Surface waters: The overlooked factor in the forestry climate mitigation debate?

Norway is pursuing sustainable climate mitigation strategies and intensified forestry practices to increase biomass harvesting (e.g. nitrogen fertilization, intensified stem-only and/or whole-tree harvesting) to sequester more carbon from the atmosphere. The decision to intensify forest biomass use has led to debate in Norway, both scientifically and publicly. While the debate is still ongoing, other potential environmental concerns might have been overseen, in particular the potential effects of intensified forestry on surface waters. Norway's lakes and rivers deliver a number of invaluable services including drinking water, recreational opportunities and habitat for a wide range of species. However, surface waters are mostly absent from the current climate mitigation debate. The interdisciplinary research project SURFER addresses various effects of intensified forestry practices on surface waters. Our goal is to provide guidance tools allowing water managers, decision makers and stakeholders to safeguard valuable surface water ecosystems in Norway. Several measures are in place to minimize the direct effects of forestry measures on water resources. These regulations and guidelines are however for the most part geared to safeguard water at the point of initiation of the measures, while there is a large degree of uncertainty related to the longer-term impacts. In addition, there is a need for clarity on sanctions against forest owners, cooperatives and municipalities when regulations are not complied with. A modelling exercise has been conducted to assess potential effects of intensified forestry on surface water quality in acid sensitive catchments. The simulations indicate that while forest fertilisation increases forest growth, it results in higher leaching of nitrate following clearcut. The 5-10-year pulse of nitrate following clearcut was larger with stem-only harvest than whole-tree harvest, but the latter causes larger acidification of surface water due to greater depletion of base cations from the soil. An assessment of effects of forestry on surface water quality was conducted using an established framework. The framework was adopted to Norwegian conditions and further developed to highlight the potential effects of intensified forestry 1, 10 and 100 years after harvest. The assessment, which is based on a literature study, concludes that severe effects can occur in areas that are especially sensitive to eutrophication or acidification. A review of international literature shows that intensification of forestry can affect freshwater biodiversity and ecosystem functioning through changes in natural resources for aquatic ecosystems. The changes will be highly dependent on management practices, forestry types and biogeographical context (e.g. acid sensitive areas). Best management practices were generally mitigating the impact of forestry but were not systematically implemented. The effects of (intensification of) forestry on aquatic ecology have only been investigated on short time scale during the logging period. So far, most studies focused on simple indicators to estimate ecological responses. However, the indicators are often not very sensitive, suggesting the need for a more mechanistic and context dependent approach. An important case study has been the fertiliser application on 70 ha of forest close to the drinking water reservoir Glitrevann in June 2017 and monitoring of surface water quality before and after the fertilising event. Some evidence was found for leaching of nitrate immediately after fertilisation, but this was small and short-lived. Short-term leaching is not expected to be a problem in the future as long as fertilisation plans are adhered to. Forest harvesting results in an increase in nitrogen delivery, which was demonstrated in one of the inlet streams where clear-felling has occurred in recent years. Future forest harvesting plans include 1 km2 around 2050 and 5 km2 around 2070. Modelling studies suggest this could result in up to a 20-23% increase in N export to the lake compared to background levels over 2017-2090. To protect the lake from harvesting-associated nitrogen fluxes, harvesting intensity should be less than 1 km2/year (approx. 2% of the catchment area) and it is also recommended to extend the use of buffer strips to non-permanent streams.

Interactions with the reference group and the stakeholder group have provided a good opportunity for mutual exchange of knowledge and information. We have arranged two meetings with the reference group (with members from Landbruksdirektoratet, Miljødirektoratet, Fylkesmannen i Trøndelag, Lier kommune, Glommen Skog, and Sabima) and two meetings with the stakeholder group (with members from Glitrevannverket, Statskog and Lier kommune). The project also received attention in local/regional media during Statskog?s fertilization of a forested area in the Glitrevann catchment in June 2017. Reports/publications, presentations, and 5 fact sheets (one per task) are made public available from the project website: https://www.niva.no/en/projectweb/surfer.

Climate change affects large parts of world with rising temperatures, changes in precipitation patterns and extreme weather events. Norway is aggressively pursuing sustainable climate mitigation strategies and intensified forestry practices to increase biomass harvesting (e.g. nitrogen fertilization, intensified stem-only and/or whole-tree harvesting) are being used to rapidly transit to a "sustainable low emission society". The decision to intensify forest biomass use has led to debate in Norway, both scientifically and publicly. While the debate is still ongoing, other potential environmental concerns have been largely ignored, in particular the potential effects of intensified forestry on surface waters. Norway's lakes and rivers deliver a number of invaluable services including drinking water, recreational opportunities and habitat for a wide range of species. However, surface waters are mostly absent from the current climate mitigation debate. We propose a highly interdisciplinary project to address the effects intensified forestry practices will have on surface waters in Norway. Our goal is to provide guidance tools allowing water managers, decision makers and stakeholders to safeguard valuable surface water ecosystems in Norway. We will address forestry effects on surface waters on different levels: (i) water policy, by investigating how intensified forestry for climate mitigation reconciles with current Norwegian laws and directives (ii) trade-offs between intensified forestry for climate mitigation and surface water acidification (iii) Effects of intensified forestry on biogeochemical cycles, mobilization of pollutants and freshwater biodiversity on multiple spatial scales and (iv) the potential effects of forest fertilization on water quality in sensitive drinking water catchment in Norway. We will deliver policy relevant assessments and recommendations on how Norway can transit to a sustainable, low emission society without damaging surface waters.