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2003 PRW Dissolved Oxygen Data (in percent saturation)

Columns are sample dates, rows are sample sites:

	17-May-03	31-May-03	14-Jun-03	28-Jun-03	12-Jul-03	26-Jul-03	9-Aug-03	23-Aug-03
P200	nd	94.4	83.0	91.8	86.8	90.8	88.9	85.68
P170	96.9	89.8	86.8	nd	84.1	90.5	74.8	90.87
P160	93.6	89.5	88.7	nd	84.6	87.7	88.0	90.76
P150	87.6	85.3	84.8	nd	81.4	81.0	87.0	89.31
P110	nd	91.8	83.0	94.1	92.7	90.7	92.9	84.17
P089	91.6	88.1	85.5	79.0	92.9	90.5	79.7	85.09
P080	89.3	81.5	85.7	83.7	96.2	91.2	93.0	70.68
P065	87.8	nd	79.0	84.1	69.7	nd	nd	83.02
P060	87.1	nd	79.4	87.9	87.7	nd	nd	81.08
P030	94.1	87.3	82.3	87.8	85.2	83.2	83.0	81.56
P020	87.0	82.3	87.4	75.6	nd	83.3	81.4	74.10
P010	97.4	87.6	86.2	86.7	89.7	94.6	77.2	65.33
OB010	41.4	37.5	28.7	6.6	24.8	12.3	nd	4.65
BB010	81.4	77.2	77.2	70.6	69.7	63.1	69.4	54.98
DB010	86.9	91.0	79.0	89.2	nd	nd	nd	81.89
PL040	83.8	77.4	76.1	61.8	69.1	nd	nd	63.26
PL030	86.5	84.4	81.1	79.6	76.6	82.5	82.7	82.69
PL020	89.3	84.0	81.7	76.6	79.6	79.3	82.9	78.83
PL010	82.6	84.1	82.1	75.8	66.8	90.1	79.1	84.17
N010	nd	nd	nd	nd	nd	nd	nd	nd
BL010	92.0	88.3	83.7	78.6	77.5	nd	78.0	55.98
CW010	nd	79.6	72.7	46.7	38.5	nd	69.3	40.16
CW020	nd	nd	83.3	65.3	73.2	nd	nd	45.09
DG010	nd	75.5	77.0	62.2	nd	63.1	74.3	57.13
L020	nd	95.6	78.6	82.5	nd	80.3	83.4	74.79
L010	79.9	71.5	76.4	60.6	69.3	73.3	71.8	76.05
IN010	72.2	66.5	68.7	31.5	38.9	nd	48.5	19.44
M030	97.6	84.7	75.4	72.2	76.7	88.4	83.6	77.93
M010	89.3	89.4	76.8	83.6	85.1	86.2	80.1	45.41
PI020	91.6	83.1	80.5	83.1	84.8	87.9	55.9	35.67
PI010	93.2	74.8	68.0	52.7	63.9	62.0	82.6	49.41
TA010	99.6	nd	79.3	55.6	60.1	64.2	67.1	62.65
TA020	nd	nd	86.2	nd	nd	nd	nd	nd
TA040	94.2	nd	85.8	87.7	87.9	88.1	82.6	81.46

WHAT DO THESE RESULTS MEAN?

The State Legislature has established statutes that classify Maine surface waters on the basis of water quality standards and intended uses. The Maine Department of Environmental Protection is charged with ensuring that these standards are met for all surface waters in the State. The classification scheme and standards for dissolved oxygen (DO) are as follows:

· Class A: suitable for drinking (after disinfection), swimming and fishing
· Class B: suitable for drinking (after treatment), swimming and fishing
· Class C: suitable for drinking (after treatment), swimming and fishing

The main stem of the Presumpscot River is Class A from the Eel Weir Dam to its confluence with the Pleasant River (just below sample site P150); Class B from the Pleasant River to the Saccarappa Dam (just below sample site P060); and Class C from the Saccarappa Dam to the estuary in Falmouth (just below the former site of the Smelt Hill Dam).

Dissolved Oxygen Standards
· Class A and B: not less than 7 parts per million (ppm) or 75% of saturation, whichever is higher
· Class C: not less than 5 ppm or 60% of saturation, whichever is higher

Class A or B sample sites are considered to be in violation of the State's water quality standards if the DO results for those sites are less than 75% saturation. For Class C sample sites, the DO cannot be lower than 60% saturation.

DO levels are considered the most important and commonly employed measurement of water quality and indicator of a water body's ability to support desirable aquatic life. The ideal DO level in percent saturation for fish is between 80 % and 100 %; most fish cannot survive very well at levels below 60 %. One of the most critical factors affecting DO concentration is temperature, which in turn is significantly affected by solar radiation. Waters with higher temperatures hold less DO. Temperature increases can be caused by a lack of mixing (stagnant water heats up more easily than moving water) and turbidity from sediments that absorb solar heat. Organic wastes also decrease DO through bacterial decomposition (bacteria use oxygen to "eat" organics). Finally, nutrients (especially phosphorus in fresh water) decrease DO by increasing plant and algal growth, which use oxygen in the process of photosynthesis.

What can be done to improve DO levels in the Presumpscot and its tributaries? According to the DEP, the most significant factor adversely affecting DO along the main stem is impoundment from dams. While dam removal is a controversial issue, there is little doubt that a free flowing river will generally have higher DO levels than a stagnant impoundment. Another significant detrimental influence on DO level originates from nonpoint source pollution (NPS). Reducing soil erosion and nutrient and organic runoff would result in corresponding improvements to DO levels. Providing more opportunities for water movement and mixing would also help to increase DO concentrations.

Key to PRW Abbreviations: P = Main stem of Presumpscot River, BB = Baker Brook, BL = Black Brook, CW = Colley Wright Brook, DG = Douglas Brook, DB = Ditch Brook, IN = Inkhorn Brook, L = Little River, M = Mill Brook, N = Nason Brook, OB = Otter Brook, PI = Piscataqua River (not the same as one at ME-NH border), PL = Pleasant River, TA = Tannery Brook.

The "% complete" column indicates the number of samples actually collected compared to the number of samples intended for collection. PRW has 8 sampling events per season, so if only 4 samples were collected for the season the completion rate would be 50%.