Water Quality Monitoring of Province Lake in 2004 Presented to PLA on July 30, 2005

2004 was the fourteenth consecutive year of water quality monitoring conducted at Province Lake. We sampled four times last season. The test results for 2004 on water samples collected by Ed Thomas, Dick & Blythe Thomas, Steve Craig, Don Harrison, and me were reviewed by the New Hampshire Department of Environmental Services (NHDES). The complete NHDES report on the quality of water in the lake for 2004 can be found at the following link: http://www.des.state.nh.us/wmb/VLAP/2004/province.pdf. In summary, it indicates the following:

1. The average amount of algae in the lake was only slightly more than that seen in 2003, as indicated by the chlorophyll concentration. We have never returned to the high levels observed during the weed removal activities of 1996 and 1997, and their lingering effects in 1998. The amount of algae is only about 2/3 of the average for New Hampshire lakes. This low level is good because dying algae forms the brown floating bottom masses that come to your shore when the wind blows hard in July and August.

2. Water transparency (a measure of how deep you can see into the water) decreased since 2003, to an average of 2.3 meters (7.7 feet). For reference, the lake was 4.9 meters (16.1 feet) deep at the place where the sampling was done this June. A map of lake depths can be obtained at the following link: http://www.des.state.nh.us/wmb/VLAP/2004/bathymetric/Province.pdf.

State reports have pointed out that Province Lake is relatively shallow, so it is important to educate lake users on the importance of operating jet skis and other boats at slow speeds in shallow areas to minimize disturbance to sediments and vegetation. Churning up the nutrient-laden bottom sediments releases phosphorous, promotes algae growth, increases turbidity (scattering of light by suspended particles), and decreases clarity.

3. Phosphorus is the nutrient that encourages plant and algae growth. The average phosphorus measurements in the upper water layer in 2004 were slightly higher than in 50% of the lakes in NH, but slightly lower than the 2003 measurements. The lower water layer was sampled only in June. Its phosphorus level was below the NH median and below the other three times it was measured in 2000-2002. Again, powered watercraft disturbance of bottom sediments is probably an important source of phosphorus for our lake.

The phosphorus concentrations at the Rt. 153 Inlet and the Island Inlet on Bonnyman Road continue to be elevated. These locations have a history of elevated and fluctuating total phosphorus concentration, but the long-term trend is that the Rt. 153 phosphorus is decreasing, in 2004 approaching its lowest recorded average. During the past 3 years, the Bonnyman Road inlet phosphorus has also been decreasing, in 2004 reaching its lowest average since sampling started in 1991. The campground inlet, sampled at the road, is low and trending downward.

4. The State reported small amounts of cyanobacteria in the plankton sample in 2004, as they had in 2002, but not 2003. If present in large amounts, cyanobacteria can be toxic to animals and humans. Large concentrations would be caused by a bloom, observable by the formation of a surface scum in a section of the lake. The best ways to avoid such blooms is to reduce nutrients entering the lake by eliminating fertilizer use on lawns, keeping the lake shore natural, and properly maintaining septic systems.

5. A pH of 6.5 to 7.0 is ideal for fish, and ours in 2003 was an average of 6.8. The average for the state is 6.6, so our lake’s pH is slightly better than average for fish in New Hampshire. In 2004, the Rt. 153 inlet had the lowest pH we have seen, with an average of 5.7. Since it drains a large wetland, it has a high concentration of tannic acid, which gives it the color of tea and reduces its pH. For comparison, its highest average pH was 6.2 in 2001, so clearly the pH range is limited and no problem is indicated.

6. The dissolved oxygen concentration was high at all depths sampled in the deep part of the lake, at about 90% saturation. A high oxygen level is a sign of the lake’s overall good health. While watercraft operating in the shallows can cause nutrient-loading problems, those same craft deserve some credit for mixing the deep waters and boosting the oxygen concentration when they are operated far from the shore.

THANK YOU NOTE: Steve Craig answered our call for a lake resident to take over responsibility for sampling and delivering the samples to Concord. He started last summer, in time to be trained by Dick Thomas, who has moved away. This year, Janet Murphy also volunteered, so we now have a team to sample together on weekdays and split the delivery duties. Thank you to both of you! I just received the Procedures Assessment done by the state biologist during the annual visit in June, and you both passed with flying colors. We can always use another volunteer, but our crisis has passed. Please contact me directly or via Steve, Janet, or any member of the PLA board if you are interested in helping out with sampling or deliveries. You may also use the general PLA e-mail address, info@ProvinceLake.org.

Respectfully submitted,

Norm Dudziak, P.E.