Diatom Metrics Research Articles

Water usage and seasonality as primary drivers of benthic diatom assemblages in a lowland reservoir

Abstract In general, reservoirs are multi-purpose objects and they often have to fulfil different tasks at the same time. The compliance with these different expectations is more manageable in reservoirs with well-separated heterogeneous basins than in homogenous ones. The Kiskore Reservoir is the second largest standing water in the Carpathian Basin. Its water level is artificially regulated which creates unique habitats with high nature conservation value. Furthermore, the Reservoir is also considered as an important recreation centre in the region. It consists of four basins with different protection degree and management strategy. Here, we tested whether spatial (usage-dependent) or seasonal (time-dependent) segregations characterized the benthic diatom composition in the Reservoir. We also tested the influence of different water usage of basins using diatom metrics and diversity indices. We hypothesized that spatial heterogeneity in diatom composition will be more pronounced than seasonal ones. We also supposed that composition and diversity of diatom assemblages as well as diatom based ecological status will clearly reflect to different management strategies in the basins, whereas we expected moderate ecological status and low diversity in basins with high level of human impact. Our first hypothesis was not confirmed by the results. While diatom composition was clearly heterogeneous in time, surprisingly no usage-dependent segregation was found. Furthermore, our second hypothesis was also only partially confirmed by the results. In early summer, diversity was significantly lower in basins with higher level of human impact, than in the other basins. In late summer, however, diversity was rather directly controlled by nutrients and light not by water usage. Moreover, diatom based ecological status positively correlated to the intensity of recreation activities and negatively to protection degree. Although these results were surprising at the first time, they clearly confirm that a balanced ecological-economical relation can be maintained with properly designed and performed strategies in artificial reservoirs. But protection strategies, because of their exclusive interest to habitat conservation of macroscopic not microscopic organisms, require careful revisions.

Ecoregion approach in the assessment of aquatic ecosystems in the west of Gaziantep (Turkey): Application of diatom metrics

Abstract The biological assessment of surface water quality is becoming more important to evaluate the deterioration of aquatic ecosystems and to accomplish environmental sustainability since the implementation of EU Water Framework Directive (WFD). This study as the first attempt was organized to evaluate the ecological status of 17 freshwater bodies in the West of Gaziantep catchment by using diatom metrics. A total of 70 diatom assemblages were identified during the present study. The first two axes of canonical correspondence analysis (CCA) explained 0.962 and 0.945 of diatom assemblages–environment correlations for streams and reservoirs, respectively. According to the CCA, nutrients (e.g., P-PO4 and N-NO3) and metal ions (e.g. Cr, Ni, Pb, and Cu) strongly affected the distribution of diatom assemblages among the water bodies. Among the studied surface waters, Karanlik stream had the highest scores of 3.30, 3.39, and 2.39 due to the TIT–Trophic Index Turkey, TI–Trophic Index, and EPI-D–Eutrophication and/or Pollution Index-Diatom, respectively. The results indicated that this stream had a bad ecological condition when the EPI-D showed a poor condition. The occurrence of pollution-tolerant taxa, associated with high nutrients and electrical conductivity (EC), confirmed the ecological conditions of this stream. On the other hand, Cinarli (TIT = 2.23) and Yamacoba (TIT = 1.96) streams were of good ecological condition and had relatively low EC and nutrients. The presence of pollution-sensitive species in Cinarli and Yamacoba streams (Meridion circulare, Cymbella affinis, Halamphora veneta, and Cymbella excisa) endorsed the ecological status of it. The loading of organic and inorganic nutrients from livestock farming, agricultural land-use, and settlements could impact the water quality of the sampling stations in this catchment. The present study emphasized the importance of the evaluation of ecological integrity based on the biological and chemical characteristics of ecosystems. Diatom indices were used herein reflected efficient results for the separation of the ecological conditions of the sampled stations. Ecological preferences and occurrences of diatom assemblages and the significant positive correlation criterion with P-PO4 confirmed the suitability of TIT for assessing the ecological status of the sampling stations. All of these results suggest that the ecological status of water bodies should be evaluated due to the indices developed in their ecoregions.

Relationships between diatom metrics based on species nutrient traits and agricultural land use.

We assessed how diatom metrics were related to different ranges of agricultural land use. Diatom assemblage composition, nutrients, and landscape characteristics were determined at 232 sites in eight agriculturally dominated study areas of the continental United States. Two regional groups based on differences in diatom relations to human disturbance were determined. Changes in diatom species composition were related to nutrients, pH, and conductivity in the eastern study areas (due to more wetlands) and more exclusively to nutrients in the west-central study areas. Homogenization of diatom flora among streams was related to high agricultural disturbance at this transcontinental scale. Species traits were developed separately for the east and west-central study groups and calculated two ways: indicator species analysis for taxa in low and high TN or TP conditions and weighted average partial least squares models of TN and TP concentration. These diatom metrics were significantly related to many indicators of agricultural land use in watersheds, especially percent row crops. Further analysis was conducted on only the west-central region due to its larger sample size. Overall, diatom metrics using species responses to N gradients were better related to agricultural land use than were species responses to P gradients. Most nutrient-based diatom metrics changed greatly in response to low ranges of percent row crops, but only a few high N diatom metrics responded to high row crop conditions. The greater response of diatoms to changes in low agriculture conditions may be due to past diatom evolution occurring when most waters had low nutrient conditions.

Limno-ecological assessment of Aras River surface waters in Turkey: application of diatom indices.

This study is the first attempt to evaluate the limno-ecological status of freshwater ecosystems in Aras River system (Turkey) using diatom metrics and multivariate analyses according to the European Union Water Framework Directive requirements. Samples were collected using the standard protocols from 17 sampling stations in August and October of 2014, and June of 2015. Deterioration of water quality in the Aras River catchment was remarked from the downstream of Karakoyunlu, Sarısu, and Bozkuş creeks, which showed higher values of trophic index Turkey (TIT), trophic index (TI), and eutrophication and/or pollution index-diatom (EPI-D). These sites were also characterized by pollution tolerant taxa e.g., Cocconeis placentula, Gomphonema parvulum, Navicula cryptocephala, Navicula trivialis, and Tryblionella angustata. Sites S14-S17 had high ecological status according to TIT, supported by the score of EPI-D which indicated a good ecological condition for S14. The occurrence of pollution-sensitive species (e.g., Hannaea arcus, Cymbella affinis, Didymosphenia geminata, Meridion circulare, and Encyonema silesiacum) and the low nutrients like total phosphorus, orthophosphate and nitrate, conductivity, and BOD5 supported the high ecological status of S14-S17. The relationships between diatom assemblages and environmental variables were also illustrated by multivariate analyses. Spearman correlation analysis revealed that TIT had positive important correlations with total phosphorus (p < 0.01, r = 0.768). Trophic index and EPI-D had also significant correlations with environmental variables, but they had lower correlation coefficient than that of TIT. It seems that TIT could be a suitable diatom metric for assessing the ecological status of sampling stations in Aras River system and Mediterranean region. Our findings showed also that ecological statuses of surface waters should be evaluated due to the indices developed in their ecoregions.

Bio-assessment of surface waters in the south-east of Gaziantep (Turkey) using diatom metrics

Diatom metrics can be used to identify the ecological status of water bodies due to their good responses to anthropogenic disturbances. Our study is aimed to use diatom metrics developed from different ecoregions for assessing the ecological status of 11 surface waters in the south-east of the Gaziantep catchment (Turkey). Ecological characterizations of the sampling stations were introduced by Trophic Index Turkey (TIT), Trophic Index (TI), and Eutrophication and/or Pollution Index-Diatom (EPI-D). According to TIT and TI, Karkamış Reservoir had a good ecological condition while it had high ecological status based on EPI-D. This good ecological condition was approved by the presence of pollution sensitive species (e.g.,Cymbella affinis,Encyonema minutum,E. silesiacum,Cymbopleura amphicephala, andNavicula radiosa) and relatively low nutrients. Kayacık (TIT ranging 3.15–3.23) and Hancağız (TIT = 3.35) reservoirs had poor and bad ecological conditions, respectively. High nutrient, conductivity, and pollution-tolerant species (e.g.,Nitzschia amphibia,N. palea,N. umbonata,N. linearis,N. phyllepta,Tryblionella calida, andPinnularia brebissonii) supported the ecological statuses of the Hancağız and Kayacık reservoirs. The first two axes of canonical correspondence analysis explained 0.943 of relationships between diatom species and explanatory variables. Explanatory variables,e.g., calcium, conductivity, orthophosphate, nitrate, nitrite, sodium, pH, and sulfur, had strong impacts on the distribution of diatom assemblages among the sampling stations. TIT and TI separated ecological statuses of sampling stations in the south-east of the Gaziantep catchment, which correlated well with the evidence of water chemistry and response of diatom assemblages.

Ecological quality assessment of running waters in the North Aegean catchment with diatom metrics and multivariate approach

Assessing ecological quality of surface waters is getting more important to achieve environmental sustainability since the implementation of EU Water Framework Directive. This study was designed to assess ecological quality of freshwater bodies in the North Aegean catchment using the trophic index Turkey (TIT), recently developed for Turkish running water assessment. This first work attempts to evaluate rivers water quality in the Northern Aegean catchment, a touristic region based on the diatom index dedicated to the Anatolia region. Data were taken from 18 sampling stations in the Northern Aegean catchment (Turkey) from August 2014 to August 2015. A canonical correspondence analysis (CCA) performed to evaluate the relationship between diatom assemblages and environmental variables especially nutrients, temperature, electrical conductivity, and biochemical oxygen demand played important roles in the distribution of diatom species. CCA explained 12.5% of the cumulative percentage variance of diatom assemblage’s data with 92.8% of the species-environment correlations. In related to the water ecological status, the lowest TIT (1.57) values was recorded in Geyikli creek, whereas the highest TIT (2.82) was calculated in Bakırçay stream. The ecological quality ratio changed between 0.58 (Bakırçay stream with moderate status) and 0.99 (Geyikli, Kar and Kemer creeks with high status). Pollution tolerant species such as Gomphonema parvulum, Navicula recens, Navicula cryptocephala, Navicula cryptotenella, Navicula trivialis, and Cyclotella meneghiniana characterized the moderate ecological status water bodies were, while the high and good ecological status sites were characterized by nutrient sensitive species such Navicula radiosa, Didymosphenia geminata, Cymbella excisa, and Hannaea arcus. The ecological status the water bodies indicated exactly the state of deterioration of these watercourses due to human activities in the catchment. A significant positive correlation between TIT values and logTP confirmed that this index as a metric is a useful biological tool for the bioassessment of regional water quality.

Assessing the influence of multiple stressors on stream diatom metrics in the upper Midwest, USA

Water resource managers face increasing challenges in identifying what physical and chemical stressors are responsible for the alteration of biological conditions in streams. The objective of this study was to assess the comparative influence of multiple stressors on benthic diatoms at 98 sites that spanned a range of stressors in an agriculturally dominated region in the upper Midwest, USA. The primary stressors of interest included: nutrients, herbicides and fungicides, sediment, and streamflow; although the influence of physical habitat was incorporated in the assessment. Boosted Regression Tree was used to examine both the sensitivity of various diatom metrics and the relative importance of the primary stressors. Percent Sensitive Taxa, percent Highly Motile Taxa, and percent High Phosphorus Taxa had the strongest response to stressors. Habitat and total phosphorous were the most common discriminators of diatom metrics, with herbicides as secondary factors. A Classification and Regression Tree (CART) model was used to examine conditional relations among stressors and indicated that fine-grain streams had a lower percentage of Sensitive Taxa than coarse-grain streams, with Sensitive Taxa decreasing further with increased water temperature (>30°C) and triazine concentrations (>1500ng/L). In contrast, streams dominated by coarse-grain substrate contained a higher percentage of Sensitive Taxa, with relative abundance increasing with lower water temperatures (<29°C) and shallower water depth (<0.3m). Quantile regression indicated that maximum water temperature appears to be a major limiting factor in Midwest streams; whereas both total phosphorus and percent fines showed a slight subsidy-stress response. While using benthic algae for assessing stream quality can be challenging, field-based studies can elucidate stressor effects and interactions when the response variables are appropriate, sufficient stressor resolution is achieved, and the number and type of sites represent a gradient of stressor conditions and at least a quasi-factorial design.

River water quality assessment based on a multi-descriptor approach including chemistry, diatom assemblage structure, and non-taxonomical diatom metrics

In the present study, the ecological status of four major South Korean rivers flowing near industrial complexes is assessed using physico-chemical analyses and various descriptors based on benthic diatom assemblages. Principal component analysis conducted with physical and chemical variables singled-out four sites as more severely impacted (higher concentration of metals and total nitrogen, higher conductivity and biological oxygen demand), while the remaining 12 sites indicated less impacted conditions, although showing nutrient enrichment. Less-contaminated sites based on physico-chemical properties showed higher cell densities, higher richness and diversity, a larger proportion of live and healthy-looking diatoms, lower production of lipid bodies (in terms of number and size) and fewer teratologies than more-contaminated sites. Non-taxonomical metrics (cell heath status, cell size, lipid bodies and valve deformities) were in good agreement with traditional taxonomical metrics (assemblage structure, richness, diversity). Overall, water quality assessment based on diatom assemblages and diatom-based metrics had a good fit with the available physico-chemical data and agreed on the most impacted sites. However, additional sites showed signs of degradation based on the diatom metrics used. This suggests that the use of biotic indicators provides useful complementary information on the health status at the selected sites.

Phytoplankton of rhithral rivers: Its origin, diversity and possible use for quality-assessment

While phytoplankton studies on large potamal rivers have increased in number in recent years, upper river sections have received considerably less attention. However, in order to better understand processes that govern the development of dominance of euplanktonic elements in the lower river sections, detailed studies of the upstream areas are necessary. We studied the composition, diversity and recruitment of the planktonic algal communities in the River Sajó and in its main tributary River Hernád, two characteristic rhithral river systems in Central Europe. Results revealed that diatoms are dominant elements of the phytoplankton in the upper river segments both in terms of taxa richness, and relative abundance. We found that composition of the phytoplankton showed the closest resemblance to that of benthic communities of soft substrates, highlighting the key role of riverbed characteristics in river phytoplankton recruitment. The occurrence of euplanktonic elements was not restricted to human impacted river segments, these taxa also occurred in pristine headwaters. Accordingly, planktonic algae potentially colonise small headwater streams naturally, although their dominance is expected to occur only at downstream reaches following impounded river segments. Diatom metrics used in ecological state assessment were calculated for the rithroplankton. These metrics fell in the range of values calculated for diatom flora on the hard substrates. However, the potential use of rithroplankton for quality assessment might be limited, because the high variability of index values at site level would result in misclassification of the ecological status.

Modelling diatom life forms and ecological guilds for river biomonitoring

Biomonitoring is central to the European Union's Water Framework Directive (WFD) and to the French water and aquatic environmental law, but most diatom indices do not separate different anthropogenic impacts. To address this gap, the effect of water chemistry on diatom ecological guilds and life forms was assessed in order to indicate stream perturbations. Generalised additive models (GAMs) were built on a large-scale data set of 1571 samples from the French monitoring network. The relationships between diatom ecological guild and life form metrics were investigated by Principal components analysis and the results predicted by GAMs. The models characterised eight chemical parameters that modified adaptive strategies (ecological guilds) and growth morphology (life forms). Total phosphorus, conductivity, nitrate and pH are the main influencing factors, followed by temperature, dissolved oxygen and organic matter. The findings confirm three groups of diatoms with different adaptive strategies: 1 – fast moving species, 2 – species growing close to the substrate and 3 – species extending to the surface layers of the biofilm. Thirteen diatom metrics displayed a variety of responses to different ranges of the eight chemical parameters. These metrics could be used to help to identify and quantify which chemical alterations are caused by polluted effluents in rivers.

Diatom taxa and assemblages for establishing nutrient criteria of lakes with anthropogenic hydrologic alteration

Stressor-response models offer guidance for concentration-based nutrient criteria in lakes under human intervention. Diatom-based statistics from biological responses were incorporated to derive taxon-specific and community-level change points (thresholds) of phosphorous and nitrogen in 77 Yangtze floodplain lakes. Diatom metrics relating with conductivity were adopted as response variables, since conductivity explained the maximum variation (38.1%) in diatom assemblages via Bootstrapped regression trees. Nonparametric change-point analysis and Threshold Indicator Taxa ANalysis showed threshold responses of diatom community structure at 0.05–0.08mgTP/L in connected lakes and 0.02–0.04mgTP/L in isolated lakes. Distinct community change points of sensitive diatoms occurred at 0.96–1.63mgTN/L in connected lakes and 0.52–0.63mgTN/L in isolated lakes. Diatom community structures of tolerant taxa were substantially altered beyond 0.22–0.23mg/L in connected lakes and 0.52–0.69mgNOx/L in isolated lakes. Hydrological river-lake connectivity differed significantly in ecological nutrient criteria with more TN/TP criteria and less NOx criteria in connected lakes. Given the ecological significance and biological integrity, diatom-based statistics can provide more reliable change points (thresholds) for nutrient criteria than Chl a-nutrient relationships.

Macroinvertebrate and diatom metrics as indicators of water-quality conditions in connected depression wetlands in the Mississippi Alluvial Plain

AbstractMethods for assessing wetland conditions must be established so wetlands can be monitored and ecological services can be protected. We evaluated biological indices compiled from macroinvertebrate and diatom metrics developed primarily for streams to assess their ability to indicate water quality in connected depression wetlands. We collected water-quality and biological samples at 24 connected depressions dominated by water tupelo (Nyssa aquatica) or bald cypress (Taxodium distichum) (water depths = 0.5–1.0 m). Water quality of the least-disturbed connected depressions was characteristic of swamps in the southeastern USA, which tend to have low specific conductance, nutrient concentrations, and pH. We compared 162 macroinvertebrate metrics and 123 diatom metrics with a water-quality disturbance gradient. For most metrics, we evaluated richness, % richness, abundance, and % relative abundance values. Three of the 4 macroinvertebrate metrics that were most beneficial for identifying disturbance in c...

Water quality assessment of rivers using diatom metrics across Mediterranean Europe: A methods intercalibration exercise

The European Water Framework Directive establishes a framework for the protection of water resources. However, common water management tools demand common understanding of assessment methods, so quality goals are equally met. Intercalibration of methods ensures the comparability of biological elements across similar geographical areas. Many aspects can influence the outcome of intercalibration: data sampling, treatment methods, taxonomic reliability of databases, choice of metrics for ecological quality status classification, and criteria for selecting reference sites. This study describes the potentials and constraints of the intercalibration of indices using diatoms for assessment of Mediterranean rivers. Harmonisation of diatom taxonomy and nomenclature was based on a previous ring test which took place at the European level. Four diatom indices (Indice de Polluosensibilité Spécifique—IPS, Indice Biologique Diatomées—IBD 2007, Intercalibration Common Metric Italy—ICMi and Slovenian Ecological Status assessment system) were intercalibrated using data from six European Mediterranean countries (Cyprus, France, Italy, Portugal, Slovenia and Spain). Boundaries between High/Good and Good/Moderate quality classes were harmonised by means of the Intercalibration Common Metric (ICM). Comparability between countries was assured through boundary bias and class agreement. The national boundaries were adjusted when they deviated more than a quarter of a class equivalent (0.25) from the global mean.All national methods correlated well with the ICM, which was sensitive to water quality (negatively correlated to nutrients). Achnanthidium minutissimum sensu lato was the most discriminative species of Good ecological status class. Planothidium frequentissimum, Gomphonema parvulum and Nitzschia palea were the most contributive to Moderate ecological status class. Some taxa were discriminative for both Good and Moderate ecological status classes due to low indication and ecological discriminative power but also due to differences in taxonomy between countries.This intercalibration exercise allowed establishment of common water quality goals across Mediterranean Europe, which is substantiated with the ICM.

Can pollution severity affect diatom succession in streams and could it matter for stream assessments?

While the succession of benthic diatoms on scoured substrata has been widely studied to better understand community recovery from high flow disturbances, how anthropogenic stressors affect this common and dynamic process has received little attention; yet, it could have consequences for bioassessment and subsequent management decisions. Our objectives were to examine if the severity of acid mine drainage (AMD), a stressor of common concern in several countries, affected patterns of community development, diversity, and stream assessment outcomes (based on diatom metrics and indices) when diatoms are sampled during succession. In southeastern Ohio (USA), we deployed unglazed ceramic tiles in three streams along an AMD-impact gradient and in a control stream with no upstream AMD sources, and we sampled diatoms on days 5, 12, 19, 26, and 33. Diatom diversity decreased as AMD severity increased. In more severely AMD-impacted streams, diatom succession was simplified with less community turnover during the 33-day study than the least impacted AMD stream and control stream. Variability in community structure, diversity, and index scores was greatest at the least impacted AMD site. This stream was misclassified during succession by the Diatom Model Affinity index (severely impaired, then unimpaired, then ultimately moderately impaired) and the AMD – Diatom Index of Biotic Integrity (fair condition, then ultimately good condition). The control stream and the two more severely AMD-impacted streams were never misclassified during succession. Severe pollution may reduce niche availability by overriding effects of other environmental gradients important to diatoms (e.g., light and nutrients). The variability at intermediate stressor levels might lead to misclassification and misdirected management decisions if care is not taken to ensure a community has fully recovered from disturbance.

Scale-dependent effects of land cover on water physico-chemistry and diatom-based metrics in a major river system, the Adour-Garonne basin (South Western France)

The scale dependence of ecological phenomena remains a central issue in ecology. Particularly in aquatic ecology, the consideration of the accurate spatial scale in assessing the effects of landscape factors on stream condition is critical. In this context, our study aimed at assessing the relationships between multi-spatial scale land cover patterns and a variety of water quality and diatom metrics measured at the stream reach level. This investigation was conducted in a major European river system, the Adour-Garonne river basin, characterized by a wide range of ecological conditions. Redundancy analysis (RDA) and variance partitioning techniques were used to disentangle the different relationships between land cover, water-chemistry and diatom metrics.Our results revealed a top-down “cascade effect” indirectly linking diatom metrics to land cover patterns through water physico-chemistry, which occurred at the largest spatial scales. In general, the strength of the relationships between land cover, physico-chemistry, and diatoms was shown to increase with the spatial scale, from the local to the basin scale, emphasizing the importance of continuous processes of accumulation throughout the river gradient. Unexpectedly, we established that the influence of land cover on the diatom metric was of primary importance both at the basin and local scale, as a result of discontinuous but not necessarily antagonist processes. The most detailed spatial grain of the Corine land cover classification appeared as the most relevant spatial grain to relate land cover to water chemistry and diatoms.Our findings provide suitable information to improve the implementation of effective diatom-based monitoring programs, especially within the scope of the European Water Framework Directive.

Using algal metrics and biomass to evaluate multiple ways of defining concentration-based nutrient criteria in streams and their ecological relevance

We examined the utility of nutrient criteria derived solely from total phosphorus (TP) concentrations in streams (regression models and percentile distributions) and evaluated their ecological relevance to diatom and algal biomass responses. We used a variety of statistics to characterize ecological responses and to develop concentration-based nutrient criteria (derived from ecological effects) for streams in Connecticut, USA, where urbanization is the primary cause of watershed alteration. Mean background TP concentration in the absence of anthropogenic land cover was predicted to be 0.017mg/l, which was similar to the 25th percentile of all study sites. Increased TP concentrations were significantly correlated with altered diatom community structure, decreased percent low P diatoms and diatoms sensitive to impervious cover, and increased percent high P diatoms, diatoms that increase with greater impervious cover, and chlorophyll a (P<0.01). Variance partitioning models showed that shared effects of anthropogenic land cover and chemistry (i.e., chemistry affected by land cover) represented the majority of explained variation in diatom metrics and chlorophyll a. Bootstrapped regression trees, threshold indicator taxa analysis, and boosted regression trees identified TP concentrations at which strong responses of diatom metrics and communities occurred, but these values varied among analyses. When considering ecological responses, scientifically defensible and ecologically relevant TP criteria were identified at (1) 0.020mg/l for designating highest quality streams and restoration targets, above which sensitive taxa steeply declined, tolerant taxa increased, and community structure changed, (2) 0.040mg/l, at which community level change points began to occur and sensitive diatoms were greatly reduced, (3) 0.065mg/l, above which most sensitive diatoms were lost and tolerant diatoms steeply increased to their maxima, and (4) 0.082mg/l, which appeared to be a saturated threshold, beyond which substantially altered community structure was sustained. These criteria can inform anti-degradation policies for high quality streams, discharge permit decisions, and future strategies for watershed development and managment. Our results indicated that management practices and decisions at the watershed scale will likely be important for improving degraded streams and conserving high quality streams. Results also emphasized the importance of incorporating ecological responses and considering the body of evidence from multiple conceptual approaches and statistical analyses for developing nutrient criteria, because solely relying on one approach could lead to misdirected decisions and resources.

Epilithic diatoms as indicators in tropical African rivers (Lake Victoria catchment)

We investigated epilithic diatoms in rivers draining to the Nyanza Bay in Lake Victoria (Kenya) with the aim of determining environmental gradients in the assemblages and testing the usefulness of diatom metrics from temperate regions. Spatial and temporal variations of assemblages were studied in 12 sites of three rivers. Kibos, Nyando, and Kisat rivers contained 224 diatom taxa collected on seven sampling occasions over 4 years. Species richness showed a marginal decrease downstream and was the lowest at sites with high conductivity and ammonia–nitrogen levels. Two-Way Indicator Species Analysis and Canonical Correspondence Analysis revealed two major groups of river sites. Conductivity, alkalinity, turbidity, dissolved oxygen, and silicate were the most important variables influencing species distribution. Ecological diatom metrics of temperate regions and the Specific Pollution sensitivity Index showed good relationships with environmental variables. Both diatom assemblages and averaged indicator values were strong in predicting sites of ecological deterioration and in differentiating an upstream site of better quality (drinking water supply of Kisumu), thereby confirming epilithic diatoms as suitable water quality indicators in equatorial rivers. The use of metrics initially designed for temperate rivers, however, appears less valuable in good quality tropical rivers because potential indicators are not considered.

Improvement of the ecological water qualification system of rivers based on the first results of the Hungarian phytobenthos surveillance monitoring

Results of an ecological quality ratio-based qualification system, developed on the basis of the analysis of 1,161 benthic diatom dataset of the Hungarian national database, are presented herein. Using Kohonen’s Self Organising Map technique, the 25 Hungarian physiographic river types were pooled into six larger distinct categories (diatom river groups). Diatom metrics were tested for their sensitivity to the targeted stressors (nutrients, COD hydromorphological alteration) in each group. The strongest relationships were found in the case of the IPS, SI and TI indices; therefore the average of these metrics (IPSITI) was proposed as a national multimetric index for Hungarian streams. Based on IPSITI values, the ratio of moderate to worse quality water was the highest in those groups containing small rivers. In the case of large, lowland and mid-altitude rivers with fine sediment, the good and moderate ecological status was more characteristic. Applicability of the IPSITI seems to be very useful in case of small- and medium-sized rivers. For these rivers, the index showed a significant relationship with nutrients and organic pollutants. In the case of very large rivers, the stressor–index relationships were not significant because of the insufficient number of samples and the small range of stressors.

Establishing expectations for pan-European diatom based ecological status assessments

The European Union (EU) Water Framework Directive depends, for effective implementation, on Member States (MSs) agreeing to a concept of the unimpacted “reference” state, which will then provide the “expected” value in Ecological Quality Ratio (EQR) calculations. Reference assemblages of organism groups will, in turn, vary, due to geological, hydrological, climatic, physicochemical and biological factors. Member States tackle this by establishing “types” which share common characteristics. However, for the purposes of ensuring consistent application, broad transboundary types were also established within five Geographical Intercalibration Groups (GIGs, referred to here as “regions”) as part of the EU's intercalibration exercise. In this paper, we evaluate these types using river diatom assemblages and also provide reference threshold values for two common metrics used in pan-European diatom assessments. A database was assembled, representing 14 EU Member States from Ireland and Portugal in the West, to Estonia and Cyprus in the East, in order to explore biogeographical patterns in assemblages unaffected by anthropogenic pressures. Multivariate analyses were used to examine this pattern and its relationship with geographic, typological and abiotic parameters. After taxonomic harmonisation, NMDS ordination of samples indicated weak differences in assemblage composition among regions. ANOSIM analyses, in turn, indicated that MS was the best factor to group similar samples whereas alkalinity, recognised as the primary environmental variable structuring diatom communities, although significant, explained less variability in the dataset. This, we believe, reflects the importance of methodological factors other than taxonomy (e.g. counting protocol, sample season) that may be constant within a MS but which vary between MSs. When two diatom metrics, the TI and IPS, were applied to the data, differences in the distribution of the metric scores between MS were generally not statistically significant even though some differences between regions were apparent. A trend of increasing values of TI (decreasing values of IPS) was observed in the sequence: Nordic<Alpine<Mediterranean<Central-Baltic<Eastern Continental regions. Additionally, some differences were observed among types within the Mediterranean and Nordic regions, though not for other regions. The data used in this exercise provides us with a region and, in some cases, a type specific benchmark dataset against which national reference data can be compared.

The effect of metals on photosynthesis processes and diatom metrics of biofilm from a metal-contaminated river: A translocation experiment

With the aim of evaluating cause-effect relationships between metal pollution and biofilm structure and function, a translocation study was performed in a metal-polluted stream (the Osor stream “la riera d’Osor”, NE Spain). Biofilm responses were measured as temporal changes in chl-a fluorescence parameters, pigment composition and diatom species composition. Biofilms from a non-polluted site were translocated to four downstream sites presenting a gradient of metal pollution, corresponding to scenarios of low and moderate metal pollution. Metal effects (Zn bioaccumulation, Fe bioaccumulation and Zn in water) were distinguished from other stressors (phosphate concentration in water). Based on the results obtained, a fast bioaccumulation of Zn (after few hours of exposure) was linked to a decrease in photosynthetic efficiency and an enhancement of mechanisms of protection through the xanthophyll cycle. After longer exposure, differences in Zn and Fe bioaccumulation and Zn water concentration between sites were linked to diatom community changes; decrease in diatom cell biovolume, along with a decrease in the IPS index of diatoms. Based on our results, we recommend including Zn in the list of priority pollutant substances of the European Water Framework Directive (2000/60/EC), due to its occurrence and toxicity. In addition, our study supports the use of chl-a fluorescence parameters together with the analysis of photosynthetic pigments of biofilms as suitable functional endpoints of early toxicity. Furthermore, diatom community studies are recommended for their clear response after chronic exposure. However, new diatom indices beyond the use of the IPS are required to increase their sensitivity to metal pollution, e.g. to identify the damage caused by moderate to low metal pollution.