@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 {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} } @article {4280, title = {Trans-Amazonian natal homing in giant catfish}, journal = {Journal of Applied Ecology}, volume = {53}, year = {2016}, pages = {1511-1520}, abstract = {

1.Knowledge of fish migration is a prerequisite to sustainable fisheries management and preservation, especially in large international river basins. In particular, understanding whether a migratory lifestyle is compulsory or facultative, and whether adults home to their natal geographic area is paramount to fully appraise disruptions of longitudinal connectivity resulting from damming.2.In the Amazon, the large migratory catfishes of the Brachyplatystoma genus are apex predators of considerable interest for fisheries. They are believed to use the entire length of the basin to perform their life cycle, with hypothesized homing behaviours. Here we tested these hypotheses, using the emblematic B. rousseauxii as a model species.3.We sampled adults close to major breeding areas in the Amazon basin (upper Madeira and upper Amazonas) and assessed their lifetime movements by measuring variations in 87Sr/86Sr along transverse sections of their otoliths (ear stones) using laser ablation multicollector mass spectrometry (LA-MC-ICPMS).4.We demonstrate that larvae migrate downstream from the Andean piedmont to the lower Amazon, where they grow over a protracted period before migrating upstream as adults. Contrary to prevailing inferences, not all fish spend their nursery stages in the Amazon estuary. By contrast, the passage in the lower or central Amazon seems an obligate part of the life cycle. We further evidence that most adults home to their natal geographic area within the Madeira sub-basin. Such long-distance natal homing is exceptional in purely freshwater fishes.5.Synthesis and applications. By using otolith microchemistry, we were able to demonstrate a seemingly compulsory basin-wide migratory life cycle of large Amazonian catfishes. This makes them the organisms performing the longest migrations (\>8000 km) in fresh waters. This exceptional life history is already jeopardized by two dams recently built in the Madeira River, which block a major migration route and access to a substantial part of their spawning grounds. Major impacts can be anticipated from the current and forthcoming hydroelectric development in the Amazon basin, not only on the populations and fisheries of this apex predator, but also on Amazonian food webs through trophic cascades.This article is protected by copyright. All rights reserved.

}, keywords = {87Sr/86Sr ratios, Amazon, anthropogenic activities, Brachyplatystoma spp, freshwater fish, giant catfish, hydroelectric dams, Migration, otoliths}, issn = {1365-2664}, doi = {10.1111/1365-2664.12665}, url = {http://dx.doi.org/10.1111/1365-2664.12665}, author = {Fabrice Duponchelle and Marc Pouilly and Pecheyran, Christophe and Hauser, Marilia and Renno, Jean-Francois and Panfili, Jacques and Darnaude, Audrey M. and Garc{\'\i}a-Vasquez, Aurea and Carvajal-Vallejos, Fernando and Carmen Garc{\'\i}a-D{\'a}vila and Doria, Carolina and B{\'e}rail, Sylvain and Donard, Ariane and Sondag, Francis and Santos, Roberto V. and Jesus Nu{\~n}ez-Rodriguez and Point, David and Labonne, Maylis and Baras, Etienne} } @article {3326, title = {Geographical origin of Amazonian freshwater fishes fingerprinted by $^{8}$$^{7}$Sr/$^{8}$$^{6}$Sr ratios on fish otoliths and scales.}, journal = {Environ Sci Technol}, volume = {48}, year = {2014}, month = {2014 Aug 19}, pages = {8980-7}, abstract = {

Calcified structures such as otoliths and scales grow continuously throughout the lifetime of fishes. The geochemical variations present in these biogenic structures are particularly relevant for studying fish migration and origin. In order to investigate the potential of the (87)Sr/(86)Sr ratio as a precise biogeochemical tag in Amazonian fishes, we compared this ratio between the water and fish otoliths and scales of two commercial fish species, Hoplias malabaricus and Schizodon fasciatus, from three major drainage basins of the Amazon: the Madeira, Solim{\~o}es, and Tapaj{\'o}s rivers, displaying contrasted (87)Sr/(86)Sr ratios. A comparison of the (87)Sr/(86)Sr ratios between the otoliths and scales of the same individuals revealed similar values and were very close to the Sr isotopic composition of the local river where they were captured. This indicates, first, the absence of Sr isotopic fractionation during biological uptake and incorporation into calcified structures and, second, that scales may represent an interesting nonlethal alternative for (87)Sr/(86)Sr ratio measurements in comparison to otoliths. Considering the wide range of (87)Sr/(86)Sr variations that exist across Amazonian rivers, we used variations of (87)Sr/(86)Sr to discriminate fish origin at the basin level, as well as at the sub-basin level between the river and savannah lakes of the Beni River (Madeira basin).

}, issn = {1520-5851}, doi = {10.1021/es500071w}, author = {Marc Pouilly and Point, David and Sondag, Francis and Henry, Manuel and Santos, Roberto V} }