High-precision measurement of phenylalanine and glutamic acid δ N by coupling ion-exchange chromatography and purge-and-trap continuous-flow isotope ratio mass spectrometry.

Rationale: Nitrogen isotopic compositions (δ N) of source and trophic amino acids (AAs) are crucial tracers of N sources and trophic enrichments in diverse fields, including archeology, astrobiochemistry, ecology, oceanography, and paleo-sciences. The current analytical technique using gas chromatography-combustion-isotope ratio mass spectrometry (GC/C/IRMS) requires derivatization, which is not compatible with some key AAs. Another approach using high-performance liquid chromatography-elemental analyzer-IRMS (HPLC/EA/IRMS) may experience coelution issues with other compounds in certain types of samples, and the highly sensitive nano-EA/IRMS instrumentations are not widely available.

Effects of concentrated poultry operations and cropland manure application on antibiotic resistant Escherichia coli and nutrient pollution in Chesapeake Bay watersheds.

Manure from poultry operations is typically applied to nearby cropland and may affect nutrient loading and the spread of antibiotic resistance (ABR). We analyzed the concentrations of nitrogen and phosphorus and the occurrence of ABR in Escherichia coli (E. coli) and extra-intestinal pathogenic E.

Kelp beds and their local effects on seawater chemistry, productivity, and microbial communities.

Kelp forests are known as key habitats for species diversity and macroalgal productivity; however, we know little about how these biogenic habitats interact with seawater chemistry and phototroph productivity in the water column. We examined kelp forest functions at three locales along the Olympic Peninsula of Washington state by quantifying carbonate chemistry, nutrient concentrations, phytoplankton productivity, and seawater microbial communities inside and outside of kelp beds dominated by the canopy kelp species Nereocystis luetkeana and Macrocystis pyrifera. Kelp beds locally increased the pH, oxygen, and aragonite saturation state of the seawater, but lowered seawater inorganic carbon content and total alkalinity.

A Ti(III) reduction method for one-step conversion of seawater and freshwater nitrate into N O for stable isotopic analysis of N/ N, O/ O and O/ O.

Rationale: The nitrogen and oxygen (δ N, δ O, and δ O values) isotopic compositions of nitrate (NO ) are crucial tracers of nutrient nitrogen (N) sources and dynamics in aquatic systems. Current methods such as bacterial denitrification or Cd-azide reduction require laborious multi-step conversions or toxic chemicals to reduce NO to N O for N and O isotopic analyses by isotope ratio mass spectrometry (IRMS). Furthermore, the O composition of N O cannot be directly disentangled using IRMS because O contributes to mass 45 ( N).

Copepod-Associated Gammaproteobacteria Respire Nitrate in the Open Ocean Surface Layers.

Microbial dissimilatory nitrate reduction to nitrite, or nitrate respiration, was detected in association with copepods in the oxygenated water column of the North Atlantic subtropical waters. These unexpected rates correspond to up to 0.09 nmol N copepod d and demonstrate a previously unaccounted nitrogen transformation in the oceanic pelagic surface layers.