WET News

24 WET NEWS MARCH 2016 INSIGHT MONITORING phosphorus (P) by around 100% and 400% respectively since the industrial revolution, H uman activities have enhanced global cycles of nitrogen (N) and Each monitoring station includes a Xylem YSI EXO2 multiparameter water quality monitoring sonde and this is having a major impact on the world's water resources, resulting in serious A solution: Continuous monitoring Sondes and dataloggers are helping an estuary research project with monitoring key water quality parameters. C hristchurch Harbour is an important water resource. It was chosen for this pro- ject because it is a relatively small and constrained estuary with easily accessible sites for monitoring. The estuary has two main rivers (the Stour and Hampshire Avon) feeding into it and exchange with coastal wa- ters is provided by a narrow channel at Mudeford. The two river catchments have similar characteristics; both containing high propor- tions of chalk in the upper and middle reaches and tertiary sands and gravels in their lower sections. The Environment Agency (EA) is already working with lo- cal water companies to imple- ment improvements to sewage treatment works that will reduce phosphate levels in the dis- charges from these plants. How- ever, there is also a requirement to lower macronutrients from other sources, such as farming, so it is convenient that a further project is being conducted in the upper reaches of the Avon, also involving continuous water quality monitoring. The Christchurch Harbour project is one of four consortium projects funded by the NERC Macronutrient Cycles Pro- gramme. The project's consorti- um is made up of a team of sci- entists from the Universities of Southampton, Portsmouth and East Anglia, and the National Oceanography Centre, South- ampton. The monitoring equip- ment was Œ rst installed in late 2013 and early 2014, and is due to run for three and a half years. In conjunction with modelling, the monitoring data will enable the scientists to produce an ac- curate assessment of the impact of nutrients entering the estuary during short-term storm in- creased ' ows in the two rivers. Data from the study are be- ing used to create a powerful statistical model of the distribu- tion of excess phosphates and nitrates, how they transfer from rivers, through estuaries and into the coastal seas and the role that storms play in this pro- cess. The team anticipates that this will allow policy makers to make more informed decisions about how to reduce nitrate and phosphate pollution in estuar- ies. The Xylem EXO2 sondes are designed to run on low power for long-term deployments. Each sonde can accommodate a large number of sensors and in this project they included dis- solved oxygen, conductivity, temperature, turbidity, chloro- phyll, depth and pH. The EXO sondes contain internal batter- ies and can be deployed on their own, but in order to provide near real-time data to the 'Storm Central' website, they were each connected to a Storm datalogger with a solar-powered battery pack. A novel 'lab on a chip' nitrate sensor also forms part of the monitoring system. Developed by engineers and scientists at the NOC, the nitrate monitor sensor performs miniature col- orimetric nitrate analysis at pro- grammable hourly intervals, with a serial output to the Storm datalogger. Consequently, the nitrate data, which reveals com- plex daily cycling and response to storm events, has been incor- porated with that from the EXO sondes. The EXO sonde was also Œ t- ted with a fDOM sensor (Fluo- rescent Dissolved Organic Mat- ter) which provides greater insight into water quality; typi- cally displaying an inverse rela- tionship with salinity revealing high DOM levels in the freshwa- ter entering the estuary. The monitoring system has the ability to output alarms when pre-set conditions occur, including relationships between di— erent sensors. Alarms can trigger emails, and text messag- es are also possible with minor additional equipment, however the alarm function was not ena- bled for this project. Automatic water samplers were also em- ployed by the project, taking samples at pre-set intervals, but if necessary the samplers could be set to initiate sample collec- tion when certain conditions oc- cur, such as a lowering of river conductivity caused by a surge of fresh water. Prof Purdie says: "We are ob- viously very pleased with the Xylem monitoring equipment; we found good correlation be- tween the macronutrient con- centrations in the frequently collected water samples and NOC's lab on chip nitrate moni- tor with the continuous data from the EXO sondes providing key water quality parameters at ten-minute intervals over a peri- od of more than a year so far. As a result, we have been able to capture continuous data throughout the life of the project and this has provided tremen- dous insight into the estuarine behaviour of macronutrients throughout all seasons and dur- ing all types of weather. The monitors are still operational, so we hope to extend the project for a longer period and further improve the models that have beneŒ ted from the data so far." THE CONCEPT œ The EXO2 sondes are designed to run on low power for long-term deployments œ The sondes were equipped with a fDOM sensor œ They were each connected to a Storm datalogger with a solar-powered battery pack THE VERDICT "We have been able to capture continuous data throughout the life of the project and this has provided tremendous insight into the estuarine behaviour of macronutrients throughout all seasons and during all types of weather Prof Duncan Purdie, project lead NEED TO KNOW 1 There is a need to better understand fluxes of N and P through estuaries 2 There is a requirement to lower macronutrients from other sources 3 The two river catchments both have high proportions of chalk in the upper and middle reaches and tertiary sands and gravels in their lower sections The challenge: Getting to grips with N and P fluxes A need to understand water quality in rivers and estuaries has led to heightened demand for instruments to operate unattended for extended periods. detrimental e— ects on water habitats leading to algal blooms and eutrophication. However, our knowledge of macronutrient ' uxes through estuaries is limited and esti- mates are ož en based on low sampling frequencies leading to large-scale approximations, so there is a need to better understand ' uxes of N and P through estuaries and how their behaviour is impacted by processes operating over a range of temporal and spatial scales. Historically, most water quality monitoring in rivers and estuaries has taken place at Œ xed time intervals that are spaced too far apart to capture severe weather events, so there is a heightened demand for instruments that are able to operate unattended for extended periods. This means that they must be robust, resistant to fouling, and able to operate on low levels of power without requiring frequent recalibration. Low power remote telemetry capability also reduces the frequency of site visits and thereby further lowers operational costs. Researchers in the South have established a small net- work of monitoring instru- ments in Christchurch Harbour and associated rivers to study the e— ects of weather events on water quality, and to better understand the magnitude and spatial / temporal variation of macronutrient ' uxes – nitro- gen, carbon (C) and phosphorus. The project, Œ nanced by a Natural Environmental Research Council grant, has involved installing three con- tinuous monitoring stations – one in the harbour itself, a second in the river Avon and a third in the river Stour. Each monitoring station includes a Xylem YSI EXO2 multiparameter water quality monitoring sonde and a Xylem Storm3 Datalogger that wirelessly transmits the data to the Storm Central 'cloud' hosted data collection platform so that readings can be viewed on the project website. With more than a year's worth of data, project lead Prof Duncan Purdie says: "We were fortunate with the storms that took place over the winter of 2013/14, because we were able to gather excellent high fre- quency data on nutrient ' uxes and water quality during severe weather, which has dra- matically improved our under- standing of the e— ect extreme river ' ows have on nutrient ' uxes into the estuary. The monitoring systems worked very well during this period and we were particularly impressed with the perfor- mance of the EXO2 sondes and the Storm loggers." In addition to monitoring macronutrient ' uxes, the pro- ject has investigated the eutrophication status of the estuary with summer reduced river ' ows leading to longer water residence times resulting in algal blooms, that can cause reduced dissolved oxygen lev- els which threatens migratory Œ sh, for example. The project has also sought to determine whether high river ' ows dur- ing the winter a— ect the estua- rine benthic habitat and local Œ sheries. Dataloggers wirelessly transmit the data to the Storm Central 'cloud' hosted data collection platform

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