Traditionally, the effects of anthropogenic disturbance on biological assemblages are elucidated by comparing an assemblage observed at a site to one that represents a minimally disturbed state. Unfortunately, defining a minimally disturbed state is extremely challenging because of the extent of human disturbance. We use a national scale dataset and a model-based approach to assess how benthic macroinvertebrate assemblages at 1748 sites would change if common anthropogenic disturbances were removed from in-stream physiochemical variables. First, we used random forest models and current landscape data to predict physiochemical conditions and then infer abiotic condition in the absence of disturbance. Second, we combined these estimates with joint species distribution models to predict the assemblage that could occur in these undisturbed conditions. Random forest models explained 48%-75% of the variation in log-transformed total nitrogen, phosphorus, sulfate, chloride, and substrate diameter. Generally, nutrient and salinity concentrations were higher, and substrates were finer than predicted to be without disturbances. Using these physiochemical data, joint species distribution models, fitted to nine separate ecoregions, accurately explained genus richness (R-2 = 0.73-0.85) and composition (Jaccard similarity index = 0.48-0.55). Depending on the ecoregion, we found that genus richness could increase or decrease at 26%-61% of sites if disturbance was removed. For example, with anthropogenic disturbance, occurrence probabilities for Ephemeroptera, Plecoptera, and Trichoptera decreased at 5%-26% of sites, while occurrence probabilities for Mollusca and other noninsect, non-arthropod taxa increased at 5%-33% and 11%-24% of sites, respectively. Importantly, our innovative framework provides a foundation for evaluating the effects of anthropogenic disturbance on macroinvertebrate assemblages without identifying reference sites.

1. Empirical evidence and theory suggest that climate warming and an increase in the frequency and duration of drying events will alter the metabolic balance of freshwater ecosystems. However, the impacts of climate change on ecosystem metabolism may depend on whether energy inputs are of autochthonous or allochthonous origin. To date, few studies have examined how warming and drying may interact to alter stream metabolism, much less how their impacts may depend on the energy-base of the food web. 2. To address this research gap, we conducted a multi-factorial experiment using outdoor mesocosms to investigate the individual and synergistic effects of warming and drought on metabolic processes in stream mesocosms with green (algal-based) vs. mixed (algal-and detritus-based) vs. brown (detritus-based) energy pathways. 3. We set up 48 mesocosms with one of three different levels of shade and leaf litter input combinations to create mesocosms with different primary energy channels. In addition, we warmed half of the mesocosms by similar to 2-3 degrees C. We assessed changes in ecosystem respiration (ER), gross primary production (GPP), net ecosystem production (NEP) and organic matter biomass in warmed and ambient temperature mesocosms before a 24 day drying event and after rewetting. 4. Surprisingly, experimental warming had little effect on metabolic processes. Drying, however, led to decreased rates of ER and GPP and led to an overall reduction in NEP. Although the effects of drying were similar across energy channel treatments, reductions in ER and GPP were primarily driven by decreases in biomass of benthic and filamentous algae. 5. Overall, we demonstrate that drying led to lower rates of NEP in mesocosms regardless of energy inputs. While warming showed little effect in our study, our results suggest that an increase in the frequency of stream drying events could greatly alter the metabolic balance of many aquatic ecosystems.

Taxon–environment relationships can elucidate a taxon’s tolerance or sensitivity to specific environmental conditions. We use a joint species distribution modeling framework to quantify relationships between ∼1700 benthic macroinvertebrate assemblages in streams and rivers across the contiguous United States and several environmental gradients that are susceptible to human alteration (e.g., nutrients, salinity, physical habitat, and climate). We found that the predicted occurrence probability for sampling units where a taxon actually occurs was 0.15 to 0.24 greater than the predicted occurrence probability for sampling units where a taxon does not occur, and a relatively large percentage (32–58%) responded to gradients of substrate diameter, mean summer air temperature, or total P. At the assemblage level, genus richness could change along environmental gradients by as many as 5 to 17 taxa depending on the ecoregion. Often, the largest change in genus richness was associated with sediment diameter. We also investigated whether a suite of traits (i.e., clinger, scraper, pollution tolerance, and thermal optima) were related to a genus’ association with an environmental gradient and found that some traits are positively related to an organism’s occurrence along one environmental gradient but negatively related to its occurrence along another. For example, in several ecoregions, thermal preference was positively related to mean summer air temperature but negatively related to nutrient concentrations. Collectively, our results showcase a multivariate approach for modeling biotic assemblages that can integrate multiple sources of information (i.e., environmental factors, biological traits, phylogenetic relationships, and co-occurrences) that are routinely collected by biomonitoring programs.

River flows change on timescales ranging from minutes to millennia. These variations influence fundamental functions of ecosystems, including biogeochemical fluxes, aquatic habitat, and human society. Efforts to describe temporal variation in river flow—i.e., flow regime—have resulted in hundreds of unique descriptors, complicating interpretation and identification of global drivers of flow dynamics. Here, we used a cross-disciplinary analytical approach to investigate two related questions: 1. Is there a low-dimensional structure that can be used to simplify descriptions of streamflow regime? 2. What catchment characteristics are most associated with that structure? Using a global database of daily river discharge from 1988-2016 for 3,120 stations, we calculated 189 traditional flow metrics, which we compared to the results of a wavelet analysis. Both quantification techniques independently revealed that streamflow data contain substantial low-dimensional structure that correlates closely with a small number of catchment characteristics. This structure provides a framework for understanding fundamental controls of river flow variability across multiple timescales. Climate was the most important variable across all timescales, especially those lasting several weeks, and likely contributes as much as dams in controlling flow regime. Catchment area was critical for timescales lasting several days, as was human impact for timescales lasting several years. In addition, both methods suggested that streamflow data also contain high-dimensional structure that is harder to predict from a small number of catchment characteristics (i.e. is dependent on land use, soil structure, etc.), and which accounts for the difficulty of producing simple hydrological models that generalize well.

Habitat fragmentation drives biodiversity loss in rivers around the world. Although the effects of anthropogenic barriers on river connectivity are well known, there has been little research on the ways in which stream drying may alter connections among habitats and resources. Given that stream drying is increasing in many regions, there is a pressing need to understand the effects of drying on habitat fragmentation. Here, we quantify spatiotemporal drying patterns under current and future climate scenarios in the Upper Blue River Basin, Oklahoma. We used a hydrologic model to simulate daily streamflow for nine climate scenarios. For each scenario, we calculated metrics of streamflow temporal continuity (dry days, dry periods, and dry period duration) and spatial connectivity (wetted length, number of dry stream fragments, length of dry stream fragments, and dendritic connectivity index) from simulated daily streamflow. We found that stream drying is likely to increase in all future climate scenarios and that increases in stream drying reduce connectivity. However, the effects of stream drying on connectivity were highly nonlinear. Specifically, we observed a threshold around which a small increase in stream drying led to a rapid drop in connectivity. We also found that the greatest increases in stream drying were not associated with the highest emission scenarios, underscoring the complex linkages among climate, water availability, and connectivity. Given that connectivity is essential to ecosystem structure and function, we discuss water management strategies informed by impacts of stream drying.

While climate change is altering ecosystems on a global scale, not all ecosystems are responding in the same way. The resilience of ecological communities may depend on whether food webs are producer- or detritus-based (i.e. 'green' or 'brown' food webs, respectively), or both (i.e. 'multi-channel' food web). Food web theory suggests that the presence of multiple energy pathways can enhance community stability and resilience and may modulate the responses of ecological communities to disturbances such as climate change. Despite important advances in food web theory, few studies have empirically investigated the resilience of ecological communities to climate change stressors in ecosystems with different primary energy channels. We conducted a factorial experiment using outdoor stream mesocosms to investigate the independent and interactive effects of warming and drought on invertebrate communities in food webs with different energy channel configurations. Warming had little effect on invertebrates, but stream drying negatively impacted total invertebrate abundance, biomass, richness and diversity. Although resistance to drying did not differ among energy channel treatments, recovery and overall resilience were higher in green mesocosms than in mixed and brown mesocosms. Resilience to drying also varied widely among taxa, with larger predatory taxa exhibiting lower resilience. Our results suggest that the effects of drought on stream communities may vary regionally and depend on whether food webs are fuelled by autochthonous or allochthonous basal resources. Communities inhabiting streams with large amounts of organic matter and more complex substrates that provide refugia may be more resilient to the loss of surface water than communities inhabiting streams with simpler, more homogeneous substrates.

Ecological flows across ecosystem boundaries are typically studied at spatial scales that limit our understanding of broad geographical patterns in ecosystem linkages. Aquatic insects that metamorphose into terrestrial adults are important resource subsidies for terrestrial ecosystems. Traits related to their development and dispersal should determine their availability to terrestrial consumers. Here, we synthesize geospatial, aquatic biomonitoring and biological traits data to quantify the relative importance of several environmental gradients on the potential spatial and temporal characteristics of aquatic insect subsidies across the contiguous United States. We found the trait composition of benthic macroinvertebrate communities varies among hydrologic regions and could affect how aquatic insects transport subsidies as adults. Further, several trait–environment relationships were underpinned by hydrology. Large bodied taxa that could disperse further from the stream were associated with hydrologically stable conditions. Alternatively, hydrologically variable conditions were associated with multivoltine taxa that could extend the duration of subsidies with periodic emergence events throughout the year. We also found that anthropogenic impacts decrease the frequency of individuals with adult flight but potentially extend the distance subsidies travel into the terrestrial ecosystem. Collectively, these results suggest that natural and anthropogenic gradients could affect aquatic insect subsidies by changing the trait composition of benthic macroinvertebrate communities. The conceptual framework and trait–environment relationships we present shows promise for understanding broad geographical patterns in linkages between ecosystems.

Intermittent rivers are spatially dynamic, expanding and contracting in response to changes in water availability, but studies that explicitly examine spatial drying patterns are scarce. We used long-term data produced by citizen scientists to map wet and dry reaches of 3 different river systems to investigate mechanisms producing temporal variation in drying patterns. We quantified the total wetted river length in each survey, and calculated ecologically scaled landscape indices that indicate the carrying capacity (population size) and habitat connectivity of large and small fish metapopulations in these systems. We found that the spatial extent of perennial water decreased over the study period in 2 of the 3 study rivers: ∼26% in the Agua Fria River from 2008 to 2016, and ∼14% in Cienega Creek from 2006 to 2016. We also observed an ∼8% decline in habitat connectivity for large fish in the Agua Fria River. We used multivariate structural equation models to infer causal relationships between spatial drying patterns and temperature, precipitation, streamflow, and drought conditions. These models explained 85% of year-to-year variation in the total length of wet reaches, and 63 and 55% of year-to-year variation in habitat connectivity for large and small fish, respectively. With the US Southwest shifting to an even more arid climate, our results suggest that this may reduce habitat connectivity of fish populations in this region.

AbstractEmergent aquatic insects transport aquatic‐derived resources into terrestrial ecosystems but are rarely studied at landscape or regional scales. Here, we investigate how stream network geometry constrains the spatial influence of aquatic insect subsidies in terrestrial ecosystems. We also explore potential factors (i.e., climate, topography, soils, and vegetation) that could produce variation in stream network geometry and thus change the extent of aquatic insect subsidies from one region to another. The stream signature is the percentage of aquatic insect subsidies traveling a given distance into the terrestrial ecosystem, relative to what comes out of the stream. We use this concept to model the spatial extent (area) and distribution (spatial patterning) of aquatic subsidies in terrestrial ecosystems across the contiguous United States. Our findings suggest that at least 8% of the subsidies measured at the aquatic–terrestrial boundary (i.e., the 8% stream signature) are typically transferred throughout the entire watershed and that variation in this spatial extent is largely influenced by the drainage density of the stream network. Moreover, we found stream signatures from individual stream reaches overlap such that the spatial extent of the 8% stream signature often includes inputs from multiple stream reaches. Landscape‐scale stream network characteristics increased the area of overlapping stream signatures more than reach‐scale channel properties. Finally, we found runoff was an important factor influencing stream network geometry suggesting a potential effect of climate on aquatic‐to‐terrestrial linkages that have been understudied.

The exchange of resources across ecosystem boundaries can have large impacts on ecosystem structures and functions at local and regional scales. In this article, we develop a simple model to investigate dynamical implications of bi-directional resource exchanges between two local ecosystems in a meta-ecosystem framework. In our model, we assume that (1) Each local ecosystem acts as both a resource donor and recipient, such that one ecosystem donating resources to another results in a cost to the donating system and a benefit to the recipient; and (2) The costs and benefits of the bi-directional resource exchange between two ecosystems are correlated in a nonlinear fashion. Our model could apply to the resource interactions between terrestrial and aquatic ecosystems that are supported by the literature. Our theoretical results show that bi-directional resource exchange between two ecosystems can indeed generate complicated dynamical outcomes, including the coupled ecosystems having amensalistic, antagonistic, competitive, or mutualistic interactions, with multiple alternative stable states depending on the relative costs and benefits. In addition, if the relative cost for resource exchange for an ecosystem is decreased or the relative benefit for resource exchange for an ecosystem is increased, the production of that ecosystem would increase; however, depending on the local environment, the production of the other ecosystem may increase or decrease. We expect that our work, by evaluating the potential outcomes of resource exchange theoretically, can facilitate empirical evaluations and advance the understanding of spatial ecosystem ecology where resource exchanges occur in varied ecosystems through a complicated network.

Recent work has shown that the biodiversity of organisms can influence geophysical processes such as the transport of streambed sediments and the erosion of soils. Yet most of this work has been conducted in small-scale fluvial system mimics, demonstrating a clear need to investigate the relationship between biodiversity and erosion in natural systems. We conducted an observational field study across 3 rivers in forested watersheds in northern Michigan, U.S.A., quantifying streambank retreat rates using aerial photos and measuring riparian plant community biodiversity and abundance. We hypothesized that more diverse riparian plant communities would produce greater woody plant stem density and basal area, which in turn would reduce erosion rates of streambanks due to increased root production. We used structural equation modelling to compare causal networks using plant biodiversity metrics to predict streambank migration rate indirectly through effects on plant abundance, as well as models that used migration rate to predict plant abundance indirectly through effects on plant biodiversity. Although structural equation models explained both causal pathways successfully, models using biodiversity to predict migration rate were a better fit to data than models that used migration rate to predict plant biodiversity and abundance. The best performing models suggested plant biodiversity was indirectly negatively correlated with erosion rate (average standardized path coefficient=-0.22), after accounting for environmental differences between sites. This work adds to a growing body of evidence indicating that biodiversity can modify geophysical processes, demonstrating the need to explicitly account for biological variation when considering ecogeomorphic feedbacks.

Intermittent rivers are spatially dynamic, expanding and contracting in response to changes in water availability, but studies that explicitly examine spatial drying patterns are scarce. We...

The acanthocephalan Acanthocephalus dirus is a trophically transmitted parasite that infects freshwater isopods as intermediate hosts and fish as definitive hosts. Using a laboratory-based experiment, we examined if parasite infection was associated with changes in mating behaviour, refuge use and neurochemical levels of infected isopods ( Caecidotea intermedius ). Infected isopods were less likely to engage in mating behaviour and more likely to be located in the open than uninfected isopods. Infected isopods also contained lower levels of serotonin (5-HT) and dopamine (DA) and had a greater mass of neural tissue (CNS) than uninfected isopods. We propose that the parasite-related changes in mating behaviour and refuge use may be modulated by the serotonergic and dopaminergic systems. We also suggest that the parasites could potentially be modulating these behavioural changes by exploiting the neural-immune system of the hosts through their neuroinflammatory responses.

Watershed managers are challenged by the need for predictive temperature models with sufficient accuracy and geographic breadth for practical use. We described thermal regimes of New England rivers and streams based on a reduced set of metrics for the May-September growing season (July or August median temperature, diurnal rate of change, and magnitude and timing of growing season maximum) chosen through principal component analysis of 78 candidate metrics. We then developed and assessed spatial statistical models for each of these metrics, incorporating spatial autocorrelation based on both distance along the flow network and Euclidean distance between points. Calculation of spatial autocorrelation based on travel or retention time in place of network distance yielded tighter-fitting Torgegrams with less scatter but did not improve overall model prediction accuracy. We predicted monthly median July or August stream temperatures as a function of median air temperature, estimated urban heat island effect, shaded solar radiation, main channel slope, watershed storage (percent lake and wetland area), percent coarse-grained surficial deposits, and presence or maximum depth of a lake immediately upstream, with an overall root-mean-square prediction error of 1.4 and 1.5 degrees C, respectively. Growing season maximum water temperature varied as a function of air temperature, local channel slope, shaded August solar radiation, imperviousness, and watershed storage. Predictive models for July or August daily range, maximum daily rate of change, and timing of growing season maximum were statistically significant but explained a much lower proportion of variance than the above models (5-14% of total).

‘What we need to do is inventory the different types of agricultural landscapes and bring to light the typical rural architecture, such as the acequias and desagües (irrigation supply canals and excess water drains). We need to find ways of conserving the landscape, including the flora and fauna as well as the role the agricultural landscape has played in the evolution of the surrounding area. Before we abandon the past (flood irrigation) for the contemporary (drip irrigation), we need a thorough analysis of the pros and cons of each system for the whole cultural landscape. The future may be one where the old and new learn to coexist, such as the hoe with the plow’ (Arellano, 2014, p. 204). WIREs Water 2015, 2:559–575. doi: 10.1002/wat2.1091This article is categorized under: Water and Life > Conservation, Management, and Awareness Engineering Water > Planning Water Human Water > Value of Water

The effects of nuptial colour, parasites and body size on reproductive success were examined in a natural population of three-spined stickleback Gasterosteus aculeatus. Reproductive males were collected, with the contents of their nests, during the embryo-guarding stage from Lynne Lake (Cook Inlet, Alaska, U.S.A.), and nuptial colour, infection status and body size were recorded. Regression analysis revealed that male body size was the only predictor, of those measured, of reproductive success in nature.

Ecosystem services, i.e., services provided to humans from ecological systems have become a key issue of this century in resource management, conservation planning, and environmental decision analysis. Mapping and quantifying ecosystem services have become strategic national interests for integrating ecology with economics to help understand the effects of human policies and actions and their subsequent impacts on both ecosystem function and human well-being. Some aspects of biodiversity are valued by humans in varied ways, and thus are important to include in any assessment that seeks to identify and quantify the benefits of ecosystems to humans. Some biodiversity metrics clearly reflect ecosystem services (e.g., abundance and diversity of harvestable species), whereas others may reflect indirect and difficult to quantify relationships to services (e.g., relevance of species diversity to ecosystem resilience, cultural value of native species). Wildlife habitat has been modeled at broad spatial scales and can be used to map a number of biodiversity metrics. In the present study, we present an approach that (1) identifies mappable biodiversity metrics that are related to ecosystem services or other stakeholder concerns, (2) maps these metrics throughout a large multi-state region, and (3) compares the metric values obtained for selected watersheds within the regional context. The broader focus is to design a flexible approach for mapping metrics to produce a national-scale product. We map 20 biodiversity metrics reflecting ecosystem services or other aspects of biodiversity for all vertebrate species except fish. Metrics include species richness for all vertebrates, specific taxon groups, harvestable species (i.e., upland game, waterfowl, furbearers, small game, and big game), threatened and endangered species, and state-designated species of greatest conservation need, and also a metric for ecosystem (i.e., land cover) diversity. The project is being conducted at multiple scales in a phased approach, starting with place-based studies, then multi-state regional areas, culminating into a national-level atlas. As an example of this incremental approach, we provide results for the southwestern United States (i.e., states of Arizona, New Mexico, Nevada, Utah, and Colorado) and portions of two watersheds within this region: the San Pedro River (Arizona) and Rio Grande River (New Mexico). Geographic patterns differed considerably among metrics across the southwestern study area, but metric values for the two watershed study areas were generally greater than those for the southwestern region as a whole. (C) 2012 Elsevier Ltd. All rights reserved.

Novel copolymers of trisubstituted ethylene monomers, halogen ring-disubstituted 2-phenyl-1,1-dicyanoethylenes, RC6H3CH=C(CN)(2) (where R is 2,3-Cl-2, 2,4-Cl-2, 2,6-Cl-2, 3,4-Cl-2, 3,5-Cl-2, 2-Cl-4-F, 2-Cl-6-F, 3-Cl-4-F) and 4-fluorostyrene were prepared at equimolar monomer feed composition by solution copolymerization in the presence of a radical initiator (ABCN) at 70 degrees C. The composition of the copolymers was calculated from nitrogen analysis, and the structures were analyzed by IR, H-1 and C-13-NMR. The order of relative reactivity (1/r(1)) for the monomers is 2-Cl-4-F (2.42) > 3,4-Cl-2(2.40) > 2,4-Cl-2(1.97) > 2-Cl-6-F (1.86) > 3-Cl-4-F (1.68) > 2,3-Cl-2 (0.89) > 3,5-Cl-2 (0.70) > 2,6-Cl-2 (0.47). High T-g of the copolymers, in comparison with that of poly(4-fluorostyrene) indicates a substantial decrease in chain mobility of the copolymer due to the high dipolar character of the trisubstituted ethylene monomer unit. Softening of the copolymers started in 194-216 degrees C range. Decomposition of the copolymers in nitrogen occurred in two steps, first in the 290-400 degrees C range with residue, which then decomposed in 400-800 degrees C range.