Lake Water Quality Monitoring

What is the SLA's Water Quality Monitoring Program (WQMP)? 

The SLA has had an active water quality monitoring program for over three decades.  Its goal is to achieve a detailed picture of the Lake's physical, chemical, and bacteriological profile.  

The Water Quality Monitoring team, in conjunction with NH DES' Volunteer Lake Assessment Program (VLAP) collects water samples between May and September sending them to the State's limnology labs for analysis.  The results form the basis of the VLAP Annual Report, the most recent of which is available in the sidebar.  

What is being measured and where? 

In 2023, the SLA, along with the Chesterfield Watershed Committee, NH DES, and FB Environmental had one of the most robust water quality monitoring programs in the state.  Over the VLAP sampling season, the team conducted four sampling events, each of which requires samples taken at 31 stations, i.e., 21 tributary stations (both shoreline and up-stream), 7 beaches, the outlet, the boat launch, and the deep spot.  

This year’s program yielded over 600 measurements.  Water flow permitting, fourteen water quality parameters are sampled during each event. These are: Dissolved Oxygen and Water Temperature by meter, Color, Chloride, E. coli bacteria, Acid Neutralizing Capacity, pH, Alkalinity, Total phosphorous, Water clarity (via Secchi disk), Conductivity, and Turbidity, Total Nitrogen, Organic Carbon, and Phytoplankton.  

This data will be invaluable as we work together to better understand, preserve, and protect the water quality of Spofford Lake.

What are the 2023 WQMP Results & Trends?

To help understand the science, use our Glossary of Lake Terms.

Many important parameters are classified as “Good.”  Bacteria levels at the beaches and the boat ramp were well below NH State standards.  Average Chlorophyl-A levels (a measure of algal growth) were less than the State median; water clarity was generally good; and pH levels were in the desirable range.  

On the worrisome front were conductivity and chloride levels.  Both were higher than the state median levels.  Historical trend analysis indicates significantly worsening conductivity levels since monitoring began.  Typical contributors to conductivity and chloride levels are road salt, faulty septic systems, and water softeners.  Elevated TP has been consistently detected at several tributary sampling stations, and at the Deep Spot.  

The level of TP, the most important parameter affecting long-term health, is a particular concern.  Total phosphorous is a “limiting element” for plant and algal growth.  Excessive TP can lead to harmful algae blooms such as cyanobacteria and accelerated plant growth which, in turn, consumes dissolved oxygen in the Lake thereby directly stressing the ability of important fish species to survive.  

The 2018 Spofford Lake Watershed Management Plan (WMP), prepared by FB Environmental, contained a Lake Loading Response Model (LLRM).  The LLRM determines the major sources of phosphorous in the Lake and predicts future loads under various development scenarios.  The 2018 LLRM report qualified the findings due to limited sampling data.  The SLA supported by the Town, has since funded a significantly more robust Water Quality Management Program (WQMP) to collect additional data.  With this new and additional data (2014-2023), the LLRM was updated in 2023 to create a “LLRM 2.0.”  The results show a significant increase in the estimated internal TP loading.  Specifically, the updated LLRM estimated three-fold increase in internal phosphorous loading from 14 kg/yr (6%) in 2017 to 42 kg/yr (~19%).

LLRM 2.0 now estimates that watershed runoff combined with baseflow contributes 46% of the TP load to the Lake, followed by atmospheric deposition (20%), internal loading (19%), septic system (12%), and waterfowl (3%).  

Here’s a quick primer on the process of internal phosphorus loading and its impacts on Spofford Lake:

• Due to soil erosion and runoff, the volume of phosphorus-laden sediment at the bottom of the Lake has increased significantly over the past four decades.
• Under normal (aerobic) conditions where DO levels are  > 1mg/l,the phosphorus would remain chemically bonded to the sediment thereby having limited impact.
• During summer months, the dissolved oxygen at the lower levels of the Lake is consumed by plant and aquatic life.  Generally, by August, the DO concentrations at the deepest portions of the Lake sink to <1mg/L.  When this happens, the chemical bond attaching the phosphorus to the sediment is no longer strong enough and phosphorus is released into the Lake.  This is referred to as internal loading.
• Internal loading is a significant source of phosphorus (~19%) for Spofford Lake and can contribute to the development of harmful algal blooms, e.g., cyanobacteria.

What about the 2024 WQMP?

FBE has recommended changes to our program, including a further expansion of our water testing program.  The SLA Water Quality team and the Town Watershed Committee are reviewing the suggestions.  Stay tuned for their decisions.

What can I as a homeowner do to help?

Take time to understand the Lake's vulnerabilities and take steps to maintain and improve Spofford Lake's water quality.  Be aware that the SLA-funded Watershed Management Plan and the SLA-funded Core Sediment Analysis provide greater context to the VLAP reports.  

Implement practices to minimize runoff from your property, for example:

• make sure that your well functioning septic systems is pumped out regularly and at a minimum in accordance with Town rules.  
• adopt “anti-runoff” practices.  Tips can be found in "Soak Up the Rain”,
• refrain from adding sand to beaches, as this only encourages plant growth and resulting decay and muck,
• reduce or eliminate winter salt on driveways and walkways,
• use a salt alternative in your water softening system.  Salt used to soften water eventually flows into Lake.   'Sodium Shield' is available at the Brattleboro Agway.,
• use “lake friendly” cleaning and lawn products.  Products labelled 'Safer Choice,' an EPA initiate, are a good choice, and 
• participate in LakeSmart, a free program to identify how your property can become more lake-friendly. 
  

Page updated March 23, 2024