Abstract: For a short-lived organism, such as a freshwater zooplankter, the ways of coping with years of local recruitment failure are either to disperse between habitats and recolonise or to disperse in time through diapause. Diapause is common among freshwater zooplankton and is generally seen as a way to escape periods of harsh environmental conditions. The egg-bank or pool of diapausing copepodites in lake sediments resulting from the production of diapausing stages has several implications for zooplankton ecology, genetics, and evolution which we outline in this review. The presence of a benthic dormant stage also creates a coupling between the benthic habitat and the pelagic, and we argue that zooplankton phenology is a result of selective forces in both habitats. The spatial distribution of diapausing eggs appears to be governed by random resuspension dynamics coupled with higher hatching rates in shallow waters. For diapausing copepodites, however, an active choice of where and how deep to enter the sediment may affect their distribution. In a reanalysis of published data, we found a size-dependent bathymetric distribution and vertical distribution in the sediment of diapausing cyclopoid copepodites. Our review of published laboratory studies showed that predictors of seasonal change such as photoperiod and temperature were the only type of cues used for the termination of diapause. We also found a relation between generation length and the type of cue used for diapause induction: copepods mainly used seasonal cues from the abiota, rotifers mainly used cues from the biotic environment, and cladocerans used a mix of both types. We describe patterns in emergence timing and contribution to population dynamics from studies using in situ estimation of emergence, and conclude that hatching from dormant stages may qualitatively and quantitatively affect zooplankton population dynamics and seasonal succession.

Abstract: An overview of different characterization methods and the possibilities for describing structural elements of humic substances from aqueous environments (HS, or refractory organic substances (ROS)) is given within this review. The application of different analytical methods for the qualitative and quantitative characterization of HS, including physical/chemical analysis (elemental analysis, acid/base titration), spectroscopic methods (UV/VIS, NMR, fluorescence, mass spectrometry), fractionation methods (gel chromatography, flow-field-flow-fractionation), and degradation methods (oxidation, pyrolysis, hydrolysis) are discussed. The paper focuses on the most commonly used chemical, spectroscopic and chromatographic methods used in the last few years. Aspects concerning information related to newer procedures are considered. Case studies representing results gained from reference samples isolated from brown water and wastewater effluents are given to cross-check results gained from several methods. The influence of different isolation procedures on the specific character of the fractions is also discussed.

Abstract: The watersheds in which we live are comprised of a complex set of physical and social systems that interact over a range of spatial and temporal scales. These systems are continually evolving in response to changing climatic patterns, land use practices and the increasing intervention of humans. Management of these watersheds benefits from the development and application of models that offer a comprehensive and integrated view of these complex systems and the demands placed upon them. The utility of these models is greatly enhanced if they are developed in a participatory process that incorporates the views and knowledge of relevant stakeholders. System dynamics provides a unique mathematical framework for integrating the physical and social processes important to watershed management, and for providing an interactive interface for engaging the public. We have employed system dynamics modeling to assist in community-based water planning for a three-county region in north-central New Mexico. The planning region is centered on a ~165-km reach of the Rio Grande that includes the greater Albuquerque metropolitan area. The challenge, which is common to other arid/semi-arid environments, is to balance a highly variable water supply among the demands posed by urban development, irrigated agriculture, river/reservoir evaporation and riparian/in-stream uses. A description of the model and the planning process are given along with results and perspectives drawn from both.

Abstract: Nitrate (NO3 –) and soluble reactive phosphorus (SRP), the two major dissolved N and P species available to aquatic biota, respond differently to varying water discharge rates (Q) in agricultural drainage pipes and rivers (Fig. 1): SRP concentrations are positively related to Q, whereas NO3 – concentrations decrease with increasing discharge rates. In addition, NO3-N concentrations exceed (in mass units) SRP concentrations up to 700-fold even though the liquid manure applied to agricultural fields has a N:P ratio equal to only about 5. Preferential flow of rainwater across the soil column and different affinities of the two nutrients for the soil matrix explain these differences in behaviour and mobility: i. Concentrations of substances that have a high sorption affinity for the soil matrix (such as SRP) tend to increase in drainage pipes and streams as water discharge increases. ii. Concentrations of species that are not retarded by sorption processes (such as NO3 –) and, hence, do not accumulate in the topsoil, tend to be negatively related to discharge rate. Differences in the availability and pool size of NO3 – and SRP in the topsoil explain the different hysteresis patterns if NO3 – and SRP concentrations are plotted versus the corresponding discharge rate during precipitation events (Fig. 2).

Abstract: Societal needs for power generation, water management/use, and land uses (e.g., urban and agricultural) have often resulted in a significant departure from the natural processes of hydrologic regimes and material transport and deposition throughout most of the rivers flowing through arid and semi-arid landscapes of the western USA. We examine the compromised ecosystem integrity of one such river, the upper Snake River in eastern Idaho, below a large irrigation and power dam that has altered hydrologic regimes and reduced channel sediment supply. We review the ecological structure and function of gravel-bed rivers as they vary across a hierarchy of landscape scales with different spatial and temporal dimensions. Major linkages within the large, alluvial river systems of the western USA include exchange of water and materials along longitudinal connections from streams to rivers, lateral connections between river and floodplain systems, and vertical surface and subsurface (hyporheic) water exchanges. Longitudinal linkages dominate confined (canyon) river reaches while unconfined (floodplain) reaches show strong affinities for lateral and vertical exchange. Hydrogeomorphic processes, driven by river power and cut and fill alluviation, produce a dynamic landscape in floodplain reaches, which we refer to as a Shifting Habitat Mosaic (SHM). The SHM fosters high physical and ecological diversity of habitats, biotic communities, and ecosystem complexity. In this case study, we examine the dynamics of a series of floodplains along a 90 km river landscape, employing an airborne spectrophotometer, producing georeferenced hyperspectral imagery, coupled with ground truth measures of river hydraulics, river depth, riparian vegetation and other surface characteristics. From these data we derived estimates of the hydraulics and hydrographic regimes necessary to mobilize channel and riparian sediments, thus reestablishing the dynamics of the river SHM. We also evaluated subsequent variation in aquatic and riparian habitat characteristics. Evaluation of these factors, which affect interactions between the river channel and the surrounding river–riparian corridor, permitted us to develop a restoration strategy focused on normative variation among the various physical and biotic processes contributing to ecosystem integrity.

Abstract: Water loss from stream ecosystems has profound effects on primary producers. The small body of literature on algal responses to desiccation has emphasized mechanisms of resistance to desiccation, recovery of metabolic activity upon rewetting, and small spatial scales. Unfortunately, small-scale patterns are difficult to interpret because of the high degree of variability in both hydrologic patterns of drying and ecological processes within individual drainage basins. Consequently, effects of drying are best examined at larger spatial scales because variation that appears random at smaller scales become incorporated into larger, more predictable patterns across an entire catchment. We present a conceptual model of the effects of water loss on primary producers applicable to the scale of the entire catchment. This perspective describes differences in susceptibility to water loss, and differential rates of decline and recovery in primary production as a function of location within the catchment. Future considerations of drying on ecosystem attributes such as primary production will be facilitated by treating streams as patchy, interconnected landscapes in space and time and recognizing spatially explicit effects of disturbance. It is likely that streams of different regions vary widely in terms of the occurrence of drought, the geophysical template, and response variables (types of organisms present and their collective metabolism). The challenge in drought research today is to determine what phenomena are general and of widespread application and which are peculiar to given regions.

Abstract: Association of benzo[a]pyrene (BaP), pyrene, 3,3′,4,4′-tetrachlorobiphenyl (TCB) and 2,2′,4,4′-tetrabromo diphenyl ether (TBDE) with natural dissolved organic matter (DOM) was studied. The DOM samples were previously collected from natural waters at five Nordic sites during fall 1999 and spring 2000, isolated by the reverse osmosis method, and thoroughly characterized. The purpose was to determine the essential characteristics that predict the sorption capacity of DOM for hydrophobic contaminants. DOM isolates were dissolved in artificial freshwater to give a dissolved organic carbon concentration of 15 mg L–1. Partition coefficients (K DOC) of the model compounds between water and DOM were measured by the equilibrium dialysis method. Further, the bioavailability of BaP and pyrene to Daphnia magna was tested in the presence of DOM with various qualities. A strong negative correlation was found for the K DOC values of BaP (R = –0.922) and pyrene (R = –0.929) with spectral absorbency ratio (A254/A400), while the correlation (R = –0.760) was weaker for the K DOC values of TCB. The K DOC values for TCB correlated (R = 0.849) strongly with specific visible absorbency (A600/TOC), while the K DOC values for TBDE correlated (R = –0.739) with relative fluorescence emission. Generally, bioavailability of BaP and pyrene to D. magna reflected the measured association of the compounds with DOM. The data emphasize the importance of aromaticity of DOM, estimated by simple spectroscopic methods, in predicting sorption capacity for polycyclic aromatic hydrocarbons. The situation with halogenated compounds still remains unclear.

Abstract: The objective of this study was to extract and evaluate key catchment characteristics explaining the main variation in properties of dissolved natural organic matter (DNOM) in surface waters draining each catchment. A number of classical and sophisticated DNOM characterisation methodologies were used for this purpose. The explanatory capability of site characteristics on the variation in descriptors of DNOM, including elemental analysis (EA), DOC fractionation, SEC, CZE, CGE, UV/Vis- and FTIR spectra, FES, TLS, ESR, ESI/MS, 13C-CPMAS-NMR, potentiometric pH titration as well as functional characteristics such as biodegradability, and the response of macrophyte and PAH partitioning coefficients were evaluated. The sampling sites were all natural, coniferous, heathery-forested catchments with bogs, forming a climatic, anthropogenic deposition and proportional biotope cover gradient. Correlations to the main principal components, as well as a correlation matrix, singled out total S-deposition as the key explanatory site parameter, accounting for most of the variation in DNOM descriptors. Other significant factors were H+ concentration, length of growing season, biotope coverage (i.e., peatland/ or lake/watershed ratio), site elevation and TOC concentration. Total sulphur (S) deposition was strongly negatively correlated to the molecular weight, aromaticity, carboxylic acidity and sorption capacity of PAH. A greater proportion of lake and Histosol biotopes of the sampling sites were reflected in a greater aliphatic character of the DNOM. PCA clustering of samples from the same site in spring and fall showed a basic site-specific DNOM quality and a weak season effect. The Hasse diagram technique (a method of partial order theory) was used to show, for instance, how the relative Histosol coverage may determine NOM quality and, in turn, how this coincides with high macrophyte response.

Abstract: The McMurdo Dry Valleys of Antarctica contain many permanently ice-covered lakes that support populations of algae and bacteria in the water column. In these lakes the concentration of dissolved organic carbon (DOC) is typically greatest at depth. In Lake Fryxell, the DOC concentration is 25 mg C/L at 18 m and 5 mg C/L at 5 m, just below the ice-cover. Dissolved humic substances account for about 20–24% of the DOC in the lake water. The DOC sources to the photic zone of this lake are streamflow, extracellular release by phytoplankton and benthic algal mats and upward diffusion across the oxycline at 9.5 m. Experiments with fulvic acids isolated from four depths show that these humic substances have the capacity to act as electron acceptors in the anoxic degradation of acetate by an iron-and humic-reducing microorganism. We used fluorescence spectroscopy to characterize the abundance and redox state of the quinone functional groups in the oxidized and reduced fulvic acids in these experiments and in filtered whole water samples from the lake. The fluorescence intensity of fulvic acid was greater in the oxycline and bottomwaters than in the photic zone. This result suggests that incorporation of quinone functional groups into humic substances may be enhanced in zones of high bacterial activity. Statistical analysis of the excitation emission matrices (EEMs) was used to evaluate trends in the fulvic acid redox state with depth. The results indicate that fulvic acid in the upper photic zone was in an oxidized state and that fulvic acid in the bottomwaters was in a reduced state. The shift in the EEMs indicating a more reduced state occurred in the vicinity of the oxycline (8 to 11 m). The shift in the EEMs began in the zone from 8 and 9 m, where dissolved oxygen concentrations range from to 5 and 10 mg L–1, suggesting that fulvic acid was oxidized upon upward diffusion from the oxycline. This oxidation may be an abiotic process in which reduced humic substances interact with ferric iron generated in this zone.

Abstract: This study shows the response of Nannochloropsis gaditana, a marine nannoplanktonic species, exposed to UV radiation for 7 days. PAR, UV-A and UV-B ratios used were within the range likely to be observed in nature, a photoperiod of 12L:12D was maintained, and light irradiances were modified daily to promote cell acclimation. Growth, pigment content, internal nitrogen and carbon content, and photochemical efficiency using PAM fluorometry were assessed in nutrient replete cultures. Cell size, autofluorescence and cell permeability were analysed by flow cytometry. Results showed a cessation of growth after day 3 and a progressive decrease was observed in Fv/Fm values in cultures exposed to UV-B (plus UV-A and PAR). Flow cytometry analysis also demonstrated an increase in membrane permeability caused by UV-B damage. Cells that showed an increase in membrane permeability also exhibited a proportional decrease in cellular nitrogen content. The results support the conclusion that UV-B radiation can affect N. gaditana nitrogen incorporation mechanisms by direct damage or indirectly by damage to membrane structure and to the photosynthetic apparatus with resulting effects on energy and reductant demand. In contrast, the presence of UV-A radiation was beneficial to cells exposed to PAR plus UV-A when compared to those exposed to only-PAR from day 4. This response resulted in cells with a higher nitrogen content and without changes in membrane permeability.

Abstract: This paper reviews the public and scientific debates over the risks and benefits of aquaculture and aquatic biotechnology worldwide, and in the United States in particular. The basic argument is that business tends to respond to uncertainty with innovation in management and technology. Technological evolution in the fish business is therefore interpreted as a continuous response to new environmental and socioeconomic uncertainties and subsequent regulation. The use of aquatic biotechnology in fish breeding is just the latest technological response, but also the most controversial. Growth-enhanced transgenic salmon may become the first bioengineered animal product approved for use as food in the United States. The fish may boost future salmon harvests, contribute to productivity increases in aquaculture and lower consumer prices for salmon. But it also faces public opposition, reluctant investors and scientific skepticism due to mainly environmental concerns. The paper argues that even though the regulatory framework in the United States is well-elaborated, it may not be able to reassure public opposition once transgenic salmon should be approved as a ‘new animal drug’. Analogous to genetically modified food crops, the consumer market rather than regulation will determine the ultimate fate of transgenic fish.

Abstract: Water from lakes and tundra ponds on Banks, Melville, Ellef-Ringnes, Ellesmere and Devon Island (74–79°N, 82–116°W) in the Canadian high Arctic was studied in batch culture experiments to test whether nitrogen, phosphorus or organic carbon limited bacterial growth and biomass accumulation. Water samples containing indigenous bacteria were amended with carbon (glucose), nitrogen (nitrate) or phosphorus (phosphate), either alone or in combination, and were incubated in the dark at ambient temperatures. Bacterial growth was measured as the rate of protein synthesis and the accumulation of bacterial cells. Bacterial growth was significantly enhanced in all cultures amended with phosphorus. There was no indication of primary carbon or nitrogen limitation in either lakes or ponds, but the combined addition of phosphorus and either carbon, nitrogen or both, had a positive effect on bacterial growth in the lakes but not in ponds. This contrasting response in Arctic lakes and ponds can be predicted from in situ concentrations of dissolved nutrients: total dissolved phosphorus was low in all systems (= 10 μg L−1), whereas total dissolved nitrogen and organic carbon was on average 24 and 7 times higher in ponds. Pelagic bacteria in lakes and ponds of the high Arctic seem to follow the general pattern of phosphorus limitation previously observed in many temperate and tropical freshwater systems.

Abstract: Fluorescence techniques have been used to identify humic substances, (e.g. aquatic fulvic acids from different origins). Synchronous scans have proven adequate for distinguishing detail and differentiating samples. As well, fluorescence has often been used to probe humic interactions with metals and xenobiotic organics. In this study, the fluorescence of a well-characterized material, Laurentian fulvic acid (LFA) was compared with that of a simple hydroquinone/quinone (H2Q/Q) model system. Synchronous fluorescence (room T) and laser-excited fluorescence experiments at 10°K were carried out to characterize the fluorophore. The synchronous fluorescence behavior of LFA displayed similarities to that of an equilibrated, aerated, H2Q/Q system, but only at higher pH. (Higher pH favours a shift of the redox equilibrium towards quinone.) In contrast, the spectra of LFA suggest the role of “quinone” groups, even at lower pH. A significant feature of these spectra is a lowest energy band. At low temperature this band was more selectively excited at 470 nm, but vibrationally resolved line narrowed spectra were not observed. Fluorescence lifetimes were very short compared to the laser pulse width of ca. 10 ns. Under the low T condition the spectra of LFA and the model are essentially identical. We suggest that the principal luminophore in LFA is a quinone-hydroquinone type, perhaps a charge transfer complex consistent with the absence of the fluorescence line-narrowing phenomenon. The spectra imply a lowest energy component of LFA emission from a fluorophore very similar to that of the simplest H2Q/Q. The significant similarities of the model system to LFA are underscored by striking parallels in the radicals in the two systems seen in well-resolved electron paramagnetic resonance (EPR) spectra that could be obtained at pH = 6.

Abstract: To gain insight into the non-equilibrium processes that affect the titration curves of bacteria, we performed pH stat experiments with suspensions of live cells of the Gram-negative bacterium Shewanella putrefaciens. The experiments lasted for 5 hours, during which acid or base addition was monitored. Periodically, the electrophoretic mobility of the cells, as well as the buffer capacity and the concentrations of cations and dissolved organic carbon (DOC) of the solution, were measured. At the end of the experiments, the viability of the cells was determined. In a limited number of cases, final solutions were screened for the presence of cell-wall constituents using gel electrophoresis. The results showed a very different behavior of the cell suspensions under acid and alkaline conditions. At pH 4, acid addition ceased after 20 minutes. The cells remained intact but were no longer viable at the end of the experiment, while little change in the buffer capacity of the solution was observed. The data at pH 4 were consistent with protonation of cell wall functional groups. At pH 8 and 10, base addition continued during the entire duration of the experiments. The cells remained viable, and the buffer capacity and DOC concentration of the solutions increased with time. Gel electrophoresis indicated that proteins and lipopolysaccharides had been released to solution at pH 10. In contrast to pH 4, the buffering capacity of the bacterial cells under alkaline conditions did not appear to be limited by the initial availability of ionisable functional groups in the cell wall. This preliminary study shows that a complex set of processes, including active metabolic responses, control the acid-base activity of live cell suspensions.

Abstract: Aquatic resources management has become increasingly challenging as human demands on water supplies compete with the needs of natural ecosystems, particularly in arid lands. A wide range of factors, both natural and human, influence aquatic environments, but an important underlying component is climate variability. Instrumental records of hydroclimatic variability from precipitation, streamflow, and snowpack are limited to 100 years or less in most areas of the western U.S., and are too short to provide more than a subset of the full range of natural climate variability. Paleoclimatic proxy data from a variety of sources can be used to extend instrumental records of climate back centuries to tens of thousands of years and longer. In this review, four drought events over the past three millennia, each documented with a number of proxy records, illustrate natural hydroclimatic variability characteristics over the western U.S. Although a small sample of paleoclimate data, these four events exemplify the wide range of natural hydroclimatic variability over space and time. Climate is now, and will continue to be, impacted by human activities, but natural climatic variability will likely be an important underlying factor in future climate variability and change.

Abstract: Pomatoschistus microps (Teleostei, Gobiidae) intensively uses the mesohaline marsh of Westerschelde estuary as a nursery and foraging ground The sampling campaign covered the semi-lunar, diel and tidal cycles The density of P microps and potential hyperbenthic prey species in the marsh creek, fullness index, evacuation rates and daily ration of common goby were calculated Mesopodopsis slabberi, Neomysis integer and Corophium volutator were the most dominant prey items in terms of biomass Numerically, copepods dominated the diet Migrating fish enter the marsh creek with a relatively empty stomach and leave the marsh with a higher stomach content Pomatoschistus microps seemed to feed more intensively during the day than the night, however the influence of the diel cycle is inferior in comparison with the tidal influence on the feeding behaviour of the common goby A significant difference in foraging activity occurred between the spring and neap tide The common goby migrated in lower abundance into the creek during spring tide but foraged more intensively At both spring and neap tide, a significant difference was found in the fullness index between day and night At spring tide, gobies feed more during the day, while they forage more intensively at night at neap tide All the three cycles (tidal, diel and semi-lunar) influenced the feeding rhythm of the common goby The tidal influence is superior over the diel variation, while the explanation of the combined effect of diel and semi-lunar cycle needs further studies

Abstract: Solubility of heavy metals in soils is one of the main parameters causing their transfer into the hydrosphere and into the biosphere. It is thus important to understand its mechanisms in order to improve the current methodologies of risk assessment. Leaching tests were performed to investigate the solubility of Cd, Pb and Zn in 458 contaminated agricultural soils sampled around two smelters in Northern France. Distilled water and acetic acid were used consecutively to characterize two strengths of heavy metal extractability.

Abstract: Many aquatic species have become endangered because of the elimination and fragmentation of their habitat, human alteration of the environment, and introduced species. New applications and insights from genetic studies of endangered species are being used to formulate management plans to prevent extinction of endangered taxa. Here we discuss three applications of genetic techniques to the conservation of endangered aquatic species in the desert Southwest, USA. First, we discuss estimation of long-term effective population size in three endangered big-river fishes, bonytail chub (Gila elegans), humpback chub (G. cypha) and razorback suckers (Xyrauchen texanus), of the lower Colorado River. For all three species, the current census number is much smaller than the estimated effective population size in which these species evolved. Second, we discuss the determination of species, ESUs, and MUs in the endangered Sonoran topminnow. Molecular genetic data show that the Gila and Yaqui topminnows are different species. Experimental examination of pre-mating and post-mating reproductive isolation demonstrates that some reproductive isolation has already developed between these two species. Finally, springsnails (Pyrgulopsis) of the lower Colorado River basin exist only in remote and isolated springs. Examination of molecular variation generally supports the morphological designation of 16 different species, although a few species have several ESUs. There does not appear to be a correlation of genetic and geographic distance between species, suggesting that they are quite old. These genetic studies provide insight into the conservation of these rare aquatic species. Although mitigating ecological factors may be most significant in preventing extinction, genetic studies can provide the evolutionary context for endangered species and identify what units are most in need of conservation.

Abstract: Retention of ferrous iron at the interface between ground- and surface water is crucial for the acidity balance of lakes influenced by acid mine drainage. Iron budgets were developed for two sediments in areas of differential groundwater inflow (ca. 1 and 10 L m–2 d–1). In both areas iron was sedimented as schwertmannite (Fe8O8(OH)x(SO4)y , 8 – x = 2y, 1,0 < x < 1,75) at rates of 5.5–5.9 mmol m–2 d–1 leading to iron(III) enriched sediments (3.9–6.2 mmol g–1 dry weight). Compared to the surface water, the inflowing groundwater had higher pH (4.5 vs. 3), ferrous iron (6–20 mmol L–1 vs. 0.8–2.0 mmol L–1) and sulfate (5–60 mmol L–1 vs. 8–13 mmol L–1) concentrations. The inflow of the groundwater caused a change in sediment pore water chemistry and an increase in pH to above 5.5. The pH increase was probably mostly due to decreased transformation rates of schwertmannite to goethite (0.27 mmol m–2 d–1 vs. 5.6 mmol m–2 d–1), also decreasing the production of H+ in the sediment. Compared to the control, in the area with groundwater inflow solid phase iron sulfide (0.011 mmol m–2 d–1vs. 0.0019 mmol m–2 d–1) and carbonate were formed at a higher rate, and more sulfate was reduced in incubation experiments. This finding can be explained by saturation indexes of siderite and by sulfate reduction becoming thermodynamically more competitive by about 40 kJ eq–1 compared to iron reduction. However, only a small fraction of the reduced ferrous iron and sulfide was retained in the sediment, emphasizing the importance of re-oxidation processes. The study demonstrates the existence of biogeochemical patterns in lake sediments due to variations in hydrologic boundary conditions in the adjacent aquifer.

Abstract: Replacement of riparian vegetation by pasture has occurred worldwide and is predicted to have strong effects on macroinvertebrate community structure and function in streams, but this has rarely been examined. In this study, leaf processing and macroinvertebrate community structure were examined in a single stream using experimental leaf-packs and surveys of natural leaf-packs. Two sites in each of three land use categories were selected to represent reaches in forest, pasture and forest-pasture boundary regions. In two experiments using tethered leaf-packs, no differences were found in mean leaf breakdown between land use types. However, shredding invertebrates were absent from the pasture sites, so leaf breakdown in pasture resulted from chemical, physical and microbial processes only. Amounts of fine particulate organic matter in experimental leaf-packs were higher in pasture reaches than the forest and boundary reaches but did not influence leaf breakdown. Macroinvertebrate species richness did not differ between land uses. A predictive model developed for species richness and total abundance enabled direct comparison of assemblages on experimental packs to natural leaf-packs. In the forest reach and at the forest-pasture boundary, macroinvertebrate species richness and total abundance increased proportionally with the number of leaves within a pack, but this relationship was not observed in the pasture reach. Pasture land use on Skenes Creek was therefore associated with weakened relationships between allochthonous inputs and macroinvertebrate communities, but this did not alter leaf breakdown.

Abstract: The effect of temperature and viscosity on the ingestion rate of Daphnia galeata and Chydorus sphaericus was investigated in short-term feeding experiments with 3H-labelled Scenedesmus quadricauda. Viscosity was manipulated independently from temperature by addition of inert polymers in two experiments. In the first experiment, the ingestion rate of D. galeata was found to be 50% lower at 10°C than at 25°C due to the combined effects of increased viscosity and lower temperature. Viscosity alone accounted for 61% of the decline in ingestion rate. In the second experiment, the ingestion rate of a different clone of D. galeata was 46–53% lower at 10°C than at 20°C and changes in viscosity alone accounted for most (>92%) of that decline. The ingestion rate of C. sphaericus was 80% lower at 10°C than at 20°C, and viscosity accounted for 65% of that decline. Thus, viscosity plays an important role in determining the ingestion rate of crustacean zooplankton. Adaptations to life in waters that undergo considerable variation in temperature and viscosity may therefore influence energy budgets and may eventually be of importance for zooplankton species succession, distribution and evolution.

Abstract: Riparian corridors of eastern Oregon and Washington, like those in other regions, comprise small portions of river drainages but provide disproportionately important ecosystem functions. However, most riparian and fluvial (streams and rivers) systems have been greatly altered. Degraded ecosystems commonly reflect influences of land-uses (e. g., mining, logging, road construction, fire suppression, livestock grazing), hydro-developments (e.g., dams, irrigation, flood control) and other human actions. Some important consequences include: degradation and fragmentation of habitats, changes in riparian plant associations, isolated fish populations, and altered flow and sediment regimes. This synthesis paper evaluates some major environmental factors that can influence the sustainability of riparian corridors and fluvial systems along lowland-arid to mountain gradients within river drainages of eastern Oregon and Washington. Four tributary rivers of the Columbia River, the Grande Ronde and John Day Rivers in northeastern Oregon, and the Yakima and Methow Rivers on the eastside of the Cascade Mountains in Washington, provide perspectives on environmental conditions. Factors evaluated include: a) dominant riparian plant associations and distributions in relation to differences in precipitation and temperature regimes along elevation gradients; b) ecological and physiochemical functions of riparian and fluvial systems along elevation gradients; c) long-term historical and contemporary cumulative impacts of human actions; and d) management provisions that could restore and sustain ecosystem functions. Ecological functions of riparian and fluvial systems are viewed as being closely coupled because of their dependence on hydrological (surface and sub-surface) and sediment routing regimes. From a river landscape perspective, achieving greater connectivity can be a key objective for analyzing and integrating the management of riparian and fluvial ecosystems. Effective management should include ensuring the delineation of major limiting factors (e.g., erosion, water shortages and temperatures) and identification of streamside and channel networks that link critical habitats at multiple landscape scales (e. g., locations and spacing of refuge habitats for fish and wildlife). Management actions should encourage the connectivity of reaches and habitats and maintenance of riparian and fluvial functions so interactions can occur. Efforts should include renewal of natural flood and sediment routing regimes and the reestablishment of habitats adjacent to ecologically intact habitats.

Abstract: The concentration, composition, and photochemical changes of dissolved organic matter (DOM) were evaluated in surface and bottom layers, and surface and subsurface tributaries of Plesne Lake, Bohemian Forest, Czech Republic, during one hydrological year. DOM was fractionated using the Amberlite XAD-8 and ion exchange resins into five fractions: hydrophilic neutrals, hydrophilic acids, hydrophilic and hydrophobic bases, hydrophobic acids, and hydrophobic neutrals. Photochemical transformations of DOM by photosynthetically active radiation (PAR) were tested with in-situ experiments using water from the surface tributary. The fraction composition of DOM was dominated by hydrophobic acids in all samples, with annual averages of 54–58% of DOM. The surface tributary differed from the subsurface one in higher and lower percentages of hydrophobic neutrals and hydrophilic neutrals, respectively. The surface and bottom water of the lake did not significantly differ in the composition of DOM fractions despite significantly higher DOM concentrations at the bottom. The results of in-situ photochemical experiments showed the significance of PAR in photochemical as well as biological transformations of allochthonous DOM in this lake. The net rates of photo-production of DIC and photochemical plus biological degradation of DOC ranged from 0.3 to 0.6 and 0.6 to 4.3 μmol L–1 day–1, respectively, with maximum values in late spring. The hydrophobic acids fraction and the remaining DOM fractions were decomposed biologically (in dark bottles) and by combined photochemical and biological degradation (in transparent bottles) at similar rates, resulting in unchanged fraction composition of DOM in the experiments.

Abstract: This paper demonstrates the applicability of high-performance size exclusion chromatography (HPSEC) to characterize lake-sediment pore-water dissolved organic matter (DOM). Two shallow nonstratified Estonian lakes – Harku and Karujarv – were investigated. The HPSEC results for pore waters were compared with those obtained by spectroscopic methods such as fluorescence spectroscopy and UV-absorption, and with other analyses carried out on sediments (sediment composition, C/N and H/C ratios). The average molecular weight values for UV absorbing DOM were close to pore waters of the studied lakes, not exceeding 5000 for weight- and 3000 for average-number, respectively. Low MW size fractions (<1000) dominated in Lake Harku pore waters, while the opposite was recorded in Lake Karujarv pore waters. Besides the traditional paleolimnological methods, the method used (HPSEC) seems to be promising in detailed sediment pore water characterization.

Abstract: Vertical profiles of soluble and particulate nutrients were analyzed at the end of summer stratification in two dimictic lakes located in northeast Germany In addition, irradiance and plankton biomass were determined The concentrations of particulate organic carbon and phytoplankton biomass in the epilimnion were higher in Lake Tiefer than in Lake Dudinghausen, even though the apparent trophic status of Lake Tiefer was higher than Lake Dudinghausen In Lake Dudinghausen, phototrophic sulfur bacteria accumulated in the hypolimnion between 8 and 10 m, whereas in Lake Tiefer low light penetration prevented the development of phototrophic bacteria in those horizons in which sulfide might be present Because both lakes have anoxic hypolimnia, we assumed that in both cases phosphorus was released from the sediment into the hypolimnion In Lake Tiefer, redox conditions and the presence of nitrate and nitrite limited the water depth range in which P-release occurred In Lake Dudinghausen, part of the released soluble reactive phosphorus was incorporated into the phototrophic sulfur bacteria biomass and thus transformed to particulate phosphorus As much as 70% of the particulate phosphorus in the hypolimnion was found in the phototrophic sulfur bacterial layer, with 15–20% of this particulate phosphorus consisting of polyphosphate storage compounds The low ratio of soluble reactive phosphorus to particulate phosphorus in the hypolimnion was, therefore, attributed to phototrophic sulfur bacteria The phototrophic sulfur bacteria appear to act as an internal nutrient filter and convert soluble reactive phosphorus into particulate phosphorus

Abstract: The Fuhrberger Feld aquifer in northern Germany provides the majority of water supply for the city of Hannover. Although parts of the recharge area have received a strong intake of nitrate from agricultural activities during the past 40 years, the extracted raw waters show little sign of nitrate contamination due to microbial nitrate reduction coupled with iron sulfide oxidation in the aquifer. Accordingly, iron and sulfate concentrations, in particular, are temporarily objectively high. To evaluate the contribution of quantitatively important processes to the development of raw water quality, all relevant natural and anthropogenic induced processes were identified, quantified and stepwise integrated in a reactive controlled material flux model using PhreeqC. Comparing measured and modeled data, long-term trends in raw water quality could be retraced. As a result, anthropogenic initiated processes such as varying nitrate influxes, conversion of wet grasslands into arable land coupled with geochemical processes (biomass degradation, oxidation of iron monosulfides in hydromorphic soils) and a partial nitrate breakthrough to the wells due to local complete consumption of iron disulfides were responsible for observed quality changes.

Abstract: Watershed management in Mexico is generally carried out based on hydrological information, whereas water quality data are mainly used in the control of wastewater discharges and water uses. Information on toxic contaminants is scarce and expensive to gather. A method was developed to predict inorganic contaminant concentration in Lake Chapala, Mexico, by using hydrological data for water balance, water quality information and analyses, sediment quality monitoring data, and applying a chemical equilibrium model to estimate the possibility of increase in cadmium concentration. It is shown that decreasing water levels in Lake Chapala can lead to a significant increase in dissolved cadmium that, in the future, may affect the lake ecosystem and the water quality for different uses. Watershed managers can use this method with one by van Afferden and Hansen (2004) as an early warning system to reduce the risk that contaminant concentrations increase in the lake.

Abstract: Strategies for protecting and restoring riparian and stream ecosystems commonly encounter uncertainties about natural processes and management practices that contribute to environmental disturbances. Improvements in management plans require landscape approaches that account for the explicit spatial distribution and variability of different land cover types that can contribute to unstable conditions. We use a spatially explicit procedure to determine erosion-risk indices and variable riparian buffer widths in watersheds. The indices are based on land cover types that can contribute to erosion either alone or collectively. Land cover information (e.g., unstable soils, immature forest stands, roads, critical slope for land failure and rain-on-snow areas) was used to estimate erosion-risk indices. Erosion-risk indices increase with greater co-occurrences of contributing land covers. The procedure was used to identify erosion-prone areas in tributary watersheds of the Beckler-Rapid River drainage (260 km2), in the State of Washington, USA. A regression analysis of the relationship between mean sediment inputs to streams and erosion-risk indices of sixteen different watersheds indicated that erosion-risk indices explained 65% of the variation associated with sediment inputs to channels. Landscape maps of erosion-risk categories, based on ranges of erosion-risk indices, allowed spatially explicit definitions of stream reach lengths susceptible to different levels of erosion. Low to high-risk categories, and reach lengths vulnerable to erosion, also permitted the identification of the distribution of channels requiring protection by variable riparian buffers widths. The applicability of the procedure to other landscapes was demonstrated by estimating erosion risk-indices and variable riparian buffer widths for watersheds in the upper Cedar River drainage near Seattle, Washington. This approach allows watershed managers to use existing records and published information to address environmental problems within highly variable landscapes.

Abstract: One-summer-old whitefish were released into three small lakes: a circumneutral lake (mean water pH 6.09, Ca2+ 0.06 mmol l-1 and total aluminium 11 μg l-1) and a moderately acidic lake (pH 5.17, Ca2+ 0.05 mmol l-1 and Altot 36 μg l-1), both with abundant perch and earlier introduced whitefish, and a highly acidified lake (pH 4.53, Ca2+ 0.03 mmol l-1 and Altot 145 μg l-1) with a sparse perch population. Three years later, when the released whitefish were expected to become sexually mature, whitefish were sampled from the lakes near the spawning time to evaluate their reproductive and physiological status. In the circumneutral lake, 72% of the captured whitefish were mature, while in the moderately acidic lake all seven captured fish were immature. Among the 27 captured whitefish in the highly acidified lake, all except one were mature. However, the ovaries of two of the 11 females (18%) contained a high proportion of atretic oocytes, and only 54% of the males had running milt compared with 94% in the circumneutral lake. This deterioration of gonadal maturation had probably resulted from physiological stress caused by the high Al and low Ca2+ concentration in the acidic water, which also appeared as a disturbed ion balance, an increased blood glucose and haemoconcentration, and a low length increment in relation to the weight increase. Apart from the imbalance in the length and weight increase, the results of the present study are consistent with those from laboratory experiments. By interfering with whitefish physiology, the acidification of freshwater lakes may also impair their reproduction.