Using high-frequency water quality data to assess sampling strategies for the EU Water Framework Directive

The EU Water Framework Directive (WFD) requires that the ecological and chemical status of water bodies in Europe should be assessed, and action taken where possible to ensure that at least "good" quality is attained in each case by 2015. This paper is concerned with the accuracy and precision with which chemical status in rivers can be measured given certain sampling strategies, and how this can be improved. High-frequency (hourly) chemical data from four rivers in southern England were subsampled to simulate different sampling strategies for four parameters used for WFD classification: dissolved phosphorus, dissolved oxygen, pH and water temperature. These data sub-sets were then used to calculate the WFD classification for each site. Monthly sampling was less precise than weekly sampling, but the effect on WFD classification depended on the closeness of the range of concentrations to the class boundaries. In some cases, monthly sampling for a year could result in the same water body being assigned to three or four of the WFD classes with 95% confidence, due to random sampling effects, whereas with weekly sampling this was one or two classes for the same cases. In the most extreme case, the same water body could have been assigned to any of the five WFD quality classes. Weekly sampling considerably reduces the uncertainties compared to monthly sampling. The width of the weekly sampled confidence intervals was about 33% that of the monthly for P species and pH, about 50% for dissolved oxygen, and about 67% for water temperature. For water temperature, which is assessed as the 98th percentile in the UK, monthly sampling biases the mean downwards by about 1 °C compared to the true value, due to problems of assessing high percentiles with limited data. Low-frequency measurements will generally be unsuitable for assessing standards expressed as high percentiles. Confining sampling to the working week compared to all 7 days made little difference, but a modest improvement in precision could be obtained by sampling at the same time of day within a 3 h time window, and this is recommended. For parameters with a strong diel variation, such as dissolved oxygen, the value obtained, and thus possibly the WFD classification, can depend markedly on when in the cycle the sample was taken. Specifying this in the sampling regime would be a straightforward way to improve precision, but there needs to be agreement about how best to characterise risk in different types of river. These results suggest that in some cases it will be difficult to assign accurate WFD chemical classes or to detect likely trends using current sampling regimes, even for these largely groundwater-fed rivers. A more critical approach to sampling is needed to ensure that management actions are appropriate and supported by data

High-frequency water quality monitoring in an urban catchment: hydrochemical dynamics, primary production and implications for the Water Framework Directive

This paper describes the hydrochemistry of a lowland, urbanised river-system, The Cut in England, using in situ sub-daily sampling. The Cut receives effluent discharges from four major sewage treatment works serving around 190,000 people. These discharges consist largely of treated water, originally abstracted from the River Thames and returned via the water supply network, substantially increasing the natural flow. The hourly water quality data were supplemented by weekly manual sampling with laboratory analysis to check the hourly data and measure further determinands. Mean phosphorus and nitrate concentrations were very high, breaching standards set by EU legislation. Though 56% of the catchment area is agricultural, the hydrochemical dynamics were significantly impacted by effluent discharges which accounted for approximately 50% of the annual P catchment input loads and, on average, 59% of river flow at the monitoring point. Diurnal dissolved oxygen data demonstrated high in-stream productivity. From a comparison of high frequency and conventional monitoring data, it is inferred that much of the primary production was dominated by benthic algae, largely diatoms. Despite the high productivity and nutrient concentrations, the river water did not become anoxic and major phytoplankton blooms were not observed. The strong diurnal and annual variation observed showed that assessments of water quality made under the Water Framework Directive (WFD) are sensitive to the time and season of sampling. It is recommended that specific sampling time windows be specified for each determinand, and that WFD targets should be applied in combination to help identify periods of greatest ecological risk. This article is protected by copyright. All rights reserved

The water quality of the River Enborne, UK: observations from high-frequency Monitoring in a rural, lowland river system

This paper reports the results of a 2-year study of water quality in the River Enborne, a rural river in lowland England. Concentrations of nitrogen and phosphorus species and other chemical determinands were monitored both at high-frequency (hourly), using automated in situ instrumentation, and by manual weekly sampling and laboratory analysis. The catchment land use is largely agricultural, with a population density of 123 persons km−2. The river water is largely derived from calcareous groundwater, and there are high nitrogen and phosphorus concentrations. Agricultural fertiliser is the dominant source of annual loads of both nitrogen and phosphorus. However, the data show that sewage effluent discharges have a disproportionate effect on the river nitrogen and phosphorus dynamics. At least 38% of the catchment population use septic tank systems, but the effects are hard to quantify as only 6% are officially registered, and the characteristics of the others are unknown. Only 4% of the phosphorus input and 9% of the nitrogen input is exported from the catchment by the river, highlighting the importance of catchment process understanding in predicting nutrient concentrations. High-frequency monitoring will be a key to developing this vital process understanding

The Feasibility of Modified Directly Observed Therapy for HIV-Seropositive African American Substance Users

Recently, modified directly observed therapy (MDOT) has emerged as a promising intervention to address nonadherence for hard-to-reach populations infected with HIV. To date, there are no existing data on MDOT focusing exclusively on African Americans. The present study sought to determine the feasibility of MDOT among 31 HIV-seropositive African American substance users in the South. An outreach worker observed the participants’ medication intake 5 days per week (once per day) for a period of 3 months (intensive phase). This phase was followed by a transition phase of 3 months during which the frequency of MDOT was gradually tapered from 5 days to once weekly. Assessments to gather demographic information, HIV risk behaviors, substance use, depression, and medication adherence were conducted at baseline, 3 months, and 6 months. Results indicated that more participants adhered to their medication regimen and had viral loads of less than 400 copies per milliliter at 3 and 6 months compared to baseline. Participants reported significantly less depressive symptoms at the 6-month assessment compared to baseline and 3 months. With regard to acceptability, 95% of participants indicated they liked having the outreach visits, 100% reported MDOT helped them take their medications, and only 5% felt MDOT was a violation of privacy. These results suggest MDOT is feasible among African American substance users in the South and a larger controlled study of MDOT with this population is warranted

Phosphorus dynamics and productivity in sewage-impacted lowland chalk stream

Hourly in situ phosphorus, conductivity, turbidity, dissolved oxygen, pH, and chlorophyll measurements were collected from January 2004 to November 2006 for the River Kennet, 2 km downstream of a sewage effluent inlet. Excess carbon dioxide pressure (EpCO2) was calculated from continuous pH and spot alkalinity measurements. EpCO2 and dissolved oxygen were used to estimate rates of photosynthesis and respiration. These parameters were examined alongside flow, water temperature and solar radiation to explore controls on phosphorus dynamics and in-stream productivity. Diurnal, event and seasonal patterns were observed in phosphorus concentrations. The diurnal and seasonal variations appeared to be related to the upstream sewage treatment works. The event patterns coincided with periods of high flow, and were attributed to diffuse sources. Chlorophyll behaved independently of phosphorus concentration and returned to baseline levels before photosynthesis rate. This indicated that, during the period of study, in-stream productivity was primarily controlled by aquatic plants other than phytoplankton

High-frequency phosphorus monitoring of the River Kennet, UK: are ecological problems due to intermittent sewage treatment works failures?

The River Kennet in southern England has exhibited excessive benthic algal growth and associated ecological problems, such as loss of macrophytes and invertebrates, since the 1980s. These ecological problems were attributed to regular peaks in phosphorus concentration, which were widely attributed to intermittent failures of the Marlborough sewage treatment works (STW). This study deployed highfrequency phosphorus auto-analysers to monitor the total reactive phosphorus (TRP) concentrations of Marlborough STW final effluent and the downstream River Kennet at hourly and 30 minute resolution respectively, between 2008 and 2009. This monitoring confirmed that the Marlborough STW was operating well within its 1000 mg l-�1 annual mean total phosphorus consent limit, with mean total P and soluble reactive P concentrations of 675 and 345 mg l-�1 respectively. There were two occasions where effluent TRP concentration exceeded 1000 mg l-�1, and only one of these resulted in a peak in TRP concentration of over 100 mg l-�1 in the River Kennet at Mildenhall. The other nine peaks of over 100 mg l-�1 in the River Kennet during the monitoring period were associated with storm events, indicating that diffuse-source inputs and remobilisation of stored within-channel phosphorus were the cause of the peaks in river concentration, rather than Marlborough STW. The value of high-frequency environmental monitoring and the problems associated with using nutrient auto-analysers in the field are discussed. Seasonal phosphorus consents for STWs could provide a useful and cost effective means to improve both water quality and river ecology in the upper River Kennet