Kálmán Tapolczai

• PhD in biodiversity, ecology, environment
• Research fellow at Balaton Limnological Research Institute

Biodiversity loss in freshwater is five times higher compared to terrestrial ecosystems and especially threatens rare species. However, even basic knowledge about rarity is missing in aquatic algal ecology, which could be the base of their conservation strategies. Therefore, we investigated rare species in benthic diatom communities of the River Da...

Human activities drive a wide range of environmental pressures, including habitat change, pollution and climate change, resulting in unprecedented effects on biodiversity1,2. However, despite decades of research, generalizations on the dimensions and extent of human impacts on biodiversity remain ambiguous. Mixed views persist on the trajectory of...

DNA metabarcoding of benthic diatoms has been successfully applied for biomonitoring at the national scale and can now be considered technically ready for routine application. However, protocols and methods still vary between and within countries, limiting their transferability and the comparability of results. In order to overcome this, routine us...

The prevalence of organic/chemical UV-filter compounds in aquatic ecosystems represents a growing environmental issue. The long-term toxicity risks of many UV-filters at environmentally relevant concentrations to aquatic biota are still less studied, especially in the case of invertebrates. This study was designed to evaluate the chronic toxicity o...

Tufa deposits in karst rivers are unique habitats created by mutual interactions between specific environmental and biotope features and inhabited by diatoms as a highly abundant and diverse algal group. This pilot study aimed to investigate the diversity of diatom communities on tufa depositing habitats and assess the Una River’s ecological status...

Diatom species identification with DNA metabarcoding is an economical, fast and reliable alternative to identification via light microscopy for river quality monitoring. Using a short DNA sequence of the rbcL gene and 'Diat.barcode', a reference barcode library, enables the identification of more than 90% of the environmental sequences to species l...

In the present study, we developed a new Swedish phosphorus diatom index (PDISE) to improve the poor fit of existing indices to match the needs of water managers to detect and mitigate eutrophication. We took advantage of a large amount of data (820 Swedish stream sites) collected in recent years. During our work, we found an unexpected bimodal res...

Both natural and anthropogenic processes can lead to the increasing salinity of surface waters. The knowledge about the ecological consequences of salinization on the biota is limited especially in case of microbiota, like diatoms. We collected the existing knowledge about the relationship between salinity and diatoms in fresh and saline waters. Ba...

A number of studies evidenced the impact of human activities on aquatic environments worldwide. The availability of nutrients in lakes is strongly influenced by watershed land use patterns depending on the share of forestry, agriculture and urbanization level. Nearly all the previous studies, which examined the relationships between the phytoplankt...

The presence of microplastics (MPs) in the global ecosystem has generated a rapidly growing concern worldwide. Although their presence in the marine environment has been well-studied, much less data are available on their abundance in freshwaters. MPs alone and in combination with different chemicals has been shown to cause acute and chronic effect...

In the present study, we developed a new Swedish phosphorus diatom index (PDI SE ) to improve the poor fit of existing indices to match the needs of water managers to detect and mitigate eutrophication. We took advantage of a large amount of data (820 Swedish sites) collected in recent years. During our work, we found an unexpected bimodal response...

Zoosporic parasites (i.e. fungi and fungi-like aquatic microorganisms) constitute important drivers of natural populations, causing severe host mortality. Economic impacts of parasitic diseases are notable in the microalgae biotech industry, affecting production of food ingredients, biofuels, pharma- and nutraceuticals. While scientific research on...

Diatoms, a unique group of algae colonising a wide range of aquatic habitats and contributing to human well-being in many ways. We list and summarise these services using the classification of the Millennium Ecosystem Assessment (MEA), i.e. supporting, regulating, provisioning and cultural services. The most relevant supporting services are photosy...

Permanent ponds are valuable freshwater systems and biodiversity hotspots. They provide diverse ecosystem services (ES), including water quality improvement and supply, food provisioning and biodiversity support. This is despite being under significant pressure from multiple anthropogenic stressors and the impacts of ongoing global change. However,...

Diatom taxonomy has evolved in recent years, with many new species described and new approaches such as molecular genetics showing the existence of cryptic diversity within currently accepted species. This cryptic diversity is not well understood even for common freshwater genera such as Fragilaria and Ulnaria. The purpose of our study was to defin...

Karst ecosystems play a unique role as exceptional natural habitats in sustaining biodiversity. This study focuses on diatoms, a diverse group of microeukaryotes in the periphytic community of a karstic river. In a multi-microhabitat study along the Krka River (Croatia), our goal was to obtain a detailed overview of diatom diversity and community s...

In this work the rapid expansion of a small-celled (<15 µm) monoraphid aquatic invasive species (AIS) along the Central European lotic systems is reported, using the integrated dataset of two large-scale monitoring programs, as supplemented by additional records. Achnanthidium delmontii Pérès, Le Cohu & Barthès 2012 (ADMO) was discovered in 2007 an...

We developed and compared the performance of freshwater benthic diatom indices calculated from (i) traditional morphological species identification, (ii) Amplicon Sequence Variants (ASVs) obtained via DNA metabarcoding, and (iii) morphological traits to indicate eutrophication in rivers and lakes in Fennoscandia. Based on the results, we provided r...

During the past decade genetic approaches have been developed to monitor biodiversity in aquatic ecosystems. These enable access to taxonomic and genetic information from biological communities using DNA from environmental samples (e.g. water, biofilm, soil) and methods based on high-throughput sequencing technologies, such as DNA metabarcoding. Wi...

Diatom biomonitoring and ecological studies can greatly benefit from DNA metabarcoding compared to conventional microscopical analysis by potentially providing more reliable and accurate data in a cost- and time-efficient way. A conventional strategy for the bioinformatic treatment of sequencing data involves the clustering of quality filtered sequ...

The process of travertine formation and carbonate deposition in the rivers is unique, delicate, and depends on the activity of algae and mosses. Although diatoms have been used extensively in hydrobiological studies, the comparative analysis data on diatom communities of the travertine barriers in karstic rivers are still scarce. The study aimed to...

Land-use imposes an important potential threat on the aquatic ecosystems of riverine habitats. In this study, DNA metabarcoding was used to assess the effect of land-use on diatom assemblages, with a special focus on cropland area as an integrative proxy for several direct-acting pressures. The so-called taxonomy-free approach was tested using exac...

Phytobenthos samples were collected at 69 sites during JDS4. Whenever possible, samples were obtained from both riverbanks and analysed by DNA metabarcoding with two markers, 18SV4 and rbcL. The genera with the most Sequence Units were Nitzschia, Navicula, Sellaphora and Amphora. The most abundant species were Navicula cf. ramosissima, N. tripuncta...

Climatic extreme events such as droughts (unpredictable), dry periods (predictable) or even flush floods, threaten freshwater ecosystems worldwide. The filtering mechanisms of these events and their strength on communities, however, can be different among regions. While time-for-adaptation theory defines whether or not water scarcity can be conside...

Recent years provided intense progression in the implementation of molecular techniques in a wide variety of research fields in ecology. Biomonitoring and bioassessment can greatly benefit from DNA metabarcoding and High-Throughput Sequencing (HTS) methods that potentially provide reliable, high quantity and quality standardized data in a cost- and...

This report presents the outcome of the joint work of PhD students and senior researchers working with DNA-based biodiversity assessment approaches with the goal to facilitate others the access to definitions and explanations about novel DNA-based methods. The work was performed during a PhD course (SLU PNS0169) at the Swedish University of Agricul...

Climate change is predicted to increase drought occurrence and severity in small continental watercourses. Here, we studied the structure and the functional diversity of benthic diatom assemblages in lowland intermittent and permanent watercourses of the Carpathian basin. We assumed that the community structure of intermittent and permanent waterco...

Extensive studies on the taxonomic resolution required for bioassessment purposes have determined that resolution above species level (genus, family) is sufficient for their use as indicators of relevant environmental pressures. The high-throughput sequencing (HTS) and meta-barcoding methods now used for bioassessment traditionally employ an arbitr...

Diatoms are used routinely to assess pollution level in rivers and lakes. Current methods are based on identification by light microscopy, which is laborious. An alternative is to identify species based on short DNA fragments and High–Throughput Sequencing (HTS). However a potential limitation is the incomplete coverage of species in reference barc...

In recent years, remarkable progress has been made in developing environmental DNA metabarcoding. However, its ability to quantify species relative abundance remains uncertain, limiting its application for biomonitoring. In diatoms, although the rbc L gene appears to be a suitable barcode for diatoms, providing relevant qualitative data to describe...

Rivers and lakes are exposed to severe pollution and alteration from anthropogenic sources. The impairment of our waters endangers not only our freshwater supply but also the organisms inhabiting them and the entire ecosystem. Several methods were developed over time to monitor water bodies and evaluate their ecological quality in order to propose...

Diatom-based ecological quality assessment methods have been implemented and used regularly in the Water Framework Directive. These indices use the species' abundance profiles along a specific environmental gradient, which they aim to assess. However, this approach has several problematic issues including the unstable and fast-changing diatom taxon...

Diatoms are excellent ecological indicators of water quality because they are broadly distributed, they show high species diversity and they respond rapidly to human pressures. In Europe, the Water Framework Directive (WFD) gives the legal basis for the use of this indicator for water quality assessment and its management. Several quality indices,...

Freshwaters worldwide face serious threats, making their protection increasingly important. Freshwater monitoring has historically produced valuable data and continues to develop. Rapid improvements to biomolecular techniques are revolutionizing the way scientists describe biological communities and are bringing about major changes in biomonitoring...

A high number of species often represents a relevant redundancy in terms of ecological adaptation strategies. Collecting species to groups based on their functional adaptations can handle this redundancy and obtain the “real” functional complexity of ecosystems. Functional traits are proxies of adaptation strategies under particular environmental c...

Benthic diatoms inhabiting littoral zones are regarded as promising bioindicators in lakes. Some pre-standard protocols were proposed and suggested to collect a single site per lake to assess its overall quality. In large lakes, such as Lake Geneva, a spatial heterogeneity of diatom assemblages was suspected, because of differing human pressures. T...

At low trophic state, stable stratified water columns may provide favorable conditions for adapted phytoplankton species to form deep chlorophyll maxima (DCM). Such maxima occur regularly in Lake Stechlin, mainly contributed by the cyanobacterial species Cyanobium sp. and occasionally by Planktothrix rubescens. In the early twenty-first century, a...

Over the last decades, mass developments by the filamentous conjugating green alga Mougeotia have been followed in three large peri-alpine lakes (Lake Geneva, Lake Garda, Lake Maggiore) and in the sub-tropical Lake Kinneret. The aim of this study is to highlight annual and interannual patterns of Mougeotia biomass in the studied lakes and select ke...

Massive developments of potentially toxic cyanobacteria in Lake Stechlin, an oligo-mesotrophic lake in the Baltic Lake District of Germany raised concerns about toxic contamination of these important ecosystems. Field samples in the phase of mass developments of cyanobacteria were used for genetic and toxicological analyses. Microcystins and microc...

In winter of 2009/2010, Aphanizomenon flos-aquae bloomed in the ice and snow covered oligo-mesotrophic Lake Stechlin, Germany. The photosynthesis of the natural population was measured at eight temperatures in the range of 2–35°C, at nine different irradiance levels in the range of 0–1,320 μmol m−2 s−1 PAR at each applied temperature. The photoadap...