Monday, March 7, 2011

What happens to a leaf when it falls into a stream? Part II

  Last fall...
 Leaves fell into the water.
They became waterlogged and sank.
They drifted into clumps, or leaf packs.
   I know leaf packs look just like piles of soggy leaves, but they are much more than that. These leaves are part of an underwater leaf-processing system, and are important to the aquatic food web.  The sunken leaves have become colonized by fungi and bacteria. This microbial conditioning makes the leaves more palatable and nutritious for the aquatic insect larvae,or shredders, that feed on the leaves.   
If you look close you can see the shredders have been at work decomposing this leaf pack.
I enjoy examining their progress on snowy winter days, by reaching into the icy water for a handful of leaves. Then I can hold in my numb hands, their delicate work.
Shredders include amphipods, isopods,and stonefly larvae.
They did a fairly thorough job on these leaves. 
 Maybe I interrupted them.  Maybe a predator like a helgramite took them from their work.
Incidentally, here is a homeschooling tip.  Take a book-weary child out to a stream for a handful of leaves.
See where a little curiosity leads.
  There are a whole lot of subjects connected with leaf packs.
For instance, as the shredders, like these amphipods, chew on the microbial conditioned leaves some crumbs (they are messy eaters) are carried down stream to filter feeding insects.

 Here filter feeders are feeding on FPOM (fine particulate organic matter) they collect from the current.

Filter feeders are fascinating. 
 But I don't want to get carried away on other subjects presently (if you get my drift), so back to the fallen leaves.

No, a leaf pack is not a mere clump of soggy leaves, but an intriguing part of a leaf processing system.
The leaves that fell into the stream are being decomposed.
Here in the headwaters, the shredders are working their delicate work.
Downstream the filter feeders will be waiting.  So will the trout and the fisherman.

See Part I:  What happens to a leaf when it falls into a stream?

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