A growing body of mostly observational research has examined how beta-diversity and its turnover and nestedness components respond to environmental gradients across taxonomic, phylogenetic and functional dimensions. To our knowledge, this is the first manipulative investigation to assess how two major environmental influences-nutrient enrichment and herbivory-control beta-diversity and its components across dimensions in phototrophs. We used algal data from field and laboratory experiments, manipulating herbivory and/or the number of added nutrients (NAN), which ranged from zero to three (N, P and Fe) or four (N, P, Fe and Mn). We compared control/nutrient treatment communities with control communities and non-grazed with grazed communities in terms of taxonomic, phylogenetic and functional diversity. Taxonomic and phylogenetic beta-diversity (beta Sor) was partitioned into turnover (beta Sim) and nestedness (beta Nes) components. We proposed a novel partitioning approach for functional beta-diversity, outperforming the conventional approach, which calculates beta Sor, beta Sim and beta Nes. Instead, we used Bray-Curtis distances derived from the number of taxa within morpho-functional groups and calculated overall functional beta-diversity (beta BC) and its balance (beta Bal) and gradient (beta Gra) components. We developed three hypotheses predicting that (i) beta Nes and beta Gra would rise at higher NAN because of increased taxonomic richness, and phylogenetic and functional diversity (hypothesis 1); (ii) grazing would either reduce (hypothesis 2a) or elevate beta Nes and beta Gra (hypothesis 2b) depending on the balance between extinction of grazer-sensitive taxa versus establishment of grazer-resistant taxa; and (iii) the relative importance of beta Nes and beta Gra would depend on NAN and dimension (hypothesis 3). Our results supported Hypotheses 1, 2b and 3. Synthesis. Across dimensions, enrichment with multiple nutrients elevated biodiversity, the nestedness and gradient components of beta-diversity and often, the overall beta-diversity. Herbivory contributed to this increase by promoting grazer-resistant but competitively inferior taxa. Thus, streams with higher levels of both micro- and macronutrients and unimpacted herbivorous fauna may represent biodiversity hotspots and targets for conservation. The relative importance of beta Nes and beta Gra increased with NAN and at the functional dimension, beta Gra was the dominant component. Therefore, shorter environmental gradients may promote turnover, while longer gradients, colonization/extinction, the latter becoming particularly prominent at the functional dimension.

While resource enrichment can shape community structure and ecosystem functioning, how species diversity and biomass production respond to the input of multiple resources across habitats—particularly between terrestrial and aquatic ecosystems—remains poorly understood. Using a meta-analysis, we show that multiple resource addition consistently increased primary production regardless of the study system, indicative of widespread resource co-limitation. Multiple resource addition, however, differentially affected plant and algal richness. As the number of added resources increased, terrestrial plant richness tended to decline, which was best explained by diminished niche dimensions and soil acidification. In contrast, aquatic algal richness tended to increase with the number of added resources, which is in agreement with the benthic model for coexistence. Resource identity also mattered as nutrient and water addition had opposing effects on terrestrial plant richness, and nitrogen addition had a weaker positive effect on algal richness than phosphorus and micronutrients. These findings suggest that different ecological mechanisms may regulate terrestrial and aquatic producer diversity, with important implications for understanding biodiversity responses to environmental change.

AimThe influences of environmental and spatial processes on species composition have been at the center of metacommunity ecology. Conversely, the relative importance of these processes for species co-occurrences and taxonomic similarity has remained poorly understood. We hypothesised that at a subcontinental scale, shared environmental preference would be the major driver of co-occurrences across species groups. In contrast, co-occurrences due to shared dispersal history were more likely in dispersal-limited taxa. Finally, we tested whether taxa co-occurring due to similar responses to environmental and spatial processes were more taxonomically similar than expected by chance.LocationThe conterminous United States.Time Period1993-2019.Major Taxa StudiedStream diatoms, insects and fish.MethodsWe generated co-occurrence networks and developed methodology to determine the proportions of nodes and edges explained by pure environment alone (after accounting for space), pure space alone (after accounting for the environment), pure environment and pure space together, and spatially structured environment. Taxonomic similarity of taxa co-occurring because of environmental and/or spatial controls or because of unmeasured processes was compared to that of a null model.ResultsPure environment alone, spatially structured environment, and pure environment and pure space together explained the greatest proportion of nodes and edges in the co-occurrence networks of diatom species and genera, and insect genera. Conversely, pure environment and pure space together best explained the nodes and edges in the co-occurrence network of fish species and genera. Co-occurring taxa were more closely related than the random expectation in all comparisons.Main ConclusionsThe environment controlled co-occurrences in all groups, while the influence of space was the strongest in fish, the most dispersal-limited group in our study. All co-occurring taxa were more taxonomically related than expected by chance due to environmental or spatial overlap or unaccounted factors.

ABSTRACT Aim Co‐occurrence networks can be described in terms of topology (i.e., size and connectance) and node degree distribution (NDD). The NDD represents the frequency distribution of nodes (species) with k number of connections (degree). The shape of the NDD, single‐scale, scale‐free (power‐law) or broad‐scale, reveals if there are species with many connections to other species (high‐degree nodes), which may have important ecological functions. However, it remains unknown how spatial extent and environmental conditions impact network topology and the NDD shape and whether these relationships depend on species dispersal capacity. Location Continental United States of America. Taxa Stream diatoms and fish. Methods We constructed landscape windows ranging in spatial extent from 160,000 to 2,560,000 km 2 . For each window, we calculated environmental heterogeneity and median environmental conditions and generated correlation‐based co‐occurrence networks. We evaluated the topology and NDD shape of each network. To each NDD, we fit six statistical models, classified as single‐scale, power‐law or broad‐scale. Contingency table analysis, redundancy analyses and variance partitioning tested the sources of variability in network topology and/or NDD shape. Results The NDDs were almost exclusively fit either by single‐scale + broad‐scale models or broad‐scale models. As spatial extent increased, network size increased, connectance decreased, and the NDD shifted in an organism‐specific manner. In both groups, network responses to spatial extent were attributed primarily to variability in climatic heterogeneity followed by urban development in diatoms. Main Conclusions Spatial extent determined co‐occurrence network properties primarily via climatic and land use factors. Broad‐scale NDDs, indicating the presence of high‐degree nodes, were more common in the well‐dispersed diatoms than in the more poorly dispersing fish. Furthermore, these NDDs increased in frequency with spatial extent and climatic heterogeneity in diatoms but decreased in fish. High‐degree nodes are likely climatic generalists in diatoms but keystone or more dispersive species in fish.

Motivation: Freshwater ecosystems have been heavily impacted by land-use changes, but data syntheses on these impacts are still limited. Here, we compiled a global database encompassing 241 studies with species abundance data (from multiple biological groups and geographic locations) across sites with different land-use categories. This compilation will be useful for addressing questions regarding land-use change and its impact on freshwater biodiversity. Main Types of Variables Contained: The database includes metadata of each study, sites location, sample methods, sample time, land-use category and abundance of each taxon. Spatial Location and Grain: The database contains data from across the globe, with 85% of the sites having well-defined geographical coordinates. Major Taxa and Level of Measurement: The database covers all major freshwater biological groups including algae, macrophytes, zooplankton, macroinvertebrates, fish and amphibians.

Benthic macroinvertebrate taxa vary in their sensitivities to water quality and habitat conditions, contributing to their extensive use as ecological indicators. As climate change and landscape alteration increasingly impact stream temperatures, interest is growing in expanding our knowledge of how macroinvertebrates are affected by current and future thermal conditions. Using samples from 3501 sites, we evaluated relationships between macroinvertebrate taxa and modeled stream temperatures across Oregon and Washington, in the U.S. Pacific Northwest. We used Maximum Weekly Maximum Temperature (MWMT) values from the NorWeST temperature dataset, which is the same metric used for numeric water temperature standards in Oregon and Washington. MWMT captures peak thermal stress, when cold-water adapted aquatic biota are closest to their upper physiological limits. For each macroinvertebrate taxon, we characterized relationships between MWMT and their distributions with three measures: 1) central thermal tendency, based on weighted average (WA) optima calculations and relative abundance data; 2) lower and upper thermal limits, based on the 10th and 90th percentiles of taxon occurrence, using presence data; and 3) thermal sensitivity curve shape, based on Generalized Additive Model (GAM) plots. We assigned 521 taxa, from species to phyla, to seven thermal preference categories, ranging from cold and warm stenotherms (narrow range) to eurythermal (wide range). Thermal sensitivity and variability within each taxonomic group were identified for establishing taxonomic targets for regional monitoring programs. We also developed the Macroinvertebrate Thermal Tolerance Index (MTTI) to represent the assemblage-level response to available thermal habitats, using WA optima and relative abundances for 324 taxa. The MTTI model had a strong relationship with modeled temperatures (R2 = 0.68) and a root-mean-square-error of 2.5 °C. Our work builds on previous regional and national efforts to identify thermal indicator taxa by using modeled stream network temperatures and a thermal metric that corresponds directly to regional water temperature standards. Both the taxa thermal preferences and the MTTI can be used to help identify causes of biological impairment, prioritize restoration and protection actions, and monitor assemblage-wide changes in thermal tolerance over time.

Hypersaline Great Salt Lake’s (GSL: Utah, USA) pelagic food web is dominated by the herbivore, Artemia franciscana. Artemia demographic responses (survival, developmental transition, and reproduction) to GSL salinities, temperatures, common phytoplankton and yeast, and food levels were examined by factorial experiment. Survival across developmental stages was best at 90 ppt salinity, and decreased as temperature increased. Transition between life stages was best at 45 ppt salinity, and increased as temperature increased. Food was most important with both survival and transitioning responding similarly to food types and increasing with amount of food. Artemia reproduce in two ways (diapausing cysts – oviparity, live young – ovoviviparity): ovoviviparous and total reproduction were greatest at 90 ppt salinity and 20 °C, while oviparous reproduction was weakly affected by salinity and greatest at 20 °C. Oviparity was greatest at low food availability, while ovoviviparity and total reproduction increased with food availability, so reproduction shifted from oviparity to ovoviviparity as food increased. Maternal effects were observed for cyst hatchability, and ovoviviparous nauplii survival and transitioning to the juvenile stage. Combinations of salinity, temperature, food taxa and food amount strongly affect demography, making single factor studies of limited value. Results explain Artemia abundance in different parts of GSL and among years.

Influential ecological research in the 1980s, elucidating that local biodiversity (LB) is a function of local ecological factors and the size of the regional species pool (γ-diversity), has prompted numerous investigations on the local and regional origins of LB. These investigations, however, have been mostly limited to single scales and target groups and centered exclusively on γ-diversity. Here we developed a unified framework including scale, environmental factors (heterogeneity and ambient levels), and metacommunity properties (intraspecific spatial aggregation, regional evenness, and γ-diversity) as hierarchical predictors of LB. We tested this framework with variance partitioning and structural equation modeling using subcontinental data on stream diatoms, insects, and fish as well as local physicochemistry, climate, and land use. Pure aggregation + regional evenness outperformed pure γ-diversity in explaining LB across groups. The covariance of the environment with aggregation + regional evenness rather than with γ-diversity generally explained a much greater proportion of the variance in diatom and insect LB, especially at smaller scales. Thus, disregarding aggregation and regional evenness, as commonly done, may lead to gross underestimation of the pure metacommunity effects and the indirect environmental effects on LB. We examined the shape of the local-regional species richness relationship, which has been widely used to infer local vs. regional effects on LB. We showed that this shape has an ecological basis, but its interpretation is not straightforward. Therefore, we advocate that the variance partitioning analysis under the proposed framework is adopted instead. In diatoms, metacommunity properties had the greatest total effects on LB, while in insects and fish, it was the environment, suggesting that larger organisms are more strongly controlled by the environment. Broader use of our framework may lead to novel biogeographical insights into the drivers of LB and improved projections of its trends along current and future environmental gradients.

Community science bioassessment has great potential to inform comprehensive stream management plans, but regional analytical tools are needed to evaluate macroinvertebrate data collected through community science programs. To this end, we modified a pre-existing professional index of biotic integrity (IBI) to create a community science IBI (CS-IBI), designed for stream macroinvertebrate data collected by community scientists with minimal training. We used data collected by both professional and community scientists to develop, calibrate, and validate the CS-IBI at 76 stream sites in the Puget Lowland and Willamette Valley ecoregions of the Pacific Northwest in the United States. Community science data were taxonomically coarser and more variable than data generated by professionals; however, IBI scores and assemblage data were statistically similar between community science and professional data. Stream impairment categories classified by family-level CS-IBI scores matched genus-level professional classifications 65% of the time and never diverged by >1 category. CS-IBI scores were negatively related to the percentage of agriculture and land development in the watershed, although this relationship was weaker than for professional IBI scores. Despite increased variability in data generated by community scientists, our findings suggest the CS-IBI performs similarly to a professional IBI across a gradient of human influence. Although we do not advocate using the CS-IBI in regulatory settings, we believe the development of community science IBIs enhances, expands, and strengthens public partnerships, thereby supporting environmental managers' efforts to monitor and restore degraded streams and rapidly respond to pollution events. Our hope is that the CS-IBI will improve the applicability of community science bioassessment data and serve as a model for how agencies can develop regionalized macroinvertebrate IBIs for use in comprehensive watershed management plans.

The species-area relationship (SAR) has over a 150-year-long history in ecology, but how its shape and origins vary across scales and organisms remains incompletely understood. This is the first subcontinental freshwater study to examine both these properties of the SAR in a spatially explicit way across major organismal groups (diatoms, insects, and fish) that differ in body size and dispersal capacity. First, to describe the SAR shape, we evaluated the fit of three commonly used models, logarithmic, power, and Michaelis-Menten. Second, we proposed a hierarchical framework to explain the variability in the SAR shape, captured by the parameters of the SAR model. According to this framework, scale and species group were the top predictors of the SAR shape, climatic factors (heterogeneity and median conditions) represented the second predictor level, and metacommunity properties (intraspecific spatial aggregation, γ-diversity, and species abundance distribution) the third predictor level. We calculated the SAR as a sample-based rarefaction curve using 60 streams within landscape windows (scales) in the United States, ranging from 160,000 to 6,760,000 km2 . First, we found that all models provided good fits (R2  ≥ 0.93), but the frequency of the best-fitting model was strongly dependent on organism, scale, and metacommunity properties. The Michaelis-Menten model was most common in fish, at the largest scales, and at the highest levels of intraspecific spatial aggregation. The power model was most frequent in diatoms and insects, at smaller scales, and in metacommunities with the lowest evenness. The logarithmic model fit best exclusively at the smallest scales and in species-poor metacommunities, primarily fish. Second, we tested our framework with the parameters of the most broadly used SAR model, the log-log form of the power model, using a structural equation model. This model supported our framework and revealed that the SAR slope was best predicted by scale- and organism-dependent metacommunity properties, particularly spatial aggregation, whereas the intercept responded most strongly to species group and γ-diversity. Future research should investigate from the perspective of our framework how shifts in metacommunity properties due to climate change may alter the SAR.

Aim Niche and dispersal processes influence biodiversity, but their relative importance along latitude is unclear. We predicted that: (a) niche processes would dominate at high latitudes due to increased climatic stress, consistent with the physiological tolerance hypothesis and the Dobzhansky-MacArthur hypothesis and (b) dispersal limitation would prevail at low latitudes due to narrower niches and smaller range sizes, as postulated by the dispersal-ecological specialization trade-off hypothesis, the latitude-niche breadth hypothesis, and Rapoport's rule. Location Central United States. Time period 1993-2019. Major taxa studied Stream algae, insects, and fish. Methods We examined the relative effects of environment (climate and physicochemistry) versus space on stream biodiversity in seven latitudinal zones, spanning 19 latitudinal degrees. In each zone, species richness (alpha-diversity) was analysed with multiple regression and variance partitioning. Compositional dissimilarity (beta-diversity) within zones was assessed with distance-based redundancy analysis (dbRDA) and variance partitioning. Results For alpha-diversity, latitudinal variability of niche and dispersal processes conformed to our predictions in all three groups, except for dispersal processes in insects. However, the drivers of beta-diversity did not follow our predictions. The latitude-niche breadth hypothesis and Rapoport's rule were weakly supported only in fish. Main conclusions The importance of niche and dispersal processes varied predictably along the latitudinal gradient only for alpha-diversity. However, the niche effects were driven mostly by physicochemistry, and the dispersal effects were not always linked with ecological specialization and range size. This suggests that climate-based biodiversity theories do not have particular relevance for the streams in our study. Niche processes had a greater impact than dispersal processes across species groups and diversity metrics, emphasizing the primary role of the environment.

Globally, freshwater systems are threatened by climate change, so projections under various climate change scenarios are needed to inform efforts to protect and conserve already vulnerable taxa. Here, the change in distribution of stream vertebrates was investigated under different greenhouse gas emission scenarios. Using occurrence data from multiple stream surveys in Washington State spanning 559 sites and 24 years, species distribution models for 23 aquatic vertebrate taxa (21 fish and two amphibians) were developed. Models projected changes in taxon distributions for 2070 under representative concentration pathways (RCPs) ranging from 2.6 to 8.5 W m(-2). To assess potential biological impacts of these predictions, changes in taxon richness and beta diversity of stream vertebrates were also investigated. Moreover, predictor variables were examined to assess which ones were more important in determining taxon distributions. Substantial changes in the spatial distribution of stream vertebrates were projected for all RCP scenarios by 2070, but the greatest changes were expected to occur under RCP 6.0 and 8.5. The taxa evaluated were predicted to experience substantial increase, decrease, or shift in distribution. Taxon richness of stream vertebrates was forecasted to increase with RCP scenario relative to historical conditions, suggesting that distributional expansions outpaced distributional contractions. However, beta diversity was predicted to decrease considerably, suggesting increased biotic homogenization. Variables important for determining future distributions varied by taxa, with most species influenced by a combination of variables. These results indicate that failing to reduce greenhouse gas emissions will lead to dramatic impacts on stream vertebrates. The magnitude of predicted future impacts was dependent upon RCP scenario, so advancements in policy to reduce carbon emissions are necessary. We also recommend as potential conservation measures preserving cold-water refugia and increasing efforts to lower stream water temperatures by, for example, expanding the riparian cover and/or linking surface water to groundwater.

The amounts and ratios of nutrients (nitrogen and phosphorus) are important determinants of producer community biodiversity and composition and their responses to climate and dispersal. However, the nutrient effects on co-occurrence network topology, particularly in freshwaters, are understudied. Here, we investigate 1) whether nutrient supply and ratio constrain topological properties of algal co-occurrence networks in streams and 2) to what extent climate and space (a surrogate for dispersal) affect co-occurrence network topology versus metacommunity composition across nutrient supply and ratio contexts. We used a subcontinental dataset of benthic algae from 840 stream localities in the conterminous US. We constructed co-occurrence networks representing nutrient supply contexts (oligotrophic versus eutrophic) and nutrient ratio contexts (N-limited versus P-limited) and statistically assessed topological variability within each pair via randomization. We then used a null model framework and direct gradient analysis to ascertain the importance of climate and space in driving, respectively, network topology and metacommunity composition. Nutrient supply was only positively related to network size (species node counts), which was driven by motile species, while other topological differences were non-significant. Climatic and spatial variables had pronounced and for the most part comparable effects on network topology that further depended on nutrient context. A comparative assessment of topological versus compositional responses to climate and space across nutrient contexts identified both similarities and differences. While climate and space contributed to both network topology and metacommunity composition, space was a stronger predictor of compositional variability than climate, regardless of nutrient context. Our findings highlight the need for developing integrative multi-level approaches (from metacommunities to co-occurrence networks) to fully understand biological responses to complex and interactive abiotic forces.

Aim Biodiversity on Earth is threatened by climate change. Despite the vulnerability of freshwater habitats to human impacts, most climate change projections have focused on terrestrial systems. Here, we examined how the current distributions and biodiversity of stream taxa might change under mitigated, stabilizing and increasing greenhouse gas emissions. Location Conterminous USA. Time period Present day to 2070. Major taxa studied Stream diatoms, insects and fish. Methods We developed species distribution models for 336 freshwater taxa from 1,227 distinct stream localities using water chemistry, watershed and climatic variables. Models based only on climate were used to project changes in the distributions and biodiversity of cold- versus warm-water taxa under representative concentration pathways (RCPs) ranging from 2.6 to 8.5 W/m(2). Results In all three organismal groups, climate emerged as the strongest predictor of species distributions, providing comparable explanatory power to water chemistry and watershed variables combined. The RCP-based projections suggested a widespread expansion of warm-water taxa, outpacing the decline of cold-water taxa. Consequently, overall species richness would increase, but beta diversity would decrease drastically with the severity of climate change. A closer look at individual taxa and functional guilds revealed that vulnerable cold-water taxa included: (a) diatom guilds forming the base and bulk of the biofilm; (b) environmentally sensitive insects, characteristic of unimpacted streams; and (c) ecologically and recreationally important salmonids, which were forecast to diminish dramatically in source habitats. Warm-water fish projected to increase their distributions include bait bucket release minnows and dominant predators. Main conclusions Our results suggest potentially devastating impacts of climate change on stream ecosystems, with the restructuring of diatom, insect and fish communities, diminished distributions of functionally important taxa and widespread expansion of warm-water taxa, giving rise to biotic homogenization. Given that the magnitude of these biotic shifts depends on the severity of climate change, appropriate current policy decisions are necessary to preserve freshwater ecosystems.

We report results from the first statewide assessment of biological health in perennial streams in Washington State. Using a probabilistic sampling survey design, we were able to make unbiased estimates of biological condition of macroinvertebrate communities throughout the state based on 346 sites sampled from 2009 to 2012. Results from randomly sampled sites were classified as either good, fair, poor in comparison with 75 regional reference sites that were sampled concurrently. We determined that approximately 34 percent of stream kilometers assessed were in poor biological condition as measured with a multi-metric index, the Benthic Index of Biotic Integrity. Additionally, we evaluated a variety of chemical and physical habitat stressors known to negatively influence macroinvertebrate communities and determined that poor substrate conditions were the most prevalent and important stressors impacting stream macroinvertebrates, with relative bed stability and percent sand/fines being the most prevalent. A relative risk/attributable risk analysis suggests that improving physical habitat conditions in streams, most notably a reduction in percent sand/fines, will have the greatest impact for improving biological condition for macroinvertebrate communities. It is estimated that approximately 60% of stream kilometers now classified as in poor biological condition in Washington could be improved by reducing the amount of percent sand/fines in the substrate. These results are consistent with those obtained from EPA's national stream surveys and suggest that poor habitat conditions are the most prevalent stressors impacting stream macroinvertebrates in Washington State.

We developed a framework for the hierarchical pathways of bottom-up (niche dimensionality) and top-down control (herbivory) on biomass of stream algae via changes in guild composition (relative abundance of low profile, high profile, and motile guilds), species richness, and evenness. We further tested (1) the contrasting predictions of resource competition theory vs. the benthic model of coexistence on how the number of added nutrients constrains species richness, (2) the relationship between species richness and evenness, and (3) the biodiversity-ecosystem-function paradigm. Implementing a combination of field and lab experiments that manipulated for the first time in benthic algae herbivory and/or niche dimensionality, i.e., the number of added nutrients (NAN), including nitrogen, phosphorus, iron, and manganese, we made the following discoveries. First, important predictors of guild composition were herbivory (field) and NAN (lab); of richness, NAN (field) and NAN and guild composition (lab); of evenness, guild composition (field and lab) and herbivory (field); and of biomass, guild composition, NAN, and richness + evenness (field and lab). Herbivory increased the proportions of the low profile and motile guilds but decreased the proportion of the high profile guild. In the absence of grazing, greater proportions of the high profile guild resulted in elevated richness and biomass but diminished evenness, whereas in the presence of grazing, these relationships generally disappeared. Second, both experiments confirmed the prediction of the benthic model that species richness increases with NAN, a pattern inconsistent with resource competition theory. Third, supplementation with manganese and/or iron increased algal richness, indicating that micronutrients, which have generally been overlooked in stream ecology, added dimensions to the algal niche. Fourth, the richness-evenness relationship, observed only in the absence of herbivory, depended on the size of the species pool. It was positive at richness lower than 49 species (lab), implying complementarity and facilitation, while at higher richness (field and lab), this relationship was negative, consistent with negative interspecific interactions. Finally, the greater dependence of biomass production on guild composition and NAN than on richness and evenness suggests that more comprehensive, environmentally explicit, and trait-based approaches are necessary for the study of the biodiversity-ecosystem-function paradigm.

Survivability of diapausing (cryptobiotic) life stages over time in nature, beyond maximum observed time for viability, is not well understood. Because these life stages are an adaptation to overcome harsh conditions, survivability over time is assumed to be high. Brine shrimp (Artemia franciscana) diapausing eggs (cysts) permit overwinter survival to initiate the population each spring. An experiment was designed to examine overwinter survival of brine shrimp cysts for 17 yr in Great Salt Lake (Utah, U.S.A.). Initial hatchability entering the winter (17.8-78.8%) and overwinter survivability (9.9-65.9%) of cysts varied dramatically among years. Better maternal nutrition increased initial hatchability. Overwinter survival of cysts decreased in part because some cysts hatch when it is too cold for the hatchlings to feed (0.8-39.4% among years), so they starve. However, overwinter cyst survival decreases the most with warmer waters in winter, and with better maternal nutrition, as both factors lead to diapause being easier to break. Annual variation in initial hatchability and survival is shown to be important to Great Salt Lake brine shrimp populations. Therefore, cryptobiotic life-stage ecology needs to be better understood, as these life stages may have highly variable hatchability and survivability with normal environmental stresses.

Biofilms, composed of periphyton, bacteria, and organic detritus, are the base of the food web in many streams and rivers. This media adsorbs and actively sequesters organic and inorganic contaminants from the water column. Here, we demonstrate the utility of using the contaminant concentrations in the biofilm matrix as an environmental media in source tracking and understanding biological impacts at higher trophic levels. Physical partitioning of polychlorinated biphenyl (PCB) and polybrominated diphenyl ether congeners is the dominant mode of uptake from water to biofilm and bioaccumulation factor: log K-ow relationships suggest that PCB uptake is often near equilibrium between log K-ow 5-7. We show that the concentrations of metals in biofilms are more effective at delineating and recording spatial and temporal differences in metal inputs than bed sediments and water samples. The burden of metals in the biofilm matrix explained adverse impacts and variability in periphyton metrics and ecological integrity in macro-invertebrates. This work provides new insights into the partitioning of organic chemicals onto biofilms and shows clear linkages between metals in the biofilm matrix and ecological health of invertebrates that depend on biofilms as a food source.