Browsing by Subject "Eutrophication"

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  • Silvonen, Soila; Niemistö, Juha; Csibrán, Adrián; Jilbert, Tom; Torma, Péter; Krámer, Tamás; Nurminen, Leena; Horppila, Jukka (2021)
    Hypolimnetic withdrawal (HW) is a lake restoration method that is based on the removal of phosphorus (P) along with near-bottom water. While it has often proven to be effective, the method also sets challenges: it is about balancing between effective P removal and maintenance of the thermal stratification of the lake. The success of different HW projects has been reviewed in some studies retrospectively, but scientific literature still lacks studies that use detailed data on the lake biogeochemistry to scale and optimize the method in advance, and to predict the outcomes of the restoration measure. In the current study, we investigated the seasonal biogeochemistry, P stocks and thermal stratification of a eutrophic lake (Lake Kymijarvi/Myllypohja basin, southern Finland) to determine an optimal withdrawal rate, to assess its effects on stratification, and to evaluate the expected success of HW. We found that by adjusting HW with P diffusive fluxes from the sediment (diffusion-adjusted HW), it is possible to remove a notable part of the cycling P without causing major disturbances to the thermal stratification even in a relatively shallow lake. Our results show that HW can have great potential in lake restoration: diffusion-adjusted HW in our study lake could increase the annual P output by 35-46%, shifting the P budget of the lake to negative. We thus propose a novel approach to optimize HW on the basis of the diffusive flux of P from the sediment, with the goal of extracting P continuously at an equivalent rate to the diffusive flux. We finally discuss how this can be achieved more effectively with HW based on a closed-circuit system. (c) 2020 The Authors. Published by Elsevier B.V.
  • Jansson, Torbjörn; Andersen, Hans Estrup; Hasler, Berit; Höglind, Lisa; Gustafsson, Bo G. (2019)
    In this study, quantitative models of the agricultural sector and nutrient transport and cycling are used to analyse the impacts in the Baltic Sea of replacing the current Greening measures of the EU’s Common Agricultural Policy with a package of investments in manure handling. The investments aim at improving nutrient utilization and reducing nitrogen leaching, based on the assumption that lagging farms and regions can catch up with observed good practice. Our results indicate that such investments could reduce nitrogen surpluses in agriculture by 18% and nitrogen concentrations in the Baltic Sea by 1 to 9% depending on the basin. The Greening measures, in contrast, are found to actually increase nitrogen leaching.
  • Jokinen, Sami A.; Koho, Karoliina; Virtasalo, Joonas J.; Jilbert, Tom (2020)
    Molybdenum (Mo) and uranium (U) contents in sedimentary archives are often used to reconstruct past changes in seafloor oxygenation. However, their sequestration processes are as yet poorly constrained in low-salinity coastal waters, which often suffer from anthropogenic eutrophication but only mild oxygen depletion. Due to the consequent lack of robust long-term paleo-redox reconstructions in such settings often characterized by a shallow front of dissolved sulfide accumulation within the sediment pore waters, inadequate understanding of the long-term drivers behind oxygen loss impedes cost-effective mitigation of this environmental problem. Here, we investigate the mechanisms of Mo and U sequestration in an oxic, low-salinity coastal setting in the northern Baltic Sea where anthropogenic eutrophication over the 20th century has resulted in formation of a shallow sulfate-methane transition zone (SMTZ) in the sediment column of this brackish-water basin. Our results demonstrate remarkably similar patterns for authigenic Mo and U sequestration, whereby the depth and intensity of the SMTZ exerts a first-order control on their solid-phase uptake. Sequential extraction analysis suggests that a large part of the authigenic Mo pool is hosted by refractory Fe-S phases such as pyrite and nanoscale FeMoS4, implying that the Fe-sulfide pathway is the dominating process of authigenic Mo scavenging. However, we also observe a pool of extremely labile Mo deep within the SMTZ, which might record an intermediate phase in authigenic Mo sequestration and/or partial switch to the organic matter (OM) pathway at low dissolved Fe levels. Authigenic U resides in acid-extractable and refractory phases, likely reflecting uptake into poorly crystalline monomeric U(IV) and crystalline uraninite, respectively. Similarly to Mo, authigenic U uptake is active at two fronts within the SMTZ, paralleled by increases in dissolved sulfide levels, suggesting coupling between sulfide production and U reduction. Our results imply that both Mo and U could provide viable proxies for mild bottom water deoxygenation in these settings, through the indirect link between seafloor oxygen conditions and the depth of SMTZ. Of these, Mo appears to more robustly capture variations in seafloor oxygen levels due to the significantly higher share of the authigenic pool. However, temporal resolution of these proxies is limited by the vertical offset between seafloor and the zone of authigenic uptake, and the superimposed character of the signal at a given depth due to vertical migrations of the SMTZ. These results have important implications for the use of Mo and U as paleo-redox proxies in other low-salinity coastal settings exposed to eutrophication.
  • Ventelä, Anne-Mari; Amsinck, Susanne Lildal; Kauppila, Tommi; Johansson, Liselotte Sander; Jeppesen, Erik; Kirkkala, Teija; Sondergaard, Martin; Weckstrom, Jan; Sarvala, Jouko (2016)
    Lake Sakylan Pyhajarvi has been an important fishing site and drinking water source for the local population for centuries. The lake has undergone significant changes: (1) the water level was lowered in the 1600s and in the 1850s; (2) planktivorous coregonid fish were successfully introduced in the early 1900s; (3) nutrient input from intensified agriculture has increased since the 1950s and (4) the effects of the current variable climate on the lake and its catchment have become more evident since the 1990s. We determined the phases of oligotrophication, eutrophication and recovery and elucidated the ecosystem changes by combining palaeolimnological records with detailed neolimnological data. The sedimentary diatom and cladoceran assemblages first showed a relatively eutrophic period followed by oligotrophic periods, linked with the artificial changes in water level and consequent shifts in macrophyte abundance. The oligotrophic period in the early 1900s is thought to represent the target trophic state for the lake. After the 1950s, introduction of vendace resulted in higher planktivory reflected by an increased relative abundance of small-bodied pelagic cladocerans. Signs of eutrophication occurred due to increased nutrient load. During the last 10 years, signs of recovery have been recorded. A complex history such as that of Lake Pyhajarvi illustrates the difficulties in selecting management targets, and the risk of setting false targets, for lakes based solely on monitoring data-both neolimnological and palaeolimnological approach are needed.
  • Taipale, Sami J.; Vuorio, Kristiina; Aalto, Sanni L.; Peltomaa, Elina; Tiirola, Marja (2019)
    Eutrophication (as an increase in total phosphorus [TP]) increases harmful algal blooms and reduces the proportion of high-quality phytoplankton in seston and the content of ω-3 long-chain polyunsaturated fatty acids (eicosapentaenoic acid [EPA] and docosahexaenoic acid [DHA]) in fish. However, it is not well-known how eutrophication affects the overall nutritional value of phytoplankton. Therefore, we studied the impact of eutrophication on the production (as concentration; μg L−1) and content (μg mg C−1) of amino acids, EPA, DHA, and sterols, i.e., the nutritional value of phytoplankton in 107 boreal lakes. The lakes were categorized in seven TP concentration categories ranging from ultra-oligotrophic (50 μg L−1). Phytoplankton total biomass increased with TP as expected, but in contrast to previous studies, the contribution of high-quality phytoplankton did not decrease with TP. However, the high variation reflected instability in the phytoplankton community structure in eutrophic lakes. We found that the concentration of amino acids increased in the epilimnion whereas the concentration of sterols decreased with increasing TP. In terms of phytoplankton nutritional value, amino acids, EPA, DHA, and sterols showed a significant quadratic relationship with the lake trophic status. More specifically, the amino acid contents were the same in the oligo- and mesotrophic lakes, but substantially lower in the eutrophic lakes (TP > 35 μg L−1/1.13 μmol L−1). The highest EPA and DHA content in phytoplankton was found in the mesotrophic lakes, whereas the sterol content was highest in the oligotrophic lakes. Based on these results, the nutritional value of phytoplankton reduces with eutrophication, although the contribution of high-quality algae does not decrease. Therefore, the results emphasize that eutrophication, as excess TP, reduces the nutritional value of phytoplankton, which may have a significant impact on the nutritional value of zooplankton, fish, and other aquatic animals at higher food web levels.
  • Carstensen, Jacob; Conley, Daniel J.; Almroth-Rosell, Elin; Asmala, Eero; Bonsdorff, Erik; Fleming-Lehtinen, Vivi; Gustafsson, Bo G.; Gustafsson, Camilla; Heiskanen, Anna-Stiina; Janas, Urzsula; Norkko, Alf; Slomp, Caroline; Villnäs, Anna; Voss, Maren; Zilius, Mindaugas (2020)
    The coastal zone of the Baltic Sea is diverse with strong regional differences in the physico-chemical setting. This diversity is also reflected in the importance of different biogeochemical processes altering nutrient and organic matter fluxes on the passage from land to sea. This review investigates the most important processes for removal of nutrients and organic matter, and the factors that regulate the efficiency of the coastal filter. Nitrogen removal through denitrification is high in lagoons receiving large inputs of nitrate and organic matter. Phosphorus burial is high in archipelagos with substantial sedimentation, but the stability of different burial forms varies across the Baltic Sea. Organic matter processes are tightly linked to the nitrogen and phosphorus cycles. Moreover, these processes are strongly modulated depending on composition of vegetation and fauna. Managing coastal ecosystems to improve the effectiveness of the coastal filter can reduce eutrophication in the open Baltic Sea.
  • El-Khaled, Yusuf C.; Nafeh, Rassil; Roth, Florian; Rädecker, Nils; Karcher, Denis B.; Jones, Burton H.; Voolstra, Christian R.; Wild, Christian (2021)
    Nitrogen cycling in coral reefs may be affected by nutrient availability, but knowledge about concentrationdependent thresholds that modulate dinitrogen fixation and denitrification is missing. We determined the effects of different nitrate concentrations (ambient, 1, 5, 10 mu M nitrate addition) on both processes under two light scenarios (i.e., light and dark) using a combined acetylene assay for two common benthic reef substrates, i.e., turf algae and coral rubble. For both substrates, dinitrogen fixation rates peaked at 5 mu M nitrate addition in light, whereas denitrification was highest at 10 mu M nitrate addition in the dark. At 10 mu m nitrate addition in the dark, a near-complete collapse of dinitrogen fixation concurrent with a 76-fold increase in denitrification observed for coral rubble, suggesting potential threshold responses linked to the nutritional state of the community. We conclude that dynamic nitrogen cycling activity may help stabilise nitrogen availability in microbial communities associated with coral reef substrates.
  • Salminen, Sarianna; Tammelin, Mira; Jilbert, Tom; Fukumoto, Yu; Saarni, Saija (2021)
    The influence of lake restoration efforts on lake bottom-water conditions and varve preservation is not well known. We studied varved sediments deposited during the last 80 years along a water-depth transect in the Enonsaari Deep, a deep-water area of the southernmost Enonselka Basin, Lake Vesijarvi, southern Finland. For the last few decades, the Enonselka Basin has been subject to ongoing restoration efforts. Varve, elemental, and diatom analyses were undertaken to explore how these actions and other human activities affected varve preservation in the Enonsaari Deep. In contrast to most varved Finnish lakes, whose water columns have a natural tendency to stratify, and possess varve records that span thousands of years, varve formation and preservation in Lake Vesijarvi was triggered by relatively recent anthropogenic stressors. The multi-core varve analysis revealed that sediment in the Enonsaari Deep was initially non-varved, but became fully varved in the late 1930s, a time of increasing anthropogenic influence on the lake. The largest spatial extent of varves occurred in the 1970s, which was followed by a period of less distinguishable varves, which coincided with diversion of sewage from the lake. Varve preservation weakened during subsequent decades and was terminated completely by lake aeration in the 2010s. Despite improvements in water quality, hypolimnetic oxygen depletion and varve preservation persisted beyond the reduction in sewage loading, initial aeration, and biomanipulation. These restoration efforts, however, along with other human actions such as harbor construction and dredging, did influence varve characteristics. Varves were also influenced by diatom responses to anthropogenic forcing, because diatoms form a substantial part of the varve structure. Of all the restoration efforts, a second episode of aeration seems to have had the single most dramatic impact on profundal conditions in the basin, resulting in replacement of a sediment accumulation zone by a transport or erosional zone in the Enonsaari Deep. We conclude that human activities in a lake and its catchment can alter lake hypolimnetic conditions, leading to shifts in lake bottom dynamics and changes in varve preservation.
  • Carstensen, Jacob; Conley, Daniel J.; Bonsdorff, Erik; Gustafsson, Bo G.; Hietanen, Susanna; Janas, Urzsula; Jilbert, Tom; Maximov, Alexey; Norkko, Alf; Norkko, Joanna; Reed, Daniel C.; Slomp, Caroline P.; Timmermann, Karen; Voss, Maren (2014)
  • Pihlainen, Sampo; Zandersen, Marianne; Hyytiäinen, Kari; Andersen, Hans Estrup; Bartosova, Alena; Gustafsson, Bo; Jabloun, Mohamed; McCrackin, Michelle; Meier, H.E. Markus; Olesen, Jørgen E.; Saraiva, Sofia; Swaney, Dennis; Thodsen, Hans (2020)
    This paper studies the relative importance of societal drivers and changing climate on anthropogenic nutrient inputs to the Baltic Sea. Shared Socioeconomic Pathways and Representative Concentration Pathways are extended at temporal and spatial scales relevant for the most contributing sectors. Extended socioeconomic and climate scenarios are then used as inputs for spatially and temporally detailed models for population and land use change, and their subsequent impact on nutrient loading is computed. According to the model simulations, several factors of varying influence may either increase or decrease total nutrient loads. In general, societal drivers outweigh the impacts of changing climate. Food demand is the most impactful driver, strongly affecting land use and nutrient loads from agricultural lands in the long run. In order to reach the good environmental status of the Baltic Sea, additional nutrient abatement efforts should focus on phosphorus rather than nitrogen. Agriculture is the most important sector to be addressed under the conditions of gradually increasing precipitation in the region and increasing global demand for food. (C) 2020 The Authors. Published by Elsevier B.V.
  • Kiani, Mina; Tammeorg, Priit; Niemistö, Juha; Simojoki, Asko; Tammeorg, Olga (2020)
    Mankind is taking advantage of numerous services by small shallow lakes such as drinking water supply, irrigation, and recreational function; however, many of these lakes suffer from eutrophication. Given the key role of phosphorus (P) in eutrophication process, one of the effective restoration methods especially for small shallow lakes is removal of sediments enriched with nutrients. In our study, we used interannual, seasonal, and spatial data to examine the changes in sediment P mobility after removal of sediments in 2016 from a 1-ha highly eutrophic lake. We measured the sediment redox potential, analyzed soluble reactive P (SRP) in the pore water and P fractional composition of the surface sediments, and calculated the P diffusive flux in three locations in two continuous years (2017 and 2018) after the excavation. Similar measurements were done before sediment removal at central site of the lake in 2015. Removing nutrient-rich sediment also removed 6400 kg of P, and thus the potential for release of P from sediments decreased on a long-term scale. However, a large pool of releasable P was rebuilt soon after the sediment removal due to high external P loading, resulting in extensive anoxia of sediment surface and associated internal P loading as high as 1450 mg m−2 summer−1. Moreover, the Fe-P and labile P fractions were the most important sources of P release, as evidenced by their considerable seasonal and interannual changes after the sediment removal. The sediment total Fe negatively correlated with sediment P diffusive flux, pore water SRP, and near-bottom water total P and SRP concentrations which indicated a strong linkage between sediment P dynamics and Fe after the restoration. Sediment removal could be a beneficial restoration approach, but the effects on lake water quality remain only short-term unless there is an adequate control on external loading to the lake.
  • Wikström, Sofia A.; Hedberg, Nils; Kautsky, Nils; Kumblad, Linda; Ehrnsten, Eva; Gustafsson, Bo; Humborg, Christoph; Norkko, Alf; Stadmark, Johanna (2020)
  • Karcher, Denis B.; Roth, Florian; Carvalho, Susana; El-Khaled, Yusuf C.; Tilstra, Arjen; Kürten, Benjamin; Struck, Ulrich; Jones, Burton H.; Wild, Christian (2020)
    While various sources increasingly release nutrients to the Red Sea, knowledge about their effects on benthic coral reef communities is scarce. Here, we provide the first comparative assessment of the response of all major benthic groups (hard and soft corals, turf algae and reef sands-together accounting for 80% of the benthic reef community) to in-situ eutrophication in a central Red Sea coral reef. For 8 weeks, dissolved inorganic nitrogen (DIN) concentrations were experimentally increased 3-fold above environmental background concentrations around natural benthic reef communities using a slow release fertilizer with 15% total nitrogen (N) content. We investigated which major functional groups took up the available N, and how this changed organic carbon (C-org) and N contents using elemental and stable isotope measurements. Findings revealed that hard corals (in their tissue), soft corals and turf algae incorporated fertilizer N as indicated by significant increases in delta N-15 by 8%, 27% and 28%, respectively. Among the investigated groups, C-org content significantly increased in sediments (+24%) and in turf algae (+33%). Altogether, this suggests that among the benthic organisms only turf algae were limited by N availability and thus benefited most from N addition. Thereby, based on higher C-org content, turf algae potentially gained competitive advantage over, for example, hard corals. Local management should, thus, particularly address DIN eutrophication by coastal development and consider the role of turf algae as potential bioindicator for eutrophication.
  • Roth, Florian; El-Khaled, Yusuf C.; Karcher, Denis B.; Rädecker, Nils; Carvalho, Susana; Duarte, Carlos M.; Silva, Luis; Calleja, Maria Ll.; Moran, Xose Anxelu G.; Jones, Burton H.; Voolstra, Christian R.; Wild, Christian (2021)
    Ecosystem services provided by coral reefs may be susceptible to the combined effects of benthic species shifts and anthropogenic nutrient pollution, but related field studies are scarce. We thus investigated in situ how dissolved inorganic nutrient enrichment, maintained for two months, affected community-wide biogeochemical functions of intact coral- and degraded algae-dominated reef patches in the central Red Sea. Results from benthic chamber incubations revealed 87% increased gross productivity and a shift from net calcification to dissolution in algae-dominated communities after nutrient enrichment, but the same processes were unaffected by nutrients in neighboring coral communities. Both community types changed from net dissolved organic nitrogen sinks to sources, but the increase in net release was 56% higher in algae-dominated communities. Nutrient pollution may, thus, amplify the effects of community shifts on key ecosystem services of coral reefs, possibly leading to a loss of structurally complex habitats with carbonate dissolution and altered nutrient recycling.
  • McCrackin, Michelle L.; Gustafsson, Bo G.; Hong, Bongghi; Howarth, Robert W.; Humborg, Christoph; Savchuk, Oleg P.; Svanback, Annika; Swaney, Dennis P. (2018)
    While progress has been made in reducing external nutrient inputs to the Baltic Sea, further actions are needed to meet the goals of the Baltic Sea Action Plan (BSAP), especially for the Baltic Proper, Gulf of Finland, and Gulf of Riga sub-basins. We used the net anthropogenic nitrogen and phosphorus inputs (NANI and NAPI, respectively) nutrient accounting approach to construct three scenarios of reduced NANI-NAPI. Reductions assumed that manure nutrients were redistributed from areas with intense animal production to areas that focus on crop production and would otherwise import synthetic and mineral fertilizers. We also used the Simple as Necessary Baltic Long Term Large Scale (SANBALTS) model to compare eutrophication conditions for the scenarios to current and BSAP-target conditions. The scenarios suggest that reducing NANI-NAPI by redistributing manure nutrients, together with improving agronomic practices, could meet 54-82% of the N reductions targets (28-43 kt N reduction) and 38-64% P reduction targets (4-6.6 kt P reduction), depending on scenario. SANBALTS output showed that even partial fulfillment of nutrient reduction targets could have ameliorating effects on eutrophication conditions. Meeting BSAP targets will require addressing additional sources, such as sewage. A common approach to apportioning sources to external nutrients loads could enable further assessment of the feasibility of eutrophication management targets.
  • Candolin, Ulrika; Voigt, Heinz-Rudolf (2020)
    Human activity is altering the dynamics of populations through effects on fecundity, mortality and migration. An increased abundance of three-spined stickleback (Gasterosteus aculeatus) in the Baltic Sea has been attributed to a human-caused decline of top predators. However, recent research indicates that a top-down effect cannot fully explain the population growth, but the contribution of a bottom-up effect has not been investigated. Yet, anthropogenic eutrophication has increased algae biomass at the spawning sites of the stickleback and, thus, the abundance of benthic prey. We investigated if increased fecundity could have contributed to the population growth of the stickleback by analysing a two decade time series of stickleback abundance, fecundity, and body size at three spawning sites. The results show an increase in the proportion of gravid females in the populations, which correlates with the population growth. In particular, the proportion of gravid females late in the spawning season has increased, which indicates enhanced food intake at the sites during the spawning season. Thus, a bottom-up effect could have contributed to the growth of the populations by increasing the number of egg clutches females produce. These results stress the importance of considering both bottom-up and top-down processes when investigating the mechanisms behind human impact on population dynamics.
  • Kiani, Mina; Raave, Henn; Simojoki, Asko; Tammeorg, Olga; Tammeorg, Priit (2021)
    Sediment removal from eutrophicated shallow lakes may not only be an effective method for lake restoration but also provides the potential for recycling nutrients from sediments to crop production. However, finding a suitable strategy for sustainably reusing the sediment remains a challenge. Therefore, current study focused on the best practices in applying the sediment from a shallow eutrophicated lake to the soil in terms of grass yield, nutrient uptake, and nutrient leaching. During a nine-month lysimeter experiment, 100-cm high columns were filled with six combinations of soil, sediment, and biochar, with or without meat bone meal organic fertilizer. Aboveground biomass, root mass distribution in soil, nutrient concentration, phosphorus (P) uptake of perennial ryegrass (Lolium perenne L.) along with easily soluble nutrients in the growing medium, and leached mineral nitrogen (N) and P levels were measured. Plant growth conditions were improved by sediment additions, as the yield and P uptake of ryegrass nearly doubled in treatments containing sediment compared to the control soil. While the sediment was richer in macro and micronutrients (e.g. P and N) compared to the soil, the leached N and P levels from both treatments were almost equivalent (N < 830 mg m−2 and P < 3 mg m−2). In addition, applying a 2-cm layer of biochar between the sediment and soil reduced P and N leaching by 50%. According to the results, applying a 75-cm thick layer of sediments on agricultural sandy loam soils surrounding the lake seems a promising practice for improving plant yield and soil nutrient status without increasing of P and N leaching from soil.
  • Svanbäck, Annika; McCrackin, Michelle L.; Swaney, Dennis P.; Linefur, Helena; Gustafsson, Bo G.; Howarth, Robert W.; Humborg, Christoph (2019)
    The separation between crop- and livestock production is an important driver of agricultural nutrient surpluses in many parts of the world. Nutrient surpluses can be symptomatic of poor resource use efficiency and contribute to environmental problems. Thus, it is important not only to identify where surpluses can be reduced, but also the potential policy tools that could facilitate reductions. Here, we explored linkages between livestock production and nutrient flows for the Baltic Sea catchment and discuss management practices and policies that influence the magnitude of nutrient surpluses. We found that the majority of nutrients cycled through the livestock sector and that large nitrogen and phosphorus surpluses often occurred in regions with high livestock density. Imports of mineral fertilizers and feed to the catchment increased overall surpluses, which in turn increased the risk of nutrient losses from agriculture to the aquatic environment. Many things can be done to reduce agricultural nutrient surpluses; an important example is using manure nutrients more efficiently in crop production, thereby reducing the need to import mineral fertilizers. Also, existing soil P reserves could be used to a greater extent, which further emphasizes the need to improve nutrient management practices. The countries around the Baltic Sea used different approaches to manage agricultural nutrient surpluses, and because eight of the coastal countries are members in the European Union (EU), common EU policies play an important role in management. We observed reductions in surpluses between 2000 and 2010 in some countries, which suggested the influence of different approaches to management and policy and that there are opportunities for further improvement. However, the separation between crop and livestock production in agriculture appears to be an underlying cause of nutrient surpluses; thus, further research is needed to understand how policy can address these structural issues and increase sustainability in food production. (C) 2018 The Authors. Published by Elsevier B.V.
  • Jenny, Jean-Philippe; Anneville, Orlane; Arnaud, Fabien; Baulaz, Yoann; Bouffard, Damien; Domaizon, Isabelle; Bocaniov, Serghei A.; Chevre, Nathalie; Dittrich, Maria; Dorioz, Jean-Marcel; Dunlop, Erin S.; Dur, Gael; Guillard, Jean; Guinaldo, Thibault; Jacquet, Stephan; Jamoneau, Aurelien; Jawed, Zobia; Jeppesen, Erik; Krantzberg, Gail; Lenters, John; Leoni, Barbara; Meybeck, Michel; Nava, Veronica; Noges, Tiina; Noges, Peeter; Patelli, Martina; Pebbles, Victoria; Perga, Marie-Elodie; Rasconi, Serena; Ruetz, Carl R.; Rudstam, Lars; Salmaso, Nico; Sapna, Sharma; Straile, Dietmar; Tammeorg, Olga; Twiss, Michael R.; Uzarski, Donald G.; Ventela, Anne-Mari; Vincent, Warwick F.; Wilhelm, Steven W.; Wangberg, Sten-Ake; Weyhenmeyer, Gesa A. (2020)
    Large lakes of the world are habitats for diverse species, including endemic taxa, and are valuable resources that provide humanity with many ecosystem services. They are also sentinels of global and local change, and recent studies in limnology and paleolimnology have demonstrated disturbing evidence of their collective degradation in terms of depletion of resources (water and food), rapid warming and loss of ice, destruction of habitats and ecosystems, loss of species, and accelerating pollution. Large lakes are particularly exposed to anthropogenic and climatic stressors. The Second Warning to Humanity provides a framework to assess the dangers now threatening the world's large lake ecosystems and to evaluate pathways of sustainable development that are more respectful of their ongoing provision of services. Here we review current and emerging threats to the large lakes of the world, including iconic examples of lake management failures and successes, from which we identify priorities and approaches for future conservation efforts. The review underscores the extent of lake resource degradation, which is a result of cumulative perturbation through time by long-term human impacts combined with other emerging stressors. Decades of degradation of large lakes have resulted in major challenges for restoration and management and a legacy of ecological and economic costs for future generations. Large lakes will require more intense conservation efforts in a warmer, increasingly populated world to achieve sustainable, high-quality waters. This Warning to Humanity is also an opportunity to highlight the value of a long-term lake observatory network to monitor and report on environmental changes in large lake ecosystems. (C) 2020 The Authors. Published by Elsevier B.V. on behalf of International Association for Great Lakes Research.
  • Maeda, Eduardo Eiji; Lisboa, Filipe; Kaikkonen, Laura Maria; Koponen, Sampsa; Kallio, Kari; Brotas, Vanda; Kuikka, Olli Sakari (2019)
    Monitoring temporal changes in phytoplankton dynamics in high latitude lakes is particularly timely for understanding the impacts of warming on aquatic ecosystems. In this study, we analyzed 33-years of high resolution (30 m) Landsat (LT) data for reconstructing seasonal patterns of chlorophyll a (chl a) concentration in four lakes across Finland, between 60°N and 64°N. Chl a models based on LT spectral bands were calibrated using 17-years (2000–2016) of field measurements collected across the four lakes. These models were then applied for estimating chl a using the entire LT-5 and 7 archives. Approximately 630 images, from 1984 to 2017, were analyzed for each lake. The chl a seasonal patterns were characterized using phenology metrics, and the time-series of LT-based chl a estimates were used for identifying temporal shifts in the seasonal patterns of chl a concentration. Our results showed an increase in the length of phytoplankton growth season in three of the lakes. The highest increase was observed in Lake Köyliönjärvi, where the length of growth season has increased by 28 days from the baseline period of 1984–1994 to 2007–2017. The increase in the length of season was mainly attributed to an earlier start of phytoplankton blooms. We further analyzed surface temperature (Ts) and precipitation data to verify if climatic factors could explain the shifts in the seasonal patterns of chl a. We found no direct relationship between Ts and chl a seasonal patterns. Similarly, the phenological metrics of Ts, in particular length of season, did not show significant temporal trends. On the other hand, we identify potential links between changes in precipitation patterns and the increase in the phytoplankton season length. We verified a significant increase in the rainfall contribution to the total precipitation during the autumn and winter, accompanied by a decline in snowfall volumes. This could indicate an increasing runoff volume during the beginning of spring, contributing to an earlier onset of the phytoplankton blooms, although further assessments are needed to analyze historical streamflow values and nearby land cover data. Likewise, additional studies are needed to better understand why chl a patterns in some lakes seem to be more resilient than in others.