Denitrification drives total nitrate uptake in small Puerto Rican streams

An intensive study that was part of the Lotic Intersite Nitrogen eXperiment II (LINX II) project was conducted to determine nitrogen transformations in nine low-order streams with contrasting land use. Short term (24-hour) additions of K15NO3 and NaBr were performed on a gradient of anthropogenically impacted streams in Puerto Rico. Nitrate uptake was determined from longitudinal decline in 15NO3 and denitrification rates were determined from the longitudinal pattern of 15N 2 and 15N2O. Several physical, chemical, and biological variables were also measured to determine controlling factors. I performed these experiments to investigate: (1) the mechanisms for NO3 uptake and denitrification in tropical streams, (2) how tropical streams differ from temperate streams in their rates and controls on NO3 uptake and denitrification and (3) the functional responses of these streams as NO3 concentrations increase due to anthropogenic impacts. Background nitrate concentrations ranged from 105 to 997 mug N L -1 and stream nitrate uptake length varied from 315 to 8480 m (median of 1200 m). Uptake length was mainly predicted by specific discharge (L s -1 m-1) and ecosystem respiration rate (multiple regression analysis; r2 = 0.71, p \u3c 0.05). The other nitrate uptake parameters (Vf, cm/s and U, mug N m-2 s -1) were primarily predicted by gross primary production and respiration, indicating strong biological control on nitrate uptake. Denitrification rates ranged from 0.01 to 2.20 mug N m-2 s-1 (median = 0.25) and the strongest predictors were respiration and fine benthic organic matter (r2 = 0.89, p \u3c 0.05). Denitrification accounted for 1 to 97% of nitrate uptake with 5 of 9 streams having 35% or more of nitrate uptake via denitrification showing that denitrification is a substantial sink for nitrate in tropical streams. In comparison to rates in other regions, nitrate uptake was low and denitrification was high. Whole stream nitrate uptake more closely followed Michealis-Menten kinetics than in other regions, indicating that high N streams are approaching nitrate saturation. The efficiency with which these streams assimilate and remove nitrate (through denitrification) generally declines with increasing nitrate concentrations and loading

Aquatic biosurvey of the Lovell River on UNH land

We assessed the physical, chemical and biological conditions at two sites along the Lovell River on University of New Hampshire (UNH) -owned conservation land. The discharge was 4.4 m3 s-1 at Site 1 and 5.7 m3 s -1 downstream at Site 2. Canopy coverage ranged from 8-25%. Canopy was dominated by Eastern Hemlock (79-84%). Much of the stream was strewn with large boulders and the substrate consisted of rocks of highly variable sizes ( 3-549 cm dia.). Specific conductivity (22.1-23.3 µS), pH (6.4) and temperature (7.9-8.3 °C) varied little between sites. Macro-invertebrate bio-indices indicated either excellent water quality with no apparent organic pollution (3.0/10) or good water quality with possible slight organic pollution (4.4/10)

Leaf-litter leachate is distinct in optical properties and bioavailability to stream heterotrophs

Dissolved organic C (DOC) leached from leaf litter contributes to the C pool of stream ecosystems and affects C cycling in streams. We studied how differences in leaf-litter chemistry affect the optical properties and decomposition of DOC. We used 2 species of cottonwoods (Populus) and their naturally occurring hybrids that differ in leaf-litter phytochemistry and decomposition rate. We measured DOC and nutrient concentration in leaf leachates and determined the effect of DOC quality on heterotrophic respiration in 24-h incubations with stream sediments. Differences in DOC composition and quality were characterized with fluorescence spectroscopy. Rapidly decomposing leaves with lower tannin and lignin concentrations leached ~40 to 50% more DOC and total dissolved N than did slowly decomposing leaves. Rates of heterotrophic respiration were 25 to 50% higher on leachate from rapidly decomposing leaf types. Rates of heterotrophic respiration were related to metrics of aromaticity. Specifically, rates of respiration were correlated negatively with the Fluorescence Index and positively with Specific Ultraviolet Absorbance (SUVA254) and T280 tryptophan-like fluorescence peak. These results reveal that leaf-litter DOC is distinctly different from ambient streamwater DOC. The relationships between optical characteristics of leaf leachate and bioavailability are opposite those found in streamwater DOC. Differences in phytochemistry among leaf types can influence stream ecosystems with respect to DOC quantity, composition, and rates of stream respiration. These patterns suggest that the relationship between the chemical structure of DOC and its biogeochemistry is more complex than previously recognized. These unique properties of leaf-litter DOC will be important when assessing the effects of terrestrial C on aquatic ecosystems, especially during leaf fall

Thinking outside the channel : modeling nitrogen cycling in networked river ecosystems

Author Posting. © Ecological Society of America, 2011. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Frontiers in Ecology and the Environment 9 (2011): 229–238, doi:10.1890/080211.Agricultural and urban development alters nitrogen and other biogeochemical cycles in rivers worldwide. Because such biogeochemical processes cannot be measured empirically across whole river networks, simulation models are critical tools for understanding river-network biogeochemistry. However, limitations inherent in current models restrict our ability to simulate biogeochemical dynamics among diverse river networks. We illustrate these limitations using a river-network model to scale up in situ measures of nitrogen cycling in eight catchments spanning various geophysical and land-use conditions. Our model results provide evidence that catchment characteristics typically excluded from models may control river-network biogeochemistry. Based on our findings, we identify important components of a revised strategy for simulating biogeochemical dynamics in river networks, including approaches to modeling terrestrial–aquatic linkages, hydrologic exchanges between the channel, floodplain/riparian complex, and subsurface waters, and interactions between coupled biogeochemical cycles.This research was supported by NSF (DEB-0111410). Additional support was provided by NSF for BJP and SMT (DEB-0614301), for WMW (OCE-9726921 and DEB-0614282), for WHM and JDP (DEB-0620919), for SKH (DEB-0423627), and by the Gordon and Betty Moore Foundation for AMH, GCP, ESB, and JAS, and by an EPA Star Fellowship for AMH

Stream denitrification across biomes and its response to anthropogenic nitrate loading

Author Posting. © The Author(s), 2008. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature 452 (2008): 202-205, doi:10.1038/nature06686.Worldwide, anthropogenic addition of bioavailable nitrogen (N) to the biosphere is increasing and terrestrial ecosystems are becoming increasingly N saturated, causing more bioavailable N to enter groundwater and surface waters. Large-scale N budgets show that an average of about 20-25% of the N added to the biosphere is exported from rivers to the ocean or inland basins, indicating substantial sinks for N must exist in the landscape. Streams and rivers may be important sinks for bioavailable N owing to their hydrologic connections with terrestrial systems, high rates of biological activity, and streambed sediment environments that favor microbial denitrification. Here, using data from 15N tracer experiments replicated across 72 streams and 8 regions representing several biomes, we show that total biotic uptake and denitrification of nitrate increase with stream nitrate concentration, but that the efficiency of biotic uptake and denitrification declines as concentration increases, reducing the proportion of instream nitrate that is removed from transport. Total uptake of nitrate was related to ecosystem photosynthesis and denitrification was related to ecosystem respiration. Additionally, we use a stream network model to demonstrate that excess nitrate in streams elicits a disproportionate increase in the fraction of nitrate that is exported to receiving waters and reduces the relative role of small versus large streams as nitrate sinks.Funding for this research was provided by the National Science Foundation

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Salinization of urbanizing New Hampshire streams and groundwater: effects of road salt and hydrologic variability

Since the 1940s, use of road salt as a deicing agent has increased substantially in regions of the US with cold winters. Despite its ubiquitous application and known negative consequences for aquatic and human health, little research has documented the effects of road salt on the water quality of either streams or groundwater in regions, such as New Hampshire (NH), with harsh northern climates. We measured stream Na(+) and Cl(-) concentrations in 44 basins spanning a gradient of urbanization in southeastern and central NH. Among all sampled basins, stream Na(+) and Cl(-) concentrations were highly correlated with basin % road pavement (r(2) = 0.75 for Na(+), and 0.78 for Cl(-)). In southeastern NH, concentrations also were correlated strongly with % impervious surface (r(2) = 0.86 for Na(+), and 0.92 for Cl(-)). Groundwater salt concentrations in 143 private wells were significantly correlated with % impervious surface within a 500-m radius of each well, but the proportion of explained variance was small (r(2) = 0.07 for Na(+), and 0.10 for Cl(-)). Concentrations of salt in streams and groundwater were surprisingly high. Mean concentrations of Na(+) ranged from \u3c1 to 298 mg/L and of Cl(-) ranged from \u3c1 to 573 mg/L. Mean Cl(-) concentration in I small stream exceeded the US Environmental Protection Agency (EPA) chronic toxicity standard of 230 mg/L, and 9% of groundwater samples exceeded the secondary EPA maximum contamination levels for drinking water (250 mg/L of either Na(+) or Cl(-)). In our long-term study basin, the Lamprey River, specific conductance increased over the period from 1978 to 2008, a result that indicated a corresponding increase in Na(+) and Cl(-) concentrations. Both Na(+) and Cl(-) concentrations in the Lamprey River were negatively correlated with flow, but the slope of the relationship decreased after a significant flood in 2006. Our data suggest that road-salting practices are contributing to the salinization of stream water and groundwater in NH, and that hydrologic variability, which is predicted to increase with climate change, could strongly affect the degree of salinization observed in surface waters

Exploration and Discovery of Hydrocarbon Seeps, Coral Ecosystems, and Shipwrecks in the Deep Gulf of Mexico

Between March 20 and April 6, 2012, the NOAA Ship Okeanos Explorer served as a platform for ship-board and shore-side scientists to explore the deep Gulf of Mexico, targeting the northern West Florida Escarpment, DeSoto Canyon, the vicinity (within 11km) of the Deepwater Horizon (DWH) well, and deepwater shipwrecks. We systematically explored and discovered natural hydrocarbon seeps, diverse coral ecosystems, wooden and iron-hulled shipwrecks more than 100 years old colonized by coral communities, and sperm whale habitat between 600 and 1200m. A total of sixteen dives took advantage of new and recent maps to explore and groundtruth both hard and soft-bottom habitats, from cretaceous carbonates to mounds of coral rubble. The final ROV dive successfully groundtruthed expected methane-release areas imaged by the ship’s mapping systems up to 1150m above the seafloor. The source of the mapping imagery was a stream of bubbles issuing from beneath thriving seep mussel communities. We visited five sites in the Mississippi Canyon (MC) area (lease blocks MC294, MC297, MC388, MC255, and MC036; the DWH incident took place in MC252). These sites were 11.3 km SW, 6.8 km SW, 7.6 km SW, 25.7 km E, and 27.4 km to the NE of the DWH, respectively. We used high-definition imaging systems on the Little Hercules ROV and Seirios camera platform to document more than 130 coral colonies and over 400 associated individual animals to continue to assessing the impact of the Deepwater Horizon oil spill. All of these efforts were conducted to provide fundamental knowledge of unknown and poorly known regions, ecosystems, and items of historical significance in the deep Gulf of Mexico

The Preventing Alzheimer\u27s with Cognitive Training (PACT) randomized clinical trial

BACKGROUND: To address the rising prevalence of Alzheimer\u27s disease and related dementias, effective interventions that can be widely disseminated are warranted. The Preventing Alzheimer\u27s with Cognitive Training study (PACT) investigates a commercially available computerized cognitive training program targeting improved Useful Field of View Training (UFOVT) performance. The primary goal is to test the effectiveness of UFOVT to reduce incidence of clinically defined mild cognitive impairment (MCI) or dementia with a secondary objective to examine if effects are moderated by plasma β-amyloid level or apolipoprotein E e4 (APOE e4) allele status. METHODS/DESIGN: This multisite study utilizes a randomized, controlled experimental design with blinded assessors and investigators. Individuals who are 65 years of age and older are recruited from the community. Eligible participants who demonstrate intact cognitive status (Montreal Cognitive Assessment score \u3e 25) are randomized and asked to complete 45 sessions of either a commercially available computerized-cognitive training program (UFOVT) or computerized games across 2.5 years. After three years, participants are screened for cognitive decline. For those demonstrating decline or who are part of a random subsample, a comprehensive neuropsychological assessment is completed. Those who perform below a pre-specified level are asked to complete a clinical evaluation, including an MRI, to ascertain clinical diagnosis of normal cognition, MCI, or dementia. Participants are asked to provide blood samples for analyses of Alzheimer\u27s disease related biomarkers. DISCUSSION: The PACT study addresses the rapidly increasing prevalence of dementia. Computerized cognitive training may provide a non-pharmaceutical option for reducing incidence of MCI or dementia to improve public health. REGISTRATION: The PACT study is registered at http://Clinicaltrials.govNCT03848312