Chironomid (Insecta: Chironomidae) community structure response to hydrological changes in the mid-1950s in lake Nam Co, Tibetan Plateau

The recent rise in air temperatures detected at high altitudes of the Tibetan Plateau has accelerated glacier melt and retreat. Moreover, enhanced monsoonal precipitation has increased runoff and transport of allochthonous material to the lakes. Consequently, water levels are rising, modifying the spatial distribution and composition of local aquatic biota. To infer these environmental and biological changes in recent decades, a 30-cm-long sediment core, representing the past ~160 years, from Nam Co, an endorheic lake, was analyzed for subfossil chironomid assemblages and sediment geochemistry. In total, 25 chironomid morphotypes were identified. Nineteen were considered as non-rare taxa (abundances ≥2%) and six as rare taxa (abundances <2%). Since 1956 ce, higher chironomid richness (S = 19) is evident compared to the previous 100 years. The simultaneous decrease in the abundance of profundal Micropsectra radialis-type and increase of both Chironomus and Procladius, taxa adapted to more eurytopic and slightly warmer water bodies, indicate increasing water temperatures and intensified primary productivity. The dominance of littoral chironomid assemblages reflects increasing lake water levels, flooded shorelines and expansion of littoral areas driven by increased precipitation and glacial meltwater input both resulting from the increase in air temperatures. This scenario is confirmed by increases in total nitrogen and Zr/Rb ratios, indicating higher productivity and coarser grain size as a consequence of increased runoff via the Niya Qu. These hydrological changes have resulted in a positive water balance that can be linked to an increase in moisture supply from the Indian summer monsoon and glacier melt, reflecting increasing temperatures and precipitation since 1956 ce, ultimately driven by anthropogenic warming

Holocene paleoenvironmental change inferred from two sediment cores collected in the Tibetan lake Taro Co

The Tibetan Plateau, also known as the “Water Tower of Asia” because of its function as a water storage and supply region, responds dramatically to modern climate changes. Paleoecological shifts inferred from lake sediment archives provide essential insights into past climate changes, and the processes that drove those shifts. This is especially true for studies of lakes in endorheic basins on the Tibetan Plateau, where lake level is regulated predominantly by Monsoon intensity. Such water bodies provide excellent opportunities to reconstruct past changes in humidity. Most paleolimnological investigations of lakes on the Tibetan Plateau, however, have involved the study of a single sediment core, making it difficult to discern between changes caused by local events and those caused by lake-wide or regional processes. Here we present results from a paleolimnological study of Lake Taro Co, a currently closed-basin lake in Central Tibet. We compared a sediment record from the central part of the lake to a record from the near-shore area, and present results of sedimentological and bioindicator (chironomid, diatom, pollen) analyses from both records. Results show three periods of lake-wide ecosystem change (> ca. 5250, 5250–2250 and < since about 2250 cal year BP), which reflect a continuous drying trend throughout the Middle and Late Holocene. In addition to this lake-wide trend, we identified two local events in the sediment core from the southeastern, nearshore site. These include (1) a hiatus between 12,400 and 5400 cal year BP and (2) an 1800-year period of distinct paleoenvironmental conditions (5400–3600 cal year BP). We hypothesize that both events were caused by relocation of a river in the southeast sector of the lake’s catchment. We propose that the first relocation caused an erosion event that removed sediment, thereby producing the hiatus. During the following 1800 years, the core site may have been located on the river delta, before another river relocation at 3600 cal year BP established the modern prodelta situation. Our study demonstrates the value of using multiple sediment cores from a lake, to better identify processes that control widespread versus local events.Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347Fellowships for Young International Scientists http://dx.doi.org/10.13039/501100010895NSFC Research Fund for International Young Scientists (CN)Deutsche Forschungsgemeinschaft (DFG) (DE)National Natural Science Foundation of China http://dx.doi.org/10.13039/501100001809Technische Universität Braunschweig (1042

Predictive value of S-100β and neuron-specific enolase serum levels for adverse neurologic outcome after cardiac surgery

AbstractObjectives: The aim of this study was to evaluate the time course of S-100β and neuron-specific enolase serum levels after cardiac surgery and their clinical relevance in predicting postoperative adverse neurologic outcomes; the 2 proteins are only released in peripheral blood in association with nervous system lesions. Methods: We neurologically assessed 190 consecutive patients undergoing elective cardiac operations for coronary artery bypass (n = 147), valve replacement (n = 29), or both (n = 14), before as well as after the operation. Postoperative outcome was classified as type I (uncomplicated), type II (confusion, agitation, disorientation, or epileptic seizures), or type III (stroke, stupor, or coma). Levels of S-100β and neuron-specific enolase were evaluated in venous blood samples drawn preoperatively and then daily in the first 5 postoperative days. Results: Levels of S-100β and neuron-specific enolase differed significantly among the 3 groups (type III > type II > type I) throughout the postoperative period and had a diagnostic specificity and specificity of 89% and 79%, respectively, in identifying patients with type III outcome. S-100β (but not neuron-specific enolase) levels were identified as significant independent predictors for type II and III outcomes (odds ratio 16.2, P < .0004). The same was true for duration of cardiopulmonary bypass (odds ratio 1.02, P < .006). Conclusions: Serum levels of S-100β are reliable markers for adverse neurologic outcomes after cardiac surgery. (J Thorac Cardiovasc Surg 2000;119:138-147

Chironomid (Insecta: Chironomidae) community structure response to hydrological changes in the mid‐1950s in lake Nam Co, Tibetan Plateau

ABSTRACTThe recent rise in air temperatures detected at high altitudes of the Tibetan Plateau has accelerated glacier melt and retreat. Moreover, enhanced monsoonal precipitation has increased runoff and transport of allochthonous material to the lakes. Consequently, water levels are rising, modifying the spatial distribution and composition of local aquatic biota. To infer these environmental and biological changes in recent decades, a 30‐cm‐long sediment core, representing the past ~160 years, from Nam Co, an endorheic lake, was analyzed for subfossil chironomid assemblages and sediment geochemistry. In total, 25 chironomid morphotypes were identified. Nineteen were considered as non‐rare taxa (abundances ≥2%) and six as rare taxa (abundances &lt;2%). Since 1956 ce, higher chironomid richness (S = 19) is evident compared to the previous 100 years. The simultaneous decrease in the abundance of profundal Micropsectra radialis‐type and increase of both Chironomus and Procladius, taxa adapted to more eurytopic and slightly warmer water bodies, indicate increasing water temperatures and intensified primary productivity. The dominance of littoral chironomid assemblages reflects increasing lake water levels, flooded shorelines and expansion of littoral areas driven by increased precipitation and glacial meltwater input both resulting from the increase in air temperatures. This scenario is confirmed by increases in total nitrogen and Zr/Rb ratios, indicating higher productivity and coarser grain size as a consequence of increased runoff via the Niya Qu. These hydrological changes have resulted in a positive water balance that can be linked to an increase in moisture supply from the Indian summer monsoon and glacier melt, reflecting increasing temperatures and precipitation since 1956 ce, ultimately driven by anthropogenic warming.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/50110000165

High‐throughput identification of non‐marine Ostracoda from the Tibetan Plateau: Evaluating the success of various primers on sedimentary DNA samples

Abstract Dwelling in a variety of aquatic habitats, one of the most abundant groups of microcrustaceans, ostracodes, are widely used indicator organisms in paleolimnological research. Typically, they are identified via traditional methods using morphological features but this may be excessively time‐consuming and prone to inter‐investigator variation. DNA barcoding and metabarcoding have become important tools for specimen identification, with a great impact in the field of taxonomy, (paleo‐)ecology and evolution. Despite its potential, metabarcoding has been rarely used to analyze the community structure of ostracodes. Here, we evaluate the performance of a metabarcoding approach for ostracode identification in surface sediment samples collected from Lake Nam Co on the Tibetan Plateau. We tested six different primer pairs amplifying fragments of three different genes, and compared their success in inferring ostracode communities, coupled with morphological identification of ostracodes from the same sediment samples. In total, depending on the primer pair used, seven to nineteen ostracode amplicon sequence variants (ASVs) were identified. Via microscopy, eight morphospecies were identified. We found considerable differences between primer pairs in yielding ostracode sequences via metabarcoding. In general, the highest proportions of ostracode reads and ASVs were found with primers amplifying fragments of the 18S rRNA gene, whereas primers for COI gene had the highest in silico amplification success and highest sequencing depth per sample but only contained <1% of ostracode sequences. As a consequence, the metabarcoding results with 18S rRNA gene were more consistent with the morphological data compared to those obtained with COI or mitochondrial 16S rRNA primers. No significant effects of treatment with different sediment quantities for DNA extraction (10 g vs. 0.5 g) were found on ostracode ASVs community composition. These results indicate that DNA metabarcoding can serve as an efficient tool for ostracode‐based environmental reconstructions but requires an informed decision on primers and target gene, as well as extending the barcoding database for improved accuracy

High‐throughput identification of non‐marine Ostracoda from the Tibetan Plateau: Evaluating the success of various primers on sedimentary DNA samples

Dwelling in a variety of aquatic habitats, one of the most abundant groups of microcrustaceans, ostracodes, are widely used indicator organisms in paleolimnological research. Typically, they are identified via traditional methods using morphological features but this may be excessively time-consuming and prone to inter-investigator variation. DNA barcoding and metabarcoding have become important tools for specimen identification, with a great impact in the field of taxonomy, (paleo-)ecology and evolution. Despite its potential, metabarcoding has been rarely used to analyze the community structure of ostracodes. Here, we evaluate the performance of a metabarcoding approach for ostracode identification in surface sediment samples collected from Lake Nam Co on the Tibetan Plateau. We tested six different primer pairs amplifying fragments of three different genes, and compared their success in inferring ostracode communities, coupled with morphological identification of ostracodes from the same sediment samples. In total, depending on the primer pair used, seven to nineteen ostracode amplicon sequence variants (ASVs) were identified. Via microscopy, eight morphospecies were identified. We found considerable differences between primer pairs in yielding ostracode sequences via metabarcoding. In general, the highest proportions of ostracode reads and ASVs were found with primers amplifying fragments of the 18S rRNA gene, whereas primers for COI gene had the highest in silico amplification success and highest sequencing depth per sample but only contained <1% of ostracode sequences. As a consequence, the metabarcoding results with 18S rRNA gene were more consistent with the morphological data compared to those obtained with COI or mitochondrial 16S rRNA primers. No significant effects of treatment with different sediment quantities for DNA extraction (10 g vs. 0.5 g) were found on ostracode ASVs community composition. These results indicate that DNA metabarcoding can serve as an efficient tool for ostracode-based environmental reconstructions but requires an informed decision on primers and target gene, as well as extending the barcoding database for improved accuracy

Sub-fossil chironomids as indicators of hydrological changes in the shallow and high-altitude lake Shen Co, Tibetan Plateau, over the past two centuries

Understanding climate and monsoonal dynamics on the Tibetan Plateau is crucial, as recent hydrological changes, evidenced by rising lake levels, will be accelerated by current global warming and may alter aquatic habitats and species inventories. This study combines chironomid assemblages with sedimentological, mineralogical and geochemical data of a short sediment core (37.5 cm) from the high-altitude (> 4,733 m asl), saline (9 g L-1) and shallow (~5 m water depth) Shen Co, located in the southern part of the central Tibetan Plateau. The predominantly littoral, species-poor (10 chironomid morphotypes) chironomid assemblages are dominated by salt-tolerant taxa, that are highly sensitive to lake level fluctuations and macrophyte vegetation dynamics, making them ideally suited for tracking lake level changes over time. Results indicate a period (from ca. 1830 to 1921 CE) of drier conditions with low runoff and high evaporation rates in the Shen Co catchment, as indicated by a dominance of low-Mg calcite and dolomite and increased Ca/Fe and Sr/Rb ratios. This resulted in a decline in lake levels, an increase in salinity and the periodic occurrence of desiccation events at the sampling site. The first chironomid morphotype to appear after the dry period is Acricotopus indet. morphotype incurvatus, which indicate still low (<2 m) but rising lake levels after 1921 CE due to increasing runoff and a lower evaporation/precipitation ratio, as reflected by coarser grain size, higher quartz content and increased TN, TOC and Al/Si ratios. A replacement of A. indet. morphotype incurvatus by Procladius is observed as lake level rise continued after 1950 CE. The highest lake level is proposed for the period since 2006 CE. From 1955 to 1960 CE and from 2011 to 2018 CE, the presence of the phytophilic taxon Psectrocladius sordidellus-type supported abundant macrophyte growth. These changes are consistent with climate reconstructions from the northern and central Tibetan Plateau, indicating warmer and wetter climate conditions since the beginning of the 20th century, which have led to an increase in lake level in a number of Tibetan lakes. Our study specifically highlights 1920 and 1950 as years with enhanced precipitation. This can be attributed to the strong, with overlapping multidecadal cycles of Westerlies and monsoon systems. This study demonstrates the significance of studying small, shallow lakes, as they frequently contain aquatic communities that respond more rapidly to the changes in the lake system. In addition, this study expands our understanding of the ecology of Tibetan chironomid morphotypes, highlighting this group’s potential as paleolimnological proxies for investigating past environmental and climatic changes

Compatibility of Diatom Valve Records With Sedimentary Ancient DNA Amplicon Data: A Case Study in a Brackish, Alkaline Tibetan Lake

Lake sediments represent valuable and widely used archives for tracking environmental and biotic changes over time. Past aquatic communities are traditionally studied via morphological identification of the remains of organisms. However, molecular identification tools, such as DNA metabarcoding, have revolutionized the field of biomonitoring by enabling high-throughput and fast identification of organisms from environmental samples (e.g., sediments and soil). Sedimentary ancient DNA (sedaDNA) metabarcoding, an approach to track the biodiversity of target organisms from sediment cores, spanning thousands of years, has been successfully applied in many studies. However, researchers seldom explore how well the signals from sedaDNA data correlate with the fossil records of target organisms. This information is essential to infer past environmental conditions and community changes of bioindicators when the increasingly popular molecular identification method, metabarcoding, is desired instead of a morphological identification approach. In this study, we explore the correlations of diatom valve records across the last ∼940 years with the diatom sedaDNA metabarcoding data from the same sediment core from lake Nam Co (Tibetan Plateau). Overall, the results from valve vs. sedaDNA data revealed concordant diatom richness as well as community patterns. However, several mismatches in the diatom taxonomic composition existed between the data sets. In general, sedaDNA data harbored much higher diatom diversity, but due to the lack of reference sequences in public databases, many molecular units (amplicon sequence variants) remained unclassified to lower taxonomic levels. As our study lake, Nam Co, is characterized by brackish water and alkaline pH, some likely cases for the observed taxonomic composition mismatches may be due to a valve dissolution issue. Nevertheless, significant drivers for the diatom richness and community structure largely corresponded between data sets. Both valve and sedaDNA data demonstrated similar breakpoints for historical diatom community shifts. A particularly strong shift in the diatom community structure occurred after ∼1950 CE, which may be associated with abrupt environmental changes on the Tibetan Plateau. Altogether, our study indicates that environmentally driven signals reflected by the diatom communities are successfully recovered via microfossil as well as molecular identification methods