graham5's picture

Orange debris in drainage ditch

Observed: 7th July 2013 By: graham5

There is a spring-fed drainage ditch running though my field which by the early summer contains large amounts of flocculent orange debris carried along by the flow. In the early parts of the year normal green algae will grow in this section of the ditch and upstream the ditch is more normal well-stocked with a variety of plants and insect larvae etc. (producing plenty of damsel/dragon flies frogs and newts). I presume that the debris is dead algae
My query is why ?
This section of the ditch is somewhat sheltered and after the trees to the north and west get into leaf there is no direct sunlight after midday - but it does get some sun as can be seen in one of the photographs. Otherwise the stream seem healthy and grass etc. grows in it and where it emerges from under the trees there is much more normal growth: reeds and watercress. However it does receive some inflow from the adjacent fields which do get a significant number of ducks and geese in a sizeable pond and the inflow to the ditch does take much of the overflow from the ducks' water so may be quite nutrient-rich.

    Likely ID
    Iron bacteria
    Confidence: It's likely to be this, but I can't be certain.
Species interactions

No interactions present.


Amadan's picture

Might be algae -

But possibly iron salts welling up from a disused mine working. Google "Saltburn Gill" for a classic example.
Sometimes the iron salts are already present, but held in solution until some environmental factor causes a pH (acidity) change, such as some limestone-sourced, alkaline water is added; whereupon they precipitate.

graham5's picture

I did wonder about Fe(II)

I didn't give the full description...but it's not very far (<150m) from a river and very much in alluvial gravels; the slightly higher ground (3-4m) which it drains and where the large pond is situated is still alluvial although in my section of the higher ground (contiguous with that of the pond) the only real difference is the depth of soil above the gravel (some 300-500mm). So I'm not sure where any iron deposits could be. That's not to say that it couldn't be Fe(II) but there is no staining of items that are in the flow: vegetation just sheds the orange material with a quick shake in the water and stone, if they are smooth remain clean while rougher ones lose the colour after a wipe. Irritatingly I have still neglected to check the pH - I must remember...
The other fact that does make me think that it is vegetable matter is that not only does it have that flocculent appearance, best seen in the photo on the right (more available if anyone is interested) but there are occasional larger pieces that do have some greater structure and do resemble algal strands.

sojr's picture

If it is dead algae then it

If it is dead algae then it is likely that all the dissolved oxygen in the water has been exhausted. High levels of nutrients, especially from run-off from agricultural fields, will cause algal blooms which will then use up a lot of the dissolved oxygen & once this is depleted the algae will die. This is bad news for the insect larvae & other aquatic life as they also require dissolved oxygen to survive, though I'm guessing it's not too severe if you get a good variety of insects year on year - though some species are more tolerant of low oxygen levels (and pH levels) than others.

Michael Funnell's picture

Oxidising bacteria

I think this colouration could be the result of ferro oxisidising bacteria. It occurs very frequently in summer in streams around the Weald when the water levels and flow are low. The effect looks like pollution giving the water a rust colour and sometimes what looks like an oily film. I wouldn't be concerned at all as there is nothing that can be done about it and it doesn't seem to cause any lasting problems. The brown colour is caused by iron compounds and there can also be flocculation
See for more detail.