Erodibility of hill peat

peer-reviewedThe project was funded by the European Union Structural Funds EAGGF distributed under the Department of Agriculture and Food Stimulus Fund.The energy necessary to entrain soil in water depends on the soil strength. Once entrained, the settling velocity of the eroded soil in water is of fundamental importance to the processes of sediment transport and deposition. In this paper, stream power theory and transport concepts coupled with the equation of continuity were used to derive a transport-limited peat concentration. The ratio of the log of the actual sediment concentration in surface run-off to the log of the transport-limited sediment concentration was the index of erosion used. The value of this index is a measure of the sensitivity of peat to erosion by sheet flow. Four peats were subjected to a range of overland flow rates under two slopes in a laboratory flume. The peats represented peat farmed in a sustainable manner (Leenane), overgrazed peat (Maam), peat undergoing erosion (Newport) and peat which had undergone weathering following exposure by a landslip (Croagh Patrick). Both in situ and surface damaged slabs were studied. The results indicate that shearing and remoulding of a wet peat surface (e.g., by animal treading) and weathering of exposed drained peat surfaces predispose peat to erosion. Defoliation by overgrazing is considered to be of secondary importance.Department of Agriculture, Food and the MarineEuropean Union Structural Funds EAGG

The Effect of Chemical Amendments Used for Phosphorus Abatement on Greenhouse Gas and Ammonia Emissions from Dairy Cattle Slurry: Synergies and Pollution Swapping

peer-reviewedLand application of cattle slurry can result in incidental and chronic phosphorus (P) loss to waterbodies, leading to eutrophication. Chemical amendment of slurry has been proposed as a management practice, allowing slurry nutrients to remain available to plants whilst mitigating P losses in runoff. The effectiveness of amendments is well understood but their impacts on other loss pathways (so-called ‘pollution swapping’ potential) and therefore the feasibility of using such amendments has not been examined to date. The aim of this laboratory scale study was to determine how the chemical amendment of slurry affects losses of NH3, CH4, N2O, and CO2. Alum, FeCl2, Polyaluminium chloride (PAC)- and biochar reduced NH3 emissions by 92, 54, 65 and 77% compared to the slurry control, while lime increased emissions by 114%. Cumulative N2O emissions of cattle slurry increased when amended with alum and FeCl2 by 202% and 154% compared to the slurry only treatment. Lime, PAC and biochar resulted in a reduction of 44, 29 and 63% in cumulative N2O loss compared to the slurry only treatment. Addition of amendments to slurry did not significantly affect soil CO2 release during the study while CH4 emissions followed a similar trend for all of the amended slurries applied, with an initial increase in losses followed by a rapid decrease for the duration of the study. All of the amendments examined reduced the initial peak in CH4 emissions compared to the slurry only treatment. There was no significant effect of slurry amendments on global warming potential (GWP) caused by slurry land application, with the exception of biochar. After considering pollution swapping in conjunction with amendment effectiveness, the amendments recommended for further field study are PAC, alum and lime. This study has also shown that biochar has potential to reduce GHG losses arising from slurry application.This research was funded by the Teagasc Walsh Fellowship Scheme and the AnimalChange Framework 7 Project (FP7-KBBE-2010-4)

Impact of pig slurry amendments on phosphorus, suspended sediment and metal losses in laboratory runoff boxes under simulated rainfall

peer-reviewedLosses of phosphorus (P) when pig slurry applications to land are followed by a rainfall event or losses from soils with high P contents can contribute to eutrophication of receiving waters. The addition of amendments to pig slurry spread on high P Index soils may reduce P and suspended sediment (SS) losses. This hypothesis was tested at laboratory-scale using runoff boxes under simulated rainfall conditions. Intact grassed soil samples, 100 cm-long, 22.5 cm-wide and 5 cm-deep, were placed in runoff boxes and pig slurry or amended pig slurry was applied to the soil surface. The amendments examined were: (1) commercial grade liquid alum (8% Al2O3) applied at a rate of 0.88:1 [Al:total phosphorus (TP)] (2) commercial-grade liquid ferric chloride (38% FeCl3) applied at a rate of 0.89:1 [Fe:TP] and (3) commercial-grade liquid poly-aluminium chloride (PAC) (10% Al2O3) applied at a rate of 0.72:1 [Al:TP]. The grassed soil was then subjected to three rainfall events (10.3 ± 0.15 mm h−1) at time intervals of 48, 72, and 96 h following slurry application. Each sod received rainfall on 3 occasions. Results across three rainfall events showed that for the control treatment, the average flow weighted mean concentration (FWMC) of TP was 0.61 mg L−1, of which 31% was particulate phosphorus (PP), and the average FWMC of SS was 38.1 mg L−1. For the slurry treatment, there was an average FWMC of 2.2 mg TP L−1, 47% of which was PP, and the average FWMC of SS was 71.5 mg L−1. Ranked in order of effectiveness from best to worst, PAC reduced the average FWMC of TP to 0.64 mg L−1 (42% PP), FeCl3 reduced TP to 0.91 mg L−1 (52% PP) and alum reduced TP to 1.08 mg L−1 (56% PP). The amendments were in the same order when ranked for effectiveness at reducing SS: PAC (74%), FeCl3 (66%) and alum (39%). Total phosphorus levels in runoff plots receiving amended slurry remained above those from soil only, indicating that, although incidental losses could be mitigated by chemical amendment, chronic losses from the high P index soil in the current study could not be reduced.The first author gratefully acknowledges the award of the EMBARK scholarship from IRCSET to support this study

Factors affecting nitrate distribution in shallow groundwater under a beef farm in South Eastern Ireland

peer-reviewedGroundwater contamination was characterised using a methodology which combines shallow groundwater geochemistry data from 17 piezometers over a 2 yr period in a statistical framework and hydrogeological techniques. Nitrate–N (NO3-N) contaminant mass flux was calculated across three control planes (rows of piezometers) in six isolated plots. Results showed natural attenuation occurs on site although the method does not directly differentiate between dilution and denitrification. It was further investigated whether NO3-N concentration in shallow groundwater (<5 m below ground level) generated from an agricultural point source on a 4.2 ha site on a beef farm in SE Ireland could be predicted from saturated hydraulic conductivity (Ksat) measurements, ground elevation (m Above Ordnance Datum), elevation of groundwater sampling (screen opening interval) (m AOD) and distance from a dirty water point pollution source. Tobit regression, using a background concentration threshold of 2.6 mg NO3-N L−1 showed, when assessed individually in a step wise procedure, Ksat was significantly related to groundwater NO3-N concentration. Distance of the point dirty water pollution source becomes significant when included with Ksat in the model. The model relationships show areas with higher Ksat values have less time for denitrification to occur, whereas lower Ksat values allow denitrification to occur. Areas with higher permeability transport greater NO3-N fluxes to ground and surface waters. When the distribution of Cl− was examined by the model, Ksat and ground elevation had the most explanatory power but Ksat was not significant pointing to dilution having an effect. Areas with low NO3 concentration and unaffected Cl− concentration points to denitrification, low NO3 concentration and low Cl− chloride concentration points to dilution and combining these findings allows areas of denitrification and dilution to be inferred. The effect of denitrification is further supported as mean groundwater NO3-N was significantly (P < 0.05) related to groundwater N2/Ar ratio, redox potential (Eh), dissolved O2 and N2 and was close to being significant with N2O (P = 0.08). Calculating contaminant mass flux across more than one control plane is a useful tool to monitor natural attenuation. This tool allows the identification of hot spot areas where intervention other than natural attenuation may be needed to protect receptors.Research Stimulus Fund, Department of Agriculture Fisheries and Food (Ireland

Exploring the relationship between groundwater geochemical factors and denitrification potentials on a dairy farm in southeast Ireland

NOTICE: this is the author’s version of a work that was accepted for publication in the journal Ecological Engineering. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Ecological Engineering, volume 37, issue 9, September 2011, 1304-1313. DOI: 10.1016/j.ecoleng.2011.03.025peer-reviewedNitrate (NO3−) loss from agriculture to shallow groundwater and transferral to sensitive aquatic ecosystems is of global concern. Denitrifying bioreactor technology, where a solid carbon (C) reactive media intercepts contaminated groundwater, has been successfully used to convert NO3− to di-nitrogen (N2) gas. One of the challenges of groundwater remediation research is how to track denitrification potential spatially and temporally within reactive media and subsoil. First, using δ15N/δ18O isotopes, eight wells were divided into indicative transformational processes of ‘nitrification’ or ‘denitrification’ wells. Then, using N2/argon (Ar) ratios these wells were divided into ‘low denitrification potential’ or high denitrification potential’ categories. Secondly, using falling head tests, the saturated hydraulic conductivity (Ksat) in each well was estimated, creating two groups of ‘slow’ (0.06 m day−1) and ‘fast’ (0.13 m day−1) wells, respectively. Thirdly, two ‘low denitrification potential’ wells (one fast and one slow) with high NO3− concentration were amended with woodchip to enhance denitrification. Water samples were retrieved from all wells using a low flow syringe to avoid de-gassing and analysed for N2/Ar ratio using membrane inlet mass spectrometry. Results showed that there was good agreement between isotope and chemical (N2/Ar ratio and dissolved organic C (DOC)) and physio-chemical (dissolved oxygen, temperature, conductivity and pH) parameters. To explain the spatial and temporal distribution of NO3− and other parameters on site, the development of predictive models using the available datasets for this field site was examined for NO3−, Cl−, N2/Ar and DOC. Initial statistical analysis was directed towards the testing of the effect of woodchip amendment. The analysis was formulated as a repeated measures analysis of the factorial structure for treatment and time. Nitrate concentrations were related to Ksat and water level (p < 0.0001 and p = 0.02, respectively), but did not respond to woodchip addition (p = 0.09). This non-destructive technique allows elucidation of denitrification potential over time and could be used in denitrifying bioreactor technology to assess denitrification hotspots in reactive media, while developing a NO3− spatial and temporal predictive model for bioreactor site specific conditions

The short-term effects of management changes on watertable position and nutrients in shallow groundwater in a harvested peatland forest

This work was funded by the Department of Agriculture, Fisheries and Food and the Environmental Protection Agency under the STRIVE program 2007 – 2013.peer-reviewedManagement changes such as drainage, fertilisation, afforestation and harvesting (clearfelling) of forested peatlands influence watertable (WT) position and groundwater concentrations of nutrients. This study investigated the impact of clearfelling of a peatland forest on WT and nutrient concentrations. Three areas were examined: (1) a regenerated riparian peatland buffer (RB) clearfelled four years prior to the present study (2) a recently clearfelled coniferous forest (CF) and (3) a standing, mature coniferous forest (SF), on which no harvesting took place. The WT remained consistently below 0.3 m during the pre-clearfelling period. Results showed there was an almost immediate rise in the WT after clearfelling and a rise to 0.15 m below ground level (bgl) within 10 months of clearfelling. Clearfelling of the forest increased dissolved reactive phosphorus concentrations (from an average of 28–230 μg L−1) in the shallow groundwater, likely caused by leaching from degrading brash mats.Environmental Protection AgencyDepartment of Agriculture, Food and the Marin

January 13, 2000

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Quantitative risk assessment of antimicrobials in biosolids applied on agricultural land and potential translocation into food

peer-reviewedThe use of biosolids as a fertiliser may be an indirect route for contaminants into the food chain. One of the main concerns regarding the spreading of biosolids on agricultural land is the potential uptake of contaminants into plants which may bio-transfer into grazing animals that supply the food chain directly (e.g. meat and milk) and hence are subsequently consumed. The aim of this project was to create a quantitative risk assessment model to estimate the fate and translocation of triclosan (TCS) and triclocarban (TCC) into the feed (grass) and food chain with subsequent human exposure. The model's results indicate that TCS and TCC have low potential to transfer into milk and beef following the ingestion of contaminated grass by dairy cows. Mean estimated TCS and TCC residues in milk and beef show that TCC had the greatest concentration (mean values of 7.77 × 10− 6 mg kg− 1 in milk and 1.36 × 10− 4 mg kg− 1 in beef). Human exposure results show that TCC was greater for milk consumption in infants (1–4 years) (mean value 1.14 × 10− 7 mg kg− 1 bw d− 1) and for beef consumption by teens (12–17 years) (mean value 6.87 × 10− 8 mg kg− 1 bw d− 1). Concentrations of TCS and TCC were well below the estimated acceptable daily intake (ADI). Human health risk was estimated by evaluation of the hazard quotient (HQ), which used the NOAEL as a toxicity endpoint, combined with milk and beef human exposure estimates. HQ results show that all values were < 0.01 (no existing risk). A sensitivity analysis revealed that the Kow and initial concentration in biosolids as the parameters of greatest importance (correlation coefficients 0.91 and 0.19, respectively). This highlights the importance of physio-chemical properties of the compounds and their detection in biosolids post wastewater treatment along with their persistence in soil following application. This model is a valuable tool in which to ascertain the potential transfer of contaminants in the environment into animal forage with knock on consequences for exposure through the human food chain

Carbon and nitrogen dynamics and greenhouse gas emissions in constructed wetlands treating wastewater: a review

peer-reviewedThe removal efficiency of carbon (C) and nitrogen (N) in constructed wetlands (CWs) is very inconsistent and frequently does not reveal whether the removal processes are due to physical attenuation or whether the different species have been transformed to other reactive forms. Previous research on nutrient removal in CWs did not consider the dynamics of pollution swapping (the increase of one pollutant as a result of a measure introduced to reduce a different pollutant) driven by transformational processes within and around the system. This paper aims to address this knowledge gap by reviewing the biogeochemical dynamics and fate of C and N in CWs and their potential impact on the environment, and by presenting novel ways in which these knowledge gaps may be eliminated. Nutrient removal in CWs varies with the type of CW, vegetation, climate, season, geographical region, and management practices. Horizontal flow CWs tend to have good nitrate (NO3−) removal, as they provide good conditions for denitrification, but cannot remove ammonium (NH4+) due to limited ability to nitrify NH4+. Vertical flow CWs have good NH4+ removal, but their denitrification ability is low. Surface flow CWs decrease nitrous oxide (N2O) emissions but increase methane (CH4) emissions; subsurface flow CWs increase N2O and carbon dioxide (CO2) emissions, but decrease CH4 emissions. Mixed species of vegetation perform better than monocultures in increasing C and N removal and decreasing greenhouse gas (GHG) emissions, but empirical evidence is still scarce. Lower hydraulic loadings with higher hydraulic retention times enhance nutrient removal, but more empirical evidence is required to determine an optimum design. A conceptual model highlighting the current state of knowledge is presented and experimental work that should be undertaken to address knowledge gaps across CWs, vegetation and wastewater types, hydraulic loading rates and regimes, and retention times, is suggested. We recommend that further research on process-based C and N removal and on the balancing of end products into reactive and benign forms is critical to the assessment of the environmental performance of CWs.The research was funded by Irish Research Council and Department of Agriculture, Food and Marine in Association with The University of Dublin, Trinity College

Use of industrial by-products and natural media to adsorb nutrients, metals and organic carbon from drinking water

• The use of waste media in the water sector results in a robust, sustainable option. • Fly ash and Bayer residue successfully adsorb TOC, nutrients and Cu. • Granular blast furnace slag and pyritic fill have good adsorption potential. • pH adjustment is not necessary for optimal adsorption of contaminants. • Kinetic studies show that at least 60% of adsorption had taken place after 8 h. a b s t r a c t a r t i c l e i n f o Filtration technology is well established in the water sector but is limited by inability to remove targeted contaminants, found in surface and groundwater, which can be damaging to human health. This study optimises the design of filters by examining the efficacy of seven media (fly ash, bottom ash, Bayer residue, granular blast furnace slag (GBS), pyritic fill, granular activated carbon (GAC) and zeolite), to adsorb nitrate, ammonium, total organic carbon (TOC), aluminium, copper (Cu) and phosphorus. Each medium and contaminant was modelled to a Langmuir, Freundlich or Temkin adsorption isotherm, and the impact of pH and temperature (ranging from 10°C to 29°C) on their performance was quantified. As retention time within water filters is important in contaminant removal, kinetic studies were carried out to observe the adsorption behaviour over a 24 h period. Fly ash and Bayer residue had good TOC, nutrient and Cu adsorption capacity. Granular blast furnace slag and pyritic fill, previously un-investigated in water treatment, showed adsorption potential for all contaminants. In general, pH or temperature adjustment was not necessary to achieve effective adsorption. Kinetic studies showed that at least 60% of adsorption had occurred after 8 h for all media. These media show potential for use in a multifunctional water treatment unit for the targeted treatment of specific contaminants