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Vertical: Hyporheic zone (pg 3 of 7)

The organisms that live in the upper layers of the hyporheic zone (immediately beneath the stream) are typical of those found on the streambed itself-macroinvertebrates such as nymphs of stoneflies, mayflies, and caddisflies.

Some aquatic insects may spend most of their life cycle in the hyporheic zone, emerging only to turn to adults and reproduce. Crayfish, sculpins, darters, and other fish may sequester themselves in the gaps in the upper layer of the hyporheic zone over winter or during floods.

Different organisms live in the deeper reaches of the zone because of the smaller interstices. No plants grow here, so there are no true herbivores. But the hyporheic zone can support detritus feeders and carnivores, which feed on fine particulate organic matter and dissolved organic matter. Deeper still live mostly meiofauna, such as midge larvae. At the greatest depths, with relatively constant temperature, low oxygen, and tiny spaces between particles, are microfauna feeding on the biofilms that form on sediments.


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