320 research outputs found
Genetic Sequencing Methodologies to Assess Human Contributions of Fecal Coliforms to a Freshwater Receiving Stream
2012 S.C. Water Resources Conference - Exploring Opportunities for Collaborative Water Research, Policy and Managemen
Denitrification and total nitrate uptake in streams of a tropical landscape
Author Posting. © Ecological Society of America, 2010. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Ecological Applications 20 (2010): 2104-2115, doi:10.1890/09-1110.1.Rapid increases in nitrogen (N) loading are occurring in many tropical watersheds, but the fate of N in tropical streams is not well documented. Rates of nitrate uptake and denitrification were measured in nine tropical low-order streams with contrasting land use as part of the Lotic Intersite Nitrogen eXperiment II (LINX II) in Puerto Rico using short term (24-hour) additions of K15NO3 and NaBr. Background nitrate concentrations ranged from 105 to 997 μg N/L, and stream nitrate uptake lengths were long, varying from 315 to 8480 m (median of 1200 m). Other indices of nitrate uptake (mass transfer coefficient, Vf [cm/s], and whole-stream nitrate uptake rate, U [μg N·m−2·s−1]) were low in comparison to other regions and were related to chemical, biological, and physical parameters. Denitrification rates were highly variable (0–133 μg N·m−2·min−1; median = 15 μg N·m−2·min−1), were dominated by the end product N2 (rather than N2O), and were best predicted by whole-stream respiration rates and stream NO3 concentration. Denitrification accounted for 1–97% of nitrate uptake with five of nine streams having 35% or more of nitrate uptake via denitrification, showing that denitrification is a substantial sink for nitrate in tropical streams. Whole-stream nitrate uptake and denitrification in our study streams closely followed first-order uptake kinetics, indicating that NO3 uptake is limited by delivery of substrate (NO3) to the organisms involved in uptake or denitrification. In the context of whole-catchment nitrogen budgets, our finding that in-stream denitrification results in lower proportional production of N2O than terrestrial denitrification suggests that small streams can be viewed as the preferred site of denitrification in a watershed in order to minimize greenhouse gas N2O emissions. Conservation of small streams is thus critical in tropical ecosystem management.This research was part of the Lotic Intersite Nitrogen
eXperiment II (LINX II) funded by the National Science
Foundation (DEB-0111410). Additional support was provided
by the National Science Foundation to the Institute of
Terrestrial Ecology at the University of Puerto Rico and the
International Institute of Tropical Forestry (DEB-0218039 and
DEB-0620919) through the Luquillo Long Term Ecological
Research (LUQ LTER) program
Hamiltonian submanifolds of regular polytopes
We investigate polyhedral -manifolds as subcomplexes of the boundary
complex of a regular polytope. We call such a subcomplex {\it -Hamiltonian}
if it contains the full -skeleton of the polytope. Since the case of the
cube is well known and since the case of a simplex was also previously studied
(these are so-called {\it super-neighborly triangulations}) we focus on the
case of the cross polytope and the sporadic regular 4-polytopes. By our results
the existence of 1-Hamiltonian surfaces is now decided for all regular
polytopes.
Furthermore we investigate 2-Hamiltonian 4-manifolds in the -dimensional
cross polytope. These are the "regular cases" satisfying equality in Sparla's
inequality. In particular, we present a new example with 16 vertices which is
highly symmetric with an automorphism group of order 128. Topologically it is
homeomorphic to a connected sum of 7 copies of . By this
example all regular cases of vertices with or, equivalently, all
cases of regular -polytopes with are now decided.Comment: 26 pages, 4 figure
Normal Values of Circulating IGF-I Bioactivity in the Healthy Population: Comparison with five widely used IGF-I immunoassays
Background: IGF-I immunoassays are primarily used to estimate IGF-I bioactivity. Recently, an IGFI
specific Kinase Receptor Activation Assay (KIRA) has been developed as an alternative method.
However, no normative values have been established for the IGF-I KIRA.
Objective: To establish normative values for the IGF-I KIRA in healthy adults.
Design: Cross-sectional study in healthy non-fasting blood donors.
Study participants: 426 healthy individuals (310 M, 116 F; age range: 18 – 79 yrs)
Main outcome Measures: IGF-I bioactivity determined by the KIRA. Results were compared with
total IGF-I, measured by five different IGF-I immunoassays.
Results: Mean (± SD) IGF-I bioactivity was 423 (± 131) pmol/L and decreased with age (β = -3.4
pmol/L/yr, p < 0.001). In subjects younger than 55 yrs mean IGF-I bioactivity was significantly higher
in women than in men. Above this age this relationship was inverse, suggesting a drop in IGF-I
bioactivity after menopause. This drop was not reflected in total IGF-I levels. IGF-I bioactivity was
significantly related to total IGF-I (rs varied between 0.46 – 0.52; P-values < 0.001).
Conclusions: We established age-specific normative values for the IGF-I KIRA. We observed a
significant drop in IGF-I bioactivity in women between 50 and 60 years, which was not perceived by
IGF-I immunoassays. The IGF-I KIRA, when compared to IGF-I immunoassays, theoretically has the
advantage that it measures net effects of IGF-binding proteins on IGF-I receptor activation. However,
it has to be proven whether information obtained by the IGF-I KIRA is clinically more relevant than
measurements obtained by IGF-I immunoassays
Range-wide sources of variation in reproductive rates of northern spotted owls
We conducted a range-wide investigation of the dynamics of site-level reproductive rate of northern spotted owls using survey data from 11 study areas across the subspecies geographic range collected during 1993–2018. Our analytical approach accounted for imperfect detection of owl pairs and misclassification of successful reproduction (i.e., at least one young fledged) and contributed further insights into northern spotted owl population ecology and dynamics. Both nondetection and state misclassification were important, especially because factors affecting these sources of error also affected focal ecological parameters. Annual probabilities of site occupancy were greatest at sites with successful reproduction in the previous year and lowest for sites not occupied by a pair in the previous year. Site-specific occupancy transition probabilities declined over time and were negatively affected by barred owl presence. Overall, the site-specific probability of successful reproduction showed substantial year-to-year fluctuations and was similar for occupied sites that did or did not experience successful reproduction the previous year. Site-specific probabilities for successful reproduction were very small for sites that were unoccupied the previous year. Barred owl presence negatively affected the probability of successful reproduction by northern spotted owls in Washington and California, as predicted, but the effect in Oregon was mixed. The proportions of sites occupied by northern spotted owl pairs showed steep, near-monotonic declines over the study period, with all study areas showing the lowest observed levels of occupancy to date. If trends continue it is likely that northern spotted owls will become extirpated throughout large portions of their range in the coming decades
The methylation status of the embryonic limb skeletal progenitors determines their cell fate in chicken
Digits shape is sculpted by interdigital programmed cell death during limb development. Here, we show that DNA breakage in the periphery of 5-methylcytosine nuclei foci of interdigital precursors precedes cell death. These cells showed higher genome instability than the digit-forming precursors when exposed to X-ray irradiation or local bone morphogenetic protein (BMP) treatments. Regional but not global DNA methylation differences were found between both progenitors. DNA-Methyl-Transferases (DNMTs) including DNMT1, DNMT3B and, to a lesser extent, DNMT3A, exhibited well-defined expression patterns in regions destined to degenerate, as the interdigital tissue and the prospective joint regions. Dnmt3b functional experiments revealed an inverse regulation of cell death and cartilage differentiation, by transcriptional regulation of key genes including Sox9, Scleraxis, p21 and Bak1, via differential methylation of CpG islands across their promoters. Our findings point to a regulation of cell death versus chondrogenesis of limb skeletal precursors based on epigenetic mechanisms.We thank Prof. Miguel Lafarga for helpful comments and advice. We thank Dr Jose E Gomez-Arozamena for helping us with the irradiation experiments. We are grateful to Montse Fernandez Calderon, Susana Dawalibi, and Sonia Perez Mantecon, for excellent technical assistance. This work was supported by a Grant (BFU2017–84046-P) from the Spanish Science and Innovation Ministry to JAM. C.S.F is recipient of a FPI grant (BES-2015–074267)
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