Mangrove mayhem

For much of the weekend the Brazilian town of Vila velha will be without water. The culprit is a burst pipe which has to be replaced, necessitating the closure of much of the town's water supply.


Now, the pipe runs through an old mangrove swamp. Mangrove mud is stuffed full of bacteria. Mangrove trees produce about a kilo of litter per metre per year, which has to be broken down, not to mention debris from fish, crabs and shrimp which make a rich organic soup. In fact, there are so many bacteria that the available oxygen is used up and anaerobic bacteria (which can survive without oxygen) flourish, including those called “sulphate reducing bacteria” - these are the ones that produce hydrogen sulphide, the “rotten egg” smell. Unfortunately, the smell is not the only problem.

The action of anaerobic bacteria causes corrosion on the surface of metal objects. Additionally, the waterlogged soil of a mangrove swamp is high in iron pyrites, and when exposed to oxygen this forms sulphuric acid. As the water level in coastal mangrove swamps goes up and down with the tide and through the seasons, sometimes aerobic, sometimes anaerobic, metal there gets attacked from both sides.


The pipe in this case was made of 1 cm thick cast iron, and laid about 30 years ago. Gradual corrosion and water pressure inside the pipe eventually caused it to burst so it had to be replaced, but as it was now 6m below ground (due to a landfill project) that was easier said than done. Hence the chaos!

Borboletas

It´s autumn in the southern hemisphere, but it feels like spring with the appearance of flowers and suddenly quite a few butterflies ("borboletas"), the most common of which seems to be this one...

I managed to identify it as the Mangrove Buckeye (Junonia evarete) thanks to the excellent field guides from fieldmuseum org (http://fm2.fieldmuseum.org/plantguides/guide_pdfs/X016-Iracambi-Butterflies.pdf ). As its name suggests, the Mangrove Buckeye rather likes mangroves, in fact from Florida to southern Brazil it is a bane of attempts to reforest coasts with these trees, the caterpillars stripping young seedlings. It's not just mangroves though, caterpillars eat Gervao (Stachytarpheta cayennensis), also know as "Brazil tea", and Sempre viva (Paepalanthus polyanthus) as well as others.

With this diverse food range it can be found far from the coast and mangroves, from Belo Horizonte in the inland mountainous state of Minas Gerais, to Brasilia, over 700 miles from the sea.

Adult females and males can be easily told apart as the males have blue patches (top) whilst the females are more discrete (above). Both have a fast and fairly erratic flight and reportedly prefer the small flowers found in grassland by roads or recently neglected land, certainly I saw these on flowers amongst long grass.