Trace elements sustain biological productivity, yet the significance of trace element mobilization and export in subglacial runoff from ice sheets is poorly constrained at present. Here, we present ...size-fractionated (0.02, 0.22, and 0.45 μm) concentrations of trace elements in subglacial waters from the Greenland Ice Sheet (GrIS) and the Antarctic Ice Sheet (AIS). Concentrations of immobile trace elements (e.g., Al, Fe, Ti) far exceed global riverine and open ocean mean values and highlight the importance of subglacial aluminosilicate mineral weathering and lack of retention of these species in sediments. Concentrations are higher from the AIS than the GrIS, highlighting the geochemical consequences of prolonged water residence times and hydrological isolation that characterize the former. The enrichment of trace elements (e.g., Co, Fe, Mn, and Zn) in subglacial meltwaters compared with seawater and typical riverine systems, together with the likely sensitivity to future ice sheet melting, suggests that their export in glacial runoff is likely to be important for biological productivity. For example, our dissolved Fe concentration (20,900 nM) and associated flux values (1.4 Gmol y−1) from AIS to the Fe-deplete Southern Ocean exceed most previous estimates by an order of magnitude. The ultimate fate of these micronutrients will depend on the reactivity of the dominant colloidal size fraction (likely controlled by nanoparticulate Al and Fe oxyhydroxide minerals) and estuarine processing. We contend that ice sheets create highly geochemically reactive particulates in subglacial environments, which play a key role in trace elemental cycles, with potentially important consequences for global carbon cycling.
Synthetic fertilizer is a potential source of uranium to natural waters, yet evidence is lacking. We analyzed dissolved uranium concentrations in lakes, reservoirs, and rivers in Ohio, USA during the ...summer of 2017. All water bodies drain areas of extensive agriculture where phosphate-rich fertilizer is applied. Uranium concentrations ranged from 0.3 to 3.9 µg L
, with the lowest concentrations observed in the most offshore Lake Erie samples. These results, especially when placed in the context of previous work on both surface and groundwater, suggest that dissolved uranium concentrations in this water emanating from agricultural lands are higher than background, and uranium should be categorized similarly to nitrate and phosphate in that it originates in part from fertilizer application.
Patterns of environmental spatial structure lie at the heart of the most fundamental and familiar patterns of diversity on Earth. Antarctica contains some of the strongest environmental gradients on ...the planet and therefore provides an ideal study ground to test hypotheses on the relevance of environmental variability for biodiversity. To answer the pivotal question, "How does spatial variation in physical and biological environmental properties across the Antarctic drive biodiversity?" we have synthesized current knowledge on environmental variability across terrestrial, freshwater, and marine Antarctic biomes and related this to the observed biotic patterns. The most important physical driver of Antarctic terrestrial communities is the availability of liquid water, itself driven by solar irradiance intensity. Patterns of biota distribution are further strongly influenced by the historical development of any given location or region, and by geographical barriers. In freshwater ecosystems, free water is also crucial, with further important influences from salinity, nutrient availability, oxygenation, and characteristics of ice cover and extent. In the marine biome there does not appear to be one major driving force, with the exception of the oceanographic boundary of the Polar Front. At smaller spatial scales, ice cover, ice scour, and salinity gradients are clearly important determinants of diversity at habitat and community level. Stochastic and extreme events remain an important driving force in all environments, particularly in the context of local extinction and colonization or recolonization, as well as that of temporal environmental variability. Our synthesis demonstrates that the Antarctic continent and surrounding oceans provide an ideal study ground to develop new biogeographical models, including life history and physiological traits, and to address questions regarding biological responses to environmental variability and change.
Summary
Antarctic subglacial environments host microbial ecosystems and are proving to be geochemically and biologically diverse. The Taylor Glacier, Antarctica, periodically expels iron‐rich brine ...through a conduit sourced from a deep subglacial aquifer, creating a dramatic red surface feature known as Blood Falls. We used Illumina MiSeq sequencing to describe the core microbiome of this subglacial brine and identified previously undetected but abundant groups including the candidate bacterial phylum Atribacteria and archaeal phylum Pacearchaeota. Our work represents the first microbial characterization of samples collected from within a glacier using a melt probe, and the only Antarctic subglacial aquatic environment that, to date, has been sampled twice. A comparative analysis showed the brine community to be stable at the operational taxonomic unit level of 99% identity over a decade. Higher resolution sequencing enabled deconvolution of the microbiome of subglacial brine from mixtures of materials collected at the glacier surface. Diversity patterns between this brine and samples from the surrounding landscape provide insight into the hydrological connectivity of subglacial fluids to the surface polar desert environment. Understanding subice brines collected on the surfaces of thick ice covers has implications for analyses of expelled materials that may be sampled on icy extraterrestrial worlds.
Understanding how terrestrial biotic communities have responded to glacial recession since the Last Glacial Maximum (LGM) can inform present and future responses of biota to climate change. In ...Antarctica, the Transantarctic Mountains (TAM) have experienced massive environmental changes associated with glacial retreat since the LGM, yet we have few clues as to how its soil invertebrate‐dominated animal communities have responded. Here, we surveyed soil invertebrate fauna from above and below proposed LGM elevations along transects located at 12 features across the Shackleton Glacier region. Our transects captured gradients of surface ages possibly up to 4.5 million years and the soils have been free from human disturbance for their entire history. Our data support the hypothesis that soils exposed during the LGM are now less suitable habitats for invertebrates than those that have been exposed by deglaciation following the LGM. Our results show that faunal abundance, community composition, and diversity were all strongly affected by climate‐driven changes since the LGM. Soils more recently exposed by the glacial recession (as indicated by distances from present ice surfaces) had higher faunal abundances and species richness than older exposed soils. Higher abundances of the dominant nematode Scottnema were found in older exposed soils, while Eudorylaimus, Plectus, tardigrades, and rotifers preferentially occurred in more recently exposed soils. Approximately 30% of the soils from which invertebrates could be extracted had only Scottnema, and these single‐taxon communities occurred more frequently in soils exposed for longer periods of time. Our structural equation modeling of abiotic drivers highlighted soil salinity as a key mediator of Scottnema responses to soil exposure age. These changes in soil habitat suitability and biotic communities since the LGM indicate that Antarctic terrestrial biodiversity throughout the TAM will be highly altered by climate warming.
Understanding how terrestrial biodiversity responded to glacial recession since the LGM can inform present and future responses of biota to climate change. By looking at how biotic communities have changed over geologic time scales since the LGM, our results add to the growing body of evidence that the diversity of arid soil ecosystems globally will be highly altered by present and projected climate warming.
Urban potable waters can be very susceptible to human activities that can impact water quality and, hence, public health. Columbus, Ohio, is currently the 14th largest city in the United States with ...an estimated population of ~860,000. Much of the urban population receives its water supply from a series of reservoirs located north of the city proper. These reservoirs are fed by river systems that drain either large agricultural lands, or rapidly growing suburban areas, or both. The agricultural activities introduce dissolved nitrate, and increased usage of de-icing salts on roads and highways within the drainage area introduce chloride into the river/reservoir systems. High nitrate in drinking water poses a potential health risk, particularly to infants, while high chloride, applied as halite, in drinking water can aid in the development of cardiovascular disease. In this work, we present a 19-month time series measuring nitrate, chloride, and sulfate in local precipitation, reservoir and household tap waters in order to better understand the relationship of the hydrologic residence time on the tap water chemistry, as well as to evaluate the anion concentrations. The highest chloride tap water concentration, 6.9 mM, occurred in early February 2011, while increases in nitrate occurred in both early summer and the middle of winter. In general, the anion concentrations in the precipitation are all equal to or lower than the reservoir waters. Similarly, the tap water had concentrations of chloride and sulfate higher than reservoir water, while nitrate was similar to reservoir water. Tap water had higher fluoride and sulfate concentrations, suggesting that they are added during the treatment of the reservoir water prior to residential distribution. These data clearly demonstrate the importance of watershed lands on the quality of water in the human distribution system.
Understanding land use/land cover (LULC) effects on tropical soil infiltration is crucial for maximizing watershed scale hydro‐ecosystem services and informing land managers. This paper reports ...results from a multiyear investigation of LULC effects on soil bulk infiltration in steep, humid tropical, and lowland catchments. A rainfall simulator applied water at measured rates on 2 × 6 m plots producing infiltration through structured, granulated, and macroporous Ferralsols in Panama's central lowlands. Time‐lapse electrical resistivity tomography (ERT) helped to visualize infiltration depth and bulk velocity. A space‐for‐time substitution methodology allowed a land‐use history investigation by considering the following: (a) a continuously heavy‐grazed cattle pasture, (b) a rotationally grazed traditional cattle pasture, (c) a 4‐year‐old (y.o.) silvopastoral system with nonnative improved pasture grasses and managed intensive rotational grazing, (d) a 7 y.o. teak (Tectona grandis) plantation, (e) an approximately 10 y.o. secondary succession forest, (f) a 12 y.o. coffee plantation (Coffea canephora), (g) an approximately 30 y.o. secondary succession forest, and (h) a >100 y.o. secondary succession forest. Within a land cover, unique plot sites totalled two at (a), (c), (d), (e), and (g); three at (b); and one at (f) and (h). Our observations confirmed measured infiltration scale dependency by comparing our 12 m2 plot‐scale measurements against 8.9 cm diameter core‐scale measurements collected by others from nearby sites. Preferential flow pathways (PFPs) significantly increased soil infiltration capacity, particularly in forests greater than or equal to 10 y.o. Time‐lapse ERT observations revealed shallower rapid bulk infiltration and increased rapid lateral subsurface flow in pasture land covers when compared with forest land covers and highlighted how much subsurface flow pathways can vary within the Ferralsol soil class. Results suggest that LULC effects on PFPs are the dominant mechanism by which LULC affects throughfall partitioning, runoff generation, and flow pathways.
Forested land covers contain more preferential flow pathways than pasture land covers, leading to increased infiltrability in forests. Infiltration measurements, time‐lapse electrical resistitivity tomography, and soil observations found that pasture soils exhibited more lateral subsurface and/or overland flow whereas forests exhibited deeper vertical bulk infiltration and no overland flow.
Previous studies have established links between
biodiversity and soil geochemistry in the McMurdo Dry Valleys, Antarctica,
where environmental gradients are important determinants of soil
...biodiversity. However, these gradients are not well established in the
central Transantarctic Mountains, which are thought to represent some of the
least hospitable Antarctic soils. We analyzed 220 samples from 11 ice-free
areas along the Shackleton Glacier (∼ 85∘ S), a
major outlet glacier of the East Antarctic Ice Sheet. We established three
zones of distinct geochemical gradients near the head of the glacier
(upper), its central part (middle), and at the mouth (lower). The upper zone had the
highest water-soluble salt concentrations with total salt concentrations
exceeding 80 000 µg g−1, while the lower zone had the lowest
water-soluble N:P ratios, suggesting that, in addition to other parameters
(such as proximity to water and/or ice), the lower zone likely represents the most
favorable ecological habitats. Given the strong dependence of geochemistry
on geographic parameters, we developed multiple linear regression and random
forest models to predict soil geochemical trends given latitude, longitude,
elevation, distance from the coast, distance from the glacier, and soil
moisture (variables which can be inferred from remote measurements).
Confidence in our random forest model predictions was moderately high with
R2 values for total water-soluble salts, water-soluble N:P,
ClO4-, and ClO3- of 0.81, 0.88, 0.78, and 0.74,
respectively. These modeling results can be used to predict geochemical
gradients and estimate salt concentrations for other Transantarctic Mountain
soils, information that can ultimately be used to better predict
distributions of soil biota in this remote region.
The average air temperature at the Earth's surface has increased by 0.06 °C per decade during the 20th century, and by 0.19 °C per decade from 1979 to 1998. Climate models generally predict amplified ...warming in polar regions, as observed in Antarctica's peninsula region over the second half of the 20th century. Although previous reports suggest slight recent continental warming, our spatial analysis of Antarctic meteorological data demonstrates a net cooling on the Antarctic continent between 1966 and 2000, particularly during summer and autumn. The McMurdo Dry Valleys have cooled by 0.7 °C per decade between 1986 and 2000, with similar pronounced seasonal trends. Summer cooling is particularly important to Antarctic terrestrial ecosystems that are poised at the interface of ice and water. Here we present data from the dry valleys representing evidence of rapid terrestrial ecosystem response to climate cooling in Antarctica, including decreased primary productivity of lakes (6-9% per year) and declining numbers of soil invertebrates (more than 10% per year). Continental Antarctic cooling, especially the seasonality of cooling, poses challenges to models of climate and ecosystem change.
The coastal regions of the McMurdo Dry Valleys, Antarctica, contain deposits of the Ross Sea Drift, sedimentary material left from the Ross Sea ice sheet from the advance of the West Antarctic ice ...sheet during the Last Glacial Maximum. Much of this deposit is ice-cored, but data on the stable isotopic composition of water from this ice, which may contain a valuable climate archive, are sparse or incomplete. Widespread thermokarstic ground subsidence in this "coastal thaw zone" of the McMurdo Dry Valleys suggests that these potential records are rapidly being lost due to the melting of ground ice and permafrost. We collected samples of massive buried ice from the Ross Sea Drift in eastern Taylor Valley for δ
18
O-H
2
O and δ
2
H-H
2
O and measured a broad range of values (δ
18
O = −27.7 to −37.3 ‰; δ
2
H = −210 to −295 ‰). These buried ice deposits do not show evidence of alteration through sublimation or evaporation, plot along the local meteoric water line, and have values that indicate ice deposition under a colder climate than present conditions. We propose that this ice was sourced from the Ross Sea ice sheet during the Last Glacial Maximum and contains a valuable and accessible climate record.
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