Comparative study of monitoring South-Finnish rivers and streams using macroinvertebrate and benthic diatom community structure

In southern Finland, most of the rivers are turbid and suffer from eutrophication and leaching of suspended solids from diffuse sources. We first related benthic diatom and macroinvertebrate structure to environmental factors using direct ordination. Second, benthic diatoms and macroinvertebrates were simultaneously sampled in several South-Finnish rivers and streams to compare two monitoring methods. The study sites constituted of some large, moderately nutrient rich rivers and some smaller, less eutrophic streams situated on the south coast of Finland. Diatom species distribution was most affected by conductivity, total P and latitude. Species distribution of macroinvertebrates was mostly related to channel width, conductivity and pH. For diatoms, separation of community structure between sampling stations was clear, but corresponding macroinvertebrate communities were more similar to each other. Correlation between diatom and macroinvertebrate pollution indices was rather low and insignificant (r = 0.28). As a whole, variation of macroinvertebrate index values (CV = 4.7%) among replicate samples was slightly lower than for diatom index (CV = 6.0%). On the contrary, community similarity between the replicate samples was slightly lower among macroinvertebrates (r = 0.770) due probably to their larger local scale spatial variation, sampling of more habitats and lower density compared to diatoms (r = 0.874). In conclusion, multiple pressures affecting the river ecosystems at different spatial and temporal scales should lead to choosing more than one biological monitoring method with clearly identifiable responses.     

The use of benthic macroinvertebrate families for river quality assessment in Lithuania

The aim of this study was to evaluate the influence of environmental factors on the distribution of macroinvertebrate taxa in different sized lowland Lithuanian rivers. A secondary aim was to assess ecological river quality and to determine the most suitable biotic index. A final aim was to determine the most appropriate macroinvertebrate families for river quality assessment in Lithuania. Species composition and quantitative characteristics of benthic macroinvertebrate communities have been investigated using standard kick-sampling method by a standard hand net in 24 different river sites in spring. Physical and chemical environmental parameters were measured in the same study site as the macroinvertebrate sampling. A total of 186 taxa representing 66 families or higher taxonomic ranks of benthic macroinvertebrates have been identified. Water temperature and current velocity influenced the highest number of ivestigated families. Seven of the most tolerant and eleven of the most sensitive macroinvertebrate taxa for hydrochemical parameters related with organic pollution were determined. The DSFI method was founded to be the best index for assessment of ecological status for Lithuanian rivers until more accurate estimation method will be created.     

Replacement of a native freshwater macroinvertebrate species by an invader: implications for biological water quality monitoring

The rate of freshwater invasions may be increasing, and macroinvertebrate invaders can have significant impacts on native macroinvertebrate assemblage structure through biotic interactions. More pollution-tolerant invaders can often replace native species. We examined implications of a species replacement for accurate biological monitoring of river systems using biotic indices. Our study uses Northern Ireland and the Isle of Man as examples of countries that possess river networks with many riverine macroinvertebrate assemblages subject to invasion. The introduced amphipod crustacean Gammarus pulex has replaced the native species G. duebeni celticus in many rivers in N. Ireland and the Isle of Man. Extensive seasonal data sets (119 sites) from three river networks, Lough Neagh and the Lagan in N. Ireland, and island-wide in the Isle of Man, were used to investigate the assumed equivalence of the native and invader in biotic indices concerned with the water quality monitoring system. Based on the derivation of the Biological Monitoring Working Party (BMWP) score, the Average Score Per Taxon (ASPT), as an example of a commonly used biotic index of water quality, we found index scores were lower in G. pulex sites compared to G. d. celticus-only sites. This indicated that assemblages were dominated by taxa more tolerant of organic pollution in the invader sites and more sensitive in the native sites. Inclusion of the invader in generation of the ASPT index, overinflated the ASPT values obtained compared to those with the native’s inclusion. This questions the accuracy of the ASPT and similar indices in rivers where the invader had replaced the native. We argue that with invasion pressures increasing, the validity of water quality indices such as the BMWP/ASPT needs to be re-examined in catchments where invaders have replaced natives. Indices such as the BMWP/ASPT are based on family level taxa and are inevitably coarse in their resolution given the wide range of water qualities tolerated by different genera within families. We argue that this resolution is even more compromised by the presence of very pollution-tolerant invaders, who may have replaced natives in disturbed or degraded river systems. The whole structure of water quality indices such as the BMWP/ASPT may need revising to take into account the presence of invasive species within monitored assemblages.     

Chironomids as water quality indicators in the River Mignone (Central Italy)

Chironomids of the River Mignone (Central Italy) were studied in order to examine their community structure and their relationship to some common biological indices (Biotic Score, Extended Biotic Index, Indice Biotique de Qualité Générale) utilizing the total macroinvertebrate fauna (chironomids generally at family level) for water quality assessment in rivers.A total of 36 taxa belonging to Tanypodinae (2 taxa), Orthocladiinae (22 taxa) and Chironominae (12 taxa) was collected at seven stations four times during a year. The results support the importance of the chironomid identification in water quality assessment studies in rivers, and demonstrate the usefulness of the factorial correspondence analysis as ordination technique based on both qualitative and quantitative chironomid data to determine environmental quality gradients.The value as bioindicator of some taxa was discussed, and chironomid assemblages were related to biological water quality of the river according to functional feeding groups.This study forms part of a larger Research project supported by MPI and CNR grants and is aimed at the biological water quality assessment of the river and at the analysis of the total macrobenthic community.     

Ecological quality of small mountainous Mediterranean streams (river type R-M4) and performance of the European intercalibration metrics

Ten small streams of high altitude were assigned to the R-M4 intercalibration river type (small/medium Mediterranean mountainous rivers) and examined to determine their benthic macroinvertebrate fauna, their physicochemical and hydromorphological parameters and their water quality, quarterly for two consecutive years. Physicochemical variables were consistent with the mountainous character of the streams and fluctuated within the European Community legislation limits for drinking water. Benthic macroinvertebrate fauna communities were diverse and sensitive to organic pollution, and samples were grouped by time more strongly than place. Site size and catchment area influenced the macroinvertebrate community more than the rest of the measured abiotic variables. The water quality was good or high, but at the smaller streams its interpretation was affected by summer drought. The water quality boundaries of the Hellenic Evaluation System were harmonised with the water quality boundaries of a European benchmark database, according to the methodology followed by the Mediterranean Intercalibration Group. Handling editor: R. H. Norris     

Benthic macroinvertebrate communities in five rivers of the Coastal Hudson Bay Lowland

As a precursor to developing a biomonitoring program for rivers of the Coastal Hudson Bay Lowland, this study characterized and compared the benthic macroinvertebrate communities and water chemistry in 5 remote, previously undescribed, rivers near Fort Severn, Ontario, Canada. The pH of river water ranged from 8.1 to 8.7, total phosphorus from 11 to 26 μg L^?1, dissolved organic carbon from 8 to 12 mg L^?1, and chloride from 56 to 153 mg L^?1. A total of 57 benthic macroinvertebrate taxa were represented, and the 10 most numerically dominant were the Chironominae (26 % of collected individuals), Orthocladiinae (16 %), oligochaetous clitellata (9 %), Hyalellidae (7 %), Hydropsychidae (6 %), Gammaridae (5 %), Elmidae (5 %), Sphaeriidae/Pisidiidae (4 %), Nemata (3 %), and Tanypodinae (3 %). Rivers’ positions in ordinations of chemical and biological datasets were similar, suggesting that water chemistry has a role in structuring riverine benthic communities in the study region. Correlations between water-chemistry or habitat predictors and site-scores in the ordination of benthic macroinvertebrate taxa counts suggested that biological community structure was most associated with river-water pH, nutrient concentrations (e.g., total phosphorus, nitrogenous compounds, dissolved organic carbon, calcium, and silicate), the relative abundance of submerged macrophytes, conductivity (i.e., the concentrations of chloride and various other dissolved ions), and several geomorphological variables (e.g., bank-full river width, current speed, and the size of the dominant inorganic particles in the pavement layer of the streambed). Interest in mineral extraction and other resource-based exploration in Ontario’s Far North is increasing. This study represents a start on baseline characterization for ecological monitoring and cumulative effects assessment that should proceed along with northern development.     

Ecological assessment of an intermittent Mediterranean river using community structure and function: evaluating the role of different organism groups

1. Reliable lotic ecological monitoring requires knowledge of river typology, environmental factors, the effect of stressors known here as ‘pressures’ and appropriate indicators of anthropogenically induced change. We sampled benthic macroinvertebrate, fish, bird and macrophyte communities along an intermittent Mediterranean river and analysed community structure (relative abundance) and function (metrics) relative to environmental and pressure gradients in order to identify suitable indicator group(s) for future monitoring and mitigation programmes. 2. Principal components analysis revealed that scale‐dependent longitudinal differences in valley form separated narrower higher lying sites and tributaries with good quality habitats from more open degraded sites lower down the river continuum on a small floodplain and large scale pressures describing changes in land use related to agriculture with associated physical bankside and channel impacts. 3. Forward selection of variables in redundancy analysis (RDA) showed that reach scale environmental variables were selected more frequently than pressure variables for each organism group. Altitude and pH were highly redundant within and between groups, indicating essentially longitudinal structural and functional distribution patterns. Redundancy was far lower between selected pressure variables, but single or no pressure variables were retained for some organism groups indicating poor association of functional data, in particular, with the identified pressures. All RDA results indicated a longitudinal pH gradient, highlighting the combined effect of multiple environmental and pressure based mechanisms on organism groups. 4. Large, mobile organisms such as fish and birds provided a reliable link between organism structure and function, environmental factors and physical disturbance of the channel, bankside and wider river corridor. Benthic macroinvertebrate and macrophyte structural data revealed distribution patterns in relation to water velocity, a key parameter for developing appropriate compensation measures. 5. Results clearly show the importance of assessing patterns of both functional and structural change across multiple organism groups in order to identify typologically appropriate links with complex environmental and pressure gradients and develop and implement appropriate monitoring systems.     

Turnover patterns in fish versus macroinvertebrates — implications for conservation planning

Spatial patterns in taxonomic richness and turnover for fish and aquatic macroinvertebrates are compared to assess the relative usefulness of each taxonomic group in mapping biodiversity patterns. Fish and aquatic macroinvertebrate species data for sites down the longitudinal axes of nine rivers in four provinces along the eastern side of South Africa were analysed. Fish and aquatic macroinvertebrate data from previous studies and recent river surveys were used in analyses of species richness and turnover. Fish proved to be not useful for mapping biodiversity patterns, as measured by turnover, whereas aquatic macroinvertebrate species patterns exhibited predictable patterns of turnover with downstream distance. Average turnover rates could be decomposed into turnover of common (‘core’) species, which were accelerated by presence of rare and narrow-range species. Disruptions to the river continuum impacted on the rate of turnover. Consistent with other research on South African rivers, aquatic macroinvertebrate communities could be grouped into upland versus lowland assemblages, and also be defined by longitudinal zones. Fish biodiversity patterns should be viewed at a riverscape scale, whereas macroinvertebrate patterns are more easily discerned at a segment-reach scale, and applied to reflect connectivity and environmental gradients respectively.     

Long-term recovery of macroinvertebrate biota in grossly polluted streams: Re-colonisation as a constraint to ecological quality

To meet targets imposed by the European Water Framework Directive (2000/60/EC) it is vital that measures to improve the status of rivers are both effective and economically viable. Achievement of such aims needs robust understanding of biological responses to changes in water quality vis-à-vis mechanisms of and constraints to the colonization of previously polluted sites. This study therefore examined the long-term chemical and biological changes in historically polluted rivers to elucidate the responses of macroinvertebrate biota to improvements in chemical water quality. For three historically polluted sites in the English Midlands, data from surveys over a period of ca. 50 years were analysed. Ammonia (NH₃) and 5-day biochemical oxygen demand (BOD₅) were used as chemical water quality indicators. Variations in the ecological recovery of the study sites were assessed using an average pollution sensitivity score (Average Score Per Taxon) and the number of taxa present (usually to family level) present in hand-net samples. Ecological recovery varied widely and was influenced by the intensity and spatial extent of the pollution and the proximity of available sources of potential colonisers. At the site most isolated from potential sources of colonizing taxa, no clean-water macroinvertebrate taxa were recorded 30 years after the major sources of pollution ceased. Where clean-water colonisers were more readily available, significant improvements in ecological quality followed within 2–5 years of the improvements in chemical quality. Macroinvertebrate communities and hence monitoring data may thus be indicative of long past conditions or of biological isolation rather than contemporaneous chemical conditions. Combined chemical and biological data were used to explore a generic model for predicting recovery rates and success. Neither BOD₅ nor NH₃ were found to provide a consistent and meaningful prediction of either average pollution tolerance of macroinvertebrate taxa or of the number of taxa present. Long-term relationships between macroinvertebrate variables and chemical water quality variables, however, were non-linear, suggesting that water quality thresholds may have to be exceeded before biological recovery can occur. Even when chemical water quality has been improved substantially, the apparent ecological status of macroinvertebrate communities may not reflect reduced pollution levels attained until adequate time to allow for re-colonisation (possibly decades) has elapsed.     

筑坝河流磷素的迁移转化及其富营养化特征

人类活动过量营养物质输入是导致河流富营养化的主要原因,而河道过度的人为调控则进一步复杂化了河流的营养状态变化。闸坝是河流人为调控的重要工程措施之一,提高水资源利用效率的同时严重干扰了河流自然的生物地球化学循环,产生诸多负面生态环境效应。磷素的迁移转化对河流的营养限制作用受到越来越多的关注,国内外已有研究在筑坝河流磷的富营养化特征方面,已经取得了较为深刻的认识:水库闸坝建设滞留大量磷素,导致河流水体磷含量升高、营养物质比例变化,沉积物储存过量磷素形成的内源释放威胁,以及进一步浮游植物和有害藻类的生长响应等,使得筑坝河流的富营养化生态风险升高;在此基础上,也提出了根据降雨分配和闸控库区储水,合理设置闸坝泄流方式,以改善筑坝河流富营养化生态风险的重要管理思路。对于闸坝调控作用与水体富营养化的定量关系还有待进一步的探讨,而且随着河流资源开发和人为调控力度的增强,河流闸坝建设所产生的系列生态环境问题日益严峻,对此提出还需要系统研究的方向:闸坝调控作用下河流磷素的富营养化机制及其与氮、碳等元素的耦合作用,筑坝河流沉积物内源污染的综合管理,以及闸控景观河流的生态建设和修复等。     

Macroinvertebrates as bioindicators of water quality in the Mkondoa River,Tanzania, in an agricultural area

The suitability of using macroinvertebrates as bioindicators of stream water quality was tested in the Mkondoa River in an agricultural area at Kilosa, using the rapid bioassessment protocol. The family biotic index (FBI) showed marked variation in water quality along the stream from values ranging from 4.1 to 5.0 in the upstream reaches, indicating good water quality, 5.3 to 5.5 in the mid-reaches and 6.0 to 6.5 in the lower reaches. The water quality index (WQI) indicated that water quality was fair (77 ± 0.98) in the upstream reach of the Mkondoa, marginal (55 ± 0.86) in the midstream reach and poor (33 ± 0.45) in the downstream reach. There were significant relationships between biological oxygen demand and dissolved oxygen and the occurrence of specific taxa, mainly Chironomus and Caenis. Significant changes in macroinvertebrate abundance were mostly related to changes in water quality. As in other parts of the world, macroinvertebrate communities proved to be good biological indicators of water quality and they should be used as bioindicators in long-term monitoring of this river.     

The invertebrate fauna of a physically modified urban river

The typical urban river is affected by various factors relating to water quality problems, physical habitat modification (for flood prevention) and flashy flows. These restrict macroinvertebrate biodiversity such that a few tolerant taxa may dominate and more sensitive organisms may be completely absent. This paper presents the findings of a year long, macroinvertebrate survey of an urban river catchment and investigates the effects of physical habitat modification on macroinvertebrates using various analytical tools. It is demonstrated that considerable variation in invertebrate species, abundance, diversity and tolerance exists between different urban rivers, sites on the same river and individual sites at different sampling times. Analysis of paired sites with similar water quality, but contrasting physical habitat, indicates that less modified sites support a slightly higher quality macroinvertebrate fauna (defined by biotic score and beta diversity) than heavily engineered sites. It is concluded that water quality is the primary limiting factor of invertebrate biodiversity in the heavily urbanized River Tame catchment. The removal of heavy engineering structures may facilitate improvements to invertebrate fauna in urban rivers only in conjunction with improvements to water quality.     

Ecological health of the Usuthu and Mbuluzi rivers in Swaziland based onselected biological indicators

Biological monitoring, using coliform bacteria and macroinvertebrate populations and diversity, was carried out monthly from August 2004 to January 2005 to determine the ecological health of the Usuthu and Mbuluzi rivers in Swaziland. Water temperature and pH were not significantly different between sites, but differed significantly between months. Bacterial species identified from both rivers were Escherichia coli, Klebsiella pneumoniae and Proteus vulgaris, with no significant differences in mean colony counts between the two rivers. Average colony counts were significantly different between months. A total of 926 macroinvertebrates, representing 28 families, were collected from both rivers and were significantly different between sites, rivers and months. Macroinvertebrate populations and diversity were negatively correlated with bacterial colony counts. Compliance with regulated water quality standards did not necessarily indicate acceptable water quality for biological communities, and thus there is a need for an integrated approach in water quality monitoring.     

Effects of Mediterranean climate annual variability on stream biological quality assessment using macroinvertebrate communities

Data on macroinvertebrates of selected reference sites were compiled from a long-term monitoring programme carried out in the Mediterranean Catalan Basins (NE Spain) that permitted analysis for nine years, from 1996 to 2004, using a homogeneous data collection procedure. This study aims to analyse the differences in composition and structure of macroinvertebrate communities at family level in five Mediterranean river types, and the values of biological quality metrics (IBMWP and IASPT indices, taxon richness and EPT) in reference conditions. Also differences between seasons (spring vs. summer) and between dry and wet periods were analysed. The dry and wet periods were determined using the Standardised Precipitation Index (SPI). A total of 29 reference sites were selected out of 184 sampling sites analysed, and 171 reference samples were available (from 1996 to 2004), of which 88 were sampled in dry periods, whereas 83 correspond to wet periods. Differences on community composition at family level were appreciated, clustering the rivers in three different groups: (1) rivers with a continuous flow regime located in siliceous zones; (2) rivers with a continuous flow regime located in calcareous zones; and (3) temporary rivers regardless of geology. Moreover, our results explain that the characteristics of hydrological periods (dry and wet) characterize the differences between communities better than just the season. The analysis of four biological quality metrics reveals clear differences between values obtained from dry and wet periods concerning taxon richness, EPT values and IBMWP biological indices, whereas the IASPT index does not show significant differences. The median taxonomic richness in wet periods is 32 macroinvertebrate families per sample while in dry periods this value falls to 22. Reference values of IBMWP index, the total number of taxa, and EPT metric are different between dry and wet periods in spring samples, while these differences are not relevant for IASPT index except for temporary streams. Hydrological specific conditions should additionally be considered in order to better calculate biological reference conditions, and to properly apply biological quality metrics used to establish the ecological status in Mediterranean rivers, especially in temporary ones. The use of the dry–wet period classification according to the climate characteristic results is a more accurate application of the Water Framework Directive in Mediterranean rivers. Implications of future climate change should be also considered from our results.     

Environmental quality assessment of the St. Clair River as reflected by the distribution of benthic macroinvertebrates in 1985

A benthic macroinvertebrate and sediment chemistry study of the St. Clair River from Lake Huron to Lake St. Clair was conducted in the spring of 1985. The purpose of the. study was to evaluate the environmental quality of the nearshore areas and assess the effectiveness of industrial and municipal abatement programs that have been implemented since 1977.A total of 112 macroinvertebratd taxa was collected from the river. Classification analysis indicated that 7 macroinvertebrate communities were evident in the river. Discriminant analysis suggested that physical habitat characteristics explained the distribution of 4 benthic communities, while sediment contaminants explained the distribution of 3 benthic communities. These analyses showed that the environmental quality of a 12 km stretch of the river along the Canadian shoreline had been degraded, probably by industrial waste discharges and spills. Toxic conditions were evident along the waterfront of Dow Chemical Canada Inc., probably a result of the combined effects of chlorinated organics, oils and greases, and mercury (historical contaminant) in the sediments. In contrast, the invertebrate fauna throughout the remainder of the St. Clair River reflected meso-eutrophic conditions, typical of a large, unstressed river.A comparison of the environmental quality as reflected by the benthic invertebrate fauna in 1985 with that in 1977 suggests that the abatement programs implemented over the past decade have improved the environmental quality along the Canadian side of the river. The total length of river adversely affected by waste discharges from Canadian industries and municipalities decreased from 21 km in 1977 to 12 km in 1985.     

The macroinvertebrate communities of two contrasting Norwegian glacial rivers in relation to environmental variables

1. Macroinvertebrate communities in two Norwegian glacial rivers, one in the western fjords (Dalelva) and one in the eastern mountains (Leirungsåi), were investigated during three time periods in 1996 and 1997.
2. Channel stability variables (substratum heterogeneity/Pfankuch index/hydraulic stress) and water temperature accounted for 54% of the total inertia in the principal components analysis (PCA) ordination of environmental variables. The importance of these variables was confirmed by cluster analysis.
3. The two rivers were well separated in the ordinations, with Leirungsåi showing much greater heterogeneity. This is explained by differences in altitudinal range, terrestrial vegetation and the importance and nature of tributary inputs.
4. Channel stability and temperature were also important in determining faunal communities in the two glacial rivers, supporting the main determining variables in the conceptual model of glacial streams ( Milner & Petts, 1994 ). However, clear temporal differences were apparent in the data, the two rivers being more similar during the summer period of high discharge dominated by glacial meltwater. During spring and especially during autumn environmental conditions and the macroinvertebrate fauna differed both within and between rivers.
5. Diamesinae dominated in the upper reaches of both rivers, with Orthocladiinae becoming more common downstream. The dominance of Diamesinae persisted further down Dalelva because of the continued influence of glacial tributaries, whereas in Leirungsåi the influence of non-glacial tributaries led to a change towards a greater proportion of Orthocladiinae. Lakes modified macroinvertebrate communities in both river systems.     

Spatial and seasonal variability of macroinvertebrate metrics: Do macroinvertebrate communities track river health?

The present study analyses the relationships of a set of 19 macroinvertebrate community metrics in relation to hydromorphological and water quality stress gradients in the Pas river basin, Northern Spain. Moreover, this study also aims to identify the most sensible season for biomonitoring this temperate Atlantic basin by means of macroinvertebrate communities. Thus, macroinvertebrate communities were analysed, along with the physicochemical characteristics of water in January, April, August and November 2005, in 9 sites. Hydromorphological conditions were evaluated using the Hydrogeomorphologic Index and by quantifying the percentage of reinforced banks, the number of low-head dams and their distance to each study site. Hydromorphological and water quality stress gradients were determined by means of two independent Principal Component Analysis. Thus, we obtained two water quality stress gradients, indicating organic pollution and watershed runoff, respectively, and a hydromorphological stress gradient. Macroinvertebrate metrics correlated better with the hydromorphological and the organic pollution stress gradients during the stable flow season, probably because of the homogenisation of water and hydraulic characteristics in the high flow season. On the other hand, relationships between macroinvertebrate metrics and watershed runoff stress gradient seem to be more dominated by hydraulic conditions than by water quality characteristics. LIFE index and the ICMi were the macroinvertebrate metrics that best correlated with the hydromorphological stress gradient, while EPTt, EPt, IBMWP, ASPT, LIFE, AsMet, Rhet, NoIns% and MACh% were well correlated with the organic pollution stress gradient in the low flow period. EPTt, EPt, ASPT, Rhet, and AsMet did not show significant seasonal differences and, thus, they are recommended as appropriate metrics to integrate biomonitoring results from different seasons in temperate European Atlantic rivers. Finally, autumn seems to be the best season to sample macroinvertebrate communities in this temperate Atlantic basin for biomonitoring purposes, and might be also the case for other similar European rivers.     

Tools for bioindicator assessment in rivers: The importance of spatial scale,land use patterns and biotic integration

This study outlines an alternative, versatile and flexible procedure to the Assessment System for the Ecological Quality of Streams and Rivers throughout Europe using Benthic Macroinvertebrates (AQEM) protocol for selecting and assessing candidate bioindicators for Water Framework Directive (WFD) compliant monitoring programmes. Based on different forms of benthic macroinvertebrate data using relative abundance of family level taxonomic groups, metrics and traits collected during spring 2010 at 96 lotic sites across northern Portugal, the procedure employs components of top down and bottom up analytical processes and introduces the concept of niche breadth to assess biological quality element response to environmental and stressor parameters across different spatial levels. Random Forest classification revealed that fractal and non-fractal land use metrics at basin and local level were extremely important determinants of Water Framework Directive determination of “Good” ecological quality, particularly at the local scale. The amount of urbanization at the lower spatial level was a particularly important determinant of ecological quality, while the extent and type of forest (especially coniferous) was more important at higher, river basin scale. Distance-based linear models (DISTLM) and distance-based redundancy analysis (dbRDA) were used to determine associations between invertebrate data and non-redundant environmental predictors selected using the Akaike Information Criterion (AIC). Results revealed a stronger association between invertebrate traits and selected environmental predictors compared to the other types of invertebrate data, although some association between invertebrate relative abundance and eutrophication was detected. Principal Components Analyses (PCA) were run for the non-redundant sets of predictors for each macroinvertebrate data set to extract an environmental quality gradient along the first axis. Niche breadth, calculated for candidate indicators to avoid bias resulting from expert judgement, was distributed by rank along its respective PCA gradient. Five candidate indicators for each data type were selected for their preference for the most pristine sites and five were selected due to their close link with the most degraded streams. Candidate bioindicators for impacted sites tended to be stenobiotic in character, due to the impoverished structural and functional diversity associated with such conditions. Finally Partial Least Squares Regression was used to refine and validate selected candidate metrics, to produce a comprehensive final list of macroinvertebrate measures of ecological quality.     

REPLY TO COMMENTS BY DR D H R HELLWIG ON PAPERS BY J.U. GROBBELAAR,M.K. SEELY & O.B. KOK

The aim of this study was to assess and compare the water quality of the Gwebi and Mukuvisi Rivers, on the basis of selected physicochemical variables and macroinvertebrate community structure. Five sites where selected on both rivers and these were sampled on three separate occasions between January and July of 1998. The water variables measured were the concentrations of iron, chromium, zinc, lead, copper, manganese, chlorides, fluorides, sulphates, total phosphates, nitrates, ammonia, total dissolved salts, dissolved oxygen, biological oxygen demand, as well as pH, conductivity, temperature, water surface velocity and discharge. The concentration of most of the chemical variables was relatively similar along the course of the Gwebi River, but there were drastic increases in the levels of iron, chromium, copper, zinc, chlorides, fluorides, sulphates, and ammonia along the Mukuvisi River. The two rivers were different with respect to the physicochemical variables, with the exception of the first site on the Mukuvisi, which was similar to sites on the Gwebi River. This was because of the differences in the levels of human activities on the two rivers. Industrial, sewage and domestic pollution has had an adverse effect on the water quality of the Mukuvisi River. There was a sharp decline in the number of macroinvertebrate taxa along the Mukuvisi River. The lower reaches of the river where dominated by oligochaetes and Chironimidae larvae. Sample score classification of water quality based on the South African Scoring System Version 4 (SASS4) showed that most of the Mukuvisi river had poor quality water quality, whilst much of the Gwebi River had fair quality water. The HABS1 habitat assessment index was used to assess habitat quality at each site. Although much of the Mukuvisi recorded fair to good habitat scores and had generally higher habitat scores than sites on the Gwebi, the SASS scores were generally lower compared to those along the Gwebi. The sample scores and average score per taxon (ASPT) of the SASS4 showed that the Mukuvisi River was of much lower quality than the Gwebi. Both the sample score and ASPT were negatively and significantly (p<0.05) correlated to most of the physicochemical variables. The water quality variables accounted for 61.1% and 59.0% of the differences in the sample score and ASPT respectively. There was a marginal decrease in the Margalef and Shannon indices along the Gwebi River, but the Simpson's index remained relatively constant. Along the Mukuvisi River, there was a clear and distinct decrease in the magnitude of all three diversity indices, indicating decreasing macroinvertebrate community structure. The change in water physicochemical variables accounted for 61.3%, 69.2% and 87.2% of the changes in the Margalef, Shannon and Simpson's index respectively. The study provides evidence that the changes in macroinvertebrate community structure along the Mukuvisi River is due to decline in the water quality. On the Gwebi, water quality is not the main factor determining macroinvertebrate community structure.