Science and Mathematicshttp://hdl.handle.net/10211.3/1301692024-03-29T12:03:50Z2024-03-29T12:03:50ZImaging Polyatomic Molecules in Three Dimensions Using Molecular Frame Photoelectron Angular DistributionsWilliams, J BTrevisan, C SJahnke, TBocharova, IKim, HUlrich, BWallauer, RSturm, FRescigno, T NBelkacem, ADorner, RWeber, ThMcCurdy, C WLanders, A Lhttp://hdl.handle.net/10211.3/1302362020-04-20T23:39:17Z0006-01-01T00:00:00ZImaging Polyatomic Molecules in Three Dimensions Using Molecular Frame Photoelectron Angular Distributions
Williams, J B; Trevisan, C S; Jahnke, T; Bocharova, I; Kim, H; Ulrich, B; Wallauer, R; Sturm, F; Rescigno, T N; Belkacem, A; Dorner, R; Weber, Th; McCurdy, C W; Landers, A L
We demonstrate a method for determining the full three-dimensional molecular-frame photoelectron
angular distribution in polyatomic molecules using methane as a prototype. Simultaneous double Auger
decay and subsequent dissociation allow measurement of the initial momentum vectors of the ionic
fragments and the photoelectron in coincidence, allowing full orientation by observing a three-ion decay
pathway, (Hþ, Hþ, CHþ
2 ). We find the striking result that at low photoelectron energies the molecule is
effectively imaged by the focusing of photoelectrons along bond directions
0006-01-01T00:00:00ZElevated ammonium concentrations from wastewater discharge depress primary productivity in the Sacramento River and the Northern San Francisco EstuaryParker, Alexander E.Dugdale, Richard C.Wilkerson, Frances P.http://hdl.handle.net/10211.3/1302342020-04-20T23:39:17Z2012-03-01T00:00:00ZElevated ammonium concentrations from wastewater discharge depress primary productivity in the Sacramento River and the Northern San Francisco Estuary
Parker, Alexander E.; Dugdale, Richard C.; Wilkerson, Frances P.
Primary production in the Northern San Francisco Estuary (SFE) has been declining despite heavy loading
of anthropogenic nutrients. The inorganic nitrogen (N) loading comes primarily from municipal wastewater
treatment plant (WTP) discharge as ammonium (NH4). This study investigated the consequences for
river and estuarine phytoplankton of the daily discharge of 15 metric tons NH4–N into the Sacramento
River that feeds the SFE. Consistent patterns of nutrients and phytoplankton responses were observed
during two 150-km transects made in spring 2009. Phytoplankton N productivity shifted from NO3 use
upstream of the WTP to productivity based entirely upon NH4 downstream. Phytoplankton NH4 uptake
declined downstream of the WTP as NH4 concentrations increased, suggesting NH4 inhibition. The
reduced total N uptake downstream of the WTP was accompanied by a 60% decline in primary production.
These findings indicate that increased anthropogenic NH4 may decrease estuarine primary production
and increase export of NH4 to the coastal ocean.
2012-03-01T00:00:00ZThe effect of inorganic nitrogen speciation on primary production in the San Francisco EstuaryParker, Alexander E.Hogue, Victoria E,Wilkerson, Frances P.Dugdale, Richard C.http://hdl.handle.net/10211.3/1302332020-04-20T23:39:17Z0006-01-01T00:00:00ZThe effect of inorganic nitrogen speciation on primary production in the San Francisco Estuary
Parker, Alexander E.; Hogue, Victoria E,; Wilkerson, Frances P.; Dugdale, Richard C.
We describe the results of a series of 96-h enclosure experiments conducted using water from stations in
the northern San Francisco Estuary (SFE) along a gradient in ammonium (NH4) and nitrate (NO3)
concentrations. Using dual-labeled 13C/15N tracers, we followed the timing and sequence of primary
(carbon, C) production and phytoplankton nitrogen (N) use during experimental phytoplankton blooms.
Our results show that diatoms consistently drive the phytoplankton blooms in the enclosures. By tracing
both C and N uptake we provide clear evidence that high rates of C uptake are linked to phytoplankton
NO3, and not NH4, use. Results from kinetics experiments demonstrated higher specific uptake rates
(VMAx) for NO3 compared to NH4 in the SFE. Finally, dissolved inorganic carbon and nutrient drawdown
ratios in the enclosures from the chronically high NH4 regions of the SFE were substantially lower than
predicted from the Redfield ratio, suggesting suppressed C uptake, in relation to other elemental uptake.
Our conceptual model of the DIN interactions that lead to higher primary production and phytoplankton
blooms in the SFE suggests that higher rates of primary production that accompany phytoplankton NO3
uptake are sufficient to outpace phytoplankton losses, leading to blooms, compared to the lower rates
associated with NH4 uptake (only 20% of that based upon NO3). Historical changes in wastewater
practices have increased the proportion of NH4 to the DIN pool in the SFE leading to reduced access to
NO3 by phytoplankton. This may help to explain some of the reduced primary production and phytoplankton
biomass observed there since the 1970s.
0006-01-01T00:00:00ZReevaluating the Generality of an Empirical Model for Light-Limited Primary Production in the San Francisco EstuaryParker, Alexander E.Kimmerer, Wim J.Lidstrom, Ulrika U.http://hdl.handle.net/10211.3/1302322020-04-20T23:39:17Z0005-01-01T00:00:00ZReevaluating the Generality of an Empirical Model for Light-Limited Primary Production in the San Francisco Estuary
Parker, Alexander E.; Kimmerer, Wim J.; Lidstrom, Ulrika U.
Depth-integrated primary production (ΣP, in grams
of carbon per square meter per day) was measured using 14C in
the northern San Francisco Estuary (SFE) fromMarch through
August of 2006 and 2007. Determinations of ΣP were then
used to calibrate a published light-utilization model that relates
ΣP to a composite parameter of chlorophyll, solar irradiance,
and photic zone depth. The resultant calibration coefficient, y,
varied by a factor of nearly two between 2006 and 2007 and
was lower than determined in previous calibrations for the
estuary. The now chronically low chlorophyll concentrations
in the SFE have resulted in lower predictive power of the lightutilization
model. The variation in y was likely the result of
interannual variation in phytoplankton assimilation number.
These results suggest that using a single y may yield large
errors in estimated estuarine production when applied overbroad
spatial and temporal scales. Given the food-limited
condition of the SFE, it appears that direct measurements of
primary production are necessary for accurately characterizing
the base of the estuarine food web.
0005-01-01T00:00:00Z