Invertebrate production within various habitats of a braided river
Thesis DisciplineEnvironmental Sciences
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Seepage streams within "flood overflow" channels are important microhabitats within braided rivers. They are important foraging zones for wading birds and may contribute to the ability of the invertebrate community to recover from disturbance. Production of dominant invertebrates was estimated along a three kilometre study reach of the Rakaia River for various channel types ranging from seepage stream microhabitats within secondary channels to the largest braids in the central river bed. The seepage and spring stream microhabitats received varying exposure to elevated summer flows, freshes, and were inundated by flows of greater than approximately 200 cumecs. Four quadrats were randomly located within 10 metre sampling transects in riffles of seepage and spring stream microhabitat in addition to minor and major braids. Riffles were sampled at six week intervals from October 1997 to August 1998, with no riffle sampled more than once. Production was estimated using the size frequency method. Seepage stream microhabitats were the most productive sites examined. Production was estimated to be 10.3 g DW m-² yr-¹ for a perennial seepage stream, 3.2 g m-² yr-¹ for a baseflow seepage stream, 1.0 g DW m-² yr-¹ for a baseflow spring stream, and 0.5 g DW m-² yr-¹ and 0.6 g DW m-² yr-¹ respectively for the minor and major braids. The two types of seepage stream had significantly greater production than the minor and major braids. Invertebrate production is likely to be affected by gradients of disturbance, temperature, algal abundance, and organic matter retention. Frequent and unpredictable flooding probably restricts production in the minor and major braids but helps maintain structure of seepage and spring stream microhabitat in secondary "flood overflow" channels.