The ECIC and I are now even more lucky. We have recently been able to buy a bit of land to turn into our own little growing space for fruit and vegetables… okay, this may not be your idea of fun, but we like it…. Whilst we’re busy digging out the brambles and nettles we have been chewing over ideas about how to look after our crops, and one of our problems to solve is water.
The land we have has no mains water. We can collect a lot of water from the roof of our shed and greenhouses (planning permission pending!), but if we need more then we’ll have to look somewhere else. One option is the small stream nearby, so we wandered over to have a look at what it’s like… and it’s ORANGE!
Good question! Well, thinking we were going to have toxic glow-in-the-dark carrots we spoke to a local Environmental Health Officer (EHO) and they told us this was a natural process due to bacteria… I was delighted and started to use the words “how interesting!” …the ECIC was good enough not to mention to the EHO that I am a Microbiologist and had never heard of them.
This odd appearance of our local stream is due to naturally occurring iron-oxidising bacteria which produce the orange colour. When iron comes into contact with water and oxygen it starts to oxidise, it goes from Fe2+ to Fe3+ (Fe is the chemical symbol for iron). The common name for iron-oxidation is rusting. Rust is iron oxide, and it is orange.
It turns out that iron-oxidising bacteria were some of the first bacteria ever discovered, way back in around 1837 by two pioneering Microbiologists called Ehrenberg and Winogradsky (now that’s a great name!).
Iron-oxidising bacteria can be aerobic or anaerobic, they are often acidophilic (liking an acidic environment) and they can be photosynthetic (using sunlight).
Some of the names of these bacteria are a bit of a giveaway to the fact that they mess about with iron:
- Parracoccus ferrooxidans
- Gallionella ferrugina
- Ferritrophicum radicicola
- Acidithiobacillus ferrivorans
- Acidiferrobacter thiooxydans
- Mariprofundas ferrooxydans
Okay, so there are plenty of others too, but you get the point… many iron-oxidising bacteria have “ferro” or something similar in their name indicating that they have some kind of interaction with iron. Clever huh?
Why are some streams orange and others not?
Apparently, the iron-oxidising bacteria are pretty much ubiquitous, being found all over the World. Whether they turn your stream orange or not is dependent on the presence of iron in the water and favourable conditions for the bacteria to grow. Given that many of these bacteria like a more acidic environment, if your stream is orange too, then the water may be a bit more acidic than other areas allowing oxidation to take place.
The EHO we spoke to said that this orange effect is often seen in streams when the water table is naturally high or has risen for some reason. The EHO wasn’t able to tell us why this happened but I can hazard a guess; I wonder if it has to do with availability of iron and acidity.
The increased availability of iron seems reasonable to me because as water rises through bedrock and subsoil it would bring minerals from deep underground to the surface. This would include iron, and more iron means more iron-oxidation by bacteria.
The change in acidity is a bit trickier to explain but I know of three reasons for increased soil acidity:
- Pine trees – decaying pine needles are very acidic and lower the pH of soil a lot (a perfect and cheap way to produce ericaceous compost for blueberries in case you are wondering!), and our stream is surrounded by lots of mature Scot’s Pine trees. Water coming up through this soil would become very acidic.
- Too much water – as water passes through soil it leaches out potassium, magnesium and calcium which results in more acidic soil; as the water table rises and more water comes into the surrounding soil, the nutrients will be washed out faster and the pH will drop.
- Excessive fertiliser – fertilisers high in nitrogen also drop the pH of soil, but I suspect this isn’t that relevant locally as much of the land has been fallow meadow for many years.
So I suspect our local stream has gone orange because of the presence of iron-oxidising bacteria and a wet winter has caused the water table to rise through the acidic subsoil and leach out the protective nutrients to create an acidic environment for the bacteria to start oxidising iron. The result is a disconcertingly bright sludgy orange stream!
Do iron-oxidising bacteria matter?
It is thought that iron-oxidising bacteria have had a major influence on the evolution of our planet. Iron is an essential element in life and these bacteria are thought to have been pivotal in changing the state of iron in early evolution (about 3.85 billion years ago) to forms that other microorganisms could use.
More recently these bacteria have been seen as more of a nuisance, causing pipes to rust and decay or block up with orange coloured sludgy debris, but I would argue this isn’t the bacteria’s fault but more an effect of our modern lifestyles impacting on the bacteria… 3.85 billion years ago the bacteria had no issues with water pipes! Who was here first?!?
Perhaps a more beneficial use of these types of bacteria is in the removal of pollutants from water such as phosphates, arsenates and humic colloids. The iron oxides produced by the bacteria bind the toxic compounds and remove them from the water. Basically, nature is cleaning up our mess AGAIN.
So just before you all start to panic, like we did, there was something the EHO did tell us that was very important… the bacteria aren’t toxic to us and the appearance will be temporary. If the water table goes down the stream will revert to a more acceptable muddy colour, added to this she said it will be safe to sprinkle on our fruit and veg. OK we saw you look quizzically sides ways just then!! I’m not sure either; I can’t really get the weirdness of a thick sludgy orange coloured stream out of my mind…! I think we’ll opt for a “water sampling kit” search on Google…
Right, I’m off for a drink, what shall I have? Carrot juice, Irn Bru or maybe just some orange squash…! No, it’s a glass of our “fresh water”!