Set-up of the aquaria – March 2014
To complement the work being carried out in the field and lab, a series of sealed aquaria containing different pond sediments were set up in a greenhouse. These allow us to test the viability of the seedbank in each pond under more controlled conditions – as each aquarium is sealed, there is no way for seeds to enter, other than from the seedbank in the sediment.
March 2014 – Aquaria being set up in the greenhouse. Each aquarium was covered with cling film (pictured), and taped shut. The sediment in the aquaria was collected during the excavation of each ghost / restored pond, and was then sealed in bags and refrigerated until the aquaria could be set up. Aquaria were then filled with filtered rainwater, treated with hydrogen peroxide to reduce algal blooms.
Aquaria have been randomised, and will be re-arranged in the greenhouse with each visit to ensure they all experience the same light / temperature conditions. In the set-up there are:
– 6 control aquaria – these contain the same sterile potting compost / sand mix as the “dispersal condition” microcosms.
– 6 aquaria containing sediment from Original ghost.
– 6 aquaria containing sediment from Horseshoe pond.
– 6 aquaria containing sediment from Crescent ghost.
– 6 aquaria containing sediment from The swimming pool.
– 6 aquaria containing sediment from Frog ghost.
– 6 aquaria containing sediment from Swift pond.
In addition to recording the number / species of plant germinations, and the presence of any zooplankton which may regenerate from the egg bank, sediment condition will also be monitored to assess germination triggers (sediment REDOX, temperature, pH and oxygen content).
This was the first visit to the aquaria. Excitingly, we already have a number of germinations, although most of these are currently too small to identify to species level.
Germination in an Original ghost aquaria – but what is it? It could be a small Potamogeton natans (broad leaved pondweed), but the jury is out until the plant gets a bit bigger! What it does prove however is that the seed bank remains viable in ghost ponds, even after decades to centuries of burial. This is exciting news, and really highlights the potential of ghost ponds.
As it stands, species including Potamogeton natans, chara sp. and Potamogeton trichoides have started germinating, both in the aquaria containing restored pond sediment, and in those containing ghost pond sediments. Daphnia have appeared in 3 aquaria, and burrows (possibly chironomid larvae), in 2 aquaria (see photo below). it is particularly exciting to see germinations occurring from the sediment fro Crescent ghost, a pond that was filled-in over 150 years ago.
Swift pond aquaria May 2014 – small burrows have appeared in the sediment in a couple of the aquaria, but their origin is as yet unknown.
Chara germination in Swift pond aquarium, May 2014.
The aquaria were re-visited this month to check on the progress of the germinations. After careful consideration, it was decided to ensure the aquaria well well sealed, and move them outside – we were concerned about the temperatures being reached in the greenhouse even in early spring, and decided to change the set up before summer.
Little had changed in the way of germinations – the same species were present, with the only notable difference being the appearance of Chara in two of The Swimming pool aquaria.
Despite moving the aquaria outside, it seems that the recent heat wave may have put some considerable stress on the germinations – in several instances plants had died, and the highest recorded water temperature was a whopping 36°C! We decided to change the water in the aquaria (filtered rain water), as sediment phosphorous release seemed to be high, and perhaps especially detrimental given the high sediment area to water volume ratio in these small tanks. Despite some set-backs, many of the aquaria did contain new germinations, including some for ‘Frog ghost’, which previously had none. Potamogeton natans and chara sp. seem to be doing particularly well, occurring in a number of aquaria.
July 2014 – One of the aquaria containing sediment from Original ghost, from which P.natans and Chara sp. have germinated. The water level is very low because I took this photo during the water change, to give a better view of the Chara. Usually the aquaria are full.
Plants in the aquaria seem to be fairing better now that the weather is cooling. This month another water change (again, filtered rainwater), was carried out, and germinations counted. While some plants have been lost since July, it is hoped that now the weather has cooled new germinations will stand a better chance of survival. One new species, Zannichellia palustris, has appeared in some of the aquaria.
August 2014 – Potamogeton natans germinations from Original ghost sediment (pond filled in 1971). In the tank in the lower picture you can see large numbers of chironomid midges, which apparently emerged from eggs in the sediment, but were then unable to escape through the cling-film covering the aquarium.
August 2014 – A close-up of one of the Chara sp. germinating in the tanks containing sediment from the Swimming pool (restored pond).
September 2014 – It is curious the difference in water clarity and colour, which is developing between tanks containing exactly the same pond sediment and rain water. Pictured above are two tanks, both containing sediment from The Swimming pool, but now looking very different.
After some very cold weather, plants in the aquaria have started to die back and over-winter. Germinations were still present in aquaria from all three of the ghost ponds, and also two of the three restored ponds. Strangely, there have been no germinations so far in sediment from Horseshoe pond, one of the restored sites (germinations have however occurred in the outdoor mesocosms and in the pond). To help protect the aquaria from winter frost damage, they have been lightly insulated with a polythene greenhouse – a winter cold snap can be an important germination trigger for some species, especially the stoneworts, so hopefully this will allow just enough insulation to prevent damage, while still allowing the water temperature to fall. Perhaps we will find some new species come the spring!
After bouts of heavy snow and frost, I was eager to see how the aquaria had fared through the worst of the winter. Air temperature inside the polythene greenhouse had ranged between -5°C and 17°C, but no aquaria had been damaged, and new growth had occurred in several aquaria. In addition, a new wave of Daphnia appears to have hatched from the sediment from the restored Swift pond.
February 2015 – New growth of stoneworts and broadleaved pondweed, in aquaria containing sediment from Original ghost – a pond which was filled-in in the 1970s. Throughout the experiment, these aquaria have consistently maintained a large number of germinations, and also maintained the clearest water.