Aquatic Primary Production Research Articles

Distribution of radiocarbon in sediments of the cooling pond of RBMK type Ignalina Nuclear Power Plant in Lithuania.

The vertical distribution of radiocarbon (14C) was examined in the bottom sediment core, taken from Lake Drūkšiai, which has served as a cooling pond since 1983 for the 26 years of the Ignalina Nuclear Power Plant (INPP) operation using two RBMK-1500 reactors (Russian acronym for”Channelized Large Power Reactor”). 14C specific activity was measured in alkali-soluble and -insoluble fractions of the sediment layers. Complementary measurements of the 210Pb and 137Cs activity of the samples provided the possibility to evaluate the date of every layer formation, covering the 1947–2013 period. In addition, 14C distribution was examined in the scales of pelagic fish caught between 1980 and 2012. Our measurements reveal that, during the period 1947–1999, the radiocarbon specific activity in both fractions exhibits a parallel course with a difference of 5 ± 1 pMC (percent of modern carbon) being higher in alkali-soluble fraction, although 14C specific activity in both fractions increased by 11.4–13.6 pMC during the first 15 years of plant operation. However, during the 2000–2009 period, other than previously seen, a dissolved inorganic carbon (DIC) → aquatic primary producers → sediments 14C incorporation pattern occurred, as the radiocarbon specific activity difference between alkali-soluble and -insoluble fractions reached 94, 25, and 20 pMC in 2000, 2006, and 2008, respectively. Measurements in different sediment fractions allowed us to identify the unexpected organic nature of 14C contained in liquid effluences from the INPP in 2000–2009. The discrepancy between 14C specific activity in fish scales samples and DIC after 2000 also confirmed the possibility of organic 14C contamination. Possible reasons for this phenomenon might be industrial processes introduced at the INPP, such as the start of operation of the cementation facility for spent ion exchange resins, decontamination procedures, and various maintenance activities of reactor aging systems and equipment.

Identifying drivers of microbial community composition associated with aquatic primary producers: metagenomic analysis of cyanobacterial cultures

The energy derived from aquatic primary production is fundamental to driving Earth’s life support systems – but they don’t achieve all this by themselves. Heterotrophic bacteria found in the photic zones of aquatic environments have a fundamental role in this too. Our group’s interest is in understanding how heterotrophs help autotrophs: who in these communities are important, and how and why they are important. Answering this is important in both natural and manmade environments so we can model these environments, and as appropriate, manipulate them, such as applying designer microbiomes to aid industrialisation of algal cultivation. Metagenomic analysis of 31 marine and freshwater cyanobacterial cultures from the Culture Collection of Algae & Protozoa resulted in assembly of >400 bacterial metagenomes (MAGs) with ca. 14 unique MAGs per culture. Community composition was clearly partitioned by salinity as a driver but collectively niche accounted for most community taxonomic variation. No universal core microbiome was identified, but taxonomic composition of marine cultures bore notable similarities to marine eukaryotic algal communities and to a natural cyanobacterial mat community found next to a northern Chilean geyser. Stable taxonomic associations imply that these taxa may have functional importance to their algal host. Functional analysis of the MAGs is underway and we will test whether the relative taxonomic variability contrasts with low functional variation between communities. If true, this implies that primary producers drive community assembly in a functionally predictable way, and that function, not taxonomy, is the more important parameter to understand.

Predicting hot spots of aquatic plant biomass in a large floodplain river catchment in the Australian wet-dry tropics

Conservation planning processes and wetland management require spatial estimations of aquatic habitats to support the maintenance of aquatic biodiversity. However, physical access to several wetlands and freshwater habitats can be restricted due to difficult topography and technological limitations associated with ground-based observations. In addition to these constraints, the distribution of some aquatic primary producers in freshwater habitats and floodplains that are difficult to reach further complicates large-scale assessment of aquatic habitats using traditional field-based techniques. The main objective of this study is to predict the spatial distribution of hot spots of primary producers (aquatic plant biomass) and assess large-scale inundation patterns in a large floodplain wetland (Flinders catchment) in the wet-dry tropics of Australia. To this end, remote sensing biophysical indicators (vegetation and inundation) were integrated with flood water depth in a classification tree model. Results indicate that in terms of floodplain total inundation, the Flinders wetland hydrology is rather restricted immediately after the summer wet season, the period when most primary production happens. While this can be attributed to the fact that much of the observed annual variability (93%) in rainfall and surface runoff (95%) occur during the wet season, post flood recession patterns are indicators that underpin the somewhat limited alimentation of the Flinders floodplain during this period. As observed in this study, post flood inundation extents in the summers of 2009 and 2019 declined by approximately 89% and 87% within fourteen and ten days, respectively. Despite having a significantly higher magnitude than the 2009 summer flood event, the 2019 extreme ‘big wet’ period did not translate to higher floodplain productivity (aquatic plant biomass and surface water distribution) immediately after summer as was the case in 2009. Furthermore, the predicted extents of aquatic plant biomass and total floodplain inundation in the downstream Flinders show substantial temporal variation and suggest the floodplain wetland hydrology is largely driven by inter-annual changes in annual rainfall. The extents of these hot spots of biomass accumulation were found to be considerably associated with total floodplain inundation extent (r=0.94), rainfall (r=0.81), and discharge (r=0.68). Furthermore, advance statistical analyses show that downstream discharge and rainfall over the Flinders are significantly correlated (r=0.72). In addition to this, observed amplitudes of discharge and rainfall in extreme wet and dry years coincided with floodplain inundation patterns and distribution of hot spots of primary producers. While these relationships emphasize the importance of flow in the nourishment of the downstream catchment, they further corroborate the composite influence of local rainfall and discharge on total floodplain inundation and hot spots of primary producers.

Genomes of the dinoflagellate Polarella glacialis encode tandemly repeated single-exon genes with adaptive functions

BackgroundDinoflagellates are taxonomically diverse and ecologically important phytoplankton that are ubiquitously present in marine and freshwater environments. Mostly photosynthetic, dinoflagellates provide the basis of aquatic primary production; most taxa are free-living, while some can form symbiotic and parasitic associations with other organisms. However, knowledge of the molecular mechanisms that underpin the adaptation of these organisms to diverse ecological niches is limited by the scarce availability of genomic data, partly due to their large genome sizes estimated up to 250 Gbp. Currently available dinoflagellate genome data are restricted to Symbiodiniaceae (particularly symbionts of reef-building corals) and parasitic lineages, from taxa that have smaller genome size ranges, while genomic information from more diverse free-living species is still lacking.ResultsHere, we present two draft diploid genome assemblies of the free-living dinoflagellate Polarella glacialis, isolated from the Arctic and Antarctica. We found that about 68% of the genomes are composed of repetitive sequence, with long terminal repeats likely contributing to intra-species structural divergence and distinct genome sizes (3.0 and 2.7 Gbp). For each genome, guided using full-length transcriptome data, we predicted > 50,000 high-quality protein-coding genes, of which ~40% are in unidirectional gene clusters and ~25% comprise single exons. Multi-genome comparison unveiled genes specific to P. glacialis and a common, putatively bacterial origin of ice-binding domains in cold-adapted dinoflagellates.ConclusionsOur results elucidate how selection acts within the context of a complex genome structure to facilitate local adaptation. Because most dinoflagellate genes are constitutively expressed, Polarella glacialis has enhanced transcriptional responses via unidirectional, tandem duplication of single-exon genes that encode functions critical to survival in cold, low-light polar environments. These genomes provide a foundational reference for future research on dinoflagellate evolution.

Carbon dioxide dynamics in an agricultural headwater stream driven by hydrology and primary production

Abstract. Headwater streams are known to be hotspots for carbon dioxide (CO2) emissions to the atmosphere and are hence important components in landscape carbon balances. However, surprisingly little is known about stream CO2 dynamics and emissions in agricultural settings, a land use type that globally covers ca. 40 % of the continental area. Here we present hourly measured in situ stream CO2 concentration data from a 11.3 km2 temperate agricultural headwater catchment covering more than 1 year (in total 339 d excluding periods of ice and snow cover). The stream CO2 concentrations during the entire study period were generally high (median 3.44 mg C L−1, corresponding to partial pressures (pCO2) of 4778 µatm) but were also highly variable (IQR = 3.26 mg C L−1). The CO2 concentration dynamics covered a variety of different timescales from seasonal to hourly, with an interplay of hydrological and biological controls. The hydrological control was strong (although with both positive and negative influences dependent on season), and CO2 concentrations changed rapidly in response to rainfall and snowmelt events. However, during growing-season base flow and receding flow conditions, aquatic primary production seemed to control the stream CO2 dynamics, resulting in elevated diel patterns. During the dry summer period, rapid rewetting following precipitation events generated high CO2 pulses exceeding the overall median level of stream CO2 (up to 3 times higher) observed during the whole study period. This finding highlights the importance of stream intermittency and its effect on stream CO2 dynamics. Given the observed high levels of CO2 and its temporally variable nature, agricultural streams clearly need more attention in order to understand and incorporate these considerable dynamics in large-scale extrapolations.

Phytoplankton pangenome reveals extensive prokaryotic horizontal gene transfer of diverse functions.

The extent and role of horizontal gene transfer (HGT) in phytoplankton and, more broadly, eukaryotic evolution remain controversial topics. Recent studies substantiate the importance of HGT in modifying or expanding functions such as metal or reactive species detoxification and buttressing halotolerance. Yet, the potential of HGT to significantly alter the fate of species in a major eukaryotic assemblage remains to be established. We provide such an example for the ecologically important lineages encompassed by cryptophytes, rhizarians, alveolates, stramenopiles, and haptophytes ("CRASH" taxa). We describe robust evidence of prokaryotic HGTs in these taxa affecting functions such as polysaccharide biosynthesis. Numbers of HGTs range from 0.16 to 1.44% of CRASH species gene inventories, comparable to the ca. 1% prokaryote-derived HGTs found in the genomes of extremophilic red algae. Our results substantially expand the impact of HGT in eukaryotes and define a set of general principles for prokaryotic gene fixation in phytoplankton genomes.

Different climate scenarios alter dominance patterns among aquatic primary producers in temperate systems

AbstractIn a future climate change perspective, the interactions among different life‐forms of primary producers will likely be altered, leading to changes in the relative dominance among macrophytes, filamentous, and planktonic algae. In order to improve the possibilities to forecast future ecosystem services and function, we therefore conducted a long‐term mesocosm study where primary producers were exposed to different climate scenarios, including both a mean increase in temperature (4°C) and a similar energy input, but delivered as “heat waves” (fluctuations 0–8°C above ambient). We show that in shallow systems, future climate change scenarios will likely lead to higher total macrophyte biomasses, but also to considerable alterations in the macrophyte community composition. The biomass of filamentous algae (Cladophora) showed no significant difference among treatments, although effect size analyses identified a slight increase at heated conditions. We also show that future climate change will not necessarily lead to more phytoplankton blooms, although a considerable alteration in phytoplankton community composition is to be expected, with a dominance of cyanobacteria and Cryptophytes, whereas Chlorophyceae and diatoms will likely play a less pronounced role than at present. In a broader context, we conclude that the total biomass of macrophytes will likely increase in shallow areas, whereas phytoplankton may not show any strong changes in biomass in a future climate change scenario. Instead, the major changes among primary producers will likely be mirrored in a considerably different species composition than at present.

Toxicity assessments of acrylamide in aquatic environment using two algae Nitzschia closterium and Scenedesmus quadricauda.

The expanding production and widespread application of acrylamide caused inevitable release to aquatic ecosystems. Contrary to its extensive attention to human and animal health, the hazards of acrylamide to the aquatic primary productivity have been rarely studied. The potential effects of acrylamide on the marine algae (Nitzschia closterium) and the limnetic algae (Scenedesmus quadricauda) were investigated by monitoring cell abundance, total chlorophyll content, maximum photosystem II (PSII) quantum yield (Fv/Fm), and reactive oxygen species (ROS). The growth of two algae was significantly inhibited by acrylamide. The 96h EC50 of acrylamide on N. closterium and S. quadricauda were 5.50mgL-1 and 45.3mgL-1, and no observed effect concentration (NOEC) were 1.07mgL-1 and 6.97mgL-1, respectively. After 96h exposure to 50mgL-1 of acrylamide, the total chlorophyll content declined to approximate 18% (N. closterium) and 48% (S. quadricauda), and Fv/Fm was observed to be 0.35 and 0.32 for N. closterium and S. quadricauda, respectively. ROS was significantly increased following higher exposure concentrations, and its levels increased around 2.1-fold and 1.4-fold following exposure to 5mgL-1 of acrylamide. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed the visible cell plasmolysis, rupture of the plasma membrane, cell vacuolization, and disintegration of chloroplasts of the algae caused acrylamide.

Satellite-derived changes in floodplain productivity and freshwater habitats in northern Australia (1991–2019)

Abstract The ecological communities supported by freshwater habitats and wetlands that persist from floodplain inundation generate numerous cultural, recreational and economic values via commercial fisheries and other human uses of these habitats. However, the alteration of flow connectivity, degradation, and disruption of physical processes that sustain different levels of organisms (e.g., primary producers) are threats that affect aquatic biodiversity and the productivity of these habitats. Therefore, the large scale assessment of freshwater habitats for proactive water resources planning and the development of climate change mitigation and resource management strategies is essential. However, such monitoring and assessment is complicated by the inaccessibility of many large wetland systems during times of inundation, making in situ sampling unfeasible at a time when high levels of aquatic primary producers are generating food and energy sources for higher order consumers. To understand the physical dynamics of aquatic primary producers and freshwater habitats (1991–2019) during such times in a large floodplain river in northern Australia (Gilbert catchment), this study integrated Landsat-derived modified normalised difference water index and normalised difference vegetation index in a classification tree model. Thereafter, key hydrological drivers (rainfall and river discharge) of floodplain productivity and connectivity were assessed using a range of multivariate techniques. Results show that the floodplain had a high aquatic plant biomass during the summer wet season based on the correlation between aquatic biomass accumulation (hot spots) and inundation ( r = 0.83 @ phase lag r = 0.68 @ lag = 1 month) at downstream Gilbert catchment appear to be a relatively stronger indicator of hot spots of floodplain biomass accumulation as opposed to local rainfall ( r = 0.57 @ lag = 3 months). While the downstream discharge explains a significant proportion of variability in the leading orthogonal mode of rainfall ( r = 0.83 ), statistical relationships developed between discharge/rainfall and the distribution of aquatic primary producers confirm that both rivers (flow) and local rainfall are key optimal predictors of inundation and sites of primary producers with river flows being a better indicator of the latter. It is therefore argued that hydro-meteorological fluctuations will be key constraints on freshwater habitats and the growth of primary producers, albeit, human disturbance of flow can impact on floodplain productivity. As illustrated in this study, such constraints are reflected in the spatial patterns and changing characteristics (connectivity and spatial heterogeneity) of hot spots of primary producers and freshwater habitats (Palustrine, Lacustrine, and Riverine ecosystems).

Hotspots of biotic compositional change in lakes along vast latitudinal transects in northern Canada.

Ecotones mark zones of rapid change in ecological structure at various spatial scales. They are believed to be particularly susceptible to shifts caused by environmental transformation, making them key regions for studying the effects of global change. Here, we explored the variation in assemblage structure of aquatic primary producer and consumer communities across latitudinal transects in northeastern North America (Québec-Labrador) to identify spatial patterns in biodiversity that indicated the location of transition zones across the landscape. We analyzed species richness and the cumulative rate of compositional change (expressed as beta-diversity) of diatoms and chironomids to detect any abrupt shifts in the rate of spatial taxonomic turnover. We used principal coordinates analysis to estimate community turnover with latitude, then applied piecewise linear regression to assess the position of ecotones. Statistically significant changes in assemblage composition occurred at 52 and 55°N, corresponding to the transition between closed- and open-crown forest, and to the southern onset of the forest tundra (i.e., the forest limit), respectively. The spatial distribution of ecotones was most strongly related to air temperature for chironomids and to vegetation- and soil-related chemical attributes of lake water for diatoms, including dissolved organic carbon content and water color. Lakes at mid- to high-latitudes currently face pressures from rapidly rising temperatures, accompanied by large increases in organic carbon inputs from their catchments, often leading to browning and its associated effects. The biota at the base of food webs in lakes located in transition zones are disproportionately affected by the cascading effects of these multi-factorial changes, concurrent with pronounced terrestrial greening observed in these regions. Similar patterns of biotic shifts have been observed along alpine aquatic transects, indicating the potential for widespread restructuring of cold, high-altitude and high-latitude freshwater communities due to global change.

Temporal variations in riverine hydrochemistry and estimation of the carbon sink produced by coupled carbonate weathering with aquatic photosynthesis on land: an example from the Xijiang River, a large subtropical karst-dominated river in China.

The coupled carbonate weathering represents a significant carbon sink and can be controlled by the riverine hydrochemical variations. However, magnitudes, variations, and mechanisms responsible for the carbon sink produced by coupled carbonate weathering are unclear. In view of this, temperature, pH, dissolved oxygen, turbidity, electrical conductivity, and discharge of the Xijiang River at Wuzhou Hydrologic Gauging Station was recorded during October 2013 to September 2015 to elucidate the temporal variations in riverine hydrochemistry and their controlling mechanisms. To obtain the complete carbon sink flux (CSF) produced by coupled carbonate weathering with terrestrial aquatic photosynthesis in the river basin, the fluxes of dissolved inorganic carbon (DIC), autochthonous organic carbon (AOC, sourced from the transformation of DIC via aquatic photosynthesis), and sedimentary AOC were all considered. The results show that seasonal hydrochemical variations in the Xijiang River were related not only to dilution effects but also aquatic primary production. These results demonstrate that the variations in discharge caused by rainfall played a dominant role in controlling the variations in the CSF due to the chemostatic behavior of DIC and dissolved organic carbon (DOC). The CSF of the Xijiang River produced by coupled carbonate weathering was calculated as 11.06tCkm-2a-1, including DIC carbon sink flux of 6.56tCkm-2a-1, AOC flux (FAOC) of 2.25tCkm-2a-1, and sedimentary AOC flux (FSAOC) of 2.25tCkm-2a-1. The FAOC and FSAOC together accounted for approximately 69% of DIC carbon sink flux, or approximately 41% of the CSF, indicating that the riverine AOC flux may be high and must be considered in the estimation of rock weathering-related carbon sinks.

Aluminium triggers oxidative stress and antioxidant response in the microalgae Scenedesmus sp

Aluminium (Al) water pollution is an increasing environmental problem and comprehensive analysis of toxic responses of aquatic primary producer organisms is imperative. We characterized the antioxidant response of Scenedesmus sp. microalga to Al-induced oxidative stress. After 72 h of exposure to Al (0, 10, and 100 μM) in a modified Bold Basal Medium (pH 5.0), we observed cell aggregation and alterations in the subcellular structure, strong lipid peroxidation and oxidative stress induction (detected with the fluorescent probe 2′,7′-dichlorodihydrofluorescein diacetate) in parallel with Al accumulation in cells. At the same time, Al toxicity caused depletion of important macronutrients like Ca, which is important for cell-wall structure. Analysis of antioxidant enzymatic activities in Al-treated Scenedesmus cells revealed that catalase, ascorbate peroxidase, as well as different isoforms of superoxide dismutase were inhibited especially at the highest Al dose (100 μM), cells that accumulated the highest concentration of Al. On the other hand, glutathione reductase activity increased at that Al concentration. Immunodetection after Western-blotting confirmed that only ascorbate peroxidase inhibition was apparently due to a decrease in enzyme levels. However, the inhibition of catalase and activation of glutathione reductase activities seemed related with post-translational modifications in protein function as protein expression decreased or increased, respectively under Al stress. Our results may help to understand toxic mechanisms triggered by Al in freshwater microalgae, which in turn could aid to select suitable biomarkers of Al contamination in aquatic ecosystems.

In‐lake transformations of dissolved organic matter composition in a subalpine lake do not change its biodegradability

AbstractIn freshwater ecosystems, dissolved organic matter (DOM) originates from terrestrial and aquatic primary production, and its microbial biodegradability is expected to vary due to differences in its biogeochemical composition. However, the interaction of various DOM sources with the aquatic microbial population remains widely debated. Here, we performed laboratory bioassays, conducted in the dark for 20 d, to examine how changes in DOM composition influence its microbial biodegradability along a hydrological continuum (i.e., lake inlet, lake layers, and lake outlet) of a subalpine lake over four seasons. Despite a predominance of terrestrial DOM and lowest initial abundance of microorganisms, the highest microbial growth rates were observed at the lake inlet (0.0076 ± 0.0011 cells mL−1 h−1) across all seasons. DOM reactivity differed more with time (seasons) than with space (sampling sites) and DOM compositional differences showed higher degradability in upper lake layers, but not at the lake outlet. Additionally, gradual humification over incubation time was observed in almost all seasons and sites. Overall, an enhanced biodegradability of DOM was not detected even though lake sites were characterized by an autochthonous, presumably labile DOM signature. However, our results highlight the potential of thriving bacteria in terrestrial‐dominated DOM environments. This observation challenges a previous hypothesis that DOM of terrestrial origin is less accessible and more recalcitrant, while emphasizing the flexible response of aquatic systems to seasonal fluctuations.

Diversity of Viruses Infecting Eukaryotic Algae.

Algae are photosynthetic organisms that drive aquatic ecosystems, e.g. fuelling food webs or forming harmful blooms. The discovery of viruses that infect eukaryotic algae has raised many questions about their influence on aquatic primary production and their role in algal ecology and evolution. Although the full extent of algal virus diversity is still being discovered, this review summarizes current knowledge of this topic. Where possible, formal taxonomic classifications are referenced from the International Committee on Taxonomy of Viruses (ICTV); since the pace of virus discovery has far surpassed the rate of formal classification, however, numerous unclassified viruses are discussed along with their classified relatives. In total, we recognized 61 distinct algal virus taxa with highly variable morphologies that include dsDNA, ssDNA, dsRNA, and ssRNA genomes ranging from approximately 4.4 to 560 kb, with virion sizes from approximately 20 to 210nm in diameter. These viruses infect a broad range of algae and, although there are a few exceptions, they are generally lytic and highly species or strain specific. Dedicated research efforts have led to the appreciation of algal viruses as diverse, dynamic, and ecologically important members of the biosphere, and future investigations will continue to reveal the full extent of their diversity and impact.

Herbicide Exposure and Toxicity to Aquatic Primary Producers.

The aim of the present review was to give an overview of the current state of science concerning herbicide exposure and toxicity to aquatic primary producers. To this end we assessed the open literature, revealing the widespread presence of (mixtures of) herbicides, inevitably leading to the exposure of non-target primary producers. Yet, herbicide concentrations show strong temporal and spatial variations. Concerning herbicide toxicity, it was concluded that the most sensitive as well as the least sensitive species differed per herbicide and that the observed effect concentrations for some herbicides were rather independent from the exposure time. More extensive ecotoxicity testing is required, especially considering macrophytes and marine herbicide toxicity. Hence, it was concluded that the largest knowledge gap concerns the effects of sediment-associated herbicides on primary producers in the marine/estuarine environment. Generally, there is no actual risk of waterborne herbicides to aquatic primary producers. Still, median concentrations of atrazine and especially of diuron measured in China, the USA and Europe represented moderate risks for primary producers. Maximum concentrations due to misuse and accidents may even cause the exceedance of almost 60% of the effect concentrations plotted in SSDs. Using bioassays to determine the effect of contaminated water and sediment and to identify the herbicides of concern is a promising addition to chemical analysis, especially for the photosynthesis-inhibiting herbicides using photosynthesis as endpoint in the bioassays. This review concluded that to come to a reliable herbicide hazard and risk assessment, an extensive catch-up must be made concerning macrophytes, the marine environment and especially sediment as overlooked and understudied environmental compartments.

Decadal variations of total organic carbon production in the inner-shelf of the South China Sea and East China Sea

Abstract Organic carbon content is one of the major proxies of aquatic primary production and implication of environmental changes. However, there is a scarcity of information regarding the decadal variation of organic carbon production in inner-shelf of South China Sea (SCS) and East China Sea (ECS). To bridge this gap of information two sediment cores were collected from the inner shelf of SCS (Leizhou Peninsula) and ECS. Then, Total Organic Carbon (TOC), Total Inorganic Carbon (TIC) and Total Nitrogen (TN) content were examined. The TOC content in the Leizhou Peninsula averaged 0.56% and varied from 0.35% to 0.81%. At decadal time scale, the TOC content of Leizhou Peninsula erratically increased in the last century, and it distinctly peaked after 1990’s. This is related to increased primary production due to the increased input of anthropogenic nutrients and rainfall level. The TOC content of the inner shelf of ECS averaged 0.5% and varied narrowly from 0.46% to 0.53%. The TOC:TN ratio of ECS averaged 5.65 and varied from 4.42 to 7.85, indicating there is high degree of organic matter degradations. The TN:TP ratios were below 10 for the periods before late-1990’s, indicating that there had been a potential nitrogen limitation in the inner shelf of ECS. Generally, this study showed that the TOC and TIC of ECS and SCS inner-shelf had undergone substantial changes in the last century.

Impact study of Beni-Haroun dam on the environmental and socio-economic elements in Kébir-Rhumel basin, Algeria

AbstractSurface water of Kébir Rhumel basin is indispensable for domestic and industrial needs of this region. Industrial development, with water excessive use and chemical products, in production and industrial treatment, and not sustainable fertilizers in agriculture, constitutes a serious threat to maintain our resources of good water quality. The majority of domestic and industrial wastewaters of the region, discharged to the stream water of Kébir Rhumel basin, promote the water enrichment in nutritious elements, phosphorus and nitrogen and particularly, the resulting increase in the aquatic primary production, mainly the planktonic or benthic algae. As a result, the physical and chemical properties of water deteriorate.This basin allows construction of the largest dam in Algeria “Beni-Haroun dam”. The infrastructure that was one of the greatest challenges of Algeria is now a reality. Hydraulic complex of Beni-Haroun remains a strategic and major achievement in the development program of water resources sector. This enormous building was constructed in the territory of the Wilaya (province) of Mila, used to meet water needs, with four million inhabitants, of eastern Algeria and other neighbouring regions that have suffered from lack of water consumption, especially in summer. In addition, it will irrigate over 42 000 ha, going thus to the several plains.Integration of sociological and environmental concerns into dams design is a recent phenomenon. It is considered at the impact study level, during which the dam study project is accompanied by a survey to assess project impact on natural environment and socioeconomic development.

Co-limitation by N and P Characterizes Phytoplankton Communities Across Nutrient Availability and Land Use

Historically, freshwater lakes have been widely assumed to be singly limited by phosphorus (P) because the dominant paradigm assumes that nitrogen fixation (N2 fixation) will compensate for any nitrogen (N) deficits. However, a growing body of evidence demonstrates that primary producer response to nutrient manipulation most frequently indicates co-limitation by N and P. Differences in N and P supply ratio have been shown to influence the identity and severity of nutrient limitation, but whether N and P concentration and the ratio of N to P concentrations can explain the frequency of co-limitation in aquatic primary producer assemblages remains unclear, especially in ecosystems subject to human perturbation that strongly increase nutrient availability. We determined how resource availability influences nutrient limitation by N and P of phytoplankton primary production across 12 lakes in Minnesota that vary in watershed land use and lake nutrient levels. We measured epilimnetic lake metabolism and indicators of N2 fixation to evaluate their influence on nutrient limitation status of planktonic algal assemblages. Despite large differences in land use (agricultural, urban, and suburban) and water column N and P availability, planktonic algal response to nutrient manipulation was consistently characterized by co-limitation by N and P across years and months. Neither P availability (as concentrations of total and inorganic forms) nor N2-flux rate predicted responses to nutrient additions. N availability significantly influenced responses of phytoplankton to nutrient additions across years, but this effect was small. The ratio of total N to total P significantly influenced the response to single additions of N and P (these effects were negative and positive, respectively) in summer 2013. Importantly, higher lake primary production and heterocyte count (number of nitrogen fixing cells) were also associated with a stronger, positive response to N + P addition. Overall, these data suggest that planktonic algal assemblages are predominantly characterized by co-limitation by N and P despite large and diverse human impacts on nutrient inputs. Additionally, higher rates of primary production increase the likelihood of co-limitation. Together, these results further support the paradigm shift toward dual management of N and P in aquatic ecosystems.

Climate-induced changes in carbon flows across the plant-consumer interface in a small subarctic lake

Reconstructions of past food web dynamics are necessary for better understanding long-term impacts of climate change on subarctic lakes. We studied elemental and stable isotopic composition of sedimentary organic matter, photosynthetic pigments and carbon stable isotopic composition of Daphnia (Cladocera; Crustacea) resting eggs (δ13CClado) in a sediment record from a small subarctic lake. We examined how regional climate and landscape changes over the last 5800 years affected the relative importance of allochthonous and autochthonous carbon transfer to zooplankton. Overall, δ13CClado values were well in line with the range of theoretical values of aquatic primary producers, confirming that zooplankton consumers in subarctic lakes, even in the long-term perspective, are mainly fuelled by autochthonous primary production. Results also revealed greater incorporations of benthic algae into zooplankton biomass in periods that had a warmer and drier climate and clearer water, whereas a colder and wetter climate and lower water transparency induced higher contributions of planktonic algae to Daphnia biomass. This study thus emphasizes long-term influence of terrestrial-aquatic linkages and in-lake processes on the functioning of subarctic lake food webs.

Controls on Dissolved Organic Carbon Bioreactivity in River Systems

Inland waters transport, transform and retain significant amounts of dissolved organic carbon (DOC) that may be biologically reactive (bioreactive) and thus potentially degraded into atmospheric CO2. Despite its global importance, relatively little is known about environmental controls on bioreactivity of DOC as it moves through river systems with varying water residence time (WRT). Here we determined the influence of WRT and landscape properties on DOC bioreactivity in 15 Swedish catchments spanning a large geographical and environmental gradient. We found that the short-term bioreactive pools (0–6 d of decay experiments) were linked to high aquatic primary productivity that, in turn, was stimulated by phosphorus loading from forested, agricultural and urban areas. Unexpectedly, the percentage of long-term bioreactive DOC (determined in 1-year experiments) increased with WRT, possibly due to photo-transformation of recalcitrant DOC from terrestrial sources into long-term bioreactive DOC with relatively lower aromaticity. Thus, despite overall decreases in DOC during water transit through the inland water continuum, DOC becomes relatively more bioreactive on a long time-scale. This increase in DOC bioreactivity with increasing WRT along the freshwater continuum has previously been overlooked. Further studies are needed to explain the processes and mechanisms behind this pattern on a molecular level.