On september 14th we’ve collected two PVC SETL plates which were on location for 4 months.
The idea is to see what grows on it over time.
These plates hang at a depth of 1 meter and are a mere 2 meters apart from each other.
The difference between the two is astonishing. The only major difference between the two is the weightbricks, which are placed at the top of the plate. These bricks are made from different material and have a different structure.
This might be of influence.
|Brick and plate.
2013 was the first trial year in which the the watermix system was not in operation. This was to see if the lake could be free of cyanobacteria on it’s own.
Thankfully bacterialevels never reached critical levels.
Watersurface temperatures of +21 celsius started at first week of july 2013 and reached a peak of 25 celsius end of july.
2014 Second trial year of the watermix system remaining inoperative.
Watersurface temperatures of +21 celsius started at first week of june 2014.
That is one month sooner than in 2013, meaning one month of extra light exposure for algea and bacteria.
The temperature peak is exactly the same for 2013 as for 2014 being end of july.
Cyanobacteria and other bacteria levels had reached a point of becoming a health hazard as this lake is used for swimming and diving.
Therefore the waterboard decided to activate the watermixing system at the beginning of august 2014 to fight cyanobacteria.
Now conditions were already very variable for some values at the watersurface.
Watermixer started in weeknr 31 and the waterchemical jolt begins See graphs
From week 30-31
Surface temperature went from 25 to 22 celsius.
but also temperatures upto a depth 15 meters were were mixed.
PH dropped from 8.7 to 8.3
Dissolved Oxygen went from 5.5 to 4.5 mg/l.
CO2 was already going ballistic even before the watermixer was started.
From week 33 until now the lake is trying to stabelize.
Question is if this too has had an effect on the plates.
Well the permanent plates also show differences eventhough they are of a different scale
These hang since last quarter of 2012.
Photostrips showing the developments of both SETL plates starting june 15th until sept 14th.
The idea is to see if there’s a change in percentages of D.polymorpha and D.bugensis rostriformis.
Well I did musselcounts on both plates to see the how many mussels are on a surface of 14×14 cm and what kind of mussels they were including the size.
I’ve used a sizescale of 0-5 mm / 6-10 mm / >10 mm.
Each mussel in the 0-3 mm range is hard to determine which species it exactly is, so I’d left them out to calculate the percentage of Dreissena polymorpha and
Dreissena bugensis rostriformis. A size of 4-5 mm were large enough to determine the types.
After removing a quarter of mussels from H135 there were freshwater sponges underneath.
Bryozoans (Crystatella) abundant at H135 as you can see in the photostrip, but there was only one colony-string left, when the plates were taken out of the water.
That died very fast after a day in the container.
H128 housed two chironomid type larvea.
The photo’s below show the endresults
A total of 526 mussels passed through my fingers grouping them in size and type.
Of H135 I had counted a quarter plate to spare time.
H128 had larger mussels in the range of 4-5 mm which were easier to determine on species. I did take out one smashed mussel of H128 which is still on the photo below.
|H128 D.bugensis rostriformis bottomleft 6-10 mm.
D.bugensis rostriformis topleft 4-5 mm.
D.species middle 0-5 mm
D.polymorpha bottomright >10 mm
D.polymorpha middleright 6-10mm
D.polymorpha utterright 4-5mm
Two chironomid larvea.
|H135 quarter dismantled
|H135 D.polymorpha = left 6-10 mm
D. bugensis rostriformis = middletop >10mm and right 6-10 mm
|H135 D.polymorpha = left >10 mm.
Dreissena species right 0-5 mm
H128 counted 121 mussels on the entire plate
H135 counted 405 mussels on a quarterplate. The total number approximately would be 1600.
These results are totally inconclusive. The conditions in 2014 were too variable to hold it against 2013. Anyway the developments on the plates are spectacular and that is pretty special for a freshwater lake.
Maybe these insignificant results can be of significance, later on in the project.