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Environmental DNA (eDNA) analysis of water samples is on the brink of becoming a standard monitoring method for aquatic species. This method has improved detection rates over conventional survey methods and thus has demonstrated effectiveness for estimation of site occupancy and species distribution. The frontier of eDNA applications, however, is to infer species density. Building upon previous studies, we present and assess a modeling approach that aims at inferring animal density from eDNA. The modeling combines eDNA and animal count data from a subset of sites to estimate species density (and associated uncertainties) at other sites where only eDNA data are available. As a proof of concept, we first perform a cross‐validation study using experimental data on carp in mesocosms. In these data, fish densities are known without error, which allows us to test the performance of the method with known data. We then evaluate the model using field data from a study on a stream salamander species to assess the potential of this method to work in natural settings, where density can never be known with absolute certainty. Two alternative distributions (Normal and Negative Binomial) to model variability in eDNA concentration data are assessed. Assessment based on the proof of concept data (carp) revealed that the Negative Binomial model provided much more accurate estimates than the model based on a Normal distribution, likely because eDNA data tend to be overdispersed. Greater imprecision was found when we applied the method to the field data, but the Negative Binomial model still provided useful density estimates. We call for further model development in this direction, as well as further research targeted at sampling design optimization. It will be important to assess these approaches on a broad range of study systems. We present an analytical framework to estimate species density in aquatic systems using eDNA and monitoring data. We tested the performance with carp eDNA data obtained in an experimental setting. We also assessed the method in a natural setting, using stream salamander data collected in the field.

This research aimed at developing the Trophic Water Quality Index (TWQI) for subtropical temperate Brazilian lotic systems based on a review of the indicative values of diatom species obtained using multivariate analysis techniques and considering the environmental gradient defined by a series of measured physical, chemical, and microbiological variables. Sampling was conducted from 2005 to 2009 in the Pardo River Hydrographic Basin, Rio Grande do Sul (RS), Brazil, and in the Andreas Stream Hydrographic Basin, RS, from 2012 to 2013. A total of 140 biological samples and 211 abiotic samples were collected. Data were analyzed by cluster analysis based on the Ward method and canonical correspondence analysis (CCA). The results indicated that total phosphate, turbidity, ammonia nitrogen, electrical conductivity, dissolved oxygen, and thermotolerant coliforms showed a significant correlation with the sample ordination made by CCA, in relation to a gradient of eutrophication. Eutrophication was operationally defined in a broad sense, including the problem of organic pollution and eutrophication of the water. The determination of the different tolerance degrees to eutrophication of the diatom taxa was used to assign trophic values of 1, 2.5, and 4 to species, corresponding to levels of low, medium, and high tolerance, respectively. By using the trophic values obtained for each diatom species, the TWQI constituted a new technological tool for environmental monitoring studies and showed a consistent, robust, and objective database for water quality assessment in subtropical temperate Brazilian lotic systems.

This research aimed at determining reference sites in southern Brazilian lotic systems, using the Water Quality Trophic Index (WQTI), based on epilithic diatom communities. Within the period of 2012 and 2016, 140 epilithic diatom samples from seven sampling sites within the spring area of the Andreas Stream Hydrographic Basin, Vera Cruz County, RS, Brazil, were analyzed quarterly. Similarly, from 2012 and 2014, water samples in these sampling sites were collected for determination of physicochemical and microbiological parameters, such as water temperature, pH, turbidity, dissolved oxygen, biochemical oxygen demand, nitrate, phosphate, total dissolved solids, and fecal coliforms. The results indicated the occurrence of two diatom samples groups with significant differences ( p < 0.05). Group 1 (sampling sites P1, P4, and P5) was classified in the oligotrophic category with an average WQTI of 1.3 ± 0.2, while group 2 (sampling sites P2, P3, P6, and P7) was classified in the β-mesotrophic category with an average value of 2.0 ± 0.4). Achnanthidium minutissimum and Platessa hustedtii the dominant species were classified as oligotrophic taxa. Thus, we proposed the upper limit of the first interval of the WQTI score scale, equal to 1.5, as a reference value to differentiate the limits between the “high” and “good” ecological status to determine “reference sites” for subtropical and temperate Brazilian aquatic systems. The physical, chemical, and microbiological water quality evaluation gives support to this proposal, as far as the results indicated a significant improvement in the water quality, classifying sampling sites P1, P4, and P5 as having good quality appropriate for multiple uses.

The widespread degradation of lotic ecosystems has prompted extensive river restoration efforts globally, but many studies have reported modest ecological responses to rehabilitation practices. The functional properties of biotic communities are rarely examined within post-project appraisals, which would provide more ecological information underpinning ecosystem responses to restoration practices and potentially pinpoint project limitations. This study examines macroinvertebrate community responses to three projects which aimed to physically restore channel morphologies. Taxonomic and functional trait compositions supported by widely occurring lotic habitats (biotopes) were examined across paired restored and non-restored (control) reaches. The multivariate location (average community composition) of taxonomic and functional trait compositions differed marginally between control and restored reaches. However, changes in the amount of multivariate dispersion were more robust and indicated greater ecological heterogeneity within restored reaches, particularly when considering functional trait compositions. Organic biotopes (macrophyte stands and macroalgae) occurred widely across all study sites and supported a high alpha (within-habitat) taxonomic diversity compared to mineralogical biotopes (sand and gravel patches), which were characteristic of restored reaches. However, mineralogical biotopes possessed a higher beta (between-habitat) functional diversity, although this was less pronounced for taxonomic compositions. This study demonstrates that examining the functional and structural properties of taxa across distinct biotopes can provide a greater understanding of biotic responses to river restoration works. Such information could be used to better understand the ecological implications of rehabilitation practices and guide more effective management strategies.

We analyzed periphyton structure, elemental composition: carbon (C), nitrogen (N) and phosphorus (P), and algal composition along an urban gradient in three water courses of Ushuaia City. We hypothesize that periphyton stoichiometric ratios (C:N, C:P and N:P) decrease with the increase of urban land use. Also, community structure is affected by urban land use; sites with major surrounding urban and higher nutrient load host larger biomass and different algae composition compared to more pristine sites. P content and mass fractions of periphyton increased along the urban gradient as well as dissolved P in the water. Periphyton molar ratios N:P and C:P showed a negative lineal relationship with the gradient of urban land use. In general, periphyton was dominated by diatoms although Chlorophyta biovolume, mainly composed of filamentous algae, increased significantly in sites with 70% of urban land use. Our data suggest that there is no homeostatic balance in the periphyton community in Sub-Antarctic streams; we detected more P in periphyton in urban sites and the community became thus less heterotrophic. This study helps to better understand the dynamics of nutrients and its influence over a sessile community in sub-Antarctic lotic ecosystems impacted by urbanization.

Aim Environmental DNA (eDNA) is a rapidly emerging methodology with important applications to environmental management and conservation. However, the effects of stream flow or discharge on eDNA have been minimally investigated in lotic (stream and river) environments. In this study, we examined the role of stream flow on eDNA concentrations and detectability of an invasive clam (Corbicula fluminea), while also accounting for other abiotic and biotic variables. Location Illinois, United States of America. Methods We used a longitudinal study over a year in two streams, as well as a seasonal study (summer, autumn) in eight streams, to investigate the effects of variable stream flow on eDNA concentrations and detectability. We used linear mixed‐effects models to assess the influence of various factors on eDNA concentration and occupancy models to make predictions on how seasonality can influence eDNA detection. Results We found higher stream flows decreased eDNA concentrations, and floods produced false negatives or non‐detections at locations where C. fluminea was relatively common. In addition, we found concentrations and detectability of C. fluminea eDNA to be higher in summer than in autumn. Main conclusions We found that stream flow dilutes eDNA concentrations, which may have serious implications for the detection of low abundance organisms. Managers and practitioners applying eDNA for rare species should seek to sample at low or base stream flows when feasible, and future studies should investigate whether our findings here are consistent for other taxa and lotic ecosystems.

Hematological studies of fishes are useful in the diagnosis of many diseases as well as investigation of the extent of damage to the blood. These parameters act as efficient and insightful index to examine health status, physiological and pathological changes occurring in various fishes, i.e., metabolic perturbations in fish body thereby acting as non-specific biomarkers in the field of environmental toxicology, deficiencies and chronic stress in natural as well as aquaculture systems and checking water quality. The assessments of these blood parameters help the biologists to understand the fish homeostasis and biomonitoring of severe and chronic patho-physiological changes inferable to nutrition, water quality, or disease so as to establish the normal reference values of different species and determine systematic relationships among them. Lot of work on various aspects of hematological parameters and their relation with ecological factors has been reported on several fish species from different parts of the world. Each study attributes one or other factors responsible for variation in hematological parameters among different fish species. Therefore, in the present study, an attempt has been made to compile the information about the hematological studies of various fish species reported from different parts of the world, and through this study, a general overview has been generated about the major factors responsible for the variation in hematological parameters of fish. The review provides an insight to the characteristics of hematological values showing that fluctuating internal environment of the fish, along with other intrinsic (age, body size, the cycle of sexual maturity, health condition, nutritional state, species) and extrinsic factors (temperature, stress, season, dissolved oxygen, water quality, lotic or lentic environment, stocking density, photoperiod, sampling conditions, laboratory techniques), are the reasons of huge variability of hematological parameters in fishes.

For many decades, river research has been focused on perennial rivers. Intermittent river research has a shorter history, and recent studies suggest that alternating dry and wet conditions alter virtually all biotic communities and biogeochemical processes in these rivers. Intermittent rivers constitute more than half of the length of the global river network and are increasing in number and length in response to climate change, land-use alteration, and water abstraction. Our views of the roles that rivers play in maintaining biodiversity and controlling material fluxes will change substantially when intermittent rivers are fully integrated into regional and global analyses. Concepts, questions, and methodologies from lotic, lentic, and terrestrial ecology need to be integrated and applied to intermittent rivers to increase our knowledge and effective management of these rivers.

Ecological restoration has grown rapidly and now encompasses not only classic ecological theory but also utilitarian concerns, such as preparedness for climate change and provisioning of ecosystem services. Three dominant perspectives compete to influence the science and practice of river restoration. A strong focus on channel morphology has led to approaches that involve major Earth-moving activities, such as channel reconfiguration with the unmet assumption that ecological recovery will follow. Functional perspectives of river restoration aim to regain the full suite of biogeochemical, ecological, and hydrogeomorphic processes that make up a healthy river, and though there is well-accepted theory to support this, research on methods to implement and assess functional restoration projects is in its infancy. A plethora of new studies worldwide provide data on why and how rivers are being restored as well as the project outcomes. Measurable improvements postrestoration vary by restoration method and measure of outcome.

The term \"environmental flows\" describes the quantities, quality, and patterns of water flows required to sustain freshwater and estuarine ecosystems and the ecosystem services they provide. Environmental flows may be achieved in a number of different ways, most of which are based on either (1) limiting alterations from the natural flow baseline to maintain biodiversity and ecological integrity or (2) designing flow regimes to achieve specific ecological and ecosystem service outcomes. We argue that the former practice is more applicable to natural and semi-natural rivers where the primary objective and opportunity is ecological conservation. The latter \"designer\" approach is better suited to modified and managed rivers where return to natural conditions is no longer feasible and the objective is to maximize natural capital as well as support economic growth, recreation, or cultural history. This permits elements of ecosystem design and adaptation to environmental change. In a future characterized by altered climates and intensive regulation, where hybrid and novel aquatic ecosystems predominate, the designer approach may be the only feasible option. This conclusion stems from a lack of natural ecosystems from which to draw analogs and the need to support broader socioeconomic benefits and valuable configurations of natural and social capital.