Denitrifying bacteria and hydrogeochemistry in a natural wetland adjacent to farmlands in Chiba, Japan

Abstract

Abstract:This study combined bacterial incubation and hydrogeochemical methods to investigate denitrification in the surface water, top soil (0-20 cm), and shallow groundwater of the Ochi wetland in Japan. Surface water was rich in nitrate (40 mg/l) and denitrifying bacteria (700 per ml). Three functional zones in the wetland were identified in the top soil and shallow groundwater. In the upstream portion of the wetland (Zone I), the counts of denitrifying bacteria in top soil increased from 5200 to 14 970 per ml and nitrate decreased from 25Ð4 to 1Ð8 mg/l. Organic carbon concentrations decreased as sulfate increased from 4Ð0 to 9Ð6 mg/l in this zone. In the middle-stream of the wetland (Zone II), all concentrations of major anions, iron, organic carbon, and total nitrogen content in top soil were relatively constant, but the counts of denitrifying bacteria increased up to 70 200 per ml. In the downstream portion of the wetland (Zone III), complete removal of nitrate resulted in sharp reduction of counts of denitrifying bacteria. Correspondingly, dissolved oxygen (DO), organic carbon, and total nitrogen increased in this zone. Counts of denitrifying bacteria were lower in shallow groundwater than in top soil; nitrate concentrations in shallow groundwater were also very low in this zone. DO and the oxidation/reduction potential data suggest that groundwater flows to the surface along an extended flow path, thus providing nitrate for the denitrifying community.

Comparison of microbial communities inside and outside of a denitrification hotspot in confined groundwater

“…Along A-A', the concentration of O 2 and ORP decreased from more than 2.0 mg l -1 and 200 mV in samples (n=2) upstream of the hotspot to less than 1 mg l -1 and negative in samples (n=3) inside of the hotspot respectively. The changing tendency was consistent with a previous study (Li et al, 2011). Additionally, the DOC concentration increased abruptly from 0.4 to 2.07 mg l -1 while the Cl concentration decrease from 64.4 to 4.4 mg l -1 between the B1 and B2 zones, possibly due to the infiltration of freshwater with DOC from the surface water.…”

Groundwater Recharge and Hydrogeochemical Evolution in Leizhou Peninsula, China

“…The analytical precision for all cation and anion concentrations was 2%. For the oxygen isotopic analysis, approximately 10 mL of each water sample was equilibrated with CO 2 by shaking for 6 hours at 25 ∘ C [24]. For the hydrogen isotopic analysis, metallic zinc was used to produce hydrogen gas using the zinc reduction method [25].…”

Spatial distribution and environmental determinants of denitrification enzyme activity in reed-dominated raised fields

“…Some preferred soil properties, which strongly control the denitrification process were selected to analyze their spatial distribution and relationships with the DEA based on the literature studies (Dhondt et al, 2004;Cao et al, 2008;Hill et al, 2000;Li et al, 2011;Al Ghadban et al, 2012;Batson et al, 2012;Pan et al, 2012;Yu et al, 2012). Significant differences in soil properties were found in the soil samples (Fig.…”

“…The nitrogen amount reduced by plant uptake and microbial immobilization is returned to soils when the environmental conditions are changed (Liu et al, 2011). Microbially-mediated denitrification is the main process to remove nitrogen permanently in significant amounts from the wetlands (Howarth et al, 1996;Li et al, 2011). Moreover, microbial denitrification is an anaerobic process and converts nitrate to N 2 O and N 2 , which are then released into the atmosphere (Khalil and Richards, 2011).…”