Browsing by Subject "SEDIMENTS"

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  • Kivilä, Elissa Henriikka; Luoto, Tomi P.; Rantala, Marttiina V.; Nevalainen, Liisa (2020)
    High latitude freshwater systems are facing changes in catchment-mediated allochthonous input, as well as physical and chemical controls triggered by on-going climate change, which may alter their carbon processing and ecological characteristics. To explore changes in chironomid functional responses and carbon utilization in relation to longterm environmental change, we studied a sediment core covering ca. 2000 years from a tundra lake in northern Finland, which was analysed for sediment geochemistry, isotopic composition of chironomid remains and their functional assemblages. We aimed to relate changes in chironomid functional feeding assemblages and resource utilization, based on Bayesian stable isotope modelling, and determined that the long-term resource utilization was more controlled by sediment geochemistry (resource availability) and climatic variables, reflecting changes in habitat and lake ontogeny, rather than the functional feeding assemblage composition. Change horizons were observed for both sediment geochemistry and functional assemblage composition. However, different timing of these changes suggests different drivers affecting the dynamics of primary production and chironomid community functionality. We also compared the recent warming period to Medieval Climate Anomaly (MCA), observing divergent patterns, which suggests that MCA may not be a good analogue for changes induced by on-going climate warming.
  • Zawiska, Izabela; Dimante-Deimantovica, Inta; Luoto, Tomi P.; Rzodkiewicz, Monika; Saarni, Saija; Stivrins, Normunds; Tylmann, Wojciech; Lanka, Anna; Robeznieks, Martins; Jilbert, Tom (2020)
    Cultural eutrophication, the process by which pollution due to human activity speeds up natural eutrophication, is a widespread and consequential issue. Here, we present the 85-year history of a small, initially Lobelia-Isoetes dominated lake. The lake's ecological deterioration was intensified by water pumping station activities when it received replenishment water for more than 10 years from a eutrophic lake through a pipe. In this study, we performed a paleolimnological assessment to determine how the lake's ecosystem functioning changed over time. A multi-proxy (pollen, Cladocera, diatoms, and Chironomidae) approach was applied alongside a quantitative reconstruction of total phosphorus using diatom and hypolimnetic dissolved oxygen with chironomid-based transfer functions. The results of the biotic proxy were supplemented with a geochemical analysis. The results demonstrated significant changes in the lake community's structure, its sediment composition, and its redox conditions due to increased eutrophication, water level fluctuations, and erosion. The additional nutrient load, particularly phosphorus, increased the abundance of planktonic eutrophic-hypereutrophic diatoms, the lake water's transparency decreased, and hypolimnetic anoxia occurred. Cladocera, Chironomidae, and diatoms species indicated a community shift towards eutrophy, while the low trophy species were suppressed or disappeared.
  • Leppänen, Jaakko; Weckström, Jan; Korhola, Atte (2018)
    Mining is one of the key industries in the world and mine water pollution is a serious threat to aquatic ecosystems. Historical monitoring data on the pollution history and impacts in aquatic ecosystems, however, are rarely available, so paleolimnological methods are required to explore the consequences of past pollution. We studied the history of cladoceran community dynamics in Lake Kirkkojarvi, southern Finland, including the periods before, during and after mining. We analyzed the geochemical composition and cladoceran subfossil remains in a Pb-210-dated sediment core to evaluate the magnitude, rate, and direction of cladoceran community changes through time. The cladoceran community was altered significantly by mining activity that occurred during the mid-twentieth century. During more recent times, however, eutrophication effects have overridden the impacts of mining. After mining ceased, the cladoceran community underwent an abrupt regime shift towards taxa that reflect more eutrophic conditions. This change was caused by intensive farming activity and fertilizer use over the past few decades. The recent history of Lake Kirkkojarvi is a textbook example of a regime shift triggered by multiple human-caused stressors. Our findings also highlight the utility of cladocerans as bio-indicators in pollution research and illustrate the sensitivity of aquatic ecosystems to anthropogenic modification.
  • Stivrins, Normunds; Briede, Agrita; Steinberga, Dace; Jasiunas, Nauris; Jeskins, Jurijs; Kalnina, Laimdota; Maksims, Alekss; Rendenieks, Zigmars; Trasune, Liva (2021)
    Modern pollen composition obtained from waterbody surface sediment represents surrounding vegetation and landscape features. A lack of detailed information on modern pollen from Latvia potentially limits the strength of various pollen-based reconstructions (vegetation composition, climate, landscape, human impact) for this territory. The aim of this study is to compare how modern pollen from natural and human-made waterbodies reflects the actual vegetation composition and landscape characteristics. Modern pollen analyses from surface sediment samples of 36 waterbodies from Latvia alongside oceanic-continental, lowland-upland, urban-rural and forested-agricultural gradients have been studied. In addition, we considered the dominant Quaternary sediment, soil type and land use around the studied waterbodies in buffer zones with widths of one and four km. The information on climate for the last 30 years from the closest meteorological station for each study site was obtained. Data were analyzed using Pearson correlation and principal component analysis. Results show that relative pollen values from surface sediment of waterbodies reflect dominant vegetation type and land use. Modern forest biomass had a positive correlation with pollen accumulation rate, indicating the potential use of pollen-based forest biomass reconstructions for the boreonemoral zone after additional research and calibration.
  • Kylander, Malin E.; Plikk, Anna; Rydberg, Johan; Löwemark, Ludvig; Salonen, J. Sakari; Fernandez-Fernandez, Maria; Helmens, Karin (2018)
    Biological proxies from the Sokli Eemian (Marine Isotope Stage 5e) paleolake sequence from northeast Finland have previously shown that, unlike many postglacial records from boreal sites, the lake becomes increasingly eutrophic over time. Here, principal components (PC) were extracted from a high resolution multi-element XRF core scanning dataset to describe minerogenic input from the wider catchment (PC1), the input of S, Fe, Mn, and Ca-rich detrital material from the surrounding Sokli Carbonatite Massif (PC2), and chemical weathering (PC3). Minerogenic inputs to the lake were elevated early in the record and during two abrupt cooling events when soils and vegetation in the catchment were poor. Chemical weathering in the catchment generally increased over time, coinciding with higher air temperatures, catchment productivity, and the presence of acidic conifer species. Abiotic edaphic processes play a key role in lake ontogeny at this site stemming from the base cation- and nutrient-rich bedrock, which supports lake alkalinity and productivity. The climate history at this site, and its integrated effects on the lake system, appear to override development processes and alters its long-term trajectory.
  • Suzuki, Satoru; Nakanishi, Sayoko; Tamminen, Manu; Yokokawa, Taichi; Sato-Takabe, Yuki; Ohta, Kohei; Chou, Hsin-Yiu; Muziasari, Windi I.; Virta, Marko (2019)
    The use of antibiotics in aquaculture causes selection pressure for antibiotic-resistant bacteria (ARB). Antibiotic resistance genes (ARGs) may persist in ARB and the environment for long time even after stopping drug administration. Here we show monthly differences in the occurrences of genes conferring resistance to sulfonamides (i.e. sul1, sul2, sul3), and tetracyclines (tet(M)) in Japanese aquaculture seawater accompanied by records of drug administration. sul2 was found to persist throughout the year, whereas the occurrences of sul1, sul3, and tet(M) changed month-to-month. sul3 and tet(M) were detected in natural bacterial assemblages in May and July, but not in colony-forming bacteria, thus suggesting that the sul3 was harbored by the non-culturable fraction of the bacterial community. Comparison of results from Taiwanese, Japanese, and Finnish aquaculture waters reveals that the profile of sul genes and tet(M) in Taiwan resembles that in Japan, but is distinct from that in Finland. To our knowledge, this work represents the first report to use the same method to compare the dynamics of sul genes and tet(M) in aquaculture seawater in different countries. (C) 2019 Elsevier B.V. All rights reserved.
  • Scopetani, Costanza; Chelazzi, David; Mikola, Juha; Leinio, Ville; Heikkinen, Reijo; Cincinelli, Alesandra; Pellinen, Jukka (2020)
  • Eriksson, Mats; Ämmälä, Kirsi; Levy, Isabelle; Gastaud, Janine; Lehto, Jukka; Scholten, Jan (2019)
    To analyze plutonium (Pu) in open ocean waters can be challenging due to the low seawater concentrations. In this study we compared two techniques for Pu determination, one in-situ MnO2 cartridge system and the more commonly used MnO2 precipitation technique. During the pre-pilot GEOTRACES cruise ANT XXX-1 (2005) we tested MnO2 cartridges for the pre-concentration of Pu from seawater at 19 sampling stations on a transect in the southeastern Atlantic Ocean between Vigo (Spain) and Cape Town (South Africa). Our in-situ sampling setup consisted of one particle cartridge followed by three MnO2 cartridges in a series. Through the system we pumped between 956 and 2700 I of surface seawater with a flow rate between 1.6 and 5.21/min. We found that the adsorption efficiency of a single MnO2 cartridge to adsorb Pu was rather constant and on average a 58 +/- 7%. The adsorption efficiency was also found to be independent of seawater: temperature in the range of 18.3-29.2 degrees C, salinity range 34.2-37.1 parts per thousand, and conductivity in the range of 46.8-58.4 mS/cm. In parallel with the in-situ sampling, discrete surface water samples between 259 and 281 I were taken and Pu was pre-concentrated using the MnO2 precipitation method. We find a good agreement between the Pu concentrations determined with the two different techniques. The in-situ pre-concentration technique requires more radiochemical work in the laboratory but has the advantage that large seawater volumes can be sampled without the necessity for radiochemical processing on-board the ship. The much larger volumes sampled with the in-situ technique compared with the precipitation technique, enables accurate determination of Pu-isotopic ratios with a low relative standard deviation. We have shown in this study that in-situ MnO2 cartridge technique can be used in a reliable way for the determination of dissolved Pu seawater concentration in open ocean waters.
  • Plado, Juri; Preeden, Ulla; Joeleht, Argo; Pesonen, Lauri J.; Mertanen, Satu (2016)
    The hill range of Vaivara Sinimaed in northeast Estonia consists of several narrow east-to northeast-trending glaciotectonic fold structures. The folds include tilted (dips 4-75 degrees) Middle Ordovician (early Darriwilian) layered carbonate strata that were studied by mineralogical, palaeomagnetic, and rock magnetic methods in order to specify the post-sedimentational history of the area and to obtain a better control over the palaeogeographic position of Baltica during the Ordovician. Mineralogical studies revealed that (titano) magnetite, hematite, and goethite are carriers of magnetization. Based on data from 5 sites that positively passed a DC tilt test, a south-easterly downward directed component A (D-ref = 154.6 degrees +/- 15.3 degrees, I-ref = 60.9 degrees +/- 9.7 degrees) was identified. The component is carried by (titano) magnetite, dates to the Middle Ordovician (Plat = 17.9 degrees, Plon = 47.3 degrees, K = 46.7, A95 = 11.3 degrees), and places Baltica at mid-southerly latitudes. Observations suggest that in sites that do not pass the tilt test, the glaciotectonic event has caused some rotation of blocks around their vertical axis.
  • Reitalu, Triin; Bjune, Anne E.; Blaus, Ansis; Giesecke, Thomas; Helm, Aveliina; Matthias, Isabelle; Peglar, Sylvia M.; Salonen, J. Sakari; Seppae, Heikki; Vaeli, Vivika; Birks, H. John B. (2019)
    Sedimentary pollen offers excellent opportunities to reconstruct vegetation changes over past millennia. Number of different pollen taxa or pollen richness is used to characterise past plant richness. To improve the interpretation of sedimentary pollen richness, it is essential to understand the relationship between pollen and plant richness in contemporary landscapes. This study presents a regional-scale comparison of pollen and plant richness from northern Europe and evaluates the importance of environmental variables on pollen and plant richness. We use a pollen dataset of 511 lake-surface pollen samples ranging through temperate, boreal and tundra biomes. To characterise plant diversity, we use a dataset formulated from the two largest plant atlases available in Europe. We compare pollen and plant richness estimates in different groups of taxa (wind-pollinated vs. non-wind-pollinated, trees and shrubs vs. herbs and grasses) and test their relationships with climate and landscape variables. Pollen richness is significantly positively correlated with plant richness (r = 0.53). The pollen plant richness correlation improves (r = 0.63) when high pollen producers are downweighted prior to estimating richness minimising the influence of pollen production on the pollen richness estimate. This suggests that methods accommodating pollen-production differences in richness estimates deserve further attention and should become more widely used in Quaternary pollen diversity studies. The highest correlations are found between pollen and plant richness of trees and shrubs (r = 0.83) and of wind-pollinated taxa (r = 0.75) suggesting that these are the best measures of broad-scale plant richness over several thousands of square kilometres. Mean annual temperature is the strongest predictor of both pollen and plant richness. Landscape openness is positively associated with pollen richness but not with plant richness. Pollen richness values from extremely open and/or cold areas where pollen production is low should be interpreted with caution because low local pollen production increases the proportion of extra-regional pollen. Synthesis. Our results confirm that pollen data can provide insights into past plant richness changes in northern Europe, and with careful consideration of pollen-production differences and spatial scale represented, pollen data make it possible to investigate vegetation diversity trends over long time-scales and under changing climatic and habitat conditions.
  • Asmala, Eero; Gustafsson, Camilla; Krause-Jensen, Dorte; Norkko, Alf; Reader, Heather; Staehr, Peter A.; Carstensen, Jacob (2019)
    Coastal ecosystems act as filters of nutrients from land to the open sea. We investigated the role of eelgrass (Zostera marina) metabolism in the coastal filter transforming nitrogen, phosphorus, and organic carbon. Field campaigns following identical methodologies were carried out at two contrasting coastal locations: the mesohaline and nutrient-rich Roskilde Fjord, Denmark, and the mesotrophic brackish Tvärminne archipelago, Finland. Over the 24-h in situ benthic incubations, we measured oxygen concentrations continuously and assessed changes in DOM characteristics and net fluxes of carbon, nitrogen, and phosphorus. Ecosystem metabolism modeled on the basis of the O2 data showed that the systems were either net heterotrophic (Roskilde Fjord; − 1.6 and − 2.4 g O2 m−2 day−1 in eelgrass meadow and bare sand, respectively) or had balanced primary production and respiration (Tvärminne; 0.0 and 0.2 g O2 m−2 day−1). Overall, initial nutrient stoichiometry was a key factor determining benthic–pelagic fluxes of nutrients, which exacerbated the deviations from Redfield ratios of N and P, indicating an efficient use of the limiting nutrient. A net diel uptake of dissolved inorganic N was observed at both locations (− 2.3 μmol l−1 day−1 in Roskilde Fjord and − 0.1 μmol l−1 day−1 in Tvärminne). Despite minor changes in dissolved organic carbon concentrations during the incubations, a marked increase of fluorescent DOM was observed at both locations, suggesting rapid heterotrophic processing of the DOM pool. Our results underline that the biogeochemical role of eelgrass in the coastal filter is not inherent, but strongly dependent on the environmental conditions.
  • Orme, Lisa Claire; Crosta, Xavier; Miettinen, Arto; Divine, Dmitry; Husum, Katrine; Isaksson, Elisabeth; Wacker, Lukas; Mohan, Rahul; Ther, Olivier; Ikehara, Minoru (2020)
    Centennial- and millennial-scale variability of Southern Ocean temperature over the Holocene is poorly known, due to both short instrumental records and sparsely distributed high-resolution temperature reconstructions, with evidence for past temperature variations in the region coming mainly from ice core records. Here we present a high-resolution (similar to 60 year), diatom-based sea surface temperature (SST) reconstruction from the western Indian sector of the Southern Ocean that spans the interval 14.2 to 1.0 ka (calibrated kiloyears before present). During the late deglaciation, the new SST record shows cool temperatures at 14.2-12.9 ka and gradual warming between 12.9 and 11.6 ka in phase with atmospheric temperature evolution. This supports the evolution of the Southern Ocean SST during the deglaciation being linked with a complex combination of processes and drivers associated with reorganisations of atmospheric and oceanic circulation patterns. Specifically, we suggest that Southern Ocean surface warming coincided, within the dating uncertainties, with the reconstructed slowdown of the Atlantic Meridional Overturning Circulation (AMOC), rising atmospheric CO2 levels, changes in the southern westerly winds and enhanced upwelling. During the Holocene the record shows warm and stable temperatures from 11.6 to 8.7 ka followed by a slight cooling and greater variability from 8.7 to 1 ka, with a quasi-periodic variability of 200-260 years identified by spectral analysis. We suggest that the increased variability during the mid- to late Holocene reflects the establishment of centennial variability in SST connected with changes in the high-latitude atmospheric circulation and Southern Ocean convection.
  • Rodil, Ivan F.; Lucena-Moya, Paloma; Tamelander, Tobias; Norkko, Joanna; Norkko, Alf (2020)
    The exchange between the water column and the seafloor is a complex process, and is particularly intensive in the shallow waters of highly productive coastal areas, where the temporal variability in the inputs of pelagic organic matter will determine many aspects of the benthic community structure. However, few studies have focused on the seasonality of inputs of organic matter to the seafloor, and on the consequent dynamics and time scales of response of benthic consumers. We conducted a 1-year study where we repeatedly sampled multiple organic compounds traditionally used as markers to study the link between the pelagic organic matter inputs and the seafloor, and the potential response of benthic macrofauna to seasonal trends in phytoplankton biomass. We simultaneously quantified the particulate organic matter in the water column, the sinking material and different seafloor compartments, and analyzed it for pigments, organic carbon and nitrogen content, C/N ratio, and stable isotopes. Seafloor sediment was also analyzed for total lipids, and the dominant macrobenthic species for isotopic signatures. Results showed a major deposition of fresh organic matter during the spring bloom followed by more degraded organic matter inputs during the late summer bloom and even lower quality of the organic matter reaching the seafloor during winter. Strong positive relationships between water column and sedimentary pigments suggest that phytoplankton was the main source of carbon to the seafloor. The isotopic signatures of the dominant macrobenthic species suggest a fast response to the organic matter inputs from the water column. However, different species responded differently to the deposition of organic matter. Macoma balthica and Marenzelleria spp. fed on more reworked and degraded sedimentary material, while Monoporeia affinis showed a shift in the feeding habits according to its life stage, with adult individuals feeding on fresher material than juveniles did. Our study highlights the seasonal variability of the benthic-pelagic coupling and the utility of a multi-marker approach to follow the temporal inputs of organic matter from the water column to the seafloor and benthic organisms.
  • Katrantsiotis, Christos; Norström, Elin; Smittenberg, Rienk H.; Salonen, J. Sakari; Plikk, Anna; Helmens, Karin (2021)
    The Last Interglacial warm period, the Eemian (ca. 130-116 thousand years ago), serves as a reference for projected future climate in a warmer world. However, there is a limited understanding of the seasonal characteristics of interglacial climate dynamics, especially in high latitude regions. In this study, we aim to provide new insights into seasonal trends in temperature and moisture source location, linked to shifts in atmospheric circulation patterns, for northern Fennoscandia during the Eemian. Our study is based on the distribution and stable hydrogen isotope composition (delta D) of n-alkanes in a lake sediment sequence from the Sokli paleolake in NE Finland, placed in a multi-proxy framework. The delta D values of predominantly macrophyte-derived mid-chain n-alkanes are interpreted to reflect lake water delta D variability influenced by winter precipitation delta D (delta Dprec), ice cover duration and deuterium (D)-depleted meltwater. The delta D values of terrestrial plant-derived long-chain n-alkanes primarily reflect soil water delta D variability modulated by summer delta Dprec and by the evaporative enrichment of soil and leaf water. The delta Dprec variability in our study area is mostly attributed to the temperature effect and the moisture source location linked to the relative dominance between D-depleted continental and polar air masses and D-enriched North Atlantic air masses. The biomarker signal further corroborates earlier diatom-based studies and pollen-inferred January and July temperature reconstructions from the same sediment sequence. Three phases of climatic changes can be identified that generally follow the secular variations in seasonal insolation: (i) an early warming trend succeeded by a period of strong seasonality (ii) a mid-optimum phase with gradually decreased seasonality and cooler summers, and (iii) a late climatic instability with a cooling trend. Superimposed on this trend, two abrupt cooling events occur in the early and late Eemian. The Sokli delta D variability is generally in good agreement with other North Atlantic and Siberian records, reflecting major changes in the atmospheric circulation patterns during the Eemian as a response to orbital and oceanic forcings. (C) 2021 The Authors. Published by Elsevier Ltd.
  • Holmqvist-Sipilä, Elisabeth; Ilves, Kristin (2022)
    We present geochemical data of soils sampled from two Late Iron Age (a.d. 550–1050) buildings at Bartsgårda on the Åland Islands, Finland. The houses had different constructions and use-patterns, one being an intensively used dwelling house, rich in finds, whereas the other, scarce in finds, had a more specialized character, linked to ceremonial rather than domestic activities. Systematic and targeted feature sampling was carried out to analyze 190 samples using energy dispersive X-ray fluorescence spectrometry (ED-XRF) to 1) identify floor/activity levels in the houses based on vertical and horizontal geochemical anomalies; 2) compare the anthropogenic activity signals of the buildings; and, 3) test a rapid and cost-efficient ex situ analytical strategy for geochemical characterization of archaeological soils. Although the long-term use of the site as a livestock paddock introduced some complexities, based on the geochemical and micromorphological data, the houses had several activity levels and markedly different anthropogenic profiles.
  • Inbal, Asaf; Cristea-Platon, Tudor; Ampuero, Jean-Paul; Hillers, Gregor; Agnew, Duncan; Hough, Susan E. (2018)
  • Rantala, Marttiina V.; Luoto, Tomi P.; Nevalainen, Liisa (2016)
    Widespread ecological reorganizations and increases in organic carbon (OC) in lakes across the Northern Hemisphere have raised concerns about the impact of the ongoing climate warming on aquatic ecosystems and carbon cycling. We employed diverse biogeochemical techniques on a high-resolution sediment record from a subarctic lake in northern Finland (70 degrees N) to examine the direction, magnitude and mechanism of change in aquatic carbon pools prior to and under the anthropogenic warming. Coupled variation in the elemental and isotopic composition of the sediment and a proxy-based summer air temperature reconstruction tracked changes in aquatic production, depicting a decline during a cool climate interval between similar to 1700-1900 C.E. and a subsequent increase over the 20th century. OC accumulation rates displayed similar coeval variation with temperature, mirroring both changes in aquatic production and terrestrial carbon export. Increase in sediment organic content over the 20th century together with high inferred aquatic UV exposure imply that the 20th century increase in OC accumulation is primarily connected to elevated lake production rather than terrestrial inputs. The changes in the supply of autochthonous energy sources were further reflected higher up the benthic food web, as evidenced by biotic stable isotopic fingerprints.
  • Oksman, Mimmi; Juggins, Stephen; Miettinen, Arto Ilmari; Witkowski, Andrzej; Weckström, Kaarina (2019)
    Sound knowledge of present-day diatom species and their environments is crucial when attempting to reconstruct past climate and environmental changes based on fossil assemblages. For the North Atlantic region, the biogeography and ecology of many diatom taxa that are used as indicator-species in paleoceanographic studies are still not well known. Using information contained in large diatom-environment calibration datasets can greatly increase our knowledge on diatom taxa and improve the accuracy of paleoenvironmental reconstructions. A diatom calibration dataset including 183 surface sediment samples from the northern North Atlantic was used to explore the distribution and ecology of 21 common Northern Hemisphere diatom taxa. We define the ecological responses of these species to April sea ice concentrations and August sea surface temperatures (aSSTs) using Huisman-Olff-Fresco (HOF)-response curves, provide distribution maps, temperature optima and ranges, and high-quality light microscope images. Based on the results, we find species clearly associated with cold, warm and temperate waters. All species have a statistically significant relationship with aSST, and 15 species with sea ice. Of these, Actinocyclus curvatulus, Fragilariopsis oceanica and Porosira glacialis are most abundant at high sea ice concentrations, whereas Coscinodiscus radiants, Shionodiscus oestrupii, Thalassionema nitzschioides, Thalassiosira angulata, Thalassiosira nordenskioeldii and Thalassiosira pacifica are associated with low sea ice concentrations/ice-free conditions. Interestingly, some species frequently used as sea ice indicators, such as Fragilariopsis cylindrus, show similar abundances at high and low sea ice concentrations with no statistically significant relationship to sea ice.
  • Virta, Leena; Teittinen, Anette (2022)
    The responses of biotic communities and ecosystems to climate change may be abrupt and non-linear. Thus, resolving ecological threshold mechanisms is crucial for understanding the consequences of climate change and for improving environmental management. Here, we present a study on the threshold responses of benthic diatom communities that are an important component of all aquatic environments and strongly contribute to global primary production. We reach beyond the taxonomic perspective by focusing on the diversity and functions of diatom communities and benthic biomass along gradients of salinity and wind disturbance, whose climate-change-induced changes have been predicted to strongly affect biotic communities in the marine and brackish systems in the future. To improve the generality of our results, we examine three self-collected datasets from different spatial scales (6-830 km) and ecosystem types. We collected samples from rock pools or from littoral stones and studied taxonomic thresholds using Threshold Indicator Taxa Analysis (TITAN2). We investigated threshold responses of community diversity, community functions, and benthic biomass using t-tests and regression analyses. Our results indicated that decreasing salinity may result in increasing diver-sity but decreasing biomass of brackish communities, while the effects of increasing wind disturbance were contradictory among spatial scales. Benthic biomass correlated with the taxonomic and functional diversity, as well as with the body size distribution of communities, highlighting the importance of considering community functions and organismal size when predicting ecosystem functions. The most pronounced effects of decreasing salinity and increasing wind distur-bance on community functions were changes in the abundance of low-profile diatom species, which, due to the high resilience of low-profile diatoms, may lead to changes in ecosystem functioning and resilience. To conclude, decreasing salinity and increasing wind disturbance may lead to threshold responses of biotic communities, and these changes may have profound effects on ecosystem functioning along marine coastal areas.
  • Saderne, Vincent; Fusi, Marco; Thomson, Timothy; Dunne, Aislinn; Mahmud, Fatima; Roth, Florian; Carvalho, Susana; Duarte, Carlos M. (2021)
    Mangroves have the capacity to sequester organic carbon (C-org) in their sediments permanently. However, the carbon budget of mangroves is also affected by the total alkalinity (TA) budget. Principally, TA emitted from carbonate sediment dissolution is a perennial sink of atmospheric CO2. The assessment of the TA budget of mangrove carbonate sediments in the Red Sea revealed a large TA emission of 403 +/- 17 mmol m(-2)d(-1), independent of light, seasons, or the presence of pneumatophores, compared to -36 +/- 10 mmol m(-2)d(-1)in lagoon sediment. We estimate the TA emission from carbonate dissolution in Red Sea mangroves supported a CO2 uptake of 345 +/- 15 gC m(-2)yr(-1), 23-fold the C-org burial rate of 15 gC m(-2)yr(-1). The focus on C-org burial in sediments may substantially underestimate the role of mangroves in CO(2)removal. Quantifying the role of mangroves in climate change mitigation requires carbonate dissolution to be included in assessments.