2018 Bi-Weekly Water Quality Testing Reports

Highland Lake Data - June 4 and June 11

posted Jun 23, 2018, 6:10 PM by Joseph Bickard [ updated Jun 23, 2018, 6:11 PM ]

Highland Lake is currently experiencing what is called the "clear water phase". The clear water phase happens in most northern lakes, and is characterized by good water clarity, and high populations of Daphnia and other zooplankton who are eating phytoplankton as soon as it appears. However, soon those zooplankton numbers will start to decline, because (1) they start to run out of food - essentially they've become so abundant the phytoplankton production can't keep up, and (2) larval fish get large enough to eat them. These are larval fish of all species - yellow perch, white perch, smelt, bass, sunfish, alewife, you name it.

On June 5th the water quality samplers were on the lake gathering basic water quality data (temperature and dissolved oxygen profiles, secchi depth (a measure of water clarity), and water grabs for nutrients). The secchi depth (a measure of water clarity) was 7 m - excellent! The temperature and dissolved oxygen profiles looked very similar to the previous sampling date (May 23rd).

This summer the water quality team is using a 45 micron mesh filter to capture algae in the water column for analysis- those are very small holes. So even with the small amounts of material in the very clear lake water, filtering still took hours.

During the week of June 11th, we were practicing our fish-sampling techniques, and looking for larval fish. We practiced using our larger purse-seine, but ended up using a larval fish net that we towed in transects across the lake at about a meter depth. We did catch some larval fish (unidentified as of this writing, but probably not alewife, yet), and clogged the net up with zooplankton - Daphnia! Thus far the larval fish are too small to eat the Daphnia, but soon all manner of larval fish will grow large enough to eat the Daphnia. The larval fish in the photo is approximately 13 mm in length. Mos tof our fish sampling will occur in the evening and early night because larval fish spread out in the dark to feed when they are less likely to be eaten by other fish.

Finally, lake sampling can be unpredictable - we enjoyed the region’s first rain for a couple of weeks while sorting through the Daphnia for tiny larval fish:

Highland Lake Data – Tuesday, May 23, 2018

posted Jun 11, 2018, 1:01 PM by Joseph Bickard [ updated Jun 11, 2018, 1:05 PM ]

Surveyors: Karen Wilson, Emma Dennison, Ericka Hutchinson

The survey crew did our first sampling on May 23^rd- a beautiful day to be on the lake. We measured temperature and dissolved oxygen from the top on the lake to the bottom of the lake to characterize the lake environment. We then took water samples to measure nutrients and chlorophyll-a from almost every meter in depth. We also captured a sample of zooplankton.

Chlorophyll-a is a pigment found in algae cells, so we use the amount of chlorophyll-a as a proxy measure of the amount of algae in the lake (a much more difficult thing to measure because the algae are so small). By the way, you might also hear us refer to “Phytoplankton” – the name means “plants that float around” – these plants are the tiny algae that we measure indirectly using the chlorophyll-a amount. Often when there are many algae in the water the water may appear green and the water clarity drops (an algal bloom!).

This year the alewife run started on May 24th – later than most runs in the region because the fish migrate upstream cue on temperature – and the Presumpscot River, originating in Lake Sebago, is colder than most. Fish are still continuing to come in to spawn, but we’ve also started to see some spawners heading back out to sea. To date (7 June), 8559 fish have been counted directly. We will use a statistical method to calculate the total number of fish at the end of the run.

Temperature and Dissolved Oxygen Profile

What does this graph mean?

The x-axis shows the depth where dissolved oxygen (DO) and temperature were measured starting from the surface (0 m) and dropping to the bottom of Highland Lake (18 m). DO remained relatively stable as depth increased.

In contrast, temperature at the surface of the water was 20.1°C and slowly dropped to 17.7°C at 4 m (see figure). From 4 to 8 meters the temperature dropped rapidly, marking the thermocline, and the transition to the colder hypolimnion. The difference in temperature between the top (epilimnion) and bottom (hypolimnion) sections of the lake will increase as the summer continues.

Fish and Zooplankton Things!

On May 23^rd there were copious amounts of Daphnia and Bosmina in our zooplankton tows, with several other species of rotifers, calanoids, and cyclopoids. These preliminary results show very similar trends to zooplankton samples from Highland Lake in previous years. We are interested in these organisms because many consume algae as their primary food source. Most Daphnia had ephippia in the back of their carapaces - ephippia are hard “resting eggs” that Daphnia produce when their population numbers are high and food is getting scarce. The ephippia will sink to the lake sediments, and hatch only when the right cues happen (temperature often). The photo shows a Daphnia from Highland with the ephippia (white, two black spots) behind (to the right) of it’s question-mark gut. You can see the swimming arms on the left, the eye spot in the upper left.

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