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Science Roundtable on Highland Lake Summary

posted May 14, 2018, 11:23 AM by Joseph Bickard   [ updated May 14, 2018, 11:24 AM ]

The following summary of the December 1, 2017 Science Roundtable on Highland Lake has been prepared for the board of directors of the Highland Lake Association. Highland Lake is an important resource to the region and well worth the stewardship required to protect it. This represents fulfillment of the first subtask under Task 1 of the proposal submitted by DK Water Resource Consulting LLC on November 1, 2017. Jeff Dennis prepared a summary of historic Highland Lake water quality dated September 20, 2017. Some of the information from that report is included by reference below but the bulk of the report is not repeated. That report should be consulted as background material that laid the groundwork for the Science Roundtable. This summary was presented to the Highland Lake Board of Directors on December 14, 2017.

In recent years, a small species of cyanobacteria (picocyanobacteria or PC) has been observed in Highland Lake. Over the past 4 years, the PC species has reached much higher densities than previously observed. From mid-July to mid-August of 2014 -2017, densities of the PC were sufficient to reduce water transparency from approximately 5 meters before and after this period to 2 meters during this period. Reports of lake users during this period suggest that the lake looks cloudy.This has been characterized as a bloom.The nature, origins and control of this bloomwas the focus of the Science Roundtable discussion.

The PC bloomhas been characterized as being comprised primarily of a single celled cyanobacteria of the genus Synechoccus. This is the only known bloomof this genus in New England although this genus is commonly present in lakes. Identification of the particular species or groups of species comprising the bloom will take additional analysis. DNA fingerprinting was discussed as possible cost effective way to identify the individual species. Bigelow labs has the capability to perform such fingerprinting. During the onset of the bloomboth chlorophyll a (a measure of the greenness of the water) and total phosphorus (the most critical nutrient in lakes) concentrations were relatively low perhaps suggesting that the PC were obtaining phosphorus from another source. The shallow sediments were suggested as a possibility.

The initial part of the science roundtable was focused on what information was known. This included the following:

  1. There is currently a very long and detailed water quality data set available for Highland Lake thanks to the volunteer monitoring team led by Keith Williams. This puts Highland Lake in strong position for identifying and characterizing changes in water quality.

  2. Work from Steve Norton of the University of Maine suggests that the deep sediments of highland Lake are currently not a large source of phosphorus due to the amount of aluminum in the soils in the Highland Lake watershed. Aluminum holds onto phosphorus and keeps it in the sediments even when oxygen is depleted in the overlying water (oxygen depletion in deep waters is observed in Highland Lake).

  3. Increased development pressure without aggressive phosphorus controls will add additional phosphorus to Highland Lake.

  4. The populations of adult and young alewives have increased in recent years due to the re-establishment of the natural run. Adult alewives live in the ocean and run into freshwater lakes and ponds to spawn in the spring to early summer. They then return to salt water over the summer. Young alewives hatch in the lake and grow to approximately 3 inches over the summer and then leave the lake for the ocean in the late summer or early fall.

Rosie Hartzler and Board of Directors December 17, 2017
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5. Highland Lake has experience warmer summers in recent years with a longer growing season.

The second part of the science roundtable identified important pieces of the story that are currently unknown and highlighted a number of questions to be answered. These included:

  1. Do the PC pick up phosphorus from the sediment surface and then transport this phosphorus up to the surface layers of the lake?

  2. Where are the PC in the water column? We know they are in the surface layers but are they in other layers as well?

  3. Do food chain effects make the bloom worse?

    1. Is zooplankton grazing on algae (and PC) reduced in the summer?

    2. Do alewives transport phosphorus to the lake, make phosphorus available through excretion, reduce zooplankton population?

    3. What is the role of other fish species in the lake on the “bloom?”

  4. Is warming making the “bloom” worse?

  5. Is the “bloom” toxic? If so, under what conditions is it toxic and what toxins are present?

  6. What is the species(s) responsible for the “bloom?”

  7. What is the current phosphorus budget for Highland Lake? Where is the phosphorus coming from currently and how is that likely to change in the future?

There was considerable discussion of possible scientific reasons for the PC bloomon Highland Lake. Many of these hypotheses need to be tested through specific testing and analysis in the coming months and years. It is likely that there are a number of contributing factors to the bloom.A combination of the factors will likely need to be addressed to reduce the bloom.

  1. The PC “bloom” is fueled by phosphorus wither from the water column, the sediments or both.

  2. Biological interactions in Highland Lake make the bloom worse or more persistent.

  3. Warming has made lake conditions more favorable for blooms.

The final portion of the science roundtable focused on what the next steps were and what needed to be done. These included:

  1. Fill gaps in the data that will help understand the factors contributing to the PC “bloom.” To that end, the science group should reconvene to set up monitoring priorities for 2018 and beyond.

  2. Control phosphorus. There are no future scenarios where additional phosphorus loading will make the situation better. A goal might be to keep in-lake phosphorus concentrations consistently below 10 ug/l. Reevaluation of the watershed planning efforts from the early 2000’s would be worthwhile to see what is working, what is not working and to inventory new potential sources that did not exist when the plan was developed.

  3. Evaluate alewife (and other fish species) impact further.

    1. This might include population estimates, timing of migrations and impacts on the zooplankton community. One of the tools that may be helpful is bioenergetics (already being used by University of Southern Maine to answer questions on Highland Lake)

    2. Evaluate data from other similar lakes to Highland lake both with and without alewife populations.

  4. Apply for grant funding to help pay for future efforts to understand and control the PC “bloom.” One potential source of funding is the Mitchell Center. It is highly recommended that the Highland Lake Association and collaborating researchers apply for funding this year.

Rosie Hartzler and Board of Directors December 17, 2017
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The level of concern and the talent of the board and committees of the Highland Lake Association is not common among lake associations. That coupled with the interest from the academic and regulatory community greatly increases the chances that the origins of this bloom will be determined and the lake association will be able to take the actions necessary to reduce or eliminate it. I applaud your continuing efforts. 

Highland Lake 2018 Monitoring Strategy

posted May 14, 2018, 11:06 AM by Joseph Bickard

Highland Lake 2018 Monitoring Strategy

This Strategy proposes a monitoring program that addresses some of the questions and hypotheses raised at the Highland Lake Science Roundtable and in subsequent discussion with various members of that group and incorporates strategies identified in those discussions.  Its principle objective is to collect data necessary to identify the reason(s) that Highland Lake, unique (as far as we know) among all lakes in New England and rare in North America, has from 2014 through 2017 supported epilimnetic blooms (< 2m SDT) of picocyanobacteria (Pcy), most likely of the genus Synechococcus.

Elements of the Strategy

1.     Pcy Bloom Toxicity.  Assess the potential toxicity of the Pcy bloom.

1.1.  Assess the level of microcystin and BMAA in the epilimnion immediately before, throughout, and after the bloom.  Rationale – It is essential to learn if the bloom is potentially toxic for obvious reasons.  Sampling throughout and after the bloom is necessary because toxins may be only produced and released during certain stages of the bloom.

2.     Basic Limnology.  Collect basic limnological data frequently throughout the open water season with particular emphasis on July and August.

2.1.  secchi disc transparency (SDT) (frequent).  Rationale – SDT indicates density and, potentially, location of epilimnetic biomass. 

2.2.  dissolved oxygen (DO)/temperature profiles (frequent).  Rationale – Temperature profiles define the density stratification within the lake, and therefore indicate potential, or lack thereof, for vertical mixing as well as the depth(s) at which detritus and plankton may concentrate.  In the thermocline and deeper waters DO concentration indicates suitability for various fish and invertebrate taxa as well as the relative balance of photosynthesis and respiration, and hence the abundance of live algae and respiring organisms (bacteria, detritus, zooplankton).  It also indicates, in part, when and where there is potential for release of iron bound phosphorus from the bottom sediments.

3.     Phosphorus and Chlorophyll Dynamics.  Assess how phosphorus, chlorophyll, phycocyanin and phycoerythrin are distributed vertically in the water column and how that distribution changes over time, especially before, during and after the bloom.

3.1.  Dense vertical profile sampling of total phosphorus at the deep hole and to a lesser degree at two shallower stations, with a concentration of sampling events in July and August.  Rationale – Nearly all the current phosphorus data on the lake are epilimnetic cores, with an occasional deep hypolimnetic sample.  This type of data does not support accurate estimations of the phosphorus mass in the lake or the distribution of that mass vertically and horizontally over time.  Phosphorus concentration at each discrete sampling depth can be multiplied by the volume of water in the lake at that depth to estimate the mass represented in that portion of the water column.  Understanding how and when phosphorus moves vertically within the water column, how the mass of phosphorus in the lake changes over time and how each of these relate to the onset and crash of the Pcy bloom is essential to evaluating the role of phosphorus in controlling and supporting the bloom.

3.2.  Epilimnetic core sampling for chla (both spectrophotometric and fluorometric), as well as discrete vertical profile samples measured fluorometrically for chla, phycocyanin and, if possible, phycoerythrin at the deep hole with a concentration of sampling events in July and August.  Rationale – These photosynthetic pigments indicate the amount of algal biomass in a sample, at least relative to other samples.  The relative abundance of the three pigments in a sample will inform understanding of the taxonomic composition of the algal community.  The core samples provide data that is comparable to previous years and also a calibration check of the fluorescence data.  The vertical profile fluorescence data will allow us to track movement of the algal community within the epilimnion and the metalimnion, which will inform our understanding of the effect of the Pcy on transparency, the relation of the Pcy bloom to phosphorus dynamics in the water column, and perhaps the source of the seed population for the Pcy bloom.

4.     Water Column Aluminum, Iron and P interactions.  Rule out the possibility that Al and/or Fe are involved with the accumulation of P in the epilimnion.

4.1.  Sample for total and dissolved Al, Fe and P at various depths in the epiliminion and metalimnion before during and after the Pcy bloom.  Rationale – Some of the phosphorus in the epilimnion may at times be complexed with aluminum and/or iron making it unavailable for algal production.  These data should indicate whether or not that is the case and further our understanding of phosphorus dynamics in the system.

5.     Pcy Taxonomy.  Characterize the taxonomic composition of the picocyanobacteria population before, during and after the bloom.

5.1.  Collect vertical profile samples for flow cytometry and cyano-specific DNA sequencing analyses to identify the specific taxa involved in the bloom.  Rationale – Though we are fairly sure the blooming Pcy genus is Synechococcus, we do not know the species or, more appropriately for Pcy, operational taxonomic unit (OTU) of Synechococcus associated with the bloom.  OTUs for Pcy cannot be determined morphologically and must be differentiated using genomic analysis.  Tracking the genomic signature of Pcy at various depths before, during and after the bloom may help understand the origins of the bloom (e.g. Do the blooming Pcy migrate from deeper waters into the epilimnion?  Are the blooming taxa the same as the taxa in the lake’s background Pcy population?).

6.     Trophic Web Interactions.  Assess interactions between various levels of the food chain before, during and after the bloom.

6.1.  eDNA sequencing on epilimnetic and metalimnetic composite samples and zooplankton analyses of vertical net haul samples before, during and after the bloom.  Rationale – The change over time in DNA signals for various compartments of the smaller organism food web and the change over time in the abundance of different compartments of the larger zooplankton community will help identify any trophic cascade effects within the plankton community.

6.2.  Check for multiyear correlation between large zooplankton density and onset of Pcy bloom.  Use 2016 and 2017 data if sampling frequency from those years is adequate.  Rationale – If, over a period of several years, there is a strong correlation between the timing of the loss of large zooplankton and the onset of the bloom it is circumstantial evidence of an alewife driven trophic cascade resulting in the bloom.  If there is no correlation, i.e. if they occur at different times, a cascade resulting from alewife predation is unlikely.  

7.     Alewife Migration.  Estimate the magnitude and timing of adult alewife migration into the lake.

7.1.  Count alewives hourly during the spawning run.  Rationale – It is important to understand how the size and timing of the alewife run affects the size and growth of the YOY alewife population and, indirectly, the impact on the trophic web.

8.     Young of the Year (YOY) Alewife Growth and Population Dynamics.  Describe, to the extent feasible, the changes in the juvenile alewife population over the summer. 

8.1.  Monitor the growth, diet and abundance/biomass of the YOY alewife population over the course of the summer using purse and beach seines; analysis of stomach contents; and stable isotope analyses to assess spatial and temporal variation in feeding strategies.  Rationale – Understanding the timing of population and individual growth, the changes in prey taxa over time and the migration from different lake habitats will help identify and characterize the relationships of the alewife population with changes in other compartments of the trophic web.

9.     Shallow Sediment Studies.  Assess the potential for phosphorus release from metalimnetic sediments.

9.1.  Measure the aluminum, iron and phosphorus content in the surficial sediments in contact with the mid and late summer metalimnion (6-7m).  Rationale – We know that phosphorus release from deep water sediments is minimal because of relatively high Al:Fe ratios and because of low hypolimnetic phosphorus concentrations.  There is a mid to late summer metalimnetic depression of dissolved oxygen that could create conditions that would allow release of P from these sediments if the AL:Fe ratio was lower than in the deep hole.  We currently do not have sediment chemistry for metalimnetic sediments nor do we have many phosphorus data points in the metalimnion, so we cannot rule out release from these sediments as a significant phosphorus source during the bloom without sediment chemistry data.

10.  Bathymetry.  Create a better bathymetric map of the lake in order to accurately track changes in phosphorus mass over time.

10.1.               Collect a dense array of depth measurement throughout the lake using LEA’s GPS fathometer rig.  Convert it into an accurate contour map of the bottom and create an accurate hypsometric curve for the lake.  Rationale – High resolution bathymetry is required to use phosphorus profile data to accurately estimate the mass of phosphorus in the lake and in various compartments of the lake, and to track changes in these over time.



·      Project Oversight and Coordination?

o   USM – oversees intern(s), field prep, sampling, sample distribution to partners

o   DEP – oversees training, sediment coring, some sample analysis

o   HLA – coordinates water monitoring volunteers, boat storage, etc 

·      Monitoring Teams

o   Water Quality Team.  2 to 3 person team (trained intern(s) and HLA volunteer(s))

o   Alewife Pelagic Team. 3 person, USM

o   Alewife Littoral Team. 3 person, USM

o   Sediment Coring Team.  2 person, DEP or DEP and intern

o   Bathymetry Team.  2 person?, HLA


Equipment and Supplies

·      Boats

o   HLA’s sampling boat

o   USM (Karen & Theo)’s 16’ – could be kept on the lake; appropriate for fish work. Need easy night-time access.

·      Sampling equipment

o   Kemmerer bottles/van Dorn bottles (discrete depth grabs) (HLA, USM)

o   Coring tube and/or pump to collect integrated water column samples

o   Basic profiling equipment (HLA): Temp/DO meter, secchi

o   Filtering apparatus (USM)

o   Fish-catching gear (USM)

o   Zooplankton net – 50 u mesh?

·      Expendable supplies

o   (reusable) Water Sample bottles for P, Fe, Al, Chlorophyll, flow-cytometry – USM has 250 ml and 1 liter bottles IF the majority can be returned. Might need to order more (250 ml?) bottles depending on turnover with lab analyses.

o   HCl and P-free soap for preparing sample bottles (USM)

o   Filters for chlorophyll analyses – need to be purchased. (~$100)

o   Zooplankton preservatives (~$100 to USM to replenish stocks)

o   Vials for eDNA samples



·      Weekly communications between HLA, USM, DEP, others

o   Plan B for sampling that might change due to late spring, large storms, etc.

·      Staging and Sample Processing Space

o   USM

o   Somewhere on the shores of Highland Lake

·      Sample Transport to Labs

UNH, Bigelow, where else?


Appendix A.  Draft 2018 Sampling Schedule

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