268 research outputs found
Lake browning counteracts cyanobacteria responses to nutrients: Evidence from phytoplankton dynamics in large enclosure experiments and comprehensive observational data
Lakes worldwide are affected by multiple stressors, including climate change. This includes massive loading of both nutrients and humic substances to lakes during extreme weather events, which also may disrupt thermal stratification. Since multi-stressor effects vary widely in space and time, their combined ecological impacts remain difficult to predict. Therefore, we combined two consecutive large enclosure experiments with a comprehensive time-series and a broad-scale field survey to unravel the combined effects of storm-induced lake browning, nutrient enrichment and deep mixing on phytoplankton communities, focusing particularly on potentially toxic cyanobacterial blooms. The experimental results revealed that browning counteracted the stimulating effect of nutrients on phytoplankton and caused a shift from phototrophic cyanobacteria and chlorophytes to mixotrophic cryptophytes. Light limitation by browning was identified as the likely mechanism underlying this response. Deep-mixing increased microcystin concentrations in clear nutrient-enriched enclosures, caused by upwelling of a metalimnetic Planktothrix rubescens population. Monitoring data from a 25-year time-series of a eutrophic lake and from 588 northern European lakes corroborate the experimental results: Browning suppresses cyanobacteria in terms of both biovolume and proportion of the total phytoplankton biovolume. Both the experimental and observational results indicated a lower total phosphorus threshold for cyanobacterial bloom development in clearwater lakes (10-20 mu g P L-1) than in humic lakes (20-30 mu g P L-1). This finding provides management guidance for lakes receiving more nutrients and humic substances due to more frequent extreme weather events
Cyanotoxin Occurrence and Diversity in 98 Cyanobacterial Blooms from Swedish Lakes and the Baltic Sea
The Drinking Water Directive (EU) 2020/2184 includes the parameter microcystin LR, a cyanotoxin, which drinking water producers need to analyze if the water source has potential for cyanobacterial blooms. In light of the increasing occurrences of cyanobacterial blooms worldwide and given that more than 50 percent of the drinking water in Sweden is produced from surface water, both fresh and brackish, the need for improved knowledge about cyanotoxin occurrence and cyanobacterial diversity has increased. In this study, a total of 98 cyanobacterial blooms were sampled in 2016-2017 and identified based on their toxin production and taxonomical compositions. The surface water samples from freshwater lakes throughout Sweden including brackish water from eight east coast locations along the Baltic Sea were analyzed for their toxin content with LC-MS/MS and taxonomic composition with 16S rRNA amplicon sequencing. Both the extracellular and the total toxin content were analyzed. Microcystin's prevalence was highest with presence in 82% of blooms, of which as a free toxin in 39% of blooms. Saxitoxins were found in 36% of blooms in which the congener decarbamoylsaxitoxin (dcSTX) was detected for the first time in Swedish surface waters at four sampling sites. Anatoxins were most rarely detected, followed by cylindrospermopsin, which were found in 6% and 10% of samples, respectively. As expected, nodularin was detected in samples collected from the Baltic Sea only. The cyanobacterial operational taxonomic units (OTUs) with the highest abundance and prevalence could be annotated to Aphanizomenon NIES-81 and the second most profuse cyanobacterial taxon to Microcystis PCC 7914. In addition, two correlations were found, one between Aphanizomenon NIES-81 and saxitoxins and another between Microcystis PCC 7914 and microcystins. This study is of value to drinking water management and scientists involved in recognizing and controlling toxic cyanobacteria blooms
Kan antalet vÀxtplanktonprovtagningar minskas frÄn sju till fyra gÄnger per Är utan att betydelsefull information förloras?
VÀxtplankton Àr en grupp av organismer som reagerar snabbt pÄ bÄde kemiska och biologiska variabler. Det innebÀr att variationen inom och mellan Är kan vara stor. De nationella monitoringprogrammen har under en lÀngre tid provtagit vÀxtplank-ton mÄnadsvis under tillvÀxtsÀsongen vilket innebÀr sju provtagningar per Är. VÀxtplankton bör provtas ofta för att man inte ska missa förÀndringar i succes-sionsstadier och produktionsmaxima som kan ge indikationer pÄ vattenkvalitetsför-Àndringar. Dessa missar man lÀtt Àven med sju provtagningar per Är. Med fyra provtagningar fokuserar man pÄ vÄrens tidiga successionsstadium (april och maj) och sensommarens bÄde biomasse- och strukturmÀssigt mer stabila stadium (juli och augusti). Antalet vÀxtplanktonprovtagningar i det nationella Trendsjöpro-grammet har sedan 2007 minskat frÄn sju till fyra gÄnger per Är. Inom IKEU-programmet har vÀxtplankton fortsatt att analyseras sju gÄnger per Är och nu finns det en önskan att utreda vilken information man missar om man reducerar antalet provtagningar frÄn sju till fyra gÄnger per Är i alla sjöar. Studien visar att om man vill detaljstudera vÀxtplanktons samhÀllsstruktur mellan sjöar eller grupper av sjöar som ingÄr i IKEU-programmet, blir det ingen större skillnad i resultat om man istÀllet för sju tillfÀllen endast analyserar fyra tillfÀllen (april, maj, juli och augusti). MÄnga mindre vanliga taxa försvinner med minskat antal prov men alla taxa som kan ses som sjögruppsspecifika (sura referenser, neu-trala referenser, kalkade, överkalkade och kalkavslutade sjöar) finns kvar. LikasÄ blir det inga stora skillnader i vilka miljövariabler som bÀst samvarierar med vÀxt-planktons samhÀllsstruktur Àven om förklaringsgraden minskar nÄgot nÀr Ärsme-delvÀrdena baseras pÄ fyra istÀllet för sju provtagningstillfÀllen. Analyserar man dÀremot alla ingÄende data utan att göra nÄgra sammanslagningar av provtagnings-tillfÀllen (medelvÀrden) blir förklaringsgraden tvÀrtom nÄgot högre med minskat antal provtagningar, vilket antagligen beror pÄ den stora variationen hos vÀxtplank-ton under försommar och höst
Phytoplankton biomass in northern lakes reveals a complex response to global change
Global change may introduce fundamental alterations in phytoplankton biomass and community structure that can alter the productivity of northern lakes. In this study, we utilized Swedish and Finnish monitoring data from lakes that are spatially (135 lakes) and temporally (1995-2019, 110 lakes) extensive to assess how phytoplankton biomass (PB) of dominant phytoplankton groups related to changes in water temperature, pH and key nutrients [total phosphorus (TP), total nitrogen (TN), total organic carbon (TOC), iron (Fe)] along spatial (Fennoscandia) and temporal (25 years) gradients. Using a machine learning approach, we found that TP was the most important determinant of total PB and biomass of a specific species of Raphidophyceae - Gonyostomum semen - and Cyanobacteria (both typically with adverse impacts on food-webs and water quality) in spatial analyses, while Fe and pH were second in importance for G. semen and TN and pH were second and third in importance for Cyanobacteria. However, in temporal analyses, decreasing Fe and increasing pH and TOC were associated with a decrease in G. semen and an increase in Cyanobacteria. In addition, in many lakes increasing TOC seemed to have generated browning to an extent that significantly reduced PB. The identified discrepancy between the spatial and temporal results suggests that substitutions of data for space-for-time may not be adequate to characterize long-term effects of global change on phytoplankton. Further, we found that total PB exhibited contrasting temporal trends (increasing in northern- and decreasing in southern Fennoscandia), with the decline in total PB being more pronounced than the increase. Among phytoplankton, G. semen biomass showed the strongest decline, while cyanobacterial biomass showed the strongest increase over 25 years. Our findings suggest that progressing browning and changes in Fe and pH promote significant temporal changes in PB and shifts in phytoplankton community structures in northern lakes
Declining calcium concentration drives shifts toward smaller and less nutritious zooplankton in northern lakes
Zooplankton community composition of northern lakes is changing due to the interactive effects of climate change and recovery from acidification, yet limited data are available to assess these changes combined. Here, we built a database using archives of temperature, water chemistry and zooplankton data from 60 Scandinavian lakes that represent broad spatial and temporal gradients in key parameters: temperature, calcium (Ca), total phosphorus (TP), total organic carbon (TOC), and pH. Using machine learning techniques, we found that Ca was the most important determinant of the relative abundance of all zooplankton groups studied, while pH was second, and TOC third in importance. Further, we found that Ca is declining in almost all lakes, and we detected a critical Ca threshold in lake water of 1.3 mg L-1, below which the relative abundance of zooplankton shifts toward dominance of Holopedium gibberum and small cladocerans at the expense of Daphnia and copepods. Our findings suggest that low Ca concentrations may shape zooplankton communities, and that current trajectories of Ca decline could promote widespread changes in pelagic food webs as zooplankton are important trophic links from phytoplankton to fish and different zooplankton species play different roles in this context.Among five environmental variables tested, we found that low lake calcium (Ca) concentrations shape most zooplankton communities in northern lakes. When lake water Ca falls below a threshold of 1.3 mg L-1, the relative abundance of zooplankton shifts toward dominance of Holopedium and small cladocerans at the expense of Daphnia and cyclopoid and calanoid copepods. The current trajectory of Ca declines found in northern lakes implies community shifts toward dominance of smaller and less nutritious zooplankton. Ca declines potentially have strong repercussions for lake food webs and productivity as zooplankton are important trophic links from phytoplankton to fish.imag
Effects of trophic status, water level, and temperature on shallow lake metabolism and metabolic balance: A standardized panâEuropean mesocosm experiment
Important drivers of gross primary production (GPP) and ecosystem respiration (ER) in lakes are temperature, nutrients, and light availability, which are predicted to be affected by climate change. Little is known about how these three factors jointly influence shallow lakes metabolism and metabolic status as net heterotrophic or autotrophic. We conducted a panâEuropean standardized mesocosm experiment covering a temperature gradient from Sweden to Greece to test the differential temperature sensitivity of GPP and ER at two nutrient levels (mesotrophic or eutrophic) crossed with two water levels (1 m and 2 m) to simulate different light regimes. The findings from our experiment were compared with predictions made according the metabolic theory of ecology (MTE). GPP and ER were significantly higher in eutrophic mesocosms than in mesotrophic ones, and in shallow mesocosms compared to deep ones, while nutrient status and depth did not interact. The estimated temperature gains for ER of ~â0.62âeV were comparable with those predicted by MTE. Temperature sensitivity for GPP was slightly higher than expected ~â0.54âeV, but when corrected for daylight length, it was more consistent with predictions from MTE ~â0.31âeV. The threshold temperature for the switch from autotrophy to heterotrophy was lower under mesotrophic (~â11°C) than eutrophic conditions (~â20°C). Therefore, despite a lack of significant temperatureâtreatment interactions in driving metabolism, the mesocosm's nutrient level proved to be crucial for how much warming a system can tolerate before it switches from net autotrophy to net heterotrophy
Challenges in supplying empirical proof for predictions derived from Species Distribution Models (SDMs): the case of an invasive cyanobacterium
Species distribution models (SDMs) calibrated with bioclimatic variables revealed a high probability for range expansion of the invasive toxin producing cyanobacterium, Raphidiopsis raciborskii to Sweden, where no reports of its presence have hitherto been recorded. While predictions focused on the importance of climate variables for possible invasion, other barriers to dispersal and successful colonization need to be overcome by the species for successful invasion. In this study, we combine field-based surveys of R. raciborskii (microscopy and molecular analysis using species-specific primers) of 11 Swedish lakes and in-silico screening of environmental DNA using 153 metagenomic datasets from lakes across Europe to validate the SDMs prediction. Field-based studies in lakes with high/low predicted probability of occurrence did not detect the presence of R. raciborskii, and in-silico screening only detected hints of its presence in 5 metagenomes from lakes with probability ranging from 0.059 to 0.825. The inconsistencies between SDMs results and both field-based/in-silico monitoring could be due to either sensitivity of monitoring approaches in detecting early invasions or uncertainties in SDMs that focused solely on climate drivers. However, results highlight the necessity of proactive monitoring with high temporal and spatial frequency
Fokus pÄ MÀlaren 2021 : sammanfattande resultat frÄn miljöövervakning och forskningsprojekt knutna till samarbetet mellan SLU och MÀlarens vattenvÄrdsförbund
MĂ€larens vattenvĂ„rdsförbund och Sveriges lantbruksuniversitet fortsĂ€tter att samarbeta med fokus pĂ„ MĂ€laren. Under 2021 pĂ„verkade pandemin möjligheten att ses under Ă„rsstĂ€mman pĂ„ vĂ„ren men MĂ€larseminariet pĂ„ hösten kunde hĂ„llas som hybridmöte med ungefĂ€r 40 deltagare pĂ„ plats pĂ„ SLU i Uppsala och lika mĂ„nga deltog via videolĂ€nk. Digitala MĂ€larinarier hölls vid fyra tillfĂ€llen och var Ă€ven de vĂ€lbesökta. Faruk Djodjic Ă€r ny kontaktperson tillsammans med Stina Drakare frĂ„n SLU. Vid vinterprovtagningen hade alla stationer is vilket Ă€r första gĂ„ngen sedan detta samarbete startade 2017. Nederbördsrika mĂ„nader blev maj och augusti och sommarmĂ„naderna juli och augusti var varma. Statusbedömningen visar att stationer med mĂ„ttlig status dominerar och att det finns flera stationer med otillfredsstĂ€llande (7) och dĂ„lig status (5). Bara tvĂ„ stationer hade god status och ingen hade hög status. Antalet stationer med bra status vĂ€xlar mellan tvĂ„ och fyra stycken mellan Ă„ren vilket beror pĂ„ vilka stationer ingĂ„r just det Ă„ret. Dessa statusbedömningar kopplar frĂ€mst till övergödningsproblematik vilket provtagningsprogrammet Ă€r designat för att följa. Tre doktorander med Ă€mnen som berör MĂ€laren har försvarat sina avhandlingar under perioden. TvĂ„ av dem berör just övergödningsproblematik och behandlade Ă€mnen som bra verktyg för att minska transport av nĂ€ringsĂ€mnen som fosfor frĂ„n land till MĂ€laren och för att inaktivera fosfor pĂ„ sjöbottnar för att minska internbelastning frĂ„n bottensediment. Den tredje avhandlingen gav verktyg för att förbĂ€ttra dricksvattenrening nĂ€r man har problem med organiska miljöföroreningar. Andra vetenskapliga publikationer av intresse för MĂ€laren som presenteras kortfattat Ă€r t.ex. ett verktyg för att identifiera potentiella högrisksubstanser i akvatisk miljö kopplat till pĂ„verkan frĂ„n avloppsreningsverk, att förbruningen av vĂ„ra vatten verkar ha avstannat dĂ€r det finns en tydlig brytpunkt Ă„r 2010. Ytterligare en publikation visar med en första studie att antibiotikaresistensgener Ă€r vanliga och tĂ€cker in flera typer av antibiotika i vatten runt VĂ€sterĂ„s, Uppsala, Eskilstuna och Stockholm. Ă
rets kandidatarbeten gjordes i vÄtmarker med fokus pÄ sÄdana som anvÀnds som fosforfÀllor och i hÀsthagar för att ta reda pÄ om nÀringslÀckage frÄn dessa kan minskas genom att mocka i hagen. PÄ masternivÄ handlade det om att ta reda pÄ vid vilka förhÄllanden kvÀvefixerande cyanobakterier trivs och att mÀta algblomningar med sensorer för högre tids- och djupupplösning
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