Contrasting responses of lake ecosystems to environmental disturbance: a paleoecological perspective from northern Patagonia (Argentina)

Paleoecological studies are crucial for understanding ecosystem disturbance and resilience dynamics. However, nearly all the research related to the response of aquatic communities to disturbances has been developed at short-term ecological scales. In this study, we investigate the long-term response of chironomid insects of two lakes, to volcanic and other environmental disturbances that have taken place during the last 200 years. The studied lakes, Lake Verde and Lake Toncek, are located in the Nahuel Huapi National Park (northern Patagonia, Argentina), under contrasting environmental settings. Our results show that the main driver of faunal changes in both lakes is volcanism. Indeed, after the impact of the 1960 Puyehue/Calbuco volcanic events, the chironomid assemblage of Lake Verde recovered to initial conditions showing high resistance and a strong resilience to the impact. In this lake, the canopy, the presence of macrophytes, and the dynamic of the watershed are important determinants of resilience providing habitats for species colonization and/or by giving refugia to the community. Contrarily, chironomid assemblages from Lake Toncek did not recover to the original state after the impact of the ash. This lake is located above the tree line, and therefore it is highly probable that the lack of vegetation cover in the basin offered no protection for the aquatic environment, leaving the ecosystem highly exposed to the effect of the volcanic ashes. Subordinate to the effects of the volcanism, rising temperatures in the last 50 years and/or increasing human activities in the area, especially in L. Toncek, may also be responsible for the changes in chironomid assemblages.Instituto de Limnología "Dr. Raúl A. Ringuelet

Climate change threatens the most biodiverse regions of Mexico

International audienceClimate change threatens Earth's biodiversity, although its impacts are variable and depend on the capacity of species and ecosystems to cope with the magnitude and speed of change. Natural protected areas (NPAs) constitute potential refugia for species' persistence and for sustaining the provisioning of ecosystem services. Biosphere reserves are NPAs that are less altered by human actions and provide habitat to endemic, threatened or endangered species. Here, we aim to evaluate the threat imposed by climate change on the network of biosphere reserves in Mexico. Focusing on five bioclimatic variables, we computed the climatic space – measured as an n-dimensional hypervolume – of 40 NPAs. Increases in temperature are predicted for all NPAs by 2050, whereas decreases in annual rainfall are predicted for 30 NPAs. By 2050, 31 NPAs that provide habitat to 22,866 recorded species are predicted to lose 100% of their baseline climatic space, shifting to completely novel climates. On average, the other nine NPAs are predicted to lose 55.7% (SD = 26.7%) of their baseline climatic space, while 54.5% (SD = 32.5%) of the future climatic space will be novel. Seventeen NPAs may lose climate variability (homogenization), decreasing species' niches. The extent to which non-analogue conditions will remain within the tolerance of species and ecosystems is currently unknown. Finally, we propose a vulnerability index to categorise NPAs based on their loss of existing climatic space, total geographic area, species richness, and uniqueness of species composition, finding los Tuxtlas and Tiburon Ballena as the most and least vulnerable NPAs, respectively

Modeling streamflow response to persistent drought in a coastal tropical mountainous watershed, Sierra Nevada de Santa Marta, Colombia

Droughts constitute natural hazards that affect water supply for ecosystems and human livelihoods. In 2013-2016, the Caribbean experienced the worst drought since the 1950s, and climate projections for the southern Caribbean predict less rainfall by the end of the 21st century. We assessed streamflow response to drought for a watershed in the Colombian Caribbean by analyzing the effects of drought length and land cover on streamflow recovery. We generated a calibrated SWAT model and created annual and monthly drought scenarios from rainfall records. We used our model to predict water yield for selected land covers (wet forest, shade coffee, shrub, and dry forest) under drought conditions. Annual scenarios resulted in water yield reductions of ~15 mm month -1 (wet forest, coffee, and shrub) and 5 mm month -1 (dry forest) for the first month after a two-year drought. Maximum water yield reductions for monthly scenarios occurred after a 10-month drought and were ~100 mm month -1 (wet forest, coffee, and shrub) and 20 mm month -1 (dry forest). Streamflow recovered within nine months (annual scenarios), and two to eight months (monthly scenarios) after drought termination. Drought response seems to be conditioned by climatic factors (rainfall seasonality and spatial variability) and catchment properties

Tropical freshwater ostracodes as environmental indicators across an altitude gradient in Guatemala and Mexico

Ostracodes are bivalve microcrustaceans with calcium carbonate shells that preserve well in lake sediment. They are very sensitive to environmental variables and are therefore powerful tools in paleoclimate and paleoenvironmental studies that cover time periods from decades to millions of years. Detailed knowledge of species ecological preferences and robust taxonomy are prerequisites for such studies. Such information, however, is still lacking for many areas of the world, including the Neotropics. Previous studies in the northern Neotropics were conducted mainly in the karst lowlands of the Yucatán Peninsula, but higher-altitude areas remained relatively poorly investigated. This study was designed to expand our knowledge of the modern, Neotropical freshwater ostracode fauna, across an altitudinal gradient from the karst lakes in the lowlands of El Petén, Guatemala (~100 - 500 m asl), to the mid-elevation water bodies of the Lacandón forest (~500 - 1000 m asl), to the higher-altitude lakes of Montebello, Chiapas, México (~1000 - 1500 m asl). Eighteen ostracode species were identified in 24 lakes. Ostracodes were absent in Lakes Amarillo and Lacandón (mid-altitude), and San Diego (lowlands). Statistical analysis indicated that the most abundant species, Cypridopsis vidua, Cytheridella ilosvayi, Pseudocandona antillana, and Darwinula stevensoni have a continuous distribution along the entire altitudinal gradient. Other species display more restricted distributions, determined by temperature, precipitation and conductivity. For example, Eucypris sp. is restricted to the lowlands, Vestalenula sp. and Cypria sp. were found only at middle elevations, and a Cyprididae species was restricted to the highlands. Species diversity is slightly greater in warm lakes at middle altitudes (Haverage = 1.09) than in water bodies in the lowlands (Haverage = 0.94) and in cooler lakes in the highlands (Haverage = 0.94). LOESS regressions provided ecological preference information for the four most frequent and widely distributed species, with respect to temperature, conductivity, bicarbonate (HCO3-) concentration, precipitation, and pH. Cypria petenensis, Heterocypris punctata, and Paracythereis opesta display higher abundances in lowland lakes, whereas, Cytheridella ilosvayi, and Pseudocandona antillana prefer lowland and mid-elevation lakes. Environmental conditions in the higher-elevation lakes of Montebello favor the presence of Darwinula stevensoni. Such quantitative ecological information will improve ostracode-based paleoenvironmental reconstructions in southern México and northern Guatemala, and our approach serves as a model for future paleoecological studies that employ other aquatic bioindicators, such as testate amoebae, cladocerans, and chironomids

Freshwater juvenile ostracode data of sediment core PI-6 (85 ka BP) from Lake Petén Itzá, Guatemala (ICDP-2004/03)

Ostracodes and pollen preserved in a 75.9-m-long sediment core (PI-6) recovered from Lake Petén Itzá, Guatemala were used to assess the magnitude and velocity of aquatic and terrestrial community responses during the last 85,000 years. Our juvenile ostracode data includes information on species abundances and richness, diversity index

Freshwater ostracode and pollen data of sediment core PI-6 (85 ka BP) from Lake Petén Itzá, Guatemala (ICDP-2004/03)

Ostracodes and pollen preserved in a 75.9-m-long sediment core (PI-6) recovered from Lake Petén Itzá, Guatemala in 2006 were used to assess the magnitude and velocity of aquatic and terrestrial community responses during the last 85,000 years. The composite sediment sequence from three holes was recovered from a water depth of 71 m, and subsampled every ~ 20 cm for biological analysis. Our ostracode data (adults and juveniles) includes information on species abundances and richness, diversity index, DCA species scores along the first two DCA axes, stratigraphic DCAs (axes 1 and 2), ecological change and rates of ecological change. The following pollen data are provided as well: Taxa richness, diversity (pollen sum), DCA taxa scores along the first two DCA axes, stratigraphic DCAs (axes 1 and 2), ecological change and rates of ecological change

Detrended correspondence analysis and ecological change of freshwater ostracode and pollen data of sediment core PI-6 (85 ka BP) from Lake Petén Itzá, Guatemala (ICDP-2004/03)

Ostracodes and pollen preserved in a 75.9-m-long sediment core (PI-6) recovered from Lake Petén Itzá, Guatemala were used to assess the magnitude and velocity of aquatic and terrestrial community responses during the last 85,000 years. Our ostracode data (adults and juveniles) includes information on Detrended Correspondence Analysis (DCA) species scores along the first two DCA axes, stratigraphic DCAs (axes 1 and 2), ecological change and rates of ecological change. The following pollen data are provided as well: DCA taxa scores along the first two DCA axes, stratigraphic DCAs (axes 1 and 2), ecological change and rates of ecological change

Pollen taxa diversity of sediment core PI-6 (85 ka BP) from Lake Petén Itzá, Guatemala (ICDP-2004/03)

Ostracodes and pollen preserved in a 75.9-m-long sediment core (PI-6) recovered from Lake Petén Itzá, Guatemala were used to assess the magnitude and velocity of aquatic and terrestrial community responses during the last 85,000 years. The following pollen data are provided: Taxa diversity (pollen sum)

Freshwater adult ostracode data of sediment core PI-6 (85 ka BP) from Lake Petén Itzá, Guatemala (ICDP-2004/03)

Ostracodes and pollen preserved in a 75.9-m-long sediment core (PI-6) recovered from Lake Petén Itzá, Guatemala were used to assess the magnitude and velocity of aquatic and terrestrial community responses during the last 85,000 years. Adult ostracode data includes information on species abundances and richness, diversity index