Tuesday, 10 July 2018

FOSSC: a chemistry lesson

The lake at Frampton is now somewhat blighted by weed. I say somewhat, but in the fifteen years I've been sailing there, I've never seen it so bad. It's an accumulation of unintended consequences, I think.

A few years ago, we had a very dry summer followed by an unusually dry winter which saw the water levels in the lake, fed by water table, drop to an unprecedented low. We then had an exceptionally wet spring, the lake refilled and then overflowed, flooding out and into the village.

c. Feb 2013
c. Feb 2013
As I understand it, since then, the village has, understandably, been very keen on the sluice that relieves excess water levels from the lake being set at a level that minimises the chance of this ever happening again.

Last year, as the water levels dropped across spring and into summer, the lake was hit with blooms of blue-green algae. Nasty stuff, really upsets the system if you ingest water tainted with it, and is potentially fatal to dogs; walking around the 50 acre lake is a favourite with dog walkers, for obvious reasons. We're not allowed to swim in the lake, but dogs are, lucky things, and do frequently.

This spring, the Club Committee deployed bales of barley straw around the margins of the lake. The stuff evidently suppresses blue-green algae.

Now I'm neither a chemist nor a biologist, but I do keep fish so have a layman's understanding of the nitrogen cycle. Essentially, organic matter breaks down into nasty ammonia, friendly bacteria convert the ammonia into less toxic nitrite, and even more friendly bacteria convert the nitrite into much, much less harmful nitrogen. In a fish tank, this is the process you essentially replicate in your filter. An aquarium filter isn't really about removing physical detritus, but is instead a pretty neat chemistry experiment that replicates a very cool natural process.

The point of all this, aside from meaning fish don't ultimately poison themselves in their own waste, is that nitrogen is food for plants, a major component of chlorophyll which, of course, is the green stuff plants use to turn sunlight, carbon dioxide and water into sugar and oxygen. This is one of the fundamental processes that gives us life on Earth. In a fish tank, the aquarium plants are typically insufficient to use up all of the nitrogen generated by the fish waste, so in addition to or instead of growing plants in the tank, you control the nitrogen levels through frequent, partial water changes. But I digress.

My guess is that the barley straw rotted down, sorting out the blue green algae problem exactly as hoped. As a consequence we got crystal clear waters and a huge nitrogen dump. Lots of light, lots of food equals very little algae but loads and loads of weed.

Natural England, the government quango responsible for such things, apparently thinks this is great. Frampton Town Lake is designated an SSSI, or "Site of Special Scientific Interest" and the weed is great for biodiversity, of interest in itself plus gives lots of cover for fish fry and prey fish, so they should flourish too.

I should add that the lake isn't natural for all of Natural England's interest. It's an old gravel pit; gravel dug from here was, I believe, used to build the motorway and old Severn Bridge.

Not so good for dinghy sailors. Hitting the weed is akin to running aground on a mud bank, and when racing at Frampton now, navigating a path through the weed is, I guess, not dissimilar to picking the quickest route through the waves when racing at sea. Although I'd have to say waves are distinctly more fun.

It's not so bad in the Laser, at least not in the light, drifting conditions we've had in recent weeks. The Laser's rudder is small and under-powered, so if you cant it at an angle of less than 45 degrees of the vertical, the weed just slides off. Very manageable in light winds, you just have to remember to avoid the worst clumps of weed, clear the dagger board frequently, and pray no sudden, unexpected gust blows through because with your rudder offset, the extra weather-helm will either break something or knock you over.

Some of the other designs of boat aren't so fortunate however. Again, centreboards and dagger-boards aren't really too much of an issue, but if your rudder can't accommodate you sailing with it offset from vertical, then it becomes a nightmare.

Of course, if we get an especially lively day, the rudder's going to have to go back to vertical. I don't know how that's going to play out with the weed.

I've heard rumour that the Sailing Committee have considered suspending racing. It's all a bit of a worry. In the meantime we're still race, and another balmy drift is forecast for Wednesday evening. I'll be there, of course.

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