Las diatomeas de agua dulce del Ecuadorpropuesta metodológica y empleo como bioindicadores ambientales

Abstract

Water pollution and the degradation of water resources are among the most critical environmental challenges. While many countries have traditionally relied on physicochemical parameters for water quality assessment, this approach is limited as it does not fully reflect the ecological health of aquatic ecosystems. Consequently, biomonitoring methods that focus on living organisms, considering both their sensitivity indices and water conditions, have been widely promoted. In this context, diatoms have proven to be highly effective bioindicators for water quality monitoring, particularly in lotic environments (rivers and streams). Diatom-based metrics leverage the relative abundance of indicator taxa, their sensitivity to environmental changes, and their ecological optimum along a pollution gradient. In South America, the use of diatoms for water quality assessment has gained traction in recent years. However, much of the region’s taxonomic work has been influenced by European studies, leading to the assumption that diatoms are cosmopolitan (adaptable to diverse global environments). This has resulted in the adoption of generalized indices or those from nearby regions, which may produce inaccurate assessments when local ecological conditions are not adequately considered. For this reason, the primary objective of this doctoral research is to establish the scientific foundation for the taxonomic and ecological study of diatoms in Ecuador. To achieve this, the study focused on (I) determining physicochemical and microbiological parameters in various freshwater ecosystems of continental Ecuador, (II) cataloging the diversity of epilithic diatom species in Ecuador’s aquatic systems using optical and electron microscopy alongside molecular methods, and (III) defining the autoecological parameters of key diatom species to evaluate their use as indicators of environmental quality. The research involved extensive monitoring of freshwater ecosystems across Ecuador’s three main geographic regions—Coastal, Andean, and Amazonian—as well as tropical glaciers. Samples were collected from rivers, lagoons, and cryoconite depressions. This data was used to establish a detailed baseline of diatom communities in these ecosystems, enabling the development of tools for water quality management in the country. Additionally, the exploration of extreme environments, such as tropical glaciers, facilitated the creation of protocols tailored to the unique ecological characteristics of these ecosystems, such as cryoconite holes on glacier surfaces hosting specialized microbial communities. These protocols are replicable across glaciers, offering a valuable resource for similar studies worldwide. Article I examines eutrophication in the Pita River, a lotic ecosystem in Ecuador’s highlands. Analysis of epilithic diatom communities revealed a clear eutrophication gradient, with high-quality waters in the river’s headwaters and increasingly polluted conditions downstream. The study identified high diatom species diversity for tropical regions, with species richness ranging from 34 taxa in the headwaters to 42 taxa downstream. However, existing trophic values for these species, as reported in the literature, did not align with local conditions, underscoring the need for a region-specific trophic index for the Ecuadorian Andes. Article II provides the first documentation of diatom diversity in 54 cryoconite holes on Antisana Volcano, an active tropical glacier in Ecuador. This study uncovered an extraordinarily diverse diatom community of allochthonous origin, though with a low abundance of individuals compared to other glaciers. A total of 278 taxa were recorded, including 12 species new to science. The dominant species were Psammothidium germainii (Manguin) Sabbe, Planothidium lanceolatum (Brébisson ex Kützing) Lange-Bertalot, and Sellaphora atomoides (Grunow) Wetzel & Van de Vijver. The distribution of diatom communities was primarily influenced by altitude rather than physicochemical water characteristics or cryoconite morphology, indicating that elevation is a key factor in these ecosystems. Article III develops specialized methodologies and protocols for studying diatoms in cryoconite depressions. Innovations include optimized sampling techniques, improved digestion processes for purifying diatom samples, and enhanced microscopic mounting techniques for more accurate identification. Molecular taxonomy using DNA was also incorporated. These methods provided a more precise characterization of diatom communities, a group essential for the ecological balance of aquatic ecosystems. Given the limited representation of tropical species in existing databases, especially in mountain ecosystems, this integrative approach was crucial for generating reliable and detailed results. Article IV introduces the Ecuadorian Diatom Index (EDI), a new tool for assessing water quality in the country’s freshwater ecosystems. The EDI is based on diatoms as ecological indicators and is specifically designed to reflect the limnological conditions of Ecuadorian rivers and lakes. The index was developed using abiotic and biological data collected from 111 monitoring stations across Ecuadorian watersheds. Statistical analyses revealed significant differences in the floristic composition and autoecological parameters of diatoms, enhancing the reliability of the EDI compared to traditional methods like the Pollution Sensitivity Index (IPS). From a practical standpoint, this research provides specific tools, such as the EDI, which not only lay the groundwork for future taxonomic and ecological studies of diatoms in Ecuador but also offer methodologies applicable to water quality assessment in any freshwater ecosystem. This study strengthens the understanding of Ecuador’s aquatic biodiversity and has tangible applications for long-term environmental monitoring. The tools and methodologies developed represent valuable resources for managing water resources in an Ecuador increasingly vulnerable to climate change.