Hydrometeorological and climatic control over lake phytoplankton: the importance of time scales

[eng] In the present thesis we focus on the two extremes of the wind speed – storms and atmospheric stilling – and analyse their impacts on lake environments and phytoplankton dynamics over short and long periods. As we realised the importance of the time scale in the context of our wind effect studies, we decided to have a closer look at other environmental data in the Lake Võrtsjärv database addressing the questions how the variability in environmental factors (thermal, wind, light- and water-level regimes) and phytoplankton variables is partitioned among different time scales from days to decades and whether matching shares can help to determine the leading factors responsible for phytoplankton dynamics

Post-soviet changes in nitrogen and phosphorus stoichiometry in two large non-stratified lakes and the impact on phytoplankton

The post-soviet period in Eastern Europe brought about fast changes in economy, land use, and environmental protection, whereas legacy effects of the previous era of heavy contamination continued emerging in the status of water bodies. In this paper, we analysed the post-soviet (since 1992) changes in catchment nutrient loadings and stoichiometry of nitrogen (N) and phosphorus (P) in two large non-stratified lakes in Estonia – Võrtsjärv and Peipsi. The drastic reduction in the application of P-fertilisers and P discharges with wastewaters since the early 1990s reduced P loadings and increased N/P loading ratio into both lakes. However, it was hard to find clear evidence of reduced in-lake nutrient concentrations and improved water quality. In both lakes, water transparency constantly decreased and phytoplankton biomass increased. Over the years, the difference in N/P ratio between the two lakes became smaller while the large differences in the cyanobacterial community composition remained. Although common thresholds in nutrient ratios favouring N2-fixing species could be revealed in both lakes, the phytoplankton in Võrtsjärv, strongly dominated by Limnothrix spp., remained mostly light-limited and the relationship with N/P stoichiometry was indirect. Random Forest analysis indicated an important role of light limitation in both lakes. Constantly lower levels of N in the deeper Lake Peipsi favoured N2-fixing species, which, as a paradox, became P-limited. As climate warming reinforces eutrophication phenomena in lakes by increasing internal nutrient loading and favouring bloom-forming cyanobacteria, more stringent measures would be needed to further limit nutrient loads (especially that of P) to lakes through improved wastewater treatment and increased efficiency of fertiliser application.Main financial support for EMU: European Union’s Horizon 2020 research and innovation programme Under the Marie Skłodowska-Curie Action, Innovative Training Networks, European Joint Doctorates.Project name, acronym and grant number: Management of climatic extreme events in lakes and reservoirs for the protection of ecosystem services, MANTEL, grant agreement No 722518.Publication date and, if applicable, length of embargo period: 20.11.2020, no embargo period

Phytoplankton responses to meteorological and hydrological forcing at decadal to seasonal time scales

One of the challenges for predicting global change effects on aquatic ecosystems is the vague understanding of the mechanisms of multiple controlling factors affecting phytoplankton dynamics at different time scales. Here we distinguish between hydrometeorological forcing of phytoplankton dynamics at time scales from days to decades based on a 54-year monthly phytoplankton time series from a large shallow Lake Võrtsjärv (58 160N, 26 020E) in Estonia, combined with daily data on forcing factors— thermal-, wind-, light- and water-level regimes. By using variance partitioning with linear mixed effect modelling (LME), we found a continuum from the large dominant K-selected filamentous cyanobacteria with strongest decadal scale variation (8–30%) to r-selected phytoflagellates with large stochastic variability (80–96%). External forcing revealed strong seasonal variation (up to 80%), while specifically water level and wind speed had a robust decadal variation (8% and 20%, respectively). The effect of external variables was proportionally manifested in the time scales of phytoplankton variation. Temperature, with a clear seasonal variation, had no impact on the dominant cold tolerant filamentous cyanobacteria in Lake Võrtsjärv. We found the LME as a reliable method for resolving the temporal cross-scale problem. It yielded quantitative results that matched our intuitive understanding of the dynamics of different variables.Supplementary Information The online version of this article (https://doi.org/10.1007/s10750-021-04594-x) contains supplementary material, which is available to authorised users.This study was funded by MANTEL ITN (Management of climatic extreme events in lakes and reservoirs for the protection of ecosystem services) through European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 722518 and by the Estonian Research Council grants (PRG1266 and PRG1167). We would also like to thank Estonian Environment Agency for the long-term data used on this study.This study was funded by MANTEL ITN (Management of climatic extreme events in lakes and reservoirs for the protection of ecosystem services) through European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 722518 and by the Estonian Research Council grants (PRG1266 and PRG1167). We would also like to thank Estonian Environment Agency for the long-term data used on this study

Storm impacts on phytoplankton community dynamics in lakes

In many regions across the globe, extreme weather events such as storms have increased in frequency, intensity, and duration due to climate change. Ecological theory predicts that such extreme events should have large impacts on ecosystem structure and function. High winds and precipitation associated with storms can affect lakes via short-term runoff events from watersheds and physical mixing of the water column. In addition, lakes connected to rivers and streams will also experience flushing due to high flow rates. Although we have a well-developed understanding of how wind and precipitation events can alter lake physical processes and some aspects of biogeochemical cycling, our mechanistic understanding of the emergent responses of phytoplankton communities is poor. Here we provide a comprehensive synthesis that identifies how storms interact with lake and watershed attributes and their antecedent conditions to generate changes in lake physical and chemical environments. Such changes can restructure phytoplankton communities and their dynamics, as well as result in altered ecological function (e.g., carbon, nutrient and energy cycling) in the short- and long-term. We summarize the current understanding of storm-induced phytoplankton dynamics, identify knowledge gaps with a systematic review of the literature, and suggest future research directions across a gradient of lake types and environmental conditions.Peer reviewe

Hüdrometeoroloogiliste ja kliimategurite mõju järvede fütoplanktonile : ajaskaalade olulisus

A Thesis for applying for the degree of Doctor of Philosophy in Environmental Sciences and Applied Biology.Väitekiri filosoofiadoktori kraadi taotlemiseks rakendusbioloogia erialal.Phytoplankton reflects changes in the environment and plays a vital role in biogeochemical cycles and the climate system. The thesis attempts to link the phytoplankton dynamics with the timing, intensity, and duration of the local forcing factors at different time scales. We highlight the influence of two extremes of the wind gradient – storms and atmospheric stilling, on lake environments and phytoplankton dynamics over short and long periods, several aspects of which are poorly understood. Until recently, atmospheric stilling as a climatic phenomenon has been largely overlooked in lakes studies. To fill this research gap, we focussed on a large shallow polymictic lake (Võrtsjärv, Estonia), that was affected by a 30% decrease in average wind speed since 1996, and for which a long-term (54 years) phytoplankton and hydrometeorological database was available. Further, a contradiction between the continuous decrease in the lake’s nutrient loading and an increasing trend in phytoplankton biomass emerged as a topic of interest for this thesis. We summarise how storms interact with and alter the dynamic of phytoplankton communities. Further, we highlight to what extent this impact can change the ecological processes (e.g., nutrient, carbon, and energy cycling) within lakes and their environmental conditions in the short and long term. Using Nonmetric Multidimensional Scaling ordination of phytoplankton community composition for the years 1964–2017, we revealed three distinct periods with breaking points coinciding with abrupt changes in the wind and/or water level. We introduced a concept of "light niche," a newly discovered mechanism of meteorological control over phytoplankton in light-limited shallow lakes. Combining the monthly phytoplankton data with daily data on hydrometeorological forcing factors — thermal, light, wind, and water-level regimes and using variance partitioning with linear mixed effect modelling (LME), we found that (i) the external forcing factors relevant for each phytoplankton variable could be individualised by having a similar variance partitioning among time scales as the particular phytoplankton variable; (ii) with the largest seasonal variation component, the dominant shade-tolerant filamentous cyanobacteria were most affected by seasonal factors such as solar irradiance and water level; (iii) the LME was proven appropriate for resolving the temporal cross-scale issues.Hüdrometeoroloogiliste ja kliimategurite mõju järvede fütoplanktonile: ajaskaalade olulisus Fütoplankton peegeldab muutusi keskkonnas ja mängib olulist rolli biogeokeemilises aineringes ning kliimasüsteemis. Doktoritöö uurib seoseid fütoplanktoni dünaamika ning erinevates ajaskaalades (päevane, sesoonne, aastatevaheline) toimivate tegurite ajastuse, intensiivsuse ja kestusega. Töös tuuakse esile kahe vastandliku tuulte olukorra – tormide ja tuulevaikuse mõju järvekeskkonnale ja fütoplanktoni dünaamikale, mille mitmed aspektid on seni vähe uuritud. Kuni viimase ajani on järveuuringutes suuresti tähelepanuta jäänud tuulte nõrgenemise kui kliimanähtuse mõju. Selle uurimislünga täitmiseks keskendusime suurele madalale polümiktilisele Võrtsjärvele, mida mõjutavate tuulte keskmine kiirus on alates 1996. aastast vähenenud 30% ning mille kohta on olemas pikaajaline (54 aastat) fütoplanktoni ja hüdrometeoroloogia andmebaas. Tuulte mõju uurimine võimaldas selgitada ka näilist vastuolu järve toiteainete hulga pideva vähenemise ja fütoplanktoni biomassi kasvutrendi vahel. Töö esimene osa võtab kokku teadmised tormide mõju kohta järvede fütoplanktonikoosluste dünaamikale. Tuuakse välja, kuidas tormid mõjutavad ökoloogilisi protsesse järvedes (nt toiteainete kättesaadavust, süsiniku- ja energiaringet) ning nende kaudu fütoplanktoni elutingimusi lühi- ja pikaajalises lõikes. Aastate 1964–2017 Võrtsjärve fütoplanktonikoosluse mitmemõõtmeline analüüs eristas koosluse muutustes kolm perioodi, mille murdepunktid langesid kokku tuule ja/või veetaseme järskude muutustega. Nende seoste põhjal sõnastati nn "valgusniši" kontseptsioon, mis kirjeldab varem tundmatut fütoplanktoni meteoroloogilise kontrolli mehhanismi häguse veega madalates järvedes. Kasutades enam kui poole sajandi vältel kogutud igakuiseid fütoplanktoni andmeid ja kombineerides neid igapäevaste andmetega hüdrometeoroloogiliste tegurite (temperatuur, valgus, tuul ja veetase) kohta uuriti lineaarsete segamudelite abil muutlikkuse jaotumise erinevate ajaskaalade vahel. Leiti, et fütoplanktoni erinevate rühmade jaoks olulisi välistegureid saab kindlaks teha selle järgi, et vastava rühma ja seda mõjutavate tegurite muutlikkus jaotub erinevate ajaskaalade vahel sarnastes proportsioonides. Nii mõjutasid suurima sesoonse muutlikkuse komponendiga tsüanobaktereid enim sesoonsed tegurid, flagellaatide puhul, sarnaselt tuulega, ulatus aga juhusliku ja lühiajalise varieeruvuse komponent 80%-ni. Kokkuvõttes osutusid lineaarsed segamudelid sobivaks tööriistaks erinevates ajaskaalades toimivate tegurite mõju uurimiseks.Publication of this thesis is supported by the Estonian University of Life Sciences

ASSESSMENT OF THE ASSOCIATION BETWEEN DUST STORMS AND COVID-19 INFECTION RATE IN SOUTHWEST IRAN

This study assesses a plausible correlation between a dust intrusion episode and a daily increase in COVID-19 cases. A surge in COVID-19 cases was observed a few days after a Middle East Dust (MED) event that peaked on 25th April 2020 in south west Iran. To investigate potential causal factors for the spike in number of cases, cross-correlations between daily combined aerosol optical depths (AODs) and confrmed cases were computed for Khuzestan, Iran. Additionally, atmospheric stability data time series were assessed by covering before, during, and after dust intrusion, producing four statistically clustered distinct city groups. Groups 1 and 2 had diferent peak lag times of 10 and 4-5 days, respectively. Since there were statisti cally signifcant associations between AOD levels and confrmed cases in both groups, dust incursion may have increased population susceptibility to COVID-19 disease. Group 3 was utilized as a control group with neither a signifcant level of dust incursion during the episodic period nor any signifcant associations. Group 4 cities, which experienced high dust incur sion levels, showed no signifcant correlation with confrmed case count increases. Random Forest Analysis assessed the infuence of wind speed and AOD, showing relative importance of 0.31 and 0.23 on the daily increase percent of confrmed cases, respectively. This study may serve as a reference for better understanding and predicting factors afecting COVID-19 transmission and difusion routes, focusing on the role of MED intrusions

Health risk assessment of the European inhabitants exposed to contaminated ambient particulate matter by potentially toxic elements

PM10-associated potential toxic elements (PTEs) can enter the respiratory system and cause health problems. In the current study, the health risk indices caused by PM10 inhalation by adults, children, and infants in 158 European cities between 2013 and 2019 were studied to determine if Europeans were adversely affected by carcinogenic and non-carcinogenic factors or not. The Mann–Kendall trend test examined PM10's increasing or decreasing trend. Random Forest analysis was also used to analyse meteorological factors affecting PM10 in Europe. Hazard quotient and cancer risk were estimated using PM10-associated PTEs. Our results showed a decline in continental PM10 concentrations. The correlation between PM10 concentrations and temperature (−0.40), PBLH (−0.39), and precipitation were statistically strong (−0.21). The estimated Pearson correlation coefficients showed a statistically strong positive correlation between As &amp; Pb, As &amp; Cd, and Cd &amp; Pb during 2013–2019, indicating a similar origin. PTEs with hazard quotients below one, regardless of subpopulation type, posed no noncancerous risk to Europeans. The hazard quotient values positively correlated with time, possibly due to elevated PTE levels. In our study on carcinogen pollution in Europe between 2013 and 2019, we found unacceptable levels of As, Cd, Ni, and Pb among adults, children, and infants. Carcinogenic risk rates were highest for children, followed by infants, adult women, and adult men. Therefore, besides monitoring and mitigating PM concentrations, effective control of PM sources is also needed.</p