Changes In Diatom Assemblages Research Articles

Tracking ∼200 years of water quality in Muskrat Lake, a eutrophic lake trout lake in Ontario (Canada) with cyanobacterial blooms

Simmatis B, Nelligan C, Rühland KM, Jeziorski A, Castro V, Paterson AM, Smol JP. 2020. Tracking ∼200 years of water quality in Muskrat Lake, a eutrophic lake trout lake in Ontario (Canada) with cyanobacterial blooms. Lake Reserv Manage. 36:260–277. Muskrat Lake is a deep (64 m), eutrophic lake in southeastern Ontario, Canada, that supports a natural lake trout population. Frequent algal blooms and low deep-water dissolved oxygen concentrations have generated management concerns. Based on anecdotal reports, algal blooms first occurred in the 1920s. Concern regarding recreational activities has escalated since the early 1980s. Monitoring records for total phosphorus (TP) and dissolved oxygen concentrations are sparse, requiring paleolimnological methods to extend our knowledge of past lake conditions. We inferred trends in past whole-lake primary production using visual-range spectroscopy-inferred chlorophyll a, nutrients using diatom assemblage changes, and end-of-summer volume-weighted hypolimnetic oxygen concentrations (VWHO) using chironomids to assess environmental conditions in Muskrat Lake over the past ∼200 years. Diatom taxa indicative of mesotrophic conditions were present throughout the sedimentary record, which suggests that Muskrat Lake was moderately productive before European settlement, with conditions worsening somewhat after ca. 1920, following land clearance and agricultural development. Chironomid-inferred VWHO trends suggest that the hypolimnion was not naturally well oxygenated, but deep-water oxygen levels declined further after ca. 1900 following European settlement. After ca. 1990, changes in diatom assemblage composition were consistent with climate-mediated increases in thermal lake properties, which might have contributed to cyanobacterial dominance. Whole-lake primary production increased after ca. 1900 and peaked ca. 1960, remaining stable until ca. 2006, after which it declined. Overall, Muskrat Lake has been productive over the past ∼200 years, but the cumulative effects of changes in nutrient loading and mixing patterns should be considered in future management decisions.

Long-term ecological changes in Mediterranean mountain lakes linked to recent climate change and Saharan dust deposition revealed by diatom analyses

Anthropogenic climate change and the recent increase of Saharan dust deposition has had substantial effects on Mediterranean alpine regions. We examined changes in diatom assemblage composition over the past ~180 years from high-resolution, dated sediment cores retrieved from six remote lakes in the Sierra Nevada Mountains of Southern Spain. In all lakes, changes in diatom composition began over a century ago, but were more pronounced after ~1970 CE, concurrent with trends in rising regional air temperature, declining precipitation, and increased Saharan dust deposition. Temperature was identified as the main predictor of diatom assemblage changes, whereas both Saharan dust deposition drivers, the Sahel precipitation index and the winter North Atlantic Oscillation, were secondary explanatory variables. Diatom compositional shifts are indicative of lake alkalinization (linked to heightened evapoconcentration and an increase in calcium-rich Saharan dust input) and reduced lake water turbulence (linked to lower water levels and reduced inflows to the lakes). Moreover, decreases in epiphytic diatom species were indicative of increasing aridity and the drying of catchment meadows. Our results support the conclusions of previous chlorophyll-a and cladoceran-based paleolimnological analyses of these same dated sedimentary records which show a regional-scale response to climate change and Saharan dust deposition in Sierra Nevada lakes and their catchments during the 20th century. However, diatom assemblages seem to respond to different atmospheric and climate-related effects than cladoceran assemblages and chlorophyll-a concentrations. The recent impact of climate change and atmospheric Saharan deposition on lake biota assemblages and water chemistry, as well as catchment water availability, will have important implications for the valuable ecosystem services that the Sierra Nevada provides.

Biodiversity patterns of Arctic diatom assemblages in lakes and streams: Current reference conditions and historical context for biomonitoring

Abstract Comprehensive assessments of contemporary diatom distributions across the Arctic remain scarce. Furthermore, studies tracking species compositional differences across space and time, as well as diatom responses to climate warming, are mainly limited to paleolimnological studies due to a lack of routine monitoring in lakes and streams across vast areas of the Arctic. The study aims to provide a spatial assessment of contemporary species distributions across the circum‐Arctic, establish contemporary biodiversity patterns of diatom assemblages to use as reference conditions for future biomonitoring assessments, and determine pre‐industrial baseline conditions to provide historical context for modern diatom distributions. Diatom assemblages were assessed using information from ongoing regulatory monitoring programmes, individual research projects, and from surface sediment layers obtained from lake cores. Pre‐industrial baseline conditions as well as the nature, direction and magnitude of changes in diatom assemblages over the past c.200 years were determined by comparing surface sediment samples (i.e. containing modern assemblages) with a sediment interval deposited prior to the onset of significant anthropogenic activities (i.e. containing pre‐1850 assemblages), together with an examination of diatoms preserved in contiguous samples from dated sediment cores. We identified several biotypes with distinct diatom assemblages using contemporary diatom data from both lakes and streams, including a biotype typical for High Arctic regions. Differences in diatom assemblage composition across circum‐Arctic regions were gradual rather than abrupt. Species richness was lowest in High Arctic regions compared to Low Arctic and sub‐Arctic regions, and higher in lakes than in streams. Dominant diatom taxa were not endemic to the Arctic. Species richness in both lakes and streams reached maximum values between 60°N and 75°N but was highly variable, probably reflecting differences in local and regional environmental factors and possibly sampling effort. We found clear taxon‐specific differences between contemporary and pre‐industrial samples that were often specific to both ecozone and lake depth. Regional patterns of species turnover (β‐diversity) in the past c.200 years revealed that regions of the Canadian High Arctic and the Hudson Bay Lowlands to the south showed most compositional change, whereas the easternmost regions of the Canadian Arctic changed least. As shown in previous Arctic diatom studies, global warming has already affected these remote high latitude ecosystems. Our results provide reference conditions for future environmental monitoring programmes in the Arctic. Furthermore, diatom taxa identification and harmonisation require improvement, starting with circum‐Arctic intercalibrations. Despite the challenges posed by the remoteness of the Arctic, our study shows the need for routine monitoring programmes that have a wide geographical coverage for both streams and lakes.

Regional gold mining activities and recent climate warming alter diatom assemblages in deep sub-Arctic lakes

Previous paleolimnological investigations have examined the effects of gold mining operations, local land-use changes, and regional climate warming on the aquatic biota from shallow lakes in Yellowknife, Northwest Territories, Canada. However, the long-term impacts of these multiple environmental stressors on the biota of deeper lakes that support large-bodied fish species have not been investigated. In this study, we examined multiple sedimentary proxies from two deep lakes around Yellowknife to assess the long-term effects of metalloid contamination, development of the city, and recent warming over the past ~ 200 years. The sedimentary metalloid profiles tracked the influence of mining operations and local land-use changes in the Yellowknife area and there were some similarities in the diatom responses to multiple stressors across the two lakes. However, the increases in sedimentary metalloid concentrations, eutrophic diatom taxa, and whole-lake primary production were more pronounced at Grace Lake relative to Alexie, likely because Grace is located nearer to the gold mines, as well as local city development. The overall lake primary production and the relative abundance of the planktonic diatom Discostella stelligera increased at both sites suggesting that some of the biological changes may be influenced by changes in thermal stratification, as has been documented in a wide spectrum of lakes across the Northern Hemisphere. Furthermore, the diatom assemblage changes in these deep lakes differed from those observed from shallow lakes in the region, suggesting that site-specific limnological characteristics will influence the biological responses to multiple environmental stressors through time.

Benthic diatom community dynamics in Mediterranean intermittent streams: Effects of water availability and their potential as indicators of dry-phase ecological status

The study of intermittent rivers is a critical and timely issue due to their worldwide increase, triggered by several causes including climate change. The need to understand the response of intermittent river biota to water intermittency led us to conduct this study using benthic diatoms collected in southern Portugal. Benthic diatoms were explored in terms of assemblages, diversity indices, the Specific Pollution Sensitivity (SPI) Index, functional metrics (i.e. ecological guilds and life-forms) and conservation status. We verified that changes in water physico-chemical characteristics were highly controlled by flow intermittency, which in turn is directly linked to meteorological variables (air temperature and precipitation). Changes in diatom assemblages reflect the aquatic regime of sites, changes in aquatic states through time and mesohabitats (dry biofilm, samples collected in pools or under flowing conditions). Species richness, on the other hand, did not reflect these differences, whilst Shannon diversity and Pielou's Evenness indices only reflected mesohabitat differences. The SPI distinguished sampling periods, and mesohabitats. The relative abundance of ecological guilds changed with aquatic states, with the low-profile guild dominating in eurheic and arheic conditions (except during Summer), being replaced by motile taxa in summer arheic conditions, reflecting increases in nutrient and siltation. The hypothesis that benthic diatom assemblages in dry biofilm can be used as an indicator of ecological status during the dry-phase was validated, since no differences between the Ecological Quality Ratio determined in dry biofilm collected in Summer 2017 and the previous Spring 2017 in flowing water. A method is proposed for diatom sampling in dry biofilm, contributing to an integrated ecological status evaluation, which considers the dry-phase and enhances the reach of biomonitoring programs.

Evaluating climate change impacts on mountain lakes by applying the new silicification value to paleolimnological samples.

The evaluation of climate change impact on lakes typically relies on statistical methods like the reorganisation of organism communities (beta diversity) or transfer functions. A new method uses the silicification of diatoms that correlates with temperature and nutrients. The so-called silicification value (SiVa) overcomes problems of descriptive statistics or absent indicator species. Averaged over diatom communities, it related inversely to lake surface temperatures in mountain lakes. Hence, its change over time (δ SiVa) in a lake was hypothesised to reflect global change-driven lake warming quantitatively, which supposedly climaxes in shallow lakes. Sixteen different δ SiVa calculation approaches were tested. They (1) included or excluded planktic diatoms, (2) integrated fixed or variable time series referring to climate data or changes in diatom assemblages, (3) employed a top-bottom or regression approach and (4) expressed the δ SiVa as relative or absolute values. Subfossil diatom assemblages from 24 sediment cores from Bavarian and north Tyrolian mountain lakes served as sample set. All possible approaches were evaluated for their explanatory power for lake characteristics using GLMs. The top-bottom benthic approach with fixed climate data-based time series appeared to be the best model based on AIC and the extent of variable integration. In line with the hypothesis, the strongest decrease of δ SiVa was evident in most shallow lakes. Segmented regression further highlighted a positive correlation with depth if shallower than 10m. By referring to the negative SiVa-summer temperature relation, δ SiVa also enabled the quantification of lake warming within the last decades, which ranged mainly between 0.1°C and 1.1°C per decade, consistent with existing literature. Additionally, a 100year temperature reconstruction from a varved sediment core successfully validated the approach. Further studies may focus and extend its application to deeper lakes, but it can already serve as a powerful tool in palaeolimnological studies of shallow lakes like hard-water mountain lakes.

Trends in development of diatom flora from sub-recent lake sediments of the Lake Bolshoy Kharbey (Bolshezemelskaya tundra, Russia)

We studied diatom assemblages of the proglacial arctic lake Bolshoy Kharbey (Bolshezemelskaya tundra, Russian Arctic) from a short sediments core covering the last ca. 200 years. In total, 121 taxa from 2 classes, 5 orders, 18 families, and 50 genera were identified. The diatom flora included species with mainly cosmopolitan distribution. The assemblages were dominated by alkaliphilic benthic diatoms preferring standing — flowing waters, indifferent to salinity and moderate temperature conditions. The main changes in diatom assemblages took place in ca. 1870 and 1980. After 1870, which can be attributed to the end of the Little Ice Age, the species richness rose, especially of planktonic centric and small penate diatoms. This rise of diatom diversity took place most probably in response to climate warming, related to it prolongation of the growing season and period of open water. A negative trend in the evenness of the diatom assemblages during the last decades can be seen as an early-warning signal indicating a decrease of stability of the lake ecosystem.

Exploring the use of nuclear alterations, motility and ecological guilds in epipelic diatoms as biomonitoring tools for water quality improvement in urban impacted lowland streams

Abstract In this study we explored the use of less conventional diatom metrics (motility, nuclear abnormalities and ecological guilds) to measure changes in diatom assemblages related to the transfer of epipelic communities from urban impacted streams to less impacted sites. Three lowland streams in the Argentine Pampean plain were selected, and two sites were established per stream for a total of six sites. Three sites were referenced as low urban impact (LI), as they run through peri-urban areas, and three downstream sites were referenced as high impact sites (HI), since they run through a dense urban area. Six germination trays filled with stream sediment were placed at each HI site, and three at each LI site, and left to be colonized for 30 days before transferring three trays from the HI sites to their respective LI site upstream. Samples were collected at days 0, 15, 30 and 45 days from each tray, and diatom species were identified and classified into ecological guilds. Motility variables were measure per individual of the genera Nitzschia (path length, velocity and maximum velocity) through video recording. Also, the frequency of abnormal nuclear locations and nuclear membrane breakage were determined. Results showed that there were no significant differences in any motility metrics, while the nuclei variables exhibited higher proportion of abnormally positioned nuclei and nuclear membrane breakage at the HI sites. The proportion of nuclear membrane breakage decreased over time in the translocated assemblage, indicating that it could be a sensitive indicator of water quality improvement, while the ecological guilds showed significant differences on the proportion of high profile and motile diatoms. The improvement in water quality produced a significative increase in the proportion of the high profile guild in the translocated biofilm. Despite the motile forms being the dominant group, the water quality improvement allowed the high profile forms, to colonize the substrate. These results emphasize the possible use of the ecological guilds as a suitable indicator of water quality improvement in Pampean streams, especially in nutrient rich environment. These tools can provide a rapid assessment of diatom condition and could be considered supplementary to biomonitoring protocols in lowland streams.

A high‐resolution diatom‐based Middle and Late Holocene environmental history of the Little Belt region, Baltic Sea

The large‐scale shifts in the salinity of the Baltic Sea over the Holocene are well understood and have been comprehensively documented using sedimentary proxy records. More recent work has focused on understanding how past salinity fluctuations have affected other ecological parameters (e.g. primary productivity, nutrient content) of the Baltic basin, and salinity changes over key events and over short time scales are still not well understood. The International Ocean Drilling Program Expedition 347 cored the Baltic basin in order to collect basin‐wide environmental records through a glacial–interglacial cycle. Site M0059 is located in the Little Belt between the Baltic Sea and the Atlantic Ocean. A composite splice section from Site M0059 was analysed at a decadal resolution to study changes in salinity, nutrient conditions and other surface water column parameters based on changes in diatom assemblages and on quantitative diatom‐based salinity inferences. A mesotrophic slightly brackish assemblage is seen in the lowermost analysed depths, corresponding to 7800–7500 cal. a BP. An increase in salinity and nutrient content of the water column leads into a meso‐eutrophic brackish phase. The observed salinity increase is rapid, lasting from 7500 to 7150 cal. a BP. Subsequently, the Little Belt becomes oligotrophic and is dominated by tychopelagic diatoms from c. 7100 to c. 3900 cal. a BP. This interval contains some of the highest salinities observed followed by diatom assemblages similar to those of the Northern Atlantic Ocean, composed primarily of cosmopolitan open ocean marine diatoms. A return to tychopelagic productivity is seen from 3850 to 980 cal. a BP. Anthropogenic eutrophication is detected in the last 300 years of the record, which intensifies in the uppermost sediments. These results represent the first decadally resolved record in the region and provide new insight into the transition to a brackish basin and subsequent ecological development.

A multibasin comparison of historical water quality trends in Lake Manitou, Ontario, a provincially significant lake trout lake

Nelligan C, Jeziorski A, Rühland KM, Paterson AM, Meyer-Jacob C, Smol JP. 2019. A multibasin comparison of historical water quality trends in Lake Manitou, Ontario, a provincially significant lake trout lake. Lake Reserv Manage. 36:243–259. Lake Manitou, on Manitoulin Island (Ontario, Canada), is a two-basin lake that supports a natural lake trout population and currently experiences late-summer hypolimnetic oxygen concentrations below the provincial criterion set to support this sensitive coldwater fish species. However, limited direct monitoring data make it difficult to assess long-term changes in hypolimnetic oxygen concentrations, and to identify what stressors may be responsible for those changes. Dated sediment cores from each basin of Lake Manitou were used to reconstruct end-of-summer volume-weighted hypolimnetic oxygen (VWHO) over the past ∼150 years using assemblages of sedimentary chironomid remains. To assess the influence of nutrients, regional warming, and lake browning, VWHO reconstructions were compared with sedimentary diatom assemblage changes, and spectrally derived trends in both sedimentary chlorophyll a (and its main diagenetic products) and sediment-inferred lakewater total organic carbon. The chironomid-inferred VWHO reconstructions suggest that deepwater oxygen concentrations are currently lower in both basins of Lake Manitou than they were prior to the 20th century (decreasing in the late 1880s coincident with the development of Manitoulin Island by European settlers). In both basins, post-1950 diatom assemblage shifts and whole-lake primary production (sedimentary chlorophyll a) trends suggest that increased nutrient inputs and warming-related changes (i.e., enhanced thermal stability) may be contributing to the current low-oxygen conditions of Lake Manitou. In the west basin, all paleolimnological proxies underwent more pronounced (and often earlier) changes than in the east basin, an observation that suggests more targeted management strategies may be needed to protect Lake Manitou’s coldwater fish population.

Varve Distribution Reveals Spatiotemporal Hypolimnetic Hypoxia Oscillations During the Past 200 Years in Lake Lehmilampi, Eastern Finland

We investigated 34 sediment cores to reconstruct spatiotemporal variations in hypolimnetic hypoxia for the past 200 years in Lehmilampi, a small lake in Eastern Finland. As hypoxia is essential for varve preservation, spatiotemporal changes in varve distribution were used as an indicator for hypolimnetic hypoxia oscillations. The hypoxic water volume was used as a variable reflecting hypolimnetic hypoxia and determined for each year by estimating the water volume beneath the water depth where shallowest varves were preserved. As a result, seven hypoxia periods, highlighting the variations in hypolimnetic hypoxia, are established. These periods may be influenced by bioturbation, lake infill, and lake level changes. Furthermore, we evaluated the relationship between hypolimnetic hypoxia oscillations and climatic factors. Diatom assemblage changes were also analyzed to estimate whether the hypoxia periods could be related to anthropogenic eutrophication. The diatom analyses suggest relatively stable nutrient conditions for the past 200 years in Lake Lehmilampi. Climate, on the other hand, seems to be an important driver of hypoxia oscillations based on correlation analysis. The role of individual forcing factors and their interaction with hypolimnetic hypoxia would benefit from further investigations. Understanding climatic and anthropogenic forcing behind hypolimnetic hypoxia oscillations is essential when assessing the fate of boreal lakes in a multi-stressor world.

Identifying temporal and spatial patterns of diatom community change in the tropical Andes over the last c. 150 years

AbstractAimLakes in the Ecuadorean Andes span different altitudinal and climatic regions, from inter Andean plateau to the high‐elevation páramo, which differ in their historical evolution in the several centuries since the pioneering Humboldt expeditions. Here, we evaluate temporal and spatial patterns of change in diatom assemblages between historical (palaeolimnological) and modern times.LocationEcuadorean AndesMethodsWe compared historical (pre‐1850) and modern (2017) diatom assemblages from 21 lakes and determined the relative role of environmental (water chemistry and climate) and spatial factors (distance‐based Moran's eigenvectors maps) on both assemblages using non‐metric multidimensional scaling (NMDS) with environmental fitting. In addition, we used redundancy analysis (RDA) with variance partitioning to estimate the historical (measured using downcore assemblage composition) effects on modern diatom assemblages and identified diatom species that contributed most to dissimilarity between the two times.ResultsDiatom changes between the two time points were limited across the group of lakes, as indicated by the NMDS ordination. Variance partitioning indicated that modern diatom assemblages were affected by environmental and spatial effects, but with non‐significant effects of past diatom species composition. Ordination results showed that variables related to elevation and water chemistry affected both modern and historical diatom assemblages. Diatom species with the best fit on NMDS axes (i.e. >70%) were influenced by elevation and climatic variables. The most distinctive change between the two time periods was the higher relative abundance of planktic diatom species in top‐core assemblages of some lakes, but in a highly variable fashion across gradients of increased elevation and water depth.Main conclusionsLandscape palaeolimnological analyses of varied Ecuadorean Andean lakes demonstrate both environmental and spatial controls on diatom metacommunities. The multi‐faceted ecological control of the altitudinal gradient on both historic and contemporary diatom assemblages suggests species sorting and dispersal constraints operating at centennial time‐scale. Although a few individual lakes show substantive change between the 1850s and today, the majority of lakes do not, and the analysis suggests the resilience of lakes at a regional scale. We emphasize the potential of diatom palaeolimnological approaches in biogeography to test ecologically relevant hypotheses of the mechanisms driving recent limnological change in high‐elevation tropical lakes.

Diatom ecological response to deposition of the 833-850 CE White River Ash (east lobe) ashfall in a small subarctic Canadian lake.

A <5 mm thick volcanic ashfall layer associated with the White River Ash (east lobe [WRAe]) originating from the eruption of Mount Churchill, Alaska (833-850 CE; 1,117–1,100 cal BP) was observed in two freeze cores obtained from Pocket Lake (62.5090°N, −114.3719°W), a small subarctic lake located within the city limits of Yellowknife, Northwest Territories, Canada. Here we analyze changes in diatom assemblages to assess impact of tephra deposition on the aquatic biota of a subarctic lake. In a well-dated core constrained by 8 radiocarbon dates, diatom counts were carried out at 1-mm intervals through an interval spanning 1 cm above and below the tephra layer with each 1 mm sub-sample represented about 2 years of deposition. Non-metric Multidimensional Scaling (NMDS) and Stratigraphically Constrained Incremental Sum of Squares (CONISS) analyses were carried out and three distinct diatom assemblages were identified throughout the interval. The lowermost “Pre-WRAe Assemblage (Pre-WRAeA)” was indicative of slightly acidic and eutrophic lacustrine conditions. Winter deposition of the tephra layer drove a subsequent diatom flora shift to the “WRAe Assemblage (WRAeA)” the following spring. The WRAeA contained elevated abundances of taxa associated with oligotrophic, nutrient depleted and slightly more alkaline lake waters. These changes were only apparent in samples within the WRAe containing interval indicating that they were short lived and only sustained for a single year of deposition. Immediately above the WRAe horizon, a third, “Post-WRAe Assemblage (Post-WRAeA)” was observed. This assemblage was initially similar to that of the Pre-WRAeA but gradually became more distinct upwards, likely due to climatic patterns independent of the WRAe event. These results suggest that lacustrine environments are sensitive to perturbations such as deposition of ash fall, but that ecological communities in subarctic systems can also have high resilience and can recover rapidly. If subsampling of the freeze cores was carried out at a more standard resolution (0.5–1 cm) these subtle diatom ecological responses to perturbation associated with the WRAe depositional event would not have been observed. This research illustrates the importance of high-resolution subsampling when studying the environmental impact of geologically “near instantaneous” events such as episodic deposition of ashfalls.

Biological and geochemical changes in shallow lakes of the Hudson Bay Lowlands: a response to recent warming

The Hudson Bay Lowlands (HBL) region of the far north of Ontario (Canada) is expected to undergo considerable physical, chemical and biological change as a result of ongoing climatic change. Previous research in the region has shown marked limnological changes during the past ~ 20 years in relatively deep lakes that have been attributed to increased air temperatures and changes in sea ice phenology in Hudson Bay since the mid-1990s. Here, we present diatom assemblage, primary production and geochemical data from lake sediments documenting recent limnological change in two shallow sub-arctic lakes in the Sutton River region of the HBL. Both lakes recorded increased whole-lake production and diatom diversity changes that are consistent with a longer ice-free period and growing season. Changes in diatom composition at Wolfgang Lake were characterized by a response amongst benthic/periphytic taxa whereas a modest increase in planktonic diatoms was observed at Sam Lake. Geochemical changes (δ15N, C/N and %N) were temporally coherent with diatom assemblage changes, but showed different responses in the two study lakes. Thus, although the biological and geochemical changes were consistent with recent warming, differences in the nature and timing of these shifts illustrate the heterogeneous nature of shallow lakes, and suggest that local (catchment-specific) factors are important determinants of the trajectory of limnological change in these sensitive systems.

Diatom Assemblage Changes in Agricultural Alluvial Plain Streams and Application for Nutrient Management.

In large, alluvial floodplains dominated by agriculture, small streams have the potential to experience nutrient enrichment affecting algal assemblage structure and metabolism. Nutrient enrichment is largely driven by application of nutrients and altered hydrologic regimes. To inform stressor-response-based nutrient reduction goals for agricultural alluvial plain streams, diatom assemblages were sampled from 25 streams located within the Mississippi Alluvial Plain (MAP) with various land management practices and associated P and N inputs. From August through September 2015, epidendric diatom assemblage samples were collected from instream woody debris. Field nutrient gradients were skewed toward higher concentrations, and ranges of previously reported diatom assemblage response thresholds indicative of oligotrophic conditions were not well represented. Ordination analysis identified a gradient in species composition associated with increasing P and decreasing dissolved oxygen. A significant shift in diatom assemblage structure occurred when total P concentrations in the MAP streams exceeded 0.12 mg L-. Phosphorus-enriched systems were represented by a distinct set of indicator species, lower abundances of ubiquitous species, greater abundances of highly tolerant species, and greater abundances of high-P indicator species. No relationships were observed among diatom assemblage measures or traits with increasing N. Current results do not address potential criteria for identifying high-quality, oligotrophic streams. However, measures of diatom assemblage structure have potential for helping set benchmarks to reduce nutrient impacts and monitor effects of agricultural best management practices on MAP streams.

Vertical distribution of benthic diatoms in a large reservoir (Alqueva, Southern Portugal) during thermal stratification

Freshwater diatom communities are known to respond to a wide range of environmental factors, however, the depth gradient is usually neglected and few studies are available, especially in large reservoirs. During the ALqueva hydro-meteorological EXperiment (ALEX) field campaign, diatom communities were studied in the margins and in three platforms (from the surface to the bottom of the reservoir) located in the limnetic zone of the Alqueva reservoir, one of the largest artificial lakes in western Europe. A detailed meteorological and physico-chemical characterization of the reservoir was carried out from June to September in Summer 2014, when the reservoir was stratified, to relate these variables with diatom assemblages. Despite the large dimensions of the reservoir, no differences in the water physico-chemical characteristics and diatom descriptors were detected among platforms. Small changes in diatom assemblages, ecological guilds, taxa richness and Shannon diversity index were observed between sampling campaigns. Nevertheless, differences in diatoms were detected along a depth gradient, both in terms of diatom assemblages and ecological guilds. Taxa richness, Shannon diversity index, Pielou's evenness and Specific Pollution sensitivity Index (SPI) also differed with depth, with the lowest values of all indices detected at surface samples, increasing with depth, reaching the highest values at 20 m for taxa richness, Shannon diversity and Pielou's evenness indices.

Ecophysiological linkage of nitrogen enrichment to heavily silicified diatoms in winter

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 604:51-63 (2018) - DOI: https://doi.org/10.3354/meps12747 Ecophysiological linkage of nitrogen enrichment to heavily silicified diatoms in winter Dongyan Liu1,*, Patricia M. Glibert2 1State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200062, PR China 2University of Maryland Center for Environmental Science, Horn Point Laboratory, Cambridge, MD 21613, USA *Corresponding author: dyliu@sklec.ecnu.edu.cn ABSTRACT: Over recent decades, increased anthropogenic nitrogen and reduced land-based loading of silica in many coastal waters have asymmetrically changed the nitrogen:silica ratios. These changes have contributed to shifts in phytoplankton assemblages from diatoms to non-diatoms, as well as increases in the frequency and magnitude of non-diatom harmful algal blooms. Here we show a subtle and counterintuitive change in diatom assemblage, i.e. heavily silicified diatoms significantly increased in winter after nitrogen enrichment, based on paleoecological and contemporary seasonal water column data from 2 eutrophic bays in the Yellow Sea. The heavily silicified diatom Paralia sulcata showed an increasing trend over time in parallel with nitrogen enrichment, which was associated with low temperature, and low dissolved inorganic nitrogen:phosphorus, high dissolved nitrogen:silica, and low ammonium:nitrate ratios on a seasonal basis. Applying recent insights regarding diatom nitrogen metabolism and its putative urea cycle, a physiological mechanism linking nitrogen, carbon, and silica metabolism is suggested to explain the phenomenon of increased silicification under winter conditions at the cellular level. Winter sequestration of silica in P. sulcata valves also has biogeochemical consequences, including a weakening of the silica pump and a slowing of biogenic silica dissolution, thereby reducing the availability of silica for further diatom growth in subsequent seasons and increasing the window of opportunity for summer growth of non-diatom harmful algal bloom species. KEY WORDS: Paralia sulcate · Nitrification · Diatom metabolism · Photosynthesis · Phytoplankton shift · Si cycling Full text in pdf format PreviousNextCite this article as: Liu D, Glibert PM (2018) Ecophysiological linkage of nitrogen enrichment to heavily silicified diatoms in winter. Mar Ecol Prog Ser 604:51-63. https://doi.org/10.3354/meps12747 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 604. Online publication date: October 04, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Diatom responses to 20th century shoreline development and climate warming in three embayments of Georgian Bay, Lake Huron

Abstract We used high-resolution diatom-based paleolimnological techniques to assess the effects of shoreline development and recent climate warming on three large embayments of Georgian Bay, Lake Huron (two impacted and one minimally impacted by shoreline development). The sedimentary diatom assemblages recorded subtle shifts at the impacted sites (North and South Bays) as a result of the establishment of permanent settlements and recreational resorts around the turn of the 20th century. No turn-of-the-century changes were observed at the reference site (Tadenac Bay). The abrupt increase in epiphytic Cocconeis placentula and benthic fragilarioid taxa during the ~1950s at the shallower impact site (South Bay) was likely due to increased habitat provided by macrophytes. The increase in relative abundances of pennate (Asterionella formosa and Fragilaria crotonensis) and/or small centric (Cyclotella ocellata, C. comensis, and C. gordonensis) planktonic diatoms across the three sites after the 1970s suggests that recent warming-mediated changes to thermal properties (and related effects) are driving biological changes in these embayments. These recent diatom compositional changes are consistent with similar trends reported across Ontario and the Laurentian Great Lakes, where warming and its effects on aquatic ecosystem processes often favor small-celled centric diatoms. Differences in the timing and nature of diatom responses to similar environmental stressors across the three embayments highlight the importance of understanding site-specific characteristics when interpreting changes in diatom assemblages in paleolimnological records from the Laurentian Great Lakes.

A diatom-based paleolimnological survey of environmental changes since ~ 1850 in 18 shallow lakes of the Athabasca Oil Sands Region, Canada

Aerially transported contaminants from the industrial development of the bituminous sands in the Athabasca Oil Sands Region (AOSR) of western Canada may threaten the water quality and community structure of the region’s lakes. This environmental threat is further compounded by the region’s changing climate (i.e. increased temperatures and reduced moisture). Because environmental monitoring began ~ 30 years after the initiation of the region’s bitumen-based industry (~ 1967), a paleolimnological approach is required to document pre-disturbance conditions and to determine how lakes have changed, if at all, in response to environmental stressors. Our bottom–top (before and after) study of dated sediment records compared pre-disturbance (~ 1850) and modern subfossil diatom assemblages from 18 shallow, isolated lakes (which are typical of the region), located along a spatial gradient (up to ~ 110 km) relative to the main area of local industry. Despite the region’s substantial environmental stressors, the changes in mostly benthic-dominated diatom communities were minor at 15 of the 18 lakes. We conclude that the muted biological responses may be a consequence of naturally high nutrient concentrations and/or the typically subtle nature of changes in assemblages dominated by benthic generalist taxa. At all sites, including three lakes with marked changes, we found no evidence of a diatom assemblage response to airborne inputs of contaminants (i.e. dibenzothiophenes) and nutrients (i.e. bioavailable nitrogen) from the AOSR industry. Instead, it is likely that regional warming played a role in the modest diatom assemblage changes observed in these shallow lakes, with responses mediated by lake-specific characteristics.

Eutrophication histories of three contrasting lakes in a naturally nutrient-rich boreal watercourse

The Iisalmi Route watercourse in central-eastern Finland contains a number of highly eutrophic lakes. Despite substantial impacts from anthropogenic activity, the region appears to be naturally eutrophic because of its geological setting. A passive continental ice sheet deposited fine-grained basal till that contributes to the naturally eutrophic status of the lakes. Detailed paleolimnological studies in the Iisalmi Route are few. Therefore, we studied the eutrophication histories of three contrasting Iisalmi Route lakes: (1) small headwater Lake Saarisjarvi, (2) larger, but very shallow headwater Lake Nalantojarvi, and (3) large central basin, Lake Porovesi. We compared the suitability of three diatom-total phosphorus transfer functions for application to fossil samples. A local transfer function, specifically targeted to the Iisalmi Route, was the most suitable for the headwater lakes. In contrast, two regional transfer functions, which have larger geographical coverage, performed equally well for the large central basin. All three lakes proved to have been naturally eutrophic for thousands of years. Highest natural variability occurred in the longest core, from shallow headwater Lake Nalantojarvi. This variability reflects the dynamic development of the basin and its catchment after deglaciation. Diatom assemblage changes in cores from Lakes Saarisjarvi and Porovesi suggest cultural eutrophication, most likely after the region was colonized in the sixteenth century, followed by salinization in more recent times. Our study deepens understanding of naturally eutrophic boreal lakes that are located on fine-grained tills and their sensitivity to natural and anthropogenic forcing. Our results also highlight the importance of selecting appropriate transfer functions and realistic restoration targets when dealing with naturally eutrophic lakes.