Following the issues with weed in 2019 much research has now been undertaken to confirm the weed type and to establish the most appropriate methods of control at NCSC. Sources of information include the Centre for Ecology and Hydrology, Dr J.R Newman (an expert in this field), and several sailing clubs experiencing similar problems with weed.
The predominant weed type has been confirmed as Elodea Nuttallii, (Nuttall’s pondweed) with possibly a small proportion of Elodea Canadensis (Canadian Waterweed). Both these weed types are classed as alien invasive species.
Elodea Nuttallii can grow in water up to 4.5 meters deep and over-winters as shoots lying on the lake bed; these shoots start to regenerate new side shoots as the lake temperature reaches 6-8°C.
The side shoots grow rapidly towards the surface without branching to reach the water surface to get sufficient light for photosynthesis. Once close to the surface these primary runners began to produce more shoots to form a canopy structure to maximise the absorption of light energy. Under favourable conditions, E. nuttallii forms a densely branched canopy during mid-late summer, and this canopy easily detaches to form dense, free-floating mats. (Does anybody recognise this!!!)? During the late autumn and winter these floating mats break up and sink to the lake bed for the cycle to repeat; or are blown to the lee shore.
PROPOSED CONTROL METHOD
Varying methods of control have been considered and those most appropriate to employ at NCSC include, club members will need to volunteer to ensure this is done:-
- Harrowing of the lake bed during late Winter / early Spring in areas known to support the growth of weed; – this disturbs the overwintering stems and growth shoots and delays by up to 6-8 weeks the formation of shoots rising to the surface. This then limits the period available for the growth spreading at or just below the surface, hence reducing the overall biomass.
- Cutting of weed at the lake bed in late spring / early summer to remove rising stems before the period when they reach the surface and expand aggressively to form a floating mat. The collection of a limited amount of cut weed will be required.
- The introduction of liquid blue dye to inhibit photosynthesis and reduce weed growth
- The regular collection of any floating weed that appears in late summer / autumn
- The removal of weed blown to a lee shore
ACTIONS TAKEN TO DATE – 14/3/2020
In addition to the research the following actions have been executed to date and will continue as appropriate:-
- In December 2019 the NCSC Exec Committee approved the purchase of liquid blue that is more expensive but significantly easier to apply than the powdered blue dye as used in recent years. There is also a perception that this liquid dye as used initially by the club was more effective.
- A temperature data logger has been placed in the lake and data down loaded on a regular basis. This enables us to make sure that the initial dose of liquid dye is applied before the lake temperature exceeds 6°C on a regular/permanent basis and weed growth is accelerated
- The lake overflow has been checked on a regular basis and cleared of debris as necessary to ensure that the lake level drops as quickly as possible to enable the blue dye to be applied without significant loss via the overflow.
- In January 2020 working parties removed substantial amounts of last year’s weed that had blown on to the lee shore.
- A diving team has made a part survey of the lake bed, but reported poor visibility and little weed in the areas surveyed
- A chain harrow has been assembled and towed behind red safety in February and March in areas around and between buoys seven, eight, nine and ten together with the rib moorings, all areas of recognised weed growth. More harrowing is still required – see Volunteering below.
- The fabrication of a V shaped weed cutting blade, similar to that used by other clubs and aquatic contractors, has been commissioned. The blade has now been fabricated and successfully trialled ready for use late Spring / early Summer.
- An underwater camera with remote video screen and recording facility has been purchased to monitor the weed growth on the bed of the lake, the effect of harrowing, and the rate and density of weed growth during the season. The camera has now been trialled and footage recorded of overwintering shoots / early season growth.
- Fifty percent of the initial blue dye dose was applied in February, unfortunately the latest flooding will have diminished its effect, but the increased turbidity of the flood water will have had a similar effect of reducing light penetration. A futher dose was applied on March 14.
PLANNED AND ONGOING ACTION
As the year progresses the following is planned:-
- To continue harrowing the lake bed during March and April
- To continue monitoring the lake temperature
- To apply the third stage of the initial blue dye dosage. NB this can’t be done until the lake level drops to below the lip of the overflow control weir.
- To take bi-weekly samples of the lake water to monitor the degradation of the blue dye due to sunlight and dilution.
- To apply top up doses of blue dye as required on a monthly basis from now until the end of August
- To undertake monitoring of weed growth using the underwater camera so that harrowing and later weed cutting at the lake bed can be targeted.
- To undertake surface monitoring of weed growth.
- A lake map will be posted in the club house for members to record sighting of weed growth.
- The purchase of purpose designed light weight weed rakes for collection of cut / floating weed.
- A survey of the lake depth to help confirm the lake volume for the dosing of dye and establish all areas of a depth of 4.5m and below which have a potential for supporting the growth of weed
VOLUNTEERING – Your Club Needs YOU
To implement the ongoing proposed weed control we need a band of willing volunteers. Martin Hart as vice commodore will be managing and co-ordinating these activities. A schedule of weed work party activities will be posted, but please make offers of assistance to firstname.lastname@example.org , advising which activities you can to assist with, and your typical availability. A sign-up sheet will also be posted on the club notice board.
GUARANTEES AND PLAN ‘B’
Whilst the above proposals to be managed and executed by club volunteers are aimed at limiting weed growth to the extent that it does not significantly affect our sailing activities as in previous years there are NO guarantees.
With this in mind quotations have been obtained for the hire of specialist weed cutting boats and/or aquatic contractors to undertake weed clearance in the late summer- however this is an expensive option which we hope will be avoided if sufficient active involvement is received from club members.
Finally many thanks to all those that have assisted to date. Martin Hart – Vice Commodore. March 2020
Weed Control Statement for Web and Notice Board 15 March 2020 -1 (pdf version of above)