2004 Welcome Slough Monitoring Data

Description of Site

Welcome Slough is located on Puget Island in Wahkiakum County in the lower Columbia River estuary in Washington. Welcome Slough is a narrow, canal-like waterbody, closed at one end and opening to the Columbia River at the other. It is tidally influenced. In recent years, an infestation of the state-listed noxious freshwater weed Eurasian watermilfoil (Myriophyllum spicatum) and to a lesser extent native Canadian waterweed (Elodea canadensis) has been impacting navigation, recreation, and aesthetics in the slough. At least 50 recreational boats and 13 commercial fishing vessels are moored in Welcome Slough and their owners reported significant problems in navigating out of the Slough.

Because slough areas in the Columbia are known to be rearing areas for juvenile salmon, the Washington Department of Fish and Wildlife requested that the local citizens monitor water conditions before and after the herbicide treatment. The purpose of monitoring was to document the effect of the 2,4-D application on the dissolved oxygen concentrations in Welcome Slough.

 Treatment

In July 13, 2004, 20 acres of the littoral zone of Welcome Slough were treated with the aquatic herbicide 2,4-D (DMA*4IVM™). This herbicide was applied by a state-licensed applicator using sub-surface injection. A total of 160 gallons was applied with a target water concentration of 2-4 ppm. The application was timed to coincide with neap tides to increase the contact time between the herbicide and plants. A group of citizen volunteers who live on Welcome Slough monitored the Slough for dissolved oxygen (DO), water temperature, and presence of distressed or dead fish for two weeks after the herbicide application. The aquatic plant management company who applied the herbicide developed the monitoring protocol, trained the volunteers in instrument calibration and monitoring techniques, and loaned them the monitoring equipment.

Sampling Protocols

Dissolved Oxygen and Temperature: Four sampling stations were established at equal distances along Welcome Slough from the end of the slough to the mouth. Station 1 was located at the end of the slough furthest from the Columbia River and Station 4 was located at the mouth of the slough closest to the Columbia River. Stations 2 and 3 were approximately equidistance between Stations 1 and 4 (see aerial photograph below).

Dissolved oxygen and temperature were measured at each station on the high tide seven days before treatment and for seven days following treatment. At each station, a water column profile was taken from the surface and at one foot intervals to the bottom. These measurements were taken with a YSI® digital DO/Temperature meter. The results are seen in tables below.

2,4-D Residue Sampling: Surface water samples for 2,4-D were taken by volunteers at Station 1 and Station 4, 24 hours and 5 days after treatment. The samples were stored on ice and delivered to an Ecology-accredited laboratory for analysis.

Fish: In addition to taking water measurements, the volunteers patrolled the waters of Welcome Slough by boat looking for dead or distressed fish. They were instructed to record the location of any dead or distressed fish, the number of fish observed, and the species (if known). In addition, they were asked to determine if the mortality was recent, to collect a sample, and to notify the applicator and the County.

Results

 2,4-D Residues: The drinking water standard is 0.070 mg/L. At five days after treatment, the residues are well below this standard

Station 24 hours 5 days
1 0.120 mg/L 0.001 mg/L
4 1.300 mg/L 0.054 mg/L

Temperature: Temperatures in Welcome Slough varied little between most sampling stations and the temperatures increased over the 14-day sampling period. This was expected since the weather was hot and sunny over this time period. The temperature in Welcome Slough in July always exceeded the Water Quality Standard for salmon core rearing areas (16 degrees C), even at the mouth of the slough. It is not likely that the herbicide treatment had any impact on water temperatures.

Dissolved oxygen: There appeared to be little impact of the herbicide treatment on dissolved oxygen at the sampling stations. The oxygen levels remained relatively high before and after treatment, although they were generally always below the minimum dissolved oxygen concentration for core salmon rearing (9.5 mg/L) both before and after herbicide treatment.

Fish Observations: There were no distressed or dead fish observed during this two week period in Welcome Slough.

Summary of Dissolved Oxygen and Temperature Data

Welcome Slough

Station 1 (6N) - end of the slough – Dissolved oxygen - ppm

Before Treatment After Treatment
Feet 1 2 3 4 5 6 7 8 9 7/14 10 11 12 13 14
1 9.75

8.95

7.44

7.03

6.62

7.15

9.03

7.39

8.39

8.63

7.91

8.39

6.49

8.04

2 9.42

9.08

7.09

7.05

7.26

7.59

10.1

7.72

7.89

8.53

8.47

8.11

7.01

8.05

3 9.49

9.8

7.4

6.93

7.41

7.28

9.68

8.62

7.41

8.37

9.53

8.1

7.28

8.01

4 9.45

8.31

6.78

7.4

7.54

7.48

9.55

9.71

8.03

8.06

8.74

8.17

6.78

7.68

5 9.25

8.29

6.86

7.35

7.57

7.17

7.88

8.39

8.05

7.89

8.09

8.01

6.52

6.92

6 9.1

7.71

6.55

7.07

6.58

6.38

7.78

 

7.18

7.61

8.08

8.23

 

6.01

7  

8.42

6.86

 

6.07

           

7.37

   
8  

8.16

                       
9  

7.93

                       

Temperature

Before Treatment After Treatment
Feet 1 2 3 4 5 6 7 8 9 7/14 10 11 12 13 14
1

22

22.5

21.5

20.9

21.6

22.2

23.2

23.2

23.5

23.6

25.4

27.3

25.5

23

2

22

22.5

21.4

21.2

21.4

21.9

22.4

22.9

23.4

23.5

25.3

25.4

25.4

22.6

3

22

22.5

21.4

21.2

21.2

21.7

22.2

22.9

23.3

23.3

24.8

24.6

25.3

22.3

4

22

22.3

21.4

21.2

21.2

21.6

22.2

22.9

23.2

23.2

24.5

24.4

25.1

22.2

5

22

22.2

21.4

21.1

21.2

21.4

21.9

22.5

22.2

23

23.9

24.3

25

22.1

6

22

22.2

21.4

21.1

21.1

21.2

21.8

 

22.9

22.9

23.6

24.1

 

22.1

7  

22.2

21.4

 

21.1

           

24

   
8  

22.2

                       
9  

22

                       

Station 2 (100N) – Dissolved oxygen - ppm

Before Treatment After Treatment
Feet 1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 8.95

8.33

7.46

7.67

7.24

7.76

8.61

7.84

7.9

7.6

8.68

7.53

8.3

8.92

2 8.98

8.49

7.19

7.6

5.9

7.32

8.01

7.79

8.21

6.7

8.96

8.06

8.7

9.01

3 8.57

8.15

7.04

7.69

5.88

7.19

7.66

7.75

8.43

7.51

9.52

8.23

8.47

9.22

4 9.13

8.32

7.09

7.74

6.61

7.48

7.69

8.13

8.48

7.38

9.06

8.27

8.56

8.89

5 9.2

8.79

7.03

7.39

6.44

7.51

8.28

8.19

8.39

8.03

8.49

8.16

8.41

9.25

6 9.31

8.41

6.99

7.47

5.93

7.16

8.59

7.64

7.73

6.28

8.55

8.07

7.88

8.23

7  

7.89

6.64

7.21

6.07

7.06

7.97

7.25

7.75

6.81

 

8.07

7.4

9.03

8  

8.41

6.85

6.2

5.38

7.11

7.22

6.65

 

7.55

 

7.17

   
9  

7.64

6.09

6.68

             

7.18

   
   

8.27

                       

 Temperature

Before Treatment After Treatment
Feet 1 2 3 4 5 6 7 8 9 10 11 12 13 14
1

21.1

20.8

20.3

20.1

20.5

21.5

22.6

22.2

22.5

22.5

23.7

23.5

24.1

22.9

2

21.1

20.8

20.3

20.1

20.4

20.9

22.1

22.2

22.2

22.3

23.8

23.3

24.1

22.8

3

21.1

20.8

20.3

20

20.3

20.8

21.8

22.1

21.8

22

23.5

22.9

24.1

22.5

4

21.1

20.8

20.3

20

20.2

20.6

21.2

21.9

21.7

21.8

23.2

22.7

23.8

22.5

5

21.1

20.8

20.3

20

20.1

20.5

21.1

21.5

21.6

21.8

22.9

22.6

23.7

22.5

6

21.1

20.8

20.3

20

20.1

20.4

20.9

21.4

21.5

21.8

22.6

22.6

23.2

22.4

7  

20.8

20.3

20

20.1

20.4

20.8

21.1

21.5

21.7

 

22.5

23.1

22.4

8  

20.8

20.3

19.9

20.1

20.3

20.3

20.8

 

21.7

 

22.4

   
9  

20.8

20.2

19.9

             

22.4

   
   

20.7

                       

Station 3 (186 N) - Dissolved Oxygen – ppm

Before Treatment After Treatment
Feet 1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 9

8.13

7.56

7.6

7.43

7.75

8.08

7.87

7.9

7.52

9.49

7.55

9.05

9.04

2 8.55

8.4

7.88

7.27

7.22

7.68

8.51

8.38

8.21

7.61

9.33

7.58

9.08

8.23

3 8.68

8.03

7.94

7.37

7.54

7.46

8.03

8.65

8.43

8.91

9.11

8.35

8.9

8.69

4 8.29

8.58

8.17

8.17

7.9

6.99

7.95

7.91

8.48

7.47

8.91

8.92

8.78

9.09

5 8.67

8.85

8.55

8.25

7.78

7.8

7.54

8.15

8.39

7.59

8.87

8.65

8.65

8.89

6 8.4

8.16

8.52

7.87

7.41

6.8

8.02

8.65

7.73

7.93

8.67

8.75

8.57

8.69

7 8.58

8.59

8.66

8.25

7.17

7.02

7.51

8.2

7.75

8.82

8.11

8.67

8.54

9.05

8 8.15

8.44

8.5

 

6.43

 

7.42

8.29

 

8.4

 

7.98

   
9 8.24

8.07

             

7.65

       
10 8.54

8.43

                       

Station 3 – Temperature

Before Treatment After Treatment
Feet 1 2 3 4 5 6 7 8 9 10 11 12 13 14
1

20.5

20.8

19.6

19.7

19.8

20.3

21.7

21.3

21.6

22

23

23.1

22.7

22.3

2

20.5

20.8

19.7

19.7

19.8

20.2

21.2

20.9

21.5

21.8

23

22.2

22.7

22.3

3

20.5

20.8

19.7

19.6

19.8

20

20.8

20.8

21.2

21.7

22.6

22.4

22.7

22.3

4

20.5

20.8

19.7

19.6

19.7

19.9

20.6

20.7

21.1

21.6

22.4

22.3

22.7

22.2

5

20.5

20.8

19.7

19.6

19.6

19.8

20.5

20.5

21.1

21.5

22.2

22.2

22.7

22.2

6

20.5

20.8

19.7

19.6

19.6

19.7

20.4

20.5

21

21.4

22.1

22.1

22.7

22.1

7

20.5

20.8

19.7

19.6

19.6

19.7

20.3

20.4

21

21.4

22

22.1

22.7

22.1

8

20.5

20.8

19.7

 

19.5

 

20.3

20.4

21

21.4

 

22

   
9

20.5

20.8

           

21

21.4

       
10

20.5

20.7

                       

 Station 4 (271 N) - mouth of the slough – Dissolved Oxygen - ppm

Before Treatment After Treatment
Feet 1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 9.43

9.03

8.71

8.72

8.5

8.81

9.35

8.92

8.55

9.17

9.3

9.55

8.57

9.04

2

9.44

8.97

8.46

8.66

8.31

8.74

9.34

8.45

8.37

9

9.11

9.44

8.58

8.23

3

9.38

8.91

8.47

8.77

8.37

8.54

9.41

8.45

8.16

8.89

8.92

9.11

7.99

8.69

4

9.37

8.82

8.46

8.37

7.71

8.25

9.68

8.21

7.81

8.72

8.89

9.07

 

9.09

5

9.11

8.42

7.99

 

7.59

   

7.94

 

8.51

 

9.16

 

8.89

6

8.81

8.18

                     

8.69

7

8.34

 

                     

9.05

8

7.87

 

                       

 Station 4 – Temperature

Before Treatment After Treatment
Feet 1 2 3 4 5 6 7 8 9 10 11 12 13 14
1

20.2

19.9

19.8

19.9

19.8

20.2

20.7

20.6

21.3

21.8

22.3

22.4

22.1

22.1

2

20.2

20

19.8

19.9

19.7

20

20.5

20.6

20.9

21.5

22.1

22.1

22

22.1

3

20.2

20

19.8

19.9

19.7

19.9

20.4

20.4

20.8

21.3

22

22

22

22.1

4

20.2

20

19.8

19.8

19.7

19.9

20.4

20.3

20.8

21.2

21.8

21.9

 

22.1

5

20.2

20

19.8

 

19.7

   

20.4

 

21.2

 

21.8

 

22.1

6

20.2

20

                     

22

7

20.2

 

                     

 

8

20.2