A moving target—incorporating knowledge of the spatial ecology of fish into the assessment and management of freshwater fish populations

Freshwater fish move vertically and horizontally through the aquatic landscape for a variety of reasons, such as to find and exploit patchy resources or to locate essential habitats (e.g., for spawning). Inherent challenges exist with the assessment of fish populations because they are moving targets. We submit that quantifying and describing the spatial ecology of fish and their habitat is an important component of freshwater fishery assessment and management. With a growing number of tools available for studying the spatial ecology of fishes (e.g., telemetry, population genetics, hydroacoustics, otolith microchemistry, stable isotope analysis), new knowledge can now be generated and incorporated into biological assessment and fishery management. For example, knowing when, where, and how to deploy assessment gears is essential to inform, refine, or calibrate assessment protocols. Such information is also useful for quantifying or avoiding bycatch of imperiled species. Knowledge of habitat connectivity and usage can identify critically important migration corridors and habitats and can be used to improve our understanding of variables that influence spatial structuring of fish populations. Similarly, demographic processes are partly driven by the behavior of fish and mediated by environmental drivers. Information on these processes is critical to the development and application of realistic population dynamics models. Collectively, biological assessment, when informed by knowledge of spatial ecology, can provide managers with the ability to understand how and when fish and their habitats may be exposed to different threats. Naturally, this knowledge helps to better evaluate or develop strategies to protect the long-term viability of fishery production. Failure to understand the spatial ecology of fishes and to incorporate spatiotemporal data can bias population assessments and forecasts and potentially lead to ineffective or counterproductive management actions.     

Influence of natural dissolved organic carbon on the bioavailability of mercury to a freshwater alga

Bioavailability of mercury (Hg) to Selenastrum capricornutum was assessed in bioassays containing field-collected freshwater of varying dissolved organic carbon (DOC) concentrations. Bioconcentration factor (BCF) was measured using stable isotopes of methylmercury (MeHg) and inorganic Hg(II). BCFs for MeHg in low-DOC lake water were significantly larger than those in mixtures of lake water and high-DOC river water. The BCF for MeHg in rainwater (lowest DOC) was the largest of any treatment. Rainwater and lake water also had larger BCFs for Hg(II) than river water. Moreover, in freshwater collected from several US and Canadian field sites, BCFs for Hg(II) and MeHg were low when DOC concentrations were >5mg L(-1). These results suggest high concentrations of DOC inhibit bioavailability, while low concentrations may provide optimal conditions for algal uptake of Hg. However, variability of BCFs at low DOC indicates that DOC composition or other ligands may determine site-specific bioavailability of Hg.     

Adsorption of chloridazon from aqueous solution on modified kerolite-rich materials

The adsorption of chloridazon (5-amine-4-chloro-2-phenylpyridazin-3(2H)-one) on kerolite samples heated at 110 degrees C (K-110), 200 degrees C (K-200), 400 degrees C (K-400), 600 degrees C (K-600) and acid-treated with H(2)SO(4) solutions of two different concentrations (0.25 and 0.5 M) (K-0.25 and K-0.5, respectively) from pure water at 25 degrees C has been studied by using batch and column experiments. The adsorption experimental data points were fitted to the Freundlich equation in order to calculate the adsorption capacities (K(f)) of the samples; K(f) values ranged from 184.7 mg kg(-1) (K-0.5) up to 2253 mg kg(-1) (K-600). This indicated that the heat treatment given to the kerolite greatly increases its adsorption capacity for the herbicide whereas the acid treatment produces a clear decrease in the amount of chloridazon adsorbed. The removal efficiency (R) was also calculated; R values ranging from 52.8% (K-0.5) up to 88.3% (K-600). Thus, the results showed that the 600 degrees C heat-treated kerolite was more effective in relation to adsorption of chloridazon and it might be reasonably used in removing this herbicide from water.     

Correlates of mercury in fish from lakes near Clyde Forks, Ontario, Canada

Subsurface soils near Clyde Forks, Ontario, Canada, can have naturally high concentrations of mercury (Hg) from local geological sources. To investigate Hg in local aquatic food webs, Hg was measured in fish dorsal muscle (mainly yellow perch [YP] and pumpkinseed sunfish [PS]) and surface sediments from 10 regional lakes. Water chemistry, along with fork length, weight, and stable isotopes (delta15N, delta13C, delta34S) in fish were also measured. No lake sediments had elevated (>0.3microg/g dw) Hg, and average Hg concentrations in fish were not sufficiently high (<1microg/g dw) to be of concern for fish-eating wildlife. Variance in fish Hg was best explained by dietary carbon source (delta13C), and certain lake variables (e.g., pH for YP). PS with more pelagic feeding habits had higher delta34S and Hg than those with more littoral feeding habits. Potential biological linkages between fish Hg and delta34S, a parameter that may be related to the lake sulphate-reducing bacteria activity, requires further investigation.     

Neurotoxic effect and metabolic responses induced by a mixture of six pesticides on the earthworm Aporrectodea caliginosa nocturna

The effects of a mixture of insecticides and/or fungicides at different environmental concentrations were investigated on a Aporrectodea caliginosa nocturna population. This laboratory experiment was carried out in order to reproduce Gaillac (France) vineyard conditions. Neurotoxicity (cholinesterase), metabolisation (glutathione-S-transferase) and oxidative stress (catalase) enzymes were studied as biomarkers in earthworms after short-term exposure in terraria. The aim was to observe the global effects of pesticide exposure, as in a vineyard, rather than focus on each isolated biomarker variation, or on each compound's impact. ChE activity was inhibited after a few days of insecticide and/or fungicide exposure, indicative of a neurotoxic effect in earthworms. The significant increase in GST and CAT activities revealed the metabolisation of these products resulting in the production of reactive oxygen species. After a long period of exposure or high concentrations, earthworms were physiologically damaged: they could not cope with the high toxicity (cellular dysfunction, protein catabolism...). Chemical analysis showed that pesticide bioaccumulation in earthworm tissues, even in those exposed to the highest concentrations and for the longest periods, was very low (under LOD) or absent. However, the study of pesticide residues in terraria after 34 days in a climate chamber suggested that earthworms participate in soil pesticide breakdown.     

Humic substances

GOAL, SCOPE AND BACKGROUND: Freshwater bodies which chemistry is dominated by dissolved humic substances (HS) seem to be the major type on Earth, due to huge non-calcareous geological formations in the Northern Hemisphere and in the tropics. Based on the paradigm of the inertness of being organic, direct interactions of dissolved HS with freshwater organisms are mostly neglected. However, dissolved organic carbon, the majority of which being HS, are natural environmental chemicals and should therefore directly interact with organisms. Major results that widened our perspective on humic substance ecology come from experiments with the compost nematode, Caenorhabditis elegans, which behaved contradictorily to textbook knowledge and provoked an in-depth re-consideration of some paradigms. APPROACH: To overcome old paradigms on HS and their potential interactions with organisms, we reviewed recent international literature, as well as 'grey' literature. We also include results from own ongoing studies. RESULTS: This review focuses on direct interactions of dissolved HS with freshwater organisms and disregards indirect effects, such as under-water light quenching. Instead we show with some macrophyte and algal species that HS adversely interfere with photosynthesis and growth, whereby closely related algal species show different response patterns. In addition to this, HS suppress cyanobacteria more than eukaryotic algae. Quinones in the HS appear to be the effective structure. Furthermore, HS can modulate the offspring numbers in the nematode C. elegans and cause feminization of fish and amphibians--they possess hormone-like properties. The ecological consequences of this potential remain obscure at present. HS also have the potential to act as chemical attractants as shown with C. elegans and exert a mild chemical stress upon aquatic organisms in many ways: induction of molecular chaperons (stress proteins), induction and modulation of biotransformation and anti-oxidant enzymes. Furthermore, they produce an oxidative stress with lipidperoxidation as one clear symptom or even stress defense strategy. Stronger chemical stresses by HS may even lead to teratogenic effects as shown with fish embryos; all physiological responses to HS-mediated stress require energy, which were compensated on the expense of yolk as shown with zebra fish embryos. One Finnish field survey supports the view of a strong chemical stress, as the weight yield in fish species decreases with increasing HS content in the lakes. DISCUSSION: HS exert a variety of stress symptoms in aquatic and compost organisms. According to current paradigms of ecotoxicology, these symptoms have to be considered adverse, because their compensation consumes energy which is deducted from the main metabolism. However, the nematode C. elegans looks actively for such stressful environments, and this behavior is only understandable in the light of new paradigms of aging mechanisms, particularly the Green Theory of Aging. In this respect, we discuss the mild HS-mediated stress to aquatic and compost organisms. New empirical findings with HS themselves and HS building blocks appear to be consistent with this emerging paradigm and show that the individual lifespan may be expanded. At present the ecological consequences of these findings remain obscure. However, a multiple-stress resistance may be acquired which improves the individual fitness in a fluctuating environment. CONCLUSIONS: It appears that dissolved HS have to be considered abiotic ecological driving forces, somewhat less obvious than temperature, nutrients, or light. PERSPECTIVES: The understanding of the ecological control by dissolved humic substances is still fragmentary and needs to be studied in more details.     

An enzyme-linked immunosorbent assay for the determination of dioxins in contaminated sediment and soil samples

A 96-microwell enzyme-linked immunosorbent assay (ELISA) method was evaluated to determine PCDDs/PCDFs in sediment and soil samples from an EPA Superfund site. Samples were prepared and analyzed by both the ELISA and a gas chromatography/high resolution mass spectrometry (GC/HRMS) method. Comparable method precision, accuracy, and detection level (8 ng kg(-1)) were achieved by the ELISA method with respect to GC/HRMS. However, the extraction and cleanup method developed for the ELISA requires refinement for the soil type that yielded a waxy residue after sample processing. Four types of statistical analyses (Pearson correlation coefficient, paired t-test, nonparametric tests, and McNemar's test of association) were performed to determine whether the two methods produced statistically different results. The log-transformed ELISA-derived 2,3,7,8-tetrachlorodibenzo-p-dioxin values and log-transformed GC/HRMS-derived TEQ values were significantly correlated (r=0.79) at the 0.05 level. The median difference in values between ELISA and GC/HRMS was not significant at the 0.05 level. Low false negative and false positive rates (<10%) were observed for the ELISA when compared to the GC/HRMS at 1,000 ng TEQ kg(-1). The findings suggest that immunochemical technology could be a complementary monitoring tool for determining concentrations at the 1,000 ng TEQ kg(-1) action level for contaminated sediment and soil. The ELISA could also be used in an analytical triage approach to screen and rank samples prior to instrumental analysis.     

Changes in sewage sludge carbon forms along a treatment stream

The behaviour and fate of macronutrients and pollutants in sewage sludge applied to the land are affected by the chemical composition of the sludge organic matter, which in turn is influenced by both sewage source and by sewage treatment processes. In this study, (13)C nuclear magnetic resonance (NMR) spectroscopy was used to characterise the organic matter of sludges collected at three different points along the treatment stream of a municipal sewage works with a domestic catchment. Sludge at the first point, an undigested liquid (UL) sludge, had a substantially different composition to the anaerobically digested (AD) and dewatered sludge cake (DC) materials, which were similar to each other. In particular, the UL sludge contained more alkyl C than the AD or DC sludges. All three sludges were found to contain mobile alkyl C that is poorly observed using the cross polarisation (CP) technique, necessitating the use of the less sensitive, but more quantitatively reliable direct polarisation (DP) technique to obtain accurate distributions of C types.     

Empirical and simulated critical loads for nitrogen deposition in California mixed conifer forests

Empirical critical loads (CL) for N deposition were determined from changes in epiphytic lichen communities, elevated NO(3)(-) leaching in streamwater, and reduced fine root biomass in ponderosa pine (Pinus ponderosa Dougl. ex Laws.) at sites with varying N deposition. The CL for lichen community impacts of 3.1kg ha(-1) year(-1) is expected to protect all components of the forest ecosystem from the adverse effects of N deposition. Much of the western Sierra Nevada is above the lichen-based CL, showing significant changes in lichen indicator groups. The empirical N deposition threshold and that simulated by the DayCent model for enhanced NO(3)(-)leaching were 17kg N ha(-1) year(-1). DayCent estimated that elevated NO(3)(-) leaching in the San Bernardino Mountains began in the late 1950s. Critical values for litter C:N (34.1), ponderosa pine foliar N (1.1%), and N concentrations (1.0%) in the lichen Letharia vulpina ((L.) Hue) are indicative of CL exceedance.     

Influence of Na2S on the degradation kinetics of CCl4 in the presence of very pure iron

This paper presents the results of kinetic studies to investigate the effect of FeS film formation on the degradation rate of CCl(4) by 99.99% pure metallic iron. The film was formed by submersing metallic iron grains in an oxygen free HCO(3)(-)/CO(3)(2-) electrolyte solution. When the grains had reached a quasi steady-state value of the corrosion potential, Na(2)S((aq)) was injected. Upon injection, a microm thick poorly crystalline FeS film formed immediately on the iron surface. Over time, the iron became strongly corroded and both the FeS film and the metallic iron grains began to crack leading to exposure of bare metallic iron to the solution. The effect of the surface film on the degradation rate of CCl(4) was investigated following four periods of aging, 1, 10, 30, and 60 days. Relative to the controls, the 1-day sulfide-aged iron showed a substantial decrease in rate of degradation of CCl(4.) However, over time, the rate of degradation increased and surpassed the degradation rate obtained in the controls. It has been proposed that CCl(4) is reduced to HCCl(3) by metallic iron by electron transfer. The FeS film is substantially less conducting than the bulk iron metal or non-stoichiometric magnetite and from the results of this study, greatly decreases the rate of CCl(4) degradation relative to iron that has not been exposed to Na(2)S. However, continued aging of the FeS film results in breakdown and stress-induced cracking of the film, followed by dissolution and cracking of the iron itself. The cracking of the bulk iron is believed to be a consequence of hydrogen embrittlement, which is promoted by sulfide. The increase in CCl(4) degradation rate, as the FeS films age, suggests that the process of hydrogen cracking increases the surface area available for charge transfer.