Planktonic diatom assemblage seasonal diversity used to assess environmental health in a coastal wetland of southern Chile

ABSTRACTAlthough planktonic diatoms are one of the most abundant taxonomic groups in coastal wetlands, their assemblages have not been used to determine the environmental health of these ecosystems. Studies of ecosystem environmental health have been based on other taxonomic groups; we propose that diatom genera diversity represents a viable alternative for this purpose. Thus, our aim was to determine the alpha and beta diversities of the planktonic diatom assemblage present in Caulín Bay, Chiloé Island (41° 49’S; 73° 38’O), southern Chile, during the austral winter and spring of the years 2012 and 2014. Inasmuch Caulín Bay is an important site for aquatic bird observation and conservation, hunting is prohibited on a national scale and, internationally, the site has been declared an Important Bird and Biodiversity Area (IBA). Our results indicate different diversities between sampling stations, but not between the years studied. In total, we recorded 53 diatom genera, of which the most abundant were Coscinodiscus (21.99%) and Cocconeis (16.23%). The study area presented high genera diversity (i.e., H’(log2) >3.74) and beta diversity indicated that Caulín presents a low level of heterogeneity and is a low genera replacement environment. Consequently, we infer that Caulín Bay is productive and environmentally stable ecosystem. This leads us to conclude that diatom diversity determination is a viable alternative to establish aquatic ecosystem environmental health and we recommend that future conservation strategies be established for Caulín Bay.RESUMENSi bien las diatomeas planctónicas son uno de los grupos taxonómicos más abundantes de los humedales costeros, sus ensambles no se han utilizado para determinar el estado ambiental de estos ecosistemas. Aunque se han realizado estudios de la salud ambiental de un ecosistema utilizando otros grupos taxonómicos, nosotros proponemos que la diversidad de géneros de diatomeas representa una alternativa viable. Por lo tanto, el objetivo de este estudio fue determinar las diversidades alfa y beta del ensamble de diatomeas planctónicas presentes en la Bahía de Caulín, Isla de Chiloé (41 ° 49’S; 73 ° 38’O), sur de Chile, durante las temporadas de invierno y primavera austral de los años 2012 y 2014. Bahía Caulín es un sitio importante para la observación y conservación de aves acuáticas por lo que a nivel nacional se ha prohibido la caza y a nivel internacional fue decretada un Área Importante para la Conservación de Aves, AICA. Los resultados de este estudio indicaron diferencias en las diversidades entre las estaciones de muestreo, pero no entre los años estudiados. En total, se identificaron 53 géneros de diatomeas; los más abundantes fueron Coscinodiscus (21,99%) y Cocconeis (16,23%). El área de estudio presentó una alta diversidad de géneros (i.e., H’(log2) >3.74) y la diversidad beta indicó que Caulín presentó bajo nivel de heterogeneidad y es un entorno con bajo reemplazo de géneros. Así, inferimos que Bahía Caulín es un ecosistema productivo y ambientalmente estable, por lo cual concluimos que la determinación de las diversidades de diatomeas es una alternativa para establecer la salud ambiental de los ecosistemas acuáticos y recomendamos establecer futuras estrategias de conservación para Bahía Caulín.PALABRAS CLAVE: diatomeas, diversidades ecológicas, plancton, humedales costeros, desembocadura

Estimation of Organic Pollution of the Jinyaoshi Lake Based on the Diatom Assemblage of the Lake Sediments

From 2015 to 2019, samples of surface mud from the bottom of the artificial lake in Tianjin Normal University were collected for diatom analysis and identification in May and June. 1296 diatoms were identified and divided into 25 species. DAIpo (Diatom Assemblage Index to organic water pollution) was calculated: 56 in 2015, 76 in 2017, 58 in 2018 and 63 in 2019. In 2017, it was β-oligosaprobic, and in 2015, 2018 and 2019, it belonged to α-oligosaprobic. The Jinyaoshi Lake is an artificial lake where groundwater is exposed by artificial excavation, and its water source mainly comes from groundwater, then by precipitation. It shows that the pollution degree of the Jinyaoshi Lake was not serious since 2015, and its pollution level was α or β-oligosaprobic.

Diatoms as indicators of the effects of river impoundment at multiple spatial scales

River impoundment constitutes one of the most important anthropogenic impacts on the World’s rivers. An increasing number of studies have tried to quantify the effects of river impoundment on riverine ecosystems over the past two decades, often focusing on the effects of individual large reservoirs. This study is one of the first to use a large-scale, multi-year diatom dataset from a routine biomonitoring network to analyse sample sites downstream of a large number of water supply reservoirs (n = 77) and to compare them with paired unregulated control sites. We analysed benthic diatom assemblage structure and a set of derived indices, including ecological guilds, in tandem with multiple spatio-temporal variables to disclose patterns of ecological responses to reservoirs beyond the site-specific scale. Diatom assemblage structure at sites downstream of water supply reservoirs was significantly different to control sites, with the effect being most evident at the regional scale. We found that regional influences were important drivers of differences in assemblage structure at the national scale, although this effect was weaker at downstream sites, indicating the homogenising effect of river impoundment on diatom assemblages. Sites downstream of reservoirs typically exhibited a higher taxonomic richness, with the strongest increases found within the motile guild. In addition, Trophic Diatom Index (TDI) values were typically higher at downstream sites. Water quality gradients appeared to be an important driver of diatom assemblages, but the influence of other abiotic factors could not be ruled out and should be investigated further. Our results demonstrate the value of diatom assemblage data from national-scale biomonitoring networks to detect the effects of water supply reservoirs on instream communities at large spatial scales. This information may assist water resource managers with the future implementation of mitigation measures such as setting environmental flow targets.

Freshwater diatoms from Pleistocene-Holocene sediments in Bunger Oasis (East Antarctica)

The monodominant freshwater diatom assemblage was in first established in Quaternary sediments at an altitude of 24 m in the outcrop on the western shore of the Rybiy Khvost Bay in the Bunger Oasis (East Antarctica). The diatom assemblage is dominated by the benthic Navicula shackletoni, characteristic of hypersaline lakes.The diatom assemblage reflects the conditions for the formation of deposits in a shallow lake with high salinity. This diatom assemblage differs from the previously established diatom associations in the Holocene sediments of the freshwater lakes of the Bunger Oasis.