High nitrate, muddy estuaries as nitrogen sinks:the nitrogen budget of the River Colne estuary (United Kingdom) 'Department of Biological & Chemical Sciences, University of Essex, Colchester C 0 4 3SQ, United Kingdom 'Environmental Health. School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom ABSTRACT. The muddy estuary of the River Colne, east coast UK, is hypernutrified, with strong gradients of N 0 3 a n d NH,+up the estuary due to inputs from the river and sewage treatment works. There were no significant transformations of nitrogen detected in the water colun~n. In the sandy sediment at the mouth of the estuary nitrification occurred with N0,export from the sediment, but the muddy sedi m e n t~ higher up the estuary were large sinks for NO3-and major sites of denitrification. The flux of NO3-into the sediment at these sites was correlated with the water column NOo-concentration, and there was a large capacity for the sediments to respond to increases in the water column N O , concentration. A seasonal cycle occurred with maximum denitrification during early winter, when water column NO< was greatest and low temperatures favoured denitrification over NO3-ainmonihcation. Highest unit area rates of denitrificatlon were measured by acetylene inhibit~on at the uppermost site in the estuary, but when allowance was made for the area of sediment surface in each sector the middle reaches of the estuary were more significant to the estuarine nitrogen budget. Approximately 50% of the NO3-flux through the estuary was denitrified during 1993-1994. In addition, measurements of denitrification by the '5N03' isotope pairing technique suggested that coupled nitrification-denitrification within the sediment was also important, and when this was also allowed for the sediments removed by denitrification between 18 and 27% of the total nitrogen flux through the estuary. There was some question, however, of whether the coupled nitrification-denitrification was overestimated if the anammox reaction was occurring in the highly organic, high NO3-sediments at the river end of the estuary. It is concluded that in these turbid, muddy estuaries the sediments are not only major attenuators of the flux of NO;, but are also very effective traps for organically bound nitrogen. This suggests that the loads of nitrogen through these estuaries to the North Sea, which are usually derived from river gauging above the high tide mark, significantly overestimate the real load as they do not take into account attenuation of nitrogen flux within the estuary. While this attenuation may decrease the nitrogen loads, it implies that any environmental impact in coastal waters may be the result of much lower loads of nitrogen than hitherto assumed.
Hypernutrified estuaries as sources of N 2 0 emission to the atmosphere: the estuary of the River Colne, Essex, UK 'Department of Biological Sciences. University of Essex, Colchester C 0 4 3SQ, United Kingdom 2Environmental Health. School of Chemistry. University of Birmingham, Birmingham B15 2TT. United Kingdom ABSTRACT: Measurements in the estuary of the River Colne, Essex, UK, showed strong gradients of nitrate and ammonium concentrations, increasing upriver due to inputs from the nver and a large sewage treatment works. In the low salinity region (
Purpose Nitrous oxide (N 2 O) is a potent greenhouse gas which is mainly produced from agricultural soils through the processes of nitrification and denitrification. Although denitrification is usually the major process responsible for N 2 O emissions, N 2 O production from nitrification can increase under some soil conditions. Soil pH can affect N 2 O emissions by altering N transformations and microbial communities. Bacterial (AOB) and archaeal (AOA) ammonia oxidisers are important for N 2 O production as they carry out the ratelimiting step of the nitrification process. Material and methods A field study was conducted to investigate the effect of soil pH changes on N 2 O emissions, AOB and AOA community abundance, and the efficacy of a nitrification inhibitor, dicyandiamide (DCD), at reducing N 2 O emissions from animal urine applied to soil. The effect of three pH treatments, namely alkaline treatment (CaO/NaOH), acid treatment (HCl) and native (water) and four urine and DCD treatments as control (no urine or DCD), urine-only, DCD-only and urine + DCD were assessed in terms of their effect on N 2 O emissions and ammonia oxidiser community growth. Results and discussion Results showed that total N 2 O emissions were increased when the soil was acidified by the acid treatment. This was probably due to incomplete denitrification caused by the inhibition of the assembly of the N 2 O reductase enzyme under acidic conditions. AOB population abundance increased when the pH was increased in the alkaline treatment, particularly when animal urine was applied. In contrast, AOA grew in the acid treatment, once the initial inhibitory effect of the urine had subsided. The addition of DCD decreased total N 2 O emissions significantly in the acid treatment and decreased peak N 2 O emissions in all pH treatments. DCD also inhibited AOB growth in both the alkaline and native pH treatments and inhibited AOA growth in the acid treatment. Conclusions These results show that N 2 O emissions increase when soil pH decreases. AOB and AOA prefer different soil pH environments to grow: AOB growth is favoured in an alkaline pH and AOA growth favoured in more acidic soils. DCD was effective in inhibiting AOB and AOA when they were actively growing under the different soil pH conditions.
The computed tomography adnexal mass score combines CT scan findings, CA-125, and patient age into an equation to predict the malignant probability of an adnexal mass.
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