Special Report: Smaller lawn footprints

BIOBASED - 21850 lmageMost of the environmental impacts of lawn area establishment and maintenance result from the properties and production of soil substrate, according to a lifecycle assessment (LCA) case study.  In our living environment, green lawns are also sources of environmental impacts, especially when nicely managed. One might think that machinery would be the most important source of greenhouse gasses, but, on the other hand, lawns would be good targets for the circulation of nutrients in organic material as an alternative to peat. These aspects were the background of our approach.

In the LCA case study, we analysed the environmental impacts of the establishment and maintenance of lawns, including the production and use of various soil substrates. Many materials can be used in the production of substrates for various landscaping purposes. Anyway, substrate material must be homogeneous, safe and applicable for the roots of the plant to adhere and grow. The substrate must not contain harmful compounds, products or organisms that endanger the health of lawn plants and must be safe to manage and use. We focused on comparing substrates with different peat and compost contents mixed with mineral soil in the substrate. The study included different composting materials (e.g. sludge and municipal biowaste) and composting methods (e.g. use of woodchips or peat as adhesive material). Lifecycle assessment methodology and ISO standards 14040 and 14044 were used in environmental impact assessments. Primary environmental impact categories, which we assessed, were climate change and aquatic eutrophication. We regarded the lifetime of lawn to be 20 years, and fertilisation of the establishment phase to endure for the first ten years. Carbon dioxide from peat degradation is regarded as fossil, and that from organic compost and woodchips as biogenic.

A 20 cm thick substrate layer, which means two thousand tonnes of substrates per hectare of lawn area, were assumed to be needed when establishing a new lawn field. This is a large amount of material to be managed and moved. Climate impact of the lifecycle of lawn areas using different pilot substrates varied between 25 and 51kg CO2-eq/m2 lawn (in the lifetime of 20 years).

Degradation of peat appeared to be the most significant factor of the influence of climate; the contribution of peat degradation was up to 80% of the total carbon footprint when amount of peat in the substrate was 44 kg/m2 lawn area.

The percentage of compost to emissions was 38% in substrate, which contained 55 mass-% compost. Thus, the most effective means of reducing the impact of landscaping on climate is to replace peat with circulated organic material as compost.

Nitrous oxide and methane emissions were related to the use of compost. There is the next challenge to develop treatment of compost to avoid these emissions.

The significance of fuel consumption by machinery in lawn establishment and mowing was low. The high contents of N and P in compost-based substrates may lead in wet situations to nutrient emissions into water systems, which can have significant local impact. Local conditions must be considered when choosing raw materials for substrate. Lawn mowing, even with conventional machinery, does not have a significant climate change impact on the entire lifecycle of landscaping. New solar panel-operated lawn mowers would minimise this impact.

We developed guidelines for comparing conventional and highly recycled material content lawns at various intensity levels and a calculation tool to optimise landscaping from an ecological perspective. Our developed LCA calculation tool helps to optimise soils substrate contents in order to manage the environmental impacts. Various organic materials in substrates can be compared by the tool on a case-by-case basis.

This study was carried out in LIFE09ENV FI 00570 LCA IN LANDSCAPING project that was supported by the EU LIFE Programme.