The freshwater macroinvertebrate communities of the Waikato, Waihou and Waipa Rivers

Report: TR 2001/12

Author: Andrew Taylor

About this report

Invertebrate populations in aquatic macrophytes in the Waikato, Waihou and Waipa Rivers were examined to study longitudinal changes and differences between invertebrate communities in these rivers. Eight sites were sampled on the Waikato, five on the Waihou and three sites on the Waipa River. Both the Waikato and Waihou Rivers had an abundance of macrophyte beds, dominated by Egeria densa in the Waikato and Elodea canadensis in the Waihou River. The lack of macrophyte beds in the lower Waipa River restricted the comparability of the samples with the other two rivers, hence analyses of the data was carried out only on the Waikato and Waihou Rivers. Macrophyte samples were taken from the edge of the channel at each site: Egeria densa from the Waikato sites, and Elodea canadensis in the Waipa and Waihou River sites. A comparison of the invertebrate assemblages of both E. densa and E. canadensis in the Waihou (Te Aroha site) showed the high comparability of the invertebrate communities of these two macrophyte species.

The Waikato, Waihou and Waipa Rivers showed moderate diversity in species sampled – 35, 40 and 34 taxa respectively. The relatively low numbers of mayflies and stoneflies observed in the samples was attributed to the high water temperatures at that time of year (summer). The Waikato River showed a general decline in species number, MCI and QMCI scores moving downstream. Taxonomic composition showed a wide range of dominant taxa groups with no clear transition moving downstream. The Waihou River, however, showed a decrease in the total number of invertebrates and number of taxa – no clear trend was seen in MCI/QMCI scores moving downstream. Taxonomic composition in the Waihou River was similar between the different sites with some increases in the dominance of molluscs and a decrease in the dominance of dipteran taxa at the lower sites. The Waipa River showed a decline in the MCI scores moving downstream, the other indices showed a strong decline at the Pirongia site.

The taxonomic composition of the invertebrate communities showed a wide variance in the Waikato River, whereas the communities in the Waihou were much more closely related. MCI, QMCI and taxa numbers were significantly higher in the Waihou River when compared to the Waikato River. The Waipa River showed strong dominance by molluscs in the upper two sites with a more varied community structure at the Pirongia site.

The decreasing MCI and QMCI scores on the Waikato River were attributed to the decline of water quality moving downstream. The high variance in invertebrate community composition in the Waikato River was attributed to the hydro-regulation of the flow regimes of the river.

The Freshwater Macroinvertebrate Communities of the Waikato, Waihou and Waipa Rivers [PDF, 374 KB]