Sediment Nutrient Accumulation and Nutrient Availability in Two Tidal Freshwater Marshes Along the Mattaponi River, Virginia, USA

Sediment deposition is the main mechanism of nutrient delivery to tidal freshwater marshes (TFMs). We quantified sediment nutrient accumulation in TFMs upstream and downstream of a proposed water withdrawal project on the Mattaponi River, Virginia. Our goal was to assess nutrient availability by comparing relative rates of carbon (C), nitrogen (N), and phosphorus (P) accumulated in sediments with the C, N, and P stoichiometries of surface soils and above ground plant tissues. Surface soil nutrient contents (0.60–0.92% N and 0.09–0.13% P) were low but within reported ranges for TFMs in the eastern US. In both marshes, soil nutrient pools and C, N, and P stoichiometries were closely associated with sedimentation patterns. Differences between marshes were more striking than spatial variations within marshes: both C, N, and P accumulation during summer, and annual P accumulation rates (0.16 and 0.04 g P m−2 year−1, respectively) in sediments were significantly higher at the downstream than at the upstream marsh. Nitrogen:P ratiosbiomass, surface soils, and sediments suggest that N limits primary production in these marshes, but experimental additions of N and/or P did not significantly increase above ground productivity in either marsh. Lower soil N:P ratios are consistent with higher rates of sediment P accumulation at the downstream site, perhaps due to its greater proximity to the estuarine turbidity maximum

THE EFFECTS OF LOAD MASS ON THE KINEMATICS OF STIFF-LEGGED DEADLIFT

The purpose of this study was to investigate the effects of load mass on the kinematics of lower extremity joint movements during the stiff-legged deadlift (SLD) lift exercise. Five participants performed the SLD at 40%, 60%, and 80% of their estimated 1 repetition maximum. Measurements of the joint angle and angular velocity of the spine, hip, knee, and ankle were analyzed to understand the influence of various load masses in the SLD lifting technique. No statistical significant differences were found in the joint angles and angular velocities of the spine and lower extremity between different loads. Therefore, this study suggests that performing stiff-legged exercise up to 80% is safe to perform as long as the participants are experienced with this lifting technique

The ABC's of affine Grassmannians and Hall-Littlewood polynomials

We give a new description of the Pieri rule for $k$-Schur functions using the Bruhat order on the affine type-$A$ Weyl group. In doing so, we prove a new combinatorial formula for representatives of the Schubert classes for the cohomology of affine Grassmannians. We show how new combinatorics involved in our formulas gives the Kostka-Foulkes polynomials and discuss how this can be applied to study the transition matrices between Hall-Littlewood and $k$-Schur functions

A tt-generalization for Schubert Representatives of the Affine Grassmannian

We introduce two families of symmetric functions with an extra parameter $t$ that specialize to Schubert representatives for cohomology and homology of the affine Grassmannian when $t=1$. The families are defined by a statistic on combinatorial objects associated to the type-$A$ affine Weyl group and their transition matrix with Hall-Littlewood polynomials is $t$-positive. We conjecture that one family is the set of $k$-atoms

Effect of a Lay Counselor Intervention on Prevention of Major Depression in Older Adults Living in Low- and Middle-Income Countries:A Randomized Clinical Trial

Importance: Preventing depression in older adults living in low- and middle-income countries is important because of the scarcity of treatment resources and the risk of disability, suicide, and dementia. Objective: To assess whether an intervention for depression prevention provided by lay counselors is effective in older adults from low- and middle-income countries. Design, Setting, and Participants: This parallel-group randomized clinical trial with masked outcome assessment was performed in 181 older adults (≥60 years) with subsyndromal depressive symptoms at rural and urban primary care clinics in Goa, India. The first participant entered the trial on March 31, 2015, and the last exited on June 2, 2017. Data analysis used the intention-to-treat approach. Interventions: Lay counselors provided problem-solving therapy, brief behavioral treatment for insomnia, education in self-care of common medical disorders such as diabetes, and assistance in accessing medical and social programs. Main Outcomes and Measures: The main outcome was incidence of major depressive episodes. The study also assessed symptom change during 12 months (12-item General Health Questionnaire [GHQ-12]; score range of 0 to 12, with higher scores indicating greater symptoms of depression and anxiety), functional status (World Health Organization Disability Assessment Schedule 2.0; score range of 12 to 60, with higher scores indicating greater disability), cognition (Hindi Mini-Mental State Examination; score range of 0 to 30, with higher scores indicating better cognitive functioning), blood pressure, and body mass index to provide further clinical context. Results: The study enrolled 181 participants (mean [SD] age, 69.6 [7.2] years; 114 [63.0%] female): 91 to the intervention arm (depression in later life [DIL] intervention) and 90 to care as usual (CAU). Incident episodes of major depression were lower in the DIL intervention than in the CAU group (4.40% vs 14.44%; log-rank P =.04; number needed to treat, 9.95; 95% CI, 5.12-182.43). The 12-month Kaplan-Meier estimates of percentage of depression-free participants were 95.1% (95% CI, 90.5%-99.9%) in the DIL group vs 87.4% (95% CI, 80.4%-95.1%) in the CAU group. The incidence of depressive symptoms (GHQ-12) was also less (12-month mean difference, -1.18; 95% CI, -2.03 to -0.31; group × time interaction P <.001). There were no changes in measures of disability or cognition. The DIL intervention was associated with a significantly greater lowering of systolic blood pressure (12-month mean difference, -6.98; 95% CI, -11.96 to -2.01; group × time interaction P <.001) and change in body mass index (12-month mean difference, 0.23; 95% CI, -0.97 to 1.43; P =.04). Conclusions and Relevance: The DIL intervention is effective for preventing episodes of major depression in older persons with subsyndromal symptoms. If replicated, the DIL intervention may be effective in older adults living in low- and middle-income countries

Nonlinear Elasticity in Biological Gels

Unlike most synthetic materials, biological materials often stiffen as they are deformed. This nonlinear elastic response, critical for the physiological function of some tissues, has been documented since at least the 19th century, but the molecular structure and the design principles responsible for it are unknown. Current models for this response require geometrically complex ordered structures unique to each material. In this Article we show that a much simpler molecular theory accounts for strain stiffening in a wide range of molecularly distinct biopolymer gels formed from purified cytoskeletal and extracellular proteins. This theory shows that systems of semi-flexible chains such as filamentous proteins arranged in an open crosslinked meshwork invariably stiffen at low strains without the need for a specific architecture or multiple elements with different intrinsic stiffnesses.Comment: 23 pages, 5 figures, submitted to Natur

Reduced Snow Cover Alters Root-microbe Interactions and Decreases Nitrification Rates in a Northern Hardwood Forest

Snow cover is projected to decline during the next century in many ecosystems that currently experience a seasonal snowpack. Because snow insulates soils from frigid winter air temperatures, soils are expected to become colder and experience more winter soil freeze-thaw cycles as snow cover continues to decline. Tree roots are adversely affected by snowpack reduction, but whether loss of snow will affect root-microbe interactions remains largely unknown. The objective of this study was to distinguish and attribute direct (e.g., winter snow-and/ or soil frost-mediated) vs. indirect (e.g., root-mediated) effects of winter climate change on microbial biomass, the potential activity of microbial exoenzymes, and net N mineralization and nitrification rates. Soil cores were incubated in situ in nylon mesh that either allowed roots to grow into the soil core (2 mm pore size) or excluded root ingrowth (50 μm pore size) for up to 29 months along a natural winter climate gradient at Hubbard Brook Experimental Forest, NH (USA). Microbial biomass did not differ among ingrowth or exclusion cores. Across sampling dates, the potential activities of cellobiohydrolase, phenol oxidase, and peroxidase, and net N mineralization rates were more strongly related to soil volumetric water content (P \u3c 0.05; R2 = 0.25–0.46) than to root biomass, snow or soil frost, or winter soil temperature (R2 \u3c 0.10). Root ingrowth was positively related to soil frost (P \u3c 0.01; R2 = 0.28), suggesting that trees compensate for overwinter root mortality caused by soil freezing by re-allocating resources towards root production. At the sites with the deepest snow cover, root ingrowth reduced nitrification rates by 30% (P \u3c 0.01), showing that tree roots exert significant influence over nitrification, which declines with reduced snow cover. If soil freezing intensifies over time, then greater compensatory root growth may reduce nitrification rates directly via plant-microbe N competition and indirectly through a negative feedback on soil moisture, resulting in lower N availability to trees in northern hardwood forests