Search

Animal waste contains high numbers of microorganisms and therefore can present a potential biological threat to human health. During episodic rainfall events resulting in runoff, microorganisms in the waste and soil may migrate into surface runoff, contaminating surface water resources. A probabilistic human exposure (HE) model was created to determine exposure to faecal indicator bacteria (FIB): total coliforms (TC), E. coli and enterococci following application of bio-based fertiliser (dairy cattle slurry, digestate) to grassland; using a combination of experimental field results and literature-based data. This step was followed by a quantitative microbial risk assessment (QMRA) model for pathogenic E. coli based on a literature-based dose-response model. The results showed that the maximum daily HE (HE daily ) is associated with E. coli for unprocessed slurry (treatment T1) on day 1, the worst-case scenario where the simulated mean HE daily was calculated as 2.84 CFU day -1 . The results indicate that the overall annual probability of risk (P annual ) of illness from E. coli is very low or low based on the WHO safe-limit of P annual as 10 -6 . In the worst-case scenario, a moderate risk was estimated with simulated mean P annual as 1.0 × 10 -5 . Unpasteurised digestate application showed low risk on day 1 and 2 (1.651 × 10 -6 , 1.167 × 10 -6 , respectively). Pasteurised digestate showed very low risk in all scenarios. These results support the restriction imposed on applying bio-based fertiliser if there is any rain forecast within 48 h from the application time. This study proposes a future extension of the probabilistic model to include time, intensity, discharge, and distance-dependant dilution factor. The information generated from this model can help policymakers ensure the safety of surface water sources through the quality monitoring of FIB levels in bio-based fertiliser., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Background: Grazed grassland management regimes can have various effects on soil fauna. For example, effects on earthworms can be negative through compaction induced by grazing animals, or positive mediated by increases in sward productivity and cattle dung pats providing a food source. Knowledge gaps exist in relation to the behaviour of different earthworm species i.e. their movement towards and aggregation under dung pats, the legacy effects of pats and the spatial area of recruitment. The present study addressed these knowledge gaps in field experiments, over 2 years, using natural and simulated dung pats on two permanent, intensively grazed pastures in Ireland., Results: Dung pats strongly affected spatial earthworm distribution, with up to four times more earthworms aggregating beneath pats, than in the control locations away from pats. In these earthworm communities comprising 11 species, temporally different aggregation and dispersal patterns were observed, including absence of individual species from control locations, but no clear successional responses. Epigeic species in general, but also certain species of the anecic and endogeic groups were aggregating under dung. Sampling after complete dung pat disappearance (27 weeks after application) suggested an absence of a dung pat legacy effect on earthworm communities. Based on species distributions, the maximum size of the recruitment area from which earthworms moved to pats was estimated to be 3.8 m 2 per dung pat. Since actual grazing over 6 weeks would result in the deposition of about 300 dung pats per ha, it is estimated that a surface area of 1140 m 2 or about 11% of the total grazing area can be influenced by dung pats in a given grazing period., Conclusions: This study showed that the presence of dung pats in pastures creates temporary hot spots in spatial earthworm species distribution, which changes over time. The findings highlight the importance of considering dung pats, temporally and spatially, when sampling earthworms in grazed pastures. Published comparisons of grazed and cut grasslands probably reached incorrect conclusions by ignoring or deliberately avoiding dung pats. Furthermore, the observed intense aggregation of earthworms beneath dung pats suggests that earthworm functions need to be assessed separately at these hot spots.

In Ireland, the land application of biosolids is the preferred option of disposing of municipal sewage waste. Biosolids provide nutrients in the form of nitrogen, phosphorus, potassium and increases organic matter. It is also an economic way for a country to dispose of its municipal waste. However, biosolids may potentially contain a wide range of pathogens, and following rainfall events, may be transported in surface runoff and pose a potential risk to human health. Thus, a quantitative risk assessment model was developed to estimate potential pathogens in surface water and the environmental fate of the pathogens following dilution, residence time in a stream, die-off rate, drinking water treatment and human exposure. Surface runoff water quality data was provided by project partners. Three types of biosolids, anaerobically digested (AD), lime stabilised (LS), and thermally dried (TD)) were applied on micro plots. Rainfall was simulated at three time intervals (24, 48 and 360 h) following land application. It was assumed that this water entered a nearby stream and was directly abstracted for drinking water. Consumption data for drinking water and body weight was obtained from an Irish study and assigned distributions. Two dose response models for probability of illness were considered for total and faecal coliform exposure incorporating two different exposure scenarios (healthy populations and immuno-compromised populations). The simulated annual risk of illness for healthy populations was below the US EPA and World Health Organisation tolerable level of risk (10 -4 and 10 -6 , respectively). However, immuno-compromised populations may still be at risk as levels were greater than the tolerable level of risk for that subpopulation. The sensitivity analysis highlighted the importance of residence time in a stream on the bacterial die-off rate., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

During episodic rainfall events, land application of treated municipal sludge ('biosolids') may give rise to surface runoff of metals, which may be potentially harmful to human health if not fully treated in a water treatment plant (WTP). This study used surface runoff water quality data generated from a field-scale study in which three types of biosolids (anaerobically digested (AD), lime stabilised (LS), and thermally dried (TD)) were spread on micro-plots of land and subjected to three rainfall events at time intervals of 24, 48 and 360h following application. Making the assumption that this water directly entered abstraction waters for a WTP without any grassed buffer zone being present, accounting for stream dilution, and modelling various performance scenarios within the WTP, the aim of this research was to conduct a human health risk assessment of metals (Cu, Ni, Pb, Zn, Cd and Cr), which may still be present in drinking water after the WTP. Different dose-response relationships were characterised for the different metals with reference to the lifetime average daily dose (LADD) and the Hazard Quotient (HQ). The results for the LADD show that child exposure concentrations were highest for Cu when the measured surface runoff concentrations from the LS biosolids treatment were used as input into the model. The results for the HQ showed that of all the scenarios considered, Cu had the highest HQ for children. However, values were below the threshold value of risk (HQ<0.01 - no existing risk). Under the conditions monitored, metal concentrations in the biosolids applied to grassland were not considered to result in a risk to human health in surface water systems., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Treated municipal sewage sludge ("biosolids") and dairy cattle slurry (DCS) may be applied to agricultural land as an organic fertiliser. This study investigates losses of nutrients in runoff water (nitrogen (N) and phosphorus (P)), metals (copper (Cu), nickel (Ni), lead (Pb), zinc (Zn), cadmium (Cd), chromium (Cr)), and microbial indicators of pollution (total and faecal coliforms) arising from the land application of four types of treated biosolids and DCS to field micro-plots at three time intervals (24, 48, 360 h) after application. Losses from biosolids-amended plots or DCS-amended plots followed a general trend of highest losses occurring during the first rainfall event and reduced losses in the subsequent events. However, with the exception of total and faecal coliforms and some metals (Ni, Cu), the greatest losses were from the DCS-amended plots. For example, average losses over the three rainfall events for dissolved reactive phosphorus and ammonium-nitrogen from DCS-amended plots were 5 and 11.2 mg L(-1), respectively, which were in excess of the losses from the biosolids plots. When compared with slurry treatments, for the parameters monitored biosolids generally do not pose a greater risk in terms of losses along the runoff pathway. This finding has important policy implications, as it shows that concern related to the reuse of biosolids as a soil fertiliser, mainly related to contaminant losses upon land application, may be unfounded., (Copyright © 2015 Elsevier B.V. All rights reserved.)

In North Atlantic Europe intensive dairy farms have a low nitrogen (N) use efficiency, with high N surpluses often negatively affecting water quality. Low feed input systems on heavy textured soils often need artificial drainage to utilise low cost grassland and remain profitable. Heavy textured soils have high but variable N attenuation potential, due to soil heterogeneity. Furthermore, drainage system design can influence the potential for N attenuation and subsequent N loadings in waters receiving drainage from such soils. The present study utilises end of pipe, open ditch and shallow groundwater sampling points across five sites in SW Ireland to compare and rank sites based on N surplus, water quality and “net denitrification”, and to develop a conceptual framework for the improved management of heavy textured dairy sites to inform water quality N sustainability. This includes both drainage design and “net denitrification” criterion, as developed within this study.N surplus ranged from 211 to 292 kg N/ha (mean of 252 kg N/sourha) with a common source of organic N across all locations. The predicted soil organic matter (SOM) N release potential from top-subsoil layers was high, ranging from 115 to >146 kg N/ha. Stable isotopes analyses showed spatial variation in the extent of specific N-biotransformation processes, according to drainage location and design. Across all sites, nitrate (NO 3 -N) was converted to ammonium (NH 4 + -N), which migrated offsite through open ditch and shallow groundwater pathways. Using the ensemble data the potential for soil N attenuation could be discriminated by 3 distinct groups reflecting the relative dominance of in situ N-biotransformation processes deduced from water composition: Group 1 (2 farms, ranked with high sustainability, NH 4 + < 0.23 mg N/l, δ 15 N-NO 3 − > 5‰ and δ 18 O-NO 3 − > 10‰), low NH 4 + -N concentration coupled with a high denitrification potential; Group 2 (1 farm with moderate sustainability, NH 4 + < 0.23 mg N/l, δ 15 N-NO 3 − < 8‰ and δ 18 O-NO 3 − < 8‰), low NH 4 + -N concentration with a high nitrification potential and a small component of complete denitrification; Group 3 (2 farms, ranked with low sustainability, NH 4 + > 0.23 mg N/l, 14‰ > δ 15 N-NO 3 − > 5‰ and 25‰ > δ 18 O-NO 3 − > −2‰), high NH 4 + -N concentration due to low denitrification. The installation of a shallow drainage system (e.g. mole or gravel moles at 0.4 m depth) reduced the “net denitrification” ranking of a site, leading to water quality issues. From this detailed work an N sustainability tool for any site, which presents the relationship between drainage class, drainage design (if present), completeness of denitrification, rate of denitrification and NH 4 -N attenuation was developed. This tool allows a comparison or ranking of sites in terms of their N sustainability. The tool can also be used pre-land drainage and presents the consequences of future artificial land drainage on water quality and gaseous emissions at a given site. [ABSTRACT FROM AUTHOR]

Groundwater contamination was characterised using a methodology which combines shallow groundwater geochemistry data from 17 piezometers over a 2yr 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 (<5m below ground level) generated from an agricultural point source on a 4.2ha 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 2.6mg NO3-NL−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. [Copyright &y& Elsevier]

This study examined the quantity of mineral N in soil and nitrate-N losses to groundwater from grassland-based dairy production in 2001 and 2002. There were four treatments with different inputs of N, through fertilizers, concentrates and biological fixation, and four associated stocking densities. Nitrogen inputs were 205, 230, 300 and 400 kg ha−1, respectively, and annual stocking densities were 1·75, 2·10, 2·50 and 2·50 cows ha−1. There were 18 cows per treatment. Grazed herbage accounted for 0·64, grass-silage for 0·26 and concentrates 0·10 of annual DM consumed by the cows. Quantities of mineral N (nitrate-N and ammonium-N) in soil were measured, following extraction in 2 M KCl (1:2 w/v) shaken continuously for 2 h, on three occasions between late September and early February each winter. Concentrations of nitrate-N in groundwater from wells inserted vertically to a depth of 1 m were determined throughout both winters. Quantities of mineral N in the soil increased ( P < 0·001) with higher N inputs and declined ( P < 0·001) with later sampling date. There were no relationships between nitrate-N concentrations in groundwater and N inputs, N surpluses, deposition of excreta-N at the soil surface and soil mineral N during both winters. Low losses of nitrate-N to groundwater were primarily attributed to high rates of denitrification associated with a heavy soil texture, wet anaerobic soil conditions, relatively high organic carbon contents throughout the soil profile and mild soil temperatures throughout the year. Uptake of N by herbage made an important contribution to low N losses over the winter. [ABSTRACT FROM AUTHOR]

Highlights • We measured soil nitrous oxide flux, methane flux and soil respiration followiing driange installation. • We measuered water filled pore space (WFPS), soil mineral nitrogen (N), herbage N uptake, soil organic carbon (SOC) and soil total nitrogen (TN) following the installation of mole and gravel mole drainage systems in a clay-loam soil in two experiments over 36 months. • Drainage treatment deepened the water table and decreased WFPS. • Mole and gravel mole drainage had no impact on soil GHG fluxes, soil N mineralisation, soil N nitrification, SOC and TN. Abstract Shallow drainage (e.g. mole and gravel mole drainage installed at 0.55 m below soil surface) is used on pasture-based farms to reduce soil moisture, deepen water table depth and thus increase grass utilization on soils with impeded drainage. There is, however, a lack of research on the effect that these drainage techniques have on soil greenhouse gas (GHG) emissions. Hence the objective of this study was to investigate the effects of mole and gravel mole drainage on soil GHG fluxes. Soil nitrous oxide (N 2 O), soil root respiration (CO 2) and soil methane (CH 4) fluxes were measured in two experiments conducted over a 36 month period. The experiments were conducted on permanent grassland with impeded drainage on a eutric gleysol (humic) in Ireland (52°30′N, 08°12′W). Both experiments were arranged in randomized complete block design. There were three treatments: (i) undrained control, (ii) mole drainage and (iii) gravel mole drainage. Soil GHG fluxes, soil water filled pore space (WFPS) and soil temperature were measured on a weekly basis and soil mineral nitrogen (N), herbage N uptake, soil organic carbon (SOC) and soil total N (TN) were measured seasonally and annually over the sampling period. Drainage treatments (P < 0.05) deepened (mean ± SE) the water table by 0.17±0.03 m and decreased WFPS by 7±0.2%. However no (P > 0.05) impact of drainage treatment was detected on soil average daily GHG fluxes (9.84±6.34g N 2 O-N ha−1day−1, 34.05 ± 12.90 kg CO 2 -C ha−1day−1 and −0.91 ± 3.70 g CH 4 -C ha-1day-1), soil N mineralisation, soil N nitrification, SOC and TN in both experiments. The results indicate that mole and gravel mole drainage can be installed on farms with similar management and soil type to that described in the present study without impact on the soil GHG emissions. [ABSTRACT FROM AUTHOR]

Large quantities of organic manures and soiled water are generated by cattle housing every year. These organic wastes are stored until soil conditions are suitable for landspreading or there is a crop requirement for nutrients. After land application, some nitrogen (N) is lost through the direct emission of nitrous oxide (N 2 O), a powerful greenhouse gas (GHG) produced by nitrification and partial denitrification of mineral N. The objective of this research was to investigate whether N 2 O losses could be mitigated after applying cattle slurry pre-mixed with the nitrification inhibitor dicyandiamide (DCD) during anaerobic storage. Contrary to our initial hypothesis, DCD mixed with slurry did not degrade for up to six months post amendment during an incubation study. These results highlight the feasibility of amending cattle slurry with DCD directly into slurry tanks any time before land application. This incubation experiment also showed that a slow release of DCD in slurry could be achieved if the amendment used was beads of a chitosan xerogel impregnated with DCD. A field study revealed that slurry application to grassland plots can cause large N 2 O emissions under wet and mild conditions when ammonia emissions are expected to be low. Slurry incubated with DCD for six month was effective at significantly ( P < 0.01) decreasing N 2 O net cumulative emissions, which were 88% lower than in the slurry treatment with no DCD. The addition of DCD to slurry also reduced the fraction of N 2 O in the total GHG net cumulative emissions from 52% down to just 10%. Mixing slurry with DCD during storage could therefore offer farmers a cost-effective, practical, mitigation alternative to DCD broadcast application for the reduction of agricultural N losses. [ABSTRACT FROM AUTHOR]