1
2
3
Supplementary Table (S1): Table with all chemical data
Electronic appendix, See separate pdf file.
4
Supplementary Table (S2). Saturation indices calculated with Phreeqc (Parkhurst and Appelo, 1999) for selected minerals in selected
5
samples.
Mineral phase
P9S-1
P9S-2
EMS1
EMS2
EMS3
EMS1-1
EMS1-2
EMS1-3
P5S-1
P5S-2
P5S-5
Groundwater
gw
gw
sw
sw
sw
gw
gw
gw
gw
gw
gw
(gw)/surface
gravel
gravel
gravel
water (sw)
pit lake
pit
pit
lake
lake
Depth [masl]
1.1
0.4
-6.0
-12.0
-0.10
-6.0
-9.5
18.5
-1.6
-5.1
-17.1
Anhydrite
CaSO4
-2.24
-2.23
-2.79
-2.78
-2.72
-1.83
-2.26
-2.36
-2.18
-2.05
-2.05
Barite
BaSO4
0.39
0.51
1.04
1.05
1.10
0.24
0.15
0.09
0.36
0.69
0.60
Calcite
CaCO3
1.91
1.71
1.15
1.17
1.23
0.89
0.75
0.68
0.62
0.48
0.52
6
Dolomite
CaMg(CO3)2
3.51
3.13
3.06
3.09
3.23
1.92
2.12
1.95
1.62
1.61
1.75
Gypsum
CaSO4:2H2O
-1.78
-1.78
-2.27
-2.26
-2.21
-1.39
-1.82
-1.93
-1.73
-1.61
-1.62
Halite
NaCl
-6.51
-6.59
-3.87
-3.88
-5.86
-5.37
-3.69
-3.70
-3.93
-3.57
-3.31
Supplementary Information (S3)
The evaporative end member of an area under local climate conditions is (equation 7 in Skrzypek et al.
2015):
ℎ𝜕 +𝜀
𝐴
𝜕 ∗ = ℎ−𝜀.10
−3
(1)
is the limiting isotopic composition under local climatological conditions (Gat and Levy,
1978; Gat, 1981) in which h is the atmospheric relative humidity (ranging from 0 to 1)
normalized to the saturation vapor pressure at the temperature of the air-water interface, δA is the
isotopic composition of ambient moisture (precipitation), and
𝜀 = 𝜀 ∗ + 𝜀𝐾
(2)
where ε is the total isotopic separation factor including both equilibrium ε* and kinetic εK
components. The equilibrium separations can be evaluated using the empirical equations
determined experimentally by Horita and Wesolowski (1994) where ε* is a function of T.
Kinetic enrichment factors εK are dependent on both the boundary layer conditions and the
humidity deficit evaluated according to
𝜀𝐾 = 𝐶𝐾 (1 − ℎ)
(3)
where constant, experimentally-determined CK values of 14.2‰ for oxygen and 12.5‰ for
hydrogen are used as representative of typical lake evaporation conditions (Gonfiantini, 1986).
Supplementary Table (S4). Input values and results of the calculation for Evaporation over
inflow rate calculated with the Microsoft Excel spreadsheet published by Skrzypek et al. 2015.
The ambient air moisture A is based on Rain only. The values for Pool water initial values are
taken from sample gravel pit lake sample EMS1 that falls on the estuarine mixing line and is
assumed to be representative of the inflowing groundwater. The resulting E/I ratios for several
combinations of T and h are listed in table 2 in the main text. Note that also parameters 6 through
15 change with T and H but are not all reported here for every T and H combination listed in
Table 2.
Ambient air moisture A based on
Par
ameter
Symbol
Description
Rain only
no
1
T
h
Rain
13.70
13.70
0.77
0.77
-42.40
-6.75
-45.77
-7.03
Relative humidity [fraction],
annual average
3
18O
Temperature [°C], annual
average.
2
2H
Rainfall, mean between
sampling from Longinelli and
Selmo (2003), Comacchio
weather station, along coast.
4
P
Pool water initial value [‰]
or inflow, sampling #1 (Nr. EMS1)
5
L
Pool water final value [‰],
sampling #2 (average of sample
Nr. EMS2 and EMS3)
6
LEL
A
-3.83
-
-
-123.13
-16.94
2.88
3.27
92.07
10.36
87.18
13.52
12.50
14.20
1.0921
1.0104
Slope of Local Evaporation
Line Unknown, calculated
7
-29.71
Air ambient moisture [‰],
Unknown calculated based on
rainfall.
8

Kinetic isotope fractionation
factor [‰] (h dependent)
9
+
Equilibrium isotope
fractionation factor [‰] (T
dependent)
10

Total isotope fractionation
[‰]
11
Ck
The kinetic fractionation
constant [‰]
12

Equilibrium isotope
fractionation factor [‰] (T
dependent)
13

Limiting isotopic composition
[‰]
14
m
E/I
0.64
2.93
3.24
0.29
0.21
Calculation factor (h)/(1-h+k)
15
-11.17
Result for steady-state
model: Evaporation over Inflow
ratio
Supplementary Information (S5): Waterbalance and evaporation concentration.
The annual water balance equation for a gravel pit lake with a constant water level (maintained
by the drainage system) can be described by:
VP + VGW-in = VE + Vlake-out
(1)
where Vp [m3/year] is the volume of precipitation added to the lake in a year, VGW-in is the
volume of groundwater flowing into the lake each year, VE is the volume of water evaporating
from the lake surface in a year and Vlake-out is the volume of lake water flowing out of the lake
into the aquifer downgradient of the lake. With this we can calculate the amount of groundwater
flowing into the lake, the only unknown in the equation since we have an estimate for the amount
of precipitation, evaporation and drainage out of the lake:
VGW-in = VE + Vlake-out - VP
(2)
The initial Cl mass of in the lake is:
M lake at t=0 = Vlake × C lake_initial
(3)
where Vlake is the volume of the lake and C lake_initial is the initial concentration of Cl in the
lake. One year later, the mass of Cl in the lake equals the initial Cl mass (M lake at t=0 ) plus the
added Cl mass coming in with precipitation and inflowing groundwater, minus the salt mass that
disappeared with the outflowing lake water:
Mt=i+1 = Mlake at t=0 + (VP × CP) + (VGW-in × CGW-in) – (Vlake-out × Clake-out )
(4)
The subscript “i” is a counter for the number of years since the start of excavation of the lake
and is an integer zero or larger. CP is the concentration of Cl in precipitation, CGW-in is the
concentration of Cl in in-flowing groundwater, and Clake-out is the concentration of Cl in the water
leaving the lake downstream.
The Cl concentration in the lake one year later is:
C t=i +1 = M t=i+1 / Vlake
(5)
Here we imply that the water disappearing from the gravel pit lake by evaporation or by
outflow towards the pumping station is replaced by brackish/saline groundwater. We also
assume that CP is 10 mg L-1 (Stuyfzand 1993).
The mass balance calculations so far do not take into account the fact that the material
excavated from the gravel pits is also replaced by brackish/saline groundwater. The mass of salt
added to the lake due to replacement of mined gravel and water by saline groundwater is:
Mmining = VL × f × CGW-in
(6)
where Mmining is the added salt mass due to replacement of mined gravel and water with
groundwater, VL is the volume of the lake, f is the fraction of the lake volume that is taken out by
mining water and gravel together. Fraction f is 0.7 is the extreme case where we assume that
only the gravel is mined and all of the original porosity is replace by brackish groundwater (no
water mining). f is 1.0 is the extreme case where all the original gravel and all original (pore)
water of the gravel pit is replaced by groundwater. In reality f will fall between the two
extremes.
Supplementary Figure (S6)
Photographs of gravel pit lake Standiano.