The soil nematode fauna of five locations situated in Parque Nacional del Agua (PNA) in Costa Rica is characterized and analyzed. Four ecosystems were sampled in each location: primary (undisturbed) forest, secondary (naturally regenerated) forests, tree plantations (cleared and replanted with timber trees), and pastures (cleared of trees). Five soil samples of 100 g were analyzed in each location and ecosystem, resulting in a total of 100 samples. One hundred and thirty-one nematode genera were identified, and their abundance and biomass were estimated and analyzed by means of nonmetric multidimensional scaling (NMDS) and redundancy analysis (RDA). The observed nematode abundance was 1237 ± 520 specimens per soil sample for the whole survey, similar to previously reported from tropical soils. Dominance-diversity curves, based on nematode abundance, follow a similar ‘hollow curve’ pattern, with only 20 of the genera representing 84.6% of the total abundance, and only 12 of the genera representing 88% of the total biomass. Helicotylenchus, tylenchids, criconematids, Belondira, Longidorus, Xiphinema, Monotrichodorus, Prismatolaimus and Steinernema are important in the assemblages due their abundance or biomass in the different samples. Monotrichodorus and Discocriconemella appear related to undisturbed ecosystems, and they could have potential as disturbance indicators. Biomass-based dominance-diversity curves have similar qualitative and quantitative behavior to those observed in abundance distribution, but the dorylaims, Aporcelinus and Aporcelaimoides, which represented only the 0.35% of the abundance, having a major part of the total biomass (4.33%). NMDS analysis segregated locations into two groups, sampled sites were arranged according to the life zone where they belong. Ecosystems were segregated into natural ecosystems and plantations but having overlapping zones. Whereas RDA analysis indicated that organic matter and Cu are the most relevant edaphic variables for explaining the distribution of nematode assemblages, however few genera appear important in the ordination, Mesocriconema, Longidorus, Xiphinema and Belondira between them.

Introduction: Sludge Biotic Index (SBI) is one of the most used indices for the characterization of the community of microorganisms present in the activated sludge of wastewater treatment systems. However, this index takes into consideration only the density of the predominant functional groups of protozoa that inhabit this sludge. Objective: To evaluate whether the SBI value can be directly related to the number of protozoos and metazoos species found in the activated sludge of two wastewater treatment systems. Methods: This study was carried out on the wastewater generated by the San Vicente de Paul Hospital in Heredia Province, Costa Rica, during the months of February, March, and April 2022. Physicochemical, environmental, operational, and biological parameters were analyzed in a total of 36 samples from a Conventional activated sludge wastewater treatment system and from a Membrane Bioreactor (MBR) (n = 18 for each treatment system). Results: All the parameters evaluated are related to the abundance of microorganisms in the samples analyzed. The SBI value had an important effect on the number of organisms and can be related to the performance of the treatment system in terms of the percentage of Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) removal, especially for the MBR system. Conclusions: The SBI can be improved so its calculation not only considers functional groups but also includes genus and species of protozoos and metazoos present in the activated sludge. Which in turn would refine its bioindication potential by being more specific in terms of abundance, behavior and specific requirements of each species. | Introducción: El Índice Biológico de Lodos (IBL) es uno de los índices más utilizados para la caracterización de la comunidad de microorganismos presentes en el lodo activado de los sistemas de tratamiento de agua residual. Sin embargo, este índice toma en consideración únicamente la densidad de los grupos funcionales de protozoos predominantes que habitan este lodo. Objetivo: Evaluar si el valor del IBL puede relacionarse directamente con la cantidad de las especies de protozoos y metazoos encontradas en el lodo activado de dos sistemas de tratamiento de aguas residuales. Métodos: Esta investigación se realizó en las aguas residuales generadas por el Hospital San Vicente de Paul en la provincia de Heredia, Costa Rica, durante febrero, marzo y abril del 2022. Se analizaron parámetros fisicoquímicos, ambientales, operacionales y biológicos en un total de 36 muestras de un sistema de tratamiento por lodos activados Convencional y de un Biorreactor de Membrana (MBR) (n= 18, para cada sistema de tratamiento). Resultados: Todos los parámetros fisicoquímicos, ambientales y operacionales evaluados se encuentran relacionados con la abundancia de microorganismos en las muestras analizadas. El valor del IBL ejerció un efecto importante en la cantidad de organismos, y puede relacionarse con el desempeño del sistema de tratamiento en cuanto al porcentaje de remoción de la Demanda Bioquímica de Oxígeno (DBO) y Demanda Química de Oxígeno (DQO), sobre todo para el sistema MBR. Conclusiones: El IBL puede ser mejorado de manera que en su cálculo no solo considere grupos funcionales, sino que se incluya el género o especie de los protozoos y metazoos presentes en el lodo activado. Lo cual a su vez afinaría su potencial de bioindicación al ser más específico en cuanto a la abundancia, comportamiento y requerimientos específicos de cada especie.