On the human appropriation of wetland primary production

Humans are changing the Earth\u27s surface at an accelerating pace, with significant consequences for ecosystems and their biodiversity. Landscape transformation has far-reaching implications including reduced net primary production (NPP) available to support ecosystems, reduced energy supplies to consumers, and disruption of ecosystem services such as carbon storage. Anthropogenic activities have reduced global NPP available to terrestrial ecosystems by nearly 25%, but the loss of NPP from wetland ecosystems is unknown. We used a simple approach to estimate aquatic NPP from measured habitat areas and habitat-specific areal productivity in the largest wetland complex on the USA west coast, comparing historical and modern landscapes and a scenario of wetland restoration. Results show that a 77% loss of wetland habitats (primarily marshes) has reduced ecosystem NPP by 94%, C (energy) flow to herbivores by 89%, and detritus production by 94%. Our results also show that attainment of habitat restoration goals could recover 12% of lost NPP and measurably increase carbon flow to consumers, including at-risk species and their food resources. This case study illustrates how a simple approach for quantifying the loss of NPP from measured habitat losses can guide wetland conservation plans by establishing historical baselines, projecting functional outcomes of different restoration scenarios, and establishing performance metrics to gauge success

Adjunctive rifampicin for Staphylococcus aureus bacteraemia (ARREST): a multicentre, randomised, double-blind, placebo-controlled trial.

BACKGROUND: Staphylococcus aureus bacteraemia is a common cause of severe community-acquired and hospital-acquired infection worldwide. We tested the hypothesis that adjunctive rifampicin would reduce bacteriologically confirmed treatment failure or disease recurrence, or death, by enhancing early S aureus killing, sterilising infected foci and blood faster, and reducing risks of dissemination and metastatic infection. METHODS: In this multicentre, randomised, double-blind, placebo-controlled trial, adults (≥18 years) with S aureus bacteraemia who had received ≤96 h of active antibiotic therapy were recruited from 29 UK hospitals. Patients were randomly assigned (1:1) via a computer-generated sequential randomisation list to receive 2 weeks of adjunctive rifampicin (600 mg or 900 mg per day according to weight, oral or intravenous) versus identical placebo, together with standard antibiotic therapy. Randomisation was stratified by centre. Patients, investigators, and those caring for the patients were masked to group allocation. The primary outcome was time to bacteriologically confirmed treatment failure or disease recurrence, or death (all-cause), from randomisation to 12 weeks, adjudicated by an independent review committee masked to the treatment. Analysis was intention to treat. This trial was registered, number ISRCTN37666216, and is closed to new participants. FINDINGS: Between Dec 10, 2012, and Oct 25, 2016, 758 eligible participants were randomly assigned: 370 to rifampicin and 388 to placebo. 485 (64%) participants had community-acquired S aureus infections, and 132 (17%) had nosocomial S aureus infections. 47 (6%) had meticillin-resistant infections. 301 (40%) participants had an initial deep infection focus. Standard antibiotics were given for 29 (IQR 18-45) days; 619 (82%) participants received flucloxacillin. By week 12, 62 (17%) of participants who received rifampicin versus 71 (18%) who received placebo experienced treatment failure or disease recurrence, or died (absolute risk difference -1·4%, 95% CI -7·0 to 4·3; hazard ratio 0·96, 0·68-1·35, p=0·81). From randomisation to 12 weeks, no evidence of differences in serious (p=0·17) or grade 3-4 (p=0·36) adverse events were observed; however, 63 (17%) participants in the rifampicin group versus 39 (10%) in the placebo group had antibiotic or trial drug-modifying adverse events (p=0·004), and 24 (6%) versus six (2%) had drug interactions (p=0·0005). INTERPRETATION: Adjunctive rifampicin provided no overall benefit over standard antibiotic therapy in adults with S aureus bacteraemia. FUNDING: UK National Institute for Health Research Health Technology Assessment

Subsurface Controls on Carbon Dynamics in a Changing Arctic Ecosystem

With climate change in the Arctic, temperatures are expected to rise at twice the rate as in temperate latitudes. This rapid change has the potential to disrupt local ecosystems and feed back to the global climate as frozen soils thaw and warm. Large stocks of carbon have accumulated in Arctic soils, protected from decomposition by cold, wet, and frozen conditions. With warming and thawing due to climate change, decomposition of this carbon is expected to increase, releasing it to the atmosphere as the greenhouse gases CO2 and methane. While a number of modeling efforts have attempted to quantify this potential feedback, the future Arctic carbon balance remains unknown due to uncertain mechanisms stabilizing soil carbon and complex interactions between vegetation and soils. In studies based in Barrow, Alaska, I address three sources of this uncertainty: (1) the magnitude of methane emissions following soil thaw, (2) interactions between plants, soil carbon, and microbial decomposers, and (3) the sensitivity of soil carbon cycling changes in microclimate. First, I ask how methane formation, consumption within the soil, and net emission to the atmosphere may change with soil thaw in the Arctic. Loss of permafrost (perennially frozen ground) can lead to large-scale landscape changes, redistributing water and soil. Such physical changes can strongly influence emissions of methane, a greenhouse gas roughly 25 times as potent as CO2, whose future emission rates are highly uncertain. Combining field measurements with statistical modeling, I assess soil methane emissions and microbial methane processes (production and consumption) across a gradient of permafrost thaw. In contrast with many previous studies, I find that more degraded sites have lower methane emissions, a different primary methanogenic pathway, and greater methane oxidation than intact permafrost sites. These differences are greater than soil moisture or temperature data can explain. Additional microtopographic controls accounting for these observations may include differences in water flow and vegetation between intact and degraded polygons.Second, I ask how changes in plant activity due to climate change may influence the rate of soil carbon decomposition (the priming effect), through interactions between plant roots, microbial decomposers, and soil carbon compounds. In a two-year field experiment, I simulate increased plant root activity and measure its influence on soil carbon decomposition, plant CO2 uptake, mineral nitrogen availability, and microbial communities. I find no measurable relationship between substrate additions and soil organic matter decomposition, nutrient supply, or microbial population size. Treatment-level differences in primary production, however, indicate possible longer-term interactions between vegetation and decomposition. The absence of a measurable priming effect contrasts with numerous published reports documenting a positive priming effect under tightly controlled conditions. This difference may be due to high background variability in ecosystem respiration, a property of this in situ experiment. This chapter is one of the first studies evaluating this plant-soil interaction in a field experimental context, with a representative degree of environmental variability.Third, I ask how decomposition rates of fast-cycling and slow-cycling soil carbon may be influenced by microclimatic changes. The rate of soil carbon turnover and its sensitivity to environmental variables such as temperature and oxygen availability are both highly uncertain and highly influential for model predictions of the global carbon cycle. In two laboratory incubations, I use natural abundance radiocarbon measurements of CO2 and soil organic matter to determine how fast-cycling and slow-cycling carbon pools respond to temperature changes and transitions between anaerobic and aerobic conditions. Using a novel analytical approach, I find that fast- and slow-cycling carbon pools from these Barrow, Alaska soils have comparable temperature sensitivities, with decomposition from both pools increasing by ~40 % for a 5°C temperature increase. Similarly, decomposition rates were highly sensitive to aerobic vs. anaerobic conditions, with no significant difference in sensitivity between pools. Radiocarbon contents of CO2 and soil organic matter indicate that ancient, slow-cycling carbon is sensitive to decomposition under soil temperature increases and water table changes

THE CHANGING BIOGEOCHEMICAL CYCLES OF TUNDRA

Tundra is experiencing more intense warming than any other ecosystem on earth. While warming is the most direct effect of climate change on tundra, warming leads to a cascade of environmental changes such as permafrost thaw, altered precipitation regimes, and increased wildfires. This chapter will first focus on how climate change is changing the environment of Arctic and subarctic tundra and then focus on how climate change is altering tundra's carbon, nitrogen, and phosphorus cycles with a focus on soils. Overall, tundra soils are shifting from being a carbon sink into a carbon source as rising temperatures increase microbial activity—a positive feedback to climate change. However, those rising temperatures are also increasing nutrient mineralization rates, which could increase ecosystem carbon storage via enhanced plant productivity as well as increase emissions of nitrous oxide, a powerful greenhouse gas. There is currently a disconnect between the large soil carbon losses measured in many in situ experiments and the strong plant carbon gains predicted by models. Ultimately, more research is needed on the interplay between tundra soils, nutrients, and plants to determine the magnitude of tundra's feedback to climate change

Shallow soils are warmer under trees and tall shrubs across Arctic and Boreal ecosystems

Abstract Soils are warming as air temperatures rise across the Arctic and Boreal region concurrent with the expansion of tall-statured shrubs and trees in the tundra. Changes in vegetation structure and function are expected to alter soil thermal regimes, thereby modifying climate feedbacks related to permafrost thaw and carbon cycling. However, current understanding of vegetation impacts on soil temperature is limited to local or regional scales and lacks the generality necessary to predict soil warming and permafrost stability on a pan-Arctic scale. Here we synthesize shallow soil and air temperature observations with broad spatial and temporal coverage collected across 106 sites representing nine different vegetation types in the permafrost region. We showed ecosystems with tall-statured shrubs and trees (>40 cm) have warmer shallow soils than those with short-statured tundra vegetation when normalized to a constant air temperature. In tree and tall shrub vegetation types, cooler temperatures in the warm season do not lead to cooler mean annual soil temperature indicating that ground thermal regimes in the cold-season rather than the warm-season are most critical for predicting soil warming in ecosystems underlain by permafrost. Our results suggest that the expansion of tall shrubs and trees into tundra regions can amplify shallow soil warming, and could increase the potential for increased seasonal thaw depth and increase soil carbon cycling rates and lead to increased carbon dioxide loss and further permafrost thaw