SCIENCE & RESEARCH INTERNAL REPORT NO.123 AQUATIC INVERTEBRATES OF LOWER MANGAHAO AND MANGATAINOKA RIVERS, WAIRARAPA CONTENTS AQUATIC INVERTEBRATES OF LOWER MANGAHAO AND MANGATAINOKA RIVERS, WAIRARAPA
Benthic invertebrates and sediments were collected from Mangahao River at Marima Domain and from a site on Mangatainoka River to obtain background data on conditions preceding the annual flush of sediment from dams in the upper Mangahao catchment. It was intended to compare pre-flush and post-flush sediment conditions and benthic invertebrate faunas in each river. However, following the first sampling trip it was found that a routine sediment flush would not be carried out in 1992, and so the
... 1992, and so the study was aborted. Results of the first sampling trip are presented in this report. Benthic invertebrate faunas were dominated numerically and gravimetrically by Deleatidium spp. Biomass of Deleatidium spp. was similar at both sites but densities were higher at the Mangahao River site (mean of five 0.1 m2 Surber samples = 305). Similar numbers of taxa were recorded on average at both sites (16.6-18.0 O.lm-2). Mean weights of coarse sand (1-2 mm) and fine sand (0.25-1 mm) were considerably higher at the Mangatainoka River site (103 and 143 g.0.1m-2), but silt levels were greater at Marima Domain on Mangahao River (32 g.0.1m-2 cf 10 g.0.1m-2).