Controls of Organic Carbon and Nutrient Export from Unmanaged and Managed Boreal Forested Catchments

Abstract

Understanding the anthropogenic and natural factors that affect runoff water quality is essential for proper planning of water protection and forest management, particularly in the changing climate. We measured water quality and runoff from 10 unmanaged and 20 managed forested headwater catchments (7–12,149 ha) located in Finland. We used linear mixed effect models to test whether the differences in total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) export and concentrations observed can be explained by catchment characteristics, land use, forest management, soil fertility, tree volume and hydrometeorological variables. Results show that much of variation in TOC, TN and TP concentrations and export was explained by drainage, temperature sum, peatland percentage and the proportion of arable area in the catchment. These models explained 45–63% of variation in concentrations and exports. Mean annual TOC export in unmanaged catchments was 56.4 ± 9.6 kg ha−1 a−1, while in managed it was 79.3 ± 3.3 kg ha−1 a−1. Same values for TN export were 1.43 ± 0.2 kg ha−1 a−1 and 2.31 ± 0.2 kg ha−1 a−1, while TP export was 0.053 ± 0.009 kg ha−1 a−1 and 0.095 ± 0.008 kg ha−1 a−1 for unmanaged and managed, respectively. Corresponding values for concentrations were: TOC 17.7 ± 2.1 mg L−1 and 28.7 ± 1.6 mg L−1, for TN 420 ± 45 µg L−1 and 825 ± 51 µg L−1 and TP 15.3 ± 2.3 µg L−1 and 35.6 ± 3.3 µg L−1. Overall concentrations and exports were significantly higher in managed than in unmanaged catchments. Long term temperature sum had an increasing effect on all concentrations and exports, indicating that climate warming may set new challenges to controlling nutrient loads from catchment areas.

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

“…This approach allows identification of nutrient export hotspots for planning forest management and water protection, and prediction of climate change effect on nutrient concentrations in surface waters. The simulated N and P export in the baseline scenario (Table 3) were similar to those measured for managed boreal catchments [12,24,53,54] and simulated concentrations were in line with the 38.2 µg l −1 for P and 1048 µg l −1 for N (means of period 2008-2018), reported for Lake Kuonanjärvi (Table 43, 44 and 45 on p.85 in [55]), giving a good basis for the model application in weather and forest management scenarios. However, in the absence of sufficient time series for a thorough morel performance evaluation, the result should be interpreted in relative terms.…”

“…Nutrient export from forested catchments to surface waters is a complex process that is simultaneously affected by weather conditions, catchment characteristics and forest management [17,[50][51][52][53][54]. Here we present a model application, where the role of the contributing factors can be quantified, and the effect of varying weather conditions can be compared to the effect of forest management.…”

Browning of boreal lakes: Do public perceptions and governance align with the biological foundations?

“…As for peatland forestry, this would require a transition from the prevailing intensive, even‐aged forest management practices to more natural and diverse actions with continuous cover forestry, mixed forest cover, and improved catchment retention (Härkönen et al, 2023; Kritzberg et al, 2020). In river basins located in Northern Europe, leaching of organic carbon, nutrients, and iron from managed terrestrial systems is a major concern, with recent research revealing the scale and intensity of the issue (Aaltonen et al, 2021; Estlander et al, 2021; Finér et al, 2021; Lepistö et al, 2021; Škerlep et al, 2020, 2022). While global and local processes interact to set trends in water color (Lepistö et al, 2021), the green transition and associated intensifying land use should be balanced against the deterioration of aquatic environments (Marttila et al, 2020).…”

Water Retention Characteristics of Mineral Forest Soils in Finland: Impacts for Modeling Soil Moisture

“…According to the soil map, ca. 80% of the catchment is on medium-textured soils [42,67]. The long-term mean (1981-2010) annual temperature is +3.5 • C and precipitation (P) is 711 mm.…”