Long-Term Nitrogen and Phosphorus Dynamics in Waters Discharging from Forestry-Drained and Undrained Boreal Peatlands

Abstract

Contradictory results for the long-term evolution of nitrogen and phosphorus concentrations in waters discharging from drained peatland forests need reconciliation. We gathered long-term (10–29 years) water quality data from 29 forested catchments, 18 forestry-drained and 11 undrained peatlands. Trend analysis of the nitrogen and phosphorus concentration data indicated variable trends from clearly decreasing to considerably increasing temporal trends. While the variations in phosphorus concentration trends over time did not correlate with any of our explanatory factors, trends in nitrogen concentrations correlated positively with tree stand volume in the catchments and temperature sum. A positive correlation of increasing nitrogen concentrations with temperature sum raises concerns of the future evolution of nitrogen dynamics under a warming climate. Furthermore, the correlation with tree stand volume is troublesome due to the generally accepted policy to tackle the climate crisis by enhancing tree growth. However, future research is still needed to assess which are the actual processes related to stand volume and temperature sum that contribute to increasing TN concentrations.

Post‐drainage stand growth and peat mineralization impair water quality from forested peatlands

“…Climatic conditions in the study region correspond to those given by Nieminen, Sarkkola, Hasselquist, et al. (2021).…”

“…Mitigating C and nutrient exports from drained peatland forests is significantly complicated by poorly understood mechanisms behind upward trends in their nutrient concentrations. These mechanisms may include hydrological factors such as changes in water pathways due to drainage (Nieminen, Piirainen, et al., 2018), biotic factors such as enhanced microbial activity resulting in increased release of nutrients and C from peat (Nieminen, Sarkkola, Hasselquist, et al., 2021), as well as abiotic factors such as changes in the chemistry of atmospheric deposition and increasing air and water temperatures due to climate warming (Finstad et al., 2016; Fork et al., 2020; Sarkkola et al., 2009; Wang et al., 2015).…”

“…Nieminen, Sarkkola, Hasselquist, et al. (2021) and Nieminen, Sarkkola, Sallantaus, et al. (2021) hypothesized that the primary reason for upward nutrient and C concentration trends would be post‐drainage forest succession (i.e., maturing and growing of the tree stands with time since initial drainage and a resulting increase in their evapotranspiration capacity).…”

Exploring the Role of Weather and Forest Management on Nutrient Export in Boreal Forested Catchments Using Spatially Distributed Model

“…Due to the ongoing climate change, the mean temperatures and the annual total precipitation rates are projected to increase in Finland and other Nordic countries [62], which might lead to increased nutrient export [9]. Forest regeneration with clear-cutting further increases these risks, and can amplify the effect of runoff increase on nutrient leaching, particularly in drained peat land forests [37]. Spatially explicit nutrient release and transport modelling enables considering multiple factors that simultaneously influence the complex dynamics of nutrient export.…”

“…The ecological status of the lakes in the study area is classified from excellent to poor. Forestry activities and changes in air temperature, precipitation and runoff induced by climate change are expected to increase the N and P load risk for these lakes [9,37].…”