Freshwater Residence Research Articles

Global spatial analysis of toxic emissions to freshwater: operationalization for LCA

There is increasing interest in using fate and exposure models to spatially differentiate the impacts of chemical emissions. This work aims at exploring the operationalization in life cycle assessment (LCA) of spatially differentiated models for toxic emissions into freshwater. We analyse and compare the variability of fate and exposure factors at high resolution with aggregated factors at different levels of lower resolution. We developed a spatially resolved fate and exposure characterization model and factors for toxic emissions into freshwater with global coverage at 0.5° × 0.5° resolution, extending a global hydrological model to account for removal processes, namely chemical and biological degradation, sedimentation, and volatilization. We analysed the variation in fate and exposure factors for water ingestion, identifying the main factors of influence. We then developed archetypes for ecosystems and human fate and exposure. Using a case study of emissions of arsenic from red mud disposal as a waste from alumina production, we tested practical solutions to apply spatial characterization factors aggregated at different resolution in LCA, comparing archetype-based with region-based approaches. World maps show up to 5 orders of magnitude variation for chemical fate in fresh water across all 0.5° × 0.5° grid cells and up to 15 orders of magnitude for human intake fractions. The freshwater residence time to the sea and the equivalent depth—over all downstream cells—were the most influential landscape parameters. They were used to define four freshwater landscape archetypes. These archetypes capture variation in fate well, better than country or continent-aggregated values, but are not able to reflect variation in intake fraction. The case study on arsenic from alumina production shows that the determination of industry-specific weighted average represents a pragmatic way to account for sector-specific location of emissions. The population-weighted approach is primarily applicable for emissions that are related to population density, such as household emissions. The developed global freshwater model demonstrates large spatial variations in fate and exposure. Archetypes for fate in fresh water provide substantial reductions in variability compared to country or continental averages, but are more difficult to apply to LCA than rural or urban archetypes for air emissions. The 0.5° × 0.5° grid model and the fate archetypes may also be used in the context of ecological scenarios to identify hotspots. In practice, population-weighted and sector-specific average characterization factors may represent the most operational way to account for specific distribution patterns of toxic emissions in LCA.

Unravelling habitat use of Coilia nasus from the Rokkaku River and Chikugo River estuaries of Japan by otolith strontium and calcium

The migratory history of the engraulid fish Coilia nasus in the Rokkaku and Chikugo River estuaries of the Ariake Sea, Japan was assessed using otolith strontium (Sr) X-ray intensity maps and strontium:calcium (Sr:Ca) ratio life history transects by an electron probe microanalyzer (EPMA). The results showed that seven of the ten specimens from the Rokkaku River Estuary (LJC) and all 15 specimens collected in the Chikugo River Estuary (ZHC) had low Sr:Ca ratios (⩽3) at the central otolith area, indicating their riverine origin and initial freshwater residence. After the first regime shift adjacent to natal regions, the Sr level mapping displayed a wide variety of color patterns, and the Sr:Ca ratios obtained by the line transect analysis could be divided into one to six significantly different phases indicative of gradual life history transition. The other three specimens from the Rokkaku River Estuary had high Sr:Ca ratios (3–6.7) at the central otolith area but showed alternating changes between low and high values outside the natal region, suggesting that estuarine-origin individuals occurred in the Rokkaku River Estuary. The two-dimensional maps of the Sr level and average of the otolith Sr:Ca ratios along the life-history transects could be used as effective tools for reconstruction of past habitat use of the tapertail anchovy in estuaries of the Ariake Sea, Japan.

Short-term desalination of Pulicat lagoon (Southeast India) due to the 2015 extreme flood event: insights from Land-Ocean Interactions in Coastal Zone (LOICZ) models

IntroductionWe investigated the magnitude and duration of desalination of Pulicat—a coastal lagoon ecosystem connected to the Bay of Bengal on the South-eastern coast of India—during the 2015 South India flood event which was a period of high-magnitude precipitation and riverine flooding.MethodsWe estimated freshwater runoff into the lagoon using flow accumulation models for a period of 55 days (November 1 to December 25, 2015) using daily gridded precipitation data from the Global Precipitation Measurement and a digital elevation model. Using the estimates of freshwater runoff, direct precipitation and observed salinities, we simulated water and salinity fluxes of the lagoon using the Land-Ocean Interactions in the Coastal Zone model. Further, we also used Monte Carlo simulation to estimate the uncertainty in system salinity, the residual salinity at the boundary and the freshwater residence times in the lagoon.ResultsWe estimated that a high volume (~ 760 × 106 m3) of relatively low salinity waters (residual salinity = 23.47 psu) had been exported from the lagoon to the Bay of Bengal during the period which is likely to have caused a strong dip in the daily salinity profile of the coastal sea. We contend that the lagoon experienced ~ 40% desalination due to the 2015 event with a freshwater residence time of 18.5 days.ConclusionsThe study highlighted the short-term, high-magnitude desalination undergone by Pulicat lagoon during the 2015 South India floods. Considering the high residual and exchange volumes obtained from the study, we conclude that Pulicat could be a major exporter of relatively low salinity waters to the Bay of Bengal during monsoons.

Short‐term Physiological Response Profiles of Tagged Migrating Adult Sockeye Salmon: A Comparison of Gastric Insertion and External Tagging Methods

AbstractA variety of electronic tag types are routinely applied to fish to better understand migration biology. However, tagging procedures have the potential to affect the postrelease behaviour and survival of tagged individuals. In this study, wild adult Sockeye Salmon Oncorhynchus nerka from the Harrison River, British Columbia, were radio‐tagged by gastric insertion or external attachment techniques immediately after capture to understand the short‐term physiological response to these two tagging methods. Plasma cortisol, glucose, lactate, sodium, and potassium levels, as well as white muscle lactate and glycogen concentrations, were measured in samples obtained from fish upon capture (0 h) as well as 1 or 4 h after the tagging treatment. The effects of key biological variables, such as sex and proximity to spawn, on the physiological response to the tagging events were also evaluated. Tagging occurred during two distinct time periods representing fish of different maturation states and durations of freshwater residency. Overall, the physiological response to the tagging scenarios was characteristic of the disturbance associated with exhaustive exercise. There were no significant differences detected in the response profiles following gastric or external tagging procedures. This was despite procedural differences such as stomach perforations observed in 68% of the gastric insertions in the late sampling period, and external attachments taking three times longer (43 s) than gastric insertion (15 s). Moreover, the tagged fish showed similar response profiles to control fish that were handled but not tagged. These results suggest that the capture and handling associated with a tagging event induced physiological disturbance, and that the addition of a quick tagging procedure appeared to be nonadditive over the 4‐h assessment period. Sex and proximity to spawn had significant main and interaction effects on some of the physiological response variables, indicating that biological context is important for interpreting physiological assessments in experiments that manipulate exercise and stress responses in migrating adult Pacific salmon.

Effects of past and projected river discharge variability on freshwater production in an anadromous fish

AbstractKnowledge about population responses to environmental variability, including extreme climatic events, is crucial for understanding their current status and likely fate under future environmental change. The frequency and intensity of extreme events is projected to increase, especially in freshwater ecosystems.Anadromous fishes depend on freshwater habitats for spawning and juvenile rearing, making them sensitive to altered hydrologic regimes. Here, we evaluate the effect of past and projected variability in river hydrology on freshwater production of naturally spawning coho salmon populations from coastal river systems in Washington,USA.Using a stage‐based life‐cycle model, we show that juvenile production during freshwater residence depends on river flow characteristics. Most importantly, juvenile production is reduced by low minimum stream flows during summer.Based on climate model projections suggesting more extreme summer droughts in the region, we then simulate changes in river flow characteristics and quantify the effects of more frequent and severe low flows during summer on juvenile production as well as the harvest that can be sustained in these populations.Our results demonstrate that changes in hydrologic regimes due to environmental change, especially extreme low flows during summer, may significantly affect juvenile production in anadromous fishes such as coho salmon and the services these populations provide to their ecosystems and humans. Understanding population responses to extreme climatic events is thus essential for improving species conservation and risk assessments.

Unravelinghabitat use of Coilia nasus from Qiantang River of China by otolith microchemistry

The habitat use and life history characteristics of the estuarine tapertail anchovy, Coilia nasus from Qiantang River were studied by examining the environmental signatures of Sr and Ca in otoliths using otolith microchemical analysis. The results indicate the C. nasus in the present study could be briefly divided into three types: Types 1/Type 2 of riverine origin and initial relative long-term/short-term freshwater residence, and Types 3 of estuarine origin and initial brackish early life history. The availability and fluctuation of certain levels of Sr:Ca ratios (i.e., Sr:Ca×1000) between salinity scale of 3.00 and 7.00 reveal that the C. nasus analyzed in this study spent much more time in brackish habitat of the river’s estuary. This study has established that the C. nasus of Qiantang River Estuary has a diverse and complex pattern of life history and habitat use which makes their life history and migration pattern vary from those of the Yangtze River.

The influence of a new water infrastructure development on the relative abundance of two Australian freshwater turtle species

Development of water infrastructure benefits water security and agriculture but poses risks to habitat and aquatic fauna. Wyaralong Dam was constructed on Teviot Brook in 2010 to provide future urban water supplies for South East Queensland, Australia. Construction of the dam created a large impoundment area and environmental impact assessment predicted significant impacts upon resident freshwater turtle species and their habitats. Differences in habitat requirements, life-history characteristics and sensitivity to change between the Macquarie River turtle (Emydura macquarii macquarii) and the common saw-shelled turtle (Myuchelys latisternum) were expected to influence the impact of the dam on the spatial and temporal abundance of these species. The relative abundance of each species was monitored at sites located within, upstream and downstream of the impoundment across wet and dry seasons during the dam’s first five years of operation. The results of this monitoring program indicate that spatial and temporal variability in the relative abundance of E. macquarii macquarii and M. latisternum occurred during the study but not all expected impacts were realised. Contrary to expectation, the relative abundance of E. macquarii macquarii did not increase over time within, upstream or downstream of the dam. M. latisternum showed greater temporal variability at some sites; however, no clear relationship between relative abundance and operational years was observed during the monitoring program. Spatial variability in relative abundance between sites was dependent upon season, with trends generally consistent across both turtle species. Where differences between species were observed, these are suspected to have resulted from the influence of environmental conditions on species-specific movement behaviours. The monitoring program confirmed the use of the upper limits of the impoundment and the plunge pool below the dam wall by both turtle species but relative abundance within the main body of the impoundment remained low throughout monitoring. The results of the study allow for consideration of the suitability of predefined management measures and the development of recommendations for future monitoring programs prescribed for water infrastructure developments.

A Model Study on the Summertime Distribution of River Waters in Long Island Sound

Long Island Sound (LIS), a large urban estuary in the northeastern USA, receives freshwater from many rivers along its northern shore. The size of these rivers varies widely in terms of basin area and discharge. The Regional Ocean Modeling System (ROMS) was applied with conservative passive tracers to identify the distribution, mixing, freshwater residence times, and storm response for all of LIS’s river systems during the summer of 2013. A watershed model was applied to overcome the lack of adequate river discharge observations for coastal watersheds. The Connecticut River was the largest contributor to riverine freshwater throughout the estuary despite its entry point near the mouth. The Connecticut River strengthened bulk stratification in the eastern LIS the most but acted to weaken stratification near the mouths of other rivers and in far western LIS by freshening waters at depth. The Housatonic and Hudson Rivers had the strongest influence on stratification in central and western LIS, respectively. Smaller coastal rivers were the most influential in strengthening stratification near the southwestern Connecticut shoreline. The influence of small coastal rivers was amplified after a major storm due to shorter storm response times relative to the larger rivers. Overall, river water was close to a well-mixed state throughout LIS, but more stratified near river mouths. Freshwater residence time estimates, meanwhile, indicated monthly to multi-seasonal time scales (43 to 180 days) and grew longer with greater distance from the LIS mouth.

Seasonal variability of the inorganic carbon system in a large coastal plain estuary

Abstract. Carbonate geochemistry research in large estuarine systems is limited. More work is needed to understand how changes in land-use activity influence watershed export of organic and inorganic carbon, acids, and nutrients to the coastal ocean. To investigate the seasonal variation of the inorganic carbon system in the Delaware Estuary, one of the largest estuaries along the US east coast, dissolved inorganic carbon (DIC), total alkalinity (TA), and pH were measured along the estuary from June 2013 to April 2015. In addition, DIC, TA, and pH were periodically measured from March to October 2015 in the nontidal freshwater Delaware, Schuylkill, and Christina rivers over a range of discharge conditions. There were strong negative relationships between river TA and discharge, suggesting that changes in HCO3− concentrations reflect dilution of weathering products in the drainage basin. The ratio of DIC to TA, an understudied but important property, was high (1.11) during high discharge and low (0.94) during low discharge, reflecting additional DIC input in the form of carbon dioxide (CO2), most likely from terrestrial organic matter decomposition, rather than bicarbonate (HCO3−) inputs due to drainage basin weathering processes. This is also a result of CO2 loss to the atmosphere due to rapid water transit during the wet season. Our data further show that elevated DIC in the Schuylkill River is substantially different than that in the Delaware River. Thus, tributary contributions must be considered when attributing estuarine DIC sources to the internal carbon cycle versus external processes such as drainage basin mineralogy, weathering intensity, and discharge patterns. Long-term records in the Delaware and Schuylkill rivers indicate shifts toward higher alkalinity in estuarine waters over time, as has been found in other estuaries worldwide. Annual DIC input flux to the estuary and export flux to the coastal ocean are estimated to be 15.7 ± 8.2 × 109 mol C yr−1 and 16.5 ± 10.6 × 109 mol C yr−1, respectively, while net DIC production within the estuary including inputs from intertidal marshes is estimated to be 5.1 × 109 mol C yr−1. The small difference between riverine input and export flux suggests that, in the case of the Delaware Estuary and perhaps other large coastal systems with long freshwater residence times, the majority of the DIC produced in the estuary by biological processes is exchanged with the atmosphere rather than exported to the sea.

Impact of flow diversion by run-of-river dams on American dipper diet and mercury exposure.

Run-of-river dams produce lower greenhouse gas emissions than large hydropower projects, but there is a paucity of research on their potential ecotoxicological impacts through disruption of natural flow regimes. We used stable isotopes (δ13 C, δ15 N, δ34 S) to reconstruct diet and trace methylmercury in a predatory river-resident passerine, the American dipper (Cinclus mexicanus), at 7 regulated and 6 free-flowing mountain streams in coastal British Columbia, Canada. Assimilated diets were comparable among regulated and unregulated streams, dominated by benthic macroinvertebrates and resident freshwater fish, with negligible contributions from anadromous Pacific salmon. Although invertebrates at unregulated streams were isotopically similar along their gradient, dippers and invertebrates sampled below dams on regulated streams had 34 S-depleted tissues, suggesting increased activity of sulfate-reducing bacteria and more Hg methylation below the dams. Mercury concentrations in dipper blood (417.6 ± 74.1 standard error [SE] ng/g wet wt at regulated streams, 340.7 ± 42.7 SE ng/g wet wt at unregulated streams) and feathers (1564 .6 ± 367.2 SE ng/g dry wt regulated, 1149.0 ± 152.1 SE ng/g dry wt unregulated), however, were not significantly different between stream types. Relative to other passerines across western North America, dippers in these densely forested mountain streams experienced high mercury exposure; and one recently regulated stream supported dippers with mercury concentrations of potential toxicity concern (up to 8459.5 ng/g dry wt in feathers and 1824.6 ng/g wet wt in whole blood). Elevated mercury in dippers is likely attributable to the birds' relatively high trophic position and high regional inorganic mercury deposition; however, biogeochemical conditions in reservoirs of some regulated streams may be contributing to methylmercury production. Environ Toxicol Chem 2018;37:411-426. © 2017 SETAC.

Decadal-scale variation in COD and DIN dynamics during the summer in the inner area of the Ariake Sea, Japan

More than 30 years of chemical oxygen demand (COD) and dissolved inorganic nitrogen (DIN) data for the inner area of the Ariake Sea were analyzed with a box model to show the changes in the average seasonal budget and the decadal-scale variation during the summer. The COD peaked in August and March on average. This summertime peak can be explained by an enhanced riverine load and increased primary production. The peak in March suggested additional organic matter production. There were also two peaks in DIN concentration on average: a summertime peak that could be explained by an enhanced riverine load, and a peak in December that was more complicated to explain. From the 1970s to the early 1990s, the bottom water in this area became increasingly hypoxic due to increased COD during the summer, even though there were minimal increases in terrestrial COD and nutrient loads and there were tidal flats covering a widespread area during this period. The increase in COD was caused by increased net ecosystem production, which was due to enhanced primary production induced by an increased freshwater residence time and decreased bivalve grazing. There was a negative feedback control in which hypoxia progressively increased, leading to declines in bivalve biomass, which in turn decreased the grazing pressure limiting primary production, meaning that primary production increased and the area became even more hypoxic. The net DIN production decreased during the 1980s and the 1990s. This was consistent with the change in net ecosystem production according to the COD.

Environmental DNA as a tool to inventory resident and juvenile freshwater salmonids

Environmental DNA as a tool to inventory resident and juvenile freshwater salmonids

Use of Morphological and Physiological Indices to Characterize Life History Diversity in Juvenile Hatchery Winter‐Run Steelhead

AbstractSteelhead Oncorhynchus mykiss exhibit significant life history plasticity, including variation in freshwater residence time, age of smoltification, and maturation that are influenced by exceeding specific thresholds in size or body energy stores. Fish that do not reach minimum thresholds for smoltification or exceed thresholds for maturation may “residualize” in freshwater. Understanding life history diversity is important in steelhead hatchery programs. The objective of this investigation was to characterize life history diversity in Hood River, Oregon, hatchery winter‐run steelhead prior to release. We used both morphological and physiological indices to assess degree of smoltification in both sexes and maturation in males. Smoltification was categorized by measuring size, visual smolt index, and gill Na+/K+‐ATPase activity. All females were determined to be immature. Male reproductive development required histological staging of testes. Other indices of maturation—including gonadosomatic index, plasma 11‐ketotestosterone, and pituitary fshb and lhb and testis ifg3 and amh gene expression—were also employed, with varying degrees of success. Five phenotypes were described: (1) immature male and female parr; (2) precociously mature male parr; (3) male smolts in early to mid‐spermatogenesis that are likely to spawn after <1 year in the ocean; (4) males that might have attempted maturation, but failed; and (5) immature male and female smolts that could mature after >1 year in the ocean. Over three brood years, we estimated that 3–4% of the population could potentially residualize due to failure to smolt or precocious male maturation, 1–12% could mature after <1 year in the ocean (one salt male), and 84–95% could mature after >1 year in the ocean (two to three salt males and females). Based on previous studies conducted in the Hood River basin, the residualism rate estimated for this hatchery population is lower than that of naturally rearing Hood River steelhead.Received November 2, 2016; accepted February 14, 2017 Published online May 11, 2017

Fluvio-marine travelers from South America: Cyclic amphidromy and freshwater residency, typical behaviors in Genidens barbus inferred by otolith chemistry

Catfish Genidens barbus is a commercially fished species from the south-western Atlantic Ocean. Overfishing of this species during the last few years has caused a collapse of fisheries and in turn has led to a ban of its exploitation. In order to identify the migratory patterns of this species in four migration corridors from South America, we determined the Sr:Ca and Ba:Ca ratios in otoliths, by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS). Sr:Ca and Ba:Ca ratios range between 0.90 and 9.83mmol/mol (mean±standard deviation: 3.86±1.05mmol/mol) and between 0.00013 and 0.10mmol/mol (mean±SD: 0.0094±0.0160mmol/mol), respectively. Three types of amphidromous and cyclical (annual) patterns that include the use of freshwater, estuarine and marine environments are detected. Resident freshwater fish (6.5%) are found only in Patos Lagoon. Depending on the study site, between 18 and 45% of the analyzed fish population were spawned in freshwater, while the rest were spawned in estuarine waters. The change-point analysis shows a positive correlation between changes in the transects of Sr:Ca and Ba:Ca ratios (r=0.63, p=0.0001), whereas the Kruskal-Wallis test shows no significant differences in the number of changes in transects of the Sr:Ca ratio between sampling sites (H=2.1, p=0.53). Only for Patos Lagoon the analyses show a significantly higher number of changes for the Ba:Ca ratio (H=9.1, p=0.03). The data indicate that the average number of movements among environments is similar between the four corridors. The number of changes of the Ba:Ca ratio appears to be higher and more variable in relation to the Sr:Ca ratio, indicating that the former could be more sensitive to environmental changes. In conclusion, this work describes for the first time, annual amphidromous migrations and dependence on freshwater for different fluvial-marine systems. The understanding of the habitat use will help design species and estuarine-specific management actions with the ultimate goal of recovering fisheries.

Implications of absence of seawater-type mitochondria-rich cells and results of molecular analyses for derivation of the non-parasitic Ukrainian brook lamprey Eudontomyzon mariae

The Ukrainian brook lamprey Eudontomyzon mariae is the most widespread lamprey species in eastern Europe. Although E. mariae is generally considered a derivative of Eudontomyzon danfordi, an exclusively freshwater parasitic species, it has alternatively been suggested that it was recently derived from a now extinct anadromous Black Sea ancestor. Several non-parasitic lampreys and the landlocked sea lamprey, which have recently evolved from anadromous ancestors, still develop a seawater-type mitochondria-rich cell (SW-MRC) in their gills. In contrast, this cell type is not present in the gills of either Lampetra aepyptera, a non-parasitic lamprey of ancient origin, or the parasitic Ichthyomyzon unicuspis and I. castaneus that likewise have long evolutionary histories in fresh water. Eudontomyzon mariae from the Vistula River in the Baltic River basin does not possess SW-MRC, which is inconsistent with a recent origin from an anadromous ancestor. Mitochondrial DNA sequence data were thus used to infer the relationship between different populations of E. mariae and E. danfordi, and to reconstruct the transition from anadromy to freshwater residency. The results suggest that E. mariae evolved independently in the Baltic, Black, and Caspian Sea basins, and not recently from an anadromous ancestor. Although E. mariae in the Danube River may have arisen relatively recently from E. danfordi (differing by 0.7–1.1% in cytochrome b gene sequence), other E. mariae populations (including in the Vistula River) are genetically closer (0.6%) to the hypothetical ancestor of both E. mariae and E. danfordi. That ancestor was probably a freshwater resident, since SW-MRCs are not rapidly lost following confinement in fresh water.

Can environmental impact assessments alone conserve freshwater fish biota? Review of the Chilean experience

Chile was one of many countries that initiated environmental impact assessments in the 1990s, and has relied on their use for species conservation and territorial planning without the use of larger-scale environmental and ecological planning. The capacity of Chile's environmental impact assessment system (SEIA) to evaluate resident freshwater fishes and the potential impacts of water projects and aquaculture activities – two categories of projects that create direct threats to freshwater fishes – are assessed. Of the 3997 such submissions to the SEIA, only 0.6% conducted any freshwater fish assessment, and only 0.1% conducted any quantitative assessment of expected impacts from the associated project. The small number of assessments was characterized by poor study design, inconsistent sampling methodology, and species misidentification. Traditional assessments failed to include freshwater fish ecology in the general assessment framework. The new strategic environmental evaluation system only underscores the need for vastly improved field sampling protocols and assessment methodologies.

Freshwater Fish Inventory of the Aleutian Archipelago, Alaska

Abstract Freshwater fish surveys were conducted at 178 lakes and streams at 13 islands in the Aleutian Archipelago and two islands in the Pribilof Islands during May-September 2002 and 2006-2010. Seven fish species were documented: coho salmon (Oncorhynchus kisutch), rainbow trout (O. mykiss), Dolly Varden (Salvelinus malma), anadromous, and resident freshwater threespine stickleback (Gasterosteus aculeatus species complex), ninespine stickleback (Pungitius pungitius), coastrange sculpin (Cottus aleuticus), and Alaska blackfish (Dallia pectoralis). Resident freshwater threespine stickleback and Dolly Varden were the most commonly trapped fish. Ninespine stickleback were found only in the Near Islands group. Populations of resident freshwater threespine stickleback containing a low frequency of individuals with two or four dorsal spines were collected in the Near Islands group and at Adak Island. Sympatric species pairs of anadromous and resident freshwater threespine stickleback were collected in the Andr...

Do Eurasian minnows (Phoxinus phoxinus L.) inhabiting brackish water enter fresh water to reproduce: Evidence from a study on otolith microchemistry

AbstractDynamics of coastal fish assemblages in the Baltic Sea are still rather poorly understood. In particular, little information is available on migrations and movements of the small‐bodied littoral fish species like Eurasian minnow (Phoxinus phoxinus L.). Minnow is considered typically as a river and lake species, but it also inhabits brackish coastal waters of the Baltic Sea. In this study, we investigated movement patterns of brackish water inhabiting minnows using otolith microchemistry. Fish were collected from four different sites (from two bays and two stream mouths) around Saaremaa Island. The results indicated that at least three distinct migration patterns exist: (i) seawater residency, (ii) fast springtime migrations to fresh water or to bays with lower salinities (areas near stream mouths) and (iii) prolonged migrations to fresh water (some cases overwintering in streams). Migration patterns listed above were not evenly distributed among sites, and some individuals did not migrate to fresh water in every year. None of the analysed fish were freshwater residents. Additionally, potentially ontogenetic effects on Mn and Sr concentrations were observed in the otolith core regions, which may have important implications for the interpretation of otolith chemistry data. The overall findings of this study demonstrate that much more complex migration patterns exists in brackish water inhabiting minnow populations than previously thought and at least some individuals do enter freshwater to reproduce.

Young-of-the-year Coho Salmon Oncorhynchus kisutch recruit in fresh waters of remote Patagonian fjords in southern Chile (51°S)

Salmonid invasions are currently recognized as one of the main threats to the conservation of freshwater ecosystems in Patagonia. Although a number of salmonid species have been introduced to Patagonia over the last century not all species have succeeded at establishing widespread and large populations. To date, there are no reports of established self-sustaining Coho Salmon (Oncorhynchus kisutch) populations in southern Chile despite propagule pressure from aquaculture. Here, we assessed the natal origin of young-of-the-year Coho Salmon collected from estuaries and lakes associated with remote Patagonian fjords (51°S) by examining their otolith microchemical composition. Low strontium concentrations along a line transect from the otolith edge to its core in fish collected in one lake are consistent with freshwater residence until the moment of capture. Fish caught in estuaries displayed instead, relatively high strontium concentrations only at the otolith edge. This pattern suggests very recent movement from freshwater down to the estuary. Our findings are consistent with the hypothesis that the juvenile Coho Salmon collected in estuaries originated in the local freshwater system (lake) and provide the first ever evidence of recruitment and probable establishment of self-sustaining Coho Salmon population in Patagonia.

Riverine Bacterial Communities Reveal Environmental Disturbance Signatures within the Betaproteobacteria and Verrucomicrobia.

Riverine bacterial communities play an essential role in the biogeochemical coupling of terrestrial and marine environments, transforming elements and organic matter in their journey from land to sea. However, precisely due to the fact that rivers receive significant terrestrial input, the distinction between resident freshwater taxa vs. land-derived microbes can often become ambiguous. Furthermore, ecosystem perturbations could introduce allochthonous microbial groups and reshape riverine bacterial communities. Using full- and partial-length 16S ribosomal RNA gene sequences, we analyzed the composition of bacterial communities in the Tar River of North Carolina from November 2010 to November 2011, during which a natural perturbation occurred: the inundation of the lower reaches of an otherwise drought-stricken river associated with Hurricane Irene, which passed over eastern North Carolina in late August 2011. This event provided the opportunity to examine the microbiological, hydrological, and geochemical impacts of a disturbance, defined here as the large freshwater influx into the Tar River, superimposed on seasonal changes or other ecosystem variability independent of the hurricane. Our findings demonstrate that downstream communities are more taxonomically diverse and temporally variable than their upstream counterparts. More importantly, pre- vs. post-disturbance taxonomic comparison of the freshwater-dominant Betaproteobacteria class and the phylum Verrucomicrobia reveal a disturbance signature of previously undetected taxa of diverse origins. We use known traits of closely-related taxa to interpret the ecological function of disturbance-associated bacteria, and hypothesize that carbon cycling was enhanced post-disturbance in the Tar River, likely due to the flux of organic carbon into the system associated with the large freshwater pulse. Our analyses demonstrate the importance of geochemical and hydrological alterations in structuring bacterial communities, and illustrate the response of temperate riverine bacteria on fine taxonomic scales to a disturbance.