The Stangrove Pond Survey - 2006

Stangrove Pond Slide Show


I noticed a marked decline in the aquatic flora and fauna, throughout the summer months, and eventually concluded that some sort of chemical agent had been added to the pond, in an effort to subdue the duckweed, which had been such a problem in the previous year. I contacted The Town Clerk, Christine Lane, who confirmed that, in fact, a biological agent had been sanctioned for use and applied earlier in the season.

I must state here that I am not trying to apportion blame, or mark out individuals, and am absolutely sure that everyone involved acted with the very best of intentions, on the best of advice available to them. I make the following comments only in an objective effort to clarify the current situation, which, given the poor overall state of the pond, may have arisen in any case as a collective result of the other negative factors acting upon it.

The Town Council's Head Gardener, Tim, has been particularly helpful in assisting me to understand the nature of the product used. I do, however, have to admit to being a little miffed as to why no one thought to inform me of the intention to take this action before I had completed the survey, as it seems contrary to the whole purpose of commissioning it in the first place.

I will not name the agent used, for legal reasons, but in general this genre of products are only a stop gap treatment and offer no substitute to correct long term management. Generally, biological pond additives are of the 'mud guzzler' variety and act on the detritus in the bottom silt layer to break down nutrients and liberate oxygen. In this case I am told that the agent, consisting of seven separate species of bacteria, has a similar action but also acts on the flora present in the surface few inches of water and has a herbicidal element which helps to suppress duckweed growth. I was unable to establish exactly how specific this 'element' was, to duckweed, or how it may affect other aquatic plants.

The agent was applied in April of this year, after which the flora, which it must be said, was in a very poor state following smothering by duckweed throughout the previous season and may have continued on the downward path in any case, declined progressively. The duckweed, much of which had already been removed manually, never reestablished and eventually disappeared completely.

By mid-August not only the entire flora, but also all discernible fauna, had gone, leaving a completely dead aquatic environment, above microbial level.

It is only a personal theory, but I fancy that what happened is that the agent eradicated not only any aquatic vascular plants and filamentous algae but also the free swimming, single celled, algae, which form the basis of this particular food chain. With these removed the whole aquatic ecosystem-already under stress- collapsed, leaving us with the present problem.

Investigations of the agent used, discovered that it had been withdrawn from the market place at the end of 2005 (this information was divulged by the sales department of the supplier). The technical department confirmed what Tim had already told me but could not advise as to how long it may remain active, or exactly why it had been withdrawn.

A few other questions are raised, regarding the conditions under which the agent was stored, the period of time which lapsed between purchase and application, and the implications of these factors on the eventual outcome. Another issue arising is, that as a living agent: how long will it continue to affect the situation? Will it eventually dissipate and die off, or are we left with a long-term problem, which may prove to be insoluble?

The question of renewed applications, if this be the favoured means of control, are no longer at issue, due to unavailability, but the suppliers original recommendation was to re-treat every sixty days, suggesting that it's effects do, in fact, reduce with time. Only time will tell.

Debate concerning biological agents and any other management methods are minor asides, compared to drying up, which was the situation by mid-August. The level dropped through the summer, by around two-and-a-half feet, from the spring high water. On a pond with a maximum depth of around four feet the outcome is quite devastating and exaggerates all of the other relevant factors by dramatically concentrating their effects. There is also the question of rising temperatures and even lower oxygen levels: all of which have a very negative impact. Certainly in the case of the myriad sludge worms which inhabited the pond, I believe that this was the main cause of their demise. They were not poisoned. They were cooked! At least in the shallow margins.

I understand that low water was also a problem last year and can offer little practical defense against this problem, with an, apparently, permeable bed and no input, other than rainfall. We have endured the most protracted period of drought for at least seventy years, across the last two-year period, and hopefully this problem will not recur for a considerable time. If the current situation turns out to be an ongoing, and regular, symptom of global warming, then, sadly, problems with Stangrove Park Pond may turn out to be the least of our worries.