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.
This study shows that female Saimiri sciureus acclimated to a stable laboratory environment show a seasonal ovulatory response to a regime of exogenous hormones. This response is minimal during periods of high humidity, highest when humidity is lowest and is probably correlated with changes, rather than absolute levels of humidity. Monkeys require at least 9 months to acclimate to the laboratory environment.
Air pollutant effects are commonly investigated using panel studies employing daily measurement of changes in peak expiratory flow (PEF). Variable orifice PEF meters are inaccurate with a nonlinear relationship to actual PEF. The impact on a panel study of correcting these errors was examined.Twice-daily PEF readings were taken by 147 9-yr old children for 8 weeks and corrected using an equation derived from the response of 32 Vitalograph meters to a servomechanism-controlled pump. Pollutant effect estimates for corrected and uncorrected readings were derived using a regression approach incorporating appropriate confounders.Correction impacted little on mean PEF values (333.1±334.2 L . min), but did alter effect sizes. Nonsignificant nitrogen dioxide estimates for the entire panel decreased by up to 73%, but, for symptomatic/atopic children, a significant 5-day mean result was lost (decrease in effect size from -2.53 to -0.90% per 10 parts per billion (ppb)) and lag 0 became significant (decrease from -0.51 to -1.22% per 10 ppb). Mass concentration estimates of particles with a 50% cut-off aerodynamic diameter of 2.5 mm moved in both directions (-0.22 changed to 0.11% per 10 mg . m -1 lag 3 and -0.29 to -0.73 % per 10 mg . m -3 for the 5-day mean). Correction of nonlinearity of peak expiratory flow meters influenced the overall outcome of this panel study, and the changes in effect estimates would be sufficient to alter the interpretation of some studies. For adults, a greater change in effect estimates may follow the larger correction required for their usual peak expiratory flow range. Eur Respir J 2000; 15: 137±140.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.