Effect of litter nitrogen on decomposition and microbial biomass inSpartina alterniflora.

The effect on decomposition of 4 different levels of nitrogen in aerial tissue ofSpartina alterniflora, collected at the end of its growing season litter, was studied in laboratory percolators for 56 days at 20‡C. The CO2 evolution and the release of organic nitrogen and organic carbon were monitored. From these data, the ash-free dry weight (AFDW), nitrogen (N) content, and carbon∶nitrogen (C/N) ratio were calculated at various times during decomposition. Fungal biomass, bacterial biomass, and the relative autoradiographic activity of bacteria were measured at the end of the study. Decomposition was significantly affected by the nitrogen content of the litter. A 55% increase in plant N increased overall weight loss and k by 50% and 40%, respectively. Furthermore, k (calculated from time course weight loss data) responded linearly to the 4 different levels of nitrogen inSpartina tissue. Fungi appear to dominate the microbial community. At the end of the experiment, fungal biomass was between 2.23 and 3.08% of the AFDW, and was calculated to contain 12 to 22% of the nitrogen in the litter. Bacterial biomass was 1/10 of the fungal biomass, and 12-17% of the bacteria were active. The total microbial biomass was not affected by increased plant nitrogen. In the course of decomposition, the organic nitrogen and carbon were highest in the effluent water in all treatments during the first 8 days. The respiration rate (CO2 evolution) first increased to a maximum at day 18 and then decreased to a constant rate (1-2 mg C/day/g detritus). Respiration was highest in the high N litter. The C/N ratio in all treatments increased from the start to day 8, then decreased to day 20. In low N litter, C/N then increased again as a result of increased total organic nitrogen (TON) loss relative to carbon mineralization. In the high N, this was reversed.

Biomagnification of aroclor 1242 in decomposing spartina litter.

The accumulation of a polychlorinated biphenyl (PCB) mixture (Aroclor 1242) in the process of detritus formation by a shredded marshgrass (Spartina alterniflora) under aerobic conditions was monitored in percolators for 4 months at 20 degrees C. Dissolved PCB in the influent solution was 14 to 16 mug/liter. Parameters monitored in addition to PCB accumulation were CO(2) evolution, NH(4) uptake, NO(3) production, and total organic nitrogen and carbon in the effluent. An NaN(3-) poisoned control served to assess nonbiological PCB absorption. Up to 90% of the PCB dissolved in the influent water was removed by the biologically active detritus. Biomagnification resulted in three to four times higher PCB concentrations in the active detritus than in the abiotic control. Evolution of CO(2) was slightly depressed by PCB, but the overall quality (C:N ratio) of the detritus was not affected. The results indicate that bioaccumulation of PCB in detritus is an important means of entry for this pollutant into estuarine food webs.

Biodegradation of 1,2,3- and 1,2,4-trichlorobenzene in soil and in liquid enrichment culture.

The biodegradation of radiochemically pure (99%) 1,2,3- and 1,2,4-trichlorobenzene (TCB) in soil was investigated. Experimental difficulties posed by the high volatility and slow biodegradation rate of the TCBs were partially overcome by using a specially designed incubation and trapping apparatus. Evolution of (14)CO(2) from active versus poisoned soil dosed with 50 mug of the individual TCBs per g gave conclusive proof that both isomers are biodegradable. At 20 degrees C, 1,2,4-TCB was mineralized at an approximate rate of 1 nmol/day per 20 g of soil sample, and 1,2,3-TCB was mineralized at one-half to one-third that rate. Mineral fertilizers or cosubstrates failed to increase TCB mineralization rates in soil. Anaerobic conditions had a negative effect on mineralization, and increased temperatures had a positive effect. With increasing 1,2,4-TCB concentrations, (14)CO(2) evolution exhibited saturation kinetics with an apparent K(m) of 55.5 nmol per g of soil. Recovery of total radioactivity was good from soil containing high organic matter concentrations. From low-organic-matter soil, some of the radioactivity was recovered only on combustion, and overall recovery was lower. In soil-inoculated liquid culture, the cosubstrates glucose and benzene caused a slight stimulation of 1,2,4-TCB mineralization. Cochromatography of known standards with the extracts of soil pretreated with [(14)C]TCBs indicated that 3,4,5-trichlorophenol, 2,6-dichlorophenol and, to a lesser degree, 2,3-dichlorophenol were present in soils incubated with 1,2,3-TCB. 2,4-, 2,5-, and 3,4-dichlorophenol were present in soils incubated with 1,2,4-TCB.

Apparatus for monitoring the mineralization of volatile C-labeled compounds.

Quantitative mineralization studies on radiolabeled compounds having high vapor pressures need to cope with several technical difficulties. An incubation and trapping system is described that was successfully used in mineralization studies on highly volatile trichlorobenzenes and other xenobiotic pollutants.