Page 197 - Freshwater-Biology-and-Ecology-Handbook

Subterranean streams are subject to similar environmental permeable strata beneath the karst. The deployment of a
pressures as surface streams, including pollution, drift net at a spring source or resurgence for 24 to 48 hours
particularly from agriculture. However, these impacts are can be a useful surrogate method to assess the diversity
rarely investigated, despite subterranean faunas being of a local aquifer if subterranean sampling is not viable.
at risk and having the same intrinsic value as surface Springs that rise through gravels can be similarly sampled
faunas. The subterranean fauna include rare and endemic using the Bou-Rouch pump at the issue point (Figure 4.7).
macroinvertebrates and widespread species such as Alternatively, invertebrates can be sampled from wells and
Niphargus aquilex (Figure 4.12). However, even the common, boreholes with suitable nets. Macroinvertebrates from larger
widespread species are rarely encountered by most cave streams are sampled by similar methods to surface
freshwater biologists. streams, with the same equipment including standard hand
nets (Figure 4.13 and 4.14). The method of deploying them
Epikarst is the layer of weathered carbonate bedrock will depend on the size of the stream and the nature of the
between the soil and bedrock and it can form the roof of substrate, which can be a shallow layer over bedrock or
caves. It is usually sampled using funnels to collect dripping much deeper. One of the key considerations in method
water in a cave. It can also be sampled indirectly from selection at subterranean locations is the logistics of
drip-fed pools, but drip-fed pools can have different faunas transporting the equipment through cave systems or mines.
and be affected by predation (Pipan & Culver, 2005). (63) This can sometimes involve long arduous journeys to the
sampling sites with a variety of obstacles to traverse, ranging
Subterranean streams can be fed by sinking surface streams from narrow and very low passages to deep pitches and
(allogenic), infiltration from the epikarst (autogenic), or a even flooded sections requiring scuba equipment to pass.
combination of both. Subterranean streams originating from
surface streams vary in size, chemistry, and flow patterns The bulk and encumbrance of any sampling equipment
and can form underground rivers. They rely on nutrients and therefore has to be kept to a minimum, especially when one
often biota too from the surface, outside the cave system. considers that other equipment including rope, electron
Subterranean streams fed by epikarst tend to be smaller, ladders, karabiners and scuba cylinders might also need to
poor in nutrients and contain more specialised biotas. be carried as well.
Subterranean streams emerge on the surface as relatively
small springs or larger resurgences, sometimes far from the Although cave streams support a range of different sub-
location of the cave where they are studied. The location habitats, meso-habitat heterogeneity is restricted compared
of springs is determined by local geology, with water being to surface watercourses; diversity of subterranean streams
forced to the surface as it comes into contact with less is generally much less than that of surface streams.

Freshwater Biology and Ecology Handbook | 197
–