(1.40)>East(1.30)>West(1.25) and

South(28.37)>North(25.87)> Middle-North(12.94)>East(10.72)>Middle-South(7.72)>

West(4.20); The sequences of r×lg(Dspt rate) and BD(Fe)/Al[NaOH25] in six regions

were Caohai(3.35)>South(2.51)>Middle-South(1.70)>Middle-North(1.61)>

East(1.42)> West(1.01) and South(0.58)> Middle-

North(0.43)>Caohai(0.41)>East(0.38)>Middle-South(0.34)>West(0.32).

Reference:

34

Gibbs, M., Zkundakci, D., 2011. Effects of a modified zeolite on P and N processes and fluxes

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Knight, R.L., Gub, B., Clarke, R.A., Newman, J.M., 2003. Long-term phosphorus removal in

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Shand, C., Lunsdon, D., Blackwell, M., Wearing, C., Cooper, P., Wendler, R., Brown, L.,

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