CULTIVATION OF NEW LAND INCREASES NUTRIENTS IN RIVERS AND LAKES

The cultivation of new land is a means to increase food production for a growing population. BIOWATER is concerned with what happens to our freshwaters when the land use is changed, and this is a concern that we share with our stakeholders. Based on requests from regional and national authorities, we have therefore conducted a literature survey to increase our knowledge on how freshwaters are affected by transforming forests or outfields to agriculture. The study has been jointly financed by the Norwegian Agricultural Agency and BIOWATER.

The literature study compared losses of suspended sediments, phosphorus and nitrogen from two types of land use: Agriculture and forest/outfields, mainly in Norwegian and Nordic catchments. In addition, the corresponding losses during the cultivation process were evaluated. The method has embedded uncertainty, since agricultural land usually is found on other soil types than forested land. Nevertheless, direct studies of changed nutrient and sediment losses from cultivation of new land are scarce and, hence, this was regarded as the best available method.

The results showed the following average differences in losses between agricultural land and forests/outfields:

  • Nitrogen losses on average17 times higher in agriculture than forests/outfields.
  • Phosphorus losses on average 56 times higher in agriculture than forests/outfields.
  • Suspended sediment losses on average 106 times higher in agriculture than forests/outfields.

During the process of new cultivation, problems are related to tree-harvesting and seedbed preparation. Under various weather conditions, heavy machinery used for forest harvesting may damage the soil and create compaction and the risk for erosion in the wheel tracks. Changing forests to agricultural land may also affect the hydrology, water temperature, light conditions and therefore impact biodiversity. The report recommends that environmental mitigation measures should be implemented when new land is cultivated.

Read the entire literature study here: NIBIO Report 59(6) 2020.

(Feature photo: Eva Skarbøvik)