seasonal patterns in the relative importance of organic acids and sulfate in episodic acidification...
TRANSCRIPT
Seasonal Patterns in the Relative Importance of Organic Acids and Sulfate in Episodic Acidification of
Downeast Salmon Rivers
By Mark Whiting, Maine DEP & William Otto, U of Maine at
Machias
Cove BrNarraguagus R
Pleasant R
Machias R
E Machias RDennys R
Pleasant R Data Sonde at Columbia Falls
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
J J J J F F F M M M M A A A A M M M J J J J J J J J A A A A S S S O O O O N
Date
Ra
in i
n I
nc
he
s
3
3.5
4
4.5
5
5.5
6
6.5
7
7.5
8
pH
RainpH
Summary of GMC Hypothesis
• These river are naturally acidic• The important acidity is natural organic
acidity (Dissolved Organic Carbon, or DOC), this drives day to day pH and our episodic acidification events
• Salmon recovery may be hindered by low pH, but since it is natural, the original salmon decline must be from other causes
How do you tell which acids are the important ones?
Review available data
• 700 total samples from all rivers, from 1999 – 2002
• Water samples were taken by volunteers from salmon river watershed councils
• Analysis done by George Mitchell Center
• Samples ranged from N = 19 (Tunk Stream) to N = 142 (Sheepscot R.)
Episodic acidification occurs in all downeast salmon rivers
• Low pH is driven by rain events and especially runoff and snowmelt
• Low pH events occur October - May
• pH will respond to either changes in the concentration of acids or bases, this report concentrates on the sources of acidity
Pleasant R sonde at Columbia Falls, August 10-12, 2005
6.3
6.4
6.5
6.6
6.7
6.8
6.9
7
7.1
7.2
7.3
Date - Time
Fiel
d pH
The role of CO2
• Carbon dioxide concentrations vary diurnally, with a low at night and a high in the afternoon, following the relative amounts of photosynthesis and respiration
• pH varies ± 0.2 pH unit around the daily mean in the peak of the summer season due to CO2
PH
SO
4D
OC
PH
NO
3
SO4 DOC NO3
correlations for Pleasant R, estuary sites removed
Pleasant River, All Samples
Narraguagus, Stormwater Only
PH
SO
4
PH
DO
C
SO4 DOC
Narraguagus, DEP data, Stormwater only
Seasonal scale pH variation
• Regressions are variable, different acids are important at different times and places
• Two acids, DOC often important overall and in some stormwater data sets
• Sulfate is sometimes more important than DOC in specific stormwater data sets (i.e., depending on the river, specific storms, during acidic episodes, etc)
Analysis of low pH events
• Plot pH by month for each river, include plots of the acidic anions by month, which acid source accounts for pH minima?
• One ueq/l of an acid is needed to neutralize one ueq/l of a base, so the dominant anion is the one with the most ueq’s above baseflow values
10 2 3 4 5 6 7 8 9MONTHS
4
5
6
7
PH
10 2 3 4 5 6 7 8 9MONTHS
0
10
20
30
40
50
60
70
80
DO
C
10 2 3 4 5 6 7 8 9MONTHS
40
50
60
70
80
90
100
SO
4
10 2 3 4 5 6 7 8 9MONTHS
0
5
10
15
20
NO
3
Tunk Stream, All Sites by Month, in UEQ
10.0002.000
3.0004.000
6.0007.000
8.0009.000
MONTHS
4
5
6
7
8
PH
10.0002.000
3.0004.000
6.0007.000
8.0009.000
MONTHS
0
50
100
150
200
DO
C
10.0002.000
3.0004.000
6.0007.000
8.0009.000
MONTHS
10
20
30
40
50
60
70
80
SO
4
10.0002.000
3.0004.000
6.0007.000
8.0009.000
MONTHS
0
5
10
15
NO
3
Pleasant R, all sites and flows, in UEQ
10.0002.000
3.0004.000
6.0007.000
8.0009.000
MONTHS
5
6
7
8
PH
10.0002.000
3.0004.000
6.0007.000
8.0009.000
MONTHS
0
10
20
30
40
50
60
70
80
90
100
DO
C
10.0002.000
3.0004.000
6.0007.000
8.0009.000
MONTHS
0
50
100
150
SO
4
10.0002.000
3.0004.000
6.0007.000
8.0009.000
MONTHS
0
10
20
30
40
50
NO
3
Narraguagus R, All Data, in UEQ
10.0003.000
4.0006.000
7.0008.000
9.000
MONTHS
4
5
6
7
8
PH
10.0003.000
4.0006.000
7.0008.000
9.000
MONTHS
10
20
30
40
50
60
70
80
90
DO
C
10.0003.000
4.0006.000
7.0008.000
9.000
MONTHS
10
20
30
40
50
60
70
80
90
100
110
SO
4
10.0003.000
4.0006.000
7.0008.000
9.000
MONTHS
0
1
2
3
4
NO
3
Machias R, All Data, in UEQ
10.0002.000
3.0006.000
7.0008.000
9.000
MONTHS
4
5
6
7
8
PH
10.0002.000
3.0006.000
7.0008.000
9.000
MONTHS
10
20
30
40
50
60
70
80
90
100
110
DO
C
10.0002.000
3.0006.000
7.0008.000
9.000
MONTHS
10
20
30
40
50
60
70
80
90
100
110
SO
4
10.0002.000
3.0006.000
7.0008.000
9.000
MONTHS
0
5
10
15
NO
3
E Machias, All Sites, All Flows, in UEQ
10.000
11.000
6.0007.000
8.0009.000
MONTHS
5.5
6.0
6.5
7.0
7.5
PH
10.000
11.000
6.0007.000
8.0009.000
MONTHS
0
50
100
150
DO
C
10.000
11.000
6.0007.000
8.0009.000
MONTHS
0
50
100
150
200
SO
4
10.000
11.000
6.0007.000
8.0009.000
MONTHS
0
1
2
3
NO
3
Dennys R, All Sites and Flows, in UEQ
Summary
• Overall Sulfate and DOC are about equal when measured in ueq/L
• Sulfate, DOC and combinations of the two are apparently the acids responsible for low pH events
• In this data set, during low pH events Sulfate dominates in Tunk, the Narraguagus, and Pleasant Rivers
Summary (continued)
• Sulfate and DOC both play a role in acidic episodes on the Machias, E Machias and Dennys
• Only in the Dennys is DOC more abundant during low pH events than Sulfate
• Nitrate often peaks in high flow periods, but the concentration are still very low
Conclusions
• Acid rain is our oldest, best known, and most studied problem affecting salmon survival downeast
• Our low pH events are classic episodic acidification with acid rain components, esp. sulfate the primary driver
• DOC is important in baseflow, and sometimes in stormwater acidity