Search

R code and eDNA input files to train a taxon-independent community index (TICI) for 53 riverine monitoring sites in New Zealand

The condition of New Zealand's remnant wetlands has been documented by landscape-scale assessments such as the Index of Ecological Integrity and Wetland Condition Index. We explored the potential for microscopic aquatic biota (epiphytic diatoms) to provide complementary information about wetland condition using data from 77 lowland sites (mainly palustrine swamps) with circumneutral pH. In the South Island, correspondence between diatoms and wetland indices or water quality was weak. In the North Island, conductivity and total dissolved nitrogen (TDN) together explained 49% of the variance in assemblage composition and several diatom genera were indicative of high or low conductivity, dissolved phosphorus and TDN. Changes in these water quality variables may trigger changes in wetland condition, which are eventually reflected by the landscape-scale indices. Diatoms respond rapidly to water quality changes suggesting potential for diatom indicator taxa to provide early warning of wetland degradation or to track restoration.

Cyanobacterial blooms pose health risks to recreational water users. In New Zealand, cyanobacteria biovolumes are used to assess risk, but analyses can be time-consuming and costly. In this study, measurements from a handheld phycocyanin sensor (Cyclops-7, Turner Designs, USA) were compared with biovolumes from five lakes and a river in the Rotorua district over two years (2016, n = 121; 2017, n = 63). In the laboratory, relationships between sensor phycocyanin and biovolumes were assessed for four species to investigate precision and detection limits. The relationship between phycocyanin and biovolume was generally weak (

Exotic trees, such as willow (Salix spp.), have become invasive around New Zealand waterways. Lowland wetlands in particular are vulnerable, with invasions changing hydrology and causing biodiversity loss. Applying herbicide to the willow canopy is a cost-effective control method, however uncertainty remains around effects on wetland aquatic invertebrates. Within a North Island, New Zealand, wetland, we conducted a paired before-after, control-impact study to determine if aerially applied glyphosate (with adjuvants) affected invertebrate assemblages. No effect on communities was detected during the first year after glyphosate treatment, however significant differences between control and spray-exposed communities were found during the second year, coinciding with a significant drought event in March 2013. By the third year, no statistically significant differences were found between communities from control and spray-exposed sites. This study suggests that glyphosate use, in comparable environments, is unlikely to affect aquatic invertebrates. Furthermore, the study illustrates invertebrate communities’ resilience to drought events.

The Opuha Dam was designed for water storage, hydropower, and to augment summer low flows. Following its commissioning in 1999, algal blooms (dominated first by Phormidium and later Didymosphenia geminata) downstream of the dam were attributed to the reduced frequency and magnitude of high-flow events. In this study, we used a 20-year monitoring dataset to quantify changes associated with the dam. We also studied the effectiveness of flushing flows to remove periphyton from the river bed. Following the completion of the dam, daily maximum flows downstream have exceeded 100 m(3) s(-1) only three times; two of these floods exceeded the pre-dam mean annual flood of 203 m(3) s(-1) (compared to 19 times100 m(3) s(-1) and 6 times203 m(3) s(-1) in the 8 years of record before the dam). Other changes downstream included increases in water temperature, bed armoring, frequency of algal blooms, and changes to the aquatic invertebrate community. Seven experimental flushing flows resulted in limited periphyton reductions. Flood wave attenuation, bed armoring, and a shortage of surface sand and gravel, likely limited the effectiveness of these moderate floods. Floods similar to pre-dam levels may be effective for control of periphyton downstream; however, flushing flows of that magnitude are not possible with the existing dam infrastructure. These results highlight the need for dams to be planned and built with the capacity to provide the natural range of flows for adaptive management, particularly high flows.

We examined catchment-scale transport of sodium monofluoroacetate (‘1080’) in rainfall run-off. We developed a hydrological model describing the overland transport of 1080 and validated model results using field data from a headwater catchment, where we intensively sampled a stream during a rainfall event (28 mm in 8 h) that followed 1080 aerial application. Only one stream sample contained a measurable concentration of 1080 (0.1 µg/l; collected 105 min from the start of rainfall), while 1080 was below detection limits (0.1 µg/l) in all other samples. Absence of visually observable overland flow conditions (puddles and saturated areas connected to the stream) early during the rainfall event suggested that overland transport might not have been the dominant mechanism in this catchment. Moreover, analyses of soilwater samples collected from lysimeters installed in the catchment indicated the propensity of 1080 to leach into soil, suggesting the need to investigate subsurface transport pathways.

Temporal variability of wetland invertebrates was examined at two scales—inter-annual and seasonal—to determine whether it could confound results of spatially extensive wetland surveys. The inter-annual study collected samples from the Bullock Creek wetland (BCW) each summer for 4 years; the seasonal study collected samples quarterly for 14 months from two wetlands (Mahinapua and Shearer). Water pH, temperature and conductivity were also measured concurrently. Three site groupings were identified in BCW, reflecting differences in physical–chemical parameters, which varied temporally but never converged. Few annual differences were found in invertebrate relative abundances in BCW, and ordination produced three sample groups, each of which contained distinct invertebrate communities. Water pH differed consistently between Mahinapua and Shearer. Relative abundances of nine taxa varied seasonally; however, ordination showed that both wetlands always supported discrete invertebrate communities. These ...

Few studies have examined the effects of low flows on stream biota—a paradoxical situation considering the mounting pressure on streams as a result of increased human abstraction. We present a conceptual model describing processes operating in rivers during low flows and argue that such processes reflect both direct effects of reduced flow on benthic invertebrates and indirect effects of enhanced plant growth occurring during such periods. Our model suggests that the longer the duration of low flow, the more the plant community will change and, in turn, the more habitat quality will change, with consequences to benthic invertebrate communities and higher trophic levels. A fundamental part of the model is the recognition of different stream types, based on a habitat-template matrix of resource supply, interflood velocity, and substrate stability during flood events. This habitat template results in 12 stream types, each of which supports specific plant communities that set the antecedent plant conditions prior to a low-flow period. During low flows, hydraulic factors interact with the antecedent plant communities, which undergo specific responses. For example, in low-nutrient streams with gravel substrates and dominated by diatoms, low-flow conditions will cause little or no change to the antecedent plant community because this plant community is structured by top-down grazing pressure. Consequently, benthic invertebrate composition will not change. In contrast, cover and biomass of filamentous green algae in higher-nutrient gravel-bed streams will increase during low-flow events, and this increase will affect habitat suitability for invertebrates over and above those caused solely by hydraulic changes. The greatest changes to invertebrate communities are expected in macrophyte-dominated streams because these plants change instream habitat conditions the most during extended periods of low flow. Therefore, current flow-management techniques must consider the type of plant communities that exist prior to low flows and be cognizant of that fact that these plant communities can have dramatic influences on benthic communities during low-flow periods.

Large‐scale control of Australian possums throughout New Zealand uses toxic cereal baits containing 1080 (sodium fluoroacetate). These baits are often aerially applied over rough terrain where ground application is impractical. Many small streams flow in these areas, so 1080 baits can potentially fall into them. The ecological effect of 1080 leaching from baits was assessed on freshwater fish and invertebrate communities in four streams using a BACI experimental design. Four sites were selected in each stream: 10m and 100m below and 10m and 100m above where 1080 baits were placed. All sites were monitored 4 days and 1 day before and after baits were added, respectively. Separate experiments were conducted to assess impacts of 1080 on native fish and invertebrate communities. Baits were added to each stream to achieve bait densities 10 × greater than found after normal control operations. Three species of native fish, longfin eels (Anguilla dieffenbachii), koaro (Galaxias brevipinnis), and upland ...

Forty‐eight streams were surveyed during four aerial 1080 operations in New Zealand's South Island to quantify the number of 1080 baits falling into streams. Bait size used in each operation varied considerably: small (2g) baits in Marlborough, medium‐sized (6–7 g) baits in Canterbury and the West Coast, and large (11 g) baits in Lewis Pass. The number of baits found in streams varied widely, and was related only to bait size, with more of the small baits found in streams than the large baits. There was no relationship between stream width or canopy cover and the number of baits found within a stream. These findings suggest that the potential number of baits falling into a stream cannot be calculated from the bait application rate and the stream size. The fate of submerged 1080 baits was also examined in a laboratory flow tank. Submerged baits fragmented within 3–4 days. 1080 was rapidly leached from submerged baits: almost 50% of original 1080 had leached after 5h, and >90% after 24h. Such rapid...

Patch selection for cobbles covered by different food types, with and without deposited sediment, by two common New Zealand stream invertebrates, the snail Potamopyrgus antipodarum (Hydrobiidae) and the mayfly Deleatidium sp. (Leptophlebiidae), was quantified. Each taxa was exposed to cobbles covered by (1) filamentous green algae (FGA) or diatoms, and (2) diatoms or heterotrophic biofilms. Two cobbles of each food type were used in each trial, one of which was contaminated by deposited sediment. All cobbles were embedded in plaster in small basins to prevent animals hiding under them, and a known number of animals placed into each basin. The location of each animal was recorded over time, with some observations being made during darkness to see whether this influenced animal movement. More Potamopyrgus were found on cobbles covered by FGA than cobbles covered by diatoms. Sediment-contaminated cobbles covered with FGA also supported more snails than uncontaminated cobbles covered with diatoms. More Potamopyrgus were found on cobbles covered by diatoms than biofilms, and sediment reduced their preference for both these foods. More Deleatidium nymphs were found on diatom-covered cobbles than FGA-covered cobbles. Sediment reduced the preference of Deleatidium for diatoms, but more animals were found on cobbles with sediment-contaminated diatoms than uncontaminated FGA. Patch selection was similar between cobbles covered by either diatoms or biofilms, but sediment reduced the preference of both these foods to Deleatidium. More Deleatidium were recorded on bare plaster during darkness, suggesting they were more mobile at night and searching for new habitats. These results help explain the common occurrence of Potamopyrgus in streams draining developed catchments where FGA blooms and deposited sediment are common, and of Deleatidium in streams draining less developed catchments where FGA and deposited sediment are uncommon.

Effects of high suspended-sediment (SS) levels (up to c. 20,000 NTU) from fine clay on 5 species of New Zealand stream insects and the crayfish Paranephrops planifrons were assessed by short-term (24 h) exposures to different SS concentrations. There were no patterns of increasing mortality over 24 h with increasing SS concentrations. Effects of longer-term exposure (14 days) of repeated 4 h exposures to lower SS concentrations (c. 1000 NTU) on the common leptophlebiid mayfly Deleatidium were also investigated. No difference in mortality was found between the test and control solutions. We suggest that so-called ‚sensitive’ invertebrates are tolerant of high SS concentrations, and that even repeated exposures to high SS concentrations have little effect on survival. Absence of these animals from catchments with high SS concentrations thus most likely reflects adverse changes to instream habitat conditions, such as filling of interstitial spaces, contamination of food sources, or both.

Landscape classifications, such as ecoregions, are widely promoted as spatial frameworks for aquatic conservation and environmental management. The River Environment Classification (REC) is an alternative approach to landscape-scale river classification. The REC classifies individual sections of river networks according to the climate, topography, geology, and land cover of the unique upstream watershed of each section. The classification is hierarchical and is based on the assumption that climate, topography, geology, and land cover are dominant causes of spatial variation in physical and biological characteristics of rivers at 4 spatial scales. The ability of the REC to explain variation in invertebrate samples collected from 237 sites in New Zealand was compared to that of region-based classifications using classification strength tests. Classifications with differing numbers of classes were compared using relative classification strengths calculated by expressing absolute classification stren...

We examined the effects of summer low‐flow on invertebrate communities in two New Zealand rivers of contrasting enrichment and associated periphyton development. Quantitative benthic samples were collected and hydraulic measurements made from three runs in each river over a 6‐week period. Although hydraulic conditions and time since last flood disturbance were similar in both rivers, invertebrate communities were dissimilar. This dissimilarity reflected differences in periphyton communities within each river. The invertebrate community in the low enrichment river (Okuku River) was dominated by high numbers of “clean‐water” insect taxa, and this community changed little over time. Periphyton biomass was low here, and the community was composed of diatoms. Major changes occurred to the invertebrate community in the high enrichment river (Waipara River) over the summer, where the relative abundance of dominant invertebrate taxa changed from insects and snails to ostracods. Periphyton biomass was hig...

Many foothill rivers in the eastern regions of New Zealand undergo severe reductions in flow during summer. These reductions are often exacerbated by abstractions for out‐of‐river uses. It has been observed that at such times some river ecosystems are more detrimentally affected by reduced flows than others. We hypothesised that the degree of degradation in river ecosystems during summer low‐flows is dependent on a river's enrichment status. We examined the effect of low flows on periphyton community dynamics in two Canterbury rivers of contrasting enrichment. Three runs in each river were sampled on four occasions over a summer low‐flow period, during which discharge was amongst the lowest on record for these rivers. Percentage cover of major periphyton groups on the riverbed was estimated across five transects in each run, and periphyton was scraped from five replicate rocks per run to quantify taxonomic richness, community composition, and chlorophyll a biomass. Periphyton communities in each ...

The effect of deposited sediment on invertebrate drift was experimentally assessed by adding fine sediment to three of six cobble‐lined artificial channels. One invertebrate species, Deleatidium spp., was added to the channel after the addition of sediment, whereas other taxa had colonised the channel naturally before the addition of sediment. Invertebrate drift was collected from each channel after the added sediment had worked its way into the interstitial spaces of the cobbles. Drift was collected every evening and morning for 3 days, after which time benthic densities in the channels were assessed. The percentage of benthos in the drift was significantly higher from sediment‐treated channels than from untreated channels for Paracalliope fluviatilis, Oxyethira albiceps, Hydrobiosis sp., and chironomid larvae. Drift of these animals from sediment‐treated channels was more than double that from untreated channels, with an average of over 5% of the benthos drifting from the sediment‐treated chann...

Substrate stability in streams is fundamental to benthic communities, many of which decline in biomass and taxon richness with decreased stability. Although of obvious importance in describing a stream's disturbance regime, substrate movement is often difficult to quantify accurately. Traditional techniques rely either on subjective scoring systems (e.g., Pfankuch stability score), or require repeated site visits to follow downstream displacement of painted stones. Newbury's Instability Index measures substrate movement based on calculations of a stream's tractive force at bankfull discharge, but the assumptions on which this method is based limit its use to lowland streams. We have developed a new method to assess substrate movement suitable for shallow, steep mountain streams with a high bed roughness, based on an extensive review of existing hydraulic literature. We calculated the % of the streambed in motion at bankfull discharge (P BF ) in 48 New Zealand headwater streams using our method, t...

Effects of 3 disturbance parameters (% of the streambed in motion at bankfull discharge [P BF ], catchment-specific discharge [SPECQ BF ], and frequency of bankfull floods [N BF ] on aquatic bryophyte richness and community composition were assessed. Relationships between taxonomic richness and P BF and SPECQ BF were strongly curvilinear, such that richness was low in both stable and highly unstable streams, and in streams of both low and high SPECQ BF . Richness was highest in streams with moderate P BF and SPECQ BF . Interspecific competition may have reduced species richness at stable sites. In contrast, only a few bryophyte taxa were able to grow at unstable sites. Low richness at sites with a low SPECQ BF most likely reflects the intolerance of some species to desiccation. Low richness at sites with high SPECQ BF may reflect differences in the resistance of different taxa to high discharges. Community compo...

The effects of the aquatic moss Fissidens rigidulus on near-bed flow structure in a cobble-lined flume were investigated. Moss-covered cobbles were placed in the flume, and velocities were measured at six vertical profiles upstream, above, and downstream of the cobbles. All measurements were replicated at three different discharges. An acoustic doppler velocimeter (ADV) was used to measure velocity fluctuations in three dimensions at each point, at a 0.04-s sampling interval for 2 min. Following this, the moss was removed without disturbing the cobbles' spatial arrangement, and measurements were repeated to characterize background hydraulic conditions. We investigated mean local velocities, Reynolds stresses, total turbulence energy, relative turbulence intensities, and velocity spectra with and without the moss. Two flow layers were observed in all our experiments: an upper logarithmic layer and a lower roughness sublayer. Velocities in the upper layer followed the standard logarithmic law, whereas velocities in the roughness sublayer did not, because of interaction between flow and the roughness elements. The presence of Fissidens caused a reduction in average longitudinal velocity, Reynolds stress, and total turbulence energy. Relative turbulence intensity was much higher in the presence of the moss. An internal boundary layer (IBL) around the moss was also observed; this IBL was destroyed behind the moss by turbulent mixing in the roughness sublayer. The IBL thickness increased with increasing flow.

A broadscale survey of 118 streams was made throughout New Zealand's South Island to establish relationships between aquatic bryophytes and selected environmental variables. Bryophytes were found in 95 of the streams examined, and covered large areas of the substratum (mean cover of 17%, maximum cover of 86%). TWINSPAN analysis revealed the existence of five sample groupings, of which one supported no bryophytes. Streams without bryophytes typically flowed through developed catchments (pasture or pine) composed of easily eroded rocks. Nutrient levels were high in these streams, and low‐flow events were also common. Streambed stability was low, reflecting lack of stable bedrock and boulder substrata. TWINSPAN identified two major groups of streams with bryophytes: those supporting mosses and those supporting liverworts. These streams differed from those without bryophytes by having a higher streambed stability, and fewer low‐flow events. These two variables thus appear fundamental in controlling a...

Tributary alpine streams in six sub‐catchments in Arthur's Pass National Park (South Island, New Zealand) were surveyed to assess the frequency of streams supporting aquatic bryophytes. Relationships between streambed stability and bryophyte occurrence were examined. Invertebrate communities associated with bryophytes were characterised, and compared between streams flowing above the tree line, and below. Of 103 tributary streams encountered, 53 were above the tree line, and 50 were below. Aquatic bryophytes occurred in half these streams irrespective of riparian shading, but bryophyte distributions were strongly influenced by streambed stability. Invertebrate communities associated with bryophytes were dominated by Nematoda, Chironomidae, Oligochaeta, and Copepoda. This is fundamentally different from the bryofauna outside New Zealand, and may reflect the absence of certain bryophyte‐dwelling families of Trichoptera, Plecoptera, and Ephemeroptera from New Zealand. Invertebrate densities within b...

The variability and abundance of potential invertebrate foods in two contrasting alpine streams were investigated. Potential foods examined included periphyton and detritus on artificial substrates, and naturally occurring organic matter in gravel and bryophyte habitats. Artificial substrates simulating rocks (plain tiles), and bryophytes (tiles covered with grass carpet) were used to sample periphyton. Chlorophyll a levels were higher at the unshaded site (3.42 μg cm−2 of tile) than the shaded (0.56 μ.g cm−2 of tile) and were also higher on artificial bryophytes (3.61 μg cm−2 of tile) than rocks (0.38 μg cm−2 of tile). Periphyton colonising artificial bryophytes at the unshaded site also had a much lower temporal variability than that colonising plain tiles (coefficient of variation for total periphyton pigments = 5.7% on artificial bryophytes; 10.8% on plain tiles). Variation in periphyton biomass was also higher at the unshaded site (CV = 8.3%) than the shaded site (CV = 4.4%). This reflects t...

Meiofauna associated with bryophyte and gravel habitats in two small alpine streams was investigated to determine its potential importance to stream communities. These invertebrates are traditionally neglected in stream surveys and their ecological roles poorly understood. Twenty‐one operational taxonomic units (OTUs) were found during the study, of which at least six were undescribed (two Copepoda and four Acarina). Meiofaunal densities were higher at the unshaded site than the shaded site, and higher within bryophyte than gravel habitats. Stepwise multiple regression analyses illustrated the importance of bryophytes to members of the meiofauna in each stream, and different meiofaunal communities were found associated with aquatic bryophytes and gravels. The high densities of Chironomidae, Nematoda, Copepoda, Tardigrada, and Rotifera associated with bryophytes may reflect the food value of the high periphyton biomass associated with these plants, and the shelter they offer from fast water curren...

An artificial substratum invertebrate sampler, designed to mimic bryophytes, is described and evaluated. Invertebrate and algal colonisation of these structures was rapid, and invertebrate abundance peaked after 4 weeks. Following an exposure period of 2 months, total invertebrate density, taxonomic richness, and densities of many taxa were similar to those usually found on natural bryophytes, although densities of Nematoda, Limonia hudsoni (Tipulidae), and an empidid were lower. Taxa that are characteristic of riffles (e.g., Deleatidiwn sp. and Nesameletus sp. (Ephemeroptera), or Stenoperla prasina and Zelandobius sp. (Plecoptera) did not colonise the “stems” of the artificial bryophytes very extensively, but were present on the bases of these structures and on the underlying bedrock. TWINSPAN classifications identified a strong similarity between faunas of the artificial bryophytes and their real counterparts, but dissimilarity to faunas associated with riffles. Thus, the artificial bryophytes ...