Relationships between benthic biota and hydrological indices in New Zealand streams

1. The objective of this study was to identify the most ecologically relevant hydrological indices for characterizing hydrological regimes in New Zealand streams. To do this we related measures of periphyton chlorophyll a, ash-free dry mass (AFDM), species richness, and diversity and invertebrate density, species richness and diversity, to thirty-four hydrological variables derived from daily flow records at eighty-three sites. The hydrological variables included some describing average flow conditions, flow variability, floods, and low-flow characteristics. 2. A principal components analysis showed that the interrelationship between many of the hydrological variables was high, and most variables correlated significantly with Principal Component 1 (PC1). The flood frequency variables formed a distinct component of the flow regime and were the main contributor to PC2. 3. We found that both the average flow conditions and some measure of variability were significantly related to most of the biological variables, and these individual hydrological variables were more strongly correlated to the biological measures than the composite principal components. Only four of the thirty-four flow variables were significantly correlated (P < 0.05) with measures of periphyton biomass (chlorophyll a and AFDM), whereas twenty-four variables were correlated with periphyton diversity. Conversely, thirty-one of the thirty-four flow variables were correlated with total invertebrate density, whereas only four variables correlated with diversity. 4. We selected the flood frequency (FRE₃), where a flood is defined as flows higher than three times the median flow, as the most ecological useful overall flow variable in New Zealand streams because it explained a significant amount of the variance in four out of the six main benthic community measures, and it had a clear mechanism of control of the biota which was commensurate with current stream ecosystem theory. Periphyton biomass decreased with increasing FRE₃, whereas invertebrate density had an increasing/curvilinear relationship with FRE₃. Periphyton species richness and diversity decreased with increasing FRE₃.     

大型无脊椎动物群落指数和群落数量指数在河流水质评价中的应用

本文介绍了新西兰常用的大型无脊椎动物群落指数(MCI)和大型无脊椎动物群落数量指数(QMCI)的原理及使用方法,并利用MCI和QMCI对新西兰惠灵顿地区40条河流53个监测点进行评价.结果表明:MCI和QMCI均与河流营养指标呈极显著相关关系,可用来监测和评价水体的营养污染状况;二者快速准确地监测出惠灵顿地区河流水质总体良好,但部分河流污染严重,并分析了污染的原因.MCI与QMCI存在极显著相关关系,但MCI与营养指标间的相关关系大于QMCI,可以准确地反映出水体中营养元素的富集状况.     

永定河流域大型底栖动物群落分布格局及其影响因子

人类干扰造成了全球河流生态系统的普遍退化。流域尺度的水生生物分布特征及其影响因素研究对于河流生态系统的保护与恢复具有重要意义。本研究以永定河流域大型底栖动物群落为研究对象,分别于2017年春季(3月)、夏季(7月)、秋季(11月)开展全流域尺度的大型底栖动物调查。研究表明: 永定河流域以摇蚊科为主,优势类群包括直突摇蚊属、摇蚊属、雕翅摇蚊属以及多足摇蚊属。聚类分析表明,大型底栖动物群落结构存在显著的空间差异性,按照群落相似性可分为2组: 组1主要包含桑干河和东洋河水系,以直突摇蚊为主要优势种;组2主要包含洋河、妫水河以及永定河干流部分河段,以雕翅摇蚊为主要优势种。单因素方差分析表明,组2生物量、Shannon指数、Margalef指数、Pielou均匀度指数以及物种丰富度均显著高于组1,指示了该区域内更好的生态状况。大型底栖动物的季节差异显著,夏季的密度、生物量和各多样性指数均显著低于春季和秋季。典范对应分析显示,影响永定河大型底栖动物空间分布的环境因子主要包括水温、铵氮、pH、溶解氧和总磷。从水文因子的角度,流量和流速与主要生物参数存在显著相关性。组2中流速和流量与大型底栖动物密度和EPT%存在显著的正相关关系,表明急流生境有利于EPT(蜉蝣目、襀翅目、毛翅目)敏感类群的生存;但流量和流速与多样性指数呈负相关关系,表明过高流量和流速的生境条件不利于大型底栖动物多样性的维持。总之,水环境因子、水文因子都显示出了对大型底栖动物群落结构和多样性特征的影响,表明永定河流域生态系统受到多类型人为活动的影响。减少水质污染、适度恢复部分河段的流量是永定河流域生态系统修复的重要环节。     

Are landscape-based wetland condition indices reflected by invertebrate and diatom communities?

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.     

Local disturbance history and habitat parameters influence the microdistribution of stream invertebrates

1. We investigated the effects of local disturbance history and habitat parameters (abiotic and biotic) on the microdistribution of benthic invertebrates during several floods in two streams, the Schmiedlaine in Germany (four events) and the Kye Burn in New Zealand (two events). 2. Bed movement patterns were quantified using metal‐link scour chains. Before and after each flood, quantitative invertebrate samples were taken from replicate bed patches that had experienced sediment scour, fill or remained stable. 3. Patterns of invertebrate density in the different bed stability types (i.e. scour, fill, stable) varied between floods, sampling dates and streams, but invertebrate density was highest in stable patches in >50% of all the patch type effects detected and lowest in fill patches in 75% of all detected effects. Stable bed patches acted as a refugium for Liponeura spp. and Leuctra spp. in the Schmiedlaine and for Hydracarina and Deleatidium spp. in the Kye Burn. 4. Averaged across both streams, only near‐bed current velocity was correlated with invertebrate distribution on the streambed more often than disturbance history. In the Kye Burn, disturbance history and water depth were the most influential habitat parameters. 5. Our results suggest that a thorough understanding of the microdistribution of benthic invertebrates requires knowledge of disturbance history, as well as more readily measured habitat parameters such as current velocity or water depth.     

Impacts of climatic stability on the structural and functional aspects of macroinvertebrate communities after severe drought

1. Unpredictable, extreme climatic events (e.g. droughts) can potentially destabilize aquatic communities. From 1998 to 2002, southwestern Georgia, U.S.A., experienced the third worst drought of the last 100 years, leading to loss of surface flow in many small streams. We sampled macroinvertebrates, flow and water chemistry in small headwater streams from 2001 to 2007 in two adjacent coastal plain streams of contrasting headwater type (wetland and groundwater‐fed seep) following resumption of flow. 2. Decreasing water temperature, conductivity and nutrient concentrations within the first 2 years of the study indicated flushing of the streambed associated with increased discharge. Invertebrate community composition became less variable over time and during wetter years, reflecting water chemistry, hydrological and climate conditions. 3. A core set of species appeared immediately following breaking of the drought in both streams, reflecting a shared species pool. These species exhibited resilience traits, including short life cycles and resistance to desiccation, which allowed for rapid recovery from disturbance. Such species, which were small‐bodied, sclerotized and abundant in the drift, were then replaced as flows increased by those that were larger, soft‐bodied and rare in drift, suggesting a more stable and less ephemeral habitat. 4. Hydrologic regime and long‐term precipitation indices were strongly correlated with invertebrate community and trait structure. Long‐term data allowed for better interpretation of the effects of infrequent disturbances on aquatic ecosystems. Additionally, long‐term precipitation indices (i.e. 48‐month standardized precipitation index) can indicate the likelihood of a return to drought, allowing for the collection of pre‐disturbance data.     

The Impact of Hydrological Restoration on Benthic Aquatic Invertebrate Communities in a New Zealand Wetland

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.     

Distinctive invertebrate assemblages in rockface seepages enhance lotic biodiversity in northern New Zealand

We measured water quality, recorded physical habitat characteristics and collected aquatic invertebrates from 17 rockface seeps, five springs and five streams in a geologically diverse region of New Zealand's North Island to investigate factors influencing invertebrate distribution and community composition within and among these habitats. A total of 147 aquatic invertebrate taxa was found; 84 taxa occurred in seepage samples and 53% of these were found only in those habitats, including several new species. Where paired stream-seepage comparisons could be made, seeps contributed on average 35% of new species to the total species pool. The invertebrate faunas of all habitats were dominated taxonomically by Trichoptera and Diptera, but seepages were relatively depauperate in Ephemeroptera and richer in Coleoptera taxa compared to streams and springs. Seepage faunas were dominated numerically by Mollusca, and had lower percent abundance of aquatic insects (23% overall) compared to springs (77%) and streams (93%). Seepages underlain by different geologies generally had distinct water quality signatures, with seeps draining greywacke, sandstone and volcanic rocks grouping close to their receiving streams in a Principal Component Analysis. Seepage invertebrate community composition reflected underlying geology and associated differences in water chemistry, as well as seepage size and cover by moss. Incorporation of seepage habitats into conservation planning and aquatic ecosystem protection, and maintenance of their function and connectivity with lotic and groundwater ecosystems are important considerations for freshwater biodiversity management. Maintenance of riparian plant cover over seepages should help sustain supplies of organic matter, moss cover and shade, providing habitat complexity and low water temperatures.     

Quantitative hydrological preferences of benthic stream invertebrates in Germany

Current knowledge regarding the flow preferences of benthic stream invertebrates is mostly based on qualitative data or expert knowledge and literature analysis. These established flow preferences are difficult to use in predictions of the effects of global change on aquatic biota. To complement the existing categories, we performed a large-scale analysis on the distribution of stream invertebrates at stream monitoring sites in order to determine their responses to various hydrological conditions.We used 325 invertebrate surveys from environmental agencies at 238 sites paired to 217 gauges across Germany covering a broad range of hydrological conditions. Based on these data, we modelled the respective probabilities of occurrences for 120 benthic invertebrate taxa within this hydrological range using hierarchical logistic regression models.Our analyses revealed that more than one-third of the taxa (18–40%) can be considered as ubiquitous and having a broad hydrological tolerance. Furthermore, 22–41% of the taxa responded to specific ranges of flow conditions with detectable optima. “Duration high flow event” represented the flow parameter that correlated best with the abundance of individual taxa, followed by “rate of change average event”, with 41 and 38% of the taxa showing a peak in their probability of occurrence at specific ranges of these metrics, respectively. The habitat suitability for these taxa may be potentially affected by global change-induced hydrological changes.Quantified hydrological traits of individual taxa might therefore support stream management and enable the prediction of taxa responses to flow alteration. The hydrological traits of stream benthic invertebrates may be used in forecasting studies in central Europe, and the methods used in this study are suitable for application in other regions with different flow regimes.     

Invertebrate fauna of ephemeral streams on Hauturu-o-Toi/Little Barrier Island in northern New Zealand

ABSTRACT

The invertebrate fauna of five ephemeral forest streams on Hauturu-o-Toi/Little Barrier Island in northern New Zealand was assessed in January 2014. Low summer flows restricted benthic sampling largely to pools that would, during periods of ‘normal’ flow, be main-channel riffle/run habitat. Additionally, adult stages of aquatic insects were sampled by light trapping. Fifty-three aquatic species/morphospecies were recorded during the study, including 25 new records, bringing total island species richness to 65. The fauna was dominated by Ephemeroptera and Trichoptera; species richness of Plecoptera and Diptera was low, and only single species of Mollusca and Crustacea were recorded. Species found were either common with broad New Zealand distributions, or species restricted to the North Island. No species was endemic to the island. Faunal comparisons with adjacent mainland streams indicated the island had similar assemblages of core taxa, but generally lower species richness, likely resulting from physiographic differences found there.     

Do stream macroinvertebrates use instream refugia in response to severe short-term flow reduction in New Zealand streams?

1. Demand for water is increasing and water managers need to know how much they can remove from a stream before there are significant detrimental effects on its biological integrity. Flow reduction alters a number of habitat variables known to be important to aquatic invertebrates such as depth, velocity, temperature and fine sediment accumulation. Some taxa may attempt to use instream refugia to mitigate the effects of flow reduction.
2. We experimentally manipulated flows by constructing weirs and diversions in three small New Zealand streams. Discharge was reduced by 88–96%. We tested the hypothesis that macroinvertebrates would use pools and the hyporheic zone as refugia during short-term (1-month) periods of reduced flow.
3. We sampled hyporheic invertebrates with colonization chambers and pool invertebrates with kick nets within a before-after, control-impact (BACI) experimental design. A suite of physicochemical parameters was measured concurrently including surface and hyporheic temperatures.
4. Flow reduction significantly decreased velocity (60–69%) in all streams. Depth (18–61%) and wetted width (24–31%) tended to decrease but these changes were not always significant. Sediment cover increased the most in farmland streams (10–80%). Apart from decreasing temperature range (18–26%), flow reduction had little impact on the surface water temperatures.
5. Flow reduction had no impact on the abundance of common pool macroinvertebrates or on the abundance, vertical distribution or community composition of hyporheic macroinvertebrates.
6. Our results suggest that aquatic macroinvertebrates are resistant to short-term, severe flow reduction as long as some water remains.     

Invertebrate communities and hydrological variation in Cairngorm mountain streams

Macroinvertebrates, discharge and 16 chemical variables were monitored over a 14-year period in four small streams (catchment area <15 km²) in the Cairngorm mountains, Scotland. Canonical Correspondence Analysis (CCA) was used to assess relationships between invertebrates and environmental conditions on the day of sampling, average conditions over the preceding 1, 2 and 3-month periods and indices of hydrological and hydrochemical variation over preceding monthly intervals.CCA detected subtle inter-catchment differences in invertebrate community structure, with catchments separated along axes representing streamwater calcium, alkalinity and total organic carbon concentrations. Invertebrate communities varied seasonally, with spring, summer and autumn samples separated along CCA axes representing temperature, orthosilicate and discharge. Hydrochemically, spring was the most variable season, characterised by increased frequency of both high and low flow events and acid, snowmelt episodes. In two of the streams, invertebrate community structure varied more in spring than in other seasons.CCA ordinations using indices of hydrological and hydrochemical variation over preceding time periods were more successful (increased eigenvalues) at explaining temporal variation in invertebrate community structure than those using conditions on the day of sampling or average conditions over preceding time periods. For one of the catchments, 40% of the seasonal and between-year variation over the 14-year period could be explained by the frequency of high and low flow events, maximum and minimum water temperatures and acid episodes in the two months prior to the invertebrate samples being collected. The single most important flow parameter (longest CCA arrow) was the frequency of high flow events greater than three times the median discharge.No significant trends in invertebrate community composition were found in any of the streams over the 14-year period so, despite the apparent importance of hydrological and hydrochemical variation, communities appeared stable over the long-term.     

Testing the pressure‐specific invertebrate index (PSI) as a tool for determining ecologically relevant targets for reducing sedimentation in streams

相似文献   

Macroinvertebrate community structure across a wetland hydroperiod gradient in southern New Hampshire,USA

We conducted a field study to examine the influence of hydroperiod and concomitant changes in abiotic (wetland size, pH, conductivity, dissolved oxygen and water temperature) and biotic (predatory fish presence) characteristics on macroinvertebrate communities in isolated wetlands in southern New Hampshire. Invertebrates were sampled using dipnet sweeps in 42 wetlands with short (<4 months), intermediate (4–11 months) or long (permanent) hydroperiods in 1998 and 1999. We found that invertebrate genera richness, and to a lesser degree abundance, increased linearly along the hydrological gradient, and in response to temperature and dissolved oxygen. Relative abundance of genera also differed markedly with respect to hydroperiod. Most notably, invertebrate communities changed from Acilius-dominated communities to Notonecta-dominated communities. Invertebrate relative abundances in permanent wetlands also differed with respect to the occurrence of predatory fish. Some genera (e.g., Libellula, and Dytiscus) were more likely to occur in permanent wetlands without fish, whereas other genera (e.g., Buena, and Basiaeshna) were more likely to occur in wetlands with predatory fish. Because aquatic invertebrate communities differed markedly with respect to wetland hydroperiod, and in relation to the occurrence of predatory fish, it is essential to retain a diversity of wetlands in the landscape to ensure the long-term persistence of aquatic invertebrate biodiversity.     

Dynamic Processes in New Zealand Land-Water Ecotones

This paper reviews current knowledge of dynamic processes in New Zealand land-water ecotones drawing on published quantitative data wherever possible. Basic ecosystem processes in forested and natural unforested land-water ecotones are compared, and dynamic processes are discussed under the following headings: time scales of change; water movement; sediment trapping and transport; dissolved nutrient dynamics; dissolved oxygen; trophic interactions. Environmental "resetting" agents such as floods, fires and storms have been shown to be important regulators of change at the land-water interface. However, an element of stability is imparted by continuous allochthonous inputs from evergreen vegetation into the water at the interface, as well as an important contribution from terrestrial insects. Stable isotope studies have shown that such inputs are translated as a carbon source through aquatic food chains in some New Zealand streams. Dynamics of sediment movement and nutrients are governed by the complex patterns of water movement along the ecotone. Patterns of water movement at this interface are controlled by obstructions to flow providing eddies and "dead zones". Manning's coefficient of drag is a convenient measure of the degree of obstruction by aquatic vegetation, fallen branches etc. Nutrient dynamics along the land-water interface of lakes and streams are affected not only in moving surface water, but also in groundwater. New Zealand studies have, in recent years, concentrated on nitrogen pathways in ground waters at the interface where denitrification is shown to be an important N sink. This is controlled largely by dissolved oxygen and prevailing redox conditions. Implications for management of New Zealand land-water ecotones where ecosystem dynamics are governed by periodic physical disruptions such as floods, fires or dry-wet cycles are discussed.     

Does macrophyte fractal complexity drive invertebrate diversity,biomass and body size distributions?

Habitat structure is one of the fundamental factors determining the distribution of organisms at all spatial scales, and vegetation is of primary importance in shaping the structural environment for invertebrates in many systems. In the majority of biotopes, invertebrates live within vegetation stands of mixed species composition, making estimates of structural complexity difficult to obtain. Here we use fractal indices to describe the structural complexity of mixed stands of aquatic macrophytes, and these are employed to examine the effects of habitat complexity on the composition of free-living invertebrate assemblages that utilise the habitat in three dimensions. Macrophytes and associated invertebrates were sampled from shallow ponds in southwest England, and rapid digital image analysis was used to quantify the fractal complexity of all plant species recorded, allowing the complexity of vegetation stands to be reconstructed based on their species composition. Fractal indices were found to be significantly related to both invertebrate biomass–body size scaling and overall invertebrate biomass; more complex stands of macrophytes contained a greater number of small animals. Habitat complexity was unrelated to invertebrate taxon richness and macrophyte surface area and species richness were not correlated with any of the invertebrate community parameters. The biomass–body size scaling relationship of lentic macroinvertebrates matched those predicted by models incorporating both allometric scaling of resource use and the fractal dimension of a habitat, suggesting that both habitat fractal complexity and allometry may control density–body size scaling in lentic macroinvertebrate communities.     

Macrozoobenthos patterns along environmental gradients and hydrological connectivity of oxbow lakes

Hydrological connectivity and the frequency and intensity of floods are the key factors determining the structure of macroinvertebrates inhabiting wetland ecosystems in river valleys. In 2007, water and macroinvertebrate samples were collected on four occasions in the middle course of the S?upia River and in five oxbow lakes (Northern Poland) to determine the hydrological relations in a regulated lowland river environment marked by a moderate climate. The water bodies selected for the study featured different types of connections with the main river valley: two of them were completely cut off from the valley, one was connected via a single branch, one featured a forced-flow connection through drainage pipes, and one was connected by a system of drainage channels. Macroinvertebrates, mostly Chironomidae larvae, were predominant in the eutrophic waters of the river. The prevalent macroinvertebrates found in the eutrophicated oxbow lakes isolated from the river were Chironomidae larvae and Crustacea (mainly Asellus aquaticus). In unobstructed oxbow lakes, the main component of benthic fauna was Crustacea, while Ephemeroptera were found mostly in the water body connected to the river via a drainage channel. A canonical correspondence analysis (CCA) showed that hydrological connectivity was the main factor responsible for the structure of invertebrate populations, followed by the physical and chemical parameters of the local environment. A non-conformance analysis revealed that hydrological connectivity enhanced invertebrate abundance and biological diversity, while the overall abundance was marked by unimodal distribution. The developed general model indicates that in the group of measured environmental variables, nitrite concentrations were highly correlated with Shannon diversity and invertebrate composition, while sulphate levels were closely associated with invertebrate abundance in the waters of the analyzed ecosystems.     

Effects of floods versus low flows on invertebrates in a New Zealand gravel-bed river

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 (Q_sample), maximum and minimum flow between successive samples (Q_max and Q_min, respectively), and the number of days since the last bed‐moving flood (N_days). 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 Q_min and Q_max, and positively correlated to N_days, 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 Q_sample, Q_max and Q_min. 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.     

Restoration of Sphagnum and restiad peatlands in Australia and New Zealand reveals similar approaches

Peatlands in Australia and New Zealand are composed mainly of Restionaceous and Cyperaceous peats, although Sphagnum peat is common in wetter climates (Mean Annual Precipitation > 1,000 mm) and at higher altitudes (>1,000 m). Experimental trials in two contrasting peatland types—fire‐damaged Sphagnum peatlands in the Australian Alps and cutover restiad bogs in lowland New Zealand—revealed similar approaches to peatland restoration. Hydrological restoration and rehydration of drying peats involved blocking drainage ditches to raise water tables or, additionally in burnt Sphagnum peatlands, peat‐trenching, and the use of sterilized straw bales to form semipermanent “dam walls” and barriers to spread and slow surface water movement. Recovery to the predisturbance vegetation community was most successful once protective microclimates had been established, either artificially or naturally. Specifically, horizontally laid shadecloth resulted in Sphagnum cristatum regeneration rates and biomass production 3–4 times that of unshaded vegetation (Australia), and early successional nurse shrubs facilitated establishment of Sporadanthus ferrugineus (New Zealand) within 2–3 years. On severely burnt or cutover sites, a patch dynamic approach using transplants of Sphagnum or creation of restiad peat “islands” markedly improved vegetation recovery. In New Zealand, this approach has been scaled up to whole mine‐site restoration, in which the newly vegetated islands provide habitat and seed sources for plants and invertebrates to spread onto surrounding areas. Although a vegetation cover can be established relatively rapidly in both peatland types, restoration of invertebrate communities, ecosystem processes, and peat hydrological function and accumulation may take many decades.     

Invertebrate community dynamics and insect emergence in response to pool drying in a temporary river

相似文献