Decrease In Nutrient Concentrations Research Articles

Elevated Contribution of Low Nucleic Acid Prokaryotes and Viral Lysis to the Prokaryotic Community Along the Nutrient Gradient From an Estuary to Open Ocean Transect.

Prokaryotes represent the largest living biomass reservoir in aquatic environments and play a crucial role in the global ocean. However, the factors that shape the abundance and potential growth rate of the ecologically distinct prokaryotic subgroups [i.e., high nucleic acid (HNA) and low nucleic acid (LNA) cells] along varying trophic conditions in the ocean remain poorly understood. This study conducted a series of modified dilution experiments to investigate how the abundance and potential growth rate of HNA and LNA prokaryotes and their regulating factors (i.e., protozoan grazing and viral lysis) change along a cross-shore nutrient gradient in the northern South China Sea. The results showed that the abundance of both HNA and LNA cells was significantly positively correlated with the abundance of heterotrophic nanoflagellates and viruses, whereas only HNA abundance exhibited a significant positive correlation with nutrient level. With a decreasing nutrient concentration, the potential growth rate of the HNA subgroup declined significantly, while that of the LNA subgroup was significantly enhanced, leading to an elevated relative potential growth rate of the LNA to HNA subgroup under decreasing nutrient levels. Furthermore, our data revealed different regulatory roles of protozoan grazing and viral lysis on the HNA and LNA subgroups, with HNA suffering higher mortality pressure from grazing than from lysis in contrast to LNA, which experienced equivalent pressures. As the nutrient levels declined, the relative contribution of lysis to the mortality of the HNA subgroup increased significantly, in contrast to the insignificant change in that of the LNA subgroup. Our results indicated the elevated role of LNA cells in the prokaryotic community and the enhanced viral lysis pressure on the total prokaryotes under oligotrophic conditions. This implies a weakened efficiency of carbon cycling within the microbial loop and enhanced viral lysis to shunt more carbon and energy flow in the future ocean, in which oligotrophication will be strengthened due to global warming.

Soil Nutrients Effects on the Performance of Durum Wheat Inoculated with Entomopathogenic Fungi

Entomopathogenic fungi (EFs) are widely used as biological control agents. However, some strains of Beauveria bassiana and Metarhizium brunneum can also promote plant growth and increase nutrient uptake. We examined the effects of soil properties on the performance of Triticum durum inoculated by seed dressing with these EFs and grown on 12 agricultural soils. The plants were supplied with all nutrients except P and Zn (essential for yield and the grain quality of wheat). Fungal inoculation increased the grain yield and harvest index significantly with B. bassiana (17% and 14%, respectively) but not with M. brunneum (6% and 6%, respectively). The increase in grain yield was positively and moderately correlated with the soil available phosphorus (POlsen) in plants inoculated with B. bassiana and with the soil content in poorly crystalline Fe oxides with M. brunneum. In addition, the increase in aerial dry matter resulting from inoculation with B. bassiana was negatively correlated with soil available Zn. Furthermore, the observed increase in grain yields due to fungal inoculation resulted in P and Zn grain dilution (grain nutrient concentrations decrease). Inoculation with B. bassiana increased grain Zn uptake and the proportion of Zn in grain relative to that in aerial dry matter. Success in the mutualistic relationship between EF and wheat plants depends on the fungal strain and soil properties.

Landscape Drivers of Dynamic Change in Water Quality of U.S. Rivers.

Water security is a top concern for social well-being, and dramatic changes in the availability of freshwater have occurred as a result of human uses and landscape management. Elevated nutrient loading and perturbations to major ion composition have resulted from human activities and have degraded freshwater resources. This study addresses the emerging nature of streamwater quality in the 21st century through analysis of concentrations and trends in a wide variety of constituents in streams and rivers of the U.S. Concentrations of 15 water quality constituents including nutrients, major ions, sediment, and specific conductance were analyzed over the period 1982-2012 and a targeted trend analysis was performed from 1992 to 2012. Although environmental policy is geared toward addressing the long-standing problem of nutrient overenrichment, these efforts have had uneven success, with decreasing nutrient concentrations at urbanized sites and little to no change at agricultural sites. Additionally, freshwaters are being salinized rapidly in all human-dominated land use types. While efforts to control nutrients are ongoing, rapid salinity increases are ushering in a new set of poorly defined issues. Increasing salinity negatively affects biodiversity, mobilizes sediment-bound contaminants, and increases lead contamination of drinking water, but its effects are not well integrated into current paradigms of water management.

Biochar Affects Essential Nutrients of Carrot Taproots and Lettuce Leaves.

Essential nutrient concentrations in crops can affect human health. While biochar has the potential as a soil amendment to improve crop yields, it may also affect the concentrations of nutrients such as Ca, Fe, K, Mg, Mn, and Zn in edible portions of crops. To better characterize effects of biochar on important human nutrients in food crops, we evaluated the effects of biochar on lettuce (Lactuca sativa L. cv. Black-Seeded Simpson) leaf and carrot [Daucus carota subsp. sativus (Hoffm.) Schübl. cv. Tendersweet] developing taproot nutrients. Plants were grown in pots in a greenhouse using sandy loam (Coxville, fine, kaolinitic, thermic Typic Paleaquults) and loamy sand (Norfolk, fine-loamy, kaolinitic, thermic Typic Kandiudults,) series soils, amended with biochar produced from four feedstocks: pine chips (PC), poultry litter (PL), swine solids (SS), and switchgrass (SG); and two blends of PC plus PL [Pc/PL, 50%/50% (55) and 80%/20% (82) by weight]. Biochar was produced at 350, 500, and 700 °C from each feedstock. Lettuce leaf and carrot taproot total nutrient concentrations were determined by inductively coupled plasma analysis. Biochar (especially at least in part manure-based, i.e., PL, SS, 55, and 82 at nearly all temperatures) primarily decreased nutrient concentrations in lettuce leaves, with Ca, Mg, and Zn affected most. Carrot taproot nutrient concentrations also deceased, but to a lesser extent. Some biochars increased leaf or taproot nutrient concentrations, especially K. This study indicated that biochar can both decrease and increase leaf and taproot nutrient concentrations important for human health. Thus, potential effects on nutrients in plants should be carefully considered when biochar is used as a soil amendment with vegetable crops.

Thin-layer fine-sand capping of polluted sediments decreases nutrients in overlying water of Wuhan Donghu Lake in China.

Capping water body sediments with a thin layer of sand is an effective technique to decrease nutrient concentrations in the water column and accelerate ecological restoration of eutrophic water bodies. However, long-term effects of thin-layer sand capping in shallow lakes are reported less often. Using clean fine sand and geotextile mats as capping materials for sediments collected from Wuhan Donghu Lake in China, we designed a 290-day tank experiment with 3 cm of sand capping at four percentages of sediment coverage from 25 to 100% and a control (no capping). We monitored total nitrogen (TN), total phosphorus (TP), nitrate (NO3-), ammonia (NH4+), and soluble reactive phosphorus (SRP) in the overlying water every 7 days. Mean TN and NO3- concentrations were significantly the lowest (P < 0.05) at 50% coverage. Further increase in coverage kept them slightly fluctuating. NH4+ concentration was significantly lowest (P < 0.05) at 75% coverage. The relation between coverage and mean TP and SRP concentrations indicated that 75% coverage significantly decreased (P < 0.05) them, and increasing coverage to 100% decreased them even more. The fluxes of TN and TP estimated between sediments and overlying water showed that the thin fine-sand layer significantly increased the function of sediments as a sink of TN from overlying water and the potential of a sand layer to block release of TP from sediments (P < 0.05). Our results suggested that if thin-layer sand capping were applied to Wuhan Donghu Lake, more than 50% coverage is required to decrease nutrients in the lake's water.

Changes in chlorophyll concentration and phenology in the North Sea in relation to de‐eutrophication and sea surface warming

AbstractAt least two major drivers of phytoplankton production have changed in recent decades in the North Sea: sea surface temperature (SST) has increased by ~ 1.6°C between 1988 and 2014, and the nitrogen and phosphorus loads from surrounding rivers have decreased from the mid‐1980s onward, following reduction policies. Long time series spanning four decades (1975–2015) of nutrients, chlorophyll (Chl), and pH measurements in the Southern and Central North Sea were analyzed to assess the impact of both the warming and the de‐eutrophication trends on Chl. The de‐eutrophication process, detectable in the reduction of nutrient river loads to the sea, caused a decrease of nutrient concentrations in coastal waters under riverine influence. A decline in annual mean Chl was observed at 11 out of 18 sampling sites (coastal and offshore) in the period 1988–2016. Also, a shift in Chl phenology was observed around 2000, with spring bloom formation occurring earlier in the year. A long time series of pH in the Southern North Sea showed an increase until the mid‐1980s followed by a rapid decrease, suggesting changes in phytoplankton production that would support the observed changes in Chl. Linear correlations, however, did not reveal significant relationships between Chl variability and winter nutrients or SST at the sampling sites. We propose that the observed changes in Chl (annual or seasonal) around 2000 are a response of phytoplankton dynamics to multiple stressors, directly or indirectly influenced by de‐eutrophication and climate warming.

Hysteretic response of Microbial Eukaryotic Communities to Gradually Decreased Nutrient Concentrations in Eutrophic Water.

External environments to microbial eukaryotic communities often change gradually with time. However, whether the responses of microbial eukaryotic communities to these gradually changed environments are continuous or hysteretic and the mechanisms underlying these responses are largely unknown. Here, we used a microcosm to investigate the temporal variation of microbial eukaryotic communities with the gradually decreased nutrient concentrations (nitrogen and phosphorus). We found the differences of microbial eukaryotic community composition and species richness between the control and treatment groups were low during the days 0 to 12, although the nutrient concentrations decreased rapidly during this period in treatment group. However, these differences were clear during the days 14 to 18, although the nutrient concentrations decreased slowly during this period in treatment group. The mechanisms for these results are that the strong homogenous selection (perhaps due to the biotic factors) during the days 8 to 10 in treatment group might enhance the stability of microbial eukaryotic communities. However, the continuously decreased nutrient concentrations weakened the homogenous selection and promoted the strength of environmental filtering, and therefore resulted in the distinct change of microbial eukaryotic communities during the days 14 to 18 in treatment group. Fungi, Chlorophyta and Chrysophyta which associated with the nutrient removal played important roles in this hysteretic change of microbial eukaryotic communities. Overall, our findings suggest that disentangling the non-linear response of communities to gradual environmental changes is essential for understanding ecosystem restoration and degradation in future.

Exogenous Zinc Forms Counteract NaCl-Induced Damage by Regulating the Antioxidant System, Osmotic Adjustment Substances, and Ions in Canola (Brassica napus L. cv. Pactol) Plants

Salinity is the principal natural obstacles for sustainable agriculture, adversely impacting 30% of the world’s irrigated land, resulting in food insecurity, particularly in arid and semi-arid areas. Zinc has several functions in plants; nevertheless, the promising roles of nano-zinc oxide particle in plants under salinity stress are not clear. The current study aims to investigate the roles of zinc (water, 75 mg L−1 zinc sulfate (Zn), and 10 mg L−1 zinc oxide nanoparticle (ZNP)) on the mitigation of NaCl stress (6000 mg L−1) on morpho-physiological attributes and yield of canola plants. Salinity exhibited a substantial reduction in canola plant growth, enhanced photosynthetic pigment degradation, and decreased nutrient concentrations. A decrease in the overall yield and a decrease in various individual components were considerably stimulated by zinc application under non-salinized and salinized conditions. Salinity caused a visible increase in membrane permeability (MP%), malondialdehyde (MDA), and hydrogen peroxide (H2O2) concentrations. Interestingly, zinc application significantly decreased MP%, MDA, and H2O2 concentrations by the upregulation of antioxidant enzymes (superoxide dismutase, catalase, peroxidase) and levels of non-enzymatic antioxidants (ascorbic, carotenoids, and total soluble phenolic compounds). Furthermore, zinc application also enhanced osmoregulation by increasing proline and total soluble carbohydrates accumulation, as well as increased nitrogen, potassium, and phosphorus in the plant tissues in correlation with a decline in sodium and chloride contents. Zinc’s, especially ZNP, role in the mitigation the negative effects of salinity on canola growth and yield may be connected with the upregulating oxidative defense system and osmolyte synthesis as well as ionic regulation.

Zooplankton changes during bottom-up and top-down control due to sustainable restoration in a shallow urban lake

Long-term cyanobacterial blooms and hypereutrophic state have been typical for the shallow, urban Swarzędzkie Lake for many years. Diversion of sewage did not change its trophic status, so restoration began in autumn 2011 using the sustainable approach based on three methods. The aim of the study was to analyse how sustainable restoration affects zooplankton. We hypothesised that bottom-up and top-down methods reconstructed zooplankton composition. Thus, the abundance of large-size cladocerans increased and controlled phytoplankton effectively. The elimination of cyanobacteria bloom, the decrease of rotifer abundance and the twofold increase of filter-feeder effectiveness were observed in summer 2012. However, high phosphorus concentration, lack of regular cyprinid removal and insufficient fish stocking together with high temperature prevented zooplankton from controlling cyanobacteria bloom in summer 2013. Rotifer domination with high trophy species was noted, as before restoration. The number of rotifers decreased in 2014, while crustaceans increased due to the significant decrease of nutrient concentrations and an intensification of biomanipulation treatments. Therefore, summer phytoplankton growth was low, without cyanobacteria dominance. The rebuilding of zooplankton in Swarzędzkie Lake was observed during sustainable restoration. However, the treatments should be intensified when adverse changes were observed to obtain better results for the improvement of water quality.

Effects of flooding regime and meteorological variability on the removal efficiency of treatment wetlands under a Mediterranean climate

The modeling of free-water surface constructed wetlands (FWS-CWs) provides an improved understanding of their processes and constitutes a useful tool for the design and management of these systems. In this work, a dynamic simulation model for FWS-CWs was developed and used to simulate the operation of a FWS-CW proposed for improving the treatment of sewage effluents entering the Tablas de Daimiel National Park in central Spain. The process-based model simulates carbon, nitrogen and phosphorus dynamics, including key hydrological processes for wetlands under a fluctuating Mediterranean semiarid climate. The model allows for the simulation of the operation of FWS-CWs with variable flooding regimes, relating the surface water level to the flooded area and the water outflow. Simulations of the proposed FWS-CW under different water management schemes and scenarios were run, and the consequences of those management strategies on the treatment efficiency were analyzed. Under the Mediterranean climate and geology of the study area, namely, high water losses through evapotranspiration and infiltration, the decrease in nutrient concentrations was higher when the flooded area was reduced in summer than when a constant flooded area was maintained. Moreover, the meteorological variability introduced in different scenarios produced different results in terms of water outflow, but differences in terms of nutrient concentrations were not significant. The ability of the model to simulate different hydrological scenarios and their consequences on water quality makes it a useful decision-support tool.

Long-term changes in spatially structured benthic diatom assemblages in a major subtropical wetland under restoration

ABSTRACTBiological communities often comprise core species that are locally abundant and regionally common. Benthic diatoms are crucial primary producers in wetlands and reflect ecosystem responses to long-term hydrological and nutrient changes, yet few studies explicitly focus on patterns and drivers of diatom core species abundance in these ecosystems. We investigated how benthic diatom core species abundance varies over space, time, and environmental gradients in a major shallow wetland, the Florida Everglades, where environmental gradients and diatom assemblages are spatially structured by water diversion and nutrient loading. We analysed a long-term dataset of species and environmental data collected over 6 locations in 2 major Southern Everglades drainages. We hypothesized that (1) the abundance of 4 diatom core species (present in >90% of the samples with relative abundance >5%) and water depth, benthic algal mat mineral weight and organic content, and mat total phosphorus and total nitrogen would vary more across space than time; and (2) the cumulative diatom core species abundance would increase with decreasing nutrient concentrations and depth. We found that (1) the abundance of 2 of the core species and the environmental conditions varied more between sites than between seasons and years, and (2) the cumulative abundance of the 4 diatom core species increased with oligotrophic and shallow water conditions. This study shows how, on average, the 4 diatom core species comprise ∼82% of the total diatom abundance in the Everglades’ benthic algal mats because these species are adapted to nutrient limitation and water scarcity. Similar dynamics may be at play in other wetlands undergoing hydrological and nutrient changes, thus warranting future work to predict these primary producers’ responses to such changes.

Spatio-temporal dynamics in the dissolved nutrient waste plume from Norwegian salmon cage aquaculture

AEI Aquaculture Environment Interactions Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AEI 10:385-399 (2018) - DOI: https://doi.org/10.3354/aei00276 Spatio-temporal dynamics in the dissolved nutrient waste plume from Norwegian salmon cage aquaculture H. M. Jansen1,2,*, O. J. Broch3, R. Bannister1, P. Cranford4, A. Handå3, V. Husa1, Z. Jiang5, T. Strohmeier1, Ø. Strand1 1Institute of Marine Research, Nordnesgaten 50, 5005 Bergen, Norway 2Wageningen University and Research, Wageningen Marine Research (WMR), PO Box 77, 4400 AB Yerseke, The Netherlands 3SINTEF Ocean, Postboks 4762 Torgarden, 7465 Trondheim, Norway 4Fisheries and Oceans Canada, St. Andrews Biological Station, 125 Marine Science Dr., Saint Andrews, New Brunswick E5B 0E4, Canada 5Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, 106 Nanjing Road, Qingdao, Shandong Province, PR China *Corresponding author: henrice.jansen@wur.nl ABSTRACT: The aim of this study was to define the waste plume dynamics around a salmon farm in Norway. Systematic water sampling and numerical modeling were implemented to define nutrient concentrations in the upper water column at long-term (seasonal) and short-term (between and within days) time scales. Nutrient enhancement was observed for ammonium only, while the concentrations of orthophosphate and organic wastes were never higher than the background values. The spatial magnitude of cage effluent dispersion was limited. Empirical results detected enhanced concentrations up to 100 m down-current of the farm when fish biomass was high. Model results showed that the zone of influence could occasionally reach to >1000 m. In the first year of production, when fish biomass was low, no enhancement was detected, and in April and September of the following year, average ammonium concentrations were respectively 0.2 and 0.8 µM above the background concentrations. Taking the ambient seasonal variability into account, this resulted in 1.6 times higher concentrations for both sampling months. The measured short-term temporal variability in nutrient concentrations near the cages varied up to 2 times from day to day and were 3.5 times higher in the evening compared to the morning. As seasonal investigations were performed in the morning, maximum enhancement was likely underestimated. The rapid decrease in nutrient concentrations with increasing distance from the cages suggests that the farm studied here is currently not causing significant degradation of surface water quality. Results of this study contribute to evaluating the potential for ecological mitigation of waste nutrients and provide directions for design of optimized integrated multi-trophic aquaculture facilities. KEY WORDS: Atlantic salmon · Farm scale · Nutrients · Nitrogen · Integrated multi-trophic aquaculture · IMTA · Pelagic · Environmental impact Full text in pdf format Supplementary material PreviousNextCite this article as: Jansen HM, Broch OJ, Bannister R, Cranford P and others (2018) Spatio-temporal dynamics in the dissolved nutrient waste plume from Norwegian salmon cage aquaculture. Aquacult Environ Interact 10:385-399. https://doi.org/10.3354/aei00276 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 10. Online publication date: September 27, 2018 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2018 Inter-Research.

Nutrient and phytoplankton dynamics driven by the Beaufort Gyre in the western Arctic Ocean during the period 2008–2014

Nutrient and phytoplankton pigment data were collected during summer cruises in 2008–2014 to examine how the Beaufort Gyre (BG) affected regional differences in nutrient stocks and the phytoplankton community. The results showed a gradual decrease in nutrient concentrations and increasing depth of the chlorophyll maxima toward the center of the gyre. A horizontal map of nitrate at a depth of 50 m indicated nitrogen deficiency in the gyre compared with that in the surroundings. Biogeochemical model simulations suggested that an increased freshwater convergence, driven by the strengthened BG and sea ice retreat, was primarily responsible for the decrease in nutrient stocks. In the BG zone, the contribution of diatoms to the phytoplankton community decreased, accompanied by the increased contribution of small flagellates. The current state of the BG under anticyclonic winds negatively affected the diatom biomass and biological carbon pump. The possible rotation of wind regimes from anticyclonic to cyclonic might relieve the nitrogen deficiency for phytoplankton growth in the western Arctic Ocean.

The relationship between transpiration and nutrient uptake in wheat changes under elevated atmospheric CO2.

The impact of elevated [CO2 ] (e[CO2 ]) on crops often includes a decrease in their nutrient concentrations where reduced transpiration-driven mass flow of nutrients has been suggested to play a role. We used two independent approaches, a free-air CO2 enrichment (FACE) experiment in the South Eastern wheat belt of Australia and a simulation study employing the agricultural production systems simulator (APSIM), to show that transpiration (mm) and nutrient uptake (g m-2 ) of nitrogen (N), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg) and manganese (Mn) in wheat are correlated under e[CO2 ], but that nutrient uptake per unit water transpired is higher under e[CO2 ] than under ambient [CO2 ] (a[CO2 ]). This result suggests that transpiration-driven mass flow of nutrients contributes to decreases in nutrient concentrations under e[CO2 ], but cannot solely explain the overall decline.

Long-term decline of the canopy-forming algae Gelidium corneum, associated to extreme wave events and reduced sunlight hours, in the southeastern Bay of Biscay

Canopy-forming macroalgae are experiencing large biogeographical shifts due to climate change. One of them (Gelidium corneum) has shown a dramatic decline in biomass in northern Spain, in the past 20 years. We investigate here two most plausible hypotheses to explain its decline: (i) a combination of increasing wave energy and decrease of irradiance in the growth season; and (ii) a combination of increasing light in summer and decreasing nutrient concentration. Using a dataset of biomass and environmental variables (1993–2016), in three sectors and three water depths, we have determined that the variables explaining more biomass variability were: suspended solids, nitrate, sunlight hours, significant wave height threshold exceedances (Hs5m), temperature, silicate, and nitrite. When undertaking multiple regression analyses for the whole depth range, only the model including sunlight hours with Hs5m was selected, being highly significant (p < 0.0001) and explaining 37% of the variability. When comparing the macroalgal biomass between the initial period of the series (where the biomass was stable) and final period (showing biomass decline), 45% decrease was observed while the Hs5m increase was 41%, detaching the algae from the substratum during the growth season. The decline rate in biomass with time, at each sector and depth, was highly correlated (p < 0.001) to the wave energy flux received at each depth, which was higher at 5 m in all sectors, decreasing with depth. In turn, nutrients, instead of decreasing, have increased, and only nitrate presented a significant negative correlation with G. corneum biomass, which was not significant after detrending. The significant (p = 0.001) increase in rainfall over the studied period can explain the increase of those nutrients. Hence, we question whether the effect of nutrients is such, as already described. The most likely factor explaining the decline of this macroalga was the combination of sunlight hours decrease and Hs5m increase.

Seasonality and spatial heterogeneity of the surface ocean carbonate system in the northwest European continental shelf

In 2014–5 the UK NERC sponsored an 18 month long Shelf Sea Biogeochemistry research programme which collected over 1500 nutrient and carbonate system samples across the NW European Continental shelf, one of the largest continental shelves on the planet. This involved the cooperation of 10 different Institutes and Universities, using 6 different vessels. Additional carbon dioxide (CO2) data were obtained from the underway systems on three of the research vessels. Here, we present and discuss these data across 9 ecohydrodynamic regions, adapted from those used by the EU Marine Strategy Framework Directive (MSFD). We observed strong seasonal and regional variability in carbonate chemistry around the shelf in relation to nutrient biogeochemistry. Whilst salinity increased (and alkalinity decreased) out from the near-shore coastal waters offshore throughout the year nutrient concentrations varied with season. Spatial and seasonal variations in the ratio of DIC to nitrate concentration were seen that could impact carbon cycling. A decrease in nutrient concentrations and a pronounced under-saturation of surface pCO2 was evident in the spring in most regions, especially in the Celtic Sea. This decrease was less pronounced in Liverpool Bay and to the North of Scotland, where nutrient concentrations remained measurable throughout the year. The near-shore and relatively shallow ecosystems such as the eastern English Channel and southern North Sea were associated with a thermally driven increase in pCO2 to above atmospheric levels in summer and an associated decrease in pH. Non-thermal processes (such as mixing and the remineralisation of organic material) dominated in winter in most regions but especially in the northwest of Scotland and in Liverpool Bay. The large database collected will improve understanding of carbonate chemistry over the North-Western European Shelf in relation to nutrient biogeochemistry, particularly in the context of climate change and ocean acidification.

Ecological characterization of intertidal rockpools: Seasonal and diurnal monitoring of physico-chemical parameters

Diurnal and seasonal variations in temperature, salinity, oxygen concentration, carbonate chemistry parameters and nutrient concentration were monitored within mid-tidal rockpools on the north-western coast of Brittany, France. We also examined the importance of rockpool physical characteristics (e.g. shore height, surface, volume and depth) on the physico-chemical variability. Rockpool shore height and depth appeared as the main physical factors driving physico-chemical variations. Shallow upper shore rockpools exhibited the largest diurnal and seasonal fluctuations of temperature, oxygen concentration and pHT. Conversely, deeper and lower shore rockpools experienced weaker variations, excepted for salinity and nutrient concentrations. The physico-chemical environment was likely to be strongly influenced by rockpool community composition, especially in summer when rockpools were colonized by dense canopy-forming algae. During the day-time emersion, photosynthesis increased oxygen concentration and pHTbut decreased nutrient concentrations in upper shore rockpools. The increase in rockpool pHT provided an alkaline environment conducive to coralline algal calcification. Conversely, at night, upper shore rockpools presented a strong decrease in oxygen concentration and pHT due to the high community respiration, increasing the dissolution in coralline algae. Therefore, rockpools are characterized by complex interactions between physical and chemical parameters and biological processes. Rockpools appear as suitable environments to examine the physiological processes set up by species to face natural variability, especially in a context of climate change.

Influence of Different Nutrient Concentrations and Population Densities on the Root System of Arabidopsis thaliana

This study examined the modifications made to the root system architecture of Arabidopsis thaliana when subjected to an increase in population (biotic) and a decrease in nutrient concentration (abiotic). Population density was found to have significant effect on number of root hairs (p 0.05). This work could serve as a guideline when considering sowing density and fertilizer application to other crop species.

Mixotrophic species influencing phytoplankton community structuring during the filling phase of a subtropical reservoir

Aiming to evaluate temporal alterations in the dynamics of the phytoplankton community in response to environmental changes occurring during the filling phase of Santa Clara reservoir, samples were taken weekly from April to June 2005 in the region close to the dam, following vertical gradients of light and temperature. Sampling depths comprised the subsurface (sup), upper limit of the euphotic zone (Zeu), lower limit of the epilimnion (Zmix) and near the bottom (Zmax). Low light availability hindered phytoplankton growth throughout the period. Descriptor species (biovolume > 5%) were classified in 17 functional groups (FGs): X2, Y, D, C, P, Lo, E, B, Na, MP, A, J, K, S1, Ws, F and M. Phytoplankton biovolume was low during the filling phase, and characterized a meso-oligotrophic environment. Mixotrophic species belonging to functional groups X2, Y, Lo and E provided the greatest contribution to total biovolume and dominated throughout the period. Water column thermal structure and a tendency of a decrease in nutrient concentrations influenced the change in the dominance of FGs. Our results suggest that mixotrophic strategy was determinant for phytoplankton production and biomass, representing a competitive advantage over strictly autotrophic phytoplankton, suggesting that during the filling phase of Santa Clara reservoir, the microbial loop played an important role in the flow of energy and carbon to higher trophic levels of the food web. Therefore, our initial hypothesis that the disruption of longitudinal connectivity in the river and alterations in the mixing regime and light availability would change phytoplankton community structure causing a replacement in the dominance of FGs containing turbulence-tolerant species by FGs containing species with a higher demand for water column stability and light availability was not corroborated. Although a species replacement was observed, this was not due to enhanced resource availability, but rather due to the trophic abilities of the FGs.

Effects of long term nutrient and climate variability on subfossil Cladocera in a deep, subalpine lake (Lake Garda, northern Italy)

Albeit subfossil Cladocera remains are considered as a reliable proxy for tracking historical lake development, they have been scarcely studied in large subalpine lakes south of the Alps. In this study, subfossil Cladocera remains from Lake Garda in northern Italy were analyzed to track the lake’s environmental changes since the Middle Ages. One core was retrieved from the largest sub-basin of Lake Garda (Brenzone, 350 m deep) and two cores were retrieved from the profundal and littoral zone of the smaller lake sub-basin (Bardolino, 80 and 40 m deep, respectively). The species distribution of Cladocera remains in recent sediment layers was similar to that observed in contemporary water samples. The deepest sections of the three cores were characterized by species sensitive to water temperature, which suggest a key role of major climatic events in driving the lake response during the late Holocene. The most evident change in Cladocera assemblages in the studied cores was observed during the 1960s, when planktonic taxa such as Daphnia spp. and Bosmina spp. became dominant at the expense of littoral taxa. Despite the highly coherent general pattern of subfossil Cladocera, the cores showed a set of minor differences, which were attributed to different morphological and hydrological features of the two basins forming Lake Garda. Multivariate analysis revealed a clear relation of Cladocera to climate variability during periods of low lake nutrient levels (i.e. before the 1960s). This provides additional information on past ecological responses of Lake Garda, as contrast previous data from subfossil diatom and pigment analyses did not fully capture effects of climate change during the same period. Since the 1960s shifts in assemblage composition of Cladocera and diatoms were highly coherent, in response to nutrient increase and the following, less pronounced, decrease in nutrient concentrations. During the last five decades, the response of the Cladocera to climate variability appeared to be masked by nutrient change. This work points up the potential of the multi-proxy approach for disentangling the multifaceted biological responses to multiple environmental stressors in large and deep lakes.