Water quality is significantly affected by the forest logging activities that are carried out in drained peatlands, which causes a notable enhancement in sediment loading and nutrient export to water bodies. Furthermore, the seasonal fluctuations in nutrient concentrations in the runoff further underscore the need for efficient water protection tools in peatland forestry.
To address these issues, biochar-based adsorption methods can potentially offer an effective alternative for water protection in peatland forestry. The current thesis investigates the potential for adsorption-based nutrient recovery from clear-cut peatland runoff water using Norway spruce and Silver birch biochars. In particular, the aim is to i) study the adsorption characteristics in relation to biochar properties and nutrient compounds in runoff waters in a small-scale laboratory experiment (Paper I); ii) investigate the adsorption characteristics of nitrogen (N) compounds from runoff water in a meso-scale laboratory experiment that utilises biochar reactors (Paper II); and iii) investigate the dynamics of biochar adsorption and desorption under fluctuating total nitrogen (TN) concentrations in runoff water (Paper III).
Biochar made from birch and spruce were shown to efficiently adsorb N compounds from the water. Across all experiments, the TN content declined significantly, irrespective of the scale, or whether the runoff volume ranged from litres (I and III) to hundreds of litres (II). Furthermore, the TN content at the beginning of the experiment declined at the fastest rate. The results indicate that cases of relatively low adsorption capacity were attributed to the low initial TN concentrations in the water. In addition, TN adsorption occurs above a threshold concentration in natural runoff water. The spruce did not adsorb TN when the concentrations in the runoff water fell below 0.4 mg L-1. In this thesis, biochar emerges as a compelling water protection solution, particularly in regions where clear-cut peatlands release substantial quantities of nutrients.
Export of dissolved organic carbon and nitrogen (DOC and DON) from terrestrial ecosystems to watercourses has increased in the boreal zone. However, the effects of decomposing material and soil food webs on the release rate and quality of DOC and DON are poorly known. The objective of this study was to quantify the release of carbon (C) and nitrogen (N) from mor and peat, which are the most common organic soil types in the boreal zone. The impact of soil fauna on the release processes was also estimated. Decomposition products were divided into intermediate products (DOC and DON) and mineralised end products, i.e. carbon dioxide (CO2-C) and ammonium (NH4+-N). The release of C and N into the soil solution, extractable pools, and CO2-C efflux were measured. DOC and DON were further divided into high molecular weight (HMW) and low molecular weight (LMW) fractions.
Carbon release was slightly different in each soil type. In absolute terms, the peat released less C and in relative terms more DOC than mor. Enchytraeids worms (Cognettia sphagnetorum) affected the quantity and composition of the decomposition products by enhancing mineralisation and the release of HMW-DOC.
In the slightly decomposed peat, the net release of N occurred in the form of DON, whereas the other soil types mainly released NH4+-N. The slightly decomposed peats are typically located close to water bodies, in the topmost soil layer, where the water discharge is the highest. Therefore, the slightly decomposed peats might have an important role in controlling the quality and quantity of N export.
The results were used to further develop the decomposition model ROMUL to account for DOC and DON processes and the division between intermediate and end products. The parameterisation and structure of the model was analysed by means of the GLUE (Generalised Likelihood Uncertainty Estimation) method, and several simultaneously measured variables, which is novel in this research field.