Duncan P. Gray

Braided river benthic diversity at multiple spatial scales: a hierarchical analysis of β diversity in complex floodplain systems

Abstract Despite the global occurrence of braided rivers and the frequency with which they are anthropogenically modified, the benthic diversity of their floodplains and, in particular, lateral and longitudinal patterns in their communities have been neglected. A spatially nested, hierarchical survey was conducted of 11 braided rivers in the South and North Islands of New Zealand to investigate benthic invertebrate diversity at multiple spatial scales. In each river, 6 reaches and up to 5 floodplain habitat types within each reach were sampled. From a total of 203 sites, 145 taxa were identified. Benthic invertebrate diversity was highly variable at the island, river, reach, and habitat scales. Diversity differences between islands were driven by high regional endemism. Diversity at the whole-river scale ranged from 99 taxa in the Wairau River to only 56 in the Waiapu River. At the reach scale, no significant differences in diversity or abundance were found longitudinally down the rivers. At the habitat scale, lateral floodplain habitats, particularly spring creeks, consistently had greater richness and abundance than did adjacent main channel habitats. Comparisons of Whittakers multiplicative β at different spatial scales revealed that the greatest range and mean value of taxon turnover was among habitats within reaches. Additive partitioning of β diversity indicated that diversity values at the broad spatial scales of reach and river contributed disproportionately to overall diversity. Our results indicate that river managers concerned with maintaining diversity should focus their efforts at the whole-river scale rather than attempting management of smaller units representing local scales. However, at finer scales, lateral floodplain habitats (particularly springs and floodplain ponds) are hot spots of diversity and protection and remediation of these habitats are particularly important.

Spatial biodiversity patterns in a large New Zealand braided river

Abstract At the catchment scale, braided rivers are recognised as physically unstable, dynamic landscapes, yet at finer spatial scales they are a mosaic of micro‐habitats including physically unstable braided channels and more stable spring‐sources, spring creeks, and groundwater zones. We investigated benthic invertebrate communities at 103 sites in braided channels, springs and hillslope streams in the Waimakariri River, New Zealand over 3 months. One hundred taxa were identified, including a number of rare phreatic species. Highest total taxonomic richness occurred in springs (81 taxa), whereas main braids and hillslope streams had fewer taxa (54 and 56, respectively). Spring‐fed habitats also had the highest diversity of unique taxa (22), whereas main channels had five and hillslope streams 11 taxa, respectively. Several taxa including the mayfly Deleatidium and orthoclad chironomids were ubiquitous, whereas others such as the flatworm Prorhynchus had restricted habitats. Our results highlight the high spatial heterogeneity of braided river habitats and the importance of springs as centres of invertebrate diversity within braided river catchments.

Acid Mine Drainage Index (AMDI): a benthic invertebrate biotic index for assessing coal mining impacts in New Zealand streams

Abstract Acid mine drainage (AMD) is a widespread phenomenon globally. Drainage into streams from coal mines often contains a cocktail of acidic waters high in dissolved metals, and consequently stream invertebrate communities may be severely impacted. Traditionally, the intensity of impacts has been assessed by combinations of water chemistry and benthic invertebrate metrics; however, a metric specifically designed for assessing mining impacts has not been developed. We propose a benthic invertebrate biotic index: the Acid Mine Drainage Index (AMDI), based on species presence data. The AMDI has been developed by associating water chemistry and benthic invertebrate community data collected from 91 sites. AMD indicator scores for 57 taxa were calculated using weighted averaging. Site scores can range from 0 (severely impacted) to 100 (unimpacted) and sites can be categorised as ‘severely impacted’, ‘impacted’ or ‘unimpacted’. Comparisons between AMDI and traditional indices indicated the AMDI is more accurate at detecting mine drainage.

A new species of Zelandobius (Plecoptera: Gripopterygidae: Antarctoperlinae) from the upper Rangitata River, Canterbury, New Zealand.

Abstract Zelandobius edensis n. sp. is described from a spring‐fed creek in the headwaters of the Rangitata River catchment, South Canterbury, New Zealand. Adult males exhibit varying degrees of brachyptery and the only female collected also had short wings. Larvae are easily identified by their covering of long translucent hairs not found in other members of the Zelandobius confusus‐group. The link between adult and nymph was confirmed by comparing 600‐base‐pair sequences of the mitochondrial gene, cytochrome c oxidase 1. Observations suggest the life cycle may be strongly synchronised by temperature constraints on nymphal growth and development, and/or a short season suitable for feeding and reproduction by the terrestrial adults.

Multi-scaled environmental determinism of benthic invertebrate communities in braided rivers: evidence for complex hierarchical controls on local communities

Globally many braided river systems have become highly modifi ed, however in their natural state they include a wide range of habitats that support high benthic invertebrate diversity. Here we investigate the determinants of this diversity by assessing the infl uence of environmental variables on invertebrate communities across eleven braided rivers in New Zealand. Within each river, six reaches were sampled and within each reach up to fi ve fl oodplain habitat types (main channels, side braids, spring sources, spring creeks and ponds). Environmental variables either measured in the fi eld or derived from GIS and hydrological data bases were compared to invertebrate distributions. Communities in all habitat types were infl uenced by catchment scale hydrology, which partially regulated factors at lesser scales. However, the spatial scale of environmental factors with the greatest infl uence varied between habitat types. Main channel communities were infl uenced equally by catchment and habitat scale conditions, whereas spring communities were primarily regulated at the habitat level. There was considerable cross-scale correlation in the effect of environmental factors suggestive of complex hierarchical controls. Invertebrate diversity was regulated by the environment across a range of scales. Programs concerned with the conservation of braided river systems should incorporate this hierarchical environmental determinism within catchments and acknowledge the value of lateral fl oodplain habitats.

Remediation of a major acid mine drainage point source discharge restores headwater connectivity for a diadromous native fish

ABSTRACT Rivers receiving acid mine drainage (AMD) are frequently depauperate in fish and impacts may extend long distances downstream. AMD inputs may form chemical barriers for migratory species and isolate fish in unimpacted headwaters. We investigated the response of a diadromous fish, kōaro (Galaxias brevipinnis), to remediation of an AMD tributary in a 5th order river in New Zealand. A 2005 survey indicated limited recruitment of kōaro in the river likely due to the chemical barrier of AMD. By 2010, water treatment in the contaminated tributary had raised pH from a median value of 4.3 to 6 and reduced metals in the lower river, notably aluminium from a median of 2.48 to 0.41 mg/L. In 2012, kōaro density had increased by an order of magnitude relative to 2005. Furthermore, a greater proportion of juvenile fish were present. These results indicate that large-scale remediation of discharges can reverse the impacts of AMD on fish migration.