In this study, predefined exposure periods and subsequent laboratory extractions were compared with high-resolution data sets for total oxidisable nitrogen, total phosphorus and total reactive phosphorus that were collected at established monitoring stations. Multiple cartridges were deployed on 14 occasions in a variety of river systems in an effort to rigorously validate their use in rivers. These transfer risk patterns are summarised as showing indications of high P or N in storm flows and/or in inter-storm periods and from a variety of point and diffuse sources, the latter from both lateral (P) and vertical (N) flows. This allowed the accurate determination of time- and flow-weighted mean concentrations for the sampling periods that ranged from 3 to 5 weeks. A departure from the original systematic experimental design (a single river system, multiple deployment periods) occurred due to emerging factors relating to variable and under-estimation of flowweighted mean concentrations. Hence the deployment strategy was extended to a number of river systems with different hydrological responses and nutrient transfer risks to ensure that any issues were not related to one particular site. Variability existed in the P and N concentrations returned by the cartridges compared to those measured by the high-resolution monitoring equipment. It included under- and over-estimates of nutrient fluxes (as flow-weighted mean concentrations) from near-continuous time series data. Experiments were subsequently conducted to investigate the discrepancies that existed between passive sensor results and high-resolution data. Hydrodynamic simulations were conducted using a two-dimensional lattice Boltzmann discrete element methodology. This allowed fluid movement around the cartridge to be modelled as discrete particles, and simulations demonstrated flow divergence round the cartridges rather than into them. Issues were raised regarding the accumulation of detritus around the cartridges during storm events, the effectiveness of the cartridges during low flow, and the implications of invertebrate and algal colonisation. To test adsorbance and tracer salt loss, and to eliminate external environmental variables, cartridges were exposed to standard solutions of known (P and N) concentration and ambient river samples via controlled pumping. Concentrations of P and N determined by cartridges in the pump test trials still displayed discrepancies in comparison to actual concentrations determined by standard methods in the river samples. However, estimation of cartridge throughflow using tracer salt dissolution rate appeared to be a reliable methodology, but only when flow was forced through the cartridge under pumped pressure. The issues of temporal coverage for chemical monitoring in rivers remain highly important for future evaluation of catchment policy measures. Multiple factors have been highlighted regarding the performance of the cartridges and their variable recoveries when compared with flow-proportional data. Further investigation into these factors would allow the true effectiveness of the passive sensor cartridge to be quantified in Irish river systems and informed adaptations made to the cartridge design to improve function. As these issues become resolved, the passive system could be extremely useful to the WFD authorities mentioned above, in tandem with current monitoring programmes, and possibly form part of a complementary suite of smart infrastructure for ongoing and future water monitoring programmes.

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Macintosh, K.   "Flow-proportional Passive Sensor Validation of Phosphorus and Nitrogen in Irish Rivers (Flow-Pro)". Associated datasets and digitial information objects connected to this resource are available at: Secure Archive For Environmental Research Data (SAFER) managed by Environmental Protection Agency Ireland https://eparesearch.epa.ie/safer/resource?id=4cd29df8-414a-102f-8c70-b53a025bc1b8 (Last Accessed: 2025-01-24)

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SAFER-Data Display URL	https://eparesearch.epa.ie/safer/iso19115/display?isoID=233
Resource Keywords	Nitrogen, flow, phosphorus, river basin districts, catchments
EPA/ERTDI/STRIVE Project Code	2008-ET-MS-5-S2
EPA/ERTDI/STRIVE Project Theme	Water Quality
Resource Availability:	Public-Open
Limitations on the use of this Resource	Any attached datasets, data files, or information objects can be downloaded for further use in scientific applications under the condition that the source is properly quoted and cited in published papers, journals, websites, presentations, books, etc. Before downloading, users must agree to the "Conditions of Download and Access" from SAFER-Data. These appear before download. Users of the data should also communicate with the original authors/owners of this resource if they are uncertain about any aspect of the data or information provided before further usage.
Number of Attached Files (Publicly and Openly Available for Download):	2
Project Start Date	Tuesday 1st January 2008 (01-01-2008)
Earliest Recorded Date within any attached datasets or digital objects	Tuesday 1st January 2008 (01-01-2008)
Most Recent Recorded Date within any attached datasets or digital objects	Thursday 1st September 2011 (01-09-2011)
Published on SAFER	Thursday 6th October 2011 (06-10-2011)
Date of Last Edit	Thursday 6th October 2011 at 11:24:15 (06-10-2011)
Datasets or Files Updated On	Thursday 6th October 2011 at 11:24:15 (06-10-2011)

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Description of Geographical Characteristics of This Project or Dataset
For field monitoring, the main station used in this project was a 5 km2 sub-catchment of the Blackwater River in Co. Monaghan. These data were augmented by a similar station in Co. Tyrone, also a 5 km2 subcatchment of the Blackwater River. Both sites were part of a previous large-scale project, Blackwater TRACE (Jordan et al., 2008). These two sites were typical of flashy drumlin hydrological systems with both point and diffuse pressures, typically with high P and low N background and storm concentrations. Subsequent to the start of the project, a number of other sites were used that had the potential for: high P and high N concentrations (part of the Dee system in Co. Louth); low P and high N concentrations (part of the Slaney system in Co. Wexford); and low P and low N concentrations (part of the Robe system in Co. Mayo); see Fig. 2.1. Each site had hydrometry and waterquality instrumentation measuring discharge, P and N on a sub-hourly basis

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