@article {8099, title = {Aquatic biota responses to temperature in a high Andean geothermal stream}, journal = {Freshwater Biology}, year = {2021}, month = {Nov-07-2022}, abstract = {The impact of global warming on mountain ecosystems is predicted to be high, and particularly in the tropical region. Geothermal streams have provided comprehensive evidence about how aquatic biodiversity changes across natural thermal gradients, but current knowledge is restricted to arctic and temperate zones. Thermal tolerances are different in tropical biological communities, resulting in high thermal sensitivity and low capacity to endure change in their thermal environments. This feature can change the response of aquatic organisms to warming, yet there is little empirical evidence to support this assumption.
In this study, we address this issue by evaluating how water temperature affects biodiversity, and the structure of primary and secondary producers of a high-elevation geothermal stream system (4,500\ m above sea level) in the Bolivian Andes. We analysed multi-taxa responses to increased water temperature using benthic macroinvertebrate families, benthic algae and cyanobacteria, fishes, and macrophytes as study organisms. Different models were run to assess the response of aquatic biota to temperature. In addition, threshold indicator taxa analysis (TITAN) was used to identify changes in macroinvertebrate taxa distributions along the thermal gradient.
We found that macroinvertebrate richness decreased at 24{\textendash}25{\textdegree}C due to the different taxon-specific responses to temperature. Threshold indicator taxa analysis identified 17 temperature thresholds for each family of macroinvertebrates. Changes in macroinvertebrate community composition were significantly associated with changes in water temperature. Similarly, changes in macrophytes were associated with temperature differences, and high macrophyte richness was found at 19{\textendash}20{\textdegree}C. Chlorophyll-a\ concentration of green algae and diatoms was higher at intermediate temperatures 20{\textendash}22{\textdegree}C, macroinvertebrates density peaked at 27{\textdegree}C, and fish body size reduced linearly with temperature.
Temperature increase in the geothermal stream resulted in a reduction of aquatic diversity and primary and secondary producers by simplifying the community structure to a few warm-adapted taxa and reduced body size. These patterns differed from those obtained in temperate/arctic geothermal streams, but are similar to other studies at high-elevation. In a context of increasing warming, the ecological structure of high-elevation streams might lose cold-adapted taxa, and change to smaller populations. Additional studies based on ecosystem functioning of geothermal streams could lead to a better understanding on how warming affects high-elevation streams.}, issn = {0046-5070}, doi = {10.1111/fwb.13798}, url = {https://onlinelibrary.wiley.com/doi/10.1111/fwb.13798}, author = {Quenta-Herrera, Estefania and Daza, Antonio and Lazzaro, Xavier and Jacobsen, Dean and Dangles, Olivier and Cauvy-Frauni{\'e}, Sophie} } @article {5754, title = {Algal Bloom Exacerbates Hydrogen Sulfide and Methylmercury Contamination in the Emblematic High-Altitude Lake Titicaca}, journal = {Geosciences}, volume = {8}, year = {2018}, abstract = {

Algal blooms occurrence is increasing around the globe. However, algal blooms are uncommon in dominantly oligotrophic high-altitude lakes. Lake Titicaca, the largest freshwater lake in South America, located at 3809 m above the sea level, experienced its first recorded algal bloom covering a large fraction of its southern shallow basin in March{\textendash}April 2015. The dominant algae involved in the bloom was Carteria sp. Water geochemistry changed during the bloom with a simultaneous alkalinization in heterotrophic parts of the lake and acidification in eutrophic shallow areas. A decrease in oxygen saturation (from 105 to 51\%), and a dramatic increase in hydrogen sulfide (H2S) concentrations (from \<0.02 to up to 155 {\textmu}g.L-1) resulted in the massive death of pelagic organisms. Such changes were brought by the exacerbated activity of sulfate-reducing bacteria (SRB) in this sulfate-rich lake. Although levels in total mercury remained stable during the event, MMHg \% rose, highlighting higher conservation of produced MMHg in the water. Such an increase on MMHg \% has the potential to produce exponential changes on MMHg concentrations at the end food web due to the biomagnification process. Our physicochemical and climatological data suggest that unusually intense rain events released large amounts of nutrients from the watershed and triggered the bloom. The observed bloom offers a hint for possible scenarios for the lake if pollution and climate change continue to follow the same trend. Such a scenario may have significant impacts on the most valuable fish source in the Andean region and the largest freshwater Lake in South America. Furthermore, the event illustrates a possible fate of high altitude environments subjected to eutrophication.

}, issn = {2076-3263}, doi = {10.3390/geosciences8120438}, url = {http://www.mdpi.com/2076-3263/8/12/438}, author = {Dar{\'\i}o Ach{\'a} and Gu{\'e}dron, Stephane and Amouroux, David and Point, David and Lazzaro, Xavier and Fernandez, Pablo Edgar and Sarret, G{\'e}raldine} } @article {5231, title = {Mercury contamination level and speciation inventory in Lakes Titicaca and Uru-Uru (Bolivia): Current status and future trends}, journal = {Environmental Pollution}, volume = {231, Part 1}, year = {2017}, pages = {262 - 270}, abstract = {

Aquatic ecosystems of the Bolivian Altiplano (\~{}3800 m a.s.l.) are characterized by extreme hydro-climatic constrains (e.g., high UV-radiations and low oxygen) and are under the pressure of increasing anthropogenic activities, unregulated mining, agricultural and urban development. We report here a complete inventory of mercury (Hg) levels and speciation in the water column, atmosphere, sediment and key sentinel organisms (i.e., plankton, fish and birds) of two endorheic Lakes of the same watershed differing with respect to their size, eutrophication and contamination levels. Total Hg (THg) and monomethylmercury (MMHg) concentrations in filtered water and sediment of Lake Titicaca are in the lowest range of reported levels in other large lakes worldwide. Downstream, Hg levels are 3-10 times higher in the shallow eutrophic Lake Uru-Uru than in Lake Titicaca due to high Hg inputs from the surrounding mining region. High percentages of MMHg were found in the filtered and unfiltered water rising up from \<1 to \~{}50\% THg from the oligo/hetero-trophic Lake Titicaca to the eutrophic Lake Uru-Uru. Such high \%MMHg is explained by a high in situ MMHg production in relation to the sulfate rich substrate, the low oxygen levels of the water column, and the stabilization of MMHg due to abundant ligands present in these alkaline waters. Differences in MMHg concentrations in water and sediments compartments between Lake Titicaca and Uru-Uru were found to mirror the offset in MMHg levels that also exist in their respective food webs. This suggests that in situ MMHg baseline production is likely the main factor controlling MMHg levels in fish species consumed by the local population. Finally, the increase of anthropogenic pressure in Lake Titicaca may probably enhance eutrophication processes which favor MMHg production and thus accumulation in water and biota.

}, keywords = {Titicaca}, issn = {0269-7491}, doi = {https://doi.org/10.1016/j.envpol.2017.08.009}, url = {https://www.sciencedirect.com/science/article/pii/S0269749117320572}, author = {S. Gu{\'e}dron and D. Point and D. Acha and S. Bouchet and P.A. Baya and E. Tessier and M. Monperrus and C.I. Molina and A. Groleau and Laurent Chauvaud and J. Thebault and E. Amice and L. Alanoca and C. Duwig and G. Uzu and Lazzaro, Xavier and A. Bertrand and S. Bertrand and C. Barbraud and K. Delord and Gibon, Francois-Marie and C. Ibanez and M. Flores and P. Fernandez Saavedra and M.E. Ezpinoza and C. Heredia and F. Rocha and C. Zepita and D. Amouroux} } @article {5175, title = {Pollution at Cohana Bay, Lake Titicaca (Bolivia): challenges and opportunities to promote its recovery}, journal = {Ecología en Bolivia}, volume = {52}, year = {2017}, month = {September 2017}, pages = {65-76}, issn = {1605-2528}, author = {Molina, Carlos I and Lazzaro, Xavier and Gu{\'e}dron, S and Dar{\'\i}o Ach{\'a}} } @article {4627, title = {Association of a Specific Algal Group with Methylmercury Accumulation in Periphyton of a Tropical High-Altitude Andean Lake}, journal = {Archives of Environmental Contamination and Toxicology}, year = {2016}, pages = {1{\textendash}10}, abstract = {

Periphyton relevance for methylmercury (MeHg) production and accumulation are now well known in aquatic ecosystems. Sulfate-reducing bacteria and other microbial groups were identified as the main MeHg producers, but the effect of periphyton algae on the accumulation and transfer of MeHg to the food web remains little studied. Here we investigated the role of specific groups of algae on MeHg accumulation in the periphyton of Schoenoplectus californicus ssp. (Totora) and Myriophyllum sp. in Uru Uru, a tropical high-altitude Bolivian lake with substantial fishing and mining activities accruing around it. MeHg concentrations were most strongly related to the cell abundance of the Chlorophyte genus Oedogonium (r 2\ =\ 0.783, p\ =\ 0.0126) and to no other specific genus despite the presence of other 34 genera identified. MeHg was also related to total chlorophyll-a (total algae) (r 2\ =\ 0.675, p\ =\ 0.0459), but relations were more significant with chlorophyte cell numbers, chlorophyll-b (chlorophytes), and chlorophyll-c (diatoms and dinoflagellates) (r 2\ =\ 0.72, p\ =\ 0.028, r 2\ =\ 0.744, p\ =\ 0.0214, and r 2\ =\ 0.766, p\ =\ 0.0161 respectively). However, Oedogonium explains most variability of chlorophytes and chlorophyll-c (r 2\ =\ 0.856, p\ =\ \<\ 0.001 and r 2\ =\ 0.619, p\ =\ 0.002, respectively), suggesting it is the most influential group for MeHg accumulation and periphyton algae composition at this particular location and given time.

}, issn = {1432-0703}, doi = {10.1007/s00244-016-0324-2}, url = {http://dx.doi.org/10.1007/s00244-016-0324-2}, author = {Lanza, William G. and Dar{\'\i}o Ach{\'a} and Point, David and Masbou, Jeremy and Alanoca, Lucia and Amouroux, David and Lazzaro, Xavier} } @conference {4385, title = {Comparison of MODIS and LANDSAT-8 retrievals of chlorophyll-a and water temperature over lake Titicaca}, booktitle = {IEEE International Symposium}, year = {2016}, publisher = {Geoscience and Remote Sensing (IGARSS)}, organization = {Geoscience and Remote Sensing (IGARSS)}, address = {10-15 july 2016, Beijing, China}, author = {Ruiz-Verd{\'u}, A and Jim{\'e}nez, JC and Lazzaro, Xavier and Tango, C and Delegido, J and Pereira, M and Sobrino, JA and Moreno, J} }