It has been found in the Trent Waterway in Ontario, CA.  You might try looking for answers there.

http://www.insidebelleville.com/news-story/4034743-scientists-researching-ways-to-prevent-spread-of-invasive-plant-in-trent-river/

Hi Piotr,

It effectively has come to cover the entire lake (see attached photo taken in July this year!), although there are submerged macrophytes present. The species is in fact native to eastern parts of the UK, where this lake is located, but is believed to have been introduced at this particular site. 

Douglas & Elias - Many thanks for the links will try and get in touch with the work they are doing.

Hi Drew,

Similar situation as in your picture in a series of ponds in the Lincolnshire Limewoods area. Again, the species was introduced. You may want to contact Lincolnshire Wildlife Trust:

http://www.lincstrust.org.uk/

They administer the Limewoods reserves and organised a working party for removal, but I'm unsure as to whether they tested the effect of removal by controlled experiment. I have pre-control data myself (before the Stratiotes took over) as one of them was a study pond for my postgrad work, but there may not be any immediate pre-treatment or post-treatment data.

Cheers,

Rich

Hi Drew,

That's certainly an impressive growth!

When you say 'slightly elevated TP and TN', what sort of values are we talking? And what is the lake used for, if anything?

What other macrophytes are present? As you are within the biogeographic area for the plant there is an argument for keeping it. Water soldier can be quite good for some biodiversity, especially dragonflies. But certainly some management is needed.

Probably dense water soldier growth like this will affect DO concentrations in the water column. On the other hand, it's likely to be very effective at suppressing algal blooms. Biomass harvesting of the soldier may also be quite an effective way of reducing nutrient concentrations in the lake, provided that catchment sources are under control. If I were managing the lake I think I'd harvest rotationally / in stages to reduce the risk of 'flipping' the lake into a turbid state..

Regards

Tristan

Piotr – thanks for the article link. It was believed to have been introduced in 2004.

Rich – thanks will contact Lincs WT.

Hi Tristan – typically annual avg TP and TON values are 55-60µg/l and 2mg/l respectively. Monthly averages show that TON becomes exhausted in late summer with TP increasing to a peak of 110 µg/l in July. The limitation of TON appears to be preventing phytoplankton growth with Chl-a concentrations peaking in late spring and reaching winter levels by late summer. The lake forms part of a SSSI and is also used for fishing and bird watching, with the SSSI citation mentioning its importance for breeding birds.

The lake has some fringed Norfolk reed, although this has thought to have decreased in extent, and there is the presence of the following submerged macrophytes: rigid hornwort, Chara globularis, Mare’s tail, common & ivy-leaved duckweed, spiked water milfoil, Nitella flexilis, Potamogetons: crispus, pectinatus, pusillus, and trichoides, fan-leaved water crowfoot and bladderwort. The submerged plants contribute towards Natural England’s Condition Assessment for the lake. An obvious concern is that the water soldier will already be adversely impacting on these species by shading them out and elevated nutrient levels are a risk in encouraging the dominance of nutrient tolerant species.

Consideration will need to be given whether to retain some water soldier, which would have an ongoing maintenance cost given how vigorous the species is. I agree with phased harvesting, it’s knowing how much and how often, without creating long term detrimental impacts. The intention would be to have ongoing monitoring during the removal to keep an eye on any changes with nutrient releases and phytoplankton levels. Any further thoughts are welcome.

OK, yes that's what I would describe as 'slightly elevated' too, with a fairly typical eutrophic flora to match. Good to see there are no non-native invasives - things like Elodea and Crassula are all too common.

One other thing you could also consider would be the fish community - are there lots of roach, carp and bream that could encourage a forward switch to phytoplankton if plants were removed.

Well Drew you have certainly raised an interesting question here.  I would prefer to have Elodea to be honest. The water soldier in our nearby Lough Derg (Ireland), in the margins of the lake at one site, in the last eight years has increased to a number of hectares in shallows of about the depth you describe. I consider it to be introduced.  Its appearance in SE Britain and on the continent may have followed at a time when this region was part of a river prior to the rise in sea-level.  Should this be the case then it is not a native here.  The behaviour is the same as in the other sites described by contributors above.  I think it should be eliminated but as you have asked how to do this.  there are mining insects in abundance in the stands of this plant, even in the leaves of submerged rosettes and these do not seem to stem its expansion.  I guess we are no longer permitted to use Caseron G or other chemicals.

The stands are so dense that in places the rosettes are facing upwards at about 75 degrees and it is not possible to even get a canoe through the surface mat they create.  In one region - a small unused harbour - the plants have formed a dense sward and at the entrance to the lake they are calving like icebergs from a glacier.  The concern is its spread to other parts of the lake.

To say I am very interested in any practical elimination plan.  Do not plan to swim with these plants!!

Photographs: 1. backwater behind river delta entering Lough Derg. 2. Harbour with dense stand .

Dan

The question about status Stratiotes aloides considered in the article by R. S. Forbes (2000) «Assessing the status of Stratiotes aloides L. (Water-soldier) in Co. Fermanagh, Northern Ireland (v.c. H33)».

Removing Stratiotes to lead to a change in the trophic status of the waterbody. The mass development of phytoplankton and cyanobacteria is expected, exudates Stratiotes inhibit their development. Further reduction of competition would increase the projective cover of submerged hydrophytes (hydatophyts) such as Elodea canadensis, Potamogeton spp. et al.

Mechanical removal can temporarily reduce the biomass, however, as the plant spreads lateral shoots, it is important to prevent them from spreading. This is probably the most effective in this case.

Excessive concentrations of sulfates and nitrates and low carbonate content also limit the development of the species. Experience of application of this technique is unknown to me.

Fungi of the genus Fusarium sp. and some nematodes can also constrain growth. However, the experience of their application and technology is not known.

Some effects can be achieved as the drainage water, winter freezing of the bed, but a temporary lowering ineffective.

Of the herbicides used for aquatic plants diquat, sulfate and copper chelates, acrolein trebutin, endotol’s salt, sodium arsenite, but due to their low toxicity and effective application is limited.

It has been a while, but I thought I would provide an update about management actions undertaken to help control the water soldier situation on the lake of concern. A phased removal of the water soldier using Truxor machines began in October 2016 and happened again in September 2017. In September 2017 a boom was also inserted to prevent its spread back in to the removed area. It was our intention to have the boom in from the start of the first removal phase, but limited funds unfortunately prevented this. In total c.20-25% of WS has been removed. Monthly monitoring has been taking place to inform chemical and biological responses, with the boom allowing differences to be observed between open water areas versus those dominated by WS. It would also allow us to observe whether any desirable submerged macrophyte species, which used to dominate / be present, will re-establish. We will continue to monitor the situation and assess the changes in the lake prior to deciding whether further WS should be removed again later this year. I have attached some photos showing the inserted boom (0991 & 0992 are September 2017 and 1019 October 2017). The red buoys are some of the monitoring points.

Hi Drew,

Did you make any progress with the use of Truxors for removal of Watersoldier?

In the Netherlands, and Belgium, Truxors have been used with succes of removal Krabbescheer,as we call Water soldiers.

Just as examples:

https://www.waterschaprivierenland.nl/_flysystem/media/beheer-en-onderhoudsplan_maaien-watergangen_def_juli-2019.pdf

https://purews.inbo.be/ws/portalfiles/portal/719040/Louette_etal_2008_BepalenMaximaalGoedEcologischPotentieelAlsookHuidigeToestandZeventienVlaamseWaterlichamenVergelijkbaarMetCategorieMeren.pdf

Hi Ruud,

Thanks for you examples I will take a look. I have not been involved with the work for >5 years now, so I am unsure of the progress and latest with the project. I will try and find out and update if I find anything out.

thank you

Good Morning Drew,

This is a difficult one. In Ireland there are some introduced populations and some would appear to have disappeared. Really unsure why this has happened. This is a situation where over a many decades ago the plant was present and now no longer exists. I have been studying a population in a water-level controlled lake and the population continues to expand in a small number of shallow sheltered areas. My concern is that in the wintertime small drift daughter plants drift from this population and now there are observations of it appearing elsewhere in the same lake - I have yet to make full study on this.

One possibility of 'control' might be leaf miners (see below). I have seen their galleries on sub-surface leaves, but in this lake it did not appear to reduce their spread.

best wishes

Dan