8 research outputs found
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Coexisting ecosystem states in a tropical coastal lagoon under progressive eutrophication in the northern Cuban keys
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
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Towards the construction of a carbon fluxes inventory of tropical waters: A unifying method pipeline
The relevance of inland waters in the global carbon cycle has been stressed recently, particularly because of a reassessment of their capacity for carbon exportation to the atmosphere and to the sediments. Global surveys have also highlighted the acute lack of information on tropical systems, which are exposed to crescent problems in the Global Change panorama, such as contamination and eutrophication, as well as important impacts related to water management strategies and water supply (e.g., water level fluctuations). Oxygen dynamics, a method left behind in the past, has been revised and is now being increasingly implemented to estimate primary production and ecosystemic respiration due to the urgency to understand carbon fluxes in aquatic systems. Therefore the details (advantages and disadvantages) of modern implementation of oxygen dynamics are revised and discussed here, particularly oriented to facilitate and promote their aplication in tropical aquatic systems (where it seems an adequate strategy). We suggest a unifying method pipeline in order to obtain comparable results among systems, towards the construction of a carbon flux inventory at larger (spatial and temporal) scales. This effort would contribute to understand the role and responses of tropical aquatic systems and regions (particularly as carbon sources or sinks) facing Global Change
Towards the construction of a carbon fluxes inventory of tropical waters: A unifying method pipeline
The relevance of inland waters in the global carbon cycle has been stressed recently, particularly because of a reassessment of their capacity for carbon exportation to the atmosphere and to the sediments. Global surveys have also highlighted the acute lack of information on tropical systems, which are exposed to crescent problems in the Global Change panorama, such as contamination and eutrophication, as well as important impacts related to water management strategies and water supply (e.g., water level fluctuations). Oxygen dynamics, a method left behind in the past, has been revised and is now being increasingly implemented to estimate primary production and ecosystemic respiration due to the urgency to understand carbon fluxes in aquatic systems. Therefore the details (advantages and disadvantages) of modern implementation of oxygen dynamics are revised and discussed here, particularly oriented to facilitate and promote their aplication in tropical aquatic systems (where it seems an adequate strategy). We suggest a unifying method pipeline in order to obtain comparable results among systems, towards the construction of a carbon flux inventory at larger (spatial and temporal) scales. This effort would contribute to understand the role and responses of tropical aquatic systems and regions (particularly as carbon sources or sinks) facing Global Change
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Genetic diversity associated with N-cycle pathways in microbialites from Lake Alchichica, Mexico
Microbialites are an example of complex and diverse microbial assemblages where several metabolic pathways are interconnected for biomass formation coupled to mineral precipitation. Lake Alchichica (Mexico) is an oligotrophic environment where nitrogen (N) and phosphorus alternately limit productivity, and massive microbialite growths are found along the lake's perimeter. Previous studies have described the importance of N fixation in these microbialites, although other pathways associated with the N cycle, including denitrification, nitrification and anaerobic ammonium oxidation (anammox), had not been evaluated. This study identified the genetic diversity associated with N cycling in both metagenomic DNA and RNA expression by targeting key genes for nitrogenase (nifH), ammonia monooxygenase (amoA), nitrite oxidoreductase (nxrA, nxrB), hydrazine oxidoreductase (hzo) and nitrite (nirS and nirK) and nitrous oxide (nosZ) reductases. While the genetic potential for N fixation, ammonia oxidation, anammox and denitrification was present in the microbialites of Lake Alchichica, the most transcribed pathway was N fixation. 2 2
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Genetic diversity associated with N-cycle pathways in microbialites from Lake Alchichica, Mexico
Microbialites are an example of complex and diverse microbial assemblages where several metabolic pathways are interconnected for biomass formation coupled to mineral precipitation. Lake Alchichica (Mexico) is an oligotrophic environment where nitrogen (N) and phosphorus alternately limit productivity, and massive microbialite growths are found along the lake's perimeter. Previous studies have described the importance of N2 fixation in these microbialites, although other pathways associated with the N cycle, including denitrification, nitrification and anaerobic ammonium oxidation (anammox), had not been evaluated. This study identified the genetic diversity associated with N cycling in both metagenomic DNA and RNA expression by targeting key genes for nitrogenase (nifH), ammonia monooxygenase (amoA), nitrite oxidoreductase (nxrA, nxrB), hydrazine oxidoreductase (hzo) and nitrite (nirS and nirK) and nitrous oxide (nosZ) reductases. While the genetic potential for N2 fixation, ammonia oxidation, anammox and denitrification was present in the microbialites of Lake Alchichica, the most transcribed pathway was N2 fixation
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Vertical boundary mixing events during stratification govern heat and nutrient dynamics in a windy tropical reservoir lake with important water-level fluctuations: A long-term (2001–2021) study
Physical processes play important roles in controlling eutrophication and oligotrophication. In stratified lakes, internal waves can cause vertical transport of heat and nutrients without breaking the stratification, through boundary mixing events. Such is the case in tropical Valle de Bravo (VB) reservoir lake, where strong diurnal winds drive internal waves, boundary mixing, and hypolimnetic warming during stratification periods. We monitored VB during 21 years (2001–2021) when important water-level fluctuations occurred, affecting mixing and nutrient flux. Stability also varied as a function of water level. Hypolimnetic warming (0.009–0.028◦ C day−1) occurred in all the stratifications monitored. We analyzed temperature distributions and modeled the hypolimnion heat budget to assess vertical mixing between layers (0.639–3.515 × 10−6 m3 day−1), vertical diffusivity coefficient KZ (2.5 × 10−6 –13.6 × 10−6 m2 s−1), and vertical nutrient transport to the epilimnion. Nutrient flux from the metalimnion to the epilimnion ranged 0.42–5.99 mg P m−2 day−1 for soluble reactive phosphorus (SRP) and 5.8–101.7 mg N m−2 day−1 for dissolved inorganic nitrogen (DIN). Vertical mixing and the associated nutrient fluxes increase evidently as the water level decreases 8 m below capacity, and they can increase up to fivefold if the water level drops over 12 m. The observed changes related to water level affect nutrient recycling, ecosystemic metabolic balance, and planktonic composition of VB