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Monitoring plastic litter in the environment is critical to understanding the amount, sources, transport, fate, and environmental impact of this pollutant. However, few studies have monitored plastic litter on lakebeds which are potentially important environments for determining the fate and transport of plastic litter in freshwater basins. In this study, a self-contained underwater breathing apparatus was used for litter collection at the lakebed along five transects in Lake Tahoe, United States. Litter was brought to the surface and characterized by litter type. Plastic litter was subsampled, and polymer composition was determined using attenuated total reflection Fourier transform infrared spectroscopy. The average plastic litter from the lakebed for the five dive transects was 83 ± 49 items per kilometer. The top plastic litter categories were other plastic litter (plastic litter that did not fall in another category), followed by food containers, bottles <2 L, plastic bags, and toys. These results are in line with prior studies on submerged litter, and intervention approaches or ongoing education are needed. The six polymers most frequently detected in the subsamples were polyvinyl chloride, polystyrene/expanded polystyrene, polyethylene terephthalate/polyester, polyethylene, polypropylene, and polyamide. These observations reflect global plastic production and microplastic studies from lake surface water and sediments. We found that some litter subcategories were primarily comprised of a single polymer type, therefore, in studies where the polymer type cannot be measured but litter is categorized, these results could provide an estimate of the total polymer composition for select litter categories.

 

Anthropogenic climate change—combined with increased human-caused ignitions—is leading to increased wildfire frequency, carbon dioxide emissions, and refractory black carbon (rBC) aerosol emissions. This is particularly evident in the Amazon rainforest, where fire activity has been complicated by the synchronicity of natural and anthropogenic drivers of ecological change, coupled with spatial and temporal heterogeneity in past and present land use. One approach to elucidating these factors is through long-term regional fire histories. Using a novel method for rBC determinations, we measured an approximately 3500-year sediment core record from Lake Caranã in the eastern Amazon for rBC influx, a proxy of biomass burning and fossil fuel combustion. Through comparisons with previously published records from Lake Caranã and regional evidence, we distinguished between local and regional rBC emission sources demonstrating increased local emissions of rBC from ~1250 to 500 calendar years before present (cal yr BP), coinciding with increased local-scale fire management during the apex of pre-Columbian activity. This was followed by a regional decline in biomass burning coincident with European contact, pre-Columbian population decline, and regional fire suppression associated with the rubber boom (1850–1910 CE), supporting the minimal influence of climate on regional burning at this time. During the past century, rBC influx has rapidly increased. Our results can serve to validate rBC modeling results, aiding with future predictions of rBC emissions and associated impacts to the climate system. 

A cave‐monitoring study in Hatchet Bay Cave on the island of Eleuthera, Bahamas, has examined the origins of variations in oxygen and carbon isotopic and minor element composition in cave calcites. Every 3 to 8 months, between 2012 and 2016, temperature, humidity, cave air (δ¹³C_CO2), dripwaters (δ¹⁸O and δ²H values, and Ca, Sr, and Mg concentrations), and the chemical composition of precipitating calcite (δ¹⁸O and δ¹³C values, and Ca, Sr, and Mg concentrations) were analyzed in two rooms in the cave. Results from the elemental analyses show that throughout the cave prior calcite precipitation was a driver of the elemental chemistry of the precipitated calcites. In addition, cave calcites show that δ¹³C and δ¹⁸O values were positively correlated with Mg/Ca ratios. The Mg/Ca ratios were also positively correlated with lower calcite precipitation rates. Therefore, water/rock interactions may also influence δ¹³C and δ¹⁸O values and Mg/Ca ratios of the calcite. Differences were observed between the two rooms, with the Main Room of the cave exhibiting increased prior calcite precipitation, more ventilation, lower calcite precipitation rates, and δ¹⁸O values, which were farther from equilibrium when compared to the more isolated portion of the cave. These results also validated previous interpretations from Pleistocene stalagmites collected from a nearby Bahamian cave suggesting that a positive covariation between Mg/Ca and δ¹³C values reflects water/rock interactions.