Geomicrobiology of nitrogen in a coastal aquifer : isotopic and molecular methods to examine nitrification and denitrification in groundwater
Citable URI
https://hdl.handle.net/1912/3817Location
41°34’49”N, 70°31’27”WWaquoit, MA
DOI
10.1575/1912/3817Keyword
Groundwater; Water; Nitrogen contentAbstract
Excess nitrogen input is deleterious to coastal waters, resulting in deterioration of
the water quality, increases in harmful algal blooms and disease in commercial fish
stocks. A significant portion of this nitrogen enters coastal waters through groundwater
systems. Here we use isotopic and molecular biological methods to identify the
populations of nitrifiers and denitrifiers, where they occur, and what levels of activity are
present through the upper four meters of a coastal groundwater system. This work shows
two different populations of putative ammonia-oxidizing archaea (AOA) based on the
ammonia monooxygenase gene (amoA), one shallow population most closely related to
open ocean water column-like sequences and a deeper population that is more closely
related to estuarine-like AOA. Interestingly, while the surface population has a potential
nitrification rates (456 pmol g-1 sediment day-1) similar to marine sediments, the deeper
population does not show detectable evidence of nitrification. Between these two
archaeal populations resides an active population of ammonia-oxidizing bacteria with
similar nitrification rates as the surface AOA population. The upper meter of the aquifer
is also an active area of denitrification as evidenced by the coincident drop in nitrate
concentration and increase in both δ15N (up to + 20.1‰) and δ18O (up to + 11.7‰),
characteristic of groundwater affected by denitrification. 16S rRNA gene surveys of the
organisms present in the upper meter also are similar to soil/sediment type environments
including many potential denitrifiers. However, nitrite reductase, nirS and nirK, genes
were also recovered from the sediments with nirK dominating in the surface sediments.
This contrasts with the deep salt wedge, where the microbial community 16S rRNA
genes appear more closely related to marine or reducing sediment/wastewater type
organisms, and nirS genes become the dominant denitrification gene.
Description
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2010
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Suggested Citation
Thesis: Rogers, Daniel R., "Geomicrobiology of nitrogen in a coastal aquifer : isotopic and molecular methods to examine nitrification and denitrification in groundwater", 2010-06, DOI:10.1575/1912/3817, https://hdl.handle.net/1912/3817Related items
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