Anna-Kaisa Ronkanen

Hydraulics and flow modelling of water treatment wetlands constructed on peatlands in Northern Finland

In this study, we evaluated flow structure, effective flow area (A(eff)) and effective porosity (theta(eff)) in three peatlands using the stable isotope (18)O/(16)O ratio and tracer tests. We also applied the readily available groundwater modelling MODFLOW code for wetland flow modelling and simulated in one study site how the hydraulic performance of the wetland will be improved by changing the design of the distribution ditch. Preferential flow paths occurred in all three studied wetlands and A(eff) varied from 40% to 90% of total wetland area while theta(eff) was 0.75-0.99. Constructed flow models accurately simulated the hydraulic head across wetlands (r(2)=0.95-0.99). Similarities between the flow models and the stable isotope distributions observed in this study suggest possibilities in using MODFLOW to design peatlands. The improvement of the inlet ditch configuration (ditch length/wetland width>0.45) can prevent or reduce short-circuiting and dead zones in peatlands treating wastewater.

Water‐table‐dependent hydrological changes following peatland forestry drainage and restoration: Analysis of restoration success

A before-after-control approach was used to analyze the impact of peatland restoration on hydrology, based on high temporal resolution water-table (WT) data from 43 boreal peatlands representative of a south-boreal to north-boreal climate gradient. During the study, 24 forestry drained sites were restored and 19 pristine peatlands used as control sites. Different approaches were developed and used to analyze WT changes (mean WT position, WT fluctuation, WT hydrograph, recession, and storage characteristics). Restoration increased WT in most cases but particularly in spruce mires, followed by pine mires and fens. Before restoration, the WT fluctuation (WTF) was large, indicating peat temporary storage gain (SG). After restoration, the WT hydrograph recession limb slopes and SG coefficients (Rc) declined significantly. Drainage or restoration did not significantly affect mean diurnal WT fluctuations, used here as a proxy for evapotranspiration. Overall, the changes in WT characteristics following restoration indicated creation of favorable hydrological conditions for recovery of functional peatland ecosystems in previously degraded peatland sites. This was supported by calculation of bryophyte species abundance thresholds for WT. These results can be used to optimize restoration efforts in different peatland systems and as a qualitative conceptual basis for future restoration operations.

Optimisation of chemical purification conditions for direct application of solid metal salt coagulants: treatment of peatland-derived diffuse runoff.

The drainage of peatland areas for peat extraction, agriculture or bioenergy requires affordable, simple and reliable treatment methods that can purify waters rich in particulates and dissolved organic carbon. This work focused on the optimisation of chemical purification process for the direct dosage of solid metal salt coagulants. It investigated process requirements of solid coagulants and the influence of water quality, temperature and process parameters on their performance. This is the first attempt to provide information on specific process requirements of solid coagulants. Three solid inorganic coagulants were evaluated: aluminium sulphate, ferric sulphate and ferric aluminium sulphate. Pre-dissolved aluminium and ferric sulphate were also tested with the objective of identifying the effects of in-line coagulant dissolution on purification performance. It was determined that the pre-dissolution of the coagulants had a significant effect on coagulant performance and process requirements. Highest purification levels achieved by solid coagulants, even at 30% higher dosages, were generally lower (5%-30%) than those achieved by pre-dissolved coagulants. Furthermore, the mixing requirements of coagulants pre-dissolved prior to addition differed substantially from those of solid coagulants. The pH of the water samples being purified had a major influence on coagulant dosage and purification efficiency. Ferric sulphate (70 mg/L) was found to be the best performing solid coagulant achieving the following load removals: suspended solids (59%-88%), total organic carbon (56%-62%), total phosphorus (87%-90%), phosphate phosphorus (85%-92%) and total nitrogen (33%-44%). The results show that the use of solid coagulants is a viable option for the treatment of peatland-derived runoff water if solid coagulant-specific process requirements, such as mixing and settling time, are considered.

Changes in Pore Water Quality After Peatland Restoration: Assessment of a Large‐Scale, Replicated Before‐After‐Control‐Impact Study in Finland

Drainage is known to affect peatland natural hydrology and water quality, but peatland restoration is considered to ameliorate peatland degradation. Using a replicated BACIPS (Before-After-Control-Impact Paired Series) design, we investigated 24 peatlands, all drained for forestry and subsequently restored, and 19 pristine control boreal peatlands with high temporal and spatial resolution data on hydroclimate and pore water quality. In drained conditions, total nitrogen (Ntot), total phosphorus (Ptot), and dissolved organic carbon (DOC) in pore water were several-fold higher than observed at pristine control sites, highlighting the impacts of long-term drainage on pore water quality. In general, pore water DOC and Ntot decreased after restoration measures but still remained significantly higher than at pristine control sites, indicating long time lags in restoration effects. Different peatland classes and trophic levels (vegetation gradient) responded differently to restoration, primarily due to altered hydrology and varying acidity levels. Sites that were hydrologically overrestored (inundated) showed higher Ptot, Ntot, and DOC than well-restored or insufficiently restored sites, indicating the need to optimize natural-like hydrological regimes when restoring peatlands drained for forestry. Rich fens (median pH 6.2–6.6) showed lower pore water Ptot, Ntot, and DOC than intermediate and poor peats (pH 4.0–4.6) both before and after restoration. Nutrients and DOC in pore water increased in the first year postrestoration but decreased thereafter. The most important variables related to pore water quality were trophic level, peatland class, water table level, and soil and air temperature.

Quantifying spatial groundwater dependence in peatlands through a distributed isotope mass balance approach

The unique biodiversity and plant composition of peatlands rely on a mix of different water sources: precipitation, runoff and groundwater (GW). Methods used to delineate areas of ecosystem groundwater dependence, such as vegetation mapping and solute tracer studies, are indirect and lack the potential to assess temporal changes in hydrology, information needed in GW management. This paper outlines a new methodology for mapping groundwater-dependent areas (GDAs) in peatlands using a 2H and 18O isotope mass balance method. The approach reconstructs the initial isotopic composition of the peat pore water in the uppermost peat layer before its modification by evaporation. It was assumed that pore water in this layer subject to evaporation is a two-component mixture consisting of GW and precipitation input from the month preceding the sampling period. A Bayesian Monte Carlo isotope mixing model was applied to calculate the proportions of GW and rainwater in the sampled pore water and to assess uncertainties. The approach revealed large spatial variability in the contribution of GW to the pore water present in the top layer of peatland, covering the range from approximately 0 to 100%. Results show that the current GW protection zones determined by Finnish legislation do not cover the GDAs in peatlands and highlight a need for better classification of groundwater-dependent ecosystems and conceptualisation of aquifer-ecosystem interactions. Our approach offers an efficient tool for mapping GDAs and quantifying the contribution of GW to peatland pore water. However, more studies are needed to test the method for different peatland types. This article is protected by copyright. All rights reserved.

Evaluating the suitability of synthetic organic polymers to replace iron salts in the purification of humic and sediment-rich runoff

AbstractPeat extraction runoff water requires chemical treatment to remove organic matter and phosphorus. In Finland, ferric sulphate (FS) is normally used as coagulant agent, but significant variations in runoff water quality and the lack of optimisation of process parameters has led to increased acidity, metal and sulphate concentrations in the purified water. The use of synthetic organic polymers as an alternative to the commonly applied metal salt coagulant is suggested to better cope with typical variations in runoff water quality. This study evaluated the suitability of two synthetic organic polymers (polyDADMAC and polyAmine) for the purification of humic and sediment-rich diffuse runoff by comparing their performance to the normally applied iron-based coagulant. FS was found to require up to fourfold higher dosages but achieved higher overall purification levels than the organic polymers. In particular, removal of organic matter was substantially higher when FS was used. Of the two synthetic organ...

Runoff Curve Numbers for Peat-Dominated Watersheds

AbstractThe natural resources conservation service (NRCS) curve number method is widely used to estimate runoff from rainfall events for four hydrological soil groups (A, B, C, and D). However, the NRCS soil groups do not yet include peat soils. Therefore, this study analyzed 59 rainfall-runoff events from two peat-dominated watersheds in Finland (Marjasuo, Royvansuo) and one in Norway (Grualia). The analysis used the United States Army Corps of Engineers Hydrologic Engineering Center Hydrologic Modeling System (HEC-HMS) to calibrate curve numbers and initial abstraction ratios (Ia/S). This gave a mean Ia/S of 0.036, with a mean standard error of 0.003 and 95% confidence interval of 0.030–0.042, which is significantly lower than the value of 0.2 recommended in the NRCS curve number method. The mean curve number was 61, with a mean standard error of 0.9 and 95% confidence interval of 59–63 for the study watersheds. This study confirmed that application of the NRCS curve number method in HEC-HMS required se...

Greenhouse Gas Dynamics of a Northern Boreal Peatland Used for Treating Metal Mine Wastewater

Northern peatlands in their natural state are sinks of carbon dioxide (CO2) but sources of methane (CH4). They are often nitrogen limited and can act as sinks for greenhouse gas (GHG) nitrous oxide (N2O). Peatlands have been used to treat wastewaters from different point sources. Continuous nutrient and pollutant load to a nutrient limited peatland ecosystem may change the microbial processes and lead to increased productivity, which together are likely to change the GHG emissions. We studied the effect of wastewater derived from metal mining on N2O and CH4 emissions on two treatment peatlands in northern boreal zone. The measured CH4 fluxes from the reference point without any wastewater load were in the range of those reported from northern pristine peatlands while emissions from treatment peatlands were greatly reduced, presumably as result of high sulfate concentration in the porewater. N2O emissions were small in the reference point, but up to 300 times higher in the treatment peatlands. Methane emissions increased with increasing total organic carbon concentration and decreased with increasing sulfate concentration in the surface water, respectively, while N2O emissions increased with increasing nitrate concentrations. The data indicate drastic changes in GHG fluxes and related biogeochemical processes in treatment peatlands as compared to the reference point.

Microbial diversity along a gradient in peatlands treating mining-affected waters

ABSTRACT Peatlands are used for the purification of mining‐affected waters in Northern Finland. In Northern climate, microorganisms in treatment peatlands (TPs) are affected by long and cold winters, but studies about those microorganisms are scarce. Thus, the bacterial, archaeal and fungal communities along gradients of mine water influence in two TPs were investigated. The TPs receive waters rich in contaminants, including arsenic (As), sulfate (SO42−) and nitrate (NO3−). Microbial diversity was high in both TPs, and microbial community composition differed between the studied TPs. Bacterial communities were dominated by Proteobacteria, Actinobacteria, Chloroflexi and Acidobacteria, archaeal communities were dominated by Methanomicrobia and the Candidate phylum Bathyarchaeota, and fungal communities were dominated by Ascomycota (Leotiomycetes, Dothideomycetes, Sordariomycetes). The functional potential of the bacterial and archaeal communities in TPs was predicted using PICRUSt. Sampling points affected by high concentrations of As showed higher relative abundance of predicted functions related to As resistance. Functions potentially involved in nitrogen and SO42− turnover in TPs were predicted for both TPs. The results obtained in this study indicate that (i) diverse microbial communities exist in Northern TPs, (ii) the functional potential of the peatland microorganisms is beneficial for contaminant removal in TPs and (iii) microorganisms in TPs are likely well‐adapted to high contaminant concentrations as well as to the Northern climate.

Effects of Drainage and Subsequent Restoration on Peatland Hydrological Processes at Catchment Scale

Potential benefits of peatland restoration by rewetting include carbon sequestration, restored biodiversity, and improved hydrological functions. There is great uncertainty about how catchment hydrological processes change after restoration, with a particular lack of well-documented catchment runoff data. This study compared five formerly Disturbed (now Restored) and two undisturbed peatlands. In total, 455 and 728 hydrological events were selected for the analysis, using a three-event selection technique. Mean event runoff coefficient (RC) values varied greatly between conditions and hydrological events. RC in Disturbed conditions was slightly higher than in undisturbed conditions, but RC in Restored conditions was higher than under other conditions. Mean transit time revealed that event rainfall water reached the outlet faster in Disturbed conditions. Mean event peak flow in Disturbed conditions was higher and peaked faster than under other conditions. However, the base flow showed no noticeable difference between treatments. Significantly higher watertable (WT) rise per rainfall input (0.36–0.85 cm/mm) was observed in Disturbed conditions, due to lower specific yield (Sy) values (0.13–0.24) than under Restored and undisturbed conditions (Sy 0.25–0.50). Shallow WT showed significant positive correlations with runoff and storage properties and was a key component of the runoff generation mechanisms in peatlands. Storage-related parameters (Sy, WT rise per rainfall input) and catchment response time parameters revealed disturbance-related hydrological changes in peatlands more clearly than other runoff parameters tested (e.g., RC). Overall, with restoration, WT and storage properties recovered to the levels at undisturbed sites but increased runoff was observed occasionally due to wetter antecedent moisture conditions.