Temporal and spatial dynamics of micro-

SURFACE and Subsurface Communities

The hyporheic zone of streams, defined as the area of interstitial space below the surface sediments and above the groundwater (Ordhigan 1959, Schwoerbel 1961) has received considerable attention with most of the studies dealing with biogeochemical processes and the distribution of macroinvertebrates. The community of organisms inhabiting the hyporheic zone are called hyporheos comprising a mixture of organisms from the streambed surface and the hypogeic component (i.e. groundwater).

There are many type of organisms inhabiting the hyporheic zone, but the most abundant are members of the meiofauna (Schmid-Araya 2000, Stead et al. 2004). However, their importance within the hyporheic zone remains unstudied. They may have an impact on stream functioning as consumers of oxygen, contributing to secondary production and decomposition processes (Hakenkamp & Palmer 2000).

Quantitative sampling of the hyporheos is a difficult process but there are many methodological options.
	Stand pipe traps [Oberer Seebach, Austria]		Portable Pipe Corer [outlet of Crummock Water, Lake District, UK]

In the hyporheic zone of a gravel stream the Oberer Seebach, meiofaunal dominant groups are nematodes (31.4%), rotifers (26.9%), cyclopoid copepods (11.6%), and gastrotrichs (9.8%). The rest of the groups accounted for the remaining 20.3%. The depth distribution of Microturbellaria and Gastrotricha showed abundance peaks at sediment depths between 20-30cm (pool sites) and 30-40 (riffle sites). Nematodes, cyclopoid and harpacticoid copepods were found at higher densities within 20 and 40 cm (riffle and pool areas). The depth distribution of Rotifers (abundance peak: winter and summer) was more variable with no clear depth maxima (see below).


Depth distribution in pool (left) and riffle (right) of rotifers in the gravel stream Oberer Seebach (adapted from Schmid-Araya 1997).


Depth distribution of gastrotrichs in the gravel stream Oberer Seebach (adapted from Schmid-Araya 1997).

Depth distribution of nematodes in the gravel stream Oberer Seebach (adapted from Schmid-Araya 1997).