Diatom Communities Research Articles

The response of diatom community to small hydropower plant and fish farm

Some of the direct and indirect environmental impacts are related to the construction of fish farms (FFs) and small hydropower plants (SHPs) around the world. Diatom communities are one of the best bioindicators of various pressures like eutrophication, chemical and organic pollution. The main objective of this study was to examine the influence of SHP and FF on diatom community and water quality of the Prištavica River in Serbia. A total of 184 epilithic diatom taxa from 55 genera were identified. Sites after the FF and SHP are distinguished by the same dominant species in each season. Compared to the other sites, species diversity in summer was lower at site after SHP. In terms of spatial dynamics, four groups of taxa are distinguished. Some centric taxa were associated with sites downstream the FF and SHP. Altered physical and chemical parameters were documented at sites downstream of constructions. Water quality of the Prištavica River ranged from high to bad depending on diatom index, season, and sampling site. A greater difference in diatom index values was found at sites upstream and downstream of the FF, than at sites upstream and downstream of the SHP.

Spatial patterns of benthic diatom community structure in the largest northwestern river of Cambodia (Sangker River)

To date, very little is known about the relative importance of physicochemical factors structuring the benthic diatom community in the flood-pulse tropical ecosystems. This paper aims to investigate the spatial distribution of the benthic diatom community in a poorly studied river catchment of the Tonle Sap Basin in Cambodia. Diatom samples were collected at nineteen (19) monitoring sites from 2018 to 2023 along the Sangker River, and the hierarchical clustering technique was applied to characterize the variation in diatom community structure based on the similarity of diatom genera composition. Seventy-eight (78) diatom genera belonging to 36 families, 18 orders, and 5 classes of diatom flora were recorded. Gomphonema Ehrenberg, Nitzschia Hassall, and Navicula Bory were the most dominant diatom genera in the catchment area. Accordingly, three main diatom assemblages (Ia, Ib, and II) were classified, and 11 indicator genera were identified. Indeed, the identified assemblages reflect the change of diatiom community composition from the upstream assemblage (Ia), middle course (Ib), and floodplain assemblage (II). Dissolved oxygen (DO), pH, conductivity (EC), total phosphorus (TP), and silicon dioxide (SiO2) were the physico-chemical determinants of benthic diatom communities, while physical factors (DO, pH, and nutrients) seemed to be more important than chemical factors. Consequently, any disturbances to the physical condition of the river would drive an abrupt shift in the diatom community’s diversity and structure. These findings pave an essential step towards the establishment of sustainable biomonitoring programs in developing countries such as Cambodia to protect aquatic ecosystems from global change.

Paleoenvironmental reconstruction of climate by diatoms from sediments of three deep freshwater lakes of Evenkia (Siberia, Russia)

The study aimed to determine the species composition of diatoms in the bottom sediments of the freshwater lakes Zapovednoye, Cheko, and Peyungda, situated in the taiga zone of the southern region of Evenkia within the boundaries of the Tungussky State Nature Reserve. A total of 255 taxa have been identified in these lakes, with their ecological characteristics also established. The diatom community present in the bottom sediments of the aforementioned lakes showcases species that are common across all three lakes, as well as some that are exclusive to every single reservoir. An examination of the acquired data indicated the existence of overarching trends in the evolutionary trajectory of lakes Cheko, Zapovednoye, and Peyungda. Nevertheless, discernible discrepancies are observed in the species composition of diatoms within their bottom sediments, both in terms of quality and quantity, thereby delineating Lake Peyungda in a distinctive position in comparison to lakes Zapovednoye and Cheko. This disparity is likely attributed to the relatively shallow depth of Lake Peyungda, leading to an inclination towards a heightened level of eutrophication in its species composition, as opposed to the conditions observed in lakes Cheko and Zapovednoye.

Morphology and phylogeny of Nitzschianandorii sp. nov. (Bacillariophyceae), a new small-celled lanceolate species from a post-mining reservoir.

Post-mining reservoirs are distinguished by characteristic environmental conditions where specific diatom communities can be observed. Reservoirs created as a part of the reclamation plan after human mining activities are marked by unique chemical and physical water parameters. In the course of research on the diatoms from Bogdałów reservoir, we examined the taxonomic and morphological diversity of Nitzschia taxa from the section Lanceolatae occurring in a post-mining lignite reservoir. Our study describes a new species of Nitzschia from a post-mining reservoir, Nitzschianandorii Olszyński, Zakrzewski & Żelazna-Wieczorek, sp. nov. Morphometry and morphology analyses of new species were performed with light and scanning electron microscopy. Chloroplast morphology analysis was conducted with differential interference contrast microscopy and confocal laser scanning microscopy. Molecular data from SSU 18S, rbcL and psbC sequences were obtained from cultures of this taxon. Differential diagnosis of Nitzschianandorii Olszyński, Zakrzewski & Żelazna-Wieczorek, sp. nov. with co-occurring taxa: N.lacuum and N.alpinobacillum was performed using morphological traits and nMDS analysis of the valves' morphometry.

New data on Late Glaсial diatoms of the SE Baltic region based on the results of studying the Kulikovo section

The sediments of shallow basins formed along the coast of the Baltic glacial lake around 14,500-14,000 cal BP provide a valuable source of information for reconstructing environmental changes in the Bølling-Allerød. Radiocarbon dating and complex lithological and diatom analyzes were performed for the deposits of one of these paleo-reservoirs, exposed in the Kulikovo section (northern part of the Sambian Peninsula). Diatoms of the sediments formed 14,100 – 13,400 cal BP are mostly presented by benthic and epithytic oligohalobic species. We compared the obtained data with existing ideas about the Late Glacial diatom flora for this region to identify general and local patterns of diatom communities formed at that time.

Seasonal variation in the biological succession of marine diatoms over 316L stainless steel in a coastal environment of Chile

Characterizing seasonal changes in diatom community profiles in coastal environments is scarce worldwide. Despite diatoms being prevalent in microfouling, their role in microbially influenced corrosion of metallic materials remains poorly understood. This study reports the effect of seasonal variations on the settlement of marine diatoms and corrosion of 316 L stainless steel surfaces exposed to Chilean coastal seawater. Electron microscopy imaging revealed a diverse assembly of diatoms, exhibiting pronounced differences at genus level between summer and winter seasons, with a significant delay in diatom settlement during winter. Electrochemical measurements indicated an active role of diatoms in increasing corrosion current during biofilm development. While the final diatom composition was similar irrespective of the season, the analyses of diatom assemblages over time differed, showing faster colonization when silicate and nitrate were available. This study lays the foundation for future research on the dominant season-specific genera of diatoms to unveil the microbial interactions that could contribute to corrosion and to evaluate their potential as bioindicators for alternative surveillance strategies.

Multiple stressors determine the process of the benthic diatom community assembly and network stability in urban water bodies in Harbin

Human activities have triggered biodiversity loss, often resulting in biotic homogenization, which poses a threat to human well-being. Nevertheless, the overall influence of diverse environmental stressors on intra- and inter-community diversity remains insufficiently elucidated. This study aimed to quantify and reveal the impact of environmental stressors on the alpha and beta diversities of benthic diatom communities in the Harbin urban river network during the summer and autumn of 2022 and spring of 2023. The marked seasonal variations observed in alpha and beta diversity indices highlighted the distinct community compositions. Nonetheless, varying types of urban water pollutants were the primary drivers of biotic homogenization in terms of both taxonomic and functional diversities and played a prominent role in steering diversity shifts. These pollutants indirectly led to biotic homogenization by altering water quality parameters and affecting the ecological dynamics of benthic diatom communities. Furthermore, diverse responses to stressors were identified in taxonomic and functional diversities, providing additional insights for understanding ecological shifts in communities. Taxonomic beta diversity was related to environmental filtering, whereas functional beta diversity resulted from stressor–spatial dimension interactions. Our study emphasises that relying solely on traditional water quality monitoring may not fully reveal the current state of river ecosystem protection, and the need to study the continuous changes in biodiversity across seasons in urban waterbodies from the perspective of various stressors is highlighted.

A diatom-based approach to refine nutrient concentrations compatible with the “good” status of Northern Italy rivers

The identification of ecologically sound thresholds represents an important step toward improving the ecological status of rivers through appropriate measures to contain nutrient loads. The aim of the present study was to estimate phosphorus and nitrogen concentrations compatible with the achievement of the “good” ecological status of rivers from data collected in the Po River District, the largest hydrographic system in Italy. For this purpose, relationships between the diatom index used in Italy for the national assessment of the stream ecological status, the ICMi (Intercalibration Common Metric index), and total phosphorus and nitrate concentrations were analyzed using monitoring data collected between 2009 and 2019. The Po River Basin encompasses five distinct river types, from Alpine to Mediterranean to Lowlands, characterized by different anthropogenic pressures and water quality. Through regression analysis between the ICMi and nutrient concentrations, we estimated ranges of the latter values corresponding to a “good” ecological status for each river type. The resulting thresholds are far more stringent than the limits set by the Italian legislation for water quality classification. This is particularly true for total phosphorus, whose threshold value should be roughly halved for all river types. For nitrates, the results are more differentiated according to river type: the estimated thresholds are much more stringent than those currently in use for siliceous Alpine and Mediterranean rivers. Moreover, the availability of such a large database allowed also to assess the influence of one nutrient over the other on the diatom community and to highlight some critical issues in the formulation of ICMi for Mediterranean rivers.

Speciation, distribution and relationship of zinc and cadmium in summer coastal seawater of northern China

Considering that zinc (Zn) is essential for marine phytoplankton growth and cadmium (Cd) can replace Zn as a cofactor of mutual conversion and regulate the effect of carbonic anhydrase, we here presented the concentration, chemical speciation and relationship of Zn and Cd collected from three consecutive voyages (2019–2021) in summer coastal seawater of northern China. Dissolved Zn and Cd concentrations were determined using inductively coupled plasma mass–spectrometry (ICP–MS) and ranged from 0.37 to 3.09 μM and 1.88–13.66 nM, respectively. Natural labile Zn and Cd were determined using a highly automated electrochemical detection system and ranged from below detection limit-1.11 μM and below detection limit-5.23 nM, respectively. The speciation, distribution and interrelationships of Zn and Cd were compared with the distribution of the diatoms community, and studied by the correlation with pH and dissolved inorganic carbon (DIC). Finally, the Zn and Cd labile and inert chemical species concentrations were compared with those of the open sea and the coast. The results indicated that the dissolved Zn and Cd concentrations in surface seawater were higher than those in bottom seawater, possibly due to the dominance of exogenous inputs compared to phytoplankton uptake. Higher phytoplankton abundance was associated with lower natural labile Zn and Cd concentrations, but this was not the main factor affecting the distribution of natural labile Zn and Cd. Unlike the open ocean, there was no potential for Zn limitation of certain phytoplankton groups in this region, but both Zn and Cd played important roles in the fixation of carbon dioxide, and Cd might result in mitigating Zn uptake. Activities such as ocean currents, which bring limiting nutrient trace metals (e.g., Zn) from the coast into the open ocean, could regulate the structure of primary producers. This study has great potential for the investigation of the biogeochemical cycling of Zn and Cd and their role in marine carbon fixation in coastal seawater.

High-throughput sequencing of Diatoms using V4 region of 18S rRNA gene in Bayug Island, Iligan City, Philippines

Abstract. Estor DEP, Tabugo SR. 2023. High-throughput sequencing of Diatoms using V4 region of 18S rRNA gene in Bayug Island, Iligan City, Philippines. Biodiversitas 24: 6343-6350. Diatoms are the main contributors to aquatic primary production and are the most dominant phytoplankton. Their adaptability and growth in diverse natural resources enable them to thrive in various climates and geographical areas, making them suitable for monitoring and biotechnology applications. This study aimed to analyze the diatom composition in two study sites: a mangrove area and the estuary in Bayug Island. The analysis was conducted using metabarcoding of the V4 region of the 18S rRNA gene, amplified and sequenced on the Illumina MiSeq platform. Four amplicon libraries were generated, representing the diatom composition at the two study sites. Data processing was performed using the Parallel-Meta-Suite software. Following quality control and processing, 20,433 amplicon sequence variants (ASVs) were obtained. Among these, the genera Navicula, Thalassiosira, Chaetoceros, Guinardia, Amphora, and Minidiscus were the most abundant ASVs. The assessment of diatom alpha diversity using the Shannon index indicated a higher diversity in the estuary site. Furthermore, the analysis done within the Parallel Meta Suite suggested that the presence of these specific diatom species can be linked to salinity levels, and may indicate environmental disturbances such as water pollution. The presence of these diatoms has the potential to be utilized in ecological treatments, disease prevention, biotechnology, and as nutrient indicators for other marine organisms. Physico-chemical parameters were recorded in the estuary area (S1), with the average water pH measuring around 7.6, salinity at approximately 36.6 ppt, and water temperature at 26.7?. In contrast, the measurements in the mangrove area (S2) revealed an average water temperature of 30?, salinity of around 35 ppt, and a water pH of 7.7. This research will serve as baseline data for diatom community in the area and a pioneering work on using NGS and eDNA for diatom study.

The optimal realized niches of the diatom Paralia sulcata in the Yellow Sea and its environmental implication

The observational and paleo-ecological records on some shelves (e.g., North Sea, Yellow Sea) have indicated that the proportion of Paralia sulcata in the diatom community has been increasing since the 1980s. Because of its heavily-silicified frustules, this species is considered as an important siliceous organism, which can impact the recycling efficiency of biogenic silicon in the ocean. However, the specific environmental factors driving the increase of P. sulcata remain unclear. In this study, based on seasonal in-situ observations and historical literature in the Yellow Sea, we statistically assessed the importance of different environmental factors in determining P. sulcata abundance. Further, we quantified its optimal realized niches, using the maximum entropy and generalized additive models to predict the fate of this species. P. sulcata indicates a preference for environments with cold temperatures and high nutrient levels. The contribution of sea temperature on cell abundance reaches up to 37.2 %, which is higher than that of the nutrient concentrations (∼ 20.5 %) and salinity (∼ 17.1 %). The optimal realized niches are defined as sea temperature at 6.25 ± 3.50 °C, salinity at 32.8 ± 0.52, the concentrations of dissolved inorganic nitrogen, phosphorus, and silicate at 8.38 ± 5.42 μM, 0.42 ± 0.29 μM, and 5.87 ± 3.53 μM, respectively, and ammonium/nitrate ratio at 1.32 ± 0.19. Based on the multivariate statistical methods, the optimal realized niches indicate that the increased sea temperatures in winter and spring, combined with nitrogen enrichment, especially ammonium enrichment, are key environmental drivers for P. sulcata proliferation in the Yellow Sea.

Biodiversity in wetland+ system: a passive solution for HCH dump effluents.

The hexachlorocyclohexane isomers (HCH) are long-banned pesticides. Even though their use has been prohibited for decades, their presence in the environment is still reported worldwide. Wetland + is a registered trademark of the remedial treatment technology consisting of an aerobic sedimentary tank, a permeable reactive barrier, a biosorption system, and an aerobic wetland. This proven method combines a reductive treatment known from PRBs with the natural wetland self-cleaning processes. The average efficiency of the system is 96.8% for chlorobenzenes (ClB) and 81.7% for HCH, during the first 12 months of the system operation. The presence of the genes encoding enzymes involved in the degradation of the HCH compounds indicates that the removal of HCH and ClB occurs not only by chemical removal but also through aerobic and anaerobic combining biodegradation. Changes in abundance and the composition of the diatom community were found to be suitable indicators of the water quality and of the impact of the Wetland + operation on the water ecosystem. The system's annual operation exhibited a markedly higher number of diatom species in the closing profiles of the Ostrovský Creek, the Wetland + effluent recipient.

New diatom species Diploneis zhui sp. nov. from Jiuzhaigou National Nature Reserve, China

Diploneis zhui sp. nov. was observed in epilitic diatom communities from Jiuzhaigou National Nature Reserve. The species is described herein based on light microscopy (LM) and scanning electron microscopy (SEM) and ecological information of the type locality is provided. The species is characterized by linear to linear-elliptic valves with broadly rounded ends, 18–39 μm long, and 9.5–11.0 μm wide and partly biseriate striae, 16–18 in 10 μm. The species is compared with most similar taxa from other regions. The discovery of a new diatom species confirms the importance of Jiuzhaigou not only in terms of species richness and endemicity, but also for the biodiversity of freshwater karst ecosystems.

Exploring benthic diatom diversity in the West Antarctic Peninsula: insights from a morphological and molecular approach

Polar regions are among the most extreme habitats on Earth. However, diatom biodiversity in those regions is much more extensive and ecologically diverse than previously thought. The objective of this study was to add knowledge to benthic diatom biodiversity in Western Antarctic coastal zones via identification by means of morphology, DNA metabarcoding and cultured isolates. In addition, a taxonomically validated reference library for Antarctic benthic diatoms was established with comprehensive information on habitat, morphology and DNA barcodes (rbcL and 18SV4). Benthic samples from marine, brackish and freshwater habitats were taken at the Antarctic Peninsula. A total of 162 clonal cultures were established, resulting in the identification of 60 taxa. The combination of total morphological richness of 174 taxa, including the clones, with an additional 73 taxa just assigned by metabarcoding resulted in 247 infrageneric taxa. Of those taxa, 33 were retrieved by all three methods and 111 only by morphology. The barcode reference library of Antarctic species with the new references obtained through culturing allowed the assignment of 47 taxa in the metabarcoding analyses, which would have been left unassigned because no matching reference sequences were available before. Non–metric multidimensional scaling analyses of morphological as well as molecular data showed a clear separation of diatom communities according to water and substratum types. Many species, especially marine taxa, still have no record in reference databases. This highlights the need for a more comprehensive reference library to further improve routine diatom metabarcoding. Overall, a combination of morphological and molecular methods, along with culturing, provides complementary information on the biodiversity of benthic diatoms in the region.

Diatom and macroinvertebrate communities dynamic: A co-occurrence pattern analysis on plastic substrates

Wetlands are habitats that provide numerous ecosystem services, but are often understudied and threatened by anthropogenic pollution, particularly plastic pollution. Macroplastics are a significant component of plastic litter that have high biological impacts but are often understudied. Previous studies have highlighted negative impacts on biota, but there is a lack of information about the communities of micro and macro organisms that settle on macroplastic litter. In this context, we investigated the colonization patterns and community structures of diatoms and macroinvertebrates on virgin substrates composed of two different plastic polymers, polystyrene and polyethylene terephthalate, located at two different depths in a protected wetland in Central Italy over a period of 10 months. The results show that diatom community is not highly structured by competitive forces and aggregation patterns emerges. In contrast, macroinvertebrate community appears to be randomly structured, without the presence of patterns following specific assembly rules. Randomness in macroinvertebrates assemblages could highlight the presence of different niches available for settlement of different taxa. Combined matrix analyses show that diatoms and macroinvertebrates co-occur, and their community assemblages are sometimes structured, while they appeared to be randomly assembled at other times. Whenever non-randomness of diatoms and macroinvertebrates co-occurrences was detected, it suggested aggregation. Moreover, the possible predatory relationship between different macroinvertebrates taxa should be investigated, as it could reveal important scenarios in the establishment of macroinvertebrate structured communities on plastic litter, including taxa that exploit different ecological niches. This could lead to an enrichment of the biological community within areas impacted by plastics.

Biological and Ecological Monitoring Using Epiphytic Diatoms on Two Aquatic Plants to Estimate the Water Quality of Habbaniyah Lake, Western Iraq

The current study was conducted in Habbaniyah Lake in Anbar Governorate - western Iraq, starting from February 2022 tol July 2022. Five sites were chosen to collect water samples and epiphytic diatoms attached to two aquatic plants, Phragmites australlis (Cav.) Trin. and Ceratophylum demsrsam L.. The current study aims to employ the quality and quantity of the epiphytic diatoms community attached to the host aquatic plants to estimate the quality of the lake water, by conducting a set of environmental indicators that included biological indicators. 102 species of Bacillariophyceae class were identified. Where 84 species were diagnosed on the Ceratophyllum, while 61 species were diagnosed on the Phragmites In the current study, a set of ecological indices was conducted to characterize the water quality of Habbaniyah Lake, which included three biological indices: the Tolerance Pollution Index (PTI), where the lake was described as moderately polluted, to record values whose averages ranged (1.65-2.35), and Trophic Diatomic Index (TDI), whose average values ranged from (55.62 - 58.72), where the lake was described as mesotrophic and Shannon Diversity Index, where the waters of Lake Habbaniyah were described as having medium biodiversity, recording average values (2.22 - 2.50). An environmental index was conducted, which is the Canadian Water Quality Index (CCME), where it recorded values that ranged from (76.59 - 78.66), where the lake water was described as of moderate (Fair) quality and often threatened or weak from time to time, and the water condition deviates from the required level. or desired.

Ecological impacts of dam construction on epilithic diatom communities in estuaries: A case study of the Korean peninsula

This study, spanning 2016 to 2018, investigated diatom distribution in 324 Korean Peninsula estuaries, emphasizing the ecological impact of artificial dams. Examining environmental and biological variables, we focused on dam construction. OPEN estuaries exhibited higher urban/forest land cover and had more alkaline, saline, conductive, and oxygen-rich water. In CLOSE estuaries, agricultural farmland and nitrogen compound concentrations were higher. Dams in CLOSE estuaries correlated with lower pH, salinity, electrical conductivity, and dissolved oxygen. Regional variations were evident, with WEST OPEN estuaries showing higher salinity, turbidity, chemical oxygen demand, and total phosphorus. SOUTH estuaries displayed intermediate characteristics, while EAST OPEN estuaries had higher dissolved oxygen but lower temperature and turbidity.Diverse epilithic diatoms were identified, with OPEN estuaries displaying greater species richness, primarily dominated by Nitzschia inconspicua Grunow. CLOSE estuaries, conversely, exhibited higher richness with a different subdominant species. Indicator species analysis revealed taxa specific to estuaries and sea areas, with CLOSE ones exhibiting lower salinity and higher nitrogen/phosphorus concentrations. Nitzschia inconspicua dominated all estuaries, but subdominant species varied; N. fonticola (Grunow) Grunow in OPEN, N. paleaceae (Grunow) Grunow in CLOSE. CLOSE estuaries had higher species richness. In the West Sea, turbidity and TP levels affected diatom growth, with dams exacerbating turbidity and potentially disrupting the food chain.Results underscored intricate interactions between dams, land use, and diatom communities, offering foundational data for ecosystem management and biodiversity conservation in Korean Peninsula estuaries. Understanding the ecological consequences of artificial dams on diatom distribution is crucial for preserving estuarine health. Future research is recommended to explore additional factors influencing these ecosystems, particularly focusing on various organisms in West Sea estuaries for effective ecosystem management and conservation.

Stream diatom community assembly processes in islands and continents: A global perspective

AbstractAimUnderstanding the roles of deterministic and stochastic processes in community assembly is essential for gaining insights into the biogeographical patterns of biodiversity. However, the way community assembly processes operate is still not fully understood, especially in oceanic islands. In this study, we examine the importance of assembly processes in shaping diatom communities in islands and continents, while also investigating the influence of climate and local water chemistry variables on species distributions.LocationGlobal.TaxonStream benthic diatoms.MethodsWe used diatom datasets from five continents and 19 islands and applied beta diversity analyses with a null model approach and hierarchical joint species distribution modelling. To facilitate comparisons with continents, we used continental area equivalents (CAEs), which represent continental subsets with comparable areas and the same number of study sites as their corresponding islands counterparts.ResultsWe found that homogeneous selection (i.e., communities being more similar than the random expectation) was the dominant assembly process within islands whereas stochastic processes tended to be more important within continents. In addition, assembly processes were influenced by study scale and island isolation. Climatic variables showed a greater influence on species distribution than local factors. However, in islands, local environmental variables had a greater impact on the distributions of unique taxa as opposed to non‐unique taxa.Main ConclusionsWe observed that the assembly processes of diatom communities were complex and influenced by a combination of deterministic and stochastic forces, which varied across spatial scales. In islands, there was no universal pattern of assembly processes, given that their influence depends on abiotic conditions such as area, isolation, and environmental heterogeneity. In addition, the sensitivity of species occurring uniquely in islands to local environmental variables suggests that they are perhaps less vulnerable to climatic changes but may be more influenced by changes in local physicochemistry.

Refining the history of extreme coastal events in southern Newfoundland, NW Atlantic, with lake sediment archives

Extreme events, including tsunamis, storm surges and hurricanes, affect the western North Atlantic coast, threatening communities and impacting ecosystems. Although these extreme coastal events (ECEs) are currently thoroughly monitored in the area, older ECEs are known only from short historical evidence. Therefore, establishing a reliable ECE history that extends more than several decades into the past requires data from geological records. This study aims to refine the existing record of ECEs on the southern Burin Peninsula (Newfoundland, Canada) that extends back to the mid-18th century by providing the first lake-sediment-based reconstruction of the event history of the Canadian province of Newfoundland and Labrador. We investigated short sediment cores collected from four shallow coastal lakes. The identification of ECEs relied mainly on lithostratigraphic evidence and peak detection of sand grain counts. Diatoms, dry bulk density, and loss-on-ignition were also analyzed. The age-depth models of the cores were based on 210Pb and 137Cs dating. The correlation of our records with major historical events confirmed that statistically significant sand count peaks, sand layers, and redeposited peat clasts are indicative of major ECEs. We found that the type and characteristics of ECE records depended mainly on the availability of sediment, distance from the seashore, and magnitude of the event. Although some of our ECE markers are associated with marine inundations, only slight diatom community changes were observed, contrary to what is commonly expected from the disturbance of brackish and freshwater ecosystems by major saltwater intrusions. Combined, our records indicate that at least eight ECEs occurred since the late 17th century, three of which might correlate with historically documented events, namely the 1755 CE Lisbon tsunami, the 1775 CE Great Independence Hurricane, and the 1929 CE Newfoundland tsunami. Although further investigations are required to better constrain the type and magnitude of particular ECEs, our study confirms the suitability of geological archives for improving hazard assessment in coastal regions.

Managing the Red Lake Nation’s and Minnesota’s largest lake: monitoring and paleolimnology support a site-specific standard for Upper and Lower Red Lakes (Red Lake Nation and Minnesota, United States)

Burge DRL, Edlund MB, Bowe S, Bowe K, Anderson JP, Bouchard RW, Heathcote AJ, Leavitt PR, Engstrom DR. 2023. Managing the Red Lake Nation’s and Minnesota’s largest lake: monitoring and paleolimnology support a site-specific standard for Upper and Lower Red Lakes (Red Lake Nation and Minnesota, United States). Lake Reserv Manage. 40:1–17. Water quality and the ability of lakes to provide benefits such as recreation and aquatic life are negatively impacted by climate change, aquatic invasive species, and nutrient enrichment. To address these lake-management challenges, regionally tailored water quality criteria need to assign achievable and protective goals while minimizing assessment errors. In Minnesota, when lakes exceed state water-quality standards, restoration plans are developed and implemented based on eco-regional standards, or in cases where it is determined that the regional standard is not appropriate, a site-specific standard may be developed. Upper Red Lake and Lower Red Lake, located within the boundaries of the Red Lake Indian Reservation (the Red Lake Nation) in northwestern Minnesota (United States), have been recently experiencing cyanobacteria blooms, as well as routinely exceeding the regional water quality criteria for total phosphorus and chlorophyll a. The last 20 yr of water quality monitoring suggest a stable recent history with no significant trends. To extend this time perspective, biogeochemical evidence from paleolimnology was used to reconstruct a 150 yr history for these 2 large, shallow lakes to determine whether site-specific water quality standards might be recommended. Biogeochemical evidence (e.g., sedimentation rates, phosphorus fractions, biogenic silica, diatom community composition, and fossil algal pigments) from 10 sediment cores revealed complex sedimentary dynamics together with a small gradual increase in limnological productivity over the last 2 centuries. Despite the implied productivity change, diatom-inferred phosphorus showed no significant increase among the sediment cores. Furthermore, the reconstructed total phosphorus values were within the range of modern monitored values. Because the paleolimnological evidence suggests little change to the aquatic ecology of the Red Lakes over the last 150 yr, and monitoring data show regular exceedance of regional TP standards with no trend in the last 20 yr, site-specific water quality standards are deemed appropriate for this large, shallow lake system.