Recovery of nitrogen cycling in riparian zones after stream restoration using δ 15N along a 25-year chronosequence in northern Sweden

Abstract

Background and aims Swedish boreal streams were modified to transport timber by pushing boulders to stream sides, creating levees that disconnected streams from riparian areas. Many streams have since been restored and our goal was to understand how this affects riparian nitrogen (N) cycling. Methods We compared the natural abundance of δ 15 N isotopes in foliage and roots of Filipendula ulmaria plus soils and litter along streams restored 2-25 years ago. We measured sources of N, potential immobilization of N, namely plant diversity and biomass, and the amount and sources of carbon (C) to determine if these were important for describing riparian N cycling. Results The δ 15 N of F. ulmaria foliage changed dramatically just after restoration compared to the channelized, disconnected state and then converged over the next 25 years with the steady-state reference. Conclusions The disturbance and reconnection of the stream with the riparian zone during restoration created a short-term pulse of N availability and gaseous losses of N as a result of enhanced microbial processing of N. With increasing time since restoration, N availability appears to have decreased, and N sources changed to those derived from mycorrhizae, amino acids, or the humus layer, or there was enhanced N-use efficiency by older, more diverse plant communities.

Northern landscapes in transition: Evidence, approach and ways forward using the Krycklan Catchment Study

“…Survival experiments on fish (Serrano et al, 2008) and invertebrate population studies (Petrin et al, 2007) have been conducted in several of the monitored streams. In addition, the main stem of the Krycklan river network has been used as an unimpacted (by timber floating) reference site in a number of studies of stream hydrogeomorphology (Polvi et al, 2014), riparian plant diversity and composition (Hasselquist et al, 2015), riparian nutrient cycling (Hasselquist et al, 2017), instream ecosystem functioning (Frainer et al, 2018), and biodiversity (Hasselquist et al, 2018). Since 2007, C7 is also a part of the national freshwater monitoring program under which aquatic macroinvertebrates are annually collected to depict long-term biodiversity trends.…”

Northern landscapes in transition; evidence, approach and ways forward using the Krycklan Catchment Study

“…Survival experiments on fish (Serrano et al 2008) and invertebrate population studies (Petrin et al 2007) have been conducted in several of the monitored streams. In addition, the main stem of the Krycklan river network has been used as an unimpacted (by timber floating) reference site in a number of studies of stream hydrogeomorphology (Polvi et al 2014), riparian plant diversity and composition (Hasselquist et al 2015), riparian nutrient cycling (Hasselquist et al 2017), instream ecosystem functioning (Frainer et al 2018), and biodiversity (Hasselquist et al 2018). Since 2007, C7 is also a part of national freshwater monitoring program under which aquatic macroinvertebrates are annually collected to depict long-term biodiversity trends.…”

Effects of Early, Small-Scale Nitrogen Addition on Germination and Early Growth of Scots Pine (Pinus sylvestris) Seedlings and on the Recruitment of the Root-Associated Fungal Community

“…ECM are generally considered to enhance nutrient and water uptake by plants, seedling establishment and survival, and increased plant resilience against environmental stressors [8]. However, the ecological role of ECM can vary from mutualistic to parasitic [9][10][11], and in situations such as strong N limitation, mycorrhizal fungi can immobilize available N and aggravate plant N limitation [12][13][14].…”