Responses of testate amoebae assemblages (Amoebozoa: Arcellinida) to recent volcanic eruptions, inferred from the sediment record in Laguna Verde, southern Patagonia, Argentina

There is little knowledge about testate amoebae in lakes and their responses to volcanic eruptions. To address this knowledge gap, we studied the paleoecology of these protists in a sediment record from Laguna Verde, a lake located east of the southern Patagonian Ice Field, in Santa Cruz Province, Argentina. The lake is under the influence of volcanic eruptions from Lautaro Volcano, Chile, ~ 42 km WNW of Laguna Verde. We evaluated the response of 11 testate amoeba morphospecies in the lake to the last four Lautaro eruptions, using a 61-cm sediment core. Calcium (Ca), a major element of volcanic ash, was the most important variable explaining testate amoeba variability in the three zones determined by detretended correspondence analysis. We identified four declines in testate amoeba abundance and diversity associated with tephra deposition. Poisson regression analysis revealed that Difflugia immanata, D. bidens, and D. glans strain “glans” decrease after deposition of tephra layers. In contrast, Centropyxis constricta strain “constricta,” C. aculeata strain “aculeata” and Zivkovicia compressa respond positively to ash deposition. Our findings suggest a high resilience of testate amoebae to stochastic events such as volcanism because the same assemblage (D. immanata, D. bidens, and D. glans strain “glans”) inhabited the lake before and after the ashfalls. Nevertheless, several volcanic eruptions during the last ~ 300 years may have weakened this resilience and had a long-term effect on community diversity. Multivariate analysis showed that potassium (K) plays a significant role in shaping assemblage composition. Because of the low K content of the Lautaro tephra, we infer that higher potassium concentrations in sediments are not related with volcanic events, but rather, are associated with terrestrial input. Future studies, however, will be needed to identify the source of K in the sediment record and its relationship with testate amoebae assemblages. Our study demonstrates the potential for using lacustrine testate amoebae as environmental proxies, and illustrates the direct effects of volcanic ash deposition on their assemblage composition, diversity and distribution in southern Patagonia.Fil: Charqueño Celis, Norma Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Administración de Parques Nacionales. Parque Nacional "Nahuel Huapi"; ArgentinaFil: Sigala, Itzel. Universidad Nacional Autónoma de México. Instituto de Geofísica; MéxicoFil: Zolitschka, Bernd. Universitat Bremen. Institut Fuer Geographie; AlemaniaFil: Pérez, Liseth. Technische Universitat Carolo Wilhelmina Zu Braunschweig. Iinstitut fur Geosysteme und Bioindikation; AlemaniaFil: Mayr, Christoph. Institut Fur Geographie, Friedrich-alexander-universit; Alemania. Universitat Erlangen Nuremberg; Alemania. Ludwig Maximilians Universitat; AlemaniaFil: Massaferro, Julieta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Administración de Parques Nacionales. Parque Nacional "Nahuel Huapi"; Argentin

Testate amoebae (Amoebozoa: Arcellinidae) as indicators of dissolved oxygen concentration and water depth in lakes of the Lacandón Forest, Southern Mexico

The ecology of aquatic protists such as testate amoebae is poorly known worldwide, but is almost completely unknown in lakes of the northern Neotropics. To address this knowledge gap, we analyzed testate amoebae (Amoebozoa: Arcellinidae) in lakes of the Lacandón Forest, one of the most biodiverse parts of southern México. We set out to evaluate the diversity of testate amoebae communities and assess whether testate amoebae taxa are reliable indicators of environmental variables dissolved oxygen and water depth. We collected 17 surface sediment samples from a range of water depths in six lakes across the Naha-Metzabok Biosphere Reserve, northeastern Chiapas state. We identified 15 testate amoebae taxa distributed across seven genera. Eleven were identified to species level and four to strain (infra-subspecific level), and taxa were distributed unevenly among samples. Distribution of taxa in samples was related to dissolved oxygen (DO) concentration in the water measured near the sediment surface. Arcella discoides and Centropyxis aculeata strain “aculeata” were the most tolerant of low oxygen concentrations, whereas the other taxa require higher DO levels. The influence of oxygen was also seen at the assemblage level. Sites with low DO concentrations had Shannon Diversity Index (SDI) values <1.5, an indication of stressful ambient conditions. We identified two species assemblage types, which are distinguished by their oxygen concentration requirements. Assemblage 1 was more diverse and possessed species that are intolerant of low oxygen concentrations, whereas Assemblage 2 possessed fewer, rarer, opportunistic species that tolerate stressful conditions. Low oxygen concentrations are related to water depth and the combination of these two variables is important in determining the composition of testate amoebae assemblages in Lacandón Forest lakes. Quantitative relationships between testate amoebae assemblages and water depth will enable use of sedimented amoebae remains for paleolimnological inference of past water level changes in lakes of the Lacandón Forest.Fil: Charqueño Celis, Norma Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Administración de Parques Nacionales. Parque Nacional "Nahuel Huapi"; ArgentinaFil: Garibay, Martin. Universidad Nacional Autónoma de México; MéxicoFil: Sigala, Itzel. Universidad Nacional Autónoma de México; MéxicoFil: Brenner, Mark. University of Florida; Estados UnidosFil: Echeverria Galindo, Paula. Technische Universitat Carolo Wilhelmina Zu Braunschweig. Iinstitut fur Geosysteme und Bioindikation.; AlemaniaFil: Lozano García, Socorro. Universidad Nacional Autónoma de México; MéxicoFil: Massaferro, Julieta. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Administración de Parques Nacionales. Parque Nacional "Nahuel Huapi"; ArgentinaFil: Pérez, Liseth. Technische Universitat Carolo Wilhelmina Zu Braunschweig. Iinstitut fur Geosysteme und Bioindikation.; Alemani

Imprints of the Little Ice Age and the severe earthquake of AD 2001 on the aquatic ecosystem of a tropical maar lake in El Salvador

Using a 530-year sediment record from the maar Lake Apastepeque, El Salvador, and based on diverse geochemical and biological (cladocerans, chironomids, diatoms, ostracods, testate amoebae) indicators, we estimated climatic and environmental alterations during the Little Ice Age (LIA) and reconstructed the recent history of the lake. Results demonstrate relatively humid conditions in the mid-elevations (500 m a.s.l.) of El Salvador during most parts of the LIA, resulting in high lake levels. Contrarily, the first part of the LIA was characterized by drier climates comparable to studies from Mexico and Belize, which correlated this phase with the Spörer minimum. Regional comparison with palaeorecords from the northern Neotropics reveals a high heterogeneity in local expressions of the LIA in Central America, likely connected to the high topographic heterogeneity of the region. Since the beginning of the 20th century, Lake Apastepeque has experienced enhanced human impact expressed as increased nutrient supply. The most recent period was characterized by significant environmental disturbance, which we relate to an upper-crustal earthquake, one of the strongest over the last 500 years, that affected the region on 13th February 2001 (Mw = 6.6, epicentre at 10 km depth, 30 km from the lake). The release of toxic bottom components such as hydrogen sulphide and high turbidity and turbulence of water caused major species turnover in the lake ecosystem, resulting in a massive fish kill and colonization by large cladocerans. Modern sediments still show slightly altered biota communities compared to pre-earthquake assemblages, indicating that the ecosystem has still not fully recovered

Searching for the Little Ice Age in the last ~900 yrs record of the shallow lake Laguna Polo, Patagonia, Argentina

The records of the Little Ice Age (LIA) in lacustrine sediments from southern south America (SSA) are still rare. Indeed, most of the evidence of this period in SSA comes from tree rings records. Our main goal was identifying the signal of the LIA at Laguna Polo (49° 15’ 59.4” S, 72° 53’ 38.4” W), in Santa Cruz, southern part of Patagonia. For this multiproxy reconstruction, we analyzed a 54-cm long sediment core and conducted paleoecological analysis on testate amoebae and chironomids in combination with grain-size distribution and geochemical composition (TOC, TIC, TN, biogenic silica (BiSi), δ15N, δ13C and C/N). The age model, based on radiocarbon dates and tephrochronology, indicated a basal age of ca. AD 1300. Based on the biological proxies, we divided our record into 4 zones. In zone 3 an important ecological change in both bioproxies was detected for the period AD 1420 to 1780. On the one hand, testate amoebae show an increase in abundance but a decrease in diversity. Difflugids were highly abundant and were dominated by Difflugia glans. Chironomid assemblages, on the other hand, reveal a decrease in abundance of head capsules but an increase in diversity with the appearance of Cricotopus and Dicrotendipes. The taxa of both taxonomic groups found during this period have been reported as indicators of cold environments. Grain-size analyses indicate a concurrent proportional increase in silts and clays, whereas geochemical analyses record a decrease in TN, TOC, TIC, BiSi, δ13C and the C/N ratio, but an increase of δ15N which may be indicative of a cooler and wetter period, as has been previously described during the LIA period in Patagonia