Experiment regulation growth of nuisance watervegitation
Research project on the effects on aquatic plantgrowth by coverage of the bottom with gravel and tentcarpet
(Gerard Scheiberlich, publicationdate april 30th2011 with thanks to Roelf Pot for feedback)
In the recreational lake De Langspier an experiment has been constructed
Regularly we recieve requests from scubadivers for an update on the status of the experiment. It is not possible to allow divers acces to the researchsite because the finmovements would disturb the sedimentation measurements and growing vegetation. Therefore we urgently request everyone to substain form diving at or neat the researchsite. In order to inform all who are interested we will publish every month our progress on this website in words and images.
Introduction
The Langspier is an isolated lake between Boxtel and Esch. It’s originated from the excavation of sand for road contruction in the eighties of the twentieth century. The orientation of the lake is from NW to SE. The maximum length is 710 metres, the maximum width is 256 metres. The maximum depth is estimated at 24 metres. The bottom of the lake consist of loamsoil and sand. The waterinflux comes from rain and groundwater. When the waterlevel excedes 8 metres above NAP there will be an outflux at the NW-side. In summer the lake is clear en has been known for an abundant macrofytic growth which is domanatied by Mycrofyllum specatum, Elodea, and Pondweeds (Potamogeton spp). The deeper waterlayers are dominated by Charophytes. At the southside the lakebank is lined with reeds. The fishpopulation is a pike, perch, roach type.
The issue of aquatic nuisance vegitation
The lake is known to suffer from a nuisance vegitation as a result of clear water, ample supply of nutritients, warm watertemperatures and a vast area of shallow bottomspace. The plantgrowth hinders the bathing guests in play and swimming because it feels unpleasant and restricts movements.
Some years ago on advice of a consultant the bottom top layer in the swimming aria was replaced by beachsand. The idea was that the sand was very low on nutritients which would inhibit plantgrowth. This happened indeed for thefollowingt two years. In the following years gradually the growth augmented till a nuisance level. In the last two years as a measure for plantreduction the swimming zone is manually cleaned in spring by scubadivers. This regulates the growth to some extend but in 2010 the conclusion was that for an acceptable level the frequency should be twice a year.
Moreover the lake has been known to produce cercarien which causes swimmers-itch. The owner of the lake sees in the nuisance growth a increased risk because the plants provide shelter and food for snails which are the host of the parasites. The research question is how to significantly reduce the nuisance gowth in the swimming zone in a sustainable, natural and save way.
The research experiment in Lake Langspier
In order be able to grow aquatic plants need light and nutritients. Rooted plants also need an suitable bottom. To limit the growth of aquaticplants these three factors can be manipulated. In an experiment in Lake Langspier two intervention methods are beiing tested, namely:
1 : Limitation of light at the waterbottom and prevention of rooting by coverage of the bottom with large gravel. In the past there have been several large-scale experiments with gravel which showed that after several years the gravel cover was saturated by sedementation. This top layer created an new adequate substrate for macrofytes to root on.The nature of the gravel and the covered bottom however was not descibed.
[Engel, S., Nichols, S.A. (1984) Lake sediment
alteration for macrophyte control. J. Aquatic Plant management 22; 38-41]
In order to be able to make a prediction for sedimentation the rate of sedimentation is measured in the experiment.
2 : Limitation of light at the waterbottom by coverage with tentcarpet (fine-mazed soft plastic fabric). In Ireland succes has been achieved by using jute matting to limit lightfall on the lake bottom to control invading exotic macrofytes.
[Caffrey, J., Millane, M., Evers, S., Moran, H., Butler, M.(2010) A novel approach to aquatic
weed control and habitat restoration using biodegradable jute matting. Aquatic Invasions Volume 5,
issue 2: 123-129]
In these Irish experiments the jute matting is biodegradable and can therefore only be used once. In the Langspier experiment a non-degradable matting is used with lightreducing properties. In this way the conversion of the matting to nutrients is avoided and the application of the matting becomes controllable in time.
Research area’s on the lake bottom
To compare systematically the efects of the two methods a research area has been established on the bottom of the lake from a depth of 1,4 metres tot 2 metres. See for the detailled description the schedule below. The gravel covered areas are lined with bricks.
The measurements
During six monthes a trained team of volunteer divers will measure the macrofyte growth in quality and quantity. For systematic measuring a grid is made which devides a testarea in square metres. The grid is moved over the diferent testareas during a measurementsession. We also will measure the rate of sedimentation.
The progress of the experiment
Regularly we recieve requests from scubadivers for an update on the status of the experiment. It is not possible to allow divers acces to the researchsite because the finmovements would disturb the sedimentation measurements and growing vegetation. Therefore we urgently request everyone to substain form diving at or neat the researchsite. In order to inform all who are interested we will publish every month our progress on this website in words and images.
April 30th, 2011
In the month april ten volunteers and I have build the testareas. On land working with gravel is hard work. Under water is is not only heavy but also complicated. How do you transport gravel under the water surface? How do you spread gravel evenly over the area? How can you avoid zero visability while using gravel in water? How do get a floatable tentmat tightly placed on the research area? These are examples of questions we had to find anwers for.
An impression of the construction you’ll find in this video.
June 9th 2011
The first month of measuring plantgrowth has passed. Three observators, a cameraman and myself have trained ourselves in the research protocol.
The temperature in shallow areas of the lake has risen quickly and is now higher then 20 degrees Celcius. The visability is farther than 5 metres. The waterplants in the control areas thrive abundantly. In the areas bare and bare+gravel there is little growth. The area where the gravel is directly placed on the existing macrofyte growth shows that plantstems not completely covered sprout. The same goes for the plantstems which poke through the small mazes of the tentmat. Apart from the measurement we expericience the seasonal devellopment of the local ecosystem in our long three hour dives. Early May the algeadevelopment was clearly succeded by Daphnias. Some weeks later the tadpooles apeared an two weeks afterwards large schools of small fish emerged. There are clearly 3 zones of different macrofyte growth in the lake. The swimming zone is dominated with Mycrophillium. In front of the reed Elodea is the abundant species and the side of the underwater statue garden and nudist beach is densely grown with Potamogeton. An impression of measuring the growth and the state of the research areas you’ll find in the following video.
Juli 5th 2011
After the fifth measurementsession a number of trends become visible. First the control areas are densly grown. In two months the macrofytecoverage and heigth roughly doubled. Mainly by Macrophillium with some undergrowth of Elodea and Potamogeton. The area “Bare” has grown from 1 to 10% coverage. The areas Bare+Gravel an Plant+Mat are evenly grown for 2-3% coverage.
The areas Plant+Gravel is covered for more than 20%. Apparently the gravel on existing vegitation limits the growth to some extend but not at the level we’re aiming for.
The matting+plants and the gravel on bare bottom look quite well. In the middle of june we’ve lifted a corner of the matting to see what was happening below. The original vegetation had mainly disappeared. There were however some small Elodea sprouts.
As the mat, in contras to the gravel, is a temperarely instrument we alter the experiment in August. In consultation with Roelf Pot we’ve decided to lift the matting and place it on one of the densly grown control areas. Thus we get an impression what the effect of the mat will be on a large plantmass. Soon a third vdeo will be published on this site showing the sedimentmaesurement.
The measurementresults of the first two months show a sedimentationrate of 0,0102 ml/cm2/day.
15 augustus 2011
The experiment has been modified. On account of the results we've lifted the matting to see the effects and to follow how the plantgrowth will develop without the matting. The removed matting is placed over the plants in left controlarea where the plants are nearly two metres high.
On the area from which the matting is removed it is clearly shown that a lot of marcofyte tissue has died because of anaerobic conditions. There is a black ash-like layer on the sandbottom. There are black and brown plantroots and stems of Myriophyllum spicatum remaining with often a small piece of green which has grown through the matting.
On the right controlarea a fixed rope raster is placed because the transportable raster couldn't be placed over the high and dense plantgrowth.
Finally we were able to determine de green gelatic balls on the bottom of the testareas (and other parts of the lake). Ronald Bijkerk ((Bureau Koeman en Bijkerk B.V, ecologisch onderzoek en advies) was able to name the organisms with microscopy. They're a colony-forming ciliate Ophrydium versatile (Müller 1786) Ehrenberg 1830. The green discs in the organisms are endosymbiotc greenalgeae.
A photo of the local population.
Next publication date : 1 september 2011