Impoundment increases methane emissions in Phragmites-invaded coastal wetlands.

Saline tidal wetlands are important sites of carbon sequestration and produce negligible methane (CH4 ) emissions due to regular inundation with sulfate-rich seawater. Yet, widespread management of coastal hydrology has restricted tidal exchange in vast areas of coastal wetlands. These ecosystems often undergo impoundment and freshening, which in turn cause vegetation shifts like invasion by Phragmites, that affect ecosystem carbon balance. Understanding controls and scaling of carbon exchange in these understudied ecosystems is critical for informing climate consequences of blue carbon restoration and/or management interventions. Here, we (1) examine how carbon fluxes vary across a salinity gradient (4-25 psu) in impounded and natural, tidally unrestricted Phragmites wetlands using static chambers and (2) probe drivers of carbon fluxes within an impounded coastal wetland using eddy covariance at the Herring River in Wellfleet, MA, United States. Freshening across the salinity gradient led to a 50-fold increase in CH4 emissions, but effects on carbon dioxide (CO2 ) were less pronounced with uptake generally enhanced in the fresher, impounded sites. The impounded wetland experienced little variation in water-table depth or salinity during the growing season and was a strong CO2 sink of -352 g CO2 -C m-2  year-1 offset by CH4 emission of 11.4 g CH4 -C m-2  year-1 . Growing season CH4 flux was driven primarily by temperature. Methane flux exhibited a diurnal cycle with a night-time minimum that was not reflected in opaque chamber measurements. Therefore, we suggest accounting for the diurnal cycle of CH4 in Phragmites, for example by applying a scaling factor developed here of ~0.6 to mid-day chamber measurements. Taken together, these results suggest that although freshened, impounded wetlands can be strong carbon sinks, enhanced CH4 emission with freshening reduces net radiative balance. Restoration of tidal flow to impounded ecosystems could limit CH4 production and enhance their climate regulating benefits.

Intra-articular injection of epigallocatechin (EGCG) crosslinks and alters biomechanical properties of articular cartilage, a study via nanoindentation.

Osteoarthritis and rheumatoid arthritis are debilitating conditions, affecting millions of people. Both osteoarthritis and rheumatoid arthritis degrade the articular cartilage (AC) at the ends of long bones, resulting in weakened tissue prone to further damage. This degradation impairs the cartilage's mechanical properties leading to areas of thinned cartilage and exposed bone which compromises the integrity of the joint. No preventative measures exist for joint destruction. Discovering a way to slow the degradation of AC or prevent it would slow the painful progression of the disease, allowing millions to live pain-free. Recently, that the articular injection of the polyphenol epigallocatechin-gallate (EGCG) slows AC damage in an arthritis rat model. It was suggested that EGCG crosslinks AC and makes it resistant to degradation. However, direct evidence that intraarticular injection of EGCG crosslinks cartilage collagen and changes its compressive properties are not known. The aim of this study was to investigate the effects of intraarticular injection of EGCG induced biomechanical properties of AC. We hypothesize that in vivo exposure EGCG will bind and crosslink to AC collagen and alter its biomechanical properties. We developed a technique of nano-indentation to investigate articular cartilage properties by measuring cartilage compressive properties and quantifying differences due to EGCG exposure. In this study, the rat knee joint was subjected to a series of intraarticular injections of EGCG and contralateral knee joint was injected with saline. After the injections animals were sacrificed, and the knees were removed and tested in an anatomically relevant model of nanoindentation. All mechanical data was normalized to the measurements in the contralateral knee to better compare data between the animals. The data demonstrated significant increases for reduced elastic modulus (57.5%), hardness (83.2%), and stiffness (17.6%) in cartilage treated with injections of EGCG normalized to those treated with just saline solution when compared to baseline subjects without injections, with a significance level of alpha = 0.05. This data provides evidence that EGCG treated cartilage yields a strengthened cartilage matrix as compared to AC from the saline injected knees. These findings are significant because the increase in cartilage biomechanics will translate into resistance to degradation in arthritis. Furthermore, the data suggest for the first time that it is possible to strengthen the articular cartilage by intraarticular injections of polyphenols. Although this data is preliminary, it suggests that clinical applications of EGCG treated cartilage could yield strengthened tissue with the potential to resist or compensate for matrix degradation caused by arthritis.

Soil carbon consequences of historic hydrologic impairment and recent restoration in coastal wetlands.

Coastal wetlands provide key ecosystem services, including substantial long-term storage of atmospheric CO2 in soil organic carbon pools. This accumulation of soil organic matter is a vital component of elevation gain in coastal wetlands responding to sea-level rise. Anthropogenic activities that alter coastal wetland function through disruption of tidal exchange and wetland water levels are ubiquitous. This study assesses soil vertical accretion and organic carbon accretion across five coastal wetlands that experienced over a century of impounded hydrology, followed by restoration of tidal exchange 5 to 14 years prior to sampling. Nearby marshes that never experienced tidal impoundment served as controls with natural hydrology to assess the impact of impoundment and restoration. Dated soil cores indicate that elevation gain and carbon storage were suppressed 30-70 % during impoundment, accounting for the majority of elevation deficit between impacted and natural sites. Only one site had substantial subsidence, likely due to oxidation of soil organic matter. Vertical and carbon accretion gains were achieved at all restored sites, with carbon burial increasing from 96 ± 33 to 197 ± 64 g C m-2 y-1. The site with subsidence was able to accrete at double the rate (13 ± 5.6 mm y-1) of the natural complement, due predominantly to organic matter accumulation rather than mineral deposition, indicating these ecosystems are capable of large dynamic responses to restoration when conditions are optimized for vegetation growth. Hydrologic restoration enhanced elevation resilience and climate benefits of these coastal wetlands.

High frequency ultrasound prediction of mechanical properties of cortical bone with varying amount of mineral content.

In this study, we evaluate if high frequency ultrasound impedance measurements can predict the mechanical properties of bones where the amount of bone mineral is varied. The motivation stems from the potential utility of ultrasound as a noninvasive technique to evaluate and monitor the mechanical properties of bone during treatment of diseased states where the ratio of mineral content to organic matrix content could change (e.g., metabolic bone diseases, osteoarthritis, osteogenesis imperfecta, fracture healing). Eleven cortical bovine femur samples, which were taken along the long axis of femur, were used in each group. Bone samples with reduced mineral content (estimated to be 21% and 35% less than the control) were obtained by immersing samples into fluoride ion solution for 3 and 12 d. Control and fluoride treated samples were first tested mechanically in tension. Acoustic impedances of the mechanically tested samples were obtained by using scanning acoustic microscopy (SAM). Results from mechanical tests indicate that the tensile elastic modulus of the samples was highly correlated to the yield strength (r(2) = 0.94, p < 0.01) and to the ultimate strength (r(2) = 0.75, p < 0.01). SAM results indicate that the acoustic impedances were significantly correlated to the elastic modulus (r(2) = 0.85, p < 0.01), yield strength (r(2) = 0.86, p < 0.01) and ultimate strength (r(2) = 0.70, p < 0.01). These results show that ultrasonic techniques could potentially be used to predict the in vivo ultimate strength of bone tissue caused by changes in mineral content.

Osteopontin deficiency and aging on nanomechanics of mouse bone.

Osteoporosis is a bone disease characterized by low bone mass and deterioration of the tissue leading to increased fragility. Osteopontin (OPN), a noncollageneous bone matrix protein, has been shown to play an important role in osteoporosis, bone resorption, and mineralization. However, OPN's role in bone mechanical properties on the submicron scale has not been studied in any detail. In this study, nanoindentation techniques were utilized to investigate how OPN and aging affect bone mechanical properties. Hardness and elastic modulus were calculated and compared between the OPN-deficient mice (OPN(-/-)) and their age and sex-matched wild-type (OPN(+/+)) controls. The results show that the mechanical properties of the young OPN(-/-) bones (age < 12 weeks) are significantly lower than that of the youngest OPN(+/+) bones. This finding was confirmed by additional microindentation testing. Biochemical analysis using micro-Raman spectroscopy indicated more mineral content in young OPN(+/+) bones. Older (age > 12 weeks) bones did not show any significant differences in mechanical properties with genotype. In addition, OPN(+/+) bones show a decrease in mechanical properties between young and older age groups. By contrast, OPN(-/-) bones showed no significant change in mechanical properties with aging.

AFM study of hydrophilicity on acetaminophen crystals.

Pharmaceutical powder processing is notoriously subject to unpredictable jamming, sticking and charging disturbances. To unveil the material science underlying these effects, we use atomic force microscopy (AFM) on a common pharmaceutical, acetaminophen (APAP). Specifically, we study surface adhesion and morphology as a function of relative humidity (RH) for monoclinic acetaminophen, using both plain AFM tips and tips functionalized to be hydrophobic or hydrophilic. Results indicate that the (001) crystal face exhibits significantly higher adhesion (surface potential) than the other crystal faces. For all the faces clear peaks in adhesion occur at 50-60% RH when they are examined using hydrophilic tips. The surface morphology of some facets showed a strong dependence on RH while others showed little or no significant change. In particular, the morphology of the (1-10) faces developed large terraces at high humidity, possibly due to deliquescence followed by recrystallization. These results confirm the hypothesis that different crystal facets exhibit distinct surface potentials and morphology that change with environmental exposure. The work suggests that future studies of powder behaviors would benefit from a more detailed modeling of crystal surface contact mechanics.