The influence of stream bed stability and channel dynamics on lotic ecoystems: measurement and methodological advances : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Palmerston North, New Zealand
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Date
2010
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Massey University
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Abstract
Stream bed instability is one of the major sources of physical disturbance to benthic
invertebrate communities. Measurement of bed stability characteristics can be difficult
and the multitude of assessment methods impedes comparability between ecological
studies. This research investigated the efficiency of different measures of bed stability
in characterising the relationship between disturbance and stream invertebrate
community composition. It intended to provide recommendations for which technique is
preferable under certain conditions and to develop and advance assessment methods of
bed stability for use in stream ecology.
Bed stability was found to be highly variable within and between mountain stream
reaches in the southern North Island of New Zealand. Channel dynamics are
conditioned by intrinsic thresholds which reflect sediment supply and catchment
connectivity. Although stream ecologists use a multitude of substrate stability
measurements, each assessing a distinct subset of bed stability characteristics, a large
array of methods has not yet been adopted. A literature review and subsequent empirical
comparison found that the volume of scour derived from morphological budgeting, the
bottom component of the Pfankuch Stability Index and distance travelled by in situ
marked tracer stones had a strong link with invertebrate community composition and
diversity. Consistent employment of morphological budgeting at a large number of
reaches, highly variable in substrate and hydraulic conditions, requires selection of an
appropriate DEM interpolation method. Amongst geostatistical and local
neighbourhood approaches available in Surfer®, triangulation with linear interpolation
was best suited to realistically represent channel morphology at various reaches.
The bottom component of the Pfankuch Stability Index is quick and cost-effective
but is prone to observer-bias and examines only a small number of variables. Tracer
stones were deemed the most suitable traditional method to measure stream bed stability
relevant for invertebrate communities although it can be laborious and expensive when
many sites are involved. Consequently a new descriptive survey protocol (SBSI) was
developed that measures invertebrate community response to bed stability. Furthermore,
a macroinvertebrate index for assessment of bed stability based on taxa abundance
weighted composition of the entire community is proposed. These new methods can
facilitate monitoring the effect of physical disturbance on lotic ecosystems and could
serve as a powerful tool in river management.
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Keywords
Stream ecology, Streambed stability, Freshwater invertebrates, Pfankuch stability index