RAUK - Archived Forum - hornwort vs Can. pondweed

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hornwort vs Can. pondweed:

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ben rigsby
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Joined: 27 Apr 2010
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Posted: 10 Jun 2010
hi folks,

yes its me YET AGAIN.
youre fully entitled to groan but hey, you cant knock my enthusiasm.

this time to ask;

is our native HORNWORT (ceratophyllum demersum) as good an oxygenator as CANADIAN PONDWEED (elodea cadensis)?


got a bit of both flora at the mo but considering going "alien-free" in the autumn.
is it a good idea?


opinions/advice welcome.

thanks, ben
Diversity.
David Bird
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Joined: 17 Feb 2003
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Posted: 10 Jun 2010
I do not think the term "Oxygenator" is that useful, all plants produce Oxygen by photosynthesis when they are in sunlight and very few bodies of natural water are deficient in oxygen unless there is a lot of decomposition going on in the water and a masss of bacteria using up the oxygen or some chemical pollution. A very dense mass of Elodea would probably have the bottom leaves in the dark and respiring (remove oxygen) more than they can photosynthesise (produce oxygen). Plants under a thick layer of duckweed would also be in the same situation.
Hornwort is often said to be a more useful plant as it does not have roots and absorbtion of nutrients from the water takes place over the whole surface area of the plant, this is better in ponds that are well stocked with animals to stop the nutrient levels building up and algal blooms occuring in the spring and summer causing green or brownish water. The removal of about1/3rd of the aquatic plant in mid to late summer, after carefully washing in the pond to put back the invertebrates and tadpoles into the water and composting the plant is a good way of removing the nutients from your pond which would build up and possibly cause problems.
British Herpetological Society Librarian and member of B.H.S Conservation Committee. Self employed Herpetological Consultant and Field Worker.
Caleb
Forum Coordinator
Joined: 17 Feb 2003
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Posted: 10 Jun 2010
No idea, but you could do a kitchen-table experiment to measure it- have a look at this:

How to Measure Oxygen From Aquatic Plants

If you're more ambitious, you could rig up a 'pneumatic trough' to collect the oxygen over a period of time, and compare the amounts:


ben rigsby
Senior Member
Joined: 27 Apr 2010
No. of posts: 337


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Posted: 11 Jun 2010
thanks for your info and TIME with that chaps.
im still weighing up.
it would be nice to have a pond of only native flora but perhaps like davew has said elsewhere, maybe thats just vanity on my part.
it could be a case of not-broke-dont-fix-it.
plenty of amphibians about presently.

if i try to eradicate elodea in mid to late summer it would have to be done extremely carefully for the sake of larvae. thats plain.
and pulling it all up in one go is definately out.

maybe its not practicable to remove a single species from my pond now. especially not such a well established one as elodea.
Diversity.
Suzi
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Joined: 06 Apr 2005
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Posted: 11 Jun 2010
Things were going well in my pond until duckweed arrived. I now can't get rid of it and it gets into starwort and pondweed as well as covering the surface. I tried to establish frogbit without success but I got another lot late last autumn and chucked it in and lo and behold it is all over the pond - tangled up in the above plants! I am very tempted to put in another pond and have the frogbit and no potted plants at all. If the soil of them is enriching the water and feeding the duckweed then I am better off without them.
I have got plenty of wildlife in the pond but if I want to sit and watch it I have to brush the surface to clear a bit of free water and then the taddies and newts move into view.

Suz
ben rigsby
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Joined: 27 Apr 2010
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Posted: 11 Jun 2010
hmmm. it sounds like your duckweed prob is worse than mine then suz.
ive got it all over (my pond!) but it doesnt form any kind of dense matt anywhere owing to the other plant competition (lily, brooklime, elodea, hornwort,starwort, iris) breaking the surface.
im no expert so others please correct me if im wrong but id say its a bad idea to remove plants in an attempt to control Lemna Minor.
put it this way a guy i know emptied his duckweed pond and started again. hes never had much plantlife in it other than some marsh marigolds in one corner and a little elodea here and there. only a few weeks after the fresh start hes got a thick matt of the awful stuff once again. mines never taken over and im sure the hornwort/elodea have played a part in keeping duckweed from dominance. simply by breaking the mass up if nothing else.

not good enough for me though. i wish it were gone.
fat chance.

death to duckweed!

the downside obviously is that the hornwort and CP also block viewing.

ben

that reminds me, i must get a brush.
Diversity.
Suzi
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Joined: 06 Apr 2005
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Posted: 11 Jun 2010
Yep the duckweed forms a dense mat and even scooping as much out as poss (not in taddie season) is no good as within days it's back as bad as ever. I did used to have a good coverage of pondweed (Potamogetonaceae family) but that struggles with the duckweed. 
Suz
lalchitri
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Joined: 06 Jun 2006
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Posted: 12 Jun 2010
Spent an hour a day for the past week skimming the duckweed off my pond.
Got it down from a thick blanket to a light covering.
Though the tadpoles underneath seemed to have flourished better than ever in the ponds 5 year history, I was worried that the thick blanket may have prevented the young froglets from emerging out of the water.

Reformed Teetotaller
ben rigsby
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Joined: 27 Apr 2010
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Posted: 12 Jun 2010
i bet that was a chore lal. i applaud your hardwork and dedication.

here's another approach if you havent tried/fancy it;

the chap i referred to DOES keep one area (approx 2ft sq) pretty free of duckweed though.

by employing a barrier strategy in open water.

hes got a wooden frame (like a picture frame but with thicker framework and no glass) floating freely in the pond.
inevitably its not completely devoid of Lemna inside but its not that far off. it does a really good job of offering a "viewing hatch" to whats below and the clear water it enframes is certainly in amazingly sharp contrast to the density of the duckweed coating that lies beyond its confines. its the only place where you can see below the surface and for a garden, this is a large pond.

i see scores tadpoles and helvs (inc egg-layers) in it every day when i visit. it certainly looks like the animals are exploiting its light-offering properties by coming up within it when in need of air although obviously its hard to tell if theyre surfacing just as much elsewhere owing to the mat's obscuring "qualities".

ALWAYS loads of taddies/newts in it anyway. (along with great clouds of Daphnia- great watching the newts snap at these!)

however,

the sight of the device floating there detracts from the overall aesthetic "natural" beauty of the pool somewhat though. a small price to pay perhaps. depending how "pond proud" you are i suppose.

just to move on a little...

if left unchecked would duckweed become be a major disaster for amphibian colonies?


ive never bothered looking for them much at sites where Lemna is particularily bad. at the very sight of duckweed i often lose the will to bother and just go elsewhere!

ben
Diversity.

- hornwort vs Can. pondweed

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