Assessing the impact of long-term changes in climate and atmospheric deposition on a shallow alpine lake from southeast Tibet.

Regional warming and atmospheric nitrogen deposition have been widely recorded to impact remote catchments and alpine lakes; however, their independent roles and interactions have rarely been identified. Here, we combined down-core analyses of sedimentary mercury (Hg) and aluminum (Al) with multiple proxies (i.e. nitrogen stable isotope, chlorophyll a pigments, diatoms) for a radiometrically-dated sediment core of an alpine lake in southeast Tibet to track the atmospheric deposition of pollutants, and to examine possible effects of climate and catchment forcing over the past three centuries. The sediment data revealed that airborne deposition of Hg was recorded from the ~1860s, with an accelerating increase in anthropogenic Hg flux since the ~1960s. A synchronous decrease in reconstructed lake-water TOC indicated that acid deposition may have affected lake-water carbon concentrations and impaired catchment export of decomposed organic matter (OM). A moderate depletion of bulk sediment δ15N started from the ~1820s, but was followed by an enriching trend after the ~1970s. This positive shift of δ15N was associated with elevated sediment OM and decreased catchment runoff of clastic materials (as inferred by Al). Sediment OM content displayed an accelerating increase from the ~1960s, with an increased input of autochthonous sources (i.e. lower bulk sediment C:N ratios), such as algae (as inferred by sedimentary chlorophyll a pigments). Meanwhile, climate warming and decreased lake-water TOC enhanced the production of algae, which was characterized by a more enriched δ15N signal than that of allochthonous OM. Furthermore, atmospheric acid deposition was significantly related to diatom assemblage changes, with an increase in acidophilous taxa. Our sediment evidence revealed the dominating impact of climate and catchment processes on lake-water chemistry and algal shifts in the context of atmospheric nitrogen deposition, and highlighted an increasing link of external forcing with in-lake processes in enriching sediment δ15N signal over the last few decades.

Effectiveness of Secundum Atrial Septal Defect Occlusion with the Septal Occluder through Right-chest Small Incision: Clinical Analysis of 140 Cases.

Objective To evaluate the feasibility and effectiveness of secundum atrial septal defect(ASD)occlusion with the septal occluder through right-chest small incision. Methods The clinical data of 140 secundum ASD patients (47 males and 93 females) aged 3-63 years who were treated in our center from August 2004 to July 2014 were retrospectively analyzed. The diameter of ASD was 6 to 36 mm. Under general anesthesia, all patients underwent intraoperative transtsophageal echocardiography (TEE), during which no associated cardiac deformity was found. All patients received ASD occlusion via a small incision (3-4 cm) at the right anterior chest. The occluders were released with the help of TEE. Results The atrial septal defect closure was successfully completed in 134 cases. Six cases received surgical closure of ASD after the failure of occlusion. The reasons of conversion included postoperative dislodgement of occlusion device (n=2, both were central type with large size) and technically unsuitable for occlusion (n=4, in whom residual shunt was found in 2 case, sieve pore type in 1 case, and intraoperative dislodgement in 1 case). All of these 6 patients were treated surgically under cardiopulmonary bypass. No dislocation of the device or atrial shunt was found within 3 to 48 months after the operation. Conclusion Occlusion via small chest incision of ASD under TEE guidance without cardiopulmonary bypass is a safe, minimally invasive, effective, and convenient treatment and worth clinical application.

[Long-term pattern of diatom community structure changes in response to multiple environmental stressors at Datun Lake, Southeast Yunnan, China].

Subtropical plateau lakes in Southeast Yunnan are known to have experienced multiple environmental stressors (lake pollution, eutrophication, land reclamation and droughts) during the past decades. Here, we applied multi-proxy analyses (i.e., diatom, grain size, C and N isotopic and chronology) of lake sediments, aiming to track the history of lake environment change and the characteristics of diatom community responses in Datun Lake for the past century. The results proved that the sedimentary diatom community records showed significant changes with the replacement of Fragilaria construens by Achnanthes minutissima. Combining with multiple-proxy records (i.e., isotopic data) and modern monitoring records, the ordination analyses and variation partitioning further suggested that industrial pollution and eutrophication were the major driving factors that led to the long-term shift of diatom community. In addition, the grain size results and meteorological data revealed that the reductions in hydrodynamic and water exchange intensity associated with damming and the occurrence of extreme droughts, thus led to the corresponding diatom community change.

Industrial arsenic contamination causes catastrophic changes in freshwater ecosystems.

Heavy metal pollution is now widely recognized to pose severe health and environmental threats, yet much of what is known concerning its adverse impacts on ecosystem health is derived from short-term ecotoxicological studies. Due to the frequent absence of long-term monitoring data, little is known of the long-tem ecological consequences of pollutants such as arsenic. Here, our dated sediment records from two contaminated lakes in China faithfully document a 13.9 and 21.4-fold increase of total arsenic relative to pre-1950 background levels. Concurrently, coherent responses in keystone biota signal pronounced ecosystem changes, with a >10-fold loss in crustacean zooplankton (important herbivores in the food webs of these lake systems) and a >5-fold increase in a highly metal-tolerant alga. Such fundamental ecological changes will cascade through the ecosystem, causing potentially catastrophic consequences for ecosystem services in contaminated regions.