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Lake Sebasticook is a 4300 acre lake in Newport, Maine just off I-95 mid-way between Bangor and Waterville. Sebasticook started having water quality problems in the 1950’s due to industrial, municipal, and agricultural nutrient sources. Public concern for the lake’s problems resulted in a Federal Water Quality Control Administration study in 1965. The report of the study (MacKenthun, 1968) documented the hyper-eutrophic condition of the lake and indicated the industrial and municipal discharges to the East Branch of the Sebasticook River at Corinna and Dexter were the likely causes. Continued data collection by Maine DEP and University of Maine scientists together with a computer model of internal phosphorus cycling (Hannula, 1978) led Maine DEP to formulate a restoration plan for the lake (Maine DEP, 1977). The plan consisted of three main components:
A land disposal sewage treatment facility for Dexter was installed in the mid-80’s and a similar facility is currently under construction for Corinna. Manure storage facilities were constructed on 21 of the largest diary farms in the watershed during the 80’s. Conservation programs have also been implemented on many of the watershed farms. The lake’s outlet dam was reconstructed in the early 80’s with the first extended drawdown occurring in the fall of 1982. The drawdowns have continued each fall for the last 23 years.
The following discussion and charts show the progress that has been made in restoring Lake Sebasticook over this period. The data shows a significant decrease of phosphorus input to the lake during the spring run-off and a decrease in the apparent release of phosphorus from the sediments. The overall decrease in the lake’s phosphorus content suggests that external sources of phosphorus have been significantly reduced.
Only data from the top 12 m of the water column have been used in the following computations. The volume of water below 12 m is negligible (less than 2% of the volume is below 12 m) and the phosphorus (P) content is minor even at high concentrations. This omission is likely within the computational errors for the methods used to approximate the lake’s phosphorus content.
The following graph shows the trends in the average monthly summer secchi disc readings since 1979. Although there is significant variation in the readings, the trend in July and August is clearly improving. The August averages in the early 80’s where frequently below 1 m and are now starting to move above 2 meters. Maine DEP uses a secchi disc reading below 2 m to designate an algal bloom in lightly colored Maine lakes. In the early 80’s, the minimum secchi disc readings were frequently between 0.5 m and 1.0 m. Since 1995, the minimum July and August readings have frequently been above 1.5 m with some above 2 m. The average July and August secchi disc readings for 2003 were the best that have been recorded.
The change in P content from March to May is interesting. The March samples were collected under ice at the end of winter and the start of the spring runoff. The May samples were obtained during the spring turnover near the end of the spring runoff. From 1980-1984 the P content increased by an average of 1264 kg between the March and May samples. The increases during 1980 to 1983 ranged from 1323 kg to 1666 kg. Since 2000 the average change has been an increase of only 48 kg. The changes ranged from a drop of 1093 kg in 2003 to an increase of 745 kg in 2002. In 2002 the increase in the P content during the spring set the stage for poor water quality in July. The 2003 decrease of 1093 kg resulted from an abnormally high P concentration of 49 ppb in the 1-meter March sample. The other P values in the March 2003 samples ranged from 12 to 23 ppb more in line with other recent March values. If the 1 m concentration of 49 ppb is considered an anomaly and is replaced by the 23 ppb concentration at 3 m, the decease from March to May was only 316 kg. The low P content in May of 2003 was followed by the best summer water conditions that have been recorded. In any case, there has been a significant change from a consistently large increase in P content in the early 80’s to a variable but on average nearly stable P content in the last few years. A reduction of P export from the watershed farms due to the construction of manure storage facilities and implementation of conservation practices together with the closure of Eastland Woolen Mill might account for this change. But the timing and magnitude of the spring run-off during the drought in the early 2000’s might also be significant. Unfortunately, a decrease in the sampling frequency in the 90’s prevents a complete examination of this trend.
The P concentration has decreased from an average of 28 ppb in March and 43 ppb in May for 1980-1984 to 19 ppb in March and 18 ppb in May for 2000-2004. This is a reduction of 32% for the March concentrations and 57% for the May concentrations. The average P content has decreased from 2279 kg for March and 3543 kg for May during 1980-1984 to 1532 kg for March and 1510 kg for May during 2000-2004. The average P concentration for March and May are now nearly equal and are approaching the target of 15 ppb. Maine DEP data indicates that lightly colored Maine lakes with P concentrations below 15 ppb do not have summer algal blooms.
The increase in P content during summer (May to August) has also significantly declined. During 1979-1984 the estimated maximum P content in the top 12 m of the water column averaged 6789 kg, the minimum content averaged 2713 kg, and the change in P content averaged 4076 kg. During 2000-2004 these estimates where 2265 kg for the maximum, 1352 kg for the minimum, and 912 kg for the summer change. The average maximum content decreased approximately 67%, average minimum content decreased 50%, and the average summer change decreased 78%. The change in P content has resulted in a decrease in the average maximum August P concentration from 76 ppb for 1980-1984 to 27 ppb for 2000-2004, a 64% decrease. The summer increase in P content is thought to be P released from the sediments. It appears this release has significantly decreased. However, a net release of 900 kg P from the sediments during the summer is still significant and results in a mid-summer increase of about 11 ppb in the P concentration.
Since the P concentration maximizes in mid-September to early October, the P content in the top 3 meters of the water column in late August to early September may be used to estimate the removal of P from the lake during the fall drawdown. Since the September sampling is either before the start of the drawdown or near its beginning while the P concentration continues to increase (based on outlet P samples in late September and early October), the P content in the top 3 meters during late August to early September likely under estimates the P removed during drawdown. The estimated export of P during the fall drawdown has dropped from an average of 3430 kg during 1982-1986 to an average of 1511 kg during 2000-2004, a 56% reduction in P export. From 1982 to 2003, the fall flush has exported approximately 47,263 kg of P. About half of this (23,125 kg) has been returned during the lake refill. The fall drawdown has thus resulted in the removal of more than 24,000 kg P from the lake.
The data show a significant improvement in Lake Sebasticook water quality during the past 23 years. Phosphorus concentrations have decreased, P release from the sediments has been reduced, and nuisance algal blooms are less frequent and occur later in the summer. The reduction in overall May phosphorus content from the early 80’s to current conditions indicate that the spring external P loading has been greatly reduced. However, the average spring P concentration of 19 ppb P for 2000-04 suggests additional reduction is needed. The need for additional non-point P loading has also been suggested in Maine DEP's 2001 TMDL report for Lake Sebasticook (Maine DEP, 2001). The TMDL report estimated a total of 5,513 kg P from non-point sources (89% cultural with 52% agricultural, 22% roads, and 18% residential (including septic systems)). The TMDL report estimated a reduction of the non-point P sources to about 4,500 kg P was needed to attain 15 ppb lake P concentration target.
The impending implementation of a land disposal system for Corinna's municipal sewage should eventually result in a significant reduction in cumulative P loading downstream in Sebasticook Lake. Additional reduction of non-point P sources likely requires installation of additional conservation practices on the watershed farms to reduce run-off, adopting BMP's for road maintenance, and reducing P content in runoff from residential and commercial development. Encouraging landowners in the watershed to use methods to reduce the P content in storm run-off being developed in Minnesota (Barten 2005) might also be effective. This would require a watershed approach to educate town officials and landowners on the insidious nature of non-point pollution and possible landuse/management activities (some low in cost and simple to implement) to reduce it.
The build up of total phosphorous in the lake water during the summer has greatly declined together with an observed reduction in the length of nuisance algal blooms throughout the summer months. However, the average increase of 11 ppb during the summer recreation season for 2000-04 is still sufficient to produce nuisance algal blooms in August and early September. The fall drawdown has been successful in depleting much of the historical accumulation of phosphorus in the sediments and its release during the summer months. During the last few summers algal blooms (as measured by secchi disc readings) have peaked in mid to late September and have remained constant until late October. The fall total phosphorus concentrations have decreased, so the fall lake level drawdown to export phosphorus from the lake has lost some of its effectiveness. The data suggest that over 1,500 kg of total phosphorus is still being exported from the lake during the drawdown. The annual net export after refilling the lake due to the drawdown is probably in excess of 800 kg of total phosphorus. It appears that internal sediment loading has been greatly reduced, coinciding with observed improvements in water quality after 23 years fall lake level drawdown following outlet dam enhancement. With the continued net export of nearly 800 kg/yr, it is recommended that the fall drawdown be continued, but start in the last third of September to catch the peak of the fall algal bloom.
Morphometry Data
Dave Halliwell, Maine DEP, provided the morphometry data used in this report. This data provided surface area and volume estimates at 1 meter intervals to 15 m. The data indicate that less than 2% of the lake volume is below 12 m. For this reason only data for the top 12m of the water column have been used in the computations. This agrees with experience sampling the lake. It is very difficult to find lake depths between 12 m and 18 m, even when you know where to look.
| DEP Estimates of Lake Sebasticook Volume and Surface Area | |||
| Depth (m) | Cumulative vol (10,000,000 m³) | Layer vol (10,000,000 m³) | Layer Surface (10,000,000 m²) |
| 0 | 17.74 | ||
| 1 | 17.2 | 17.17 | 16.60 |
| 2 | 33.2 | 16.04 | 15.47 |
| 3 | 47.5 | 14.33 | 13.18 |
| 4 | 59.0 | 11.49 | 9.79 |
| 5 | 67.1 | 8.10 | 6.40 |
| 6 | 72.4 | 5.31 | 4.21 |
| 7 | 76.1 | 3.65 | 3.09 |
| 8 | 78.6 | 2.53 | 1.96 |
| 9 | 80.2 | 1.59 | 1.21 |
| 10 | 81.2 | 1.00 | 0.78 |
| 11 | 81.7 | 0.56 | 0.34 |
| 12 | 82.0 | 0.24 | 0.13 |
The phosphorus data profiles were generally collected at depths of 1, 3, 5, 7, 9, 11, 13, 15 meters. The surface 1-meter layer is assumed to be uniform and the P concentration at 1 m is taken as its average P concentration. The concentrations for the even depths are obtained by averaging the adjacent odd P sample concentrations. Adjacent P estimates are again averaged to obtain an estimated P concentration for the midpoint of each 1-meter layer. The P content of each 1-meter layer is the obtained by multiplying its estimated volume and P concentration. The total P content of the top 12 m is obtained by summing the P content of the 1-m layers. The average P concentration is obtained by dividing the estimated total P content by the estimated volume of the top 12 meters of the lake’s water column.
| Secchi Disc Reading 1979-2004 | ||||||
| Average Secchi Disc Readings | Minimum Secchi Disc Readings | |||||
| Year | June | Jul | Aug | June | Jul | Aug |
| 1979 | 2.9 | 1.2 | 1.3 | 2.9 | 1.2 | 1.3 |
| 1980 | 2.7 | 1.3 | 1.0 | 1.2 | 0.7 | 0.6 |
| 1981 | 1.7 | 2.9 | 1.3 | 2.4 | ||
| 1982 | 2.0 | 1.3 | 1.2 | 1.2 | 1.0 | 1.2 |
| 1983 | 3.7 | 1.6 | 0.9 | 3.5 | 1.5 | 0.5 |
| 1984 | 3.9 | 1.2 | 0.9 | 3.9 | 1.2 | 0.9 |
| 1985 | 3.4 | 0.8 | 1.1 | 3.0 | 0.7 | 1.1 |
| 1986 | 1.8 | 1.0 | 1.0 | 1.0 | 1.0 | 0.8 |
| 1987 | 2.8 | 1.2 | 0.8 | 2.8 | 1.2 | 0.8 |
| 1988 | 1.7 | 1.7 | ||||
| 1989 | 3.7 | 1.0 | 1.0 | 3.7 | 1.0 | 1.0 |
| 1990 | 2.8 | 1.3 | 1.3 | 2.8 | 1.3 | 1.0 |
| 1991 | 1.6 | 1.2 | 1.0 | 1.6 | 1.2 | 1.0 |
| 1992 | 1.6 | 0.5 | 0.3 | 1.6 | 0.5 | 0.3 |
| 1993 | 2.0 | 1.2 | 1.2 | 1. | ||
| 1994 | 1.2 | 1.0 | 1.2 | 1.0 | ||
| 1995 | 3.1 | 2.2 | 1.9 | 3.1 | 2.2 | 1.9 |
| 1996 | 3.2 | 1.2 | 1.7 | 3.2 | 1.2 | 1.7 |
| 1997 | 3.8 | 3.0 | 2.2 | 3.8 | 3.0 | 2.0 |
| 1998 | 2.0 | 1.4 | 2.0 | 1.4 | ||
| 1999 | 1.4 | 2.1 | 1.2 | 1.4 | 2.1 | 0.9 |
| 2000 | 3.2 | 1.5 | 1.8 | 3.1 | 1.0 | 1.5 |
| 2001 | 3.0 | 2.1 | 1.5 | 2.8 | 1.6 | 1.1 |
| 2002 | 3.2 | 1.7 | 2.1 | 3.2 | 1.5 | 1.8 |
| 2003 | 3.0 | 3.3 | 2.3 | 2.6 | 3.2 | 2.0 |
| 2004 | 3.2 | 2.7 | 1.9 | 2.9 | 2.3 | 1.6 |
| Estimated P Concentrations | P content change |
Summer P content | Estimated flush | |||
| YEAR | March | May | May-Mar | Max | Min | |
| 1979 | 44 | 43 | -88 | 6067 | 3489 | 3717 |
| 1980 | 28 | 44 | 1323 | 8718 | 3563 | 3488 |
| 1981 | 19 | 39 | 1666 | 4340 | 2160 | 2519 |
| 1982 | 21 | 39 | 1338 | 6843 | 2232 | 4130 |
| 1983 | 27 | 45 | 1565 | 9214 | 3487 | 6502 |
| 1984 | 42 | 48 | 430 | 4829 | 2124 | 2790 |
| 1985 | 22 | 3353 | 1829 | 1967 | ||
| 1986 | 16 | 24 | 841 | 4367 | 1938 | 1759 |
| 1987 | 20 | 28 | 707 | 4586 | 2103 | 2914 |
| 1988 | 44 | -528 | 3703 | 2628 | 1028 | |
| 1989 | 20 | 3654 | 1879 | 1780 | ||
| 1990 | 3135 | 1689 | 1646 | |||
| 1991 | 15 | 3181 | 2375 | 1908 | ||
| 1992 | 17 | 3505 | 3505 | |||
| 1993 | 19 | 796 | 2465 | 1922 | 1473 | |
| 1994 | 4958 | 1809 | 2903 | |||
| 1995 | 12 | 2108 | 1202 | 1046 | ||
| 1996 | 11 | 4514 | 1530 | 1177 | ||
| 1997 | 2039 | 1342 | 1188 | |||
| 1998 | 20 | 2591 | 1894 | 1524 | ||
| 1999 | 19 | 12 | -541 | 3309 | 1017 | 2178 |
| 2000 | 14 | 15 | 183 | 2783 | 1313 | 1693 |
| 2001 | 15 | 2026 | 1232 | 1188 | ||
| 2002 | 17 | 745 | 2527 | 1559 | 1301 | |
| 2003 | 29 | 16 | -1093 | 2343 | 1267 | 1664 |
| 2004 | 16 | 20 | 356 | 1645 | 1391 | 1711 |
Barten, Joh n. 2005. StormwaterManagement for Lakeshore and "Near" Lakeshore Homeowners, Lakeline, Vol. 23 No.1, Spring, 2005
Hannula, T.A. 1978, Modeling phosphorus cycling in Sebasticook Lake (Newport, Maine). OWRT Project A-039-ME, Land and Water Resource Center, University of Maine, Orono
Maine Department of Environmental Protection 1977, Restoring Sebasticook Lake, presented at a Public Hearing, Corinna, Maine, Nov. 1, 1977
Maine Department of Environmental Protection 2001, Sebasticook Lake, Total Maximum Daily (Annual Phosphorus) Load . Maine DEP (Augusta) and Maine Association of Conservation Districts (MACD).
Mackenthun, K.M., L.E. Keup, and R.K. Stewart. 1968. Nutrients and algae in Sebasticook Lake, Maine. Journal of the Water Pollution Control Federation, R72-R81