A standardised method for measuring in situ denitrification in shallow aquifers: numerical validation and measurements in riparian wetlands

A tracer test to examine in situ denitrification in shallow groundwater by a piezometer with a packer system used bromide as a tracer of dilution and acetylene (10%) to block the denitrification process at the nitrous oxide stage. During the test, dissolved oxygen, nitrate (NO3-), bromide (Br-), nitrous oxide (N2O) and dissolved organic carbon (DOC) were measured. To calibrate the experimental method, comparison with numerical simulations of the groundwater transfer were carried out, taking into account the environmental characteristics. The method was tested by measurements undertaken in different environmental conditions (geology, land use and hydrology) in two riparian wetlands. Denitrification rates measured by this method ranged from 5.7 10-6 g N-NO3-L-1 h-1 to 1.97 10-3 g N-NO3-L-1 h-1 The method is applicable in shallow aquifers with a permeability from 10-2 to 10-4m s-1

Mitigating circumstances: A model-based analysis of associations between risk environment and infrequent condom use among Chinese street-based sex workers

<div><p>Background</p><p>Little is known about how freelance street-based sex workers navigate condom use while soliciting. Traditional behavioural model may fail to account for the complex risk environment that most street-based sex workers work within. We examine first the association of self-efficacy and the infrequent condom use, then we investigated the roles of clients and venues frequented on this association.</p><p>Method</p><p>Using a purposive chain-referral sampling method, we surveyed 248 street-based sex workers in Shanghai. The survey focused on sex workers HIV risk factors, sex work patterns, HIV knowledge, and related HIV self-efficacy. Clients types and behaviours, and characteristics of the venues frequented by these commercial sex workers were also collected. We conducted a series of multiple logistic regression models to explore how the association between a sex worker’s self-efficacy with infrequent condom use change as client and venue characteristics were added to the models.</p><p>Results</p><p>We find that within the basic model, low self-efficacy was marginally associated with infrequent condom use (54.9% vs. 45.1%, AOR = 1.70, 95% CI = 0.95–3.03). As client- and venue- characteristics were added, the associations between self-efficacy and condom use were strengthened (AOR = 2.10 95% CI = 1.12–3.91 and 2.54 95% CI = 1.24–5.19 respectively). Those who reported middle-tiered income were more likely to report infrequent condom use compared to their peers of high income (AOR = 3.92 95% CI = 1.32–11.70) whereas such difference was not found between low income and high income sex workers. Visiting multiple venues and having migrant workers as clients were also associated with infrequent condom use.</p><p>Conclusion</p><p>Our findings suggest sex worker’s self-efficacy matters in their HIV risk behaviours only when environment characteristics were adjusted. Risk environment for street-based sex workers are complex. Programming addressing behavioural changes among female sex workers should adopt holistic, multilevel models with the consideration of risk environments.</p></div

Client and venue characteristics by condom use status among street-based sex workers in Shanghai, China.

<p>Client and venue characteristics by condom use status among street-based sex workers in Shanghai, China.</p

Theoretical map of factors influencing condom use among street-based sex workers.

<p>Theoretical map of factors influencing condom use among street-based sex workers.</p

Self-efficacy and demographic characteristics and their associations to condom use among street-based female street based sex worker, Shanghai, China.

<p>Self-efficacy and demographic characteristics and their associations to condom use among street-based female street based sex worker, Shanghai, China.</p

Adjusted ORs and the 95% confident intervals of the individual-, client-, and venue-level factors on the street-based sex workers’ infrequent condom use with clients in Shanghai, China.

<p>Adjusted ORs and the 95% confident intervals of the individual-, client-, and venue-level factors on the street-based sex workers’ infrequent condom use with clients in Shanghai, China.</p