Hydro-geomorphic controls of greenhouse gas fluxes in riparian buffers of the White River watershed, IN (USA)

Riparian ecosystems are defined by the nature and regularity of the interactions between a given river system and its floodplains, and past studies have often presented vegetation cover as the exclusive expression of these interactions. There has been to our knowledge, no systematic attempt at linking greenhouse gases (GHG) fluxes and types of riparian buffers. The present study was conducted to investigate the intensity and seasonality of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) fluxes in riparian buffers in three common hydro-geomorphic settings (HGM) across the White River watershed (Indiana, USA). These classes included riparian sites located: (i) in till plain depressions near 1st order streams (HGM-1), (ii) in incised narrow valleys with thin alluvium layers above glacial till (HGM-2), and (iii) along 3rd–4th order streams in broad floodplains with thick alluvial and glacial outwash deposits (HGM-3). For each class, 3 sites were selected and GHG fluxes were measured during the wet (May) and dry seasons (August). Strong relationships were found between GHG fluxes, soil properties and environmental factors, but these relationships varied with season and gas species, making it challenging to rely on these relationships for GHG fluxes upscaling. Analysis of variance and discriminant analysis showed that the HGM-defined riparian buffers were distinct in terms of GHG flux intensity. Regardless of season, the HGM-1 sites emitted CO2 at rates 1.6 times higher than at the other sites, likely due to difference in soil C quality. During the wet season, N2O emission was significantly higher at the HGM-3 than at the other sites (0.88 vs 0.27 mg N m− 2 d− 1), and was negatively related with the gradient of the adjacent channel (r2: 0.69). The riparian buffers acted as CH4 sinks, with the HGM-2 sites exhibiting CH4 uptake rates significantly greater than the other riparian types (− 0.80 vs − 0.34 mg CH4-C m− 2 d− 1). The consistency of these results underscores the potential of an HGM-based monitoring approach to derive watershed-scale GHG budgets for riparian buffers

Soil methane and carbon dioxide fluxes from cropland and riparian buffers in different hydrogeomorphic settings

Riparian buffers contribute to the mitigation of nutrient pollution in agricultural landscapes, but there is concern regarding their potential to be hot spots of greenhouse gas production. This study compared soil CO2 and CH4 fluxes in adjacent crop fields and riparian buffers (a flood-prone forest and a flood-protected grassland along an incised channel) and examined the impact of water table depth (WTD) and flood events on the variability of gas fluxes in riparian zones. Results showed significantly (P 22°C), but the effect of flooding was less pronounced in early spring (emission <1.06 mg CH4–C m−2 d−1), probably due to low soil temperature. Although CH4 flux direction alternated at all sites, overall the croplands and the flood-affected riparian forest were CH4 sources, with annual emission averaging +0.04 ± 0.17 and +0.92 ± 1.6 kg CH4–C ha−1, respectively. In the riparian forest, a topographic depression (<8% of the total area) accounted for 78% of the annual CH4 emission, underscoring the significance of landscape heterogeneity on CH4 dynamics in riparian buffers. The nonflooded riparian grassland, however, was a net CH4 sink (−1.08 ± 0.22 kg CH4–C ha−1 yr−1), probably due to the presence of subsurface tile drains and a dredged/incised channel at that study site. Although these hydrological alterations may have contributed to improvement in the CH4 sink strength of the riparian grassland, this must be weighed against the water quality maintenance functions and other ecological services provided by riparian buffers

Nitrogen preference across generations under changing ammonium nitrate ratios

Aims Nitrogen (N) in natural environments is typically supplied by a mixture of ammonia (NH4+) and nitrate (NO3−). However, factors that underlie either NH4+ or NO3− preference, and how such preference will change across generations remain unclear. We conducted a series of experiments to answer whether: (i) NH4+:NO3− ratio is the driving factor for plant N preference, and (ii) this preference is consistent across generations. Methods We conducted both: (i) field observations (as a proxy for parent or P generation) and (ii) greenhouse experiments (the first generation or F1 and the second generation or F2) using corn and soybean grown under different NH4+:NO3− ratios. Important Findings Both corn and soybean had the physiological plasticity to prefer either NH4+ or NO3− depending on NH4+:NO3− ratios, and this plasticity was consistent across generations. Corn, however, showed a stronger preference towards NO3− while soybean showed a stronger preference towards NH4+. While both plants would try to make use of the most available form of N in their growing medium, plant species, physiological characteristics (e.g. maturity) and plant nutrient status also determined the extent of N uptake. From the evolutionary and productivity perspective, this plasticity is beneficial, allowing plants to effectively acquire available N particularly in a changing climate

A phospho-deficient α3 glycine receptor mutation alters synaptic glycine and GABA release in mouse spinal dorsal horn neurons

Glycine receptors (GlyRs), together with GABA$_{A}$ receptors, mediate postsynaptic inhibition in most spinal cord and hindbrain neurons. In several CNS regions, GlyRs are also expressed in presynaptic terminals. Here, we analysed the effects of a phospho-deficient mutation (S346A) in GlyR α3 subunits on inhibitory synaptic transmission in superficial spinal dorsal horn neurons, where this subunit is abundantly expressed. Unexpectedly, we found that not only were the amplitudes of evoked glycinergic inhibitory postsynaptic currents (IPSCs) significantly larger in GlyRα3(S346A) mice than in mice expressing wild-type α3GlyRs (GlyRα3(WT) mice), but so were those of GABAergic IPSCs. Decreased frequencies of spontaneously occurring glycinergic and GABAergic miniature IPSCs (mIPSCs) with no accompanying change in mIPSC amplitudes suggested a change in presynaptic transmitter release. Paired-pulse experiments on glycinergic IPSCs revealed an increased paired-pulse ratio and a smaller coefficient of variation in GlyRα3(S346A) mice, which together indicate a reduction in transmitter release probability and an increase in the number of releasable vesicles. Paired-pulse ratios of GABAergic IPSCs recorded in the presence of strychnine were not different between genotypes, while the coefficient of variation was smaller in GlyRα3(S346A) mice, demonstrating that the decrease in release probability was readily reversible by GlyR blockade, while the difference in the size of the pool of releasable vesicles remained. Taken together, our results suggest that presynaptic α3 GlyRs regulate synaptic glycine and GABA release in superficial dorsal horn neurons, and that this effect is potentially regulated by their phosphorylation status. KEY POINTS: A serine-to-alanine point mutation was introduced into the glycine receptor α3 subunit of mice. This point mutation renders α3 glycine receptors resistant to protein kinase A mediated phosphorylation but has otherwise only small effects on receptor function. Patch-clamp recordings from neurons in mouse spinal cord slices revealed an unexpected increase in the amplitudes of both glycinergic and GABAergic evoked inhibitory postsynaptic currents (IPSCs). Miniature IPSCs, paired-pulse ratios and synaptic variation analyses indicate a change in synaptic glycine and GABA release. The results strongly suggest that α3 subunit-containing glycine receptors are expressed on presynaptic terminals of inhibitory dorsal horn neurons where they regulate transmitter release

Integrating silver compounds and nanoparticles into ceria nanocontainers for antimicrobial applications

Silver compounds and nanoparticles (NPs) are gaining increasing interest in medical applications, specifically in the treatment and prevention of biomaterial-related infections. However, the silver release from these materials, resulting in a limited antimicrobial activity, is often difficult to control. In this paper, ceria nanocontainers were synthesized by a template-assisted method and were then used to encapsulate silver nitrate (AgNO₃/CeO₂ nanocontainers). Over the first 30 days, a significant level of silver was released, as determined using inductively coupled plasma optical emission spectroscopy (ICP-OES). A novel type of ceria container containing silver NPs (AgNP/CeO₂ containers) was also developed using two different template removal methods. The presence of AgNPs was confirmed both on the surface and in the interior of the ceria containers by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Upon removal of the template by calcination, the silver was released over a period exceeding three months (>90 days). However, when the template was removed by dissolution, the silver release was shortened to ≤14 days. The antimicrobial activity of the silver-containing CeO₂ containers was observed and the minimum bactericidal concentration (MBC) was determined using the broth dilution method. Investigation on human cells, using a model epithelial barrier cell type (A549 cells), highlighted that all three samples induced a heightened cytotoxicity leading to cell death when exposed to all containers in their raw form. This was attributed to the surface roughness of the CeO₂ nanocontainers and the kinetics of the silver release from the AgNO₃/CeO₂ and AgNP/CeO₂ nanocontainers. In conclusion, despite the need for further emphasis on their biocompatibility, the concept of the AgNP/CeO₂ nanocontainers offers a potentially alternative long-term antibactericidal strategy for implant materials

Mineralization of ancient carbon in the subsurface of riparian forests

Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 113 (2008): G02021, doi:10.1029/2007JG000482.Microbial activity in saturated, subsurface sediments in riparian forests may be supported by recent photosynthate or ancient (>500 ybp) soil organic carbon (SOC) in buried horizons. Metabolism of ancient SOC may be particularly important in riparian zones, considered denitrification hot spots, because denitrification in the riparian subsurface is often C-limited, because buried horizons intersect deep flow paths, and because low C mineralization rates can support ecosystem-relevant rates of denitrification. Buried horizons are common where alluvial processes (stream migration, overbank flow) have dominated riparian evolution. Our objectives were to determine: (1) the extent to which ancient SOC directly supports subsurface microbial activity; (2) whether different C sources support microbial activity in alluvial versus glaciofluvial riparian zones; and (3) how microbial use of ancient SOC varies with depth. In situ groundwater incubations and 14C dating of dissolved inorganic carbon revealed that ancient SOC mineralization was common, and that it constituted 31–100% of C mineralization 2.6 m deep at one site, at rates sufficient to influence landscape N budgets. Our data failed to reveal consistent spatial patterns of microbially available ancient C. Although mineralized C age increased with depth at one alluvial site, we observed ancient C metabolism 150 cm deep at a glaciofluvial site, suggesting that subsurface microbial activity in riparian zones does not vary systematically between alluvial and glaciofluvial hydrogeologic settings. These findings underscore the relevance of ancient C to contemporary ecosystem processes and the challenge of using mappable surface features to identify subsurface ecosystem characteristics or riparian zone N-sink strength.We are grateful to the Cornell Program in Biogeochemistry for graduate research grants and to the U.S. EPA for a STAR Graduate Fellowship to Noel Gurwick. Support for radiocarbon analyses also came from USDANRICGP grant 99–35102– 8266, NSF cooperative agreement OCE-9807266, and an Andrew W. Mellon Foundation grant to the Institute of Ecosystem Studies. A graduate research grant to N. Gurwick from the Theresa Heinz Scholars for Environmental Research provided salary for Pete Seitz-Rundlett

Winter Rye Cover Crop Biomass Production, Degradation, and Nitrogen Recycling

Winter rye (Secale cereale L.) cover crop (RCC) use in corn (Zea mays L.) and soybean [Glycine max. (L.) Merr.] production can alter N dynamics compared to no RCC. The objectives of this study were to evaluate RCC biomass production (BP) and subsequent RCC degradation (BD) and N recycling in a no-till corn–soybean (CS) rotation. Aboveground RCC was sampled at spring termination for biomass dry matter (DM), C, and N. To evaluate BD and remaining C and N, RCC biomass was put into nylon mesh bags, placed on the soil surface, and collected multiple times over 105 d. Treatments included rye cover crop following soybean (RCC-FS) and corn (RCC-FC), and prior-year N applied to corn. Overall, the RCC BP and N was low due to low soil profile NO3–N. Across sites and years, the greatest BP was with RCC-FC that received 225 kg N ha–1 (1280 kg DM ha–1), with similar N uptake as with RCC-FS (27 kg N ha–1). The RCC biomass and N remaining decreased over time following an exponential decay. An average 62% biomass with RCC-FS and RCC-FC degraded after 105 d; however, N recycled was greater with RCC-FS than RCC-FC [22 (80%) vs. 14 (64%) kg N ha–1, respectively], and was influenced by the RCC C/N ratio. The RCC did not recycle an agronomically meaningful amount of N, which limited N that could potentially be supplied to corn. Rye cover crops can conserve soil N, and with improved management and growth, recycling of crop-available N should increase

The regional and global significance of nitrogen removal in lakes and reservoirs

Author Posting. © The Author(s), 2008. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Biogeochemistry 93 (2009): 143-157, doi:10.1007/s10533-008-9272-x.Human activities have greatly increased the transport of biologically available N through watersheds to potentially sensitive coastal ecosystems. Lentic water bodies (lakes and reservoirs) have the potential to act as important sinks for this reactive N as it is transported across the landscape because they offer ideal conditions for N burial in sediments or permanent loss via denitrification. However, the patterns and controls on lentic N removal have not been explored in great detail at large regional to global scales. In this paper we describe, evaluate, and apply a new, spatially explicit, annual-scale, global model of lentic N removal called NiRReLa (Nitrogen Retention in Reservoirs and Lakes). The NiRReLa model incorporates small lakes and reservoirs than have been included in previous global analyses, and also allows for separate treatment and analysis of reservoirs and natural lakes. Model runs for the mid-1990s indicate that lentic systems are indeed important sinks for N and are conservatively estimated to remove 19.7 Tg N yr-1 from watersheds globally. Small lakes (< 50 km2) were critical in the analysis, retaining almost half (9.3 Tg N yr-1) of the global total. In model runs, capacity of lakes and reservoirs to remove watershed N varied substantially (0-100%) both as a function of climate and the density of lentic systems. Although reservoirs occupy just 6% of the global lentic surface area, we estimate they retain approximately 33% of the total N removed by lentic systems, due to a combination of higher drainage ratios (catchment surface area : lake or reservoir surface area), higher apparent settling velocities for N, and greater N loading rates in reservoirs than in lakes. Finally, a sensitivity analysis of NiRReLa suggests that, on-average, N removal within lentic systems will respond more strongly to changes in land use and N loading than to changes in climate at the global scale.The NSF26 Research Coordination Network on denitrification for support for collaboration (award number DEB0443439 to S.P. Seitzinger and E.A. Davidson). This project was also supported by grants to J.A. Harrison from California Sea Grant (award number RSF8) and from the U.S. Geological Survey 104b program and R. Maranger (FQRNT Strategic Professor)

Prions in Milk from Ewes Incubating Natural Scrapie

Since prion infectivity had never been reported in milk, dairy products originating from transmissible spongiform encephalopathy (TSE)-affected ruminant flocks currently enter unrestricted into the animal and human food chain. However, a recently published study brought the first evidence of the presence of prions in mammary secretions from scrapie-affected ewes. Here we report the detection of consistent levels of infectivity in colostrum and milk from sheep incubating natural scrapie, several months prior to clinical onset. Additionally, abnormal PrP was detected, by immunohistochemistry and PET blot, in lacteal ducts and mammary acini. This PrPSc accumulation was detected only in ewes harbouring mammary ectopic lymphoid follicles that developed consequent to Maedi lentivirus infection. However, bioassay revealed that prion infectivity was present in milk and colostrum, not only from ewes with such lympho-proliferative chronic mastitis, but also from those displaying lesion-free mammary glands. In milk and colostrum, infectivity could be recovered in the cellular, cream, and casein-whey fractions. In our samples, using a Tg 338 mouse model, the highest per ml infectious titre measured was found to be equivalent to that contained in 6 µg of a posterior brain stem from a terminally scrapie-affected ewe. These findings indicate that both colostrum and milk from small ruminants incubating TSE could contribute to the animal TSE transmission process, either directly or through the presence of milk-derived material in animal feedstuffs. It also raises some concern with regard to the risk to humans of TSE exposure associated with milk products from ovine and other TSE-susceptible dairy species

Global divergent trends of algal blooms detected by satellite during 1982–2018

Algal blooms (ABs) in inland lakes have caused adverse ecological effects, and health impairment of animals and humans. We used archived Landsat images to examine ABs in lakes (>1 km2) around the globe over a 37-year time span (1982–2018). Out of the 176032 lakes with area >1 km2 detected globally, 863 were impacted by ABs, 708 had sufficiently long records to define a trend, and 66% exhibited increasing trends in frequency ratio (FRQR, ratio of the number of ABs events observed in a year in a given lake to the number of available Landsat images for that lake) or area ratio (AR, ratio of annual maximum area covered by ABs observed in a lake to the surface area of that lake), while 34% showed a decreasing trend. Across North America, an intensification of ABs severity was observed for FRQR (p<.01) and AR (p <.01) before 1999, followed by a decrease in ABs FRQR (p <.01) and AR (p <.05) after the 2000s. The strongest intensification of ABs was observed in Asia, followed by South America, Africa, and Europe. No clear trend was detected for the Oceania. Across climatic zones, the contributions of anthropogenic factors to ABs intensification (16.5% for fertilizer, 19.4% for gross domestic product, and 18.7% for population) were slightly stronger than climatic drivers (10.1% for temperature, 11.7% for wind speed, 16.8% for pressure, and for 11.6% for rainfall). Collectively, these divergent trends indicate that consideration of anthropogenic factors as well as climate change should be at the forefront of management policies aimed at reducing the severity and frequency of ABs in inland waters