Below is a brief update from Dr. Ken Wagner, the consultant for the Mystic Lake Alum Treatment. Ken will be the invited speaker at the IPA annual meeting on July 17.
Bob Nichols and I took a few samples Monday (5/23) afternoon at Mystic Lake and performed some assessment tasks. The next full sampling is scheduled for late June, but the opportunity for an intermediate assessment presented itself. Water clarity averaged 6 meters. Bob has gotten even higher readings lately, which is encouraging. Oxygen was depleted at the deepest area (ML-3) at 14 m depth, but was still high at 10 m there and in other areas of the lake. The alkalinity in deep water was much lower (15 mg/L) than last year (40-70 mg/L), but was similar to past measurements at the surface (12 mg/L). The lake is not really stratified yet, but the oxygen demand in that one deep hole remains substantial, and water from the bottom in that area turned orange 30 minutes after sampling, indicating high dissolved iron. It is expected that the phosphorus will not be high, as it should now be bound on aluminum, not iron, but we have to wait for the lab results to be sure. Samples from the top at ML-1 (north end, relatively shallow) and top and bottom of ML-2 and ML-3 were collected and delivered to the lab for testing of phosphorus and nitrogen. The pH is near neutral, conductivity is around 80-90 uS/cm, and turbidity is <2 NTU. There is no apparent sign of the alum treatment when viewing the sediment in treatment areas.
Zooplankton were abundant, including large bodied Daphnia, as was the case this winter. This population is usually decimated by early summer with the hatch of the annual alewife young. However, Annette Nichols has participated in the annual assessment of herring running in local streams, and reports the lowest count yet for the stream leading to Middle Pond and Mystic Lake; so we will see just how many alewife young there are this year, as reflected in the zooplankton. Planktonic algae appeared to be mainly diatoms, and I took samples, but have not yet looked at them. Filamentous green algae, most likely Spirogyra, was observed growing profusely on shallow sand and gravel, mainly along the west shore. This may be an indication of wastewater influence, but is not uncommon in Cape lakes at this time of year.
Benthic mats for hydrilla control remain in place. No hydrilla was observed, but it is still early in the growing season and we did not hunt specifically for plants. The mats will be removed in June and any germination of hydrilla from tubers will be monitored, with replacement of barriers as warranted.
Ken Wagner
Water Resource Services