Ecological assessment of the Selenga River basin,the main tributary of Lake Baikal,using aquatic macroinvertebrate communities as bioindicators

The Selenga River is the main tributary of Lake Baikal (Siberian, Russia). In 2015/2016, the water quality at previously identified contaminated hotspot regions in the lower Selenga River basin was evaluated using resident aquatic macroinvertebrate communities as bioindicators. Benthic macroinvertebrate communities within the Selenga River were found to be relatively sensitive to water pollution as was highlighted by three evaluated biotic indices:Average Score per Taxon (ASPT); Ephemeroptera-Plecoptera-Trichoptera density index (EPT); and Trent Biological Index (TBI). The human impact on the Selenga River basin water quality was evident due to the significant decrease of the biotic indices at several sample locations including downstream of the wastewater discharge point of Ulan-Ude city, in the Dzhida River downstream of the confluence of the Modonkul River, and especially in the Modonkul River near to the mining operations at Zakamensk. At the same time, our study revealed a high self-regeneration ability of the aquatic ecosystem throughout the basin; with resident benthic macroinvertebrate communities appearing to recover in both the Selenga River and the Dzhida River within two to five km downstream of the contamination source. The changes in the benthic communities at the Selenga delta sampling sites were shown to occur under the influence of natural factors such as hydrological conditions and benthic sediment type, which significantly changed from the upper to the lower regions of the delta. For the Selenga delta, a typology of benthic macroinvertebrate communities including a map of their spatial distribution is presented.     

渭河流域河流健康调查与评价

在渭河流域开展野外采样调查,并采用水文改变指标法、综合水质标识指数法、生物完整性指数法等分析和评价渭河流域的水文、水质和水生态现状。结果表明:(1)林家村、魏家堡和咸阳3个站点的水文情势改变程度为高度改变,而临潼、华县的水文情势改变程度为中度改变;(2)渭河流域丰水期水环境质量状况优于枯水期,影响渭河水系的主要环境因子为总氮(TN)和总磷(TP),影响泾河和北洛河水系的主要环境因子为电导率;(3)渭河流域鱼类和底栖动物在丰、枯水期的生物完整性差异较小,着生藻类在丰、枯水期的生物完整性差异则较大。提出以下建议:(1)控制水利工程的过量开发利用,合理调控闸坝的蓄放水过程;(2)在河道沿岸建设污水处理厂,对排河污水进行拦截和处理,并定期监测水体理化性质,重点关注TN、TP和电导率;(3)控制渭河流域内的石油开发强度,恢复河岸带及边坡生境,以保证水生生物的正常栖息和繁衍。     

伊通河城区段底栖动物完整性对水质的响应时滞

基于 2015 年和 2019—2021 年伊通河长春市城区段底栖动物调查及水质监测数据，建立底栖动物完整性指 数（benthic-index?of?biotic?integrity,?B-IBI）评价体系，对伊通河城区段水生态健康状况进行评价，并在此基础上确定 影响 B-IBI 的关键水质指标及两者间的响应时滞。结果表明：伊通河城区段底栖动物种类数在月际间无显著差异 性（P>0.05），但在年际间差异显著（P<0.05），种类数先减少后增加，主要类群由耐污种向清洁种转变； 2015—2021 年，伊通河城区段 B-IBI 年均值波动上升，河流健康整体呈逐渐好转趋势，且上游河段健康状况优于 下游；各项水质指标中，总磷对伊通河城区段 B-IBI 值及其核心指标有显著性影响，且底栖动物对总磷质量浓度变 化的响应在时间上存在滞后性，滞后时间为9 个月左右（r=?0.88）。研究可为城市河流健康评价和治理管理提供科学依据。     

Using Benthic Indicator Species and Community Gradients to Optimize Restoration in the Arid,Endorheic Walker River Watershed,Western USA

The challenge of restoring watersheds in arid regions often requires the development of novel scientific tools to guide management. The Walker Basin Program was created to reverse ecological decline in an arid, endorheic watershed through scientifically guided restoration. As part of this programme, 3 years of benthic macroinvertebrate samples were collected seasonally at 10 sites that represent the diversity of river environments from the high‐mountain headwaters to a desert terminal lake. Samples were analysed to quantify baseline conditions in reference and degraded reaches of river and identify opportunities and constraints for aquatic community restoration. Naturally harsh environments in the lower river characterized by high temperatures and low base flow combined with a weak understanding of reference conditions to limit the utility of commonly used indices for quantifying biotic integrity. A flexible approach was employed using a combination of indicator species analysis, cluster analysis, canonical correspondence analysis, and community tolerance indices to evaluate the variation of benthic macroinvertebrate community composition across a set of environmental gradients. Results demonstrate that benthic communities in the watershed are primarily influenced by a longitudinal gradient related to elevation. A strong secondary community gradient caused by anthropogenic nutrient loading may constrain restoration effectiveness in some parts of the watershed. Restoration activities should improve water quality conditions and initially target areas of the watershed less affected by nutrient loading. Results also demonstrate that benthic communities shift longitudinally. These shifts should be monitored to inform adaptive management of restoration actions. Copyright © 2014 John Wiley & Sons, Ltd.     

Sampling Benthic Communities for Sediment Toxicity Assessments Using Grab Samplers and Artificial Substrates

In this study we compared macrobenthic communities collected from the Saginaw River (Michigan), Buffalo River (New York), Indiana Harbor (Indiana), Little Scioto River (Ohio), and Mill-town Reservoir (Montana) at the same locations using artificial substrates and grab samplers. Oligochaete worms (Limnodrilus hoffmeisteri) were the predominant benthic organisms in sediment samples collected with grab samplers. Artificial substrates also collected nothing but oligochaetes, but only at the stations with the most contaminated sediment in Indiana Harbor and the Little Scioto River. Artificial substrate samples from the Saginaw River, Buffalo River, and Milltown Reservoir generally contained a more diverse assemblage of benthic taxa. Routine assessments of sediment toxicity based on analyses of benthic macroinvertebrate communities should sample all available benthic habitats. Sediment samples collected with a grab sampler and artificial substrates should both be used for evaluating benthic communities in sediment toxicity assessments.     

Using macroinvertebrate biological traits for assessing biotic integrity of neotropical streams

Several recent studies have demonstrated that a functional approach (i.e. analysis of traits indicating species ecological functions) can be successfully used for river biomonitoring. To date this approach has only been applied in temperate rivers, even though it could notably contribute toward the development of an environmental assessment system in developing countries in other climatic zones. Using a multivariate approach (Fuzzy Correspondence Analysis—FCA), we analysed functional invertebrate community characteristics (described by 40 categories of seven biological traits mostly at the family level) at 66 stream sites from neotropical Bolivia with different level of anthropogenic disturbance. We were able to separate the sites on the first FCA axis (F1) (ANOVA test) following the predefined environmental quality classes based on the observed impact. Moreover, the F1 axis scores were significantly related to scores obtained using an independent macroinvertebrate multi‐metric index previously developed to assess streams biotic condition in the same biogeographical region. The F1 axis, which thus represents a gradient of anthropogenic impacts, was significantly correlated to 30 of the 40 studied trait categories. Our results (i) clearly confirm the possible use of functional traits for water quality assessment in neotropical streams, and (ii) provides support to the River Habitat Templet hypothesis since habitat disturbances produced predictable functional changes in macroinvertebrate assemblages. Finally, this study supports the potential worldwide applicability of the species‐trait approach as a biomonitoring tool for stream integrity assessment. Copyright © 2008 John Wiley & Sons, Ltd.     

基于不同生物类群的河流健康评价研究

基于浑太河流域鱼类与大型底栖动物群落结构和功能层面上的指标,构建了多指标指数评价河流健康状况。首先,基于土地利用指数、水质和栖息地质量指数构建ILWHQ(Index of land use and water and habitat quality)指数定量筛选参照点位。然后,采用判别分析、逐步回归分析、相关分析筛选对不同压力响应敏感的核心参数。最后,采用比值法计算其多指标指数(MMI-HT)。结果表明:筛选了5个点位作为参照点,共确定8个(鲤科鱼类种类数、底栖鱼类比例、杂食性鱼类比例、耐受性鱼类个体比例、产沉性卵鱼类比例、产沉性卵鱼类个体比例、EPT、黏附者比例)核心参数构建多指标评价指数。底栖动物核心参数对底质中粗颗粒物、悬浮物和电导率变化响应更敏感,而鱼类核心参数对底质中细颗粒物、氮素、DO和Cl-浓度变化响应更敏感。二者对多重环境压力响应的敏感性不尽相同。太子河流域的35个点位中,9个为健康,6个为亚健康,7个为一般,7个为较差,6个为极差。浑河流域的19个点位中,没有点位属于健康状态,5个为亚健康,4个为一般,5个为较差,5个为极差。太子河流域较差和极差的点位共占37.14%,浑河流域较差和极差的点位共占52.63%。说明相比于太子河流域,浑河流域的健康状况较差。     

Longitudinal changes in macroinvertebrate assemblages in the Meuse River: anthropogenic effects versus natural change

A collaborative study among three nations (France, Belgium, Netherlands) along the Meuse River developed a consistent approach for collecting and interpreting macroinvertebrate data. Specific mesohabitats were sampled in 16 locations along an 800‐km stretch of this lowland regulated river. The objective was to assess the ‘river health’ using macroinvertebrate communities as indicators of biological and ecological variation in space. The main changes in assemblages were investigated using multimetric and multivariate approaches. The authors examined relationships between faunal variations and both physico‐chemical gradients and man‐made disturbances. We related species traits to faunal changes and habitat characteristics. Both a gradual shift from a macroinvertebrate assemblage dominated by insects to a community dominated by crustaceans and molluscs and a drastic decrease in biotic index values were observed along the longitudinal gradient. Taxa were distributed according to oxygen, nitrate and ammonium concentrations, pH, conductivity and summer hydraulic conditions. But major faunal differences among sites could not be explained simply by physico‐chemical variables. The trait analysis underlined the role of temporary habitats in structuring the summer macroinvertebrate community of sites of the uppermost French sector, which supported the most diverse community in terms of trait combination. Downstream the macroinvertebrate community exhibited a more simple and less stable functional organization. We concluded that the Meuse River exhibited both a high biodiversity and a ‘reasonably good’ water quality in the upper reaches. Two transition zones highlighted the influence of a high degree of human impact on stream integrity. Regulation for navigation, ship traffic and heavily polluted effluent discharges influenced instream conditions via multiple processes determining a decline of both habitat stability and diversity. However, the rare occurrence of habitat‐sensitive species in the lower reaches indicated that a partial recovery of communities may be predicted if restoration and protection of disturbed (especially riparian) habitats are fulfilled. Copyright © 2002 John Wiley & Sons, Ltd.     

Potential Impacts of Stream Crossing Traffic On Macroinvertebrate Communities in the Missouri Ozark River

Depending on intensity, physical disturbance can either decrease or increase diversity of stream macroinvertebrate communities. Recreational activities in parks are one component of physical disturbance. Our objective was to evaluate the effects of stream crossings and recreational traffic on macroinvertebrate assemblages. Five stream‐crossing sites were sampled during winter and summer in the Current River, Ozarks National Scenic Riverways, Missouri, USA. Stream‐crossing traffic was assessed using trail cameras. At each site, macroinvertebrates were collected from four locations: riffle upstream of crossing, riffle immediately downstream of crossing and second and third riffles downstream of crossing. We compared sites and locations within sites using standard metrics (taxa richness, Ephemeroptera, Plecoptera and Trichoptera richness, biotic index and diversity) and their composite stream condition index (SCI) plus multivariate analyses (Nonmetric multidimensional scaling and correlations). Stream crossings had no detectable impacts on macroinvertebrate communities in winter, but in summer location, effects were present. Patterns in SCI scores across locations varied among sites, with no consistent declines in macroinvertebrate diversity downstream of crossings. Longitudinal stream effects dominated over potential stream‐crossing effects on macroinvertebrate communities. Overall, high SCI scores indicated that current levels of stream crossings and traffic in this scenic riverway do not pose a threat to macroinvertebrate communities at the spatial and temporal scale of this study. Copyright © 2015 John Wiley & Sons, Ltd.     

AN EVALUATION OF THE RELATIVE QUALITY OF DIKE POOLS FOR BENTHIC MACROINVERTEBRATES IN THE LOWER MISSOURI RIVER,USA

A habitat‐based aquatic macroinvertebrate study was initiated in the Lower Missouri River to evaluate relative quality and biological condition of dike pool habitats. Water‐quality and sediment‐quality parameters and macroinvertebrate assemblage structure were measured from depositional substrates at 18 sites. Sediment porewater was analysed for ammonia, sulphide, pH and oxidation–reduction potential. Whole sediments were analysed for particle‐size distribution, organic carbon and contaminants. Field water‐quality parameters were measured at subsurface and at the sediment–water interface. Pool area adjacent and downstream from each dike was estimated from aerial photography. Macroinvertebrate biotic condition scores were determined by integrating the following indicator response metrics: % of Ephemeroptera (mayflies), % of Oligochaeta worms, Shannon Diversity Index and total taxa richness. Regression models were developed for predicting macroinvertebrate scores based on individual water‐quality and sediment‐quality variables and a water/sediment‐quality score that integrated all variables. Macroinvertebrate scores generated significant determination coefficients with dike pool area (R² = 0.56), oxidation–reduction potential (R² = 0.81) and water/sediment‐quality score (R² = 0.71). Dissolved oxygen saturation, oxidation–reduction potential and total ammonia in sediment porewater were most important in explaining variation in macroinvertebrate scores. The best two‐variable regression models included dike pool size + the water/sediment‐quality score (R² = 0.84) and dike pool size + oxidation–reduction potential (R² = 0.93). Results indicate that dike pool size and chemistry of sediments and overlying water can be used to evaluate dike pool quality and identify environmental conditions necessary for optimizing diversity and productivity of important aquatic macroinvertebrates. A combination of these variables could be utilized for measuring the success of habitat enhancement activities currently being implemented in this system. Published in 2011 by John Wiley & Sons, Ltd.     

珠江重要河流底栖动物水质生物学评价

2011年和2012年调查了珠江流域66个样点的底栖动物和水化学指标,利用2011年北江11个样点和郁江17个样点的底栖动物群落和水化学指标,采用主成分分析法获得综合环境因子(主成分1和主成分2)。分析36个候选底栖动物参数与环境因子间的相关性,结合参数的分布范围,确定适于珠江流域开展河流生态系统生物学质量评价的3个底栖动物参数:双翅目百分比、刮食者百分比和BI指数,进而构建了珠江流域河流生物学质量评价的综合生物指数及评价等级(清洁、轻度污染、中度污染和重度污染)。66个样点的综合生物指数评价结果显示,珠江流域河流生物学质量以轻度至中度污染为主,占80.3%,清洁占13.6%,重度污染占有6%。研究表明,在珠江流域应用底栖动物开展中大型河流水质生物学评价具有良好的应用前景。     

Variations in the Aquatic Vegetation of the Welland River (Ontario,Canada) Above and Below an Industrial Waste Discharge

The zonation of aquatic macrophytes, particularly Typha and Sagittaria sp. and associated periphyton communities, were investigated in relation to industrial point source discharges to the Welland River, Ontario. Severe reductions of macrophyte species densities and macrophyte and periphyton diversity were found immediately below the outfalls with distinct recovery zones in the downstream part. Normal macrophyte and periphyton density and diversity occurred at sites approximately 1.6 km below the outfall.     

应用底栖无脊椎动物完整性指数评价漓江水系健康状况

为了通过漓江底栖无脊椎动物状况建立适合漓江的生物完整性指数,进而评价漓江流域内水质健康状况,于2008年3月调查了漓江水系17个参照点和14个监测点的水化学与底栖无脊椎动物指标,水质化学指标检测结果显示,参照点的TP、TN、NH3-N和COD浓度一般低于监测点。通过对46个候选生物参数的计算和逐步分析,确定了构成底栖动物完整性B-IBI指数的4个生物参数:总分类单元数、EPT分类单元数、扁蜉占蜉蝣总数的百分比和优势单元数量百分比,初步确立了B-IBI健康评价标准,即B-IBI≥21为健康;B-IBI21为不健康。评价结果表明:漓江上游及各支流健康状况较好,大部分为健康;中下游干流健康状况较差,大多为不健康。     

北江大型底栖无脊椎动物群落结构及水质的生物评价

对北江25个采样点的大型底栖无脊椎动物进行采样调查,并根据大型底栖无脊椎动物的群落结构特征对水质进行生物评价。研究中共采集到大型底栖无脊椎动物46属,分别隶属于15目31科,其中水生昆虫30属,占65.22%;软体动物8属,占17.39%;环节动物6属,占13.04%;甲壳动物2属,占4.35%。出现频率最高的3个种属分别为多足摇蚊属(Polypedilum)、巴蛭属(Barbronia)以及苏氏尾鳃蚓(Branchiurasowerbyi)。应用Shannon-Wiener多样性指数、Margalef多样性指数、Pielou均匀度指数、生物学污染指数BPI(biotic pollution index)、BI(biotic index)、FBI(family biotic index)、Goodnight-Whitley修正指数(GBI)7种生物指数对北江水质进行综合评价。结果表明:与20世纪80年代的评价结果相比,北江的大型底栖无脊椎动物在种类和数量等多方面均发生了较大的变化,生物多样性减少,耐污种所占比例增加,水质理化参数恶化;7种生物指数的评价结果存在一定的差异,部分指数之间存在较高的相关性,FBI指数和BPI指数的准确性和科学性更强,适用于北江水质的生物评价。在25个采样点中,6个采样点水质综合评价等级为较差或极差,16个采样点水质评价等级为一般,3个采样点水质等级为良好,整体水质属于一般的水平。人类活动对河流的水质状况造成了一定的影响。从水质生物学的角度衡量,北江水质整体呈现下降趋势。     

梯级引水式水电站对底栖动物群落结构的影响

为研究梯级引水式水电站对底栖动物群落结构的影响,对云南景谷河3座梯级电站影响下河流底栖动物的群落结构进行了调查研究。研究结果表明,水电站的修建显著改变了河流的流速及水深;减水段和混合段水体底栖动物的物种丰度和多样性指数存在一定差异;不同级电站混合段底栖动物密度和生物量均高于减水段;功能摄食类群上混合段的滤食者、撕食者和捕食者相对丰度均显著高于减水段;丰度/生物量比较曲线表明,相对于混合段,水电站影响下减水段底栖动物群落受到了一定程度的干扰。故修建梯级小水电站时,应关注其对底栖动物的群落结构的影响。     

IDENTIFYING SENSITIVE INDICES IN THE RESPONSE OF AQUATIC BIOTA TO LANDSCAPE PATTERN CHANGES: A CASE STUDY OF THE TAIZI RIVER BASIN IN NORTH CHINA

It is widely accepted that riverine ecosystems are influenced by the landscape pattern changes of their corresponding watersheds, but few studies have identified the most sensitive and nonsensitive biotic indices, the most influential landscape metrics and the relationship between aquatic biota and landscape patterns. To address this problem, Taizi river basin of Northeast China is taken as a case study, in which GIS technology and landscape ecology method are adopted. The study is performed at both the basin scale (entire drainage area upstream from certain sample point) and the riparian scale (a certain width buffer on each side of sample point extending the length of drainage network) to direct future landscape pattern design at the corresponding scales. The results show that at the basin scale, the species richness of benthic macroinvertebrate (B‐S) and the fish index of biotic integrity (F‐IBI) are the most sensitive biotic indices to landscape metrics, whereas the species richness of phytoplankton (P‐S), the Shannon–Weaver diversity index of phytoplankton (P‐H), zooplankton (Z‐H), benthic macroinvertebrate (B‐H) and fish density (F‐D) are not sensitive to landscape pattern changes; at the riparian scale, F‐IBI, B‐S and zooplankton density (Z‐D) have significant correlations with 9 of 10 landscape metrics calculated in this study, whereas P‐S, P‐H, Z‐H, B‐H, F‐D and species richness of fish have very low correlations with riparian landscape pattern changes. At the basin scale, no landscape pattern metrics show obviously more influence on the riverine ecosystems than other metrics. At the riparian scale, Shannon's diversity index is a very influential factor. As to both of the two scales, B‐S and F‐IBI are correlated with most landscape metrics. The information derived above can help understand the impacts of landscape change on river ecosystems more clearly and provide useful scientific information on river ecosystem protection from the viewpoint of landscape. Copyright © 2013 John Wiley & Sons, Ltd.     

Use of Stable Isotopes to Trace Municipal Wastewater Effluents into Food Webs within a Highly Developed River System

Many anthropogenic inputs, such as municipal wastewater effluents (MWWEs), affect stable isotope signatures (δ¹³C and δ¹⁵N) at the base of exposed food webs creating spatial patterns reflecting their incorporation into aquatic food webs. The Grand River in southern Ontario, Canada, is a heavily modified, rapidly urbanizing river that assimilates wastewater from 30 municipal wastewater treatment plants. Stable isotope analysis was applied to resident aquatic invertebrates and fish influenced by three different wastewater outfalls in early, middle, and late summer to determine how values shifted seasonally and with differing effluent quality. There was a slight increase in δ¹³C in both invertebrates and fish in late summer downstream from the three outfalls, but it is difficult to separate effects of the effluents from downstream gradients. Downstream of two of the three outfalls, the δ¹⁵N tended to increase relative to upstream, while the remaining effluent, of the poorest quality, decreased δ¹⁵N values of both invertebrates and fish. Spatial trends in stable isotopes became more pronounced as the summer progressed with the greatest between‐site differences occurring in late summer. This study reflects the complex nutrient dynamics associated with MWWE inputs to rivers and contributes to our understanding and application of stable isotope analysis in impacted lotic ecosystems. Copyright © 2014 John Wiley & Sons, Ltd.     

Development of a submerged aquatic vegetation community index of biotic integrity for use in Lake Ontario coastal wetlands

Submerged aquatic vegetation (SAV) supports biodiversity in the Great Lakes basin by providing an important source of food and habitat for breeding marsh birds and fish and it is desirable to have indices enabling reporting on the condition of SAV, to complement already available indices for the condition of fish, aquatic macroinvertebrate, and bird communities and water quality. We developed a SAV index of biotic integrity (SAV IBI) with 6 years of quadrat-based vegetation species composition data (2003, 2005–2009) collected across 46 coastal wetlands on the Canadian side of Lake Ontario. We evaluated the suitability of thirteen potential metrics that described species richness, floristic quality, and cover. Metrics with a significant linear or non-linear response to disturbance (as assessed by a water quality index; WQI) were retained for use in the SAV IBI. Retained metrics included turbidity-intolerant species richness, native species richness, coefficient of conservatism, and total cumulative coverage. Lower SAV IBI scores indicated poorer coastal wetland conditions. Coastal wetlands in poor condition were located in more urbanized watersheds (e.g., Durham Region) relative to wetlands in more natural watersheds. Fish and breeding bird community condition showed strong significant relationships with the SAV IBI, suggesting that SAV was an important component of fish and bird biodiversity. Our SAV assessment index and its relationship to faunal diversity can be used to inform conservation decisions.     

Invertebrate response to impacts of water diversion and flow regulation in high‐altitude tropical streams

Water supply systems are critical infrastructure that provides food and energy security for developed societies. The operation of reservoirs (flow regulation) and water intakes (water diversion) has known negative impacts on aquatic ecosystems; however, quantification of ecological impacts and examination of these two types of flow alteration remain a developing area of research. We investigated the individual and combined impact of flow regulation and water diversion on stream ecosystem integrity, the freshwater macroinvertebrate community, and the population structure of flow‐sensitive insects. For 2 years, we monitored quarterly discharge, physical and chemical stream conditions, and benthic invertebrates of four high‐altitude tropical streams that are part of the water supply system of Quito, Ecuador. Flow regulation caused a loss of the hydrological seasonality of these streams, including a decrease in stream depth and biotic quality. Water diversion caused a decrease in dissolved oxygen and overall ecosystem integrity. Freshwater invertebrate density and richness decreased as a result of water diversion and flow regulation. The combined flow alteration in these streams decreased the density of nymphal stages of the widely distributed mayfly Andesiops peruvianus. Given the societal needs for food and energy security, water management for diversion (e.g., irrigation) and in‐line storage practices (e.g., hydroelectric dams) are anticipated to increase. This research suggests that the negative environmental impacts of flow alteration could be mitigated with discharge releases designed to approximate the natural hydrologic regime of undisturbed streams.     

Fate,Transport and Effects of Pollutants Originating from Acid Mine Drainage in the Olifants River,South Africa

Concentrations of pollutants were measured in water, sediment and algal samples collected along a longitudinal gradient from a stretch of the Olifants River, South Africa, that receives acid mine drainage (AMD) from the Klipspruit River. The effects of AMD were determined through macroinvertebrate biotic indices (SASS5) and multivariate analysis of macroinvertebrate communities. The acidic Klipspruit River caused increased concentrations of total Al, Fe and Mn in the Olifants River. Upon mixing of the Klipspruit with that from the alkaline Olifants River, Al and Fe precipitate rapidly, leading to lower concentrations in the dissolved phase and higher concentrations in the suspended phase and in sediment at sites in close proximity to the confluence. Similarly, filamentous algae accumulated high concentrations of Al, Fe and Zn immediately after the confluence. Mn remains in the dissolved phase, and sediment and algal concentrations increase with increasing distance downstream. Metal speciation analysis indicate that Al is rapidly converted from more toxic forms (e.g. Al³⁺ and Al(OH)²⁺) to less toxic forms (e.g. Al(OH)₃(aq) and Al(OH)^4?). In contrast, Mn remains in the soluble Mn²⁺ form. Macroinvertebrate metrics and community structure showed clear signs of deterioration in water quality in the Olifants River downstream of the point of AMD input. While total TDS concentrations at all sites fall within ranges likely to affect macroinvertebrates, the relative composition of major ions changes as a result of AMD input, which may also account for the observed changes in macroinvertebrate communities. Further downstream, the Wilge River discharges into the Olifants River and significantly improves water quality downstream of the confluence. Future mining and development activities in the Wilge catchment should be carefully managed and monitored so as to ensure sufficient flows of acceptable quality to prevent further deterioration of water quality in the Olifants River and downstream reservoirs. Copyright © 2014 John Wiley & Sons, Ltd.