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

Monitoring the long-term dynamics of lake phytoplankton can help understand their natural temporal variability, as well as assess potential impacts of interventions aimed at improving lake ecological condition. However, investigating long-term changes in lake ecosystems has received scant attention. In the present study, we analyzed a long-term dataset of phytoplankton communities collected from 1990 to 2013 from eleven of the 12 Rotorua Te Arawa lakes in New Zealand, to explore their responses to changing abiotic conditions. We used a sequential algorithm to examine the likelihood of regime shifts in abiotic and biotic factors during the study period that could be attributable to lake interventions. Our analysis suggests that lake interventions have improved the abiotic factors, whereas the response of biotic factors was less clear. Total phosphorus levels were implicated in the decline in lake condition, including in two lakes subject to lake interventions, and in four control lakes. Both abiotic and biotic factors showed diverse trends (e.g., increase, decrease or no change), and abiotic factors had more regime shifts than biotic factors. Shifts in biotic indices also displayed time lags to shifts in abiotic factors. Long-term responses of abiotic and biotic factors were also influenced by lake morphological characteristics and climatic variables. This latter finding underscores the importance of considering lake morphological characteristics and climate changes when planning management practices. A sound understanding of resilience and threshold of phytoplankton shifts to environmental changes are needed to assess the effectiveness of previous management strategies and prioritize the future conservation efforts toward water quality goals.

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 ...

Assessments of wetland condition are generally based on measures of variables related to plants or large animals (birds, fish), and catchment or landscape features. This approach ignores the considerable biodiversity and functional values of small aquatic organisms. The aim of this study was to assess the correspondence between landscape-based indices of wetland condition and the community composition of both aquatic invertebrates and diatoms across a broad range of wetlands in the West Coast region of New Zealand. Aquatic invertebrates and diatoms were sampled from 29 lowland wetlands subject to varying degrees of catchment modification. Wetland condition was assessed independently using two methods: a field-based method to give the Wetland Condition Index, and a GIS-based method that gave an Index of Ecological Integrity. Strong relationships existed between community composition and pH, so we partitioned the community data into groups according to wetland pH. We found only weak relationships between wetland condition scores and invertebrate and diatom communities within each pH group. In most cases, data describing the nutrient status of the water had the strongest influence on invertebrate and diatom communities. Lack of strong associations between measured wetland condition indices and either diatom or invertebrate community composition suggests that neither index was dominated by variables directly influencing the aquatic component of wetland biota. The challenges now are to identify the critical variables, and to develop complementary wetland scoring systems that better reflect the status of small aquatic organisms.

Drainage is a major disturbance affecting wetlands, as drains lower water tables and convert lentic habitats to lotic ones. Consequently, invertebrate communities in drained wetlands are likely to differ from those in unimpacted wetlands. This study investigated the effect of hydrological restoration on invertebrate communities in small drains in a New Zealand fen. Invertebrates were collected over 4 summers from 10 drains within the wetland, one of which was blocked as part of a restoration program. The sampling protocol thus represented a Before-After Control-Impact experiment. Invertebrate community composition varied over the 4 years, but variability was greatest in the manipulated drain before and after it was blocked. Relative abundance of the amphipod Paraleptamphopus decreased after blockage, whereas those of the midges Chironomus zelandicus and Tanypodinae increased. Relative abundances of these taxa in control sites were unchanged. Hydraulic restoration thus had a demonstrable impact on the invertebrate communities. The invertebrate community of the blocked drain was compared to that of natural wetlands in undisturbed catchments. Similarity was very low prior to drain blockage, but increased following drain blockage. Invertebrate communities in the restored drain were more similar to those of low pH wetlands than high pH wetlands. Given the goal of restoring the communities to those similar to natural conditions, this was a beneficial result. These results, coupled with studies that showed a decline in the cover of alien pasture grasses around the blocked drain, suggest that drain blockage represents a cost-effective way of restoring wetland plant and aquatic invertebrate communities, especially where connectivity allows for the natural recruitment of these organisms into restored areas.

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.

Summary 1. The impacts of low flows on invertebrates were assessed in six experimental channels placed in a lowland stream. Each channel consisted of replicate stacked gravel-filled baskets (buried 0–7, 8–14 and 15–21 cm deep) from which invertebrates were sampled. Samples were collected before, and 1 and 2 months after flows were reduced by varying amounts. We predicted that invertebrate communities would change most with the lowest flows that persisted longest. The effects of reduced flow on channel and intragravel-velocities, temperature, dissolved oxygen and algal biomass were also monitored. 2. Mean velocity (17 cm s−1) and depth (20 cm) were similar in all channels prior to flow reduction, but were reduced in five channels by 25% to 98%, a sixth channel serving as a control. Mean intragavel velocity prior to flow reduction (1.7 mm s−1) was also reduced from 17% to 51%. Flow reduction had no effect on temperature, which ranged from 11.2 °C (night) to 19.6 °C (day). Dissolved oxygen was generally high (mean = 94% saturation) but variable (range from 50% to 145%), and did not differ between channels after flow reduction. Periphyton biomass (chlorophyll a and AFDMalgae) increased over time and was positively related to velocity after 1 month of flow reduction. After 2 months, however, this relationship reversed, with higher chlorophyll and AFDMalgae in lower velocity channels. Organic matter biomass (AFDMtotal) was significantly higher in channels with lower velocities, and did not change with time. There was no relationship between AFDMtotal and velocity in baskets from different depths. 3. Greater than 85% of animals were found in the upper baskets (0–7 cm deep), and flow reduction had no influence on the vertical distribution of invertebrates. After 1 month, invertebrate density had declined roughly in proportion to the magnitude of flow reduction in all channels where flows were reduced more than 25%. Densities recovered to pre-reduction levels within 2 months. The amphipod, Paracalliope fluviatilis dominated all channels numerically prior to flow reduction, but its density declined markedly during the study. Densities of Ostracoda, Oxyethira albiceps and Cladocera increased dramatically after 2 months of flow reduction, especially in the lowest flow channels. Of the physical variables measured, chlorophyll a biomass and discharge best explained the temporal changes in the invertebrate community. 4. The effects of increased duration and magnitude of flow reduction on invertebrate communities were restricted to changes in the relative abundances of just a few taxa. Our results suggest that invertebrates in this lowland stream were resistant to the experimental flow reduction, presumably because of their broad ecological tolerances. We also found that more prolonged low flows did not result in predictable changes. This finding may have implications in terms of using hydraulic-habitat models to set minimum flows in lowland streams if invertebrates can persist at flows much lower than their supposed optima.

Native macrophytes were transplanted into a small urban stream as part of a rehabilitation program, that also meandered the previously channeled stream, naturalized stream banks, and planted native riparian vegetation. Transplanted macrophytes minimized spread of introduced macrophytes and were viewed beneficially by residents, as was the stream rehabilitation. We transplanted the native macrophyte Myriophyllum triphyllum into five larger streams dominated by exotic macrophytes—some of which were weeded prior to transplanting—to see whether Myriophyllum could prevent regrowth of weeded plants. Transplanted Myriophyllum plants were washed away in two streams, reflecting high shear stresses there. Myriophyllum cover in the other streams decreased as weeded plants regrew. Our attempt at eliminating exotic macrophytes in patches in large streams was unsuccessful. Furthermore, council authorities weeded other experimental sections following complaints from residents of excess macrophyte growth. This problem highlighted conflicting multiple values placed on urban streams by managers and the public. A repeat survey of residents living near the original rehabilitated stream showed that many respondents were now critical of excessive plant growth—both in-stream and riparian. A recurring comment made concerned the apparent lack of maintenance to the stream, giving it an untidy appearance. Difficulties with propagating and transplanting native macrophytes into larger streams, coupled with a negative perception of native vegetation (both in-stream and riparian) if it looks unmanaged, suggest that planting macrophytes or riparian plants as part of urban stream rehabilitation programs may be more problematic than realized.

Summary 1. The hydrological regime is important to the distribution of benthic organisms in streams. The objective of this study was to identify relationships between hydrological variables, describing the flow regime, and macrophyte cover, species richness, diversity and community composition in Danish lowland streams. 2. We quantified macrophyte vegetation in 44 Danish streams during summer by cover, species richness and diversity. Flow regime was characterized by 18 non-intercorrelated variables describing magnitude, frequency and duration of low and high flow events, timing or predictability of flow and general flow variability. 3. We found support in the stepwise multiple regressions analysis for our expectation that macrophyte cover is lowest in streams with high flow variability and highest in streams with long duration of low flow and low flow variability. We found support for the intermediate disturbance hypothesis as there were significant quadratic relationships between species richness and diversity as functions of disturbance frequency. There was poor discrimination in a detrended correspondence analysis (DCA) analysis of macrophyte community composition between four twinspan groups separating streams with different hydrological properties. Moreover, we did not find any relationship between the presence of disturbance-tolerant species and hydrological disturbance, suggesting that plant community composition developed independently of stream hydrology.

Summary 1. Invertebrates were collected semi-quantitatively from four relatively undisturbed wetlands in the west coast of New Zealand’s South Island: two acidic fens and two swamps. Samples were collected from up to four discrete habitats within each wetland: large open-water channels, small leads (small, ill-defined channels with emergent vegetation in them) and large (>10 m diameter) or small (

Summary 1. Floods and low flows are hydrological events that influence river ecosystems, but few studies have compared their relative importance in structuring invertebrate communities. Invertebrates were sampled in riffles and runs at eight sites along 40 km of a New Zealand gravel-bed river every 1–3 months over 2.5 years, during which time a number of large flood and low flow events occurred. Flows were high in winter and spring, and low in summer and autumn. Four flow-related variables were calculated from hydrological data: flow on the day of sampling (Qsample), maximum and minimum flow between successive samples (Qmax and Qmin, respectively), and the number of days since the last bed-moving flood (Ndays). 2. The invertebrate community was summarised by relative densities of the 19 most abundant taxa and four biotic metrics [total abundance, taxon richness, the number of Ephemeroptera, Plecoptera and Trichoptera taxa (i.e. EPT richness), and per cent EPT]. Invertebrate density fluctuated greatly, and was high in summer and autumn, and low during winter and spring. Stepwise multiple regression (SMR) analysis was used to investigate relationships between the invertebrate community and season, flow, habitat and water temperature. 3. Seasonal variables were included in almost 50% of the SMR models, while flow-related variables were included in >75% of models. Densities of many taxa were negatively correlated to Qmin and Qmax, and positively correlated to Ndays, suggesting that while high flows reduced invertebrate densities, densities recovered with increasing time following a flood. Although season and flow were confounded in this study, many of the taxa analysed display little seasonal variation in abundance, suggesting that flow-related variables were more important in structuring communities than seasonal changes in density associated with life-cycles. 4. Five discrete flood and low flow events were identified and changes to invertebrate communities before and after these events examined. Invertebrate densities decreased more commonly after floods than after low flows, and there was a significant positive relationship between the number of taxa showing reductions in density and flood magnitude. Densities of most invertebrates either remained unchanged, or increased after low flow events, except for four taxa whose densities declined after a very long period (up to 9 months) of low flow. This decline was attributed to autogenic sloughing of thick periphyton communities and subsequent loss of habitat for these taxa. 5. Invertebrate communities changed more after floods and the degree of change was proportional to flood magnitude. Community similarity increased with increasing time since the last disturbance, suggesting that the longer stable flows lasted, the less the community changed. These results suggest that invertebrate communities in the Waipara River were controlled by both floods and low flows, but that the relative effects of floods were greater than even extended periods of extreme low flow. 6. Hydraulic conditions in riffles and runs were measured throughout the study. Riffles had consistently faster velocities, but were shallower and narrower than runs at all measured flows. Invertebrate density in riffles was expressed as a percentage of total density and regressed against the flow-related variables to see whether invertebrate locations changed according to flow. Significant negative relationships were observed between the per cent density of common taxa in riffles and Qsample, Qmax and Qmin. This result suggests either that these animals actively drifted into areas of faster velocity during low flows, or that their densities within riffles increased as the width of these habitats declined.

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 ...

Efforts to rehabilitate degraded urban streams generally focus on improving physical habitat and rarely include reestablishing biota such as macrophytes. Our objectives in this study were to propagate and transplant native macrophytes into a South Island, New Zealand, urban stream undergoing rehabilitation, assess macrophyte survival and growth, and determine whether native macrophytes suppress non-native macrophytes and/or enhance stream invertebrate communities. Effects of native macrophytes on invertebrates and non-native macrophytes were assessed after transplanting patches of native macrophytes into a 230-m-long stream section. A 100-m-long section upstream was left unplanted for subsequent comparisons. Following the study, a survey was conducted to gauge public opinion about the rehabilitation project and determine whether macrophytes were prominent in perceptions of stream health. In the first growing season, native macrophyte cover in the planted stream section increased from 1.5 to 20%, and then decreased during winter. Regrowth from rhizomes led to rapid aboveground growth during the second year, when cover reached 51%. Non-native macrophytes colonized the stream the first year, but native macrophytes appeared to limit the spread of non-natives, which were absent in the planted section by the second spring. Native macrophyte establishment did not enhance invertebrate communities as predicted; few invertebrate metrics differed significantly between the planted and unplanted sections. Pollution- and sediment-tolerant invertebrate taxa were abundant in both sections, suggesting that invertebrate colonization was limited by water quality or sedimentation, not macrophyte composition. Survey respondents considered the stream to be visually and ecologically improved after rehabilitation, and macrophyte establishment was generally considered positive or neutral.

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.

The effects of habitat enhancement on the invertebrate communities in five urban streams in Christchurch, New Zealand, were investigated. All streams underwent riparian planting, while extensive channel modifications were made at two streams, where a concrete dish channel and a wooden timber-lined stream were removed and natural banks reinstated. Benthic invertebrates were collected before enhancement and 5 years after from the same locations. Invertebrates were also collected from control sites in each stream in 2001. Desired goals of enhancement activities included increasing the densities of mayflies and caddisflies, and decreasing densities of oligochaetes, snails and midges. Enhancement activities changed riparian vegetation and bank conditions, as well as substrate composition, instream organic matter and variability of instream velocities. Invertebrate communities prior to enhancement were typical of those in urban environments, and dominated by snails (Potamopyrgus, Physa), the amphipod Paracalliope, the hydroptilid caddisfly Oxyethira, oligochaetes and chironomids. Stream enhancement caused only small changes to the invertebrate community, with subtle shifts in overall abundance, species evenness, diversity, and ordination scores. Lack of a consistent strong response by invertebrates to enhancement activities, and continued absence of caddisflies and mayflies from enhanced sites may reflect lack of sufficient change to instream conditions as a result of stream enhancement, colonization bottlenecks for aerial stages of these animals, and the inability of individuals outside the urban watershed to perceive these enhanced ‘islands’ of good habitat. Alternatively, contamination of streambed sediments, excess sedimentation and reduced base flows may be limiting factors precluding successful invertebrate colonization in enhanced sites. These results highlight the importance of setting clear goals and objectives necessary to meet these goals. Enhancement of riparian zones in urban streams may not be adequate to improve benthic invertebrate communities. Identifying over-arching factors that potentially limit invertebrate communities will enable the enhancement potential of streams to be better assessed, and allow managers to identify sites where recovery of biological communities is possible, and where such recovery is not. Copyright © 2005 John Wiley & Sons, Ltd.

Effects of stream enhancement on habitat conditions in five spring-fed urban streams in Christchurch, New Zealand, were investigated. Stream enhancement consisted of riparian planting at three sites, and riparian planting and channel modifications at two sites, where a concrete dish channel and a timber-lined channel were removed, and natural banks reinstated. Sites were surveyed prior to enhancement activities and 5 years after, and changes in riparian conditions (composition, horizontal and vertical cover), instream conditions (bank modifications, inorganic and organic material on the streambed), and hydraulic conditions (wetted perimeter, cross-sectional area, depths and velocities) quantified. Enhanced sites generally had higher marginal vegetation cover, as well as increased overhanging riparian vegetation, reflecting planting of Carex sedges close to the water. Bed sediments changed at some sites, with the greatest change being replacement of a concrete channel with gravel and cobble substrate. Bryophyte cover declined at this site, reflecting loss of stable habitat where these plants grew. Bed sediments changed less at other sites, and cover of fine sediments increased in some enhanced sites, presumably from sediment runoff from nearby residential development. Filamentous algal cover decreased at one stream where shade increased, but increased in another stream where the removal of timber-lined banks and creation of a large pond decreased shade. Stream enhancement increased variability in velocity at three of the five sites, but overall changes to stream hydraulics were small. Although enhancement activities altered the physical conditions of the streams, major changes occurred only to riparian vegetation and bank conditions. Lack of other major changes to instream physical conditions most likely reflected the limited range of channel morphology alterations undertaken. Moreover, the flat topography of Christchurch and naturally low stream discharge further constrained changes to instream physical conditions from enhancement activities. Sediment inputs from continuing urban development also negated the effects of adding coarse substrates. These over-arching factors may constrain the success of future stream enhancement projects within Christchurch. Copyright © 2005 John Wiley & Sons, Ltd.

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...

1. Drag coefficients (C D ) of bryophyte-covered rocks were measured to see whether these differed between species. Replicate rocks, each supporting one of six bryophyte taxa, were attached to a base plate mounted on Teflon bearings in a flow tank. The drag force exerted on rocks with and without bryophyte material was measured by a strain gauge at different water velocities. 2. The difference in C D between rocks with and without bryophyte material was calculated for each plant, and expressed as a percentage change (δC D ). This varied significantly from 0 in three of the six taxa. The cushion-shaped moss Bryum blandum increased the C D by around 10%. The moss Blindia lewinskyae and liverwort Cryptochila grandiflora decreased the C D by around 40 and 30%, respectively, presumably reflecting their streamlined growth. 3. Drag characteristics of aquatic bryophytes may help explain differences in their resistance to fast flows. Furthermore, we suggest that some aquatic bryophytes can increase substrate stability by streamlining rocks, rendering them less prone to movement.

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...

SUMMARY 1. The influence of altitude and land-use changes on macroinvertebrate assemblages from riffles in forty-three streams in the Dolpo region of western Nepal were examined. Sampling sites ranged in altitude from 850 to 4250m, and land-use patterns fell into five categories: alpine, forest, grassland, pasture and agricultural land. 2. TWTNSPAN classification of physicochemical data separated streams into groups on the basis of climatic and physical factors. Streams from high, cold, alpine areas were separated from those in warmer, lower, agricultural areas. 3. In all, 138 macroinvertebrate taxa were collected from fifty-three insect families. Ephemeroptera were most common, especially Baetidae. 4. Taxonomic richness declined with increasing altitude. Ten insect families were significantly more abundant in lowland streams, and five were more common in alpine streams. 5. TWINSPAN and DECORANA revealed distinct invertebrate groupings of the forty-three streams surveyed. A high percentage of the variance (79.3%) in ordination space was explained by DECORANA axes 1 and 2. Altitude, temperature, stream width and land use were implicated in structuring invertebrate communities.

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...

SUMMARY 1. Artificial bryophytes were placed in a shaded and an unshaded New Zealand alpine stream to investigate why invertebrates colonized these structures and, by inference, real plants. Three experiments were conducted to investigate the influence of (i) periphyton and detritus (ii) shelter, and (iii) time, on invertebrate colonization. 2. In the first experiment, seven taxa at the unshaded site displayed a preference for substrata with high detrital and periphyton biomass, presumably reflecting a food relationship. At the shaded, less stable site, only two taxa displayed such a relationship. 3. Reducing substratum ‘stem’ density (i.e. ‘shelter’) in the second experiment had little effect on the biomass of periphyton at each site, and only at the shaded site was detrital biomass reduced on low-density substrata. Abundances of most of the twenty-two invertebrate taxa analysed were unaffected by stem density reduction: densities of only four taxa at the unshaded site, and two at the shaded site were reduced. 4. Stepwise multiple regression showed that invertebrate abundance was little affected by stem density at either site. Indeed, shelter was the primary factor influencing abundance of only two of twenty-two taxa at the unshaded site, and none at the shaded site. Abundances of most taxa were related to periphyton or detrital biomass at each site. 5. The third experiment investigated temporal relationships between invertebrate density, periphyton and detrital biomass, and exposure time of artificial bryophytes. Regression analyses indicated that of twenty-two taxa at the stable, unshaded site, eight were influenced by periphyton biomass, three by detrital biomass, and two by exposure time. At the unstable shaded site, abundances of only eight of twenty-two taxa were significantly related to the measured variables, of which exposure time was most important (four taxa).

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...

SUMMARY. 1. Quantitative samples of lotic benthic invertebrates and associated organic material were taken monthly for 18 months from bryophyte and gravel habitats in two New Zealand alpine streams in Arthur's Pass National Park, South Island; an unshaded site above the tree-line and a shaded stream flowing through mountain beech forest. This was to assess the ecological role of bryophytes in these habitats and to determine the relative effects on the fauna of algal and detrital resources. 2. Bryophytes were confined to stable bedrock substrata in shallow (mean depth of 4.5 and 10.5 cm), fast water (mean velocity of 0.21 ms−1 and 0.30ms−1) at the unshaded and shaded sites. Mean ash-free dry weight (AFDW) of organic material from bryophyte areas was similar at the unshaded and shaded sites (335.6 and 272.4 gm−2). Low stream-bed stability of the gravel areas resulted in poor retention of organic matter, with average AFDW of 59.1 and 77.9 gm−2 at the unshaded and shaded sites, respectively. Periphyton biomass, however, was much higher at the unshaded site. 3. Within bryophytes, water velocity is reduced and large quantities of periphyton and detritus accumulate. This explains the greatly enhanced invertebrate densities within bryophytes (218400 and 53500 individuals m−2), compared with gravel areas (20900 and 7400 individuals m−2) in the unshaded and shaded sites, respectively. The higher invertebrate densities at the unshaded site reflect greater periphyton biomass there. 4. Invertebrate densities followed clear seasonal patterns, attributable to changes in chironomid densities. These reflected larval chironomid hatching following adult oviposition. This illustrates the importance of these plants as oviposition sites, and as protective nurseries for small larvae where they can obtain shelter during floods and consume the abundant food sources available to them. 5. DECORANA ordination revealed taxonomically distinct invertebrate communities in each stream, and in bryophytes and gravels. Several taxa appeared restricted to either the unshaded site (e.g. Acroperla spiniger and Hydrobiosis silvicola) or the shaded site (e.g. Zelolessica

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 ...

The microfauna of benthic algal mats in eight ponds of diverse chemistry on the Ross Ice Shelf was examined. Tardigrades, nematodes and rotifers were successfully extracted from algal material by a modified Baermann funnel technique, which was robust enough to use under field conditions. Seven species of rotifer (of which 6 were bdelloids) and one species of nematode and tardigrade were found, all of which are cosmopolitan to Antarctic lentic ecosystems. Philodina sp. was the only invertebrate to occur in all ponds sampled. Rotifers were the most abundant invertebrates with average densities in all ponds of 4.26×105 individuals/m2, whereas nematodes were least abundant with densities of 4.96×104 individuals/m2. Total invertebrate densities and densities of individual taxa were significantly different in each of the 8 ponds, and of those measured environmental parameters were most strongly associated with conductivity. Cores taken from four ponds 2 cm into underlying substratum revealed that most animals live within the algal mats, with underlying sediment supporting a minimal population.

Variations in diatom communities between river habitats might have ramifications for their use as bioindicators and for the assessment of their contribution to aquatic biodiversity. Diatoms therefore were sampled from similar surface areas of the epilithon and bryophytes in 24 hill-streams in the Nepalese Himalaya to assess whether communities varied more strongly between habitats or between streams. Some diatom species (e.g. Eunotia minor and Coccaneis placentula) were significantly more abundant on bryophytes than in the epilithon. In addition, bryophytes held, on average, a significantly larger proportion of the total species pool of diatoms at each site. However, neither diversity H' nor evenness E varied between habitats, suggesting no gross differences in community structure. Also, DECORANA ordination and TWINSPAN classification showed that communities were more similar between habitats within sites, than between sites. DECORANA scores from both epilithon and bryophytes showed the same linear relationships with water chemistry (acid-base status, sulphate concentration and conductivity), so that diatom samples from either habitat reflected the same chemical gradient. These results support previous conclusions that comprehensive sampling will be required in the assessment of diatom biodiversity, while samples from just one habitat may be sufficient for water quality monitoring.