Relating Benthic Infaunal Community Structure to Environmental Variables in Estuaries using Nonmetric Multidimensional Scaling and Similarity Analysis

In 1994, 19 stations were sampled (2 replicates/station) with Young grabs in association with the EMAP-Estuaries Carolian Province Base Monitoring in Florida. A total of 295 unique benthic infauna taxa and 9647 individuals were identified and enumerated. Environmental data (bottom-water quality, sediment grain size, sediment metals, and organics) and benthic community data were analyzed using hierarchical agglomerative cluster analysis and ordination via nonmetric multidimensional scaling. Bray-Curtis similarities and Euclidean distance were used as the distance measures for biotic and abiotic data, respectively. Multivariate analyses were complemented by examining incremental contributions of benthic taxa to similarity values using a percentage similarity technique. A low-salinity site in a tributary to the St. Johns River had benthic communities uniquely different from those of moderate-to high-salinity sites. A diverse assemblage of polychaetes, gastropods, bivalves, amphipods, sipunculans, and phoronids was consistently associated with relatively unimpacted sites in the Indian River Lagoon. Infaunal community structure in the northern portion of the study area was influenced by the nearby Atlantic Ocean. Community shifts in association with latitudinal gradients and concentrations of sediment metals and organics were apparent. The nonparametric multivariate techniques used in this study were particularly effective at delineating and defining fine-scale community differences.     

Evaluating macroinvertebrate biological metrics for ecological assessment of streams in northern Portugal

A procedure to select the most relevant metrics for assessing the ecological condition of the Douro basin (north Portugal) was developed based upon a set of 184 benthic community metrics. They were grouped into 16 biological categories selected from literature using data collected over 2 years from 54 sites along 31 rivers covering the whole perceived range of human disturbance. Multivariate analyses were carried out to identify the main trends in the macroinvertebrate data, to select reference versus impaired sites, to avoid multicolinearity between metrics, and to identify those that were clearly independent from natural stream typology. Structural metrics, adaptation metrics, and tolerance measures most effectively responded across a range of human influence. We find these attributes to be ecologically sound for monitoring Portugal’s lotic ecosystems and providing information relevant to the Water Framework Directive, which asserts that the definition of water quality depends on its “ecological status”, independent of the actual or potential uses of those waters.     

Biotic and Abiotic Changes Along the Recovery Gradient of Two Impounded Rivers with Different Impoundment Use

Changes in physicochemical conditions and lotic benthic macroinvertebrates along the recovery gradient of the impounded Colorado (USA) and Duratón (Spain) Rivers were examined to identify and compare major factors affecting the structure of the macrobenthic community. Although both impounded rivers were exposed to hypolimnial releases from dams, they exhibited different impoundment use; Granby Dam (Colorado River) is used for water storage whereas Burgomillodo Dam (Duratón River) is used for hydroelectric production. The major factor responsible for macroinvertebrate responses in the Colorado River appeared to be the anomalous temperature pattern caused by Granby Dam, with relatively cool temperatures during the summer and relatively warm temperatures during the winter. In contrast, the major factors responsible for macroinvertebrate responses in the Duratón River seemed to be short-term flow fluctuations and low oxygen concentrations caused by Burgomillodo Dam. Values of taxonomic richness and relative abundances of shredders (Colorado River) and scrapers (Duratón River) increased along the recovery gradient of the impounded rivers. In general, chironomids (Diptera) were tolerant to both types of impoundment use, whereas elmids (Coleoptera) and psychomyiids (Trichoptera) were very sensitive. Overall, this environmental monitoring study denotes that the downstream changes in the biotic and abiotic components of impounded rivers is a function of the particular use of impoundments.     

Spatial scales and probability based sampling in determining levels of benthic community degradation in the Chesapeake Bay

The extent of degradation of benthic communities of the Chesapeake Bay was determined by applying a previously developed benthic index of biotic integrity at three spatial scales. Allocation of sampling was probability-based allowing areal estimates of degradation with known confidence intervals. The three spatial scales were: (1) the tidal Chesapeake Bay; (2) the Elizabeth River watershed; and (3) two small tidal creeks within the Southern Branch of the Elizabeth River that are part of a sediment contaminant remediation effort. The areas covered varied from 10^–1 to 10⁴ km² and all were sampled in 1999. The Chesapeake Bay was divided into ten strata, the Elizabeth River into five strata and each of the two tidal creeks was a single stratum. The determination of the number and size of strata was based upon consideration of both managerially useful units for restoration and limitations of funding. Within each stratum 25 random locations were sampled for benthic community condition. In 1999 the percent of the benthos with poor benthic community condition for the entire Chesapeake Bay was 47% and varied from 20% at the mouth of the Bay to 72% in the Potomac River. The estimated area of benthos with poor benthic community condition for the Elizabeth River was 64% and varied from 52–92%. Both small tidal creeks had estimates of 76% of poor benthic community condition. These kinds of estimates allow environmental managers to better direct restoration efforts and evaluate progress towards restoration. Patterns of benthic community condition at smaller spatial scales may not be correctly inferred from larger spatial scales. Comparisons of patterns in benthic community condition across spatial scales, and between combinations of strata, must be cautiously interpreted.     

Periphyton and Sediment Bioassessment in North Florida Bay

Periphyton colonization and sediment bioassessment were used ina survey to compare the relative environmental condition ofsampling sites located in Florida Bay and four peripheral sloughareas during the summer of 1995. Periphyton biomass, pigmentcontent, tissue quality and community composition weredetermined. In addition, benthic community composition and thetoxicities of whole sediments and associated pore waters weredetermined for two species of rooted macrophytes, an epibenthicinvertebrate and bioluminescent bacteria. Several locational differences were observed for the response parameters.Periphyton biomass was significantly greater in the Taylor Riverand the least in Shell Creek (P < 0.05). Most sediments were notacutely toxic to mysid shrimp nor phytotoxic. However, sedimentsfrom the Taylor River were more phytostimulatory than others (P< 0.05). Contaminant bioresidues were similar at most sites,however, mercury, chromium and nickel concentrations weregreater for periphyton colonized in the Taylor River and TroutCreek areas. Structural characteristics of the periphytic algalcommunity usually were statistically similar but a consistenttrend of lower density and diversity was evident for ShellCreek. The benthic community was the least diverse and dense inthe Canal C-111. The results of this study provide an initialindication of differences in the role of several slough areas aspossible sources of bioavailable contaminants to Florida Baywhich warrants additional investigation.     

中国北方河流底栖动物群落季节性演替对水生态环境质量评价的影响

大型底栖动物是评价水生态质量最常用的生物类群,鉴于水生昆虫的生活史特点,在一年当中群落结构会发生季节性变化,如何利用底栖动物数据准确评价水生态质量状况,反映客观实际,值得探讨。将黑龙江省2012—2015年水生生物试点监测47个采样点的108组底栖动物数据进行比较,对群落结构的相似性、物种的更替率和BMWP指数评价结果进行分析,探讨群落的演替及BMWP指数的变化规律。结果表明不同时间采集的样品底栖动物群落之间存在较大差异,评价的结果也存在差异,越是水环境质量好的区域,这种差异越明显。利用底栖动物评价水生态状况,宜选择长时间段的多个采集数据,经统计整理后,利用复合样方(年均值)的特征,评价一段时间内(如以年为单位)的水生态质量状况,使评价结果更具准确性。     

Application of the benthic index of biotic integrity to environmental monitoring in Chesapeake Bay

The Chesapeake Bay benthic index of biotic integrity (B-IBI) was developed to assess benthic community health and environmental quality in Chesapeake Bay. The B-IBI provides Chesapeake Bay monitoring programs with a uniform tool with which to characterize bay-wide benthic community condition and assess the health of the Bay. A probability-based design permits unbiased annual estimates of areal degradation within the Chesapeake Bay and its tributaries with quantifiable precision. However, of greatest interest to managers is the identification of problem areas most in need of restoration. Here we apply the B-IBI to benthic data collected in the Bay since 1994 to assess benthic community degradation by Chesapeake Bay Program segment and water depth. We used a new B-IBI classification system that improves the reliability of the estimates of degradation. Estimates were produced for 67 Chesapeake Bay Program segments. Greatest degradation was found in areas that are known to experience hypoxia or show toxic contamination, such as the mesohaline portion of the Potomac River, the Patapsco River, and the Maryland mainstem. Logistic regression models revealed increased probability of degraded benthos with depth for the lower Potomac River, Patapsco River, Nanticoke River, lower York River, and the Maryland mainstem. Our assessment of degradation by segment and water depth provided greater resolution of relative condition than previously available, and helped define the extent of degradation in Chesapeake Bay.     

Using the Sediment Quality Triad to characterize baseline conditions in the Anacostia River, Washington, DC, USA

The Sediment Quality Triad (SQT) consists of complementary measures of sediment chemistry, benthic community structure, and sediment toxicity. We applied the SQT at 20 stations in the tidal portion of the Anacostia River from Bladensburg, MD to Washington, DC to establish a baseline of conditions to evaluate the effects of management actions. Sediment toxicity was assessed using 10-day survival and growth tests with the freshwater amphipod, Hyalella azteca and the midge, Chironomus dilutus. Triplicate grabs were taken at each station for benthic community analysis and the Benthic Index of Biotic Integrity (B-IBI) was used to interpret the data. Only one station, #92, exhibited toxicity related to sediment contamination. Sediments from this station significantly inhibited growth of both test species, had the highest concentrations of contaminants, and had a degraded benthic community, indicated by a B-IBI of less than 3. Additional sediment from this station was tested and sediment toxicity identification evaluation (TIE) procedures tentatively characterized organic compounds as the cause of toxicity. Overall, forty percent of the stations were classified as degraded by the B-IBI. However, qualitative and quantitative comparisons with sediment quality benchmarks indicated no clear relationship between benthic community health and contaminant concentrations. This study provides a baseline for assessing the effectiveness of management actions in the Anacostia River.     

Spatial heterogeneity of stream environmental conditions and macroinvertebrates community in an agriculture dominated watershed and management implications for a large river (the Liao River,China) basin

Understanding the effects of watershed land uses (e.g., agriculture, urban industry) on stream ecological conditions is important for the management of large river basins. A total of 41 and 56 stream sites (from first to fourth order) that were under a gradient of watershed land uses were monitored in 2009 and 2010, respectively, in the Liao River Basin, Northeast China. The monitoring results showed that a total of 192 taxa belonging to four phyla, seven classes, 21 orders and 91 families were identified. The composition of macroinvertebrate community in the Liao River Basin was dominated by aquatic insect taxa (Ephemeroptera and Diptera), Oligochaeta and Molluscs. The functional feeding group GC (Gatherer/Collector) was dominant in the whole basin. Statistical results showed that sites with less watershed impacts (lower order sites) were characterized by higher current velocity and habitat score, more sensitive taxa (e.g., Ephemeroptera), and the substrate was dominated by high percentage of cobble and pebble. The sites with more impacts from agriculture and urban industry (higher order sites) were characterized by higher biochemical (BOD₅) and chemical oxygen demand (COD), more tolerant taxa (e.g., Chironominae), and the substrate was dominated by silt and sand. Agriculture and urban-industry activities have reduced habitat condition, increased organic pollutants, reduced macroinvertebrate abundance, diversity, and sensitive taxa in streams of the lower Liao River Basin. Restoration of degraded habitat condition and control of watershed organic pollutants could be potential management priorities for the Basin.     

Heavy Metal Transport and Behavior in the Lower Columbia river, USA

The primary objective of this study was to evaluate temporal changes in heavy metal content of lower Columbia River sediment following terminated or reduced soluble heavy metal loading from the world's largest lead-zinc refinery and mining districts in the USA and Canada. Sediment cores were collected from two fine sediment depositional sites (∼600 km downstream) in August 1999 and were analyzed for total metal content, texture, and age/dating parameters. Zinc, cadmium and lead contents in 1999 declined by only a factor of two over their depth profile maxima (dated as between 1970 and 1980). In sharp contrast, more than a 10-fold decrease in dissolved metal loading occurred during this same period. Zinc in filtered Columbia River water at downstream locations also declined by > 10-fold, consistent with the reduced upper river solute-metal loading. Once soluble metal releases are reduced or terminated, the solute half-time in Columbia River water is months versus ∼20 yr for adsorbed metals on surficial (or resuspended) bed sediments. The much slower rate of decline for sediment, as compared to the solute phase, is attributed to resuspension, transport and redeposition of irreversibly bound metals from upstream sedimentary deposits. This implies downstream exposure of benthic or particle-ingesting biota can continue for years following source remediation and/or termination of soluble metal releases. Accordingly, contaminant contents of both particulate and solute phases of river water, as well as sediment core sections, are suggested for assessing long-term biotic exposure/response to mitigation activities in the Columbia River and similar fluvial ecosystems.     

Improving the sampling strategy of the Joint Danube Survey 3 (2013) by means of multivariate statistical techniques applied on selected physico-chemical and biological data

The concept of basin-wide Joint Danube Survey (JDS) was launched by the International Commission for the Protection of the Danube River (ICPDR) as a tool for investigative monitoring under the Water Framework Directive (WFD), with a frequency of 6 years. The first JDS was carried out in 2001 and its success in providing key information for characterisation of the Danube River Basin District as required by WFD lead to the organisation of the second JDS in 2007, which was the world’s biggest river research expedition in that year. The present paper presents an approach for improving the survey strategy for the next planned survey JDS3 (2013) by means of several multivariate statistical techniques. In order to design the optimum structure in terms of parameters and sampling sites, principal component analysis (PCA), factor analysis (FA) and cluster analysis were applied on JDS2 data for 13 selected physico-chemical and one biological element measured in 78 sampling sites located on the main course of the Danube. Results from PCA/FA showed that most of the dataset variance (above 75 %) was explained by five varifactors loaded with 8 out of 14 variables: physical (transparency and total suspended solids), relevant nutrients (N–nitrates and P–orthophosphates), feedback effects of primary production (pH, alkalinity and dissolved oxygen) and algal biomass. Taking into account the representation of the factor scores given by FA versus sampling sites and the major groups generated by the clustering procedure, the spatial network of the next survey could be carefully tailored, leading to a decreasing of sampling sites by more than 30 %. The approach of target oriented sampling strategy based on the selected multivariate statistics can provide a strong reduction in dimensionality of the original data and corresponding costs as well, without any loss of information.     

The New Bedford Harbor Superfund site long-term monitoring program (1993–2009)

New Bedford Harbor (NBH), located in southeastern Massachusetts, was designated as a marine Superfund site in 1983 due to sediment contamination by polychlorinated biphenyls (PCBs). Based on risks to human health and the environment, the first two phases of the site cleanup involved dredging PCB-contaminated sediments from the harbor. Therefore, a long-term monitoring program (LTM) was developed to measure spatial and temporal chemical and biological changes in sediment, water, and biota to assess the effects and effectiveness of the remedial activities. A systematic, probabilistic sampling design was used to select sediment sampling stations. This unbiased design allowed the three segments of the harbor to be compared spatially and temporally to quantify changes resulting from dredging the contaminated sediments. Sediment was collected at each station, and chemical (e.g., PCBs and metals), physical (e.g., grain size), and biological (e.g., benthic community) measurements were conducted on all samples. This paper describes the overall NBH-LTM approach and the results from the five rounds of sample collections. There is a decreasing spatial gradient in sediment PCB concentrations from the northern boundary (upper harbor) to the southern boundary (outer harbor) of the site. Along this same transect, there is an increase in biological condition (e.g., benthic community diversity). Temporally, the contaminant and biological gradients have been maintained since the 1993 baseline collection; however, since the onset of full-scale remediation, PCB concentrations have decreased throughout the site, and one of the benthic community indices has shown significant improvement in the lower and outer harbor areas.     

江苏地表水体大型底栖无脊椎动物生物多样性状况研究

大型底栖无脊椎动物群落结构与水体水质和水生态系统健康状况关系密切,其受外界干扰后群落结构的变化趋势可以反映水体受污染的性质和程度。2008年,对江苏省主要饮用水源地,长江、京杭大运河等主要河流及太湖等重点湖泊开展底栖动物调查与评价研究,共设置调查点位154个。江苏主要饮用水源地底栖动物的物种数量为78种,主要河流发现底栖动物96种,主要湖泊底栖动物发现65种。从物种多样性指数评价结果看,主要湖泊的底栖生物多样性状况优于地表水源地和主要河流,丰富和较丰富所占比例合计达58%;主要河流的评价结果最差,丰富和较丰富所占比例合计仅达30.7%,存在11.3%物种多样性极贫乏的点位,且大部分水体底栖动物组成以耐污种为主,优势种为极耐污的霍甫水丝蚓,水质状况劣于饮用水源地和主要湖泊。     

Benthic communities of streams related to different land uses in a hydrographic basin in southern Brazil

Different land uses affect the characteristics of a hydrographic basin, reflected in the river water quality, and consequently affecting the aquatic biota. The benthic community closely reflects the alterations caused by different human activities. In this study, the effects of different land uses were evaluated by analysis of the benthic community structure in streams with urban, agricultural and pasturage influences, as well as areas in better-conserved regions. The abiotic parameters showed distinct seasonal variability, which did not occur with the benthic organisms. A degradation gradient was observed among the study sites, in the headwaters-agriculture-pasture-urban direction. By the CCA its possible to observe that the density of organisms tended to increase along this gradient, whereas richness, diversity, evenness, and EPT families decreased. The most intense effects of land use on the benthic community composition, richness, and diversity were observed in urban areas (F (1,4) = 16.0, p = 0.01; F (1,4) = 8.97, p = 0.04; respectively). In conclusion a trend in the benthic community is observed in to predict alterations caused for the different land uses, mainly, when the source point pollution, as the case of urban area.     

The distribution and extent of heavy metal accumulation in song sparrows along Arizona’s upper Santa Cruz River

Heavy metals are persistent environmental contaminants, and transport of metals into the environment poses a threat to ecosystems, as plants and wildlife are susceptible to long-term exposure, bioaccumulation, and potential toxicity. We investigated the distribution and cascading extent of heavy metal accumulation in southwestern song sparrows (Melospiza melodia fallax), a resident riparian bird species that occurs along the US/Mexico border in Arizona’s upper Santa Cruz River watershed. This study had three goals: (1) quantify the degree of heavy metal accumulation in sparrows and determine the distributional patterns among study sites, (2) compare concentrations of metals found in this study to those found in studies performed prior to a 2009 international wastewater facility upgrade, and (3) assess the condition of song sparrows among sites with differing potential levels of exposure. We examined five study sites along with a reference site that reflect different potential sources of contamination. Body mass residuals and leukocyte counts were used to assess sparrow condition. Birds at our study sites typically had higher metal concentrations than birds at the reference site. Copper, mercury, nickel, and selenium in song sparrows did exceed background levels, although most metals were below background concentrations determined from previous studies. Song sparrows generally showed lower heavy metal concentrations compared to studies conducted prior to the 2009 wastewater facility upgrade. We found no cascading effects as a result of metal exposure.     

Derivation of no-effect and reference-level sediment quality values for application at Saskatchewan uranium operations

To date, the majority of empirical approaches used to derive sediment quality values (SQVs) have focused on metal concentrations in sediment associated with adverse effects on benthic invertebrate communities. Here, we propose the no-effect (NE) approach. This SQV derivation methodology uses metal concentrations in sediment associated with unaffected benthic communities (i.e., from reference sites and lightly contaminated no-effect sites) and accounts for local benthic invertebrate tolerance and potential chemical interactions at no-effect exposure sites. This NE approach was used to propose alternative regional SQVs for uranium operations in northern Saskatchewan. Three different sets of NE values were derived using different combinations of benthic invertebrate community effects criteria (abundance, richness, evenness, Bray–Curtis index). Additionally, reference values were derived based solely on sediment metal concentrations from reference sites. In general, NE values derived using abundance, richness, and evenness (NE1 and NE2 values) were found to be higher than the NE values derived using all four metrics (NE3 values). Derived NE values for Cr, Cu, Pb, and V did not change with the incorporation of additional effects criteria due to a lack of influence from the uranium operations on the concentrations of these metals in sediment. However, a gradient of exposure concentrations was apparent for As, Mo, Ni, Se, and U in sediment which allowed for tolerable exposure levels of these metals in sediment to be defined. The findings from this assessment have suggested a range of new, alternate metal SQVs for use at uranium operations in northern Saskatchewan.     

Responses of Physical, Chemical, and Biological Indicators of Water Quality to a Gradient of Agricultural Land Use in the Yakima River Basin, Washington

The condition of 25 stream sites in the Yakima River Basin, Washington, were assessed by the U.S. Geological Survey's National Water-Quality Assessment Program. Multimetric condition indices were developed and used to rank sites on the basis of physical, chemical, and biological characteristics. These indices showed that sites in the Cascades and Eastern Cascades ecoregions were largely unimpaired. In contrast, all but two sites in the Columbia Basin ecoregion were impaired, some severely. Agriculture (nutrients and pesticides) was the primary factor associated with impairment and all impaired sites were characterized by multiple indicators of impairment. All indices of biological condition (fish, invertebrates, and algae) declined as agricultural intensity increased. The response exhibited by invertebrates and algae suggested a threshold response with conditions declining precipitously at relatively low levels of agricultural intensity and little response at moderate to high levels of agricultural intensity. This pattern of response suggests that the success of mitigation will vary depending upon where on the response curve the mitigation is undertaken. Because the form of the community condition response is critical to effective water-quality management, the National Water-Quality Assessment Program is conducting studies to examine the response of biota to gradients of land-use intensity and the relevance of these responses to water-quality management. These land-use gradient pilot studies will be conducted in several urban areas starting in 1999.     

Combining Logistic Models with Multivariate Methods for the Rapid Biological Assessment of Rivers Using Macroinvertebrates

This work represents an attempt to define a simple method to classify the relative degree of disturbance of sites in lotic systems on the basis of comparison of their faunistic composition with reference sites. Two ecotypes were selected in northern Portugal where benthic invertebrates were sampled in reaches with different levels of contamination. As a first stage, previous Geographic Information System information was used to define reference sites in each ecotype. Afterwards, multivariate techniques and non linear estimation models were combined to assess biological quality. This method allowed us to quantify sites according to increasing levels of contamination, after the probabilities of occurrence of taxa along a gradient of contamination taking into account the reference condition. The results suggest that this method is sensitive to organic pollution, easy to interpret, namely the species tolerance, and could be a good framework to establish regional rankings depending on the ecological impact of river sites.     

瓯江源头区龙泉溪底栖大型无脊椎动物多样性和群落特征

源头区溪流是河流生态系统最脆弱的部分,也是淡水底栖大型无脊椎动物(简称底栖动物)集中分布的热点区域,在流域物种库的形成和生态系统的多样性维持过程中具有不可忽视的作用。然而,目前国内对源头区溪流底栖动物多样性的系统调查研究较少。笔者对位于浙江省丽水市瓯江源头区的龙泉溪进行了底栖动物多样性调查研究,分别于2021年丰水期和平水期在覆盖龙泉溪主要山溪河流的18个样点采样,共采集获得底栖动物标本3 700余号。通过联合使用传统形态分类和DNA条形码技术,共鉴定出底栖动物165种,隶属5门、9纲、19目、68科、124属。联合使用DNA条形码可使底栖动物科、种水平的分辨力提升28.3%和34.1%。调查研究表明:龙泉溪底栖动物多样性丰富,物种组成以节肢动物为主(占比高达87.9%,145种),其中水生昆虫占绝大多数(共计8目、48科、140种,占84.8%),主要优势种为鞘翅目的狭溪泥甲属1种Stenelmis sp.1、毛翅目的纹石蛾属Hydorpsyche和短脉纹石蛾属Cheumatopsyche各1种;底栖动物群落多样性丰富,且在丰水期和平水期均维持在较高的水平;海拔和底质类型等微生境条件对底栖动物多样性分布的影响分析显示,底质类型对底栖动物分布密度的影响显著。对水生态状况的生物评估结果显示:Biotic Index污染生物指数更适合龙泉溪流域的水质健康状况评估,龙泉溪流域整体的水生态状况健康,水质属清洁或极清洁。该研究使用传统形态学和DNA条形码技术相结合的鉴定方式,提高了底栖动物物种鉴定的精度,所获得的多样性调查和水质评价结果为瓯江源头区溪流乃至整个流域的生态保护和长期监测提供了本底基础资料。     

Use of leaf litter breakdown and macroinvertebrates to evaluate gradient of recovery in an acid mine impacted stream remediated with an active alkaline doser

The spatial congruence of chemical and biological recovery along an 18-km acid mine impaired stream was examined to evaluate the efficacy of treatment with an alkaline doser. Two methods were used to evaluate biological recovery: the biological structure of the benthic macroinvertebrate community and several ecosystem processing measures (leaf litter breakdown, microbial respiration rates) along the gradient of improved water chemistry. We found that the doser successfully reduced the acidity and lowered dissolved metals (Al, Fe, and Mn), but downstream improvements were not linear. Water chemistry was more variable, and precipitated metals were elevated in a 3–5-km “mixing zone” immediately downstream of the doser, then stabilized into a “recovery zone” 10–18 km below the doser. Macroinvertebrate communities exhibited a longitudinal pattern of recovery, but it did not exactly match the water chemistry gradient Taxonomic richness (number of families) recovered about 6.5 km downstream of the doser, while total abundance and % EPT taxa recovery were incomplete except at the most downstream site, 18 km away. The functional measures of ecosystem processes (leaf litter breakdown, microbial respiration of conditioned leaves, and shredder biomass) closely matched the measures of community structure and also showed a more modest longitudinal trend of biological recovery than expected based on pH and alkalinity. The measures of microbial respiration had added diagnostic value and indicated that biological recovery downstream of the doser is limited by factors other than habitat and acidity/alkalinity, perhaps episodes of AMD and/or impaired energy/nutrient inputs. A better understanding of the factors that govern spatial and temporal variations in acid mine contaminants, especially episodic events, will improve our ability to predict biological recovery after remediation.