Christopher W. Hickey

Characterisation and classification of benthic invertebrate communities in 88 New Zealand rivers in relation to environmental factors

Benthic macroinvertebrates were sampled (seven Surber samples per site) in 88 rivers throughout New Zealand in “runs” (velocity 0.4–0.8 m s−1, depth = 0.3–0.6 m), under autumn baseflow conditions (...

Magnitude of effects of substrate particle size, recent flooding, and catchment development on benthic invertebrates in 88 New Zealand rivers

Abstract Data from runs in 88 rivers throughout New Zealand, and a comparison between areas of contrasting substrate size in the Mohaka River, were used to investigate the influences of physical factors on benthic macroinvertebrates. Substrate size preferences were more clearly demonstrated by the comparison of different substrates in the Mohaka River than between runs in the 88 rivers. Taxonomic richness and densities of most collector‐browsers were highest on small cobble‐boulder substrates. However, filterers and a facultative shredder showed strong preferences for large cobbles and boulders and an undescribed orthoclad showed a strong preference for sand. Among the 80 stony‐bedded rivers, those exposed to maximum flows of 20× their median flows had markedly lower median taxonomic richness, density, and biomass than ...

Effects of clay discharges on streams

Placer gold-mining on the West Coast of the South Island of New Zealand provided a field test-bed for investigating the impacts of fine inorganic suspensoids (clays) on streams not subjected to other abuses. The suspensions of clays (40% between 0.55 and 1 µm in diameter) seeping into the streams from gold mines were colloidally stable. The clay particles attenuated light in the streamwater with near maximum efficiency leading to severe degradation of stream optical quality. Turbidity increased from a median of 2.4 NTU upstream often to > 100 NTU (median 15 NTU) downstream. The stream waters, which were strongly-coloured by humic substances, were changed from a dark organge colour to a bright ‘muddy’ appearance downstream of mining, and visual clarity was reduced from a few metres to as low as 0.03 m (median 0.33 m). The clay discharges decreased light penetration into the stream water such that irradiance averaged over a 12 hr photoperiod at the bed (typically about 0.3 m depth in runs at baseflow) fell from about 340 µE m−2 s−1 upstream to as low as 80 µE m−2 s−1 (median 190 µE m−2 s−1) at matched downstream sites. This reduction in light proportionally reduced benthic primary productivity downstream of the mining activity. In turn this reduced benthic algal biomass and lowered the phototrophic content of the epilithon. In spite of their extremely low settling velocities (< 1 µm s−1) some clay particles were deposited on the stream bed owing to entrapment in the epilithon matrix. This decreased the organic content of the epilithon (from an average of 19% upstream to 8.5% downstream) so reducing its quality as food for invertebrate animals.

Microhabitat preferences of benthic invertebrates and the development of generalised Deleatidium spp. habitat suitability curves, applied to four New Zealand rivers

Microhabitat preferences of 12 benthic invertebrate taxa were investigated in four New Zealand rivers. Most taxa showed significant habitat preferences. Generally, taxa were more abundant in water ...

Upper thermal tolerances of twelve New Zealand stream invertebrate species

Abstract The upper thermal tolerances of 12 New Zealand freshwater invertebrate taxa were compared using a laboratory lethality testing protocol. Temperatures that were lethal to 50% of the test organisms (LT50S), following acclimation to 15°C, generally declined over the 4 day period of the tests. LT50 values after 48 and 96 h exposure ranged from 24.5 to > 34°C and 22.6 to 32.6°C, respectively, indicating that temperatures that occur in summer in many NZ streams and rivers may limit the distribution and abundance of some of these invertebrate species. Larval insects included both the most sensitive species (a plecopteran and two Ephemeroptera) and the most tolerant (the larvae of the elmid beetle Hydora sp.) in this study. The two molluscs studied (Potamopyrgus antipodarum (Prosobranchia: Hydrobiidae) and Sphaerium novaezelandiae (Bivalvia: Sphaeriidae)) showed high thermal tolerance, whilst two crustaceans (Paratya curvirostris (Atyidae) and Paracalliope fluviatilis (Eusiridae)) were moderately toleran...

Ecological characterisation, classification, and modelling of New Zealand rivers: An introduction and synthesis

Abstract A programme of research to characterise, classify, and model New Zealand rivers according to hydrological, water quality, and biological properties is introduced. The results are detailed in the accompanying eight research papers. These studies provide the first national perspective on water quality and biology in New Zealands rivers using a consistent methodology. They are also the first step toward providing managers with robust models for predicting the effects on aquatic biota of changes in flow regimes and catchment land use. A synthesis of the results is given in this paper together with recommendations for riverine ecoregions in New Zealand.

Lake sediment phosphorus release management—Decision support and risk assessment framework

Abstract The release of phosphorus (P) from the sediments of eutrophic lakes is often associated with the proliferation of nuisance algal blooms, especially cyanobacteria. The successful implementation of management actions aimed at reducing such algal blooms requires an integrated approach, including both external and internal nutrient loads. The internal load of P can be a significant source of P for primary production, with greatest inputs occurring when lakes stratify and the hypolimnetic waters become anoxic. We reviewed the nature and characteristics of New Zealand lakes in relation to factors which affect the application of technologies to manage internal P loads within individual lakes. New Zealands windy maritime climate causes lakes to mix more deeply than lakes in continental areas, which are characterised by relatively hot, calm summers. We assessed a range of management options which may be used to control internal P loads, and considered these in a de cision‐support framework aimed at identifying the key factors which may limit successful application. Methods to reduce P release from sediments include: physical approaches—such as artificial destratification, hypolimnetic aeration, enhanced lake flushing, and dredging/discing; and geochemical approaches—such as the application of alum and iron as flocculation agents, and other products as “capping” materials. The capping materials may be either a passive physical barrier (e.g., sand, gravel, clay) or an active barrier. The active barrier systems are generally pervious chemical or geochemical materials capable of binding contaminants by adsorption or precipitation processes. A decision‐support and risk assessment framework is provided to assist managers in the development of appropriate strategies for reducing or controlling internal P loads, and thus cyanobacteria blooms. A review of the sediment characteristics of lakes in the Taupo volcanic zone showed marked variability in sediment P content, and elevated geothermal arsenic concentrations in some lake sediments, which may affect the efficacy of chemical capping agents, indicating that site‐specific consideration of capping agent dose is required.

Toxicity of ammonia to nine native New Zealand freshwater invertebrate species

The toxic concentration for un-ionized ammonia (NH3) was assessed for nine native New Zealand invertebrate species. The 96-h EC50 values at 15°C and pH 7.6 and pH 8.2 ranged from 0.18 to >0.8 g/m3 NH3. The rank of species sensitivity was: shrimp (Paratya curvirostris) (least) ≈ mayfly (Zephlebia dentata) ≈ stonefly (Zealandobius furcillatus) < Oligochaeta (Lumbriculus variegatus) < fingernail clam (Sphaerium novaezelandiae) < mayfly (Deleatidium spp.) < a snail (Potamopyrgus antipodarum) < caddis (Pycnocentria evecta) < crustacean (Paracalliope fluviatilis) (most). Surprisingly, the more sensitive species were those which would normally be associated with lowland streams (the snail and crustacean) rather than the normally accepted “sensitive” species (mayflies and stoneflies). Temperature had no significant effect on the acute toxicity of un-ionized ammonia with snails tested at 15, 20, and 25°C. The invertebrates were more sensitive than the native fish species tested (inanga, EC50 1.60 g/m3 NH3; Richardson 1991). A final acute value (FAV) calculated for these species was 0.15 g/m3 NH3. This compares with the FAV value of 0.52 g/m3 NH3 derived by the US Environmental Protection Agency (EPA) as the basis for the ammonia criterion for salmonid containing waters. Thus EPA criteria may not provide adequate protection for New Zealand species. These data suggest that chronic studies would be particularly desirable on native New Zealand species to better determine their sensitivity to long term ammonia exposure.

Periphyton biomass related to point-source nutrient enrichment in seven New Zealand streams

Periphyton biomass on natural substrata at 26 sites above and below point source discharges in 7 New Zealand streams was compared with maximum potential values predicted by a laboratory calibrated model to determine the extent to which biomass was controlled by nutrients. Point-source enrichment, which increased dissolved reactive phosphorus (DRP) from 6 to 100 times the saturation level (about 25 μg/l) in five streams, was found to substantially increase biomass at all enriched sites in four streams. In two of these streams, biomass below the enrichment inputs was about 1200 mg chl a/m2. Overall, biomass averaged only 35 ± 44% of that predicted from phosphorus, velocity and temperature using the model. Furthermore, aesthetically nuisance biomass levels (i.e. > 200 mg chl a/m2) were observed at only 7 of the 19 downstream sites. In many cases, the lower than expected biomass levels were associated with high macroinvertebrate grazer densities, riparian shading or unsuitable attachment surfaces. These factors, therefore, appear to have exercised more control on periphyton biomass than nutrients, and may offer more effective alternatives for biomass control in enriched streams than lowering DRP below biomass saturating levels.

How do aquatic communities respond to contaminants? It depends on the ecological context

Context dependency refers to variation in ecological patterns and processes across environmental or spatiotemporal gradients. Research on context dependency in basic ecology has focused primarily on variation in the relative importance of species interactions (e.g., competition and predation) among communities. In this Focus article, the authors extend this concept to include variation in responses of communities to contaminants and other anthropogenic stressors. Because the structure of communities varies naturally along environmental gradients, their responses to contaminants may also vary. Similar to the way in which aquatic toxicologists assess abiotic factors associated with contaminant bioavailability, observations about context dependency could be used to test hypotheses about ecological mechanisms responsible for differences in sensitivity among communities.