1. CULVER LAKE 2016 Executive Summary of Lake Monitoring Program Observations
Executive Summary – Culver Lake Monitoring Program 2016
Prepared for: Normanoch Association
Prepared by: Robert (Bob) Kortmann, Ph.D.
February 15, 2017

2. CULVER 2016-PROFILE DATA
Thermal Stratification persisted past Sept 23, 2016
Thermal Stratification had set up by April 24, 2016
Weather was very mild during the winter of The growing season, diatom maximum, and stratification began earlier than typical in many lakes and reservoirs in the northeastern US. An examination of agricultural “Growing Degree Days” suggests that Spring-Summer started approximately a month early, and extended through October. The early Diatom Maximum and extended summer stratification resulted in significant Cyanobacteria densities during late August and September in many Lakes, Culver included.

3. CULVER 2016-PROFILE DATA
The % Saturation of dissolved oxygen in surface water (% of saturation with the atmospheric composition) is an indication of the intensity of photosynthetic activity. In lakes with intense photosynthesis (Blooms) % saturation becomes very high due to production of oxygen during photosynthesis. % DO saturation was only slightly above 100% through the summer at Culver Lake (maximum of 114 %). The surface trophogenic zone did not exhibit intense photosynthesis.

4. CULVER 2016-PROFILE DATA
Over bottom (OB) dissolved oxygen exhibited a steady decline between May and June. Deep dissolved oxygen stabilized at just over 1 mg/L for the rest of the summer. Over bottom temperature increased very gradually from May to September.

5. CULVER 2016-PROFILE DATA
The metalimnion (thermocline zone) was stable between 4-7 m deep
Although stratification began in April, several deep mixing episodes occurred; more stable stratification began in late May and persisted through early October.
Although persistent thermal stratification began in April 2016, several deep mixing episodes occurred in May. Stable and persistent stratification developed in June and lasted into October.

6. CULVER 2016-PROFILE DATA
Culver Lake exhibited early stratification (April), strong stratification through the summer (400 RTRM Units), and a strong thermocline (150 RTRM Units).
Total surface-to-bottom RTRM varied between units June-August. RTRMMax was between units (a strong thermocline).

7. CULVER 2016-PROFILE DATA
Secchi disk transparency steadily increased between March 31 and June 15. The Diatom peak probably occurred before sampling began. Following the “clear water phase” transparency decreased very gradually to a low of 3.9 ft the end of August.
Secchi transparency increased to a maximum of 10ft in June, then gradually decreased to a low of 3.9 ft in the end of August.

8. CULVER 2015-CHEMISTRY RESULTS
Surface water Total Phosphorus varied between 19 and 27 µg/L. Deep over-bottom TP remained relatively low until a modest increase in late August (maximum of 248 µg/L). The relatively low over-bottom TP was likely due to oxygen input by the hypolimnetic and layer aerators, and the availability of oxidized iron in surface sediments.
Ammonia-N also remained relatively low in the deep layer, likely due to nitrification to nitrate-N because of oxygen input from aeration.

9. CULVER 2016-CHEMISTRY RESULTS
Concentrations of iron in over-bottom water remained low, likely due to maintaining an aerobic sediment-water interface by aeration. Reducing airflow to the hypolimnetic aerator during late August could mobilize more iron for removal of P from the water column. However, operations during 2016 maintained higher oxygen input from the hypolimnetic aerator and kept iron and sediment-bound P in the sediments. That is probably the preferred operating procedure for a rainfall deficit and extended stratification year.
Silica availability was very low from May through July, and probably limited Diatom growth.

10. Cyanobacteria genera present
CULVER 2016 – ALGAE RESULTS
May 18th:
Aphanizomenon spp.
Gomphosphaeria spp.
June 16th:
July 20th:
Chroococcus spp.
Anabaena spp.
Aphanocapsa spp.
Lyngbya spp.
August 24th:
Microcystis spp.
Microcystis aeruginosa
September 23rd:
Cyanobacteria genera present
BOLD=over 3,000 cells/mL
Cyanobacteria were strongly dominant over the phytoplankton community from May through September. It is likely that the Diatom peak, crash, and “clear water phase” occurred before the May sampling (winter was very mild, Spring growing season started very early).
Although Cyanobacteria peaked in late August cell densities remained below 50,000/ml (below what is considered a “risk of cyanotoxins”). It would be prudent to add some cyanotoxin testing during late summer, perhaps using a “Secchi disk trigger” (less than 5 ft).
Cyanobacteria were strongly dominant over the phytoplankton community from May through September. It is likely that the Diatom peak, crash, and “clear water phase” occurred before the May sampling (winter was very mild, Spring growing season started very early).

11. CULVER 2016 – ALGAE RESULTS
Diatoms were scarce between May and September (likely due to silica limitation). Diatoms may have bloomed earlier in the Spring (early growing season onset in 2016).
Diatoms were scarce between May and September (likely due to silica limitation). Diatoms may have bloomed earlier in the Spring (early growing season onset in 2016).

12. CULVER 2016 - ZOOPLANKTON RESULTS
Although small-bodied cladocera and copepods were most abundant, it was very encouraging that Large-bodied zooplankton were persistent and reached a maximum density of over 7 animals per liter.
Large copepods and Cladocera were much more abundant than observed during most years at Culver Lake.

13. Aphanizomenon spp.
Lyngyba spp.
Gomphosphaeria spp.
Anabena spp.
Aphanizomenon spp.
Cyanobacteria densities during 2016, and recent years, remained lower than during Winter weather conditions tend to “set the stage” for whether Cyanobacteria peaks are high the following summer. Following very mild winters cyanobacteria peaks appear to be higher (2012, and 2016). We are also observing Cyanobacteria genera that tend to be more typical of lakes further south (e.g. Lyngbya sp.). Continuing to monitor lake conditions and Cyanobacteria will be important for responding to very variable seasonal conditions (especially winter).

14. Additional Data and Information, weather/climate patterns, etc.

15. Watch: Average Temperature January-March
Climate Change?
What should we watch to anticipate water quality in the Summer and Fall?
“Over the past decade, Winters have become more variable, severe or mild. Lakes and reservoirs of the Northeast are behaving more like the monomictic lakes and reservoirs further south (e.g. Carolinas) following mild winters with little or no ice-cover. How a reservoir or lake responds to the changing winter conditions depends on the nature of the specific lake-watershed ecosystem.”
Watch:
Average Temperature January-March
Date of Ice-Out (If Ice-Cover Developed)
Growing Degree Days (GDD) March 1, 15 and April 1, 15.
Then May - November
Development and Timing of Thermal Stratification
Timing and Duration of the “Clear Water Phase” after Diatoms
Timing, Extent, and Duration of Anoxia.
Monthly Rainfall, Leaf Fall and First Rainfall after Leaf Fall

16. Winters have been Variable*
* Through November 8
Ireen August 30
Halloween Snow
School Roof Snow
January 2017 was the warmest on record in CT, again.
Sandy Out 29
Rainfall Deficit,
Very Low Reservoir Levels

17. Most rainfall events are less than ½ inch
Most rainfall events are less than ½ inch. The initial runoff contains the highest contaminant loads (first flush). Managing the first half inch of watershed runoff can reduce reservoir nutrient and contaminant loads.

18. 10% Difference
Growing Degree Days (GDD) For most plants, phenological development is strongly related to the accumulation of heat or temperature units above a threshold or base temperature below which little growth occurs.

19. Following Severe Winter
Following Mild Winter
Following Mild Winter
Following Severe Winter
Growing Degree Days (GDD) For most plants, phenological development is strongly related to the accumulation of heat or temperature units above a threshold or base temperature below which little growth occurs.

20. 2011-12 and 2015-16 were Very Mild Winters
2016 Began even warmer than 2012
Late Spring Cold Dampened the Impact
(Recall the Apple Blossom Kill in April 2016)

21. Layer or Hypo Aeration
500 GDD
An April Cold Spell brought 2016 closer to normal by May 15 (killing apple blossoms)
In 2012 and Growing Degree Days were a Full Month Ahead on April 1
Iceout
10 GDD
Activate Circulation
75 GDD

22. Bluegreen Cyanobacteria
(See: Kortmann, 2015)
Bluegreen Cyanobacteria
Akinetes begin to germinate
Diatoms crash
when Silica < 0.5mg/L or when Temp > 15 Co
When the Growing Season begins early there is a shift in seasonal phytoplankton succession.
1 Month
With an Early Growing Season Start:
Diatoms Crash early, Cyanobacteria have more time to grow.
Thermal Stratification is prolonged, longer duration of deep anoxia, more internal loading of ATEAs and Nutrients.

23. Phytoplankton = Eukaryotic Algae and Cyanobacteria
Potential Management Approaches:
Activate Circulation and Hypolimnetic/Layer Aeration Systems by “Target Degree Days”
Spring Diatom productivity can be enhanced and prolonged by artificial circulation and maintaining silica availability
When the Growing Season begins early there is a shift in seasonal phytoplankton succession

24. Large and Deep Reservoirs and Lakes:
Climate Change?
Are Reservoir Conditions Changing and
What Might It Mean to Water Quality Management
“Over the past decade, Winters have become more variable, severe or mild. Lakes and reservoirs of the Northeast are behaving more like the monomictic lakes and reservoirs further south (e.g. Carolinas) following mild winters with little or no ice-cover. How a reservoir or lake responds to the changing winter conditions depends on the nature of the specific lake-watershed ecosystem.”
Generalizations:
Large and Deep Reservoirs and Lakes:
Early and Extended Duration of thermal stratification results in more deep anaerobic respiration
Higher concentrations of Anaerobic Respiration Products (Fe, Mn, Sulfide)
More Internal Nutrient Loading (P, N)
Early Phytoplankton Succession from Diatoms to Greens to Cyanobacteria
More time for development of Phytoplanktonic Cyanobacteria Blooms
More Cyanobacteria akinetes deposited for subsequent years
Smaller Reservoirs and Lakes with a Large Bottom Area within the Trophogenic Zone:
Early growth of Littoral Macrophytes (“weeds”) and Benthic Cyanobacteria
In reservoirs, water level fluctuation often limits rooted vegetation; favors benthic algae

25. 2017…so far.
Winter began as a typical winter, with cold temperatures in December and early ice-cover.
Then came a January Thaw that lasted all month. In many Connecticut Lakes ice-out occurred on about 1/20/ To be seen if ice-cover returns at all in February, but it will not be a continuous ice-cover winter.
The Spring Diatom Peak is likely to be early. Enhancing Spring Diatoms by artificial circulation can reduce Cyanobacteria later in the Summer.
Watch the progression of Growing Degree Days beginning March 1, 2017 to anticipate what Summer might have in store for your Reservoir or Lake.

26. CULVER 2016-OPTICAL SUITE RESULTS
Fluorometry
CULVER 2016-OPTICAL SUITE RESULTS