Lake &Watershed Resource Management Associates
P.O. Box 65; Turner, ME 04282; 207-576-7839; LWRMA@ megalink.net
2013 Boyd Pond Water Quality Report
Baseline water quality monitoring and assessment of Boyd Pond in Bristol, Maine was
conducted on September 10, 2013, in accordance with monitoring procedures and
protocol for the assessment of Maine lakes and ponds established by the Maine
Department of Environmental Protection and the Maine Volunteer Lake Monitoring
Program.
In addition to the monitoring/sampling that we conducted, water clarity (Secchi
transparency) readings were taken by Maine VLMP certified volunteer lake monitor
Peter Fischer, whose data were also used in the preparation of this report.
2013 Weather Influences :
Weather prior to, and during the summer assessment period can have a strong bearing on
lake water quality. Stormwater runoff from lake watersheds following the winter
snowmelt and spring runoff period, and into the early summer, is typically responsible for
a high percentage of the annual phosphorus and sediment loading to lakes. Spring and
early summer conditions were relatively wet in 2013, and numerous intense storm events
were documented throughout the State of Maine during the period. The weather pattern
during late summer was less active, with fewer storm events and less wind.
Location of Boyd Pond Sampling Station:
2013 Monitoring Summary:
Water clarity (aka: Secchi transparency – the distance that one is able to see down into
the lake from the surface), which is used as an indirect indicator of algal growth in lakes,
varied through the monitoring period from a low reading 2.97 meters on June 30, to the
highest (best) reading of 4.58 meters on August 10. The average for the five months
during which readings were taken in 2013 (thanks to Peter Fischer) was 3.9 meters (~12.5
feet). The historical average for Boyd Pond, which is based on nearly continuous annual
data since 1988 to the present, is also 3.9 meters. Annual water clarity for this lake has
varied from a low average of 3.3 meters in 2010, to a high of 4.3 meters in 1993. During
this period, the single highest (most clear) reading of 5.2 meters was recorded in 2000,
and the lowest reading of 2.7 meters was recorded in 1990.
The graphic below illustrates the progression of Secchi transparency readings taken on
Boyd Pond in 2013.
BOYD POND 2013 SECCHI READINGS IN
METERS
4.6
4.58
3.82
3.63
29-Sep
22-Sep
15-Sep
8-Sep
1-Sep
25-Aug
18-Aug
11-Aug
4-Aug
21-Jul
14-Jul
7-Jul
30-Jun
23-Jun
16-Jun
9-Jun
3.67
3.65
3.00
2.97
2-Jun
4.15
4
28-Jul
4
A surface (epilimnetic core) total phosphorus sample taken on September 10 measured 14
parts per billion (ppb). The historical average for this pond is 15 ppb, having ranged from
11 ppb in 2005 to 20 ppb in 2000. Phosphorus is the limiting nutrient for the growth of
planktonic algae in lakes, generally correlating well with water clarity, algal abundance,
and dissolved oxygen levels in the water during late summer.
Chlorophyll-a (CHL) is the pigment measured in lake water that is used to estimate the
concentration of algae in the lake. The September 10 sample measured 8.1 ppb, which is
the second highest single sample concentration on record for Boyd Pond. The historical
average, based on records from 7 years during the monitoring history, is 5.1 ppb. The
range of CHL values for Boyd Pond varies from a low of 2.4 ppb in 1989 to a high of 9.1
ppb in 2000.
The concentration of natural color in Boyd Pond in September, 2013 measured 38
Standard Platinum Cobalt Units (SPU), compared to the historical average of 31. Natural
lake water color (aka: the “root beer effect”) generally reflects the concentration of humic
acids in lake water. These compounds leach from wetland vegetation and from other
sources of vegetative decomposition in the watershed. Recent research has suggested that
a possible effect of longer periods of warm weather during summer months may result in
greater breakdown and mobility of organic matter from lake watersheds, possibly
resulting in higher concentrations of humic acids and other compounds in lake water. The
natural color level in Boyd Pond is high enough to be influencing the clarity of the water
and the concentration of phosphorus in the pond. When natural color levels exceed
~25SPU, the influence of this indicator on other water quality indicators should be taken
into account. The water clarity of Boyd Pond would be clearer, and total phosphorus
levels would likely be lower if not for the natural influence of somewhat high color of the
water.
A temperature and dissolved oxygen (DO)
profile taken during the early September
baseline sampling visit showed Boyd Pond to
be only weakly thermally stratified. The
surface temperature at the deep monitoring
station was 19.7 degrees C, and at 6 meters
depth, the temperature measured 15.7 C.
Surface DO measured 7.4 parts per million
(ppm), somewhat lower than might be
expected at that temperature. The DO concentration remained the same until 5 meters
depth, at which it dropped to 0.9 ppm. All factors considered, it is likely that the lake
volume had recently mixed (aka: turned over), which would be normal for a shallow
pond in early September.
Historical late summer (August) temperature and oxygen profiles for Boyd Pond show
significant dissolved oxygen loss below 3 meters depth. The lower than expected DO
reading at the surface on September 10 was likely the result of recent mixing of the water
column, during which water with very low oxygen levels mixed with well-oxygenated
surface water, causing a dilution of the oxygen level near the surface. Natural water color
may also influence DO levels in Boyd Pond. As the organic compounds that cause water
to be colored break down, oxygen may be consumed. The most effective strategy for
protecting late summer DO levels in lakes is to reduce the concentration of phosphorus
and algae in the water through the use of conservation measures throughout the lake
watershed.
Climate change represents another potential threat to summer DO levels in lakes, in that
warmer spring-summer-fall periods will likely lead to longer periods of thermal
stratification in lakes, resulting in a greater period of time during which deep, cold water
is isolated from the atmosphere between spring and fall mixing events (aka: turnover).
Although it is not possible to control the weather, which exerts a strong influence on
lakes from year to year, it is possible to reduce the flow of stormwater runoff to the pond
through the use of watershed conservation practices. The use of such practices over time
can significantly minimize the potential negative effects of untreated runoff to Boyd
Pond, and can stabilize, and possible improve overall water quality and the health of the
lake ecosystem.
Prepared by:
Scott Williams, Limnologist/Lake Biologist