Steven L. Manley

Coastal salt marshes as global methyl halide sources from determinations of intrinsic production by marsh plants

Emissions of CH3Cl, CH3Br and CH3I were measured biweekly for 12- to 24-month periods between March 2002 and March 2005 from monospecific stands of four dominant southern California coastal salt marsh plants. These measurements revealed large inherent differences between species and more detailed patterns of seasonal production than previously reported. Marsh plants displayed intrinsic abilities to produce methyl halides. Salt marsh plants produced 92% of CH3Cl and 90% of CH3Br emitted and only 41% of the emitted CH3I. Unvegetated areas emitted 7.9% of CH3Cl, 9.9% CH3Br, and 59% of the emitted CH3I. The accuracy of the estimated methyl halide emissions from a coastal marsh and probably other ecosystems can be dramatically improved with increasing the number of species being measured and including emission from barren (mudflats and soil) areas. Estimates of global salt marsh emissions based on vegetated and barren area are 130, 21, 5.5 (mg m-2 yr-1) for CH 3Cl, CH3Br, and CH3I, respectively, or 1.2, 3.9, and 0.8% of total global fluxes of these gases. Copyright 2006 by the American Geophysical Union.

Physiological and biochemical controls over methyl halide emissions from rice plants

This paper investigates physiological and biochemical aspects of methyl halide production in rice plants over two growing seasons. Multiple separate mechanisms appear to be responsible for production of methyl halides in rice plant tissues. Evidence for multiple mechanisms is found in timing of peak emissions of methyl halides from rice, inconsistent effects of competitive inhibitors on methyl halide emissions, and large differences in methyl halide emission rates when compared to plant tissue halide concentrations. Other results show that chloride, bromide, and iodide ion concentrations in plant tissue appear to be regulated throughout the season, and observed changes in leaf tissue concentration cannot explain observed methyl halide emissions. The Km for methyl iodide formation in leaf tissue cell-free extract is 0.018 mM, suggesting a very efficient mechanism. Of the seven competitive inhibitors used, only thiol had a consistently strong effect on both methyl iodide and methyl bromide. Copyright 2004 by the American Geophysical Union.

FORMATION OF NUCLEOSIDE DIPHOSPHATE MONOSACCHARIDES (NDP‐SUGARS) BY THE AGAROPHYTE PTEROCLADIA CAPILLACEA (RHODOPHYCEAE)1

The following nucleoside diphosphate monosaccharides (sugar nucleotides) were identified by HPLC from Pterocladia capillacea Born and Thur.: ADP‐glucose, UDP‐glucose, UDP‐d‐galactose, and GDP‐glucose + mannose. GDP‐l‐galactose was not identified due to the lack of a standard. Several extraction methods were evaluated for their efficacy. A freeze/ thaw (liquid N2) step fallowed by formic acid (1 M) extraction, reduced pressure evaporation, and solubilization in water was the preferred method. Differences in media nitrate that resulted in different tissue‐N levels (1.8, 2.3, and 3.5% dry wt) and agar yields (34, 31, and 28% dry wt, respectively) also resulted in a marked difference in UDP‐d‐galactose and ADP‐glucose tissue levels (decrease with increasing tissue‐N) while the levels of the other sugar nucleotide agar precursors remained unchanged. Activities of UDP‐glucose, GDP‐glucose, and GDP‐mannose pyrophosphorylases, and UDP‐D‐glucose‐4‐epimerase were detected in cell‐free extracts using unlabeled and 14C‐labeled substrates. This study‐strongly supports the proposition that the d‐galactose component of agar is synthesized via G‐1‐P → UDP‐glucose→ UDP‐d‐galactose and that, the l‐galactoae component is produced via mannose‐1‐P → GDP‐mannose → GDP‐l‐galactose.

Seasonal mass balance of halogens in simulated rice paddies

Halogens released from soil reservoirs to the atmosphere play important roles in atmospheric chemistry, including ozone loss and aerosol formation. Closed system experiments to determine controlling factors in halogen movement between the pedosphere, hydrosphere, terrestrial biosphere, and atmosphere are needed. This paper presents results from a closed system experiment on simulated rice paddies. It was observed that most water-extractable (bioavailable), halogens were swept downward from the surface during the initial watering pulse (∼50, 70, and 75% of chloride, bromide, and iodide in unadulterated soils). Soil halogens were sequestered by rice plants with 28, 4, and 24% of the remaining bioavailable chlorine, bromine, and iodine processed by the plant tissue by the end of the season. Of the bioavailable halogens taken into the rice plant, less than 1% of chlorine or bromine is volatilized as a methyl halide while over 90% of iodide is emitted as gaseous CH3I. Copyright 2004 by the American Geophysical Union.

The use of kelp sieve tube sap metal composition to characterize urban runoff in southern California coastal waters.

This study introduces an innovative method for biomonitoring using giant kelp (Macrocystis pyrifera) sieve tube sap (STS) metal concentrations as an indication of pollution influence. STS was sampled from fronds collected from 10 southern California locations, including two reference sites on Santa Catalina Island. Using ICP-MS methodology, STS concentrations of 17 different metals were measured (n=495). Several metals associated with pollution showed the highest STS concentrations and most seasonal variation from populations inside the Port of Los Angeles/Long Beach. Lowest concentrations were measured at less-urbanized areas: Santa Catalina Island and Malibu. Some metals showed a spatial gradient in STS metal concentration with increasing distance from point sources (i.e. Los Angeles River). Cluster analyses indicate that polluted seawater may affect kelp uptake of metals essential for cellular function. Results show that this method can be useful in describing bioavailable metal pollution with implications for accumulation within an important ecosystem.

Spatial and temporal variation in tissue halide levels of Salicornia virginica

Succulence, tissue chloride, bromide, and iodide levels were determined in the coastal salt marsh halophyte Salicornia virginica taken from three elevations over a 12-month period. Soil samples from each sampling area were also taken for the determination of halide concentrations. The average percent dry weight (% DWt) over the 12 months and three elevations ranged from 10.8 ± 0.4 to 16.1 ± 0.3 % (± sd), with a general increase in % DWt (decrease in succulence) in tissue from all elevations peaking in September, after the dry summer, followed by a decrease in % DWt (increase in succulence) during the rainy season. The mean halide levels in S. virginica tissues over the 12 months and three elevations ranged from 17.5 to 30.3 % Cl−, 0.27 to 0.76 % Br−, and from 3.00 to 1.21 × 104 ppm I−. Mean halide concentrations in plant water ranged from 0.66 to 1.6 M Cl−, 4.6 to 12 mM Br− and 3.3 μM to 16 mM I−. No environmental factors correlated with changes in tissue halide levels. Tissue Cl− levels tended to increase during the dry summer months and decrease during the wet winter months. Bromide levels were more stable. Large increases in tissue I− levels were found during the months of September and October when the plants were in flower, suggesting a developmental control of I− uptake. Soil concentrations of all three halides at the low elevation were consistently higher than those in the middle and high elevations. The high elevation soil Cl− was the most variable of the three halides. Higher I− soil levels in the low elevation during the spring/summer as compared to fall/winter probably reflect an increase in the biological and chemical reduction of IO3− to I−. Tissue halide levels at the three elevations did not correlate with their respective soil concentrations. Plant water halide molar ratios were lower than in seawater and soil, indicating the selective uptake of halides in the order I− > Br− > Cl−.