Geology topics

J.H. Duff

Publications and source records attributed to J.H. Duff.

21 records · Page 2Linked to original sources

USGS1990

Denitrification in sediments from the hyporheic zone adjacent to a small forested stream

Denitrifying potentials increased with increasing distance from the stream channel. Dissolved oxygen was 100% of the concentration expected in equilibrium with the atmosphere in water obtained from monitoring wells immediately adjacent to the stream but was as low as 7% of the expected value in water 11.4 m inland. Both nitrate and dissolved organic carbon decreased over summer in wells at the base of the alder-forested slope. A 48-h injection of nitrate-amended stream water into hyporheic water 8.4 m inland stimulated nitrous oxide production in the presence of acetylene. Nitrous oxide was generated as nitrate and acetylene were co-transported to a well 13 m down-gradient. Acetylene-block experiments coupled with the chemistry data suggest that denitrification can modify the chemistry of water during passage through the hyporheic zone. -from Authors

Canadian Journal of Fisheries and Aquatic Sciences↗

USGS1988

Denitrification in a sand and gravel aquifer

Denitrification was assayed by the acetylene blockage technique in slurried core material obtained from a freshwater sand and gravel aquifer. The aquifer, which has been contaminated with treated sewage for more than 50 years, had a contaminant plume greater than 3.5-km long. Near the contaminant source, groundwater nitrate concentrations were greater than 1 mM, whereas 0.25 km downgradient the central portion of the contaminant plume was anoxic and contained no detectable nitrate. Samples were obtained along the longitudinal axis of the plume (0 to 0.25 km) at several depths from four sites. Denitrification was evident at in situ nitrate concentrations at all sites tested; rates ranged from 2.3 to 260 pmol of N 2 O produced (g of wet sediment) −1 h −1 . Rates were highest nearest the contaminant source and decreased with increasing distance downgradient. Denitrification was the predominant nitrate-reducing activity; no evidence was found for nitrate reduction to ammonium at any site. Denitrifying activity was carbon limited and not nitrate limited, except when the ambient nitrate level was less than the detection limit, in which case, even when amended with high concentrations of glucose and nitrate, the capacity to denitrify on a short-term basis was lacking. These results demonstrate that denitrification can occur in groundwater systems and, thereby, serve as a mechanism for nitrate removal from groundwater.

Massachusetts↗

USGS1984

Denitrification associated with stream periphyton: Chamber estimates from undisrupted communities

Undisrupted periphyton communities from a N‐rich (NO 3 − = 63 µ mol L −1 ) and pristine (NO 3 − = 2.9 µ mol L −1 ) stream were assayed for denitrifying activity (acetylene‐blockage technique) in 40‐L chambers incubated at in situ temperature and nutrient concentrations. Nitrous oxide formation associated with periphyton from the N‐rich stream was immediate and linear (52.1 µ mol N 2 O m −2 h −1 ) in the dark, anaerobic chamber (50 kPa C 2 H 2 ). In the corresponding light, aerobic chamber (50 kPa C 2 H 2 ), N 2 O production was inhibited by 82% (9.3 µ mol N 2 O m −2 h −1 ). Nitrous oxide formation was not associated with periphyton from the pristine stream incubated in situ, either with or without NO 3 − amendment. Denitrification estimates made with undisrupted periphyton communities at in situ temperature and nutrient concentrations (40‐L chambers) were less variable than estimates made with periphyton “scrapings” in small flasks (room temperature). The calculated diel periphyton‐associated denitrification rate based on a 14‐h light‐10‐h dark day was 651 µ mol N 2 O m −2 d −1 . The data suggest denitrification within periphyton mats may contribute toward removal of NO 3 − from N‐rich fluvial environments.

Journal of Environmental Quality↗