Estados ecosistémicos coexistentes en una laguna costera tropical bajo eutrofización creciente en la cayería norte de Cuba

Through a nested suite of methods here we contrast the coexistence of different ecosystem states in a tropical coastal lagoon, the Laguna Larga, with increasing eutrophication stress between 2007 and 2009. Water temperature averaged 27.4°C in the lagoon and showed a slight positive trend during the study period. Salinity averaged 35.0±6.2, exhibiting high spatial and temporal variability, and also a slight positive trend in time. In contrast, dissolved oxygen showed a substantial decreasing trend (–0.83 ml L–1 y–1; –13.3% y–1) over the period, while nutrients increased dramatically, particularly total phosphorus (2.6 µM y–1), in both cases sustaining the progression of eutrophication in the lagoon during the three years we sampled. The Karydis nutrient load-based trophic index showed that the lagoon has a spatial pattern of increasing eutrophication from the sea and the outer sector (oligotrophic-mesotrophic) to the central (mesotrophic) and the inner sector (mesotrophic-eutrophic). Two ecosystem states were found within the lagoon. In the outer oligotrophic sector, the dominant primary producers were macroalgae, seagrasses and benthic diatoms, while mollusc assemblages were highly diverse. In the inner and central sectors (where trophic status increased toward the inner lagoon) a phytoplankton-dominated ecosystem was found where mollusc assemblages are less diverse. In spite of the progression of eutrophication in the lagoon, these two different ecosystems coexisted and remained unchanged during the study period. Apparently, the effect of water residence time, which increases dramatically toward the inner lagoon, dominated over that of nutrient loadings, which is relatively more homogeneously distributed along the lagoon. Therefore, we consider that actions that reduce the water residence time are likely the most effective management options for this and other similarly choked lagoons.Mediante la conjunción de una diversidad de métodos y observaciones, se contrasta la coexistencia de diferentes estados ecosistémicos en Laguna Larga, una laguna costera tropical sometida a una eutrofización creciente entre 2007 y 2009. La temperatura media en la laguna fue de 27.4°C y mostró una ligera tendencia positiva en este periodo. La salinidad mostró alta variabilidad espacial y temporal alrededor de una media de 35.0±6.2 y también tuvo una tendencia temporal positiva. En contraste, el oxígeno disuelto mostró una sustancial tendencia negativa (–0.83 ml L–1 y–1; –13.3% y–1) en el mismo periodo, al tiempo que los nutrientes se incrementaron drásticamente, en particular el fósforo total, a una tasa de 2.6 µM y–1, respaldando ambas tendencias el incremento de la eutrofización a lo largo de los tres años observados. El índice trófico de Karydis, basado en las cargas de nutrientes, mostró un patrón espacial de incremento de la eutrofización desde el mar hacia el sector exterior (oligotrófico-mesotrófico), el sector central (mesotrófico) y el sector interior (mesotrófico-eutrófico). Se identificaron dos estados ecosistémicos dentro de la laguna. En el oligotrófico sector exterior, los productores primarios dominantes fueron macroalgas, pastos marinos y diatomeas bénticas, en tanto que las asociaciones de moluscos fueron altamente diversas. En los sectores central e interior (incrementándose el estatus trófico hacia este último), se encontró un estado ecosistémico dominado por el fitoplancton y en el que las asociaciones de moluscos son menos diversas. A pesar del incremento de la eutrofización, estos dos ecosistemas distintos coexistieron y permanecieron sin cambios durante el periodo estudiado. En Laguna Larga, el efecto del tiempo de residencia del agua, que se incrementa dramáticamente hacia el interior de la laguna, domina aparentemente sobre el de la carga externa de nutrientes, que está distribuida de manera relativamente más homogénea a lo largo de la laguna. Por ello, consideramos que las acciones dirigidas a disminuir el tiempo de residencia del agua son probablemente las más efectivas en esta laguna y otras similarmente aisladas

Nitrogen and Phosphorous Retention in Tropical Eutrophic Reservoirs with Water Level Fluctuations: A Case Study Using Mass Balances on a Long-Term Series

Nitrogen and phosphorous loading drives eutrophication of aquatic systems. Lakes and reservoirs are often effective N and P sinks, but the variability of their biogeochemical dynamics is still poorly documented, particularly in tropical systems. To contribute to the extending of information on tropical reservoirs and to increase the insight on the factors affecting N and P cycling in aquatic ecosystems, we here report on a long-term N and P mass balance (2003–2018) in Valle de Bravo, Mexico, which showed that this tropical eutrophic reservoir lake acts as a net sink of N (−41.7 g N m y) and P (−2.7 g P m y), mainly occurring through net sedimentation, equivalent to 181% and 68% of their respective loading (23.0 g N m y and 4.2 g P m y). The N mass balance also showed that the Valle de Bravo reservoir has a high net N atmospheric influx (31.6 g N m y), which was 1.3 times the external load and likely dominated by N fixation. P flux was driven mainly by external load, while in the case of N, net fixation also contributed. During a period of high water level fluctuations, the net N atmospheric flux decreased by 50% compared to high level years. Our results outlining water regulation can be used as a useful management tool of water bodies, by decreasing anoxic conditions and net atmospheric fluxes, either through decreasing nitrogen fixation and/or promoting denitrification and other microbial processes that alleviate the N load. These findings also sustain the usefulness of long-term mass balances to assess biogeochemical dynamics and its variability.This research was funded by UNAM, PAPIIT-IN207702 and CONACYT-SEMARNAT, C01-1125 projects to M.M-

Supplement: "Localization and broadband follow-up of the gravitational-wave transient GW150914" (2016, ApJL, 826, L13)

This Supplement provides supporting material for Abbott et al. (2016a). We briefly summarize past electromagnetic (EM) follow-up efforts as well as the organization and policy of the current EM follow-up program. We compare the four probability sky maps produced for the gravitational-wave transient GW150914, and provide additional details of the EM follow-up observations that were performed in the different bands

The Helicobacter pylori Genome Project : insights into H. pylori population structure from analysis of a worldwide collection of complete genomes

Helicobacter pylori, a dominant member of the gastric microbiota, shares co-evolutionary history with humans. This has led to the development of genetically distinct H. pylori subpopulations associated with the geographic origin of the host and with differential gastric disease risk. Here, we provide insights into H. pylori population structure as a part of the Helicobacter pylori Genome Project (HpGP), a multi-disciplinary initiative aimed at elucidating H. pylori pathogenesis and identifying new therapeutic targets. We collected 1011 well-characterized clinical strains from 50 countries and generated high-quality genome sequences. We analysed core genome diversity and population structure of the HpGP dataset and 255 worldwide reference genomes to outline the ancestral contribution to Eurasian, African, and American populations. We found evidence of substantial contribution of population hpNorthAsia and subpopulation hspUral in Northern European H. pylori. The genomes of H. pylori isolated from northern and southern Indigenous Americans differed in that bacteria isolated in northern Indigenous communities were more similar to North Asian H. pylori while the southern had higher relatedness to hpEastAsia. Notably, we also found a highly clonal yet geographically dispersed North American subpopulation, which is negative for the cag pathogenicity island, and present in 7% of sequenced US genomes. We expect the HpGP dataset and the corresponding strains to become a major asset for H. pylori genomics