Umnol. Oceanagr., 23(4), 1978,821-825
© 1978, by the American Society of Limnology and Oceanography, Inc.
Relationship of rainfall and lake groundwater seepage1
Abstract—Correlations were found be
tween mean daily rainfall and groundwater in
flow rate and between the rate of groundwater
inflow and N and P inflow to a senescent lake
during summer. A simple method of collecting
and measuring groundwater inflow was repro-
1 This work was supported by the North Dakota
Water Resources Research Institute, with funds
provided by the U.S. Department of Interior, Office
of Water Resources Research, as authorized under
the Water Resources Research Act of 1964, Public
Law 88-379, the State Water Commission, and the
Oak Creek Water Management Board.
ducible at very low inflow rates. The water
collected by this method was similar in P con
centration to groundwater but higher in N
concentration.
The recharge of groundwater by pre
cipitation and the discharge of groundwater to surface waters are integral parts
of the hydrologic cycle (Davis and
DeWiest 1966). Precipitation (Schindler
et al. 1976; Peters 1977) and groundwater
seepage (Born et al. 1974; Lee 1977) con
tribute substantial amounts of water and
822
Notes
nutrients to the surface waters through
which they cycle. Precipitation and
groundwater loading are probably not in
dependent since rainfall recharges sub
surface waters which influences the rate
of groundwater seepage. To be able to
predict the water and nutrient regimes of
lakes we must measure all sources of in
put or be able to quantify their covaria
tion. We have tried to sample groundwater inflow directly, using a simple
method, and to relate it to rainfall con
ditions in the watershed. The data were
collected at Lake Metigoshe, a senescent
lake in the Turtle Mountain area of North
Dakota and Manitoba. Groundwater seep
age is thought to contribute only about
2% of the water budget of this lake
(Downing 1975; S. R. Moran unpub
lished) but soils are widely variable,
which makes whole-lake extrapolation
unrealistic.
We thank M. Vennewitz for aid in the
field and laboratory, S. R. Moran and R.
H. Peters for helpful discussion, and D.
R. Lee for criticism of the manuscript.
Groundwater was collected with the
seepage meters described and evaluated
by Lee (1977), steel cylinders which cov
er 0.25 m2 of lake bottom and collect in
flowing groundwater in a heavy (0.05 mm
thick) 4-liter translucent plastic bag. The
bags used were heavier than those used
by Lee. After the samplers were installed
a few samples of collected water (5-10
liters) were discarded without analysis to
allow flushing of trapped lake water. Af
ter this, mean flow rates were calculated
from the volume collected and chemical
analyses were done on the collected
water. Bags were removed after 500 ml
or more was collected; this sometimes
took >1 week.
Groundwater inflow was monitored
with one seepage meter at each of four
sites in 1973. In 1974 we installed six
samplers at a site with a sand bottom (site
A) and six at a site with a clay, silt, and
organic sediment bottom (site B), pairs at
1-, 2-, and 3-m depth (about 4, 8, and 12
m from shore). Samples were taken irreg
ularly in 1973 and continuously in 1974
from early June to mid-August. Some
samples were also taken in fall 1973 and
1974.
A lakeside shallow well between sites
A and B was also sampled throughout our
study so that we could compare the
chemical composition with that of the
water collected in seepage meters. The
well was about 0.2 m from the water's
edge at a depth of 2.5 m and was sampled
when seepage was sampled. The well
water level was always higher than lake
level.
NO2-N and NO3-N were measured by
the cadmium reduction method (Am.
Public Health Assoc. 1971), NHa-N by
the phenolhypochlorite method of Solorzano (1969), and orthophosphate by the
method of Murphy and Riley (1962).
These assays were checked regularly
against known standards. Alkalinity was
measured with 0.02 N H2SO4 titration
(Am. Public Health Assoc. 1971), conduc
tivity with a Beckman RB3 Solu-bridge
meter. Chloride was determined by mer
curic nitrate titration (Am. Public Health
Assoc. 1971).
Mean daily rainfall measurements dur
ing groundwater sampling periods were
obtained from gauges at Bottineau and
San Haven, North Dakota (reported in
annual summaries for 1973 and 1974 by
NOAA).
In collecting our samples, we noticed
that seepage meters collected more
groundwater during rainy periods than
during dry periods of the summer. A sig
nificant (P < 0.001) relationship was
found between mean groundwater inflow
rates and mean daily rainfall from late
June to November (Fig. 1A). This corre
lation was evident despite the large vari
ation expected in these data because
rainfall measurements were taken at least
22 km from the lake, and soils in the area
are primarily stony-sandy clay, clay, or
clayey silt and are low and heteroge
neous in permeability (S. R. Moran pers.
comm.). The relationship was not evident
during early June when groundwater in
flow rates were high and rainfall was low
(Fig. 1A), perhaps because snow meltwater caused elevation of the water table.
Absolute water table height was not mea-
Notes
823
sured but the water levels in observation
wells were high in spring, lowering in
mid-June to relatively stable levels (±2
cm), which were maintained throughout
summer and fall. During this later period
the water table was presumably highest
during periods of high mean daily
rainfall.
We found no significant variation with
depth in either groimdwater flow rate or
N and P concentration. Lee (1977) found
that flow rates decreased exponentially
with distance from shore over a 160-m
transect. In our 12-m transect to 3-m
depth, variation between replicate seep
age meters was always as great as varia
tion among depths sampled. The mean
coefficient of variation over sampling
dates, with flow rates from all six sam
plers at a site treated as samples of the
same population, was 35.6. The mean
flow rate (±SE) at site A (19.1 ± 2.5
ml-in"2-!!"1, n = 44) was similar to that at
site B (16.8 ± 2.2 ml-m^-h"1, n = 37).
The seepage meter gave results repro
ducible among replicate samplers at flow
rates 2 orders of magnitude lower than
those found by Lee (1977) at Lake Sallie.
There was no correlation evident be
tween rainfall rate or groimdwater inflow
rate and NO2, NO3, NH3, or PO4 concen
trations; thus there appeared to be no di
lution or concentration of inorganic N
and P in groimdwater entering the lake
due to high or low rainfall. Nutrient con
centrations have time to equilibrate in
groimdwater. At the overall mean inflowrate of 18 ml-m"2-h"' and assumed po
rosity of 0.3 (S. R. Moran pers. comm.),
the average interstitial velocity was 6 x
Fig. 1.
GROUNDWATER INFLOW, 10 ml m*2 h"1
A—Relationship of mean groimdwater
inflow to mean rainfall over sampling period, all
data 1973 and 1974 (Y = 2.83X + 0.536, r = 0.771).
x—Sample taken in early June when water table
was high from spring melt (not included in regres
sion). B—Relationship of groundwater PO4-P inflow
rate to groundwater inflow rate in 1974 (Y = 0.55X
- 0.063, r = 0.788), means of sampler pairs. C—Re
lationship of groundwater NH3-N inflow rate to
groundwater inflow rate 1974 (Y = 1.9LX + 1.717,
r = 0.404), means of sampler pairs. O—Data from
site A (sandy bottom).
GROUNDWATER INFIDW, 10 ml m"2 h*1
824
Notes
Table 1. Chemical characterization (mean ± SE) of water from seepage meters, groundwater well, and
lake at Lake Metigoshe during 1974. Number of samples in parentheses.
Sample type
Seepage, site A
Seepage, site B
Lakeside well
Lake water
PO4-P
(pg-liter1)
55
46
60
24
±
±
±
+
4
5
8
3
(35)
(37)
(6)
(51)
NHrN»
(fig-liter"1)
5,250
1,540
480
176
±
±
±
±
744 (34)
615(37)
135 (6)
33 (51)
Total
alkalinity
(mS-liter"1)
395
332
358
217
±
±
±
±
Specific
conductivity f
Chloride
(mg-liter"1;
673 ± 23 (27)
4.63 ± 0.42 (31)
2.88 ± 0.51 (32)
2.00 ± 0.41 (6)
<0.5|
(ftmho-cm"1)
16 (22)
26 (20)
22 (6)
600 ±36 (28)
720 ± 39 (6)
2
497 ± 9
(14)
(51)
* NO,- and NO3-N were nearly always undetectable.
f At 25eC.
j Usually undetectable.
10 5 m-h '. Rainwater entering the
groundwater 10 m from shore would take
19 years to reach the lake. The quick re
sponse of groundwater inflow to rainfall
reflects a raising of the water table which
pushes water out the other end of the hy
draulic gradient into the lake.
The total alkalinity, conductivity, and
PO4-P concentration in seepage meters
were the same as that collected from our
lakeside well and significantly different
from that of lake water (Table 1). This
indicates that we were collecting groundwater. The NH3-N concentrations were
significantly greater in the seepage me
ters than in the groundwater. This may
indicate some effects of enclosure of the
sediments and their loss of N.
P and N concentrations in seepage me
ters may be underestimates since only
soluble forms were measured and no at
tempt was made to measure P or N on
seepage bags. We found no change in P
or N concentrations over time in seepage
meters as reported by Lee (1977).
Both the PO4-P input rate and the NHr
N input rate were correlated with the rate
of groundwater inflow when data from
both sites in 1974 were considered (Fig.
IB, C). This relationship would be ex
pected if concentrations do not vary
much. The PO4-P correlation is quite
close overall (r = 0.77), but the NH3-N
correlations show quite a bit of scatter
(r = 0.40). Scatter in these relationships
seems to be due to soil differences, be
cause the P and N input (Fig. IB, C) and
concentrations (Table 1) of inflowing
groundwater at the sandy site tended to
be higher than those at the clayey site.
This may be the result of less adsorption
of P and N onto sand particles than onto
clay.
In spring and early summer, groundwater inflow rates were high, probably as
the result of snow meltwater. As the win
ter accumulation dissipated, increases in
the flow rate of groundwater, and hence
increases in the loading rate of N and P
into Lake Metigoshe, were correlated
with high rainfall. Although more specif
ic study is needed, knowledge of this in
teraction may lead to better prediction of
lake nutrient loading.
John A. Downing
Department of Biology
McGill University
1205 McGregor Street
Montreal, Quebec H3A 1B1
JohnJ. Peterka
Department of Zoology
North Dakota State University
Fargo 58102
References
American Public Health Association.
1971.
Standard methods for the examination of water
and wastewater, 13th ed.
Born, S. M., S. A. Smith, and D. A. Stephenson. 1974. The hydrogeologic regime of gla
cial terrain lakes, with management and plan
ning applications. Upper Great Lakes Regional
Comm. Madison, Wis. 73 p.
Davis, S. N., and R. J. DeWiest. 1966. Hydrogeology. Wiley.
Downing, J. A. 1975. Hydrophytes, plankton, and
water chemistry related to recreational devel
opment at Lake Metigoshe, North Dakota. M.S.
thesis, North Dakota State Univ., Fargo.
Lee, D. R. 1977. A device for measuring seepage
flux in lakes and estuaries. Limnol. Oceanogr.
22: 140-147.
Notes
Murphy, J., and J. P. Riley. 1962. A modified
single solution method for the determination of
phosphate in natural waters. Anal. Chim. Acta
27: 31-36.
PETERS, R. H. 1977. Availability of atmospheric
orthophosphate. J. Fish. Res. Bd. Can. 34: 918924.
Schindler, D. W., R. W. Newbury, K. G. Beaty,
and P. Campbell. 1976. Natural water and
825
chemical budgets for a small precambrian lake
basin in central Canada. J. Fish. Res. Bd.
Can. 33: 2526-2543.
Sol6rzano, L. 1969. The determination of ammonia in natural waters by the phenolhypochlorite method. Limnol. Oceanogr. 14:799-801.
Submitted: 30 June 1976
Accepted: 3 November 1977
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