CO2 fluxes from drained and rewetted peatlands using a new ECOSSE model water table simulation approach.

The ability of peatlands to remove and store atmospheric carbon (C) depends on the drainage characteristics, which can be challenging to accommodate in biogeochemical models. Many studies indicate that restoration (by rewetting) of damaged peatlands can re-establish their capacity as a natural C sink. The purpose of this research was to improve the biogeochemical modelling of peatlands using the ECOSSE process-based model, which will account for the effects of drainage and rewetting during simulation, and potentially contribute towards improved estimation of carbon dioxide (CO2) fluxes from peatlands, using the IPCC Tier 3 approach. In this study, we present a new drainage factor with seasonal variability Dfa (i) developed specifically for ECOSSE, using empirical data from two drained and rewetted Irish peatlands. Dfa(i) was developed from the Blackwater drained bare-peat site (BWdr), and its application was tested at the vegetated Moyarwood peatland site under drained (MOdr) and rewetted conditions (MOrw). Dfa(i) was applied to the rainfall model inputs for the periods of active drainage in conjunction with the measured water table (WT) inputs. The results indicate that Dfa(i) application can improve the model performance to predict model-estimated water level (WL) and CO2 fluxes under drained conditions [WL: r2 = 0.89 (BWdr) and 0.94 (Modr); CO2: r2 = 0.66 (BWdr) and 0.78 (MOdr)] along with model-ability to capture their seasonal trends. The prediction of WL for the rewetted period was less successful at the MOrw site, where the simulation was run for drained to rewetted, which would suggest that additional work on the water model component is still needed. Despite this, the application of Dfa(i) showed successful model simulation of CO2 fluxes at MOrw (r2 = 0.75) and model ability to capture seasonal trends. This work hopes to positively contribute towards potential future development of Tier 3 methodology for estimating emissions/sinks in peatlands.

Effects of over-winter green cover on soil solution nitrate concentrations beneath tillage land.

There is a growing need to reduce nitrogen losses from agricultural systems to increase food production while reducing negative environmental impacts. The efficacy of vegetation cover for reducing nitrate leaching in tillage systems during fallow periods has been widely investigated. Nitrate leaching reductions by natural regeneration (i.e. growth of weeds and crop volunteers) have been investigated to a lesser extent than reductions by planted cover crops. This study compares the efficacy of natural regeneration and a sown cover crop (mustard) relative to no vegetative cover under both a reduced tillage system and conventional plough-based system as potential mitigation measures for reducing over-winter soil solution nitrate concentrations. The study was conducted over three winter fallow seasons on well drained soil, highly susceptible to leaching, under temperate maritime climatic conditions. Mustard cover crop under both reduced tillage and conventional ploughing was observed to be an effective measure for significantly reducing nitrate concentrations. Natural regeneration under reduced tillage was found to significantly reduce the soil solution nitrate concentrations. This was not the case for the natural regeneration under conventional ploughing. The improved efficacy of natural regeneration under reduced tillage could be a consequence of potential stimulation of seedling germination by the autumn reduced tillage practices and improved over-winter plant growth. There was no significant effect of tillage practices on nitrate concentrations. This study shows that over winter covers of mustard and natural regeneration, under reduced tillage, are effective measures for reducing nitrate concentrations in free draining temperate soils.

Comparison of pesticide leaching potential to groundwater under EU FOCUS and site specific conditions.

The EU FOCUS scenarios are a set of nine standard scenarios based on a combination of crop, soil and weather data used throughout Europe to evaluate the leaching potential of pesticides to groundwater. In Ireland, two predefined EU FOCUS scenarios (Okehampton and Hamburg) appear to be the most appropriate to Irish conditions. However, there is concern that these scenarios may not accurately represent Irish specific conditions, especially in terms of soil and climatic weather. Therefore, the objective of this study was to parameterise a number of site specific locations in Ireland (represented by Oakpark, Clonroche, Rathangan and Elton series soils) and to compare simulated leachate levels at these locations to EU FOCUS scenarios using the PELMO (Pesticide Leaching Model) simulation model. The hydrological processes were validated using observed data for soil tension and leachate. The appropriate EU FOCUS scenarios were then simulated for the given locations and compared to the parameterised scenario. All scenarios were run using the same version of PELMO, therefore eliminating any software impacts. The models were run for 26 years using appropriate meteorological data. The results showed significant difference between the parameterised model pesticide leaching and that resulting from the EU FOCUS scenarios, the latter overestimating site pesticide leaching from 42 to 99%. The results indicated a significant conservatism in using EU FOCUS scenarios to determine potential pesticide concentration in the leachate under Irish specific conditions and ensure the desired level of protection against pesticide contamination of national water resources.

Effects of over-winter green cover on groundwater nitrate and dissolved organic carbon concentrations beneath tillage land.

Application of over-winter green cover (e.g. cover crops) as a measure for reducing nitrate losses from tillage land has been frequently investigated, especially in the unsaturated zone. Monitoring of groundwater is less common in these studies. Studies on groundwater responses to different land treatments can be challenging because they can be influenced by various conditions, such as recharge, seasonal variations, and aquifer properties, often occurring at different time scales than surface water processes. The aim of this study was to evaluate groundwater nitrate (NO(3)(-)N) and dissolved organic carbon (DOC) concentration responses to different over-winter green covers: mustard, natural regeneration and no cover. A field experiment was designed and run for three years on tillage land underlain by a vulnerable sand and gravel aquifer in the south-east of Ireland. Results showed that over-winter green cover growth on tillage land can be an effective measure to reduce groundwater NO(3)(-)N concentrations. A significant decrease in groundwater NO(3)(-)N concentrations was observed under the mustard cover compared to no cover. All treatments, including no cover, showed a decline in groundwater NO(3)(-)N concentrations over time. A significant increase in groundwater DOC was also observed under the mustard cover. Although the overall groundwater DOC concentrations were low, the increased DOC occurrence in groundwater should be accounted for in carbon balances and could potentially enhance groundwater denitrification in cases where aquifer conditions may favour it.