Microhabitat Variability in Coho Overwintering Habitats
on the Anchor River, AK
prepared by Michael Callahan, Phd Candidate
University of South Florida
For
The Kachemak Bay Research Reserve
95 Sterling Highway, Suite 2
Homer, AK 99603
Contact: Coowe Walker
coowe.walker@alaska.gov
907.226.4651
Three habitats were chosen from the larger set of 25 coho overwintering sites. Habitats
were selected to span a range of groundwater inputs and were selected based on presence
of juvenile coho salmon and accessibility. The three habitats differed in terms of size,
bathymetry, and inferred groundwater contribution, with groundwater contribution
inferred from mass-balance mixing results. The high groundwater influence site, GW14, is a
small and shallow off-channel or backwater habitat with a length of 40 meters (Figure 1).
GW14 has one deeper pool located approximately at 33 meters downstream. In August
2012, the pool at GW14 had a water depth of approximately 0.7 meters (Figure 2). The
middle groundwater influence site, GW03, is a large off-channel habitat with an
approximate length of 120 meters (Figure 3). GW03 has a large and deep pool located
between 50-80 m downstream. In August 2012, the pool at GW03 had a water depth of
approximately 1.5 meters (Figure 4). GW03 also has a groundwater seep flowing into the
off-channel habitat at approximately 45 meters downstream, discharging to the habitat just
upstream of the large and deep pool. The low groundwater influence site, NG04, is a
relatively small off-channel habitat extending 50 meters and is located in a meander bend of
the Anchor River (Figure 5). Only a small gravel bar separates the off-channel habitat from
the main river. NG04 has a small pool in the middle of the habitat located at 30 meters
downstream. In August 2012, the pool at NG04 had a water depth of approximately 0.85
meters (Figure 6).
High river stages in September 2012 severely modified the off-channel habitat at NG04 and
wiped out the majority of the instrumentation. Therefore, no water quality parameters will
be reported for NG04 in this report. Specific conductivity was elevated at both GW14 (Table
1) and GW03 (Table 2), indicating the influence of groundwater to both of these off-channel
habitats. Mean specific conductivity was 122.6 (±41.7) μS/cm at GW14 and 81.7 (±13.8)
μS/cm at GW03, supporting previous results of high groundwater influence at GW14 and
moderate groundwater influence at GW03. Although groundwater contributed to both
sites, the mechanisms and responses differed. Site GW14 had what appears to be diffuse
groundwater discharge entering throughout the off-channel habitat. Conversely, site GW03
had focused groundwater discharge entering the off-channel habitat from a spring flowing
off a hillslope and into the middle of the habitat.
Surface-water temperatures at GW14 approached freezing (0°C) in winter and were
generally consistent throughout the length of the off-channel habitat (Figure 7). All surfacewater temperatures recorded between 10/22/12 and 03/08/13 were less than 1°C. The
dissolved oxygen concentrations varied considerable during the study period, at numerous
times dipping below 8 mg/L (Figure 8). Surface-water temperatures at GW03 stayed
relatively warm throughout the winter in comparison, with a noticeable increase in
temperature near where the groundwater seep enters the off-channel habitat and the
beginning of the pool (Figure 9). The concentration of dissolved oxygen also remained high
throughout the winter (>8 mg/L) (Figure 10). It appears as if the focused groundwater
discharge at GW03 elevates surface water temperatures during the winter and keeps a
proportion of the off-channel habitat ice free, which allows dissolved oxygen concentrations
to remain high throughout the winter. While GW14 has a high proportion of groundwater,
it lacks an area of focused discharge to elevate water temperatures. Surface-water
temperatures at GW14 will decrease to the point of freezing, which can cut off oxygen
exchange with the atmosphere causing decreases in surface water dissolved oxygen.
Figure 1. Contour plot of ground surface elevation (meters) for site GW14.
Figure 2. Contour plot of August 2012 surface water levels (meters) for site GW14.
Figure 3. Contour plot of ground surface elevation (meters) for site GW03.
Figure 4. Contour plot of August 2012 surface water levels (meters) for site GW03.
Figure 5. Contour plot of ground surface elevation (meters) for site NG04.
Figure 6. Contour plot of August 2012 surface water levels (meters) for site NG04.
Table 1. Water temperature (°C), dissolved oxygen (mg/L), and specific conductivity
(μS/cm) for site GW14.
Temperature (°C)
5m
8/23/12
8.2
8/27/12 10.2
10/17/12
1.5
10/22/12
0.5
10/26/12
0.4
3/8/13
0.1
19m
8.2
1.3
0.8
0.6
0.1
33m
8.4
10.1
1.7
0.8
0.8
0.1
45m
8.8
10.3
1.1
0.7
0.5
0.1
Well 1
9.5
10.6
Well 2
8.7
8.9
Well 3
9.7
9.4
Well 4
9.6
10.2
2.8
2.0
3.5
3.0
Frozen
Frozen
0.8
0.7
33m
5.8
5.4
11.0
8.9
5.7
13.2
45m
7.2
4.8
13.1
7.5
7.8
13.4
Well 1
0.1
0.2
Well 2
0.5
0.5
Well 3
0.5
0.2
Well 4
0.1
0.2
0.3
0.5
0.4
1.3
Frozen
Frozen
0.5
0.5
33m
115
108
139
155
161
50
45m
104
109
188
158
162
49
Well 1
127
113
Well 2
194
131
Well 3
129
113
Well 4
222
203
99
101
57
32
Frozen
Frozen
119
140
DO (mg/L)
8/23/12
8/27/12
10/17/12
10/22/12
10/26/12
3/8/13
5m
7.3
5.8
13.0
7.5
5.5
13.4
SP Cond (μS/cm)
5m
8/23/12 103
8/27/12 109
10/17/12 136
10/22/12 156
10/26/12 161
3/8/13
49
19m
6.5
12.2
6.8
5.6
13.4
19m
105
136
156
159
50
Table 2. Water temperature (°C), dissolved oxygen (mg/L), and specific conductivity
(μS/cm) for site GW03.
Temperature (°C)
20m
8/23/12 8.8
8/27/12 9.0
10/16/12 3.2
10/23/12 1.4
10/26/12 1.2
3/12/13 1.6
42m
7.9
8.1
3.2
2.3
1.8
1.8
60m
7.8
8.0
3.6
2.8
2.4
2.6
77m
8.1
8.0
3.5
2.2
2.3
2.2
100m
8.1
8.0
3.6
1.6
1.9
2.1
120m
8.6
20m
12.3
10.1
15.2
15.2
15.7
9.2
42m
10.5
12.4
14.7
13.8
13.8
10.4
60m
11.5
12.3
13.7
13.6
13.6
8.6
77m
10.7
12.3
13.5
14.5
13.5
10.8
100m
9.4
12.0
13.2
13.0
12.4
10.3
120m
11.8
SP Cond (μS/cm)
20m
8/23/12
77
8/27/12
80
10/16/12
84
10/23/12
99
10/26/12
99
3/12/13
53
42m
76
77
85
99
93
58
60m
76
77
86
97
92
59
77m
76
78
86
98
92
59
100m
74
77
85
101
93
59
120m
78
3.4
1.8
2.2
2.2
Well 1
9.5
9.8
Well 2
7.9
8.6
Well 3
9.2
8.3
Well 4
11.3
11.6
Frozen
Frozen
4.7
4.7
5.4
5.4
4.2
2.8
Well 1
0.1
0.2
Well 2
0.1
0.1
Well 3
6.7
6.1
Well 4
0.2
0.7
Frozen
Frozen
0.4
0.3
0.4
3.3
0.5
0.2
Well 1
98
95
Well 2
266
280
Well 3
67
60
Well 4
121
114
Frozen
Frozen
152
139
92
54
83
76
DO (mg/L)
8/23/12
8/27/12
10/16/12
10/23/12
10/26/12
3/12/13
13.2
14.1
13.3
10.2
85
100
92
58
12
Temperature (°C)
10
8
8/23/12
8/27/12
6
10/17/12
10/22/12
4
10/26/12
3/8/13
2
0
5m
19m
33m
45m
Loca on (m)
Figure 7. GW14 surface water temperature (°C) along the length of the off-channel habitat.
18
16
Dissolved Oxygen (mg/L)
14
12
8/23/12
10
8/27/12
10/17/12
8
10/22/12
6
10/26/12
4
3/8/13
2
0
5m
19m
33m
45m
Loca on (m)
Figure 8. GW14 dissolved oxygen concentration (mg/L) along the length of the off-channel
habitat.
12
Temperature (°C)
10
8
8/23/12
8/27/12
6
10/16/12
10/23/12
4
10/26/12
2
3/12/13
0
20m
42m
60m
77m
100m
120m
Loca on (m)
Figure 9. GW03 surface water temperature (°C) along the length of the off-channel habitat.
18
16
Dissolved Oxygen (mg/L)
14
12
8/23/12
10
8/27/12
10/16/12
8
10/23/12
6
10/26/12
4
3/12/13
2
0
20m
42m
60m
77m
100m
120m
Loca on (m)
Figure 10. GW03 dissolved oxygen concentration (mg/L) along the length of the off-channel
habitat.