Climate Change and the Hydrology and Morphology of Freshwater Ecosystems - Climate Change Impacts on Freshwater Ecosystems - page 74

stream macroinvertebrates is related to current, as it provides oxygen and food
particles, shapes habitats and transports wastes. A cross-section profile of
current velocity in a straight stream reach has a more or less parabolic shape.
The velocity is highest in the middle of the profile close to the surface and
decreases towards the banks and bottom due to friction. In a straight gutter, this
pattern continues over long distances giving low habitat variability. Natural
streams are not straight gutters; they are irregularly shaped channels that induce
complex current velocity profiles. Turbulent flow patterns characterize natural
streams, and a continuously changing discharge causes the turbulence patterns
to change continuously. These processes, varying in space and time, determine
substrate composition and stability, creating a heterogeneous environment at
the habitat scale. In a review of seven case studies concerned with links among
land use, hydromorphology and river biota at different spatial scales (Sandin
2009) found that the strongest relationship was between in-stream variables
(Pedersen & Friberg 2009) or hydraulic variables (Syrovátka et al . 2009) and
biota rather than catchment characteristics (see also Wiberg-Larsen et al . 2000;
Mérigoux & Dolédec 2004).
The relationship between the benthic macroinvertebrates and the immediate
hydrology was investigated in the river Becva in the Czech Republic. Following
strong disturbance in winter, the spring distributions of animals were much more
similar in different parts of the river than those in autumn, when quiet summer
flow had allowed a differentiation of habitats. In July 1997, a high spate occurred
and changed large parts of the regulated channel structure. In five re-formed
stretches, the interactions between habitat patterns and benthic macroinvertebrates
were monitored in spring and autumn of 2004-05 (Fig. 4.4). During autumn, at
low and stable flow regimes, a habitat gradient develops from the side arms to the
main channel (lower right area of Fig. 4.4). In contrast, the spring samples are
more uniform and clustered, except for the samples from the side arms, following
the disturbance of the winter spates (upper left part of Fig. 4.4).
Stream and river species are adapted to unidirectional flow, modified by
turbulence. Morphological and behavioural adaptations of the organisms can be
classified into those involving position of the organisms, such as locomotion,
attachment and body shape (e.g. flattening, concealment, flexibility), those
associated with feeding or nutrient intake (e.g. functional feeding groups, growth
forms), those associated with physiology (e.g. respiration, temperature) and those
pertaining to reproduction. The habitat and such characteristics are related, and
there is considerable information available on the differences between organism
assemblages living on substrata, for example, on rocks, in shifting sands, on logs
and in leaf packs.
With fewer, but more extreme rainfall events, together with changes in land
use, siltation will be an even more serious problem in stream and river
ecosystems. Siltation degrades habitat diversity with generally negative
consequences for stream communities. This was exemplified in the River
Waldaist in Upper Austria, where the importance of habitat availability and
quality for different life stages of selected trichopterans in relation to siltation
was studied (Fig. 4.5). Trichopterans usually have five larval instars and one
pupal instar (developmental stage), with most instars depending on a different