The Colne Estuary

ABSTRACT Estuarine sediments are the location for significant bacterial removal of anthropogenically derived inorganic nitrogen, in particular nitrate, from the aquatic environment. In this study, rates of benthic denitrification (DN), dissimilatory nitrate reduction to ammonium (DNRA), and anammox (AN) at three sites along a nitrate concentration gradient in the Colne estuary, United Kingdom, were determined, and the numbers of functional genes (narG, napA, nirS, and nrfA) and corresponding transcripts encoding enzymes mediating nitrate reduction were determined by reverse transcription-quantitative PCR. In situ rates of DN and DNRA decreased toward the estuary mouth, with the findings from slurry experiments suggesting that the potential for DNRA increased while the DN potential decreased as nitrate concentrations declined. AN was detected only at the estuary head, accounting for ∼30% of N2 formation, with 16S rRNA genes from anammox-related bacteria also detected only at this site. Numbers of narG genes declined along the estuary, while napA gene numbers were stable, suggesting that NAP-mediated nitrate reduction remained important at low nitrate concentrations. nirS gene numbers (as indicators of DN) also decreased along the estuary, whereas nrfA (an indicator for DNRA) was detected only at the two uppermost sites. Similarly, nitrate and nitrite reductase gene transcripts were detected only at the top two sites. A regression analysis of log(n + 1) process rate data and log(n + 1) mean gene abundances showed significant relationships between DN and nirS and between DNRA and nrfA. Although these log-log relationships indicate an underlying relationship between the genetic potential for nitrate reduction and the corresponding process activity, fine-scale environmentally induced changes in rates of nitrate reduction are likely to be controlled at cellular and protein levels.

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amoAGene Abundances and Nitrification Potential Rates Suggest that Benthic Ammonia-Oxidizing Bacteria and Not Archaea Dominate N Cycling in the Colne Estuary, United Kingdom

Applied and Environmental Microbiology ◽

10.1128/aem.02654-14 ◽

2014 ◽

Vol 81 (1) ◽

pp. 159-165 ◽

Cited By ~ 60

Author(s):

Jialin Li ◽

David B. Nedwell ◽

Jessica Beddow ◽

Alex J. Dumbrell ◽

Boyd A. McKew ◽

...

Keyword(s):

Denaturing Gradient Gel Electrophoresis ◽

Dry Weight ◽

Estuarine Sediments ◽

Ammonia Oxidizer ◽

Ammonia Oxidizing Bacteria ◽

Content Type ◽

Gene Abundance ◽

Nitrification Potential ◽

Gradient Gel Electrophoresis ◽

Colne Estuary

ABSTRACTNitrification, mediated by ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA), is important in global nitrogen cycling. In estuaries where gradients of salinity and ammonia concentrations occur, there may be differential selections for ammonia-oxidizer populations. The aim of this study was to examine the activity, abundance, and diversity of AOA and AOB in surface oxic sediments of a highly nutrified estuary that exhibits gradients of salinity and ammonium. AOB and AOA communities were investigated by measuring ammonia monooxygenase (amoA) gene abundance and nitrification potentials both spatially and temporally. Nitrification potentials differed along the estuary and over time, with the greatest nitrification potentials occurring mid-estuary (8.2 μmol N grams dry weight [gdw]−1day−1in June, increasing to 37.4 μmol N gdw−1day−1in January). At the estuary head, the nitrification potential was 4.3 μmol N gdw−1day−1in June, increasing to 11.7 μmol N gdw−1day−1in January. At the estuary head and mouth, nitrification potentials fluctuated throughout the year. AOBamoAgene abundances were significantly greater (by 100-fold) than those of AOA both spatially and temporally.Nitrosomonasspp. were detected along the estuary by denaturing gradient gel electrophoresis (DGGE) band sequence analysis. In conclusion, AOB dominated over AOA in the estuarine sediments, with the ratio of AOB/AOAamoAgene abundance increasing from the upper (freshwater) to lower (marine) regions of the Colne estuary. These findings suggest that in this nutrified estuary, AOB (possiblyNitrosomonasspp.) were of major significance in nitrification.

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Roman Colchester

The Journal of Roman Studies ◽

10.2307/296003 ◽

1919 ◽

Vol 9 ◽

pp. 139-169 ◽

Cited By ~ 1

Author(s):

R. E. Mortimer Wheeler ◽

Philip G. Laver

Keyword(s):

Main Stream ◽

Open Approach ◽

The South ◽

The West ◽

Early Date ◽

Tidal Waters ◽

Colne Estuary ◽

River Valleys ◽

Favoured Region

Colchester lies at the head of an inland promontory which emerges from the undulating Essex lowlands to meet the tidal waters of the Colne estuary. On the northern and eastern sides this promontory is clasped by the winding course of the main stream, and on the south by a tributary known as the Roman River which, bending northwards, slightly restricts the otherwise open approach from the west. The eastern end of the area thus enclosed rises commandingly above the sharply-cut river valleys and the seaward marshes, which are of sufficient extent to seclude it from the risks of an open shore. The combined accessibility and security of the site at an early date attracted both the landsman and the sea-going trader, who doubtless unloaded his Gallic cargoes at wharves not far from those still frequented by a modest coastal traffic. It is no longer disputed that somewhere within the natural limits of this favoured region lay the great oppidum of the Trinovantes.

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