Abstract
A farm-to-landscape scale modelling framework combining regulating services and life cycle assessment mid-point impacts for air and water was used to explore the co-benefits and trade-offs of alternative management futures for grazing livestock farms. Two intervention scenarios were compared: one using on-farm interventions typically recommended following visual farm audits (visually-based) and the other using mechanistical understanding of nutrient and sediment losses to water (mechanistically-based). At farm scale, reductions in business-as-usual emissions to water of total phosphorus (TP) and sediment, using both the visually-based and mechanistically-based scenarios, were <5%. These limited impacts highlighted the important role of land drains and the lack of relevant on-farm measures in current recommended advisory lists for the soil types in question. The predicted impacts of both scenarios on free draining soils were significantly higher; TP reductions of ∼9% (visually-based) and ∼20% (mechanistically-based) compared with corresponding respective estimates of >20% and >35% for sediment. Key co-benefits at farm scale included reductions in nitrous oxide emissions and improvements in physical soil quality, whereas an increase in ammonia emissions was the principal trade-off. At landscape scale, simulated reductions in business-as-usual losses were <3% for both pollutants for both scenarios. The visually-based and mechanistically-based scenarios narrowed the gaps between current and modern background sediment loads by 6% and 11%, respectively. The latter scenario also improved the reduction of GWP100 relative to business-as-usual by 4%, in comparison to 1% for the former. However, with the predicted increase of ammonia emissions, both eutrophication potential and acidification potential increased (e.g., by 7% and 14% for the mechanistically-based scenario). The discrepancy of on-farm intervention efficacy across spatial scales generated by non-agricultural water pollutant sources is a key challenge for addressing water quality problems at landscape scale.
Highlights
Livestock farming sustains around 1.3 billion people worldwide and accounts for an estimated 14.5% of greenhouse gas emissions (HLPE, 2016)
At field scale on the North Wyke Farm Platform (NWFP), the estimated specific loads from the four flumes used in this work ranged from 153 to 245 kg ha− 1 for sediment and 0.45–0.65 kg ha− 1 for total phosphorus (TP)
While it is advisable to be cautious in assessing model performance using the short temporal span of the monitored data, the comparison clearly suggests that catchment systems model (CSM) is providing robust predictions
Summary
Livestock farming sustains around 1.3 billion people worldwide and accounts for an estimated 14.5% of greenhouse gas emissions (HLPE, 2016). Overstocking and modern intensive management are known to damage soil structure, cause erosion and reduce biodiversity (e.g., Sansom, 1999). Modern livestock farming can result in various unintended environmental consequences for the hydrosphere, pedo sphere, atmosphere and biosphere. Diffuse water pollution from agri culture (DWPA) reduces nutrient use efficiency at farm scale, and leads to environmental damage and economic costs at catchment scale. To generate timely and more holistic assessments at policy relevant scales, it is useful to integrate current evidence and expert opinion on the applicability and efficacy of on-farm interventions (Cuttle et al, 2016) and process understanding on key sources and pathways for diffuse pollution delivery from land to water (Forber et al, 2017) with modelling (e.g., Zhang et al, 2017). Neverthe less, many existing models do not generate a fully comprehensive list of outcomes, lack some critical process representation, fail to compute outcomes across scales and are frequently designed to explore land cover change scenarios (Kanter et al, 2018)
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