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Total Phosphorus



Phosphorus is the most important water 
quality parameter measured in our lakes. It is the 
nutrient that limits the algae’s ability to grow and 

Phosphorus sources around a lake typically
include septic systems, animal waste, lawn fertilizer,
road and construction erosion, and natural wetlands.

Total Phosphorus Ranges for New Hampshire 
Lakes and Ponds

TP (ug/L) Category
1-10 Low (Good)
11-20 Average
21-40 High
>40 Excessive

What is Phosphorus?

How is Phosphorus Measured? 

Phosphorus in Clough Pond


A table of the Clough Pond Total Phosphorus Data (pdf) from all sampling events since 2002 is available.  


Total Phosphorus, Year Over Year

Phosphorus as P, Yearly Averages
Click on the chart to enlarge.

The above chart is drawn from the average of all readings taken over each summer. Readings were taken once each in June, July, and August of most years. 





As part of the NH Department of Environmental Services (D.E.S.) Volunteer Lake Assessment Program (VLAP), Clough Pond Association volunteers take samples of the water in Clough Pond during the months of June, July, and August each year. Sometimes a D.E.S. biologist will accompany the Clough Pond Association volunteers to validate the volunteers' sampling procedures, to take duplicate samples for control purposes, and to generally discuss the water quality and surrounding environment of Clough Pond while the samples are being taken. 

During each sampling event five (5) phosphorus samples are taken: one (1) at the inlet, one (1) at the outlet, and three (3) from different depths at the deepest spot in the pond. Clough Pond stratifies into three (3) thermal layers each summer and samples are taken from the middle of each of those layers. The middle of those layers generally come at 2, 7, and 13 meters from the water surface. The samples are immediately refrigerated, kept in the dark and delivered to D.E.S. for analysis.  

Note: Some summers the Clough Pond Association Volunteers only managed two sampling events rather than the preferred three. In earlier years some summers were skipped entirely. Those omissions were driven primarily by costs. Phosphorus is the only test that is not offered free of charge within the VLAP program. It costs $20 to have each phosphorus sample analyzed and thus the Clough Pond Association incurs a $100 expense every time samples are taken.




NH D.E.S. Annual Assessments of Phosphrus 

Additional Reading 

Data Source

NHDES. Volunteer Lake Assessment Program (VLAP) Environmental Monitoring Data. New Hampshire Department of Environmental Services, Watershed Mgmt Bureau - Biology Section, Concord, NH

National Oceanic Atmospheric Administration, National Climate Data Center, Climate Data Online, Concord Municipal Airport, NH, US