Summary of Long-Term Water Quality Monitoring Data from White Pond
Concord, Massachusetts
William W. Walker, Jr.  Ph.D,   Environmental Engineer
07/17/17
Introduction Water Level Fluctuations Long-Term Trends in Transparency Transparency vs. Precipitation
Climate Change Proposed Restoration Goal Analysis of Temperature & Dissolved Oxygen Profiles Phosphorus Data
Potential Remedy for Sediment Phosphorus Releases References Friends of White Pond - Ponderings 2015
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June-July 2015 Bloom - Linked In Document Cache 2015 Bloom Photos
2017 Bloom Photos
Introduction
Following is a summary of the historical transparency and water level data collected by the Friends of White Pond between 1987 and 2013.
Supports Concord's current efforts to develop a management plan to restore & protect water quality and ecology.
The Concord Board of Selectmen Has Scheduled a Town Forum on White Pond,  Harvey Wheeler Center, 6:45 pm, January 21, 2015.
Water Level Fluctuations
Historical water levels varied over a range of approximately 60 inches ( 5 feet ), relative to the maximum depth of ~55 feet.
Variations in water levels are highly correlated with variations in precipitation averaged over 2-3 year period.
The lag time likely reflects the large volume of groundwater storage and slow discharge rates from the aquifer to downstream waterbodies.
The recent low water levels are explained by low precipitation, although increased pumping from the town well could also be a factor.
Water levels in Walden Pond are also very low, although time series data are not available.
The pond is more susceptable to effects of runoff and erosion from shoreline areas during periods of high rainfall and water level.
When water levels are low, some of the eroded materials from the watershed could be trapped in the beach area and not reach the pond.
When water levels are high, watershed loads are more likely to reach the pond and wave action could contribute to erosion of the banks.
When water levels are lower, the assimilative capacity of the pond to handle a given phosphorus load is lower.
The rate of oxygen depletion in the bottom waters would also tend to be higher in shallower years because of the smaller volume.
This could have adverse impacts on the fish habitat and increase the rate of phosphorus release from the pond bottom sediments.
Long-Term Trends in Transparency & Turbidity
Water clarity apparently improved over the 1987-2005 period (Secchi depth increased, turbidity decreased).
The improvements are possibly related to management measures taken after the 1987-1988 baseline study.
Measures included construction of an infiltration basin at the base of the boat ramp, improvements to shoreline septic systems, etc.
The improving trend was reversed around 2005.  Secchi depths were generally below the long-term median (~ 6 meters) in 2009-2014
The lower water clarity in recent years is consistent with increasing erosion at several locations around the shoreline and plugging
of the infiltration basin due to inadequate maintenance. ( see plans & photos )
Water clarity improved slightly in 2015-2017.  This could reflect lower precipitation rates and repair of the infiltration basin in 2016.
Transparency & Turbidity vs. Antecedent Precipitation
The charts above show that significant decreases in water clarity were associated with high precipitation in May of 2006.
This was the infamous "Mother's Day Storm" that totaled about 7 inches on May 12-15. Wiki Description NOAA Record
Secchi depth decreased from 10.3 meters  (~historical high) on May 7, to 8.0 meters on May 25, and 2.6 meters on June 30 (~historical low).
A single erosion event associated with extreme rainfall could have a long-term impact on both the watershed and the pond.
Unless repaired, gullies created in the steep shoreline banks would be more susceptable to erosion in subsequent smaller storms.
Nutrient loads discharged into the pond during runoff events are stored and recycled within the pond, so we would not expect a 1/1 relationship between precipitation and clarity in each year.
Climate Change