Distribution Of Diatom Species Research Articles

Determination of ecological statuses of streams in the Ceyhan River Basin using composition and ecological characteristics of diatoms.

The present study aimed to evaluate the interactions between diatoms and ecological factors in various streams and to test the suitability of diatom indices to evaluate the ecological status of 44 streams in the Ceyhan River Basin during the spring and autumn periods of 2021 and the summer of 2022. Canonical correspondence analysis indicated the significant effects of electrical conductivity (EC), dissolved oxygen, biological oxygen demand (BOD5), total phosphorus (TP), and total nitrogen (TN) on the distribution of diatom species of streams in the Ceyhan River Basin. Of the streams, Aksu and Erkenez streams were associated with high EC, BOD5, and TP and characterized by pollution-tolerant species. Pollution-sensitive species showed close integration with Aksu Spring Brook, Gözpınar Creek, Göksun Creek, and Yeşilgöz Spring Brook, which related to a high dissolved oxygen gradient. Different eco-regional diatom indices displayed different scores, representing from bad to high ecological status in the Ceyhan River basin. Among the diatom indices, Trophic Index Turkey (TIT) proved to be the more suitable metric to assess the ecological status of streams. TIT indicated deterioration of water quality in Karasu (S06), Erkenez (S07) streams, and downstream areas of the Ceyhan River and the least distributed sampling stations in the basin. Results suggested that eco-regionally developed diatom indices, like TIT, are required to more accurately assess the ecological status of streams in the Mediterranean region. The study provides a fundamental assessment of the ecological status of streams in the Ceyhan River Basin using an appropriate diatom index before the Pazarcık-centered earthquake on February 6, 2023. Findings allow someone to assess the impact of the earthquake on diatom communities and ecological factors in the region in the future studies.

Deviation from neutral species abundance distributions unveils geographical differences in the structure of diatom communities.

In recent years, the application of metagenomics techniques has advanced our understanding of plankton communities and their global distribution. Despite this progress, the relationship between the abundance distribution of diatom species and varying marine environmental conditions remains poorly understood. This study, leveraging data from the Tara Oceans expedition, tests the hypothesis that diatoms in sampled stations display a consistent species abundance distribution structure, as though they were sampled from a single ocean-wide metacommunity. Using a neutral sampling theory, we thus develop a framework to estimate the structure and diversity of diatom communities at each sampling station given the shape of the species abundance distribution of the metacommunity and the information of a reference station. Our analysis reveals a substantial temperature gradient in the discrepancies between predicted and observed biodiversity across the sampled stations. These findings challenge the hypothesis of a single neutral metacommunity, indicating that environmental differences substantially influence both the composition and structure of diatom communities.

Improvement of the knowledge of diatom ecology by coupling geochemistry, radioactivity and taxa inventory in thermo-mineral springs of a volcanic and upland area in south-central France, the Massif Central

ABSTRACT In connection with its geological history, many thermo-mineral springs are present in the Massif Central (France). The physicochemical characteristics of these springs (temperature, mineralization, gas content) result both from their deep circulation and from the geological formations or surface waters with which they interact during their ascent. In mineral springs, diatoms are well represented. To date, no study has focused on coupling the origin of water with diatom communities, whether in the Massif Central or in other parts of the world. The purpose of this study is to cross the information obtained on the water and the diatoms in order to analyse the biodiversity and improve knowledge of the species autecology. Twelve mineral springs with some of which have high levels of radioactivity were studied in the Massif Central. As results, the geochemical facies, the origin of the water and the Total Dissolved Solids influence the taxonomic composition but not the specific richness, Shannon index and Evenness. Furthermore, 222Rn influences diatom richness and community structure. Planothidium frequentissimum, Crenotia angustior and Sellaphora labernardierei were associated with high values of 222Rn activity. The water temperature was a factor that influences diatom species distribution. Some species appears to be more sensitive to the composition of water, such as Planothidium frequentissimum which attests to a mixing between deep and surface waters.

Quantitative relationship between surface sedimentary diatoms and water depth in North-Central Bohai Bay, China

To study the quantitative relationship between surface sedimentary diatoms and water depth, 67 surface samples were collected for diatom analysis on eight profiles with water depth variation from the muddy intertidal zone to the shallow sea area in North-Central Bohai Bay, China. The results showed that the distribution of diatoms changed significantly in response to the change in water depth. Furthermore, the quantitative relationship between the distribution of dominant diatom species, their assemblages, and the water depth was established. The water depth optima for seven dominant species such as Cyclotella striata/stylorum, Paralia sulcata, and Coscinodiscus perforatus and the water depth indication range of seven diatom assemblages were obtained in the study area above the water depth (elevation) of −10 m. The quantitative relationship between surface sedimentary diatoms and water depth provides a proxy index for diatom-paleo-water depth reconstruction in the strata in Bohai Bay, China.©2023 China Geology Editorial Office.

Diversity and distribution of lacustrine diatoms along the Trans‐Mexican Volcanic Belt

Abstract The Trans‐Mexican Volcanic Belt is recognised as a highly biodiverse zone and we present a study of diatom diversity and species distributions in its lakes. We aimed to identify diatom taxa with the highest regional occupancy, explore diversity at a regional level, identify the main variables associated with species distributions, and present weighted average optima for variables that could provide a valuable reference for future palaeoenvironmental research. We used the relative abundances of diatoms in surficial lake sediments to estimate different diversity metrics and alpha, beta and gamma diversities. Groups of lakes with similar diatom assemblages were identified by means of cluster analysis whereas canonical correspondence analysis (CCA) was used to evaluate the association between diatom composition and climatic, morphometric, hydrochemical and trophic status related variables. Weighted average optima were estimated for salinity and temperature. From a total of 184 diatom taxa, three were endemic to one or two lakes and eight had the largest regional occupancy, two of which were associated with high salinity environments (Stephanocyclus meneghinianus, Nitzschia frustulum) and the rest with freshwater conditions (Aulacoseira ambigua, A. granulata, A. granulata var. angustissima, Discostella stelligera, Fragilaria crotonensis, Achnanthidium minutissimum). Surprisingly, endemic taxa as well as those with high regional occupancy were mostly planktic or epipelic motile forms, with high dispersal potential. Our results showed 13 clusters of lakes with similar diatom assemblages, in close agreement with beta diversity which predicted the presence of 12 communities. There was high species turnover (βSIM = 0.97) and CCA showed not only that the main environmental variable defining these groups was salinity, but also that temperature, precipitation, depth, and soluble reactive phosphorus were meaningful variables. There was no evidence of an altitude–diversity pattern. This study emphasises the strong influence that climatic variables have on species distribution when relatively broad geographical areas, with large climatic gradients are analysed.

A diatom-based predictive model for inferring past conductivity in Chadian Sahara lakes

For decades, diatoms have been recognized as powerful bio-indicators of modern water quality. They have also been utilized in the design of transfer functions, which can be applied to diatom assemblages in lake sediment cores to infer aspects of past lake hydrochemistry and estimate variables that can be incorporated into paleohydrology models. The Ounianga lakes, in the heart of the Chadian Sahara, possess unique and well-preserved sediment records that extend back beyond the middle Holocene. Today, the lakes display a range of hydrochemical conditions, from fresh to hypersaline. Mainly fed by fossil groundwater that originates in the Nubian Sandstone Aquifer System, measured conductivity across these lakes varies from 217 to 352,000 µS cm−1, values that are influenced by factors such as hydrology, local geomorphology (e.g., depth and area), and aquatic vegetation. Although these lakes have been on the UNESCO World Heritage List since 2012, they have never been studied in detail because they are located on the fringes of the Chadian Sahara. The distribution of diatom taxa in the lakes today is closely linked to water-column physical and chemical conditions, especially conductivity. Whereas each lake has particular features that influence its diatom flora, diatoms across a conductivity gradient enabled identification of three distinct waterbody types, freshwater lakes, meso-saline to hyper-saline lakes, and freshwater springs. Relationships between diatom species distributions and environmental variables were examined using multivariate analysis, which revealed that conductivity is the variable that explains most of the variance in the diatom flora. We used modern diatom assemblages from the lakes to develop a predictive model (transfer function) for conductivity, using the weighted averaging method. Our conductivity prediction model is strong, with a coefficient of determination (R2) of 0.89 between estimated and measured values, and a value of 0.78 using jackknife estimates of prediction. This study better constrained conductivity optima and tolerance values for diatom species found in the Ounianga lakes, thereby enabling development of a model that will yield better inferences for past conductivity, using diatoms from lake sediment records in the region.

Cold-induced [Ca2+]cyt elevations function to support osmoregulation in marine diatoms.

Diatoms are a group of microalgae that are important primary producers in a range of open ocean, freshwater, and intertidal environments. The latter can experience substantial long- and short-term variability in temperature, from seasonal variations to rapid temperature shifts caused by tidal immersion and emersion. As temperature is a major determinant in the distribution of diatom species, their temperature sensory and response mechanisms likely have important roles in their ecological success. We examined the mechanisms diatoms use to sense rapid changes in temperature, such as those experienced in the intertidal zone. We found that the diatoms Phaeodactylum tricornutum and Thalassiosira pseudonana exhibit a transient cytosolic Ca2+ ([Ca2+]cyt) elevation in response to rapid cooling, similar to those observed in plant and animal cells. However, [Ca2+]cyt elevations were not observed in response to rapid warming. The kinetics and magnitude of cold-induced [Ca2+]cyt elevations corresponded with the rate of temperature decrease. We did not find a role for the [Ca2+]cyt elevations in enhancing cold tolerance but showed that cold shock induces a Ca2+-dependent K+ efflux and reduces mortality of P. tricornutum during a simultaneous hypo-osmotic shock. As intertidal diatom species may routinely encounter simultaneous cold and hypo-osmotic shocks during tidal cycles, we propose that cold-induced Ca2+ signaling interacts with osmotic signaling pathways to aid in the regulation of cell volume. Our findings provide insight into the nature of temperature perception in diatoms and highlight that cross-talk between signaling pathways may play an important role in their cellular responses to multiple simultaneous stressors.

Biogeochemical indicators (waters/diatoms) of acid mine drainage pollution in the Odiel river (Iberian Pyritic Belt, SW Spain).

Odiel river basin is located in the Iberian Pyritic Belt (IPB) and mostly of its tributaries are severely affected by acid mine drainage (AMD). It is originated when pyritic minerals from abandoned mines, especially mineral residues from waste rock dams, get in contact with air and water. Fifteen sampling points were chosen to analyze interactions between diatom communities and water hydrogeochemistry. Considering physicochemical characteristics, sampling points were assigned as highly, moderately, and unpolluted by AMD. No correlation was observed between ecological diversity indexes and physico-chemical parameters. However, a dependency relationship between diatom species distribution and specific pH, conductivity, redox potential, sulfate, and metal concentrations was observed. Cluster analysis based on Pearson correlation and rs values of the non-parametric Spearman correlation allowed to identify Pinnularia acidophila, Pinnularia subcapitata var. elongata, and Eunotia exigua as the main bioindicators of AMD-polluted Odiel streams. Finally, a principal component analysis led to associate the most abundant diatoms species to specific physico-chemical parameters.

Distribución del fitoplancton en aguas marino-costeras en tres sectores de la península de Santa Elena

The composition, distribution, abundance and ecology were studied in the phytoplankton communities during the wet season from December of 2015 to May of 2016 in six stations located in the coastal zone of Ancon, Anconcito and Punta Carnero province of Santa Elena. 36 samples were collected by surface trawls. A total of 58 species were identified in the 6 stations, in which 31 species correspond to diatoms and 26 species belong to dinoflagellates, 1 species of silicoflagellates and tintinids as part of the phytoplankton fauna present in all stations. The total density of the first trophic link reported a total of 392652 cells/100m3, in wich the highest distribution was in the sector of Ancon at E-2 with 107073 cells/100m3, followed by E-3 located in the Anconcito's sector with 84992 cells/100m3, in the sector of Punta Carnero the densities were low, reporting in the E-6 with 43358 cells/100m3, considering that the phytoplankton presented during the time of sampling a heterogeneous behavior among the three sectors. The distribution of diatom species reported their highest percentage in the Rhizosolenia imbricate species with 40.48% being present in the 6 months of sampling, but not in all stations fallowed by Rhizosolenia hebetata species with 16.84% being present only in December and absent in the other months. Lectocylindrus danicus reported 11.68% being absent in January and present in the other months. The species of Chaetoceros coarctatus, Climacodium frauenfeldianum and Cyclotella striata reported percentages between 7.35%, 5.49 and 5.47%, respectively. However, the other species presented in the study area registered their values below 5%. The dinoflagellate species reported their greatest population abundance in percentage with the species of Ceratium furca var. furca with 19.25%, followed by Ceratium fusus species with 14.73% and Ceratium tripos being present the all three species in the six months of sampling but not in all seasons. Ceratium candelabrum, Ceratium macroceros, Pyrophacus steinii and Ceratium trichoceros reported percentages between 9 and 5% respectively, the other species present in the area of study were below 5%.

A eutrofização altera a composição da comunidade e leva ao aninhamento de diatomáceas bentônicas em riachos costeiros

Abstract: Aim We evaluated changes in periphyton biomass and the composition of benthic diatom communities along a gradient of urbanization in 10 coastal streams located on the coastal plain of southernmost Brazil. Methods At each coastal stream, we obtained limnological variables and periphytic material from the stolon of the aquatic macrophyte Hydrocotyle ranunculoides for further analyses of chlorophyll a and diatoms. Results Total phosphorus was the only limnological variable selected by the statistical models, showing a positive relationship with periphyton biomass and a negative relationship with diatom species richness in these streams. Species composition (for both presence-absence and abundance data) was also explained by total phosphorus. Further, we observed a nested distribution of diatom species along the streams, in which poorer communities of streams with higher concentrations of phosphorous are subsets of richer communities from streams with lower concentrations of the nutrient. Conclusions Our study shows that water quality modifications caused by eutrophication are leading to the loss of species and changes in the structure of biological communities in ecotones such as coastal streams.

Impact of Sea‐Ice Dynamics on the Spatial Distribution of Diatom Resting Stages in Sediments of the Pacific Arctic Region

AbstractThe Pacific Arctic region is characterized by seasonal sea‐ice, the spatial extent and duration of which varies considerably. In this region, diatoms are the dominant phytoplankton group during spring and summer. To facilitate survival during periods that are less favorable for growth, many diatom species produce resting stages that settle to the seafloor and can serve as a potential inoculum for subsequent blooms. Since diatom assemblage composition is closely related to sea‐ice dynamics, detailed studies of biophysical interactions are fundamental to understanding the lower trophic levels of ecosystems in the Pacific Arctic. One way to explore this relationship is by comparing the distribution and abundance of diatom resting stages with patterns of sea‐ice coverage. In this study, we quantified viable diatom resting stages in sediments collected during summer and autumn 2018 and explored their relationship to sea‐ice extent during the previous winter and spring. Diatom assemblages were clearly dependent on the variable timing of the sea‐ice retreat and accompanying light conditions. In areas where sea‐ice retreated earlier, open‐water species such as Chaetoceros spp. and Thalassiosira spp. were abundant. In contrast, proportional abundances of Attheya spp. and pennate diatom species that are commonly observed in sea‐ice were higher in areas where diatoms experienced higher light levels and longer day length in/under the sea‐ice. This study demonstrates that sea‐ice dynamics are an important determinant of diatom species composition and distribution in the Pacific Arctic region.

Evaluation of the Relationship between Epiphytic Diatoms and Water Quality Parameters in the Büyükçekmece Reservoir

Objective: In this study carried out in Büyükçekmece Reservoir, the composition, distribution, seasonal changes of epiphytic diatoms that live on the surfaces of plants, and the effects of environmental parameters on these organisms were investigated, and it was aimed to reveal the water quality of the reservoir. Materials and Methods: In order to determine the seasonal changes of epiphytic diatom species in Büyükçekmece Reservoir, water and material samples were collected from five stations in 2019. In the study, water temperature, salinity, conductivity, dissolved oxygen, and pH values, which are among the basic ecological variables, were measured. Epiphytic diatom samples were obtained from Phragmites sp. species. Also, Spearman's rank correlation, Shannon–Weaver diversity index, Cluster (Bray–Curtis and Euclidean Distance), and ordination analysis (DCA and CCA) were applied in the study. Results: 66 epiphytic diatom species were identified in this study, and 36 of these species are new records for the reservoir. Most epiphytic diatom species were obtained in August, and the lowest number was obtained in November. According to the pH values, it was determined that the reservoir is alkaline. In addition, it was determined that the main factors affecting the distribution of epiphytic diatom species in the reservoir are temperature and conductivity, and it was revealed that ecological variables affect species distribution. Conclusion: According to conductivity and DO values, it was determined that the reservoir was of very good and of good quality, and in terms of DO values, the reservoir was mainly oligotrophic. However, station 5 was mesotrophic during the August sampling period, station 4 was mesotrophic, and station 5 was eutrophic in November. Also, Büyükçekmece Reservoir was found in poor and moderate status according to H' classification.

Epilithic diatoms in environmental bioindication and trout farm’s effects on ecological quality assessment of rivers

The main aim of this study was to investigate the application of benthic diatoms and the efficiency of diatom indices in water ecological assessment of rivers in Serbia, as well as the influence of trout farms on rivers water quality. Research was conducted in one year period along the Crnica and Radovanska rivers (Eastern Serbia), in 11 sampling sites (taking into account the position of trout fish farms that are built on both rivers). Results showed that fish farms affect the physical and chemical parameters, as well as diversity of the epilithic diatom assemblage along the rivers. Canonical correspondence analysis (CCA) indicated that among tested physical and chemical parameters, conductivity “EC”, water hardness “WH”, sulfates “SO42-”, ionized ammonia fraction “NH4+”, nitrates “NO3–“, “pH”, mud, stone and depth were the most important variables affecting the distribution of diatom species. A total of 206 epilithic diatom taxa were recorded in the Radovanska and 170 in the Crnica River. Based on diatom indices, trout fish farms have no significant negative impact on the water quality of the investigated rivers (indices are not enough sensitive). Redundancy analysis (RDA) showed a high degree of correlation between the majority of indices which mostly indicated to good water quality of studied rivers. TID and TDI were the only two indices indicating moderate and poor water quality of both rivers. Water quality based on the TIDRS, the first proposed diatom index for Serbia was differ in two classes in most sites compairing with TID.

Riqueza y distribución de las diatomeas epilíticas indicadoras de contaminación en el río Angulo afluente del río Lerma, Méxic

Background. The Angulo River has been subject to environmental deterioration as a result of agriculture practices and industrial discharges to its tributary. Goal. Determine the species of diatoms that indicate contamination and their distribution in the Angulo river, a tributary of the Lerma river. Methods. Twelve sites including 2 springs were selected during the low-water and post-rain periods of 2005. The samples were obtained by scraping the rocks to separate the attached diatoms. These were cleaned by oxidizing the sample with hydrochloric acid and hydrogen peroxide; permanent preparations were made with Naphrax® resin, for review with light microscopy. Results. 50 taxa belonging to 20 genera were identified, of which 5 species belong to central forms and 45 to pennate species. The taxa present in both periods were Achnanthidium minutissimum, Amphora pediculus, Luticola geoppertiana, Nitzschia amphibia, Nitzschia dissipata var. dissi- pata, Pleurosira laevis, Staurosira pinnata and Ulnaria ulna. The temperature, pH, dissolved oxygen and total dissolved solids in the Angulo river presented spatial variations and with it the species records. Conclusions. Representative taxa of eutrophic and non-eutrophic environments were found throughout the tributary, such as Nitzschia palea and Amphora pediculus, respectively. This study has provided relevant information re- garding the presence and distribution of diatom species that can be used as bioindicators of environmental conditions. specific.

Orbital and suborbital environmental changes in the Western Bering Sea during the last 172 ka Inferred from Diatom and Productivity Proxies

Abstract Diatom abundance and species distribution present a subtle tool for the reconstruction of the orbital and millennial-centennial climate and environmental changes in the southwestern Bering Sea during the last 172 ka, in addition to productivity proxies (chlorine, color b*, and Ca/Ti ratio), magnetic susceptibility, and biomarker proxies derived earlier and in this paper from the sediment core SO201-2-85KL recovered at the middle Shirshov Ridge (MSR). Available data indicate that the MSR area undergoes a significant seasonal sea ice influence during cold MISs 6.5–2. During the colder MIS 2, a main area of ice discharge extended southward of the MSR, likely outside of the sea, while over the coldest MIS 6.2, the MSR area was free from ice due to the shifting of the Aleutian Low to the eastern Siberian coast and the northward transfer of the warm and wet air of storm tracks into the western Bering Sea. During the warm MIS 5.5, the sea ice influence at the MSR area was negligible, nearly the same as it was over the Holocene, and it began to increase after event 26 (120.5 ka). The millennial scale variability of diatom abundance and its species distribution were triggered by Greenland Interstadials accompanied by productivity changes. The diatom species distribution showed complicated pattern of variability of the MSR environment, consistent with the millennial-centennial changes of the Greenland air temperature over the Dansgaard -Oeschger cycles. It confirms the rapid mechanisms of atmospheric teleconnection between these remote regions on the millennial-centennial time scale.

<p><strong>Climate-related morphological changes in <em>Pantocsekiella</em> (Mediophyceae) spanning 0-1.2 Ma in the Lake El’gygytgyn, northeastern Russia including <em>Pantocsekiella elgygytgynensis sp. nov.</em></strong></p>

The distribution of diatom species and their evolutionary histories are largely a result of the complex feedback mechanisms in their environment. Arctic lakes are particularly sensitive to climate changes, and the species within these environments reflect these histories. The diatom genus Pantocsekiella is widespread and notably morphologically diverse. Valves from Pantocsekiella in the Arctic Lake El’gygytgyn spanning the last 1.2 Ma were analyzed using light and scanning electron microscopy to investigate how morphological transitions are related to known regional climate events. Quantitative and qualitative observations yielded a high degree of morphological diversity with multiple morphological shifts often associated with inferred extreme cold events. Principal components analysis (PCA) on quantitative morphological variables demonstrates a gradient in morphological variability through time, with a distinct morphology persisting uninterrupted from ~550-~230 ka warranting the establishment of a new species. Valve size within this interval responds to interglacial-glacial cycles, with the largest initial valves occurring during interglacials suggesting sensitivity to lake conditions related to climate.

Marine diatom response to oceanographic and climatic changes in the NW South China Sea since the penultimate glacial interval

Abstract The species abundances and assemblage of fossil diatoms are used as micropaleontological proxy to reconstruct the northwestern South China Sea continental margin paleo-environment over the last glacial - interglacial cycle and Holocene. Analysis of fossil diatom assemblages in piston core 111PC show a flora over the most recent ~160 kyr. BP dominated by tropical-subtropical planktonic and coastal species, assigned to six local diatom assemblage zones similar to foraminifera-based marine oxygen-isotope stages (MIS 6-1). Diatom abundance and species fluctuations in the core profile study area respond to the glacial – interglacial climate gyration and climate instability. Diatom abundance was higher in the late-Wurm, compared to mid-Wurm glacial and postglacial (Holocene) stages and even lower during the Riss and early-Wurm glacial stages. Change tendency of diatom abundance is significantly different from stations to the southwest but comparable to northeast South China Sea. In MIS 5, relative abundance of tropical diatom taxa decreases upward in response to climate shifts from interglacial to last glacial interval. Diatom species distribution with higher relative abundance of coastal taxa responded to climate-fluctuation during the MIS 4 and MIS 3 transition while biased by local deposition character.

Overwhelming role of hydrology-related variables and river types in driving diatom species distribution and community assemblage in streams in Cyprus

Mediterranean streams are naturally highly-stressed environments mainly due to wide seasonal and inter-annual fluctuations in water quantity. This natural pressure will be exacerbated by climate change and is a significant challenge when establishing efficient assessment methods. We studied environmental parameters (hydromorphology, hydrology, physical and chemical variables) and analysed 171 diatom samples from 65 stations in Cyprus (south-western part). Analyses revealed 290 taxa (273 identified to the species -or intraspecific- level) belonging to 65 genera. Even a tentative application of a Red-List approach underlined the overwhelming importance of hydrology-related variables and river types in determining species distribution and community ecological attributes in the water-stressed island of Cyprus. Somewhat unexpectedly, both species from threat categories of the diatom Red List for Central Europe (2018) and species one might predict would be included in such categories in a possible future Red List tailored for Cyprus occurred more frequently and were more relevant in assemblages from sites in intermittent streams. We found a majority of motile, medium- to small-sized, diatom species, including a small number of colony-forming species. We found several species known to be effective first colonizers (pioneer species) and, among these, there was a striking preponderance (80%) of Achnanthidium species, often with several species co-occurring, particularly at reference sites. A four-factor PERMANOVA found that all type (essentially hydrology-related) variables were significant, and there was also a significant effect of season. Agglomerative hierarchical cluster analysis revealed three end-groups, with groups being separated on ecohydro(geo)logical grounds (lentic/lotic), sediment grain size, discharge and pH. The reference sites were analysed in more detail to identify environmental determinants. 28% of the variation in diatom assemblage composition was explained by the measured variables, with those associated with stream type and hydrology explaining the greatest proportions (12 and 10%, respectively) whilst season accounted for the remainder. Our study emphasised a need for detailed investigations of ecological and distributional (including Red List status) traits of diatom species, and to acknowledge the importance of the hydrological peculiarities of Mediterranean streams, in particular the dramatic seasonal variability, when developing ecological assessment protocols for the region.

Reduction of taxonomic bias in diatom species data.

Inconsistency in taxonomic identification and analyst bias impede the effective use of diatom data in regional and national stream and lake surveys. In this study, we evaluated the effect of existing protocols and a revised protocol on the precision of diatom species counts. The revised protocol adjusts five elements of sample preparation, taxon identification and enumeration, and quality control (QC) samples. We used six independent datasets to assess the effect of the adjustments on analytical outcomes. The first dataset was produced by five analysts from three laboratories following a standard protocol (Charles et al. 2002). The remaining datasets were produced by 2-3 analysts in 1-3 laboratories following a revised protocol. The revised protocol included the following modifications: 1) use of Battarbee settling chambers to prepare coverslips, 2) development of coordinated pre-count voucher floras based on morphological operational taxonomic units (mOTUs), 3) random assignment of samples to analysts, 4) post-count identification and documentation of taxa, and 5) increased QC samples. The revised protocol reduced taxonomic bias, as measured by reduction in analyst signal, and improved similarity among QC samples. Reduced taxonomic bias improves the performance of biological assessments, facilitates transparency across studies, and refines estimates of diatom species distributions.

Establishment of a diatom-total phosphorus transfer function for lakes on the Songnen Plain in northeast China

To understand the relationship between planktonic diatoms and environmental variables in the lakes on the Songnen Plain, northeast (NE) China, we investigated water quality and planktonic diatoms from 71 sampling points in 27 lakes, based on which Canonical Correspondence Analysis (CCA) was conducted. The result show that planktonic diatoms displayed certain responses to environment gradients, and the total phosphorus (TP) explained the maximum variation of planktonic diatom species among the 15 environmental variables, suggesting that TP was the most important and significant environmental parameter affecting the distribution of diatom species. In addition, we established a diatom-total phosphorus transfer (DTPT) function, of which component 5 of the weighted averaging partial least squares regression (WAPLS) was chosen to and compared with a series of weighted average regression (WA) models and WA-PLS models. According to the jackknifing statistical test, the component 5 of WA-PLS models provided a lower root-mean-square error prediction (RMSEP=0.202) and a higher correlation coefficient between observation and prediction (R2_Jack=0.759). After deletion of three outliers, the root-mean-square error prediction of the DTPT function was reduced (RMSEP=0.169) while the correlation coefficient between observation and prediction was increased (R2_Jack=0.823). Therefore, this DTPT function performed better than other regional TP models in the world. However, it remains demanding for expanding the background dataset to improve the prediction ability of the model.