8092

• UCREFRP Catalog Number: 8092
• Author: U.S. Department of the Interior.
• Title: Proceedings of the Symposium on Restoration Planning for the Rivers of the Mississippi River Ecosystem.
• USFW Year: 1993.
• USFW - Doc Type: Washington, D.C.
• Copyright Material: NO

mean discharge than did the Kettle, Snake, and
Apple rivers. Because the Namekagon and upper
St. Croix rivers drain catchments with highly per-
meable stratified sand and gravel soils, spate
events were minimized. During periods of low pre-
cipitation, streamflow in these reaches was stabi-
lized by high groundwater contributions (Table 3).
These two factors attenuated annual differences in
precipitation and resulted in more stable annual
mean streamflow.
Using the methods of Hirsch and Slack (1984),
we canied out a time-trend analysis on each sta-
tion's data set to determine if a trend in discharge
existed. The analyses revealed a statistically sig-
nificant increasing trend in discharge at the St.
Croix River stations near Danbury, Wisconsin, and
at St. Croix Falls (P < 0.10). We are unable to
account for this trend. An increase in annual pre-
cipitation would be the most likely cause of the
trend, but a similar trend analysis of long-term
precipitation records from the Spooner Experimen-

DoNFAGOANDJAYHATCH 29

tal Farm in Spooner, Wisconsin, did not reveal a
statistically significant increase in precipitation.
The amount of vegetative land-cover has changed
little in the last 30 years, and wetland losses have
been minimal.

Land-cover

Presettlement land-cover within the St. Croix
River basin included several vegetation types
within three major North American biomes: north-
ern coniferous forest, eastern deciduous forest, and
tallgrass prairie (Kiichler 1964; Wendt and Coffin
1988). The northern two-thirds of the upper basin
(including the headwaters, Namekagon, Yellow,
Clam, Pine County tributaries, Kettle, and much of
the Snake subbasins) was dominated by a mosaic
of Great Lakes pine forest (white pine, red pine,
paper birch, aspen), boreal hardwood-conifer forest
(aspen, birch, balsam fIr, white spruce, white ce-
dar), and a variety of peatlands (e.g., black spruce-

18
16
14
12
10
8
6
4
2
o
1928

I NFAR TDcr-n WI
AVERAGE ANNUAL MEAN DISCHARGE
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I I I I I I I

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z
o
o
w
II)
a:
w
n.
II)
a:
w
Iii 6D ST. CPlOIX RIVER NEAR DANBURY WI.
:E
250
10
=>
o 40
:;
W 3D
C)
~ 20
:I:
~ 10
C
Z 0
< 1915
w
:E
...J5O
<
=>
Z 40
Z
<

1938

1948

AVERAGE ANNUAL MEAN DISCHARGE

1958

1968

1988

1978

1925

1935

1945

ONE MN.

1955

1985

1965

1975

3D

AVERAGE ANNUAL MEAN DISCHARGE

/

20

10

o

1968

1978

1908

Fig. 2. Average mean discharge and annual mean discharge for the period of record at the Namekagon, St. Croix,
and Kettle rivers (Graczyk 1986).