Showing papers in "Aquatic Sciences in 2015"

A global boom in hydropower dam construction

Abstract: Human population growth, economic development, climate change, and the need to close the electricity access gap have stimulated the search for new sources of renewable energy. In response to this need, major new initiatives in hydropower development are now under way. At least 3,700 major dams, each with a capacity of more than 1 MW, are either planned or under construction, primarily in countries with emerging economies. These dams are predicted to increase the present global hydroelectricity capacity by 73 % to about 1,700 GW. Even such a dramatic expansion in hydropower capacity will be insufficient to compensate for the increasing electricity demand. Furthermore, it will only partially close the electricity gap, may not substantially reduce greenhouse gas emission (carbon dioxide and methane), and may not erase interdependencies and social conflicts. At the same time, it is certain to reduce the number of our planet’s remaining free-flowing large rivers by about 21 %. Clearly, there is an urgent need to evaluate and to mitigate the social, economic, and ecological ramifications of the current boom in global dam construction.

Extreme daily loads: role in annual phosphorus input to a north temperate lake

Abstract: Changes in fertilizer use, manure management or precipitation may alter the frequency of episodes of high nutrient runoff and thereby affect annual nutrient loads and total nutrient concentrations of lakes. We developed an empirical, stochastic model for daily P loads and used the model to project annual P loads and summer total P concentrations in Lake Mendota, Wisconsin, USA. Daily P loads (8,250 daily observations) were fit closely by a three-part gamma distribution composed of days with low, intermediate, and high P loads. High P load days happen when heavy rains or snowmelt occur on soil with abundant P, often as a result of manure or inorganic fertilizer application. In Lake Mendota, on average 29 days per year accounted for 74 % of the annual load. Simulations showed that median annual P loads increased linearly with the frequency of high P load days. However, the upper quantiles of the annual P load distribution increased more steeply than the median. Increases in the number of high P load days per year also increased summer concentrations of P in the lake. Thus increases in the frequency of high P load days due to larger precipitation events or increased application of fertilizers and manure may worsen widespread problems caused by P pollution of lakes in this agricultural watershed.

Distribution and incidence of algal blooms in Lake Taihu

Abstract: Harmful algal blooms depend on several factors linked to climate and catchment conditions. Blooms can show significant daily, monthly, seasonal, inter-annual variability as well as horizontal variation in a lake. In the present study, we use satellite data to explore the sensitivity of different sections of a large eutrophic lake (Lake Taihu) to climate and catchment-related drivers. Bloom coverage in the larger open areas of the lake, historically less eutrophic, has increased over the last 12 years even though extensive efforts were made to improve catchment conditions. Decadal trends in these lake sections were more sensitive to climate conditions and nutrient concentrations compared with the more enclosed eutrophic bays. Bloom coverage was bimodal during the year, with regional differences occurring during the second maximum. Links between climate variability, nutrients, and bloom coverage suggest that major bloom events are likely to continue to occur.

A simple procedure for the assessment of hydropeaking flow alterations applied to several European streams

Abstract: Release of water from storage hydropower plants generates rapid flow and stage fluctuations (hydropeaking) in the receiving water bodies at a variety of sub-daily time-scales. In this paper we present an approach to quantify such variations, which is easy to apply, requires stream flow data at a readily available resolution, and allows for the comparison of hydropeaking flow alteration amongst several gauged stations. Hydropeaking flow alteration is quantified by adopting a rigorous statistical approach and using two indicators related to flow magnitude and rate of change. We utilised a comprehensive stream-flow dataset of 105 gauging stations from Italy, Switzerland and Norway to develop our method. Firstly, we used a GIS approach to objectively assign the stations to one of two groups: gauges with an upstream water release from hydropower plants (peaked group) and without upstream releases (unpeaked group). Secondly, we used the datasets of the unpeaked group to calculate one threshold for each of the two indicators. Thresholds defined three different classes: absent or low pressure, medium, and high pressure, and all stations were classified according to these pressure levels. Thirdly, we showed that the thresholds can change, depending on the country dataset, the year chosen for the analysis, the number of gauging stations, and the temporal resolution of the dataset, but the outcome of the classification remains the same. Hence, the classification method we propose can be considered very robust since it is almost insensitive to the hydropeaking thresholds variability. Therefore, the method is broadly applicable to procedures for the evaluation of flow regime alterations and classification of river hydromorphological quality, and may help to guide river restoration actions.

Predation and competition effects on the size diversity of aquatic communities

Abstract: Body size has been widely recognised as a key factor determining community structure in ecosystems. We analysed size diversity patterns of phytoplankton, zooplankton and fish assemblages in 13 data sets from freshwater and marine sites with the aim to assess whether there is a general trend in the effect of predation and resource competition on body size distribution across a wide range of aquatic ecosystems. We used size diversity as a measure of the shape of size distribution. Size diversity was computed based on the Shannon-Wiener diversity expression, adapted to a continuous variable, i.e. as body size. Our results show that greater predation pressure was associated with reduced size diversity of prey at all trophic levels. In contrast, competition effects depended on the trophic level considered. At upper trophic levels (zooplankton and fish), size distributions were more diverse when potential resource availability was low, suggesting that competitive interactions for resources promote diversification of aquatic communities by size. This pattern was not found for phytoplankton size distributions where size diversity mostly increased with low zooplankton grazing and increasing nutrient availability. Relationships we found were weak, indicating that predation and competition are not the only determinants of size distribution. Our results suggest that predation pressure leads to accumulation of organisms in the less predated sizes, while resource competition tends to favour a wider size distribution.

Cyclonic circulation and upwelling in Lake Baikal

Abstract: We investigated upwelling events in the pelagic area of Lake Baikal that developed during summer stratification (July–November) using a combination of in situ and satellite observations. These upwellings appear in the centres of local cyclonic macrovortices with compensatory downwelling located on their periphery in coastal areas. The average duration of upwelling events was 5 weeks, with an observed maximum of 16 weeks. The most stable upwellings in Southern Baikal and over the Academician Ridge covered areas of up to 4,400 km2 (59 % of Southern Baikal’s surface) and 1,550 km2, respectively. Water was ascending in the upwelling zones at velocities of 1 × 10−4 to 1.2 × 10−2 cm s−1. Temperature differences of 1–4 °C and 2–13 °C were observed between the downwelling and upwelling zones in the epilimnion and metalimnion, respectively. On the surface of the lake, water temperature can drop 4–7 °C for water ascending from depths of 10–75 m, but the observed thickness of the layer within which water was ascending reached a depth of 280 m in August–September and 380 m in October; i.e. the ascending water included the entire upper layer (0–300 m). Geostrophic currents reached up to 24–38 cm s−1 on the boundary between up- and downwelling zones (usually 5–7 km offshore), but did not exceed 6–10 cm s−1 in the centres of upwelling zones. Comparison with other large lakes of the world is carried. This study is important for understanding the upwelling process that develops in Lake Baikal during summer stratification and can influence the heterogeneity of nutrients and primary production.

Fish community dynamics following dam removal in a fragmented agricultural stream

Abstract: Habitat fragmentation impedes dispersal of aquatic fauna, and barrier removal is increasingly used to increase stream network connectivity and facilitate fish dispersal. Improved understanding of fish community response to barrier removal is needed, especially in fragmented agricultural streams where numerous antiquated dams are likely destined for removal. We examined post-removal responses in two distinct fish communities formerly separated by a small aging mill dam. The dam was removed midway through the 6 year study, enabling passage for downstream fishes affiliated with a connected reservoir into previously inaccessible habitat, thus creating the potential for taxonomic homogenization between upstream and downstream communities. Both communities changed substantially post-removal. Two previously excluded species (white sucker, yellow perch) established substantial populations upstream of the former dam, contributing to a doubling of total fish biomass. Meanwhile, numerical density of pre-existing upstream fishes declined. Downstream, largemouth bass density was inversely correlated with prey fish density throughout the study, while post-removal declines in bluegill density coincided with cooler water temperature and increased suspended and benthic fine sediment. Upstream and downstream fish communities became more similar post-removal, represented by a shift in Bray-Curtis index from 14 to 41 % similarity. Our findings emphasize that barrier removal in highly fragmented stream networks can facilitate the unintended and possibly undesirable spread of species into headwater streams, including dispersal of species from remaining reservoirs. We suggest that knowledge of dispersal patterns for key piscivore and competitor species in both the target system and neighboring systems may help predict community outcomes following barrier removal.

Joint effects of climate warming and exotic litter ( Eucalyptus globulus Labill.) on stream detritivore fitness and litter breakdown

Abstract: Joint effects of climate warming and other stressors are potentially complex and difficult to predict. In stream ecosystems, exotic riparian species have the potential to alter leaf-shredding detritivorous invertebrate assemblages and leaf litter breakdown due to differences in the quality of litter inputs. This is the case for Eucalyptus plantations, which are widespread, occurring along riparian corridors of streams around the world. We hypothesised that the presence of Eucalyptus globulus (Labill.) litter (1) impairs detritivore fitness both directly (i.e., through leaf consumption) and indirectly (i.e., through leaf leachates in the water) and (2) impairs litter breakdown, (3) with stronger effects at higher temperatures. We tested these hypotheses in microcosm experiments with two detritivore species from two locations: the stonefly Diamphipnosis samali (Illies, 1960) in Chile and the caddisfly Calamoceras marsupus (Brauer 1865) in Spain. Eucalyptus leaves affected detritivore growth mainly by direct consumption, while the presence of both Eucalyptus leaves and leachates inhibited the breakdown of native litter. When both litter types were available, breakdown of Eucalyptus leaves was enhanced, possibly as a means of compensatory feeding. Increased temperature exacerbated the negative effect of Eucalyptus on native litter breakdown, possibly because it reduced detritivore survival. Our results add to the mounting evidence that joint effects of multiple stressors can be non-additive, and suggest that the sole presence of Eucalyptus leaves and leachates in the water may impact stream communities and ecosystem functions even if native litter is available, with further negative effects to be expected under a warmer climate.

Historical changes in the functional connectivity of rivers based on spatial network analysis and the past occurrences of diadromous species in Portugal

Abstract: The disruption of longitudinal connectivity caused by artificial barriers in rivers is considered to be a major threat to freshwater fish communities at the global scale. In Portugal, the construction of several big dams all through the 20th century was a major cause of disappearance or decline of long distance migratory fish species from various rivers. In this study we analysed the historical changes of functional connectivity for diadromous fish at the Tagus basin river network (Portugal), using a spatial graph approach that integrates both structural connectivity and habitat suitability. Due to the presence of many artificial barriers, the current distribution of species does not reflect natural environmental conditions. Therefore, historical data on the occurrence of species is paramount to assess the potential habitat suitability. The compilation of historical data on the distribution of diadromous species [Sea Lamprey—Petromyzon marinus (Linnaeus 1758) and Allis shad—Alosa alosa (Linnaeus 1758)] was based on geographical dictionaries and geo-referenced information for Portugal dated between 1700 and 1900. Habitat suitability was expressed as the probabilities of occurrence of empirical predictive models based on the historical records and a set of regionalized environmental data. The loss of connectivity caused by big dam construction between 1928 and 2004 was then analysed using a spatial graph approach. The output of this analysis will aid decision-makers to optimize targets of connectivity restoration actions aiming at enhancing the functional connectivity of the river network for diadromous species, using the historical situation as a benchmark.

Anthropogenic land use is associated with N-fixing cyanobacterial dominance in lakes across the continental United States

Abstract: Cyanobacteria cause many water quality problems in lakes worldwide. Although many studies have examined factors that influence the structure of cyanobacterial communities, few have explicitly compared the effects of within-lake conditions (e.g., nutrient concentrations) and watershed parameters (e.g., land use) on a diverse array of cyanobacterial taxa. Here, we analyzed data from the 2007 U.S. Environmental Protection Agency’s National Lakes Assessment to quantify how lakeshore anthropogenic land use, nutrient concentrations and ratios, and surface water temperatures predict cyanobacterial biovolume and dominance in 236 naturally-formed lakes spanning the continental U.S. We observed that anthropogenic lakeshore land use was the best predictor for cyanobacterial dominance, whereas in-lake nitrogen (N) and phosphorus (P) concentrations were the best predictors for cyanobacterial biovolume. Our analyses suggest that anthropogenic land use may influence cyanobacterial dominance via means other than increased nutrient concentrations. The sum of agricultural and human-developed lakeshore land use was the best predictor of N-fixing cyanobacterial dominance, but there was no significant relationship between anthropogenic land use and non-N-fixing cyanobacterial dominance. In addition, we observed a total N:P ratio threshold for cyanobacterial dominance in the phytoplankton community (150:1) that was much higher than previously reported ratios. Consequently, management strategies to control cyanobacteria need to account for eco-physiological variation among different cyanobacterial taxa, and should consider nutrients and the other effects of land use to control overall lake cyanobacterial biovolume and cyanobacterial dominance, as the two cyanobacterial metrics may be sensitive to different drivers.

An inter-regional assessment of concentrations and δ13C values of methane and dissolved inorganic carbon in small European lakes

Abstract: Methane (CH4) and carbon dioxide emissions from lakes are relevant for assessing the greenhouse gas output of wetlands. However, only few standardized datasets describe concentrations of these gases in lakes across different geographical regions. We studied concentrations and stable carbon isotopic composition (δ13C) of CH4 and dissolved inorganic carbon (DIC) in 32 small lakes from Finland, Sweden, Germany, the Netherlands, and Switzerland in late summer. Higher concentrations and δ13C values of DIC were observed in calcareous lakes than in lakes on non-calcareous areas. In stratified lakes, δ13C values of DIC were generally lower in the hypolimnion due to the degradation of organic matter (OM). Unexpectedly, increased δ13C values of DIC were registered above the sediment in several lakes. This may reflect carbonate dissolution in calcareous lakes or methanogenesis in deepwater layers or in the sediments. Surface water CH4 concentrations were generally higher in western and central European lakes than in Fennoscandian lakes, possibly due to higher CH4 production in the littoral sediments and lateral transport, whereas CH4 concentrations in the hypolimnion did not differ significantly between the regions. The δ13C values of CH4 in the sediment suggest that δ13C values of biogenic CH4 are not necessarily linked to δ13C values of sedimentary OM but may be strongly influenced by OM quality and methanogenic pathway. Our study suggests that CH4 and DIC cycling in small lakes differ between geographical regions and that this should be taken into account when regional studies on greenhouse gas emissions are upscaled to inter-regional scales.

Spatial variations in surface water methane super-saturation and emission in Lake Lugano, southern Switzerland

Abstract: We measured methane concentrations in the surface water of the northern basin of Lake Lugano in spring (May 2012) and autumn (October 2011, 2012), and calculated turbulent diffusive methane fluxes to the atmosphere. Surface water methane concentrations were highly variable in space and time but always exceeded atmospheric equilibrium. Methane concentrations were significantly lower in spring (on average 16 nmol L−1) than during the autumn sampling campaigns (on average 57 nmol L−1 in 2011 and 45 nmol L−1 in 2012). This suggests methane accumulation in the surface mixed layer during the summer productive season. The origin of the methane in the lake’s surface waters requires further assessment, but the observed concentration profiles indicate that the excess methane originates from a near-surface source, rather than from the large deep-water methane pool in the anoxic monimolimnion. As a consequence of the higher surface water methane concentrations and increased buoyancy turbulence caused by autumnal cooling of the surface boundary layer, diffusive fluxes were much higher in October (average ~97 μmol m−2 day−1, compared to 7 μmol m−2 day−1 in May 2012). The increase in methane concentration in the surface water between spring and autumn suggests links between methane accumulation and the annual biological cycle, yet seasonal changes in wind and temperature forcing of methane emission likely play an important modulating role. While the relative importance of biological versus physical controls on methane emission in Lake Lugano awaits further investigations, our study underscores that lakes can act as an important source of methane to the atmosphere, even when the lake-internal microbial methane filter in the water column seems to work efficiently.

Effects of water temperature on summer periphyton biomass in shallow lakes: a pan-European mesocosm experiment

Abstract: Periphyton communities play an important role in shallow lakes and are controlled by direct forces such as temperature, light, nutrients, and invertebrate grazing, but also indirectly by planktivorous fish predation. We performed a pan-European lake mesocosm experiment on periphyton colonization covering five countries along a north/south geographical/temperature gradient (Estonia, Germany, Czech Republic, Turkey, and Greece). Periphyton biomass on artificial polypropylene strips exposed at 50 cm water depth at low and high nutrient regimes (with mean total phosphorus concentration of 20 and 65 µg L−1, respectively) was compared during mid-summer. No significant effect of nutrient loading on periphyton biomass was observed as nutrient concentrations in the mesocosms were generally above limiting values. Water temperature significantly enhanced summer periphyton biomass development. Additionally, direct and indirect top-down control of snails and fish emerged as a significant factor in periphyton biomass control.

Angling baits and invasive crayfish as important trophic subsidies for a large cyprinid fish

Abstract: Invasive species and anthropogenic sources of allochthonous trophic subsidies can have substantial ecological consequences for freshwater ecosystems, including modifying the diet of consumers and altering food web structure. Here, the diet of an omnivorous cyprinid fish, European barbel Barbus barbus, was assessed in relation to the presence of invasive signal crayfish Pacifastacus leniusculus and pelletized fish-meal in four rivers in England. Pellets are often used in large quantities by river anglers and thus could provide an important trophic subsidy, not only to the fish but also indirectly via P. leniusculus. Carbon and nitrogen stable isotopes were used to estimate the proportion of diet assimilated from natural sources and from P. leniusculus and pellets by B. barbus of lengths between 420 and 800 mm. Pellets generally made a large contribution to the overall biomass of B. barbus (up to 59 % of population diet) and in the two rivers where they were present, P. leniusculus were also an important resource (up to 30 % of population diet). The proportion derived from macro-invertebrates (excluding P. leniusculus) was substantially lower. Stable isotope mixing models further demonstrated considerable intraspecific variability in B. barbus diet within the rivers, with pellets comprising up to 79 % of the biomass of individual B. barbus in rivers where P. leniusculus was absent. Where present, P. leniusculus effectively replaced and thus reduced the contribution of pellets to individual fish diet. Thus, isotopic evidence from three of the four rivers indicates that B. barbus populations are heavily reliant (>50 %) upon angler-introduced baits that act as an important allochthonous subsidy and will also prey upon invasive P. leniusculus where they are present.

Nutrient uptake and macroinvertebrate community structure in a highly regulated Mediterranean stream receiving treated wastewater

Abstract: Streamflow augmentation with treated wastewater has been suggested as a strategy for increasing flow in streams, but at the same time, concern has been raised regarding the possible deterioration of water quality. In this study, the spatial and temporal distributions of nutrient uptake rates and macroinvertebrates were measured in a Mediterranean lowland stream (Yarqon, Israel), upstream and downstream of treated wastewater input. Over the last decade, the average downstream reach’s nutrient demand, depicted as the uptake velocities of NH4 +–N, NO3 −–N, and PO4 3−–P, increased by factors of 50, 10, and 6, respectively. The decrease in the ambient concentration of NH4 +–N, from an average of 39 to 2.8 mg L−1 after upgrading the effluent quality, was the main reason for the observed improvements in uptake velocities. Nevertheless, the uptake length in the Yarqon Stream after the improvement in the quality of the treated wastewater was improved only for NH4 +–N, and deteriorated for NO3 −–N, and PO4 3−–P. Following the improvement in water quality, the uptake velocities and the macroinvertebrate communities in the downstream section are currently not significantly different from those in the upstream section. The macroinvertebrate assemblage structure reveals that tolerant taxa dominate the stream, and the increase of the taxa richness in the downstream section is attributed to rare and more sensitive taxa that recolonized this section following water quality improvement. The results suggest that improving the quality of the treated wastewater that is used for stream flow augmentation can have a positive effect on nutrient uptake velocities and macroinvertebrate assemblage structure. However, further ecological and economical cost-benefit analysis is needed to evaluate the feasibility of using treated wastewater augmentation for Mediterranean stream restoration.

Effects of increased concentrations of inorganic nitrogen and dissolved organic matter on phytoplankton in boreal lakes with differing nutrient limitation patterns

Abstract: Global changes are currently contributing to increasing concentrations of nitrogen (N) and dissolved organic matter (DOM) in boreal lakes. While these changes can affect phytoplankton, the relative importance of each of these subsidies and how their effects vary with nutrient limitation patterns remain unclear. We investigated the effects of increasing N and DOM on phytoplankton in two relatively remote boreal regions of the northern US with lakes that differ in N and DOM concentrations: Acadia National Park (ACAD) in the northeastern US, and Isle Royale National Park (ISRO) in the north-central US. Nutrient enrichment assays were conducted in two lakes from each area first to assess nutrient limitation patterns. To determine the effects of increasing N and DOM, changes in phytoplankton biomass and community structure were examined in bioassay experiments using a N gradient combined with either DOM enrichment or DOM shading treatments. Algal biomass response indicated N limitation in ISRO and N&P co-limitation in ACAD. In the N gradient experiments, algal biomass in the N-limited lake increased along the N gradient, while it was unaffected in the N&P co-limited lake. Regardless of nutrient limitation pattern, algal biomass increased with DOM enrichment, with DOM additions primarily stimulating chlorophytes, diatoms, and chrysophytes. In contrast, shading with DOM had no effect on any phytoplankton response metrics. In boreal lakes, the effects of N enrichment were dependent on nutrient limitation status of the lake, whereas the effects of DOM enrichment were observed across lakes regardless of nutrient limitation status, suggesting that increasing DOM may have widespread effects on aquatic systems.

Riparian vegetation as indicator of channel adjustments and environmental conditions: the case of the Panaro River (Northern Italy)

Abstract: Disturbances affecting flow and sediment transport regimes (e.g. dams, diversions, gravel mining, weirs, bank reinforcements, climate changes) can promote riverbed degradation and channel narrowing, and thus influence vegetation dynamics and composition. This study investigates the relationships and feedbacks between channel adjustments and riparian vegetation dynamics by combining an analysis of morphological channel changes with a wider phytosociology analysis of existing vegetation within the river corridor. These relationships were illustrated by using the case study of the Panaro River (located in the Northern Apennines, Italy), being a representative case of a deeply incised and narrowed river. More specifically we analyzed: (1) the relations between landforms and distributional patterns of vegetation types and characteristic plant species (index species): these provided information about the hydrogeomorphic condition of fluvial landforms and about channel adjustments; (2) the distance of riparian vegetation conditions from expected conditions as a consequence of human impact, based on the fact that each species and vegetation type has a given tolerance for specific disturbance regimes or stresses. Although some expected relations between landforms and vegetation types were found, we recorded significant deviations from the typical correlation pattern existing between morphology and vegetation, and this could be used to infer the intensity and the typology of human disturbances. In particular, the index species can indicate present ecological conditions and on past channel evolution. With this knowledge it might be possible to develop botanical recovery models in the future and, even more importantly, enable the recognition of the differences between temporal and spatial diversity.

Spatial and temporal variability of widespread dark production and decay of hydrogen peroxide in freshwater

Abstract: Hydrogen peroxide (H2O2) is an oxidant and reductant of redox active metals and a potential source of strong oxidants such as the hydroxyl radical (·OH). H2O2 production in freshwater has been largely attributed to photo-oxidation of chromophoric dissolved organic matter, while its decay has been linked to enzymatic processes as well as to chemical reactions with metals. More recently, however, microorganisms were postulated as a significant source as well as a sink of H2O2 in freshwater. In this study, we examined the spatial and temporal variability of dark H2O2 production rates ( $${\text{P}}_{{{\text{H}}_{ 2} {\text{O}}_{ 2} }}$$ ) and pseudo-first order dark decay rate coefficients ( $${\text{k}}_{{{\text{loss,H}}_{ 2} {\text{O}}_{ 2} }}$$ ) in incubations of water samples from sites with a range of trophic states in Colorado (CO) and Massachusetts (MA). Observed values of $${\text{P}}_{{{\text{H}}_{ 2} {\text{O}}_{ 2} }}$$ and $${\text{k}}_{{{\text{loss,H}}_{ 2} {\text{O}}_{ 2} }}$$ ranged from 3 to 259 nM h−1 and 0.02 to 8.87 h−1, respectively. Microbial cell numbers and chlorophyll content correlated strongly with $${\text{k}}_{{{\text{loss,H}}_{ 2} {\text{O}}_{ 2} }}$$ while filtering the freshwater samples removed the majority of $${\text{k}}_{{{\text{loss,H}}_{ 2} {\text{O}}_{ 2} }}$$ , indicating breakdown by biota as the major sink of H2O2. Dark production of H2O2 was also ubiquitous, but $${\text{P}}_{{{\text{H}}_{ 2} {\text{O}}_{ 2} }}$$ was not well correlated with indicators of microbial abundance. For instance, several oligotrophic sites (with low $${\text{k}}_{{{\text{loss,H}}_{ 2} {\text{O}}_{ 2} }}$$ ) exhibited moderately high $${\text{P}}_{{{\text{H}}_{ 2} {\text{O}}_{ 2} }}$$ , while a sample with unusually high chlorophyll content (and a correspondingly high $${\text{k}}_{{{\text{loss,H}}_{ 2} {\text{O}}_{ 2} }}$$ ) had a relatively low $${\text{P}}_{{{\text{H}}_{ 2} {\text{O}}_{ 2} }}$$ . One possible explanation for this phenomenon is that the ability to break down H2O2 is similar among different microorganisms, but the ability to produce H2O2 differs with microbial composition.

Historical change in fish species distribution: shifting reference conditions and global warming effects.

Abstract: Species distributions models (SDM) that rely on estimated relationships between present environmental conditions and species presence-absence are widely used to forecast changes of species distributions caused by global warming but far less to reconstruct historical assemblages. By compiling historical fish data from the turn to the middle of the twentieth century in a similar way for several European catchments (Rhone, Danube), and using already published SDMs based on current observations, we: (1) tested the predictive accuracy of such models for past climatic conditions, (2) compared observed and expected cumulated historical species occurrences at sub-catchment level, and (3) compared the annual variability in the predictions within one sub-catchment (Salzach) under a future climate scenario to the long-term variability of occurrences reconstructed during an extended historical period (1800–2000). We finally discuss the potential of these SDMs to define a “reference condition”, the possibility of a shift in baseline condition in relation with anthropogenic pressures, and past and future climate variability. The results of this study clearly highlight the potential of SDM to reconstruct the past composition of European fish assemblages and to analyze the historical ecological status of European rivers. Assessing the uncertainty associated with species distribution projections is of primary importance before evaluating and comparing the past and future distribution of species within a given catchment.

Historic catches, abundance, and decline of Atlantic salmon Salmo salar in the River Elbe

Abstract: Fisheries statistics available from the River Elbe catchment since the middle of the 16th century onwards have been compiled and analyzed to assess 1. the spatial distribution and patterns of returning salmon, 2. the total abundance of the salmon stock, as well as 3. local impacts, reasons, and time lags of salmon decline. Catch data and fisheries statistics of up to 117 years from 67 sites have been compiled covering a period from 1552 to 1949. Although often incomplete, the available data revealed strong inter-annual spatial patterns of salmon catches. In particular, last or exceptional salmon records in distant tributaries or headwaters were significantly explained by flood events. In the River Elbe, the historical salmon harvest amounts of about 4,000 salmon annually are well above recent estimates of 300–400 returning salmon. The spatio-temporal patterns of salmon decline in the River Elbe catchment strongly indicate the importance of the historical spawning sites in the upstream river sections for salmon recovery as well as the resilience of large rivers against human disturbances. Both findings underline the need for a catchment approach in salmon rehabilitation including incorporation of and longitudinal connectivity to the upper catchment headwaters.

Human induced stepping-stone colonisation of an admixed founder population: the spread of topmouth gudgeon (Pseudorasbora parva) in Europe.

Abstract: Biological invasions caused by accidental introductions often result in severe ecological impact. Revealing the pattern of spread can clarify processes which drive these types of invasions and therefore help mitigate their impact. Here, based on the genetic structure at five microsatellite loci, we reconstructed the invasion history of the topmouth gudgeon (Pseudorasbora parva). This small cyprinid fish was introduced from China in the early 1960s into countries around the Black Sea, spreading rapidly throughout Europe north, west and southward. Distribution of the genetic variation from 14 European and one Chinese founder population was analysed, revealing possible pathways of spread in Europe. Overall, the distribution of genetic diversity across populations is strongly correlated to the geographic and temporal spread of P. parva across its invasive range. Populations closest to the founder sites had high levels of genetic diversity and little genetic differentiation. Furthermore, a pattern of isolation-by-distance was found, which indicates human-mediated stepping-stone colonisation. The data also indicate that the invasive populations originate from recent admixture of divergent source populations with some recently established populations, although the admixture signal has been dampened by strong genetic drift. These results nevertheless show that despite being a human-mediated invasion, the pattern of spread resembles a natural stepping-stone colonization with a well-defined front of invasion.

Biofilm growth and nitrogen uptake responses to increases in nitrate and ammonium availability

Abstract: Nitrate (NO3 −) and ammonium (NH4 +) are the two major dissolved inorganic nitrogen (DIN) species available in streams. Human activities increase stream DIN concentrations and modify the NO3 −:NH4 + ratio. However, few studies have examined biofilm responses to enrichment of both DIN species. We examined biofilm responses to variation in ambient concentrations and enrichments in either NO3 − or NH4 +. We incubated nutrient diffusing substrata (NDS) bioassays with three treatments (DIN-free, +NO3 − and +NH4 +) in five streams. Biomass-specific uptake rates (U spec ) of NO3 − and NH4 + were then measured using in situ additions of 15N-labeled NO3 − and NH4 +. Biomass (estimated from changes in carbon content) and algal accrual rates, as well as U spec -NO3 − of biofilms in DIN-free treatments varied among the streams in which the NDS had been incubated. Higher ambient DIN concentrations were only correlated with enhanced biofilm growth rates. U spec -NO3 − was one order of magnitude greater and more variable than U spec -NH4 +, however similar relative preference index (RPI) suggested that biofilms did not show a clear preference for either DIN species. Biofilm growth and DIN uptake in DIN-amended NDS (i.e., +NO3 − and +NH4 +) were consistently lower than in DIN-free NDS (i.e., control). Lower values in controls with respect to amended NDS were consistently more pronounced for algal accrual rates and U spec -NO3 − and for the +NH4 + than for the +NO3 − treatments. In particular, enrichment with NH4 + reduced biofilm U spec -NO3 − uptake, which has important implications for N cycling in high NH4 + streams.

Short-term and seasonal variability of oxygen fluxes at the sediment-water interface in a riverine lake

Abstract: In situ measurements of sediment-water oxygen fluxes conducted in a riverine lake during different seasons were analyzed with the aim of quantifying the combined effects of hydrodynamic forcing and seasonal changes in temperature on sediment oxygen uptake rate. Oxygen fluxes measured using the eddy correlation (EC) technique varied widely between −6.4 and −84 mmol m−2 day−1, while variations observed on hourly time scales were of comparable magnitude to seasonal variations. Oxygen fluxes were most strongly correlated to current speed in the benthic boundary layer and water depth, which both co-varied with discharge, temperature, and oxygen concentration. A direct correlation of measured fluxes with temperature and corresponding seasonal flux variations could not be observed. To explore the potential effect of temperature on oxygen fluxes, we applied a simplified analytical model, which couples the effect of hydrodynamic forcing with a temperature-dependent oxygen consumption rate within the sediment. The results suggest that the flux is a non-linear function of both variables and both can have comparable effects on the magnitude of the oxygen fluxes. The model confirms our observation that short-term variations of oxygen fluxes in response to hydrodynamic forcing can mask longer-term seasonal variations driven by temperature. The model further indicates that the magnitude and form of the temperature dependence of oxygen uptake and mineralization rates in freshwater sediments obtained from laboratory incubations can be strongly affected by flow conditions during incubations. We conclude that predictions of oxygen uptake and mineralization rates under changing climatic conditions should also take potential changes of flow conditions into account.

Environmental assessment of vegetation and hydrological conditions in Everglades freshwater marshes using multiple geochemical proxies

Abstract: Paleoecological reconstructions of environmental changes provide important information for Everglades restoration targets. Traditionally this has been achieved using a combination of biological and physical indicators. However, as microfossils may be sporadically abundant in Everglades soils, organic geochemical methods can provide information at the molecular level. To reconstruct vegetation trends over the last century, soil cores from Shark to Taylor Sloughs, the primary flowpaths of the southern Everglades, were examined using several geochemical proxies. The n-alkane derived biomarker Paq effectively distinguished organic inputs from sawgrass and slough habitats. Other proxies examined include Kaurenes, cyclic diterpenoids unique to sawgrass roots; biomarkers of algae (highly branched isoprenoids (C20HBIs) and Botryococcenes); lignin phenols as vascular plant indicators; and macrofossils. At all sites, soil profiles from sawgrass marshes showed vegetation had shifted over the last 100 years, from sloughs to sawgrass-dominated marshes, reflecting decreased water levels (shorter hydroperiods) induced by water management. Paleo-assessments of modern sloughs, however, indicate these habitats remained deeper water habitats throughout the period of record, though shifts toward shorter hydroperiod vegetation were observed. In Taylor Slough, evidence of increasingly dry conditions in sloughs was confirmed by seed inputs from woody species. At 3 of the 5 sites, recent increases in C20HBIs and Botryococcene concentrations indicated greater periphyton abundance, coincidental with increased mineral concentrations observed in surface waters during the mid-20th Century. Bulk proxies such as organic content and carbon:nitrogen ratios also supported findings of changes in relative contributions of microbial and higher plants in this ecosystem.

3D modelling of dreissenid mussel impacts on phytoplankton in a large lake supports the nearshore shunt hypothesis and the importance of wind-driven hydrodynamics

Abstract: A three-dimensional hydrodynamic model (ELCOM) coupled with a biological model (CAEDYM) was calibrated with field data from Lake Simcoe (2008) and used to examine the expected impact of dreissenid mussels on the distribution of phytoplankton and nutrients, mussel energetic, and the interactions with hydrodynamic conditions. In accordance with the near-shore shunt hypothesis and the actual distribution of mussels, the model predicted a considerable impact of mussels on phytoplankton in nearshore areas (<15 m depth; −38 % phytoplankton). Horizontal advection could account for the lower (−15 % phytoplankton) offshore impact despite the absence of mussels within this region of the lake. These predictions were similar to observed long-term changes in phytoplankton biomass after the dreissenid mussel invasion. Simulated decreases in the initial mussel biomass by 50 % led to increased phytoplankton nearshore, increased mussel growth and decreased phosphorus excretion relative to ingestion. In contrast, increases in initial mussel biomass by 50 % resulted in minor changes in phytoplankton, since near-bottom depletion of phytoplankton caused growth and energy-limitation of mussels. The model, which was the first to capture metabolically-driven variations of mussel-mediated nutrient cycling, predicted a partial uncoupling of carbon and phosphorus cycling by mussels, driven by varying controls on mussel growth. A 60 % increase in the intensity of three storms during the summer had little net-effect on phytoplankton biomass, but reduced energy-limitation of mussels and increased mussel growth due to increased supply of phytoplankton. Our model demonstrates that near-bottom depletion of phytoplankton is an important process limiting the impact of mussels, and indicates that it affects the mussels’ cycling of energy and nutrients. It further suggests that stronger storm events could lead to further increase of flux of organic matter from the pelagic zone to the benthos, further altering energy pathways in the lake.

Declining diversity of egg-associated bacteria during development of naturally spawned whitefish embryos (Coregonus spp.)

Abstract: Fish eggs are associated with microbes, whose roles range from mutualism to parasitism. Recent laboratory experiments have shown that the taxonomic composition of associated microbial communities on the egg influences embryonic development. Host genetics also plays an important role in determining the consequences for embryonic growth and survival in this interaction. Moreover, it has been found that the importance of host genetics increases during embryogenesis. These findings suggest that during embryogenesis, the host increasingly influences the composition of its associated microbial community. However, little is known about the composition of microbial communities associated with naturally spawned eggs in the wild. We sampled fertilized whitefish eggs (Coregonus spp.) of different developmental stages from six sub-Alpine lakes and used a universal primer pair and 454 pyrosequencing in order to describe the taxonomic composition of egg-associated bacterial communities. We found bacterial communities on early embryos to be very diverse and to resemble the bacterial composition of the surrounding water environment. The bacterial communities on late embryos were significantly less diverse than on early embryos and displayed a clear shift in taxonomic composition that corresponded poorly with the bacterial composition of the surrounding water environment. The main bacterial components on whitefish eggs in this study were Proteobacteria, Actinobacteria, and Firmicutes, while the five most common families were Leuconostocaceae, Streptococcaceae, Comamonadaceae, Oxalobacteraceae and Moraxellaceae. Their putative relationships with the host are discussed. We conclude that natural symbiotic bacterial communities become more specialized during embryogenesis because of specific interactions with their embryo host.

Historical ecology of riverine fish in Europe

Abstract: The temporal dynamic of riverine ecosystems and their fish communities and populations has been addressed in ecological theory and management for several decades. A growing number of case studies on the historic development especially of European and North American rivers have been published. Nonetheless, a theoretical debate about the contributions and limits of historical approaches and interdisciplinary co-operation is lacking. This article presents a brief overview of the role of history in river and fish ecology and suggests historical ecology as a scientific field that can offer a framework for future research. Based on case studies compiled in this special issue on the “Historical ecology of riverine fish in Europe”, we draw conclusions on long-term changes of fish communities, on fisheries, aquatic ecosystem management and past habitat alterations and the potential of archaeological remains and written sources to study them. We discuss how modelling of historical fish data can help elucidate the effects of climate change and human influences on rivers and fish. Finally, we account for the necessity to consider appropriate spatial and temporal scales. In conclusion we call for future comparative studies on continental and global scales and methodological development, which can benefit especially from recent advances in marine historical ecology. We suggest that future interdisciplinary studies of ecologists, hydrologists, historians and archaeologists can reveal the history of riverine ecosystems as socio-ecological systems, addressing both their natural dynamics and human dimension. Such an endeavor can also support developing management plans for habitat restoration and conservation against the background of global change.

A paleolimnological perspective on aquatic biodiversity in Austrian mountain lakes

Abstract: We assessed long-term aquatic biodiversity patterns, with a focus on functional diversity (FD), by using sedimentary Chironomidae and Cladocera assemblages in four mountain lakes in the Austrian Alps. The objectives were to detect whether the invertebrate communities exhibited similar recent diversity trends in climate-sensitive alpine lakes, to observe how lake-specific limnological shifts affect biodiversity, and to test the relationship between taxonomic diversity (TD) and FD for paleolimnological biodiversity evaluations. We applied traditional TD indices to the sedimentary assemblages and used an FD index that was based on functional traits of the encountered taxa of both invertebrate groups. There were some similar long-term trends in invertebrate FD and TD among the lakes; e.g. chironomid diversity increased in two lakes and cladoceran diversity in three lakes toward the twentieth and twenty-first century, but in general the diversity patterns were variable between lakes. Overall, FD had a positive relationship with TD suggesting that functionality can be used in paleolimnological studies as a measure of biodiversity. However, cladoceran taxon richness did not correlate with FD in two lakes suggesting that TD is not always a surrogate for FD. Furthermore, TD of chironomids tended to increase more pronouncedly than FD in the top core sections indicating that increasing TD does not necessarily enhance FD and that different taxonomic entities may play similar functional roles in ecosystems. Accordingly, when evaluating biodiversity and ecological redundancy, functionality of the species pool should be carefully considered and highlighted also in paleolimnological research.

Constructed wetlands increase the taxonomic and functional diversity of a degraded floodplain

Abstract: Numerous wetland restoration projects have been implemented in recent years to mitigate the increasing loss of global wetland surface area caused by human activities. Most of these projects have focused on the local recovery of habitats and species diversity, with little evaluation of functional recovery. We aimed at demon- strating that constructing wetlands on a degraded floodplain increases not only the taxonomic, but also the functional diversity of macroinvertebrate assemblages by providing greater water quality to the local fauna. We studied the macroinvertebrate community using taxonomic and functional diversity indices, and the physicochemical characteristics of three wetlands constructed 5-25 years ago, and three relict natural wetlands on the floodplain of a regulated river (Ebro River, NE Spain). Constructed wet- lands demonstrated significantly greater taxonomic abundance and richness of macroinvertebrates than natural wetlands. At the functional level, the richness and Shannon diversity of biological traits relating to reproduction, res- piration, dispersal and feeding were also greater in constructed wetlands, which is partly explained by low inorganic nitrogen concentration in these habitats. In con- trast, a high content of phosphorus and water organic matter led to the lowest values of taxonomic and functional diversity found in natural wetlands. We conclude that it is essential to consider not only taxonomic but also functional aspects at all stages of a restoration project in order to optimize its long-term efficacy to provide and support key species and functions.

Fish remains as a source to reconstruct long-term changes of fish communities in the Austrian and Hungarian Danube

Abstract: The main objective of this paper is to investigate how archaeological fish remains and written historical records can contribute to the reconstruction of long-term developments of fish communities along the Austrian and Hungarian Danube. Although such approaches are sensitive to various factors, the chronological subdivision and relative quantification of proxy data demonstrate environmental and faunal changes from Prehistory onwards. Intensification of fisheries, decline of large specimens and massive exploitation of small and young fish point to increasing pressure along the chronological sequence towards Early Modern times. One result of this impact was the establishment of regulations and laws to protect such fish. At the same time, the rise of aquaculture and common carp cultivation can be viewed as another upshot of human impact on the Danube’s environment. Finally, the massive import of salted marine fish reflects a compensation for the undersupply caused by overexploitation of the Danube fish fauna and points to the growing demand for fish as food in late medieval and Early Modern times.