Explore the vast range of titles available.

Inland waters have been recognized as a significant source of carbon dioxide (CO2) to the atmosphere at the global scale. Fluxes of CO2 between aquatic systems and the atmosphere are calculated from the gas transfer velocity and the water-air gradient of the partial pressure of CO2 (pCO2). Currently, direct measurements of water pCO2 remain scarce in freshwaters, and most published pCO2 data are calculated from temperature, pH and total alkalinity (TA). Here, we compare calculated (pH and TA) and measured (equilibrator and headspace) water pCO2 in a large array of temperate and tropical freshwaters. The 761 data points cover a wide range of values for TA (0 to 14 200 μmol L-1), pH (3.94 to 9.17), measured pCO2 (36 to 23 000 ppmv), and dissolved organic carbon (DOC) (29 to 3970 μmol L-1). Calculated pCO2 were >10% higher than measured pCO2 in 60% of the samples (with a median overestimation of calculated pCO2 compared to measured pCO2 of 2560 ppmv) and were >100% higher in the 25% most organic-rich and acidic samples (with a median overestimation of 9080 ppmv). We suggest these large overestimations of calculated pCO2 with respect to measured pCO2 are due to the combination of two cumulative effects: (1) a more significant contribution of organic acids anions to TA in waters with low carbonate alkalinity and high DOC concentrations; (2) a lower buffering capacity of the carbonate system at low pH, which increases the sensitivity of calculated pCO2 to TA in acidic and organic-rich waters. No empirical relationship could be derived from our data set in order to correct calculated pCO2 for this bias. Owing to the widespread distribution of acidic, organic-rich freshwaters, we conclude that regional and global estimates of CO2 outgassing from freshwaters based on pH and TA data only are most likely overestimated, although the magnitude of the overestimation needs further quantitative analysis. Direct measurements of pCO2 are recommended in inland waters in general, and in particular in acidic, poorly buffered freshwaters.

We studied patterns in organic carbon pools and their origin in the Tana River Basin (Kenya), in February 2008 (dry season), September–November 2009 (wet season), and June–July 2010 (end of wet season), covering the full continuum from headwater streams to lowland mainstream sites. A consistent downstream increase in total suspended matter (TSM, 0.6 to 7058 mg l−1 and particulate organic carbon (POC, 0.23 to 119.8 mg l−1 was observed during all three sampling campaigns, particularly pronounced below 1000 m above sea level, indicating that most particulate matter exported towards the coastal zone originated from the mid and low altitude zones rather than from headwater regions. This indicates that the cascade of hydroelectrical reservoirs act as an extremely efficient particle trap. Although 7Be / 210Pbxs ratios/age of suspended sediment do not show clear seasonal variation, the gradual downstream increase of suspended matter during end of wet season suggests its origin is caused by inputs of older sediments from bank erosion and/or river sediment resuspension. During wet season, higher TSM concentrations correspond with relatively young suspended matter, suggesting a contribution from recently eroded material. With the exception of reservoir waters, POC was predominantly of terrestrial origin as indicated by generally high POC : chlorophyll a (POC : Chl a) ratios (up to ~41 000). Stable isotope signatures of POC (δ13CPOC ranged between −32 and −20‰ and increased downstream, reflecting an increasing contribution of C4-derived carbon in combination with an expected shift in δ13C for C3 vegetation towards the more semi-arid lowlands. δ13C values in sediments from the main reservoir (−19.5 to −15.7‰) were higher than those found in any of the riverine samples, indicating selective retention of particles associated with C4 fraction. Dissolved organic carbon (DOC) concentrations were highest during the end of wet season (2.1 to 6.9 mg l−1), with stable isotope signatures generally between −28 and −22‰. A consistent downstream decrease in % organic carbon (%OC) was observed for soils, riverine sediments, and suspended matter. This was likely due to better preservation of the organic fraction in colder high altitude regions, with loss of carbon during downstream spiraling. δ13C values for soil and sediment did not exhibit clear altitudinal patterns, but values reflect the full spectrum from C3-dominated to C4-dominated sites. Very low ratios of organic carbon to mineral surface area (OC : SA) were found in reservoir sediments and suspended matter in the lower Tana River, indicating that these are stable OC pools which have undergone extensive degradation. Overall, our study demonstrates that substantial differences occur in both the quantities and origin of suspended sediments and organic carbon along the river profile in this tropical river basin, as well as seasonal differences in the mechanisms causing such variations.

As part of a broader study on the riverine biogeochemistry in the Athi–Galana–Sabaki (A-G-S) River catchment (Kenya), we present data constraining the sources, transit and transformation of multiple nitrogen (N) species as they flow through the A-G-S catchment (~47 000 km2). The data set was obtained in August–September 2011, November 2011, and April–May 2012, covering the dry season, short rain season and long rain season respectively. Release of (largely untreated) wastewater from the city of Nairobi had a profound impact on the biogeochemistry of the upper Athi River, leading to low dissolved oxygen (DO) saturation levels (36–67%), high ammonium (NH4+) concentrations (123–1193 μmol L−1), and high dissolved methane (CH4) concentrations (3765–6729 nmol L−1). Riverine dissolved inorganic nitrogen (DIN; sum of NH4+ and nitrate (NO3−); nitrite was not measured) concentration at the most upstream site on the Athi River was highest during the dry season (1195 μmol L−1), while DIN concentration was an order of magnitude lower during the short and long rain seasons (212 and 193 μmol L−1, respectively). During the rain seasons, low water residence time led to relatively minimal in-stream N cycling prior to discharge to the ocean, whereas during the dry season we speculate that prolonged residence time creates two differences comparative to wet season, where (1) intense N cycling and removal of DIN is possible in the upper to mid-catchment and leads to significantly lower concentrations at the outlet during the dry season, and (2) as a result this leads to the progressive enrichment of 15N in the particulate N (PN) pool, highlighting the dominance of untreated wastewater as the prevailing source of riverine DIN. The rapid removal of NH4+ in the upper reaches during the dry season was accompanied by a quantitatively similar production of NO3− and nitrous oxide (N2O) downstream, pointing towards strong nitrification over this reach during the dry season. Nitrous oxide produced was rapidly degassed downstream, while the elevated NO3− concentrations steadily decreased to levels observed elsewhere in more pristine African river networks. Low pelagic primary production rates over the same reach suggest that benthic denitrification was the dominant process controlling the removal of NO3−, although large cyanobacterial blooms further downstream highlight the significant role of DIN assimilation by primary producers also. Consequently, the intense nitrification and uptake of N by algae leads to significant enrichment of 15N in the PN pool during the dry season (mean: +16.5 ± 8.2‰ but reaching as high as +31.5‰) compared to the short (+7.3 ± 2.6‰) and long (+7.6 ± 5.9‰) rain seasons. A strong correlation between the seasonal N stable isotope ratios of PN (δ15NPN) and oxygen stable isotope ratios of river water (δ18OH2O; as a proxy of freshwater discharge) presents the possibility of employing a combination of proxies – such as δ15NPN of sediments, bivalves and near-shore corals – to reconstruct how historical land use changes have influenced nitrogen cycling within the catchment, whilst potentially providing foresight on the impacts of future land management decisions.

Inland waters impart considerable influence on nutrient cycling and budget estimates across local, regional and global scales, whilst anthropogenic pressures, such as rising populations and the appropriation of land and water resources, are undoubtedly modulating the flux of carbon (C), nitrogen (N) and phosphorus (P) between terrestrial biomes to inland waters, and the subsequent flux of these nutrients to the marine and atmospheric domains. Here, we present a 2-year biogeochemical record (October 2011–December 2013) at biweekly sampling resolution for the lower Sabaki River, Kenya, and provide estimates for suspended sediment and nutrient export fluxes from the lower Sabaki River under pre-dam conditions, and in light of the approved construction of the Thwake Multipurpose Dam on its upper reaches (Athi River). Erratic seasonal variation was typical for most parameters, with generally poor correlation between discharge and material concentrations, and stable isotope values of C (δ13C) and N (δ15N). Although high total suspended matter (TSM) concentrations are reported here (up to ∼ 3.8 g L−1), peak concentrations of TSM rarely coincided with peak discharge. The contribution of particulate organic C (POC) to the TSM pool indicates a wide biannual variation in suspended sediment load from OC poor (0.3 %) to OC rich (14.9 %), with the highest %POC occurring when discharge is < 100 m3 s−1 and at lower TSM concentrations. The consistent 15N enrichment of the particulate nitrogen (PN) pool compared to other river systems indicates anthropogenic N loading is a year-round driver of N export from the Sabaki Basin. The lower Sabaki River was consistently oversaturated in dissolved methane (CH4; from 499 to 135 111 %) and nitrous oxide (N2O; 100 to 463 %) relative to atmospheric concentrations. Wet season flows (October–December and March–May) carried > 80 % of the total load for TSM (∼ 86 %), POC (∼ 89 %), dissolved organic carbon (DOC; ∼ 81 %), PN (∼ 89 %) and particulate phosphorus (TPP; ∼ 82 %), with > 50 % of each fraction exported during the long wet season (March–May). Our estimated sediment yield (85 Mg km−2 yr−1) is relatively low on the global scale and is considerably less than the recently reported average sediment yield of ∼ 630 Mg km−2 yr−1 for African river basins. Regardless, sediment and OC yields were all at least equivalent or greater than reported yields for the neighbouring dammed Tana River. Rapid pulses of heavily 13C-enriched POC coincided with peak concentrations of PN, ammonium, CH4 and low dissolved oxygen saturation, suggesting that large mammalian herbivores (e.g. hippopotami) may mediate the delivery of C4 organic matter to the river during the dry season. Given recent projections for increasing dissolved nutrient export from African rivers, as well as the planned damming of the Athi River, these first estimates of material fluxes from the Sabaki River provide base-line data for future research initiatives assessing anthropogenic perturbation of the Sabaki Basin.

Inland waters have been recognized as a significant source of carbon dioxide (CO2) to the atmosphere at the global scale. Fluxes of CO2 between aquatic systems and the atmosphere are calculated from the gas transfer velocity and the water–air gradient of the partial pressure of CO2 (pCO2). Currently, direct measurements of water pCO2 remain scarce in freshwaters, and most published pCO2 data are calculated from temperature, pH and total alkalinity (TA). Here, we compare calculated (pH and TA) and measured (equilibrator and headspace) water pCO2 in a large array of temperate and tropical freshwaters. The 761 data points cover a wide range of values for TA (0 to 14 200 μmol L−1), pH (3.94 to 9.17), measured pCO2 (36 to 23 000 ppmv), and dissolved organic carbon (DOC) (29 to 3970 μmol L−1). Calculated pCO2 were >10% higher than measured pCO2 in 60% of the samples (with a median overestimation of calculated pCO2 compared to measured pCO2 of 2560 ppmv) and were >100% higher in the 25% most organic-rich and acidic samples (with a median overestimation of 9080 ppmv). We suggest these large overestimations of calculated pCO2 with respect to measured pCO2 are due to the combination of two cumulative effects: (1) a more significant contribution of organic acids anions to TA in waters with low carbonate alkalinity and high DOC concentrations; (2) a lower buffering capacity of the carbonate system at low pH, which increases the sensitivity of calculated pCO2 to TA in acidic and organic-rich waters. No empirical relationship could be derived from our data set in order to correct calculated pCO2 for this bias. Owing to the widespread distribution of acidic, organic-rich freshwaters, we conclude that regional and global estimates of CO2 outgassing from freshwaters based on pH and TA data only are most likely overestimated, although the magnitude of the overestimation needs further quantitative analysis. Direct measurements of pCO2 are recommended in inland waters in general, and in particular in acidic, poorly buffered freshwaters.

Inland waters have been recognized as a significant source of carbon dioxide (CO.sub.2) to the atmosphere at the global scale. Fluxes of CO.sub.2 between aquatic systems and the atmosphere are calculated from the gas transfer velocity and the water-air gradient of the partial pressure of CO.sub.2 (pCO.sub.2). Currently, direct measurements of water pCO.sub.2 remain scarce in freshwaters, and most published pCO.sub.2 data are calculated from temperature, pH and total alkalinity (TA). Here, we compare calculated (pH and TA) and measured (equilibrator and headspace) water pCO.sub.2 in a large array of temperate and tropical freshwaters. The 761 data points cover a wide range of values for TA (0 to 14 200 μmol L.sup.-1 ), pH (3.94 to 9.17), measured pCO.sub.2 (36 to 23 000 ppmv), and dissolved organic carbon (DOC) (29 to 3970 μmol L.sup.-1). Calculated pCO.sub.2 were >10% higher than measured pCO.sub.2 in 60% of the samples (with a median overestimation of calculated pCO.sub.2 compared to measured pCO.sub.2 of 2560 ppmv) and were >100% higher in the 25% most organic-rich and acidic samples (with a median overestimation of 9080 ppmv). We suggest these large overestimations of calculated pCO.sub.2 with respect to measured pCO.sub.2 are due to the combination of two cumulative effects: (1) a more significant contribution of organic acids anions to TA in waters with low carbonate alkalinity and high DOC concentrations; (2) a lower buffering capacity of the carbonate system at low pH, which increases the sensitivity of calculated pCO.sub.2 to TA in acidic and organic-rich waters. No empirical relationship could be derived from our data set in order to correct calculated pCO.sub.2 for this bias. Owing to the widespread distribution of acidic, organic-rich freshwaters, we conclude that regional and global estimates of CO.sub.2 outgassing from freshwaters based on pH and TA data only are most likely overestimated, although the magnitude of the overestimation needs further quantitative analysis. Direct measurements of pCO.sub.2 are recommended in inland waters in general, and in particular in acidic, poorly buffered freshwaters.

The hydrological status of river systems is expected to change due to dam operations and climate change. This will affect the riverine fluxes of sediment and carbon (C). In rivers with strong seasonal and inter-annual variability, quantification and extrapolation of sediment and C fluxes can be a challenge as measurement periods are often too short to cover all hydrological conditions. We studied the dynamics of the Tana River (Kenya) from 2012 to 2014 through daily monitoring of sediment concentrations at three sites (Garissa, Tana River Primate Reserve and Garsen) and daily monitoring of C concentrations in Garissa and Garsen during three distinct seasons. A bootstrap method was applied to calculate the range of sediment and C fluxes as a function of annual discharge by using daily discharge data (1942–2014). Overall, we estimated that on average, sediment and carbon were retained in this 600 km long river section between Garissa to Garsen over the 73 years (i.e., fluxes were higher at the upstream site than downstream): integration over all simulations resulted in an average net retention of sediment (~ 2.9 Mt year− 1), POC (~ 18,000 tC year− 1), DOC (~ 920 tC year− 1) and DIC (~ 1200 tC year− 1). To assess the impact of hydrological variations, we constructed four different hydrological scenarios over the same period. Although there was significant non-linearity and difference between the C species, our estimates generally predicted a net increase of C retention between the upstream and downstream site when the annual discharge would decrease, for example caused by an increase of irrigation with reservoir water. When simulating an increase in the annual discharge, e.g. as a potential effect of climate change, we predicted a decrease in C retention.

Carbon dioxide emissions to the atmosphere from inland waters—streams, rivers, lakes and reservoirs—are nearly equivalent to ocean and land sinks globally. Inland waters can be an important source of methane and nitrous oxide emissions as well, but emissions are poorly quantified, especially in Africa. Here we report dissolved carbon dioxide, methane and nitrous oxide concentrations from 12 rivers in sub-Saharan Africa, including seasonally resolved sampling at 39 sites, acquired between 2006 and 2014. Fluxes were calculated from published gas transfer velocities, and upscaled to the area of all sub-Saharan African rivers using available spatial data sets. Carbon dioxide-equivalent emissions from river channels alone were about 0.4 Pg carbon per year, equivalent to two-thirds of the overall net carbon land sink previously reported for Africa. Including emissions from wetlands of the Congo river increases the total carbon dioxide-equivalent greenhouse-gas emissions to about 0.9 Pg carbon per year, equivalent to about one quarter of the global ocean and terrestrial combined carbon sink. Riverine carbon dioxide and methane emissions increase with wetland extent and upland biomass. We therefore suggest that future changes in wetland and upland cover could strongly affect greenhouse-gas emissions from African inland waters. Inland waters are important sources of greenhouse gases. Measurements over eight years suggest that African inland waters are a substantial source of greenhouse gases, equivalent to a quarter of the global land and ocean carbon sink.

Liver cirrhosis is a major cause of death worldwide and is characterized by extensive fibrosis. There are currently no effective antifibrotic therapies available. To obtain a better understanding of the cellular and molecular mechanisms involved in disease pathogenesis and enable the discovery of therapeutic targets, here we profile the transcriptomes of more than 100,000 single human cells, yielding molecular definitions for non-parenchymal cell types that are found in healthy and cirrhotic human liver. We identify a scar-associated TREM2 + CD9 + subpopulation of macrophages, which expands in liver fibrosis, differentiates from circulating monocytes and is pro-fibrogenic. We also define ACKR1 + and PLVAP + endothelial cells that expand in cirrhosis, are topographically restricted to the fibrotic niche and enhance the transmigration of leucocytes. Multi-lineage modelling of ligand and receptor interactions between the scar-associated macrophages, endothelial cells and PDGFRα + collagen-producing mesenchymal cells reveals intra-scar activity of several pro-fibrogenic pathways including TNFRSF12A, PDGFR and NOTCH signalling. Our work dissects unanticipated aspects of the cellular and molecular basis of human organ fibrosis at a single-cell level, and provides a conceptual framework for the discovery of rational therapeutic targets in liver cirrhosis. Single-cell RNA sequencing is used to characterize and compare the functional diversity of cells from liver biopsies of human scarred and normal liver, and identifies markers for scar-associated macrophages and endothelial cells.

Patients are increasingly being admitted with chronic atrial fibrillation, and disease-specific management might reduce recurrent admissions and prolong survival. However, evidence is scant to support the application of this therapeutic approach. We aimed to assess SAFETY—a management strategy that is specific to atrial fibrillation. We did a pragmatic, multicentre, randomised controlled trial in patients admitted with chronic, non-valvular atrial fibrillation (but not heart failure). Patients were recruited from three tertiary referral hospitals in Australia. 335 participants were randomly assigned by computer-generated schedule (stratified for rhythm or rate control) to either standard management (n=167) or the SAFETY intervention (n=168). Standard management consisted of routine primary care and hospital outpatient follow-up. The SAFETY intervention comprised a home visit and Holter monitoring 7–14 days after discharge by a cardiac nurse with prolonged follow-up and multidisciplinary support as needed. Clinical reviews were undertaken at 12 and 24 months (minimum follow-up). Coprimary outcomes were death or unplanned readmission (both all-cause), measured as event-free survival and the proportion of actual versus maximum days alive and out of hospital. Analyses were done on an intention-to-treat basis. The trial is registered with the Australian New Zealand Clinical Trials Registry (ANZCTRN 12610000221055). During median follow-up of 905 days (IQR 773–1050), 49 people died and 987 unplanned admissions were recorded (totalling 5530 days in hospital). 127 (76%) patients assigned to the SAFETY intervention died or had an unplanned readmission (median event-free survival 183 days [IQR 116–409]) and 137 (82%) people allocated standard management achieved a coprimary outcome (199 days [116–249]; hazard ratio 0·97, 95% CI 0·76–1·23; p=0·851). Patients assigned to the SAFETY intervention had 99·5% maximum event-free days (95% CI 99·3–99·7), equating to a median of 900 (IQR 767–1025) of 937 maximum days alive and out of hospital. By comparison, those allocated to standard management had 99·2% (95% CI 98·8–99·4) maximum event-free days, equating to a median of 860 (IQR 752–1047) of 937 maximum days alive and out of hospital (effect size 0·22, 95% CI 0·21–0·23; p=0·039). A post-discharge management programme specific to atrial fibrillation was associated with proportionately more days alive and out of hospital (but not prolonged event-free survival) relative to standard management. Disease-specific management is a possible strategy to improve poor health outcomes in patients admitted with chronic atrial fibrillation. National Health and Medical Research Council of Australia.