Diatom Metrics Research Articles

First diatom-based assessment of Lower Hari Rud River (a transboundary system) in Afghanistan.

It is essential to determine the dominant/indicator species and their ecological preferences to develop a comprehensive bioassessment strategy for rivers. The objective of this work was to provide dependable ecological evaluation techniques for ecosystems that experience significant human-induced disruptions, with the Hari Rud River (a transboundary water resource) serving as a case study during the May (wet) and July (dry) periods of 2023. Canonical correspondence analysis revealed that electrical conductivity (EC), dissolved oxygen, ortho-phosphate (P ), and nitrate (N ) had substantial impacts on the spatial distribution of diatom species in the basin. Relatively pollution-tolerant species, including Nitzschia brevissima, N. capitellata, N. umbonata, N. palea, N. dissipata, and Navicula cryptocephala, had close relationships with EC and P , integrated with Joi Injil and Karbar streams. Of the sampling stations, especially Hari Rud River1 and Hari Rud River2, exhibited pollution-sensitive diatom species, Cymbella excisa, Achnanthidium minutissimum, Diatoma moniliformis, Cymbella affinis, and Meridion circulare. Various eco-regional diatom metrics exhibited distinct scores, indicating a range of ecological status from high to bad in the Lower Hari Rud River basin. European diatom indices revealed good ecological status for Hari Rud River 1 and 4, but poor or bad ecological statuses for Joi Injil and Karbar streams. The findings of the current study emphasize the requirements of autecological studies to understand the regional diatom compositions and their ideal survival ranges in different locations before considering using non-regional diatom indices to evaluate the ecological status of lotic systems.

Exposure and recovery: The effect of different dilution factors of treated and untreated metal mining effluent on freshwater biofilm function and structure

Abandoned mines generate effluents rich in heavy metals, and these contaminants are released uncontrolled into the nearby aquatic ecosystems, causing severe pollution. However, no real solution exists, leaving a legacy of global pollution. In this study, the efficiency of the treatment technologies in reducing the ecological impacts of mining effluents to freshwater ecosystems with different dilution capacities was tested using biofilm communities as biological indicators. The functional and structural recovery capacity of biofilm communities after 21 days of exposure was assessed. With this aim, we sampled aquatic biofilms from a pristine stream and exposed them to treated (T) and untreated (U) metal mining effluent from Frongoch abandoned mine (Mid Wales, UK). Additionally, we simulated two different flow conditions for the receiving stream: high dilution (HD) and low dilution (LD). After exposure, the artificial streams were filled with artificial water for 14 days to assess the biofilm recovery. Unexposed biofilm served as control for biofilm responses (functional and structural) measured throughout time. During the exposure, short term effects on biofilm functioning (photosynthetic efficiency, nutrient uptake) were observed in T-LD, U-HD, and U-LD, whereas long term effects (community composition, chl-a, and diatom metrics) were observed on the structure of all biofilms exposed to the treated and untreated mining effluent. On the other hand, metal accumulation occurred in biofilms exposed to the mining effluents. However, a functional recovery was observed for all treatments, except in the U-LD in which biofilm structure did not present a significant recovery after the exposure period. The results presented here highlight the need to consider the dilution capacity of the receiving stream to assess the real efficiency of treatment technologies applied to mining effluents to mitigate the ecological impact on freshwater ecosystems.

Fuzzy logic as a novel approach to predict biological condition gradient of various streams in Ceyhan River Basin (Turkey)

Creating a method to categorize the ecological status of streams according to their biological conditions and establishing scientifically defensible nutrient criteria to protect their biotic integrity poses significant challenges. Biomonitoring of least disturbed areas is an important issue to accurately assess the ecological status of surface waters and ensure their sustainability. The fuzzy logic as a novel approach was firstly applied to evaluate the biological condition gradient of 44 sampled streams in the Ceyhan River Basin, utilizing two diatom indices, total phosphorus (TP), electrical conductivity (EC), and CORINE data. The fuzzy logic was employed to examine variations in the diatom compositions and land cover based on biological condition gradients (BCGs) of various streams and to assess the suitability of BCG in evaluating the health of studied stream systems. A three-layer fuzzy logic was constructed to predict BCGs of steams based on input data, with diatom metrics, TP, and EC representing BCGdia and land cover variables contributing to BCGland. The effects of operating variables were studied to optimize BCG results. The highest BCG score (0.85) was determined in Aksu Spring Brook in the spring, whereas the lowest value (0.05) was calculated in Erkenez Stream3 in the summer. BCGs showed strong relationships with nutrients, altitude, and EC. Results of BCGs indicated that sampling stations have various ecological statuses ranging from bad to high in the Ceyhan River Basin. The BCGdia and BCGland made important contributions to determine the ecological status of streams in the Ceyhan River Basin. Results showed that the BCG approach allows a more reliable way to determine the ecological status of streams in the Ceyhan River Basin by combining biological and chemical assessments for the sustainability of the environment. It is recommended that the BCG will be applied and evaluated in future research studies across various river basins, both within and outside of Turkey.

Assessing relationships between environmental stress and benthic diatoms in lentic habitats in the western Mediterranean basin (Turkey).

Hydrological (rainy and dry) periods can affect the water quality of lentic ecosystems, which may be useful for understanding their ecological condition in the watershed. Ecological status of various lentic ecosytems (both brackish and freshwater) in the western Mediterranean basin was evaluated by using various diatom metrics throughout rainy (May) and dry (August and October) periods to explain the diatom-stressor interactions using multivariate approaches. Canonical correspondence analysis separated freshwater habitats under the pressures of nitrate and total organic carbon from brackish ecosystems under the pressures of conductivity, nitrite, sulphate, calcium, and copper, which were characterized by different phytoplankton species. Ecological integrations of diatom species varied in the ecosystems throughout rainy and dry periods. Different ecological regional diatom indices were used to find the best index/indices indicating the ecological status of lakes and reservoirs in the basin during the two hydrological periods. The trophic diatom index developed for lakes was not found to be suitable for assessing lentic habitats. European diatom indices generally showed the distinction in the assessment of these ecosystems in the rainy and dry seasons, but others could not. Among the diatom indices, only the trophic index Turkey (TIT) showed a statistically significant correlation with TP. The TIT not only showed degradation of the water quality of ecosystems during the dry season compared to the rainy season, but it has also been successful in distinguishing the ecological conditions of lentic ecosystems.

Development of novel diatom metrics to assess ecological status of phytobenthos in Greek lakes

Mediterranean lakes present particular challenges when developing ecological assessment techniques, due partly to long histories of human activity in their catchments but also to strong interactions with climate, intensifying in recent decades due to global warming. A survey of diatoms in lakes in Greece revealed both a strong nutrient gradient and a salinity gradient. It is necessary to disentangle these when assessing ecological status in order that appropriate measures for restoring good ecological status are applied. Two approaches were used to develop a Water Framework Directive-compatible metric for assessing ecological status using diatoms. The strongest relationship was obtained using weighted averaging, but an alternative metric, generated by rescaling a well-established and widely used diatom metric performed only slightly less well. The limited number of lakes in Greece resulted in a small dataset, creating a risk of overfitting models and the rescaled metric has the advantage of drawing on a broader autecological knowledge base. Supplementary metrics to evaluate salinity are also proposed in order to ensure that lakes subject to this pressure are clearly differentiated from those where nutrient impacts predominate. Approaches to defining reference conditions and status class boundaries draw on established criteria developed for Water Framework Assessments in Europe to ensure that status assessments in Greece reflect similar levels of ambition to those established elsewhere in the European Union.

Eco-assessment of streams of Konya closed river basin (Turkey) using various ecoregional diatom indices.

Ecological assessment of freshwater ecosystems based on diatom metrics is an important issue for attaining environmental sustainability. The present study aimed to evaluate differences in the diatom-stressor relationship in relatively least disturbed streams in the Konya closed river basin using multivariate analyses and to bio-assess streams by the application of different ecoregional diatom indices. Cocconeis euglypta, Cymbella excisa, Cocconeis placentula, and Achnanthidium minutissimum are the most contributing species to the dissimilarity of sampling stations between rainy (spring) and dry (summer and fall) seasons and also between altitude (A2 800- < 1600m and A3 ≥ 1600m) groups. The first two axes of canonical correspondence analysis revealed a significant (82.8%) relationship between diatom species and stressors. Diatom species displayed distinct responses to environmental variables (electrical conductivity, Ni, Cu, B, and altitude) playing important roles on the distribution of species. Diatom indices indicate different ecological statuses of stations, from bad to high. European diatom indices except Duero Diatom Index (DDI) and Trophic Diatom Index (TDI) showed good responses to the eco-assessment of streams and indicated high ecological status for the least disturbed sampling stations symbolized as S16, S20, S24, S25, S27-29, S37, and S39. These results were also supported by abiotic evaluation. Although TIT was more competitive in the bio-assessment of streams among diatom indices, it is necessary to increase its species list by determining their trophic weights in future studies. Therefore, the use of ecoregion-specific diatom indices is suggested along with increasing the number of used species to correctly interpret the water quality.

Differences in planktonic and benthic diatoms reflect water quality during a rainstorm event in the Songhua River Basin of northeast China

Diatoms are useful indicators of lotic ecosystem environmental conditions, but little is known of differences between benthic and planktonic diatom assemblages as it relates to water quality changes in large lotic systems. Heavy rainfall event in Songhua River Basin is infrequent. The water quality of Songhua River Basin is closely implication for regional ecological health and food safety. The aim of this study was to compare the effectiveness of benthic and planktonic diatom assemblages for indicating water quality during a rainstorm event, which has been little studied. Spatial variation of benthic and planktonic diatom assemblages were investigated in Songhua River Basin during a rainstorm event. Firstly, we found that richness and abundances of benthic and planktonic diatom communities were low. Secondly, results of two-way cluster analysis (TWCA) and principal component analysis (PCA) revealed that diatom assemblage still had the potential to indicate water quality despite the strong flow caused by rainstorm event. Thirdly, alpha diversity indices (Shannon-weaver, Margalef, and Pielou indices) had a weak ability in indicating water quality during rainstorm event. Conversely, trophic diatom index (TDI) was observed closely associate with water quality change. Fourthly, Redundancy analysis (RDA) indicating that planktonic diatoms assemblages were more sensitive to changes in turbidity. RDA also revealed that benthic diatom assemblages was closely related to chemical oxygen demand (CODcr), total phosphorus (TP), and dissolved oxygen (DO) concentrations. These results demonstrate the effectiveness of water quality assessment between planktonic and benthic diatoms had a significant different. The results of the study provide a key information about diatom-based biomonitoring in the extreme condition at lotic ecosystem. Our study highlights that rational choices of appropriate diatom metrics for biological monitoring of water quality in large lotic ecosystems are critical for assessments during a rainstorm event. More studies during rainstorm period at different precipitation are required to fully understand how natural disturbance shape diatom assemblage in lotic ecosystem with aims to improve biomonitoring efforts.

A lentic microcosm approach to determine the toxicity of DDT and deltamethrin on diatom communities

Worldwide the use of pesticides has increased, especially in the industry and agriculture sector even though they contain highly toxic substances. The use of pesticides has various negative effects on the aquatic ecosystem and organisms within these ecosystems. The paper aimed to assess the effects of increased concentrations of malaria vector control insecticides (Dichlorodiphenyltrichloroethane (DDT) and Deltamethrin (DTM)) on the freshwater diatom community structure using a microcosm approach as well as determine whether a mixture (DDT 1:1 Deltamethrin) exposure will have a greater influence on the diatom community when compared to single exposures of these insecticides. Diatoms were exposed to a high and low concentration (based on LC50 data for freshwater Xenopus laevis from the USEPA Ecotox database) of DDT, DTM and a mixture in lentic microcosms over a total period of 28 days. Results indicated that irrespective of exposure concentrations, DDT, DTM and a mixture had negative effects on the diatom community including functionality and vitality as these insecticides induced changes to their chloroplasts. There was an increased percentage dead cells for all exposures compared to the control, with the insecticides having a phototoxic effect on the diatom community. Exposure to the selected insecticides caused a significant decrease in some diatom metrics indicating the negative effects these insecticides have on the diatom metrics. Therefore, diatoms may prove to be useful as bio-indicators in ecotoxicology studies when assessing the effects of any insecticide exposures.

Land use effects on water quality, habitat, and macroinvertebrate and diatom communities in African highland streams

Anthropogenic activities have increasingly subjected freshwater ecosystems globally to various pressures. Increasing land use activities have been highly linked to deteriorating freshwater ecosystems and dwindling biodiversity. For sound management and conservation policies to be implemented, relations between land use, environmental, and biotic components need to be widely documented. To evaluate the impacts of land use on biotic components, this study analyzed the diatom and macroinvertebrate community composition of the Eastern Highlands (Zimbabwe) streams to assess the main spatial diatom and macroinvertebrate community variances and how environmental variables and spatial factors influence community composition. Diatom and macroinvertebrate sampling was done in 16 streams in protected areas (national parks) and impacted sites (timber plantation and communal areas). Water (pH, phosphorus, and ammonium) and sediment (nitrogen, phosphorus, calcium, magnesium, manganese, and zinc) and habitat (substrate embeddedness, and habitat) variables differed significantly with land use. Principal Component Analysis (PCA) showed that the protected area had the best water quality, particularly marked by high pH levels and low phosphorus concentrations among environment types. Heavy metals were high in the communal areas, although mercury was higher in the national park. Significant differences were observed in diatom metrics, specifically dominance and evenness, with no significant differences observed in macroinvertebrate metrics across land uses. Diatoms differed in terms of composition in response to land use. Results provide an important scientific reference for land use optimization and guidance for the formulation of policies to protect freshwater resources in African Highland streams. Management and conservation initiatives in the Eastern Highlands are further recommended as this study detected high levels of mercury in the protected area, implying high levels of illegal mining.

DiaThor: R package for computing diatom metrics and biotic indices

Diatom-based tools like biotic indices, ecological and morphological traits, are widely used to detect changes in water quality. Here we present DiaThor, a free and open source R package for calculating biotic and ecological indices and metrics for diatom samples. A web application (in Shiny) was also developed to provide access to the package for those users not familiar with the R environment.

Bioassessment of water quality of surface waters using diatom metrics

Bioassessment of water quality of surface waters using diatom metrics

Improving biological condition assessment accuracy by multimetric index approach with microalgae in streams and lakes

<p indent="0mm">The multimetric index (MMI) approach is broadly used in ecological assessment because it integrates information of various ecologically related metrics of freshwater ecosystems and provides an easily understandable score for further evaluation and management. Accounting for natural variation and disentangling covariation between natural environmental and human disturbance factors is imperative for an accurate assessment. <italic>A priori</italic> classification of sites by regions or typologies, site-specific modeling of expected reference conditions, and varying metrics in site groups are three approaches that have been used to control natural variation in ecological assessments. Researchers have recently made a lot of progress in improving biological condition assessment accuracy by the MMI approach with microalgae in streams and lakes. All existing studies support that site-specific modeling can efficiently account for natural variation and generate an MMI with good performance. However, no strong evidence has shown that diatom/blue-algae typologies are better than regionalization frameworks in accounting for natural variation in lakes or streams. Separating the natural variation explained by site-specific modeling from that of varying metrics is necessary for a thorough and accurate evaluation of the valuableness of site-grouping by typologies. The different performances of varying metrics among site groups of streams and lakes are most probably caused by the lack of representativeness of diatom metrics on biological conditions rather than the complex multi-stressor gradients in streams and rivers. This study reviewed recent progress in defining the ecological condition of lakes and streams by the MMI approach with microalgae and some concerns in using statistical techniques to compare MMI performance.

Eco-assessment of least disturbed areas of the Antalya River basin: application of diatom indices from different ecoregions.

Biomonitoring of least disturbed areas is a crucial issue to accurately assess the ecological status of surface waters and ensure their sustainability. Diatom metrics are important tools for the assessment of environmental conditions of lotic ecosystems to achieve environmental sustainability. The present study was aimed to evaluate the ecological status of least disturbed areas in the Antalya River basin (Turkey) using diatom indices developed from different ecoregion. Diatom species such as Cymbella excisa, Achnanthidium minutissimum, Cocconeis euglypta, and Cocconeis placentula were the most contributing species to the dissimilarity of sampling stations between rainy and dry seasons. The first two axes of canonical correspondence analysis (CCA) elucidated a strong (86%) correlation between diatom taxa and stressors. Results of the Monte Carlo permutation test indicated that total phosphorus (TP), water temperature, Tin (Sn), total organic carbon, zinc, and pH are significantly influential ecological factors on the distribution of diatom taxa among sampling stations. The Spearman correlation rank test indicated that diatom indices had significant positive and negative correlations with TP gradient. Results revealed that diatom indices developed from different ecoregions have different scores for the eco-assessment of similar sampling stations. European diatom indices mostly showed similar behavior in the bioassessment of the ecological status of rivers in the Antalya region compared to the different ecoregion. Among European diatom indices, TIT was more competitive and could give better results in the bio-evaluation of rivers in the Antalya River basin. Using diatom indices developed from different ecoregions may lead to an erroneous assessment of water quality. Accordingly, ecoregional specific diatom metrics are needed to accurately determine the surface water quality. Eco-assessment of least disturbed areas of the Antalya River basin: application of diatom indices from different ecoregions: Abuzer Çelekli, Ömer Lekesiz, Tolga Çetin.

Effects of an hypersaline effluent from an abandoned potash mine on freshwater biofilm and diatom communities

Potash abandoned mines cause severe environmental damage to their bordering environment, with significant impacts on freshwater ecosystems mostly through uncontrolled discharge of hypersaline effluents. This study aimed to evaluate the ecological impact caused by a hypersaline effluent from an abandoned potash mine (Menteroda, Germany) on freshwater biofilms and, specifically, on diatom communities. Biofilm from a pristine stream was exposed under controlled conditions in microcosms to a mining effluent (ME), and its structural (algal biomass, community composition, diatom metrics) and functional (photosynthetic activity, nutrient uptake) responses were evaluated over time and compared with unexposed biofilms used as control. Biofilm exposed to ME showed drastic functional responses after one day of exposure, with a significant decrease in photosynthetic efficiency and nutrient uptake, that were recovered over time. Biofilm exposed to ME showed a progressive increase in diatom metrics (abundance, density and growth rate) over time, compared to the control. However, a significant decrease in diatom species diversity, richness and cell size was also observed in biofilm exposed to ME. This study revealed that the ME affected the biofilm causing short-term functional responses, which were recovered simultaneously with a drastic diatom community structure shift.

Sensitivity and reliability of diatom metrics and guilds in detecting the impact of urbanization on streams

• The impact of urbanization on diatoms yet to be elucidated in China. • Diatom composition constrained by %Urban, TN, COD and WD. • Simpson’s index, Shannon-Wiener index, %Stalked individuals, %Prostrate individuals and TDI significantly responded to urbanization. • TDI variation explained by urbanization and nutrients. The impact of land use changes on stream biota is the major concern of aquatic biodiversity conservation in the context of the rapid global population growth. Benthic diatoms are good indicators to detect land use impact and provide insights into environmental management. However, the impact of urbanization on benthic diatoms has not been well understood in China. In the hope of promoting the understanding of this issue, a research program is designed to examine the responses of selected diatom metrics to urbanization in the Qiantang River Basin. The study identifies a total of 143 taxa belonging to 34 genera and 20 families, with an average of 32 taxa per site. It shows that urbanization greatly has degraded stream chemical and physical quality in terms of high nutrients concentration and fine sediments. Meanwhile, the redundancy analysis reveals that urban stream diatom compositions are mainly associated with %Urban, TN, COD and WD. A total of three metrics (Simpson’s index, Shannon-Wiener index and TDI) and two guilds (%Stalked individuals and %Prostrate individuals) respond to urbanization significantly, and their variations are explained more by land uses at watershed scale than by those at local scale. Watershed land use (% Urban and % Forest) and nutrients (TN) explain 55% of the variation in TDI. The results of the study highlight the sensitive responses of diatom metrics and guilds to urbanization, which may provide effective tools in the assessment of urbanization impact on streams in China.

Eco-assessment of West Mediterranean basin's rivers (Turkey) using diatom metrics and multivariate approaches.

Bio-evaluating of surface waters is not a new approach but is becoming more important since the application of the European Water Framework Directive (WFD). The present study was designed to evaluate the limno-ecological conditions of rivers in the West Mediterranean basin of Turkey using diatom metrics and multivariate approaches according to the WFD requirements. Canonical correspondence analysis (CCA) was used to assess the relationships of diatom species and environmental variables from 17 stations of 12 rivers sampled in two seasons. The CCA indicated that nitrite, chloride, electrical conductivity (EC), sulfate, temperature, and total phosphorus (TP) are the most explanatory factors on the distribution of the diatom species. Karasu River had the most deteriorated ecosystem, distinctly revealed by the CCA. Nutrient enrichment and high EC, biological oxygen demand (BOD5), and temperature values were noticed in this ecosystem. Karasu River was also characterized by pollution tolerant diatom species (e.g., Nitzschia inconspicua, Nitzschia pusilla, Halamphora normanii, and Rhoicosphenia abbreviata). Trophic index Turkey (TIT), eutrophication and/or pollution index-diatom (EPI-D), and trophic index (TI) showed poor ecological conditions in Karasu and Hamzabey rivers when a moderate environment quality in Dalaman River (at R6 station) and a good ecological state in Kocadere River. A high ecological status was found in Dalaman (at R5 station) concerning the results of TIT and TI, while a good condition was recorded based on EPI-D. This ecosystem was also associated with pollution-sensitive diatom taxa (Achnanthidium minutissimum, Cymbella excisa, Meridion circulare, and Gomphonema olivaceum). Results of CCA were corroborated with the bio-assessment of sampling stations based on diatom metrics. TIT, TI, and EPI-D had different indices' scores, but they showed significantly positive correlations with logTP. Spearman correlation coefficient value of TIT strengthens the suitability of it for the bio-assessment of the rivers in the West Mediterranean basin of Turkey.

Blue-green algae enhanced performance of diatom-based multimetric index on defining lake condition under high level of human disturbance

Degradation of lake conditions could result from many stressors generated by human disturbance. Accurately defining lake ecological condition by multimetric index (MMI) method is of great importance for tracking source of stressors and lake management. For algal assessment, seldom have structural and functional attributes of soft-bodied planktonic algae metrics, one important dimension of biological condition, been used to develop MMI in conjunction with diatom metrics. Another thing is that some researchers found MMI method does not perform well in mid- and high-disturbed lakes. To test the aforementioned questions, we used data sets of the 2007 National Lake Assessment project of the USEPA to develop MMIs with and without using soft-bodied planktonic algae metrics for plains and lowlands area (PLNLOW, high disturbed region of the US) and across the conterminous US. Compared to site groups modeled by single diatom assemblages, we found integrating soft-bodied planktonic algae metric (especially blue-green algae metric) into developing MMIs can significantly improve performance of MMI in PLNLOW region. The separation powers of MMIs of five level III ecoregions, developed by incorporating blue-green algae metric, are consistently higher than those developed by single diatom assemblages (p-value = 0.029). However, when blue-green algae metric was applied to develop MMI along with diatom metrics in the national scale assessment, performances of MMIs are similar to that developed by diatom metrics (0.14 < p-value < 0.86). Different performance of MMIs developed by integrating blue-green algae metric at different spatial scales indicated the usefulness of blue-green algae metric in ecological assessment in mid- and high- disturbed lakes and a tiered approach for using diatom and blue-green algae metric in ecological assessment. We suggest using blue-green algae metric in combined with diatom metric to develop MMI when lakes are mid- and high-disturbed, while a routine diatom assessment would be enough for minimally disturbed sites.

Limited effects of pesticides on stream macroinvertebrates, biofilm nematodes, and algae in intensive agricultural landscapes in Sweden

Pesticides are frequently detected in surface waters, sometimes at levels exceeding ecotoxicological guidelines. We screened for almost 100 pesticides in 32 streams from intense agricultural areas in Southern Sweden, in concert with water chemistry parameters. In addition, we investigated the communities of benthic macroinvertebrates, biofilm nematodes and algae and calculated multiple bioassessment metrics. The number of pesticides found in each stream ranged between 2 and 52, but the sum of Toxic Units (ΣTU) for the mixtures was generally low, and exceeded the European Uniform Principles only in a single sample for algae and in 2% of the samples for Daphnia. Only nematode communities were significantly correlated with the ΣTU, potentially due to their higher pesticide exposure in biofilms. Diatom metrics showed that most streams were impacted by eutrophication and macroinvertebrate metrics showed good status in most streams, whereas the SPEARpesticides (SPEcies At Risk) index, specifically designed to indicate pesticide effects, showed that about half of the samples were at risk. Interestingly, SPEARpesticides was not correlated to ΣTUDaphnia, and this discrepancy suggests that redefining the boundaries for quality classes might be necessary for this index. Moreover, SPEARpesticides was positively correlated with the commonly used macroinvertebrate index ASPT, although disparate results were found for several streams. We argue that this questions the scaling of both metrics and the specificity of their responses. We discuss that the overall good/moderate status of the streams, despite the intense agriculture in the catchments, can be due to the fact that i) a sampling strategy with repeated grab samples did not capture peak pesticide concentrations, thus underestimating acute exposure, ii) pesticide run-off indeed was low, due to measures such as buffer strips, and iii) the nutrient-rich conditions and high sediment loads counteracted pesticide toxicity. We conclude that agricultural land use was the overriding stressor in the investigated streams, including strong effects of nutrients, less apparent effects of pesticides and likely impact of hydromorphological alterations (not specifically addressed in this study).

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.

The use of epilithic diatom assemblages in assessing land use in Silago, Southern Leyte, Philippines

Silago is a municipality in Southern Leyte in which logging for high-quality timber and land clearing for agricultural purposes threaten stream ecosystems. The objective of this study was to assess the response of diatom assemblages in relation to land use. Diatoms and water quality sampling was done at 27 sites on two sampling occasions (June and July 2014). Multiple diatom metrics were calculated to measure the response of diatoms to changes in land use. In all, 135 diatom species distributed to 48 genera were recorded. The results showed that diatom species and their attributes gave similar responses to those obtained in environmental variables. Pollution tolerance index classified all sampling sites as oligo-b-mesosaprobic. Meanwhile, Cymbella richness, percent motile taxa, and percent Achnanthidium minutissimum indicated good water quality in forested areas, distinguishing them from other land use types. Contrary to other studies, species richness was found to increase with greater degrees of disturbance, thus giving unreliable evaluation of water quality. Overall, the study suggests that epilithic diatoms can be applied in biomonitoring of freshwater bodies in the country.