Meta-ecosystem Frameworks Can Enhance Control of the Biotic Transport of Microplastics.

The lack of systematic approaches and analyses to identify, quantify, and manage the biotic transport of microplastics (MPs) along cross-ecosystem landscapes prevents the current goals of sustainable environmental development from being met. This Perspective proposes a meta-ecosystem framework, which considers organismal and resource flows among ecosystems to shed light on the research and management challenges related to both abiotic and biotic MP transport at landscape levels. We discuss MP transport pathways through species movements and trophic transfers among ecosystems and sub-ecosystems, and highlight these pathways in the mitigation of MP pollution. The integration of biotic pathways across landscapes prioritizes management actions for MP transport using diverse approaches such as wastewater treatment and plastic removal policies to mitigate contamination. In addition, our framework emphasizes the potential sink enhancement of MPs through habitat conservation and enhancement of riparian vegetation. By considering the mechanisms of meta-ecosystem dynamics through the processes of biotic dispersal, accumulation, and the ultimate fate of MPs, advances in the environmental impact assessment and management of MP production can proceed more effectively.

Existing levels of biodiversity and river location may determine changes from small hydropower developments.

Global ecosystems are facing anthropogenic threats that affect their ecological functions and biodiversity. However, we still lack an understanding of how biodiversity can mediate the responses of ecosystems or communities to human disturbance across spatial gradients. Here, we examined how existing, spatial patterns of biodiversity influence the ecological effects of small hydropower plants (SHPs) on macroinvertebrates in river ecosystems. This study found that levels of biodiversity (e.g., number of species) can influence the degrees of its alterations by SHPs occurring along elevational gradients. The results of the study reveal that the construction of SHPs has various effects on biodiversity. For example, low-altitude areas with low biodiversity (species richness less than 12) showed a small increase in biodiversity compared to high-altitude areas (species richness more than 12) under SHP disturbances. The increases in the effective habitat area of the river segment could be a driver of the enhanced biodiversity in response to SHP effects. Changes in the numerically dominant species contributed to the overall level of community variation from disturbances. Location-specific strategies may mitigate the effects of SHPs and perhaps other disturbances.

Tolerance values of benthic macroinvertebrates for stream biomonitoring: assessment of assumptions underlying scoring systems worldwide.

Tolerance values (TVs) based on benthic macroinvertebrates are one of the most widely used tools for monitoring the biological impacts of water pollution, particularly in streams and rivers. We compiled TVs of benthic macroinvertebrates from 29 regions around the world to test 11 basic assumptions about pollution tolerance, that: (1) Arthropoda are < tolerant than non-Arthropoda; (2) Insecta < non-Insecta; (3) non-Oligochaeta < Oligochaeta; (4) other macroinvertebrates < Oligochaeta + Chironomidae; (5) other macroinvertebrate taxa < Isopoda + Gastropoda + Hirudinea; (6) Ephemeroptera + Plecoptera + Trichoptera (EPT) < Odonata + Coleoptera + Heteroptera (OCH); (7) EPT < non-EPT insects; (8) Diptera < Insecta; (9) Bivalvia < Gastropoda; (10) Baetidae < other Ephemeroptera; and (11) Hydropsychidae < other Trichoptera. We found that the first eight of these 11 assumptions were supported despite regional variability. In addition, we examined the effect of Best Professional Judgment (BPJ) and non-independence of TVs among countries by performing all analyses using subsets of the original dataset. These subsets included a group based on those systems using TVs that were derived from techniques other than BPJ, and groups based on methods used for TV assignment. The results obtained from these subsets and the entire dataset are similar. We also made seven a priori hypotheses about the regional similarity of TVs based on geography. Only one of these was supported. Development of TVs and the reporting of how they are assigned need to be more rigorous and be better described.

Economic and ecological costs and benefits of streamflow augmentation using recycled water in a California coastal stream.

Streamflow augmentation has the potential to become an important application of recycled water in water scarce areas. We assessed the economic and ecological merits of a recycled water project that opted for an inland release of tertiary-treated recycled water in a small stream and wetland compared to an ocean outfall discharge. Costs for the status-quo scenario of discharging secondary-treated effluent to the ocean were compared to those of the implemented scenario of inland streamflow augmentation using recycled water. The benefits of the inland-discharge scenario were greater than the increase in associated costs by US$1.8M, with recreational value and scenic amenity generating the greatest value. We also compared physical habitat quality, water quality, and benthic macroinvertebrate community upstream and downstream of the recycled water discharge to estimate the effect of streamflow augmentation on the ecosystem. The physical-habitat quality was higher downstream of the discharge, although streamflow came in unnatural diurnal pulses. Water quality remained relatively unchanged with respect to dissolved oxygen, pH, and ammonia-nitrogen, although temperatures were elevated. Benthic macroinvertebrates were present in higher abundances, although the diversity was relatively low. A federally listed species, the California red-legged frog (Rana draytonii), was present. Our results may support decision-making for wastewater treatment alternatives and recycled water applications in Mediterranean climates.

Identifying reference conditions and quantifying biological variability within benthic macroinvertebrate communities in perennial and non-perennial northern California streams.

Identification of minimally disturbed reference sites is a critical step in developing precise and informative ecological indicators. We tested procedures to select reference sites, and quantified natural variation (inter-site and -annual variability) among reference conditions using a macroinvertebrate data set collected from 429 mediterranean-climate stream reaches in the San Francisco Bay Area, California (USA). We determined that a landscape GIS-based stressor screen followed by a local field-based stressor screen effectively identified least-disturbed reference sites that, based on NMS ordination results, supported different biological communities than sites identified with only landscape (GIS) or local (field) stressors. An examination of least-disturbed reference sites indicated that inter-site variability was strongly associated with stream hydrology (i.e., perennial vs. non-perennial flow) and annual precipitation, which highlights the need to control for such variation when developing biological indicators through natural gradient modeling or using unique biological indicators for both non-perennial and perennial streams. Metrics were more variable among non-perennial streams, indicating that additional modeling may be needed to develop precise biological indicators for non-perennial streams. Among 192 sites sampled two to six times over the 8-year study period, the biological community showed moderate inter-annual variability, with the 100 point index of biotic integrity scores varying from 0 to 51 points (mean = 11.5). Variance components analysis indicated that inter-annual variability explained only a fraction (5-18 %) of the total variation when compared against site-level variation; thus efforts to understand causes of natural variation between sites will produce more precise and accurate biological indicators.

Development and validation of a macroinvertebrate index of biotic integrity (IBI) for assessing urban impacts to Northern California freshwater wetlands.

Despite California policies requiring assessment of ambient wetland condition and compensatory wetland mitigations, no intensive monitoring tools have been developed to evaluate freshwater wetlands within the state. Therefore, we developed standardized, wadeable field methods to sample macroinvertebrate communities and evaluated 40 wetlands across Northern California to develop a macroinvertebrate index of biotic integrity (IBI). A priori reference sites were selected with minimal urban impacts, representing a best-attainable condition. We screened 56 macroinvertebrate metrics for inclusion in the IBI based on responsiveness to percent urbanization. Eight final metrics were selected for inclusion in the IBI: percent three dominant taxa; scraper richness; percent Ephemeroptera, Odonata, and Trichoptera (EOT); EOT richness; percent Tanypodinae/Chironomidae; Oligochaeta richness; percent Coleoptera; and predator richness. The IBI (potential range 0-100) demonstrated significant discriminatory power between the reference (mean = 69) and impacted wetlands (mean = 28). It also declined with increasing percent urbanization (R (2) = 0.53, p < 0.005) among wetlands in an independent validation dataset (n = 14). The IBI was robust in showing no significant bias with environmental gradients. This IBI is a functional tool to determine the ecological condition at urban (stormwater and flood control ponds), as well as rural freshwater wetlands (stockponds, seasonal wetlands, and natural ponds). Biological differences between perennial and non-perennial wetlands suggest that developing separate indicators for these wetland types may improve applicability, although the existing data set was not sufficient for exploring this option.

Biological traits can mediate species-specific, quasi-extinction risks of macroinvertebrates in streams experiencing frequent extreme floods.

Most research on the ecological responses to extreme floods examines impacts at short time scales, whereas long-term datasets combining hydrological and biological information remain rare. Using such data, we applied time-series analysis to investigate simultaneous effects of a biotic factor (density dependence), an abiotic factor (extreme floods), and spatial synchrony in the population dynamics of three riverine insects. Spatial synchronization of population dynamics by extreme floods varied among species. These different responses to extreme floods could be explained by species-specific biological traits. Moreover, density dependence influenced the population dynamics under the context of extreme floods. Accordingly, quasi-extinction risks were highest for species that were simultaneously influenced by biotic and abiotic factors. An understanding of ecological responses to increasing hydrological extremes may be enhanced by recognizing long-term, climatic non-stationarity.

Species dispersal along rivers and streams may have variable importance to metapopulation structure.

The ability to prioritize habitats that have spatially varied contributions to species persistence can produce synergistic benefits for regional conservation efforts. However, conservation in spatially diverse landscape-networks requires considering dispersal asymmetry in the context of ecological connectivity and metapopulation persistence. By developing an approach based on metapopulation theory, this study prioritized the importance of habitat (as determined by the habitat quality and spatial position in networks) on metapopulation structure in mountainous streams. As a case study, we examined dispersal via overland and instream networks in a riverine mayfly Rhithrogena sp. cf. japonica in a mountain range of Southwest China. Compared to flow velocity, water depth, and instream nutrient-levels, water temperature was a key factor in determining local habitat suitability for R. sp. cf. japonica. Higher water temperature was linked to poor habitat suitability. Instream pathways were the main dispersal corridors compared with overland movement between tributaries for this mayfly. In basins on the east aspect of this mountain range, either monotonically increasing (i.e., never decreasing) or unimodal (i.e., with a single peak) patterns demonstrated the importance of riverine habitats that occur along elevational gradients. However, the importance of habitat appeared to show no definite patterns with elevation on the west aspect. In terms of metapopulation structure, local quality of habitat contributed more to the regional importance of habitat than its spatial position in the networks. The framework presented highlights that the importance of riverine habitats may be quite variable in species having directional dispersal networks across the fluvial landscape in mountainous areas. Results from this framework can serve as the basis to apply a mechanistic understanding to managing and protecting native populations through regional restoration actions.

InsectChange: a global database of temporal changes in insect and arachnid assemblages.

Insects are the most ubiquitous and diverse group of eukaryotic organisms on Earth, forming a crucial link in terrestrial and freshwater food webs. They have recently become the subject of headlines because of observations of dramatic declines in some places. Although there are hundreds of long-term insect monitoring programs, a global database for long-term data on insect assemblages has so far remained unavailable. In order to facilitate synthetic analyses of insect abundance changes, we compiled a database of long-term (≥10 yr) studies of assemblages of insects (many also including arachnids) in the terrestrial and freshwater realms. We searched the scientific literature and public repositories for data on insect and arachnid monitoring using standardized protocols over a time span of 10 yr or longer, with at least two sampling events. We focused on studies that presented or allowed calculation of total community abundance or biomass. We extracted data from tables, figures, and appendices, and, for data sets that provided raw data, we standardized trapping effort over space and time when necessary. For each site, we extracted provenance details (such as country, state, and continent) as well as information on protection status, land use, and climatic details from publicly available GIS sources. In all, the database contains 1,668 plot-level time series sourced from 165 studies with samples collected between 1925 and 2018. Sixteen data sets provided here were previously unpublished. Studies were separated into those collected in the terrestrial realm (103 studies with a total of 1,053 plots) and those collected in the freshwater realm (62 studies with 615 plots). Most studies were from Europe (48%) and North America (29%), with 34% of the plots located in protected areas. The median monitoring time span was 19 yr, with 12 sampling years. The number of individuals was reported in 129 studies, the total biomass was reported in 13 studies, and both abundance and biomass were reported in 23 studies. This data set is published under a CC-BY license, requiring attribution of the data source. Please cite this paper if the data are used in publications, and respect the licenses of the original sources when using (part of) their data as detailed in Metadata S1: Table 1.

Elevation shapes biodiversity patterns through metacommunity-structuring processes.

Stochastic (e.g., via species dispersal and ecological drift) and deterministic (e.g., via environmental and biotic filtering) processes can produce diversity patterns related to changes in elevation. However, existing studies have not generally examined these processes within a compressive framework. Stream macroinvertebrates are an important and diverse component of freshwater environments in high-mountain systems. By considering metacommunity-structuring processes using Hierarchical Modelling of Species Communities (HMSC), we investigated changes in taxon richness of stream macroinvertebrates along elevational gradients in streams of the Cangshan mountain range in Southwest China. We found that increasing taxon richness along the elevation gradient until the optimum was reached could be modeled using the integrated actions of full structuring processes within the metacommunity modeling. Consistent increases in taxon-richness along the elevation gradient were able to be modeled considering environmental filtering alone. In addition, the importance of structuring processes on shaping communities decreased along spatial hierarchical-scales (from local habitat to mountain-aspect levels). These results suggest that stochastic and biotic-filtering processes can confound environmental filtering in shaping macroinvertebrate communities in high-mountain streams. A comprehensive understanding of the mechanisms underlying elevational biodiversity patterns of riverine communities can be improved through quantitative frameworks (e.g., HMSC) linking metacommunity theory to the real-world systems.

Long-term variability in bioassessments: a twenty-year study from two northern California streams.

Long-term variability of bioassessments has not been well evaluated. We analyzed a 20-year data set (1984-2003) from four sites in two northern California streams to examine the variability of bioassessment indices (two multivariate RIVPACS-type O/E scores and one multimetric index of biotic integrity, IBI), as well as eight metrics. All sites were sampled in spring; one site was also sampled in summer. Variability among years was high for most metrics (coefficients of variation, CVs ranging from 16% to 246% in spring) but lower for indices (CVs of 22-26% for the IBI and 21-32% for O/E scores in spring), which resulted in inconsistent assessments of biological condition. Variance components analysis showed that the time component explained variability in all metrics and indices, ranging from 5% to 35% of total variance explained. The site component was large (i.e., >40%) for some metrics (e.g., EPT richness), but nearly absent from others (e.g., Diptera richness). Seasonal analysis at one site showed that variability among seasons was small for some metrics or indices (e.g., Coleoptera richness), but large for others (e.g., EPT richness, O/E scores). Climatic variables did not show consistent trends across all metrics, although several were related to the El Niño Southern Oscillation Index at some sites. Bioassessments should incorporate temporal variability during index calibration or include climatic variability as predictive variables to improve accuracy and precision. In addition, these approaches may help managers anticipate alterations in reference streams caused by global climate change and high climatic variability.

Climate-change influences on the response of macroinvertebrate communities to pesticide contamination in the Sacramento River, California watershed.

Limited studies have addressed how future climate-change scenarios may alter the effects of pesticides on biotic assemblages or the effects of exposures to repeated pulses of pesticide mixtures. We used reported pesticide-use data as input to a hydrological fate and transport model (Soil and Water Assessment Tool) under multiple climate-change scenarios to simulate spatiotemporal dynamics of pesticides mixtures in streams on a daily time-step in the Sacramento River watershed of California. We predicted that there will be increased pesticide application with warming across the watershed, especially in upstream areas. Using a statistical model describing the relationship between macroinvertebrate communities and pesticide dynamics, we found that compared to the baseline period of 1970-1999: (1) most climate-change scenarios predicted increased rainfall and warming across the watershed during 2070-2099; and (2) increasing pesticide contamination and increased impact on macroinvertebrates will likely occur in most areas of the watershed by 2070-2099; and (3) lower increases in effects of pesticides on macroinvertebrates were predicted for the downstream areas with intensive agriculture compared to some upstream areas with less-intensive agriculture. Future efforts on practical adaptation and mitigation strategies can be improved by awareness of altered threats of pesticide mixtures under future climate-change conditions.

Response of macroinvertebrate communities to temporal dynamics of pesticide mixtures: A case study from the Sacramento River watershed, California.

Pesticide pollution from agricultural field run-off or spray drift has been documented to impact river ecosystems worldwide. However, there is limited data on short- and long-term effects of repeated pulses of pesticide mixtures on biotic assemblages in natural systems. We used reported pesticide application data as input to a hydrological fate and transport model (Soil and Water Assessment Tool) to simulate spatiotemporal dynamics of pesticides mixtures in streams on a daily time-step. We then applied regression models to explore the relationship between macroinvertebrate communities and pesticide dynamics in the Sacramento River watershed of California during 2002-2013. We found that both maximum and average pesticide toxic units were important in determining impacts on macroinvertebrates, and that the compositions of macroinvertebrates trended toward taxa having higher resilience and resistance to pesticide exposure, based on the Species at Risk pesticide (SPEARpesticides) index. Results indicate that risk-assessment efforts can be improved by considering both short- and long-term effects of pesticide mixtures on macroinvertebrate community composition.

Insecticide concentrations in stream sediments of soy production regions of South America.

Concentrations of 17 insecticides were measured in sediments collected from 53 streams in soy production regions of South America (Argentina in 2011-2014, Paraguay and Brazil in 2013) during peak application periods. Although environmental regulations are quite different in each country, commonly used insecticides were detected at high frequencies in all regions. Maximum concentrations (and detection frequencies) for each sampling event ranged from: 1.2-7.4 ng/g dw chlorpyrifos (56-100%); 0.9-8.3 ng/g dw cypermethrin (20-100%); 0.42-16.6 ng/g dw lambda-cyhalothrin (60-100%); and, 0.49-2.1 ng/g dw endosulfan (13-100%). Other pyrethroids were detected less frequently. Banned organochlorines were most frequently detected in Brazil. In all countries, cypermethrin and/or lambda-cyhalothrin toxic units (TUs), based on Hyalella azteca LC50 bioassays, were occasionally>0.5 (indicating likely acute toxicity), while TUs for other insecticides were <0.5. All samples with total insecticide TU>1 were collected from streams with riparian buffer width<20 m. A multiple regression analysis that included five landscape and habitat predictor variables for the Brazilian streams examined indicated that buffer width was the most important predictor variable in explaining total insecticide TU values. While Brazil and Paraguay require forested stream buffers, there were no such regulations in the Argentine pampas, where buffer widths were smaller. Multiple insecticides were found in almost all stream sediment samples in intensive soy production regions, with pyrethroids most often occurring at acutely toxic concentrations, and the greatest potential for insecticide toxicity occurring in streams with minimum buffer width<20 m.

California dragonfly and damselfly (Odonata) database: temporal and spatial distribution of species records collected over the past century.

The recently completed Odonata database for California consists of specimen records from the major entomology collections of the state, large Odonata collections outside of the state, previous literature, historical and recent field surveys, and from enthusiast group observations. The database includes 32,025 total records and 19,000 unique records for 106 species of dragonflies and damselflies, with records spanning 1879-2013. Records have been geographically referenced using the point-radius method to assign coordinates and an uncertainty radius to specimen locations. In addition to describing techniques used in data acquisition, georeferencing, and quality control, we present assessments of the temporal, spatial, and taxonomic distribution of records. We use this information to identify biases in the data, and to determine changes in species prevalence, latitudinal ranges, and elevation ranges when comparing records before 1976 and after 1979. The average latitude of where records occurred increased by 78 km over these time periods. While average elevation did not change significantly, the average minimum elevation across species declined by 108 m. Odonata distribution may be generally shifting northwards as temperature warms and to lower minimum elevations in response to increased summer water availability in low-elevation agricultural regions. The unexpected decline in elevation may also be partially the result of bias in recent collections towards centers of human population, which tend to occur at lower elevations. This study emphasizes the need to address temporal, spatial, and taxonomic biases in museum and observational records in order to produce reliable conclusions from such data.

Multiple-site and-year analyses of stream insect emergence: a test of ecological theory.

The use of existing data sets to test applicability of existing ecological theory is an uncommon but potentially cost-effective approach for exploitation of previously accumulated knowledge. Studies on the emergence of insects from small streams have been a major research topic in aquatic ecology, particularly in Austria and Germany; the availability of emergence data from these two countries, covering over 1 million identified specimens, from 18 sites, and for 32 collection years is an example of such exploitable information. Concurrent estimates of annual emergence biomass and annual benthic secondary production for 18 aquatic insect populations showed a statistically significant relationship, contradicting the premise that emergence data do not provide any quantitative measure for a given stream area. Therefore, the emergence data were examined to test various predictions from ecological theory. Observed richness of emerging species of three orders of lotic insects - the Ephemeroptera, Plecoptera, and Trichoptera (EPT) - over 15 years at one site did not agree with predictions based on either flow predictability or change in flow and the "habitat templet concept". Trends in observed richness of emerging EPT species over 1 year at 18 sites agreed weakly with predictions using either pH values or the annual temperature amplitude and the "intermediate disturbance hypothesis", or using either annual temperature amplitude or total biomass of EPT emergence and the "disturbance-productivity-diversity model". A prediction of the "river continuum concept" that abundance of the shredder functional-feeding group should decrease and that of grazers should increase along a dense- to open-canopy gradient was not consistently supported by the emergence biomass data. For shredders and grazers of all insects (12 sites) and EPT (18 sites), this trend was apparent (but not significant) only if sites with intermediate canopy density were omitted. We identified three critical elements in our study that generally interfere with such tests of these theoretical constructs: (i) species richness is a poor measure of resource limitation and/or utilization theories; (ii) restrictions of the taxonomic operational window (in our example usually to EPT) causes problems in extrapolation to a larger system (in our example to all insects); and (iii) historical constraints may affect the local result of tests of resource limitation and/or utilization theories simply because species that potentially interact are lacking in the region under examination. Problems notwithstanding, the use of existing data sets to test applicability of currently held ecological theories is a cost-effective and amenable approach for use in a variety of research topics in stream and general ecology. In this context, future tests should focus on: (i) measures that are more robust than just species richness, e.g., on measures commonly used to assign species to strategies such as r, K, or A; (ii) a variety of taxonomic groups; and (iii) gradients in historical constraints on current regional species composition.

Herbivorous caddisflies, macroalgae, and epilithic microalgae: dynamic interactions in a stream grazing system.

1. During the low-flow period (April-October) in sunlit pools of Big Sulphur Creek (northern coastal California), the attached algal community predictably changes from an assemblage dominated by lush, upright Cladophora glomerata filaments in spring and early summer to one dominated by epilithic diatoms and blue-green algae (together=microalgae) in late summer through early autumn. Previous studies in this stream indicated that grazing by the caddisflies Helicopsyche borealis and Gumaga nigricula maintain low algal biomass during the latter part of this period. We used a combination of in situ exclusion/enclosure experiments to examine (1) the separate and combined effects of these grazers on Cladophora and microalgal assemblages, and (2) food preferences, growth, and microdistribution patterns of grazers when offered these different algal foods. 2. Grazers exerted strong but divergent effects on algal assemblages. Selective grazing on Cladophora by G. nigricula greatly accelerated the transition from upright Cladophora to epilithic microalgae, whereas selective grazing on microalgae by H. borealis dramatically reduced biomass of these forms. Grazers were largely ineffective at reducing the non-preferred algal food source (i.e. Cladophora by H. borealis, microalgae by G. nigricula). In the case of each grazer, growth was highest on the preferred algal food. Together, the activity of these grazers produced a low-biomass assemblage dominated by microalgal cells. 3. Removal of the Cladophora overstory by G. nigricula resulted in a three-fold increase in the abundance of epilithic microalgae, the preferred food of H. borealis. Elimination of Cladophora by G. nigricula can increase food availability for H. borealis and, in so doing, can indirectly facilitate the growth of this grazer during food-limited conditions. However, microdistribution of G. nigricula shifts from high overlap with H. borealis in spring and early summer when Cladophora is abundant to low overlap in late summer after Cladophora has been eliminated. This may indicate intense competition between these species for limited epilithic algae, and a concomitant movement by G. nigricula to areas in the stream where food resources are more available.

Which group is best? Attributes of different biological assemblages used in freshwater biomonitoring programs.

Of the many groups of organisms proposed for use in biomonitoring, assemblages of fish, algae, and benthic macroinvertebrates are the most commonly selected. Purported advantages and disadvantages of using these groups, along with those of zooplankton, were assembled from 65 different publications and websites. From these, 13 categories of advantages and nine of disadvantages were created. The diversity of the assemblage and its importance to the ecosystem were reported as advantages in >20% of citations for each group; these similarities suggest that some redundancy exists among the different groups in terms of these features. Likewise, sampling difficulties and lack of analytic metrics were disadvantages listed in >20% of citations for each group. Few reported advantages (e.g. recreational value of fish) or disadvantages (e.g. short generation time of algae) were unique for a particular assemblage. The validity of reported advantages and disadvantages were sometimes region specific, other times incorrect. The choice of which assemblage is most appropriate for a biomonitoring program ultimately depends on the characteristics of the area to be studied and the program objectives.

Multinational, freshwater biomonitoring programs in the developing world: lessons learned from African and Southeast Asian river surveys.

Biomonitoring programs are widely used in developed countries. They also offer many advantages in assessing ecological consequences of perturbations in developing countries, including reducing the equipment-operation, maintenance, and training costs associated with physicochemical monitoring. Three case histories of river biomonitoring using freshwater organisms (fish, benthic macroinvertebrates, diatoms, zooplankton) are described that involve (1) documentation of environmental effects from long-term, large-scale applications of insecticides to control insect-vectors of river blindness (onchocerciasis) in 11 West African countries; (2) water quality assessments and restoration planning in and around national parks in three East African countries; and (3) evaluation of overall ecological health of the Lower Mekong River in four Southeast Asian countries. As in developed countries, benthic macroinvertebrates are the organisms most widely used in biomonitoring in developing countries. Conflicting opinions of system resilience and whether expected changes are within natural variation may result in differences in underlying hypotheses proposed, study designs implemented, and study execution; each may lead to uncorrectable bias. Direct transfers of approaches used from developed to developing countries are often appropriate; however, techniques dependent on pollution-tolerance values are often region specific and not transferable. Typically expressed concerns about applications of biomonitoring in developing countries include poor coordination among agencies; lack of legislation, identification keys, and trained personnel; and incomplete information on how tropical rivers function. Problems are real but solvable, as evident from accomplishments in several multicountry programs in developing countries. Developed countries requiring coordinated monitoring of international rivers may benefit from examining successful programs under way in developing countries.