Epilithic diatom communities of selected streams from the Lerma-Chapala Basin, Central Mexico, with the description of two new species

Diatom assemblages from different environments of the Acoculco Caldera associated to hydrothermal and anthropogenic activity

The use of diatoms as indicators of water quality has been studied worldwide; however, the use of diatoms as indicators of thermic anomalies has received less attention. The objective of this study is not only to provide a record on algal communities, but also to investigate the relationship between the diversity in diatom species and the physicochemical conditions of water. Evaluating its temporal variability in a caldera with low permeability and cold acid hydrothermal anomalies. Diatom assemblages were identified at 11 sites. Species composition was compared between seasons (dry and wet) in different environments, as streams, ponds and pools within the caldera. The physicochemical and environmental differences are very specific, which allowed the diatom identification from geothermal and anthropogenic sources without finding mixtures. The results show that the main diatom flora of the Acoculco caldera consists of 15 dominant species. Sulphite-rich acidic hydrothermal waters are characterized by the presence of Eunotia exigua, Eunotia bilunaris, and Pinnularia brauniana. In non-hydrothermal streams, Planothidium, Achnanthidium, and Humidophila species are the most common taxa. Other diatoms from acidic environments were Frustulia saxonica, Surirella, and Stenopterobia. The assemblages are clearly different from those of alkaline environments. Epithemia, Planothidium, and Ulnaria are present in the streams and are not associated with thermalism. Ordination of diatom assemblages showed that pH, conductivity, and nutrient concentrations, some of which are influenced by anthropogenic activities, were the main factors influencing the distribution of diatom composition.

Development of the Diatom Ecological Quality Index (DEQI) for peri-urban mountain streams in the Basin of Mexico

In the Basin of Mexico, one of the most important economic regions in the country with over 22 million inhabitants, peri-urban streams have been transformed into sewers, drains, and pipes to avoid flooding or unsanitary conditions; the change affects not only the ecosystem's goods and services but also the aquatic communities that support the natural ecological processes. We aimed to develop a diatom-based diagnosis of the ecological quality of these aquatic ecosystems through the study of epilithic diatom response to regional environmental gradients. Samples of epilithic diatoms and water were collected in 45 sites representing 12 perennial streams, and multivariate analyses were performed on environmental and biological data. The ecological quality gradient to which diatoms responded was related to oxygen saturation, soluble reactive phosphorous, dissolved inorganic nitrogen, and hydromorphological quality. Three species groups were recognized according to their ecological preferences along CCA1 axis, indicators of high and low ecological quality, and tolerant species. By assigning an indicator value to each species group, we calculated the DEQI using the formula adapted from Pantle and Buck, indicating five different ecological quality classes. This index is proposed for complementing the ecological quality evaluation as a biological metric that responds to multiple regional stressors of the structure and function of these peri-urban streams in the Basin of Mexico.

Diatom diversity and distribution in Madeira Island streams (Portugal)

BACKGROUND

Here, we present the data obtained from the samples collected in a field campaign during the spring of 2015 which aims for a better understanding of the diversity and distribution patterns of freshwater diatoms in Madeira Island. Following European and Portuguese standards and recommendations for routine diatom sampling and analysis, we collected samples in 40 sites, distributed in 27 permanent streams and identified the diatom species present, using general diatom floras and studies in Portuguese freshwater diatoms.

NEW INFORMATION

Little is known about the diversity and distribution of freshwater diatom assemblages from Madeira Archipelago. This study reports a survey in 40 sites in Madeira Island distributed in 27 permanent streams. A total of 965 diatom (Bacillariophyta) occurrences were recorded, belonging to 130 different taxa from 44 genera and 27 families. The families with the highest number of occurrences were Bacillariaceae (176), Achnanthidiaceae (135) and Naviculaceae (133). The two diatom endemisms, described previously in Madeira Island (Lange-Bertalot 1993), Nitzschia macaronesica Lange-Bertalot and Navicula madeirensis Lange-Bertalot, were only observed in a small number of sites, located mostly at Laurissilva forest. Sixty species are new records, not only to Madeira Island, but also to the Madeira Archipelago.

Temporal Evolution of Diatoms in a Temporary Pond Situated in the Massif du Sancy Mountains (Massif Central, France) and Description of a New Pinnularia Species

A floristic survey was performed on a temporary pond, “Laqui du Seignavoux”, situated in the Mont-Dore massif of the French Massif Central, between 2017 and 2019. Except in 2017, each year, we performed four sampling campaigns from April/May to December. Water samples and diatoms were collected. The temporary pond evolved from a poorly mineralized ecosystem due to snow, inducing oligotrophic and oligosaprobic water, well oxygenated in spring, to a more mineralized, less oxygenated, eutrophic–hypereutrophic, and polysaprobic environment in summer. This change in abiotic conditions was found to be linked to the presence of cattle, beginning in May, that trample and excrete in the pond, leading to higher ammonium and nitrate concentrations. During this period, the dominant species were Pinnularia sp., Nitzschia palea, and Nitzschia palea var. tenuirostris. In spring and winter, different species of Eunotia dominated the community such as Eunotia pseudogroenlandica. Finally, light microscopy (LM) and scanning electron microscopy (SEM) observations on a new species of the genus Pinnularia from the temporary pond are presented and the ecological preferences are discussed.