Extent estimates and land cover relationships for functional indicators in non-wadeable rivers

Functional indicators are being increasingly used to assess waterway health but their responses to pressure in non-wadeable rivers have not been widely documented or applied in modern survey designs that provide unbiased estimates of extent. This study tests the response of river metabolism and loss in cotton strip tensile strength across a land use pressure gradient in non-wadeable rivers of northern New Zealand, and reports extent estimates for river metabolism and decomposition rates. Following adjustment for probability of selection, ecosystem respiration (ER) and gross primary production (GPP) for the target population of order 5–7 non-wadeable rivers averaged −7.3 and 4.8 g O₂ m⁻² d⁻¹, respectively, with average P/R < 1 indicating dominance by heterotrophic processes. Ecosystem respiration was <−3.3 g O₂ m⁻² d⁻¹ for 75% of non-wadeable river length with around 20% of length between −10 and −20 g O₂ m⁻² d⁻¹. Cumulative distribution functions of cotton strength loss estimates indicated a more-or-less linear relationship with river km reflecting an even spread of decay rates (range in k 0.0007–0.2875 d⁻¹) across non-wadeable rivers regionally. A non-linear relationship with land cover was detected for GPP which was typically <5 g O₂ m⁻² d⁻¹ where natural vegetation cover was below 20% and greater than 80% of upstream catchment area. For cotton strength loss, the relationship with land cover was wedge-shaped such that sites with >60% natural cover had low decay rates (<0.02 d⁻¹) with variability below this increasing as natural cover declined. Using published criteria for assessing waterway health based on ER and GPP, 232–298 km (20–29%) of non-wadeable river length was considered to have severely impaired ecosystem functioning, and 436–530 km (42–50%) had no evidence of impact on river metabolism.     

Influence of the fish pond aquaculture effluent discharge on abiotic environmental factors of selected rivers in Northwest Poland

Pollution of rivers caused by human activity is a widely discussed problem, however there is not much attention paid to the changes of water quality that result from the inflow of effluent discharged from fish breeding ponds. The paper presents results of studies on changes of the abiotic parameters (hydrochemical and hydrological) of water observed in the yearly cycle between 2004 and 2008 in selected rivers of Northwest Poland. It was proved that the fastest reaction on the inflow of the effluent discharged from the fish ponds was reflected in changes of biogenic and organic compounds in the river water. The largest, i.e. threefold (rivers Krapiel and Tywa) or even fourfold (rivers Rurzyca and Stepnica) increase in nutrients and organic matter was recorded during the pond effluent discharge into the rivers. At that time values of the organic matter ranged from 8.9 to 18.3 mgO₂/dm³ (BOD₅), the nitrogen compounds from 16.868 to 26.930 mgN/dm³, while the phosphorus from 1.928 to 6.353 mgP/dm³. Interestingly, an additional dry mass of seston was recorded no earlier than the activity of the harmful element had been stopped and the river had resumed to the “initial” state (i.e. before the effluent discharge); that period varied from one to two months, depending on the river characteristics. The highest values of the dry seston mass (580.9 mg/dm³) was recorded in river Krapiel in November 2006. It seems that in spite of remarkable influence on values of individual physical and chemical indices of the river water quality, the effluent discharge from the fish ponds is not a factor hampering the self-purification processes of the rivers.     

Copper and zinc in Elodea canadensis from rivers with various pollution levels

The anthropogenic impact of xenobiotics contributes to environmental risk for the aquatic environment and thus, must be controlled. Elodea canadensis, a cosmopolitan aquatic macrophyte with an important role in the ecology of many littoral zones, may provide an integrated record of pollution. Therefore, it was interesting to investigate the accumulation of Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn in this species and in water and bottom sediments collected from rivers with various levels of contamination. Of these rivers one control and one polluted was selected for the collection of E. canadensis for an experiment to compare the ability of this species to accumulate Cu and Zn. These elements were supplemented at concentrations (mg L⁻¹) of 0.01, 0.02, 0.03, 0.05, 0.08 and 0.14 as CuSO₄·5H₂O, and 0.4, 0.6, 0.9, 1.4, 2.03 and 3.04 as ZnSO₄·7H₂O and in a mixture containing (mg L⁻¹) 0.01Cu + 0.4Zn, 0.02Cu + 0.6Zn, 0.03Cu + 0.9Zn, 0.05Cu + 1.4Zn, 0.08Cu + 2.03Zn and 0.14Cu + 3.04Zn. After the experiment, E. canadensis from the polluted river contained significantly higher Cu and Zn concentrations when applied separately and also significantly higher Cu and Zn concentrations when applied as a mixture compared to the control river. These higher concentrations in E. canadensis from the polluted river were found in all combinations in the experiment. Thus, E. canadensis habituated in polluted sites to the exposure, and long-term influence of elevated metal levels appeared to be better adapted, and it also exhibited a higher increase in biomass than plants from the control river in all the experimental Cu and Zn solutions. Younger leaves of E. canadensis were more resistant to the effects of Cu and Zn than older leaves. Both Cu and Zn negatively affected the cell structure of older leaves, although the influence of Cu on plasma membrane integrity and chloroplast distribution was stronger than that of Zn. The influence of the Cu + Zn mixture on E. canadensis resulted in less pronounced cell disintegration than the influence of Cu added separately.The explanation of differences in the E. canadensis biomass increase and metal concentrations under the binary Cu and Zn impact needs further examination.     

Effects of hydrology and river management on the distribution,abundance and persistence of cyanobacterial blooms in the Murray River,Australia

Major cyanobacterial blooms (biovolume > 4 mm³ L⁻¹) occurred in the main water reservoirs on the upper Murray River, Australia during February and March 2010. Cyanobacterial-infested water was released and contaminated rivers downstream. River flow velocities were sufficiently high that in-stream bloom development was unlikely. The location has a temperate climate but experienced drought in 2010, causing river flows that were well below the long-term median values. This coupled with very low bed gradients meant turbulence was insufficient to destroy the cyanobacteria in-stream. Blooms in the upper 500 km of the Murray and Edward Rivers persisted for 5 weeks, but in the mid and lower Murray blooms were confined to a small package of water that moved progressively downstream for another 650 km. Anabaena circinalis was the dominant species present, confirmed by 16S rRNA gene sequencing, but other potentially toxic species were also present in smaller amounts. Saxitoxin (sxtA), microcystin (mcyE) and cylindrospermopsin (aoaA) biosynthesis genes were also detected, although water sample analysis rarely detected these toxins. River water temperature and nutrient concentrations were optimal for bloom survival. The operational design of weirs and retention times within weir pools, as well as tributary inflows to and diversions from the Murray River all influenced the distribution and persistence of the blooms. Similar flow, water quality and river regulation factors were underlying causes of another bloom in these rivers in 2009. Global climate change is likely to promote future blooms in this and other lowland rivers.     

Enzymatic hydrolysis of organic phosphorus in river bed sediments

Enzymatic hydrolysis of phosphorus (P) in bed sediments is an important process that maintains bioavailable P in the river systems. The P bioavailability is the criterion for assessing the eutrophication potential in rivers and streams. The objective of this research was to determine potential bioavailability of organic P (OP) in the Bronx River bed sediments using native phosphatases (NPase) and phosphodiesterase (PDEase) hydrolysis. The bed sediments collected in summer 2006 and 2007 were incubated at 37 °C for 6 h at pH 7.5 with NPase. The results showed that NPase hydrolyzed a substantial amount of OP (up to 76%) under favorable temperature and pH, indicating OP could be hydrolyzed under increased temperature, and in turn increase in P availability in the river. Similarly, the resulting form sediments incubated with PDEase at 37 °C and pH 8.8 showed that up to 82% of OP could be hydrolyzed. Strong correlations between percentage of OP hydrolyzed by PDEase and organic matter (OM) were observed for sediments collected in 2006 (r = 0.745; p ≤ 0.01) and 2007 (r = 0.724; p ≤ 0.01), indicating PDEase hydrolysable P is mainly associated with OM. It is indicative that local hydro-climatic changes such as temperature increase and pH variations could hydrolyze a substantial amount of OP and increase bioavailable P in the water column, resulting in a potential threat to the river ecosystems.     

Myriophyllum aquaticum as a biomonitor of water heavy metal input related to agricultural activities in the Xanaes River (Córdoba,Argentina)

The aim of the present study was to assess the temporal variation of the heavy metal content (Co, Cu, Fe, Mn, Ni, Pb, and Zn) in surface water and sediments in relation to agricultural practices in the Xanaes River (Córdoba, Argentina). A second objective was to analyze possible relationships between the input of heavy metals on surface water and sediment, heavy metal accumulation and physiological changes in the aquatic plant Myriophyllum aquaticum. Samples were taken from the river at two contrasting sites (between April 2010 and August 2010): (1) a pristine area (mountain site), and (2) an area with intensive agricultural activity located at 60 km down river (agricultural site). The total concentration of heavy metals in surface water was higher in samples collected at the agricultural site but in sediments only the Mn concentration was higher than at the mountain site. The Fe and Mn concentrations in surface water at the agricultural site exceeded the recommended values for Argentinean Legislation of 300 μg L⁻¹ for Fe and 100 μg L⁻¹ for Mn. The accumulations of Zn and Mn in M. aquaticum were higher at the agricultural site and more elevated than the Zn and Mn concentrations in sediments at the same sites and sampling times. At the agricultural site, temporal variations of Cu, Fe and Zn were relatively similar for plants and water column, but the levels of the metals in plants were displaced over time. These results suggest that the levels of pollutants in the river came in pulses from the riverbank. These results show the potential use of M. aquaticum as a suitable accumulation biomonitor at the early stages of heavy metal pollution in rivers.     

Biomonitoring potential of a Caryophyllaeid tapeworm: Evaluation of Adenoscolex oreini infection level and health status in three fish species of the genus Schizothorax across eutrophication and pollution gradients

Endoparasitic infections vary significantly across altered aquatic ecosystems, making these organisms ideal for the biomonitoring of degraded environments. To assess the biomonitoring potential of the Caryophyllaeid tapeworm Adenoscolex oreini and the possible impact of water quality on fish species, a study was carried out in three lakes with marked eutrophication and pollution gradients. The A. oreini infection level in three host fish species of the genus Schizothorax and corresponding fish health status were determined. The pattern of cestode infection varied significantly in the three fish species across the pollution gradient. The prevalence of infection in two fish species (Schizothorax esocinus and S. curvifrons) was significantly greater (P < 0.05) in the eutrophic lake than in the reference lake, whereas in S. niger, the maximum was reached in the hypereutrophic lake. The estimated marginal mean intensity and other infection indices varied significantly (P < 0.05) across the inter- and intra-pollution gradients of lakes. Multivariate statistical analysis results revealed maximum cestode infection in the eutrophic lake. An altered seasonal pattern was observed in the highly stressed lake. The gonadosomatic index (GSI) and condition factor values were significantly greater in fish collected from the reference lake than in those collected from the other lakes. A significant negative relationship between GSI and cestode prevalence was observed in the hypereutrophic lake as compared to least eutrophic lake. These findings indicate that infection indices of the Caryophyllaeid tapeworm and health attributes of fish can act as surrogates for the environmental quality of deteriorated lentic water bodies of the north-western Himalayan region, which is currently undergoing environmental degradation.     

Analysis of spatial and temporal variation in the levels of microbial fecal indicators in the major rivers flowing into the Aegean Sea,Turkey

River watersheds in the western part of Turkey (Aegean Sea) are anthropogenically impacted areas, due to the high population density, intensive agricultural and/or industrial activities. The aim of the present survey was to assess the microbiological quality of river waters using indicators of fecal contamination. Five rivers (Meric, Bakircay, Gediz, Kucuk Menderes and Buyuk Menderes) were sampled as seasonally from 2006 to 2008 for fecal coliforms, and fecal streptococci. In order to determine the number of fecal indicator bacteria, membrane filtration method was used. The minimum fecal coliforms and fecal streptococci were counted from the samples taken from the Buyuk Menderes River (5 × 10¹–3 × 10¹ CFU/100 ml) especially in the spring and autumn. The highest fecal coliform result was obtained in winters (1.3 × 10⁶ CFU/100 ml) while maximum fecal streptococci value was detected in autumns (6.3 × 10⁴ CFU/100 ml) in the Kucuk Menderes River during 2006–2008. Additionally, the relationships between the fecal indicator bacteria and physico-chemical parameters (temperature, conductivity and pH) were also evaluated, but no significant relationships were observed between the fecal indicator bacteria and environmental parameters. Considering the findings of these studies, it can be said that there is fecal pollution in the rivers reaching the Aegean Sea. The results show that there are a great number of microbial pollution sources in the areas where the river passes through and thus, in order to implement strategies to improve water quality in these rivers, monitoring of these rivers should continue.     

Determination of food sources and trophic position in Malaysian tropical highland streams using carbon and nitrogen stable isotopes

Stable isotope analysis has been extensively used as an effective tool in determination of trophic relationship in ecosystems. In freshwater ecosystem, aquatic invertebrates represent main component of a river food web. This study was carried out to determine potential food sources of freshwater organism together with pattern of trophic position along the river food web. In this study, rivers of Belum-Temengor Forest Complex (BTFC) has been selected as sampling site as it is a pristine area that contains high diversity and abundance of organisms and can be a benchmark for other rivers in Malaysia. Stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) were applied to estimate trophic position and food web paradigm. Analysis of stable isotopes based on organic material collected from the study area revealed that the highest δ¹³C value was reported from filamentous algae (? 22.68 ± 0.126⁰/₀₀) and the lowest δ¹³C was in allocthonous leaf packs (? 31.58 ± 0.187⁰/₀₀). Meanwhile the highest δ¹⁵N value was in fish (8.45 ± 0.177⁰/₀₀) and the lowest value of δ¹⁵N was in autochthonous aquatic macrophyte (2.00 ± 1.234⁰/₀₀). Based on the δ¹⁵N results, there are three trophic levels in the study river and it is suggested that the trophic chain begins with organic matter followed by group of insects and ends with fish (organic matter < insects < fish).     

Heavy metal pollution in surface water and sediment: A preliminary assessment of an urban river in a developing country

The concentration and chemical fractionation of globally alarming six heavy metals (Cr, Ni, Cu, As, Cd and Pb) were measured in surface water and sediment of an urban river in Bangladesh. The decreasing trend of metals were observed in water as Cr > Cu > As > Ni > Pb > Cd and in sediment as Cr > Ni > Cu > Pb > As > Cd. The level of studied metals exceeded the safe limits of drinking water, indicated that water from this river is not safe for drinking and/or cooking purposes. However, the investigated metals showed low mobility except for Cd and Pb which could pose a severe threat to the aquatic environment. Contamination factor (CF) and geoaccumulation index (I_geo) demonstrated that most of the sediment samples were moderately to heavily contaminated by Cr, As, Cd and Pb. The pollution load index (PLI) values were above one (>1) indicates progressive deterioration of the sediment quality. The extent of pollution by heavy metals in the river Korotoa implies that the condition is much frightening to the biota and inhabitants in the vicinity of the river as well.     

Tetracycline-resistant bacteria as indicators of antimicrobial resistance in protected waters—The example of the Drwęca River Nature Reserve (Poland)

The objective of this study was to determine the suitability of Tet^R tetracycline-resistant bacteria as potential indicators of drug resistance, a parameter of the microbiological quality of river waters in natural reserves which are threatened by man-made pollution. The microbiological assays covered a 15-km long section of the upper reach of the Drw?ca River (Poland), a part of the European Ecological “Natura 2000” Network of nature protected areas. The quality of the investigated ecosystem was affected by surface runoffs from the river's agricultural catchment as well as outflows from three fish farms. The counts of Tet^R bacteria, incubated at 14 °C and 28 °C on TSA medium with sheep blood and tetracycline, were determined in river water samples. The highest counts of both bacterial groups were determined in samples collected from sites behind fish farms. A statistical analysis of the abundance of Tet^R14 °C and Tet^R28 °C bacteria revealed significant differences in the size of Tet^R28 °C populations at the studied sampling sites (p = 0.0011), which is why hemolytic bacteria of this group (HemTet^R28 °C) were selected for further investigations. The predominant strains in the group of 86 HemTet^R28 °C isolates obtained by 16S rRNA gene sequencing were Pseudomonas fluorescens (42 isolates) and Aeromonas hydrophila (28 isolates). Analyses of the identified HemTet^R28 °C strains demonstrated MIC ≥256 μg/ml in more than 50% isolates. The MAR index of HemTet^R28 °C was in the range of 0.67 at the control site to 1 at sites behind fish farms. The results suggest that tetracycline-resistant bacteria, in particular HemTet^R28 °C, are a reliable indicator of antimicrobial resistance and the microbial quality of surface waters polluted due to human activity. The above can be attributed to several factors: (I) the highest percentage share of HemTet^R28 °C among HPC28 °C was noted at sites behind fish farms, (II) tetracycline-resistant bacteria quickly respond to environmental changes, as demonstrated by the high level of resistance to tetracycline and a very high MAR index, and (III) genera/species that are easy to culture under laboratory conditions dominate in the qualitative and quantitative composition of the studied bacteria.     

A framework to assess the health of rocky reefs linking geomorphology,community assemblage,and fish biomass

The recovery of historic community assemblages on reefs is a primary objective for the management of marine ecosystems. Working under the overall hypothesis that, as fishing pressure increases, the abundance in upper trophic levels decreases followed by intermediate levels, we develop an index that characterizes the comparative health of rocky reefs. Using underwater visual transects to sample rocky reefs in the Gulf of California, Mexico, we sampled 147 reefs across 1200 km to test this reef health index (IRH). Five-indicators described 88% of the variation among the reefs along this fishing-intensity gradient: the biomass of piscivores and carnivores were positively associated with reef health; while the relative abundances of zooplanktivores, sea stars, and sea urchins, were negatively correlated with degraded reefs health. The average size of commercial macro-invertebrates and the absolute fish biomass increased significantly with increasing values of the IRH. Higher total fish biomass was found on reefs with complex geomorphology compared to reefs with simple geomorphology (r² = 0.14, F = 44.05, P < 0.0001) and the trophic biomass pyramid also changed, which supports the evidence of the inversion of biomass pyramids along the gradient of reefs’ health. Our findings introduce a novel approach to classify the health of rocky reefs under different fishing regimes and therefore resultant community structures. Additionally, our IRH provides insight regarding the potential gains in total fish biomass that may result from the conservation and protection of reefs with more complex geomorphology.     

Excessive nitrogen and phosphorus in European rivers: 2000–2050

Rivers export nutrients to coastal waters. Excess nutrient export may result in harmful algal blooms and hypoxia, affecting biodiversity, fisheries, and recreation. The purpose of this study is to quantify for European rivers (1) the extent to which N and P loads exceed levels that minimize the risk of harmful algal blooms and (2) the relative shares of sources of N and P in rivers. This may help to identify effective management strategies to reduce coastal eutrophication. We focus on 48 rivers in 27 countries of the European Union (EU27). We used the Global Nutrient Export from Watersheds (NEWS) model to analyze nutrient export by rivers and the associated potentials for coastal eutrophication as reflected by Indicator for Coastal Eutrophication Potential (ICEP). In 2000, 38 of the 48 EU rivers indicated in our study had an ICEP > 0, indicating a relatively high potential for harmful algal blooms. These 38 rivers cover 60% of EU27 land area. Between 2000 and 2050 nutrient export by European rivers is projected to decrease. However, by 2050 still 34 EU rivers, covering 48% of the land area, have an ICEP > 0. This indicates that in these scenarios little progress is made in terms of environmental improvement. About one-third of the rivers with ICEP > 0 are N limited, and about two-thirds P limited. In N-limited rivers reducing N loads is a more effective way to reduce the risk for coastal eutrophication than reducing P, and vice versa. For N-limited rivers agriculture or sewage are the dominant sources of nutrients in river water. In P-limited rivers, sewage is found to be the dominant source of P, except for rivers draining into the Atlantic Ocean, where agriculture can also be dominant. A basin-specific approach is needed to effectively reduce N and P loads.     

The effects of feeding on the swimming performance and metabolic response of juvenile southern catfish,Silurus meridionalis,acclimated at different temperatures

To test whether the effects of feeding on swimming performance vary with acclimation temperature in juvenile southern catfish (Silurus meridionalis), we investigated the specific dynamic action (SDA) and swimming performance of fasting and feeding fish at acclimation temperatures of 15, 21, 27, and 33 °C. Feeding had no effect on the critical swimming speeding (U_crit) of fish acclimated at 15 °C (p = 0.66), whereas it elicited a 12.04, 18.70, and 20.98% decrease in U_crit for fish acclimated at 21, 27 and 33 °C, respectively (p < 0.05). Both the maximal postprandial oxygen consumption rate (VO_2peak) and the active metabolic rate (VO_2active, maximal aerobic sustainable metabolic rate of fasting fish) increased significantly with temperature (p < 0.05). The postprandial maximum oxygen consumption rates during swimming (VO_2max) were higher than the VO_2active of fasting fish at all temperature groups (p < 0.05). The VO_2max increased with increasing temperature, but the relative residual metabolic scope (VO_2max? VO_2peak) during swimming decreased with increasing in temperature. The present study showed that the impairment of postprandial swimming performance increased with increasing temperature due to the unparalleled changes in the catfish's central cardio-respiratory, peripheral digestive and locomotory capacities. The different metabolic strategies of juvenile southern catfish at different temperatures may relate to changes in oxygen demand, imbalances in ion fluxes and dissolved oxygen levels with changes in temperature.     

Growth performance and starch utilization in common carp (Cyprinus carpio L.) in response to dietary chromium chloride supplementation

A nutrition trial was conducted on juvenile common carp (Cyprinus carpio), initial mean body weight 15 ± 0.4 g within a controlled facility at 25 ± 0.5 °C. Six diets containing various levels of supplementary Cr (0, 0.2, 0.5, 1.0, 1.5, and 2.0) mg Cr/kg of diet as Cr chloride hexahydrate were fed to carp for a period of 10 weeks. Lower growth performance was observed in fish fed on the control diet and the diet supplemented with the highest level of Cr (2.0 mg Cr/kg). Although fish fed 0.5 mg Cr/kg showed the best growth performance, this was not significantly different (P > 0.05) from fish fed 1.0 mg Cr/kg. The regression of plasma glucose concentration was linear (R² = 0.97 and P value = 0.001) as the Cr content of the diet increased (up to 1.5 mg Cr/kg).Cr carcass content was elevated with an increasing level of dietary Cr supplementation up to 1.5 mg Cr/kg; but fish fed on the diet supplemented with the highest level of Cr (2.0 mg Cr/kg) showed a decrease in Cr carcass content.Histological examination to evaluate the impact of different Cr supplementation on liver and gut tissues showed notable changes. The higher level of Cr (2.0 mg Cr/kg) in the diet gave rise to elevated hepatocyte vacuolization and changes in gut tissue morphology.It appeared that Cr chloride significantly improved growth within a defined range (0.2–1.5) mg Cr/kg without any negative impact, while 2.0 mg Cr/kg in carp diet seems to be the threshold for the initiation of toxicity.     

Relationships of hydrology and life-history strategies on the spatio-temporal habitat utilisation of fish in European temperate river floodplains

Floodplain inundation is considered as crucial for the recruitment of fish in lowland rivers, by either providing suitable spawning areas as well as breeding habitats for young-of-the-year fish (YOY), as well as for supporting species that exhibit different life history-strategies in order to be differently adapted to long term discharge patterns. Fish communities in a set of 38 waterbodies on the Lower Rhine floodplain, representing different long-term frequencies of inundation and differently affected by seasonal inundations, were sampled by means of electro fishing (point abundance sampling, total n = 42,701 points) over a four-year period in order to identify species-specific and life-history strategy related patterns of spatio-temporal floodplain habitat utilisation. For 18 species (total catch: n = 107,150), typically occurring in European lowland rivers and representing different ecological guilds, different responses towards seasonal inundations were found. YOY of most species closely associated to the periodic strategy (e.g., Abramis brama, Aspius aspius, Blicca bjoerkna) were highly abundant in frequently inundated waterbodies, provided these were subject to inundations occurring in spring and early summer and coincided with temperatures required for spawning. However, recruitment in these species was impaired or failed when no inundations in this time frame occurred, although adults were present. In contrast, most species associated to the opportunistic strategy (e.g., Gasterosteus aculeatus, Pseudorasbora parva, Leucaspius delineatus) had highest recruitment in waterbodies unaffected by inundations in this time frame, which had detrimental effects on these predominantly small sized species. Spatio-temporal floodplain habitat utilisation of YOY fish (most rheophilic species as well as eurytopics) is suggested to be size-related, since most fast growing periodic strategists left the floodplain at given connectivity at latest in winter and were then absent in the subsequent year. Smaller YOY fishes and all opportunistic species either remained in more isolated waterbodies, or dispersed from there across the floodplain to some degree during extensive winter floods. These findings suggest adaptations to the long-term hydrograph of large river systems, with flood-related recruitment patterns predominantly occurring in periodic strategists and low-flow recruitment strategies in opportunistic strategists and stagnophilic species. The results of this study point to the significance of hydrological transversal floodplain gradients that provide diverse communities and population maintenance of different life-history strategies, evidencing that fish communities within the floodplain act as indicators for the hydrological conditions.     

Alternative alert system for Ganga river eutrophication using alkaline phosphatase as a level determinant

Short-term variations in phosphorus (P) concentrations must be considered while assessing the long-term changes in trophic status and estimating the P load and export. Furthermore, given the challenges of conventional monitoring of river systems, a sediment-specific biomonitoring tool may be more successful inferring P related human controls. In this study, conducted along a 37 km river channel representing up-and downstream urban control, and through a trajectory from a major point source (Assi drain), we tested the patterns of concordance between alkaline phosphatase (AP) activity and soluble reactive-P (SRP) and between AP activity and trophic status in the Ganga River. To validate data comparison, we selected a reference site at Dev Prayag, situated ∼1130 km upstream to the main study stretch. Samples were collected for three consecutive year (March 2013 to February 2016) with respect to atmospheric deposition, surface runoff, point source loading, river water and sediment analysis. For trajectory analysis, samples were collected from 15 locations starting from the drain outlet (zero distance) upto 1.5 km downstream with sampling location 100 m away from the preceding one. We found marked spatial and temporal variations in P concentrations which could be traced by quantifying the AP activity. The AP activity, recorded highest at reference site, declined with increases in P; and at drain mouth it was close to zero reflecting strong influence of P level on alkaline phosphatase activity in the river. We used canonical correlation analysis (CCorA) to test the degrees of concordance and similarity in different variables. Most of the environmental variables and indicators of eutrophy appear largely clustered at one side of the coordinate separating AP activity and dissolved oxygen towards opposite side of the axis. The dynamic fit function relating AP activity with different variables showed significant positive correlation with DO (R² = 0.67; p < 0.001) and negative correlations with BOD (R² = 0.82; p < 0.001), Chl a biomass (R² = 0.52; p < 0.001) and trophic status index (R² = 0.54 (Chl a), 0.96 (DRP); p < 0.001). Furthermore, the enzyme activity did not show significant negative correlation with heavy metals in sediment. Because anthropogenic activities continue to enhance P loads; AP is inhibited directly by P availability; and eutrophy feedbacks sediment P release, our observations on P-AP activity relationship provide a valuable alternative means for detecting P related controls on water quality, trophic status and biogeochemical feedbacks in human impacted rivers.     

Saxitoxin monitoring in three species of Florida puffer fish

Beginning in April 2002, three species of Florida puffer fish from around the state of Florida, USA were monitored for the presence of saxitoxin (STX). In total, 873 southern (Sphoeroides nephelus), 171 checkered (S. testudineus), and 53 bandtail (S. spengleri) puffer fish were collected between 2002 and 2006 from eight regions: Jacksonville, the Indian River Lagoon, Tequesta, the Florida Keys, Charlotte Harbor, Tampa Bay, Cedar Key, and Apalachicola. Emphasis was placed on collecting specimens from the Indian River Lagoon (IRL), where recreational harvesting of puffer fish led to 28 cases of saxitoxin puffer fish poisoning (SPFP) between January 2002 and May 2004. Southern puffer fish from the northern IRL routinely contained the highest concentrations of STX, with average levels in the skin of 1787 μg STXequiv./100 g tissue. Elevated concentrations were also found in the muscle (1102 μg STXequiv./100 g), gut contents (539 μg STXequiv./100 g), gonads (654 μg STXequiv./100 g), and liver (214 μg STXequiv./100 g). Lower, yet significant (above the action limit of 80 μg STXequiv./100 g tissue), concentrations of STX were also detected in the skin (599 μg STXequiv./100 g), muscle (233 μg STXequiv./100 g), gut contents (197 μg STXequiv./100 g), and gonads (239 μg STXequiv./100 g) of southern puffer fish from Tequesta in the southern IRL, as well as in the gonads (122 μg STXequiv./100 g) of Jacksonville southern puffer fish and the skin (265 μg STXequiv./100 g) of Tampa Bay southern puffer fish. STX concentrations above the action limit were also found in the skin of bandtail puffer fish from the IRL (620 μg STXequiv./100 g), Tequesta (374 μg STXequiv./100 g), and the Florida Keys (230 μg STXequiv./100 g). Checkered puffer fish collected from the IRL, Tequesta, and the Florida Keys on average were nontoxic, containing STX levels below the action limit in all tissues.     

Support vector machines to model presence/absence of Alburnus alburnus alborella (Teleostea,Cyprinidae) in North-Western Italy: Comparison with other machine learning techniques

Alburnus alburnus alborella is a fish species native to northern Italy. It has suffered a very sharp decrease in population over the last 20 years due to human impact. Therefore, it was selected for reintroduction projects. In this research project, support vector machines (SVM) were tested as possible tools for building reliable models of presence/absence of the species. A system of 198 sites located along the rivers of Piedmont in North-Western Italy was investigated. At each site, 19 physical-chemical and environmental variables were measured. We verified that performances did not improve after feature selection but, instead, they slightly decreased (from Correctly Classified Instances [CCI] = 84.34 and Cohen's k [k] = 0.69 to CCI = 82.81 and k = 0.66). However, feature selection is crucial in identifying the relevant features for the presence/absence of the species. We then compared SVMs performances with decision trees (DTs) and artificial neural networks (ANNs) built using the same dataset. SVMs outperformed DTs (CCI = 81.39 and k = 0.63) but not ANNs (CCI = 83.03 and k = 0.66), showing that SVMs and ANNs are the best performing models, proving that their application in freshwater management is more promising than traditional and other machine-learning techniques.     

Characterization of the toxicity of Cochlodinium polykrikoides isolates from Northeast US estuaries to finfish and shellfish

Harmful algal blooms caused by Cochlodinium polykrikoides are annual occurrences in coastal systems around the world. In New York (NY), USA, estuaries, bloom densities range from 10³ to 10⁵ mL^?1 with higher densities (≥10⁴ cells mL^?1) being acutely toxic to multiple fish and shellfish species. Here, we report on the toxicity of C. polykrikoides strains recently isolated from New York and Massachusetts (USA) estuaries to juvenile fish (Cyprinodon variegates) and bay scallops (Argopecten irradians), as well as on potential mechanisms of toxicity. Cultures of C. polykrikoides exhibited dramatically more potent ichthyotoxicity than raw bloom water with 100% fish mortality occurring within ～1 h at densities as low as 3.3 × 10² cells mL^?1. More potent toxicity in culture was also observed in bioassays using juvenile bay scallops, which experienced 100% mortality during 3 days exposure to cultures at cell densities an order of magnitude lower than raw bloom water (～3 × 10³ cells mL^?1). The toxic activity per C. polykrikoides cell was dependent on the growth stages of cultures with early exponential growth cultures being more potent than cultures in late-exponential or stationary phases. The ichthyotoxicity of cultures was also dependent on both cell density and fish size, as a hyperbolic relationship between the death time of fish and the ratio of algal cell density to length of fish was found (～10³ cells mL^?1 cm^?1 yielded 100% fish mortality in 24 h). Simultaneous exposure of fish to C. polykrikoides and a second algal species (Rhodomonas salina or Prorocentrum minimum) increased survival time of fish, and decreased the fish mortality suggesting additional cellular biomass mitigated the ichthyotoxicity. Frozen and thawed-, sonicated-, or heat-killed-, C. polykrikoides cultures did not cause fish mortality. In contrast, cell-free culture medium connected to an active culture through a 5 μm nylon membrane caused complete mortality in fish, although the time required to kill fish was significantly longer than direct exposure to the whole culture. These results indicate that ichthyotoxicity of C. polykrikoides isolates is dependent on viability of cells and that direct physical contact between fish and cells is not required to cause mortality. The ability of the enzymes peroxidase and catalase to significantly reduce the toxicity of live cultures and the inability of hydrogen peroxide to mimic the ichthyotoxicity of C. polykrikoides isolates suggests that the toxicity could be caused by non-hydrogen peroxide, highly reactive, labile toxins such as ROS-like chemicals.