## 3 Literature Review
#### 3.1.2. Peatland Management and Restoration Strategies
After rewetting, ditch systems or networks of plugged or backfilled canals are left open, and the rise in the water table results in CH\({}_{4}\) emissions [128]. Few studies have shown that CH\({}_{4}\) emissions from peatlands in northern regions have been rewetted for more than ten years [106]. For this reason, changes in GHG emissions from these peatlands remain to be discovered. After peatland rewetting, litter decomposes faster, which may raise CH\({}_{4}\) emissions for up to 30 years [37, 112]. One of the latest studies has shown that drained peatland rewetting can cause an increase in CH\({}_{4}\) emissions of 0.033 \(\pm\) 0.003 Mg CH\({}_{4}\)-C ha\({}^{-1}\) on average after rewetting yearly [29]. CH\({}_{4}\) emissions could be reduced through diverse vegetation growth [37, 40, 112]. _Nitrous oxide (N\({}_{2}\)O)_  
Where drainage has been previously performed, peatlands can act as a potent or insignificant N\({}_{2}\)O emission source. This depends on land use and geographical location [39]. Natural peatlands usually emit low amounts of N\({}_{2}\)O. Rewetting has often been proposed to reduce GHG emissions from drained peatlands. An assumption made by the IPCC is that undrained and rewetted peatlands do not emit N\({}_{2}\)O. It is based on research results that saturated and undrained peatlands emit nitrous oxide in minimal amounts [129]. During the rewetting of drained peatlands, the production of N\({}_{2}\)O and, thus, its emissions may increase in the short term [39]. Vastly degraded peat with a high nutrient availability contributes to increased nitrification and denitrification [39]. Studies on changes in nitrous oxide emissions after rewetting are fewer for degraded peatlands. Comparative studies have been conducted on the N\({}_{2}\)O emissions of rewetted and naturally formed peatlands. According to the estimations, emissions from nutrient-poor peatlands are 0.08 m\({}^{-2}\) a\({}^{-1}\), and from nutrient-rich peatlands, they are 0.05 m\({}^{-2}\) a\({}^{-1}\). Peat rewetting effectively reduces N\({}_{2}\)O emissions in drained peatlands, and it has been believed that by rewetting, it is possible to achieve emissions close to the state of natural peatlands, producing from 0.022 to 0.191 m\({}^{-2}\) a\({}^{-1}\) annually [129]. If the water level throughout the year approaches the surface, the emissions are minimal or even non-existent. If the water level annually is 10 to 30 cm below the soil surface [29], both aerobic and anaerobic conditions are maintained on top of the soil, and nitrification and denitrification produce N\({}_{2}\)O. Thus, with this water level, peatland rewetting can create N\({}_{2}\)O-N emissions [29, 45, 72, 125]. In the literature, rewetting is considered the most effective approach to decreasing N\({}_{2}\)O emissions from degraded peatlands. An estimated reduction in N\({}_{2}\)O emissions by \(\sim\)70% in the next 30 years has been reported [45], and all degraded peatlands in Europe are rewetted--an essential step towards climate goals [11, 129]. Rewetting less degraded peatlands first would give an estimated 30% reduction in emissions. It is important to understand the processes generating each GHG separately. However, there is also a need to assess the total emissions of multiple GHGs objectively. The cumulative N\({}_{2}\)O, CO\({}_{2}\), and CH\({}_{4}\) emissions after peat rewetting should be evaluated because these gases accumulate in the atmosphere, but the duration of their residence there is different [11]. _Nutrients and dissolved organic carbon (DOC)._  
The drainage of peatlands results in nutrient accumulation in the upper layer of the peat. Therefore, rewetted peatlands can be phosphate and ammonium nutrient sources. Regarding nitrate, rewetted peatlands can be a sink of nutrients [39]. It has been confirmed that the drainage of peatlands causes increased concentrations and fluxes of dissolved organic carbon (DOC) in streams and rivers [130].