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Groundwater : : journal of the Association of Ground-Water Scientists and Engineers, a division of the National Ground Water Association (2021). doi:10.1111/gwat.13087, Published by Wiley-Blackwell, Oxford [u.a.]

The increasing awareness of the importance of groundwater for ecosystems limits the possibilities for groundwater usage. In Finland, for instance, several projects aiming to establish new groundwater intakes have been stuck in legal processes for more than ten years or even decades. A typical conflict in the legal process relates to potential negative impacts of the project on protected areas, such as Natura 2000 areas, or habitats of endangered species.Managed aquifer recharge (MAR) is one of the solutions to secure the water balance in groundwater dependent ecosystems, or to produce drinking water from artificial instead of natural groundwater. In MAR, surface water is infiltrated into the ground to add water and facilitate increased groundwater extraction in an aquifer. As the surface water quality typically differs from precipitation by a higher content of organic matter, dissolved solids, bacteria and viruses, infiltration of lake water leads to a different groundwater quality compared to natural recharge formed from precipitation.The sustainability of MAR largely depends on an aquifer’s capacity to remove organic matter over the long term. We studied the impact of surface water infiltration on groundwater quality by using a natural lake-aquifer system as a surrogate for MAR. Natural infiltration of lake water to groundwater has been going on for millennia at our research site, providing information over a much longer time span compared to constructed infiltration sites or laboratory tests.The groundwater flow velocity at the site was estimated with a MODFLOW based flow model. The share of lake water infiltrate in the aquifer was estimated from stable oxygen and hydrogen isotopes. Total organic carbon (TOC), dissolved organic carbon, oxygen, iron and manganese concentrations, conductivity and pH were monitored from lake and ground water. According to our measurements, the mean concentration of TOC in lake water was 3.0 mg/L (Jylhä-Ollila et al., 2020). Within the distance of 3 m from the lake bank (retention time 7–15 days), already 46% of TOC was removed. At greater distances along the main flowpath in the aquifer, 80–90% of TOC was removed. Signs of organic matter accumulation in the aquifer were not observed, which is positive in terms of long term sustainability of MAR. Several processes had an impact on oxygen levels in the aquifer, which led to spatial and seasonal changes in the redox conditions and in the iron and manganese concentrations in groundwater. The results showed that an aquifer can remove organic matter from surface water over a long time span, but possible oxygen depletion and iron and manganese release should be taken into account in MAR projects aiming to secure groundwater dependent ecosystems. Jylhä-Ollila, M., Laine-Kaulio, H., Niinikoski-Fuβwinkel, P., Leveinen, J., Koivusalo, H. 2020. Water Quality and Organic Matter Removal in Natural Bank Infiltration at a Boreal Lake in Finland. Hydrogeology Journal, in print.

Reducing the strain on water bodies caused by sediment loads released after ditch network maintenance (DNM) is addressed in operational peatland forestry by implementing sediment control structures in ditches. This study evaluates computationally alternative sediment control scenarios in a 5.2 ha deep peat site in eastern Finland. Coupled to a distributed hydrological model, peat erosion and transport in the ditches were simulated for the first year after DNM with 15 scenarios consisting of individual structures (e.g., sedimentation ponds) and their combinations. One scenario represented the prevailing conditions with a V-notch weir at the catchment outlet. All scenarios were evaluated against a baseline scenario in which no structures affected the catchment sediment processes. The results suggested that bed erosion can be efficiently prevented with breaks in cleaning and structures ponding water. It was proven less efficient to trap already eroded material with sedimentation ponds and pits. The structures raising ditch water level had limited effects on water table levels in the strips between ditches, plausibly not impairing tree growth. The process-based modeling presented here provided a yet unexplored approach to comprehensively evaluating alternatives for sediment control, which is highly needed to address the gap between existing scientific knowledge and operational peatland forestry practices.

Funding Information: This work was funded by Ministry of Agriculture and Forestry, Finland; Schlumberger Foundation Faculty for the Future, Academy of Finland (no 326787, WaterWorks2017 ERA-NET Cofund) and Maa- ja vesitekniikan Tuki ry. The study was part of the UrbanStormwaterRisk and EviBAN (Evidence based assessment of NWRM for sustainable water management) projects. Elisa Lähde, a landscape architect, designed the alternative stormwater management designs assessed in this study. The rainfall data for design simulations came from a rain gauge operated by the City of Turku. The streamflow data for rural reference watershed (Savijoki) and semi-urban reference watershed (Kuninkoja) came from monitoring stations maintained by the Finnish Environment Institute (SYKE) and Turku University of Applied Sciences (TUAS), respectively. Funding Information: This work was funded by Ministry of Agriculture and Forestry, Finland; Schlumberger Foundation Faculty for the Future, Academy of Finland (no 326787, WaterWorks2017 ERA-NET Cofund) and Maa- ja vesitekniikan Tuki ry. The study was part of the UrbanStormwaterRisk and EviBAN (Evidence based assessment of NWRM for sustainable water management) projects. Elisa Lähde, a landscape architect, designed the alternative stormwater management designs assessed in this study. The rainfall data for design simulations came from a rain gauge operated by the City of Turku. The streamflow data for rural reference watershed (Savijoki) and semi-urban reference watershed (Kuninkoja) came from monitoring stations maintained by the Finnish Environment Institute (SYKE) and Turku University of Applied Sciences (TUAS), respectively. Publisher Copyright: © 2021 The Author(s) The goal of Low Impact Development (LID) is to restore and maintain the pre-development flow regime. The static storage capacity, which is often used as a parameter in LID designs, provides the maximum capacity of an LID type and is easily quantifiable already at the design phase. However, the static storage approach does not consider the inter-event recovery of storage capacity by infiltration and evapotranspiration. This study investigated dynamic storage capacities of three stormwater management designs with increasing proportions of LID units on a 1.2 ha urban residential block in Southern Finland, to compare their cost-efficiency, as well as their potential in restoring the pre-development flow regime. The cost-efficiency of LID designs was assessed based on their ability to contribute to water losses, and on the additional construction costs required when comparing them to conventional solutions (e.g. asphalt replaced with permeable pavement). The design with a small storage capacity and a large captureratio, i.e., the ratio of contributing area to LID area, was the least efficient albeit its small construction cost. The design with an appropriate balance between the capture ratio and the LID provided storage capacity was the most efficient option. In assessing the potential of stormwater designs in restoring the pre-development flow regime, the sum of infiltration and flow in storm sewer networks was more representative of the catchment total runoff than flow alone. Finally, an extensive simulation of a large set of differently placed LID units proved useful in a priori identification of the most influential units in the treatment train.

In this study, HSPF (Hydrologic Simulation Program-FORTRAN) was used to analyze the potential impact of climate change on the streamflow of four major river basins in Ethiopia: Awash, Baro, Genale, and Tekeze. The calibrated and validated HSPF model was forced with daily climate data of 10 CMIP5 (Coupled Model Intercomparison Project phase 5) Global Climate Models (GCMs) for the 1971–2000 control period and the RCP4.5 and RCP8.5 climate projections of 2041–2070 (2050s) and 2071–2100 (2080s). The ensemble median of these 10 GCMs projects the temperature in the four study areas to increase by about 2.3 °C (3.3 °C) in 2050s (2080s), whereas the mean annual precipitation is projected to increase by about 6% (9%) in 2050s (2080s). This results in about 3% (6%) increase in the projected annual streamflow in Awash, Baro, and Tekeze rivers whereas the annual streamflow of Genale river is projected to increase by about 18% (33%) in the 2050s (2080s). However, such projected increase in the mean annual streamflow due to increasing precipitation over Ethiopia contradicts the decreasing trends in mean annual precipitation observed in recent decades. Regional climate models of high resolutions could provide more realistic climate projections for Ethiopia’s complex topography, thus reducing the uncertainties in future streamflow projections.

Subsurface drain trenches are important pathways for water movement from the field surface to subsurface drains in low permeability clayey soils. The hydrological effects of trenches installed with well conducting backfill material and gravel inlet patches are difficult to study with only experimental methods. Computational three-dimensional soil water models provide additional tools to assess spatial processes of such drainage system. The objective was to simulate water flow pathways with 3-D FLUSH model in drain spacing and trench depth scale with two model configurations: (1) the total pore space of soil was treated as a single continuous pore system and (2) the total pore space was divided into mobile soil matrix and macropore systems. Both model configurations were parameterized almost solely with field data without calibration. Data on soil hydraulic properties and drain discharge measurements were available from a clayey subsurface drained agricultural field in southern Finland. The effect of soil hydraulic variability on water flow pathways was assessed by generating computational grids in which the hydraulic properties were sampled randomly from five measured soil sets. Both model configurations were suitable to describe the recorded drain discharge, when model was parameterized in finer scale than drain spacing and the parameterization described highly conductive subdomains such as macropores in a dual-permeability model or the trench in a single pore system model. Models produced similar hourly discharge and water balance results with randomly sampled soil hydraulic properties. The results provide a new view on consequences of soil heterogeneity on subsurface drainage. The practical implication of the results from different drainage scenarios is that gravel trench appears to be important only in soils with a poorly conductive subsoil layers without direct macropore connections to subsurface drains. Solely drain discharge data was not sufficient to determine the differences in water flow pathways between the two model configurations and more output variables, such as groundwater level, should be taken into account in making assessments on the effects of different drainage practices on field drainage capacity. (C) 2016 Elsevier B.V. All rights reserved.

Elevated suspended sediment (SS) loads released from peatlands after drainage operations and the resulting negative effect on the ecological status of the receiving water bodies have been widely recognized. Understanding the processes controlling erosion and sediment transport within the ditch network forms a prerequisite for adequate sediment control. While numerous experimental studies have been reported in this field, model based assessments are rare. This study presents a modeling approach to investigate sediment transport in a peatland ditch network. The transport model describes bed erosion, rain-induced bank erosion, floc deposition, and consolidation of the bed. Coupled to a distributed hydrological model, sediment transport was simulated in a 5.2 ha forestry-drained peatland catchment for two years after ditch cleaning. Comparing simulation results to measured SS concentrations suggested that the loose peat material, produced during excavation, contributed markedly to elevated SS concentrations immediately after ditch cleaning. Both snowmelt and summer rainstorms contributed critically to annual loads. Springtime peat erosion during snowmelt was driven by ditch flow whereas during summer rainfalls, bank erosion by raindrop impact was identified as an important process. Relating modeling results to observed spatial topographic changes in the ditch network was challenging and the results were difficult to verify. Nevertheless, the model has potential to identify risk areas for erosion. The results demonstrate that modeling is effective in separating the importance of different processes and complements pure experimental approaches. Modeling results can aid planning and designing efficient sediment control measures and guide the focus of experimental studies. This article is protected by copyright. All rights reserved.

Urbanization leads to the replacement of natural areas by impervious surfaces and affects the catchment hydrological cycle with adverse environmental impacts. Low impact development tools (LID) that mimic hydrological processes of natural areas have been developed and applied to mitigate these impacts. Hydrological simulations are one possibility to evaluate the LID performance but the associated small-scale processes require a highly spatially distributed and explicit modeling approach. However, detailed data for model development are often not available for large urban areas, hampering the model parameterization. In this paper we propose a methodology to parameterize a hydrological model to a large, ungauged urban area by maintaining at the same time a detailed surface discretization for direct parameter manipulation for LID simulation and a firm reliance on available data for model conceptualization. Catchment delineation was based on a high-resolution digital elevation model (DEM) and model parameterization relied on a novel model regionalization approach. The impact of automated delineation and model regionalization on simulation results was evaluated for three monitored study catchments (5.87–12.59 ha). The simulated runoff peak was most sensitive to accurate catchment discretization and calibration, while both the runoff volume and the fit of the hydrograph were less affected.

Research on the water quality of urban runoff has so far focussed on the post-development phase of urban catchments, whereas water quality in developing areas under construction has remained less understood. The construction phase, however, may constitute a considerable source of diffuse pollution in urban areas. This study investigated the mechanisms affecting water quality in residential areas during the construction and post-construction phases. Water quality (suspended solids, total phosphorus, total nitrogen and chemical oxygen demand) and runoff were monitored over a period of 5 years in three catchments located in the city of Espoo in Southern Finland. The catchments included an urbanizing area under construction and low-density and high-density residential areas. The water quality was quantified in terms of event mean concentrations and loads. The key influential variables explaining the water quality in a multiple linear regression analysis included hydrological variables (event volume and intensity), antecedent conditions and a variable describing the ongoing construction projects. Construction activities in the developing catchment had a profound impact on water quality. Inclusion of the variables describing activities, such as earth moving works, paving, house construction and temporary wastewater discharges, was necessary to explain water quality variations in the developing catchment. The importance of antecedent conditions as an explanatory variable depended on the site and the pollutant in question. Copyright © 2015 John Wiley & Sons, Ltd.

Ditch network maintenance in drained peatland forests increases sediment load and causes harmful effects on downstream watercourses. The objective of this study was to identify the immediate erosion processes in the ditch network and quantify the impact of the ditch network maintenance on suspended solids (SS) load at the catchment outlet. Ditch level processes were measured by conducting field campaigns and catchment-level responses were obtained by using the paired catchment approach. Measurements were conducted at two nested catchments in Koivupuro, Eastern Finland, where runoff and turbidity were monitored continuously at the catchment outlets and erosion and deposition were measured in selected ditches with a pin meter, erosion pins and sediment collectors. According to the results, the sediment load was at its highest during the first year after the ditch network maintenance and especially high during the first spring snow-melt period. Pin-meter measurements, sediment-collector data and results of ditch-bed erosion pins showed that the erosion was more severe in the ditch cut into mineral subsoil than in the ditch cut into thick peat. The SS load from the whole Koivupuro catchment during the first year after the ditch network maintenance was, depending on the estimation method, 185 or 250 kg treated-ha −1 a −1 (0.56 or 0.75 kg ditch-m −1 ), while the net erosion within the ditch network was much higher, 6300 kg treated-ha −1 a −1 (19 kg ditch-m −1 ), indicating that suspended solids were deposited before reaching the outlet of the catchment. Compared to the earlier studies which have focused on the catchment-level effects of ditch network maintenance on the SS loads, the current study succeeded in showing erosion processes and their variability within the ditch network and provided information for improving water protection during ditch network maintenance.

Urbanization strongly changes natural catchment by increasing impervious coverage and by creating a need for efficient drainage systems. Such land cover changes lead to more rapid hydrological response to storms and change distribution of peak and low flows. This study aims to explore and assess how gradual hydrological changes occur during urban development from rural area to a medium-density residential catchment. The Stormwater Management Model (SWMM) is utilized to simulate a series of scenarios in a same developing urban catchment. Sub-hourly hydro-meteorological data in warm season is used to calibrate and validate the model in the fully developed catchment in 2006. The validated model is then applied to other cases in development stage and runoff management scenarios. Based on the simulations and observations, three key problems are solved: (1) how catchment hydrology changes with land cover change; (2) how urban development changes pre-development flows; (3) how stormwater management techniques affect catchment hydrology. The results show that the low-frequency flow rates had remarkably increased from 2004 to 2006 along with the increase of impervious areas. Urbanization in the residential catchment expands the runoff contributing area, accelerates hydrological response, raises peak flows in an order of magnitude of over 10, and more than doubles the total runoff volume. The effects of several LID controls on runoff hydrograph were simulated, and the techniques were able to reduce flows towards the pre-development levels. However, the partly restored flow regime was still clearly changed in comparison to the pre-development flow conditions.

Dyes are valuable tracers in visualizing flow patterns and pathways in soil. We applied the dye Acid Blue 9 to unsaturated and saturated soil profiles at a boreal forest hillslope consisting of glacial sandy till, and determined the soil physical properties from soil samples. The objective was to characterize preferential flowpaths, investigate their porosity, extent and connectivity, and complement earlier findings on subsurface flow formation at the site. According to the results, preferential flowpaths were formed by roots, erosion related to soil water flow, freezing–thawing cycles, and soil fauna. The role of roots and stones in the formation of preferential flowpaths was emphasized. Porosity of preferential flowpaths was 5.1 ± 1.8%, and they extended to a depth of about 55 cm from the soil surface; the deepest roots reached the same depth. When the soil saturated, individual preferential flowpaths self-organized into continuous and well-connected lateral flow systems along the slope. At the slope shoulder, preferential flow network covering the entire soil profile, as well as preferential flowpaths on the underlying bedrock surface, were considered crucial for runoff generation. In the midslope area, runoff generation was characterized by lateral preferential flow and the transmissivity feedback phenomenon. At the slope foot, preferential flowpaths in soil below the eluvial horizon were the major runoff contributors. A full saturation of the soil profile at the slope is unlikely under natural conditions. However, lateral flow was found to occur also in unsaturated soil.

Summary Hydrological model simulations can be applied to evaluate the performance of low impact development (LID) tools in urban areas. However, the assessment for large-scale urban areas remains a challenge due to the required high spatial resolution and limited availability of field measurements for model calibration. This study proposes a methodology to parameterize a hydrological model (SWMM) with sufficiently high spatial resolution and direct accessibility of model parameters for LID performance simulation applicable to a large-scale ungauged urban area. Based on calibrated high-resolution models for three small-scale study catchments (6–12 ha), we evaluated how constraints implied by large-scale urban modelling, such as data limitations, affect the model results. The high-resolution surface representation, resulting in subcatchments of uniform surface types, reduced the number of calibration parameters. Calibration conducted independently for all catchments yielded similar parameter values for same surface types in each study catchment. These results suggest the applicability of the parameter values calibrated for high resolution models to be regionalized to larger, ungauged urban areas. The accessibility of surface specific model parameters for LID simulation is then also retained. Conducted perturbations in spatial resolution through sewer network truncation showed that while the runoff volume was mostly unaffected by resolution perturbations, lower resolutions resulted in over-simulation of peak flows due to excessively rapid catchment response to storm events. Our results suggest that a hydrological model where parameter values are adopted from high-resolution models and that is developed based on a minimum conduit diameter of 300 mm provides good simulation performance and is applicable to large-scale urban areas with reasonable effort.

In boreal-drained peatland forests, tree growth is retarded by the gradual deterioration of drainage ditch networks. In order to avoid the development of suboptimal growth conditions, ditch network maintenance (DNM) operations (ditch cleaning and/or complementary ditching) are annually conducted on an area of about 70,000 ha in Finland. The previous studies indicate that the depth of the water table prior to DNM may influence the magnitude of the growth response to DNM. Tree growth does not necessarily increase after DNM at sites with large stand volume and subsequent low water levels due to tree stand evapotranspiration. We investigated how the pre-treatment water table depth (pre-WTD) in late summer relates to the growth of Scots pine (Pinus sylvestris L.) stands after the DNM operation in 12 field experiments. The increase in mean annual volume growth caused by DNM was negatively related to the pre-WTD, with the highest growth response in stands where the pre-WTD was less than 25–30 cm. DNM di...

This article analyzes the optimal rotation age and the size of the buffer zone when society values harvest revenue, water quality and biodiversity. In a theoretical model we extend the traditional Faustmann rotation model to include the possibility of leaving an unharvested riparian buffer zone between the cut area and the watercourse in order to reduce nutrient load damages to the watercourse and increase biodiversity benefits in the buffer zone. We then analyze how the optimal rotation age and optimal size of the buffer zone are chosen simultaneously. In an empirical analysis, we use Finnish data including simulation results of nitrogen loads to find the social optimal solution with a numerical model. Biodiversity is valuated as a willingness to pay for retention trees left in the buffer zone. According to the empirical results in the social optimum it is not optimal to allocate any land to an unharvested buffer zone when we consider the reduction of the nitrogen load as the only benefit provided by the buffer zone. However, when we add the biodiversity benefits into the empirical analysis, the optimal size of the buffer zone is 4% of the area in the social optimum. Under the current damage valuation, the empirical results do not give any support to the hypothesis that prolonged rotation ages could be used to reduce the damage from the nutrient load.

In this study climate change impacts on water balance components were estimated from transient climate scenarios for 1951–2099 in Finland. The future changes in evapotranspiration and discharge in annual and seasonal scales as well as annual mean high and low flows were projected for four catchments in different parts of Finland. The assessment was carried out using temperature and precipitation series simulated by four regional climate models (RCMs) as input to a conceptual hydrological model. The daily data from RCMs was bias corrected with the quantile–quantile mapping method and statistical properties of the simulated discharges were analysed to detect trends over time. Without bias correction the simulated discharges in the control period did not match the observed discharges, but the fit was improved considerably after bias correction. The results showed that seasonal changes, most importantly increase in winter runoff, were clearly visible and consistent in different climate scenarios and catchments. Individual scenarios also produced changes in annual mean, high and low flows, but without consistency in scenarios. The use of bias corrected RCM data as input to the hydrological model enables transient simulations, but the simulation results aggregate considerable uncertainties from the climate modelling, bias correction and the hydrological model.

Ditch networks in drained peatland forests are maintained regularly to prevent water table rise and subsequent decrease in tree growth. The growing tree stand itself affects the level of water table through evapotranspiration, the magnitude of which is closely related to the living stand volume. In this study, regression analysis was applied to quantify the relationship between the late summer water table depth (DWT) and tree stand volume, mean monthly summertime precipitation (Ps), drainage network condition, and latitude. The analysis was based on several large data sets from southern to northern Finland, including concurrent measurements of stand volume and summer water table depth. The identified model demonstrated a nonlinear effect of stand volume on DWT, a linear effect of Ps on DWT, and an interactive effect of both stand volume and Ps. Latitude and ditch depth showed only marginal influence on DWT. A separate analysis indicated that an increase of 10 m3·ha–1 in stand volume corresponded with a drop of 1 cm in water table level during the growing season. In a subsample of the data, high bulk density peat showed deeper DWT than peat with low bulk density at the same stand volume.

The purpose of this study was to quantify how vegetation influences the flow and sediment processes relevant to the design and management of environmental compound channels. Therefore, a two-year field investigation was conducted in a cohesive two-stage channel, focusing on the flow resistance and net deposition in five subreaches with different floodplain vegetation conditions. In the grassy subreaches, the cross-sectional blockage factor was the key vegetation property governing the flow resistance, with a process-based model providing reliable estimates under widely variable hydraulic and vegetative conditions. The net deposition of cohesive sediment was best explained by vegetation height while high stand length and density created supply-limited conditions on the inner floodplain. These results showed that the two-stage approach offers potential for controlling the sediment processes through appropriate vegetation maintenance. The novelty of this research is that straightforward analyses acco...

© 2015. American Geophysical Union. All Rights Reserved. Peatland drainage has been an important component of forestry management in the boreal zone and the resulting ditch networks are maintained regularly to sustain forest productivity. In Finland, this is recognized as the most detrimental forestry practice increasing diffuse loads of suspended solids. Alongside forestry management on peatlands, interest in peatland restoration has grown lately. Distributed hydrological modeling has the potential to address these matters by recognizing relevant physical mechanisms and identifying most suitable strategies for mitigating undesired outcomes. This study investigates the utility of such a modeling approach in a drained peatland forest environment. To provide a suitable tool for this purpose, we coupled channel network flow to the three-dimensional distributed hydrological model FLUSH. The resulting model was applied to a 5.2 ha drained peatland forest catchment in Eastern Finland. The model was calibrated and validated using field measurements obtained over frost-free periods of five months. The application showed that distributed modeling can disentangle the importance of spatial factors on local soil moisture conditions, which is significant as peatland drainage aims to control these conditions. In our application, we limited the spatial aspect to the topography and the drainage network, and found that the drainage configuration had a clear effect on the spatial soil moisture patterns but that the effect was less pronounced during the wetter summer. Future applications of distributed modeling in this field comprises investigating the impacts of other spatial factors, modeling channel erosion and solid transport to address strategies for their mitigation, and evaluating restoration schemes.

The objective of this study was to investigate with aid of a hillslope hydrological model (1) how landscape forms and land-use types control runoff generation and nitrogen leaching and (2) how the inevitable simplifications made when representing the entire catchment by a single hillslope (characteristic profile) affect modelled water and nitrogen fluxes. Analysis of the effect of hillslope shape parameters (e.g. length and slope) indicated that in forested hillslopes the modelled nitrogen export had a strong linear relationship with the share of subsurface runoff from the total runoff. The fraction of subsurface runoff, however, showed a non-linear relationship to changes in the profile length and slope. Decrease in length, and increase in slope, lead to a greater fraction of subsurface runoff. The non-linearity in the relationship implies that estimation of both the subsurface fraction and the nitrogen load is distorted when sub-areas producing large fractions of subsurface flow are aggregated with areas generating only little subsurface runoff into a single characteristic profile. In constructing the characteristic profile, aggregation of areas having different forest stand/soil properties causes the upslope drainage areas and the flow pathways to the stream to become distorted. The effects of such distortion were found to be particularly high for ammonium as its behaviour – due to efficient retention in soil – is highly non-linear with respect to the distance from the source area into the stream (i.e. size of buffer zone). In case of nitrate, which was considered not to be retained in soil, the role of groundwater table at the source area (clear-cut) was identified to be a more important control than the buffer zone size. As the upslope parts of a catchment have a significant role in determining the groundwater table at the treatment site, a question arises whether in addition to buffer zones one should also turn the attention upslope of the nitrogen source areas. Clearly patterns of landscape, such as distribution of nitrogen source areas in this study, pose challenges in selecting the spatial description for environmental simulation models. In nutrient leaching models, which easily become complex when based on process descriptions, compromises are needed to trade off between model complexity and the way how realistically landscape is described.

A two dimensional model, FEMMA, to describe water and nitrogen (N) fluxes within and from a forested first-order catchment (Kangasvaara in Eastern Finland) was constructed by linking the most significant processes affecting the fluxes of water, ammonium, nitrate and dissolved organic nitrogen along a hillslope from the water divide to the stream. The hillslope represents the average flowpath of water in the catchment and the model was used to estimate the N fluxes for a catchment in eastern Finland before and after clear-cutting. The simulated results were in reasonable agreement with the nitrate, dissolved organic N and dissolved total N measurements from the study catchment and with other results in the literature. According to the simulations, the major sinks of N after clear-cutting were immobilisation by soil microbes, uptake by ground vegetation and sorption to soil. These sinks increased downslope from the clear-cut area, indicating the importance of an uncut buffer zone between the stream and the clear-cut area in reducing N exports. The buffer zone retained 76% of the N flux coming from the clear-cut area. Nitrification was a key process in controlling the N export after clear-cutting and N increases were mainly as nitrate. Most of the annual N export took place during the spring flood, when uptake of N by plants was minimal.

The purpose of this study was to explore the applicability of terrestrial laser scanning (TLS) in determining floodplain ground level and vegetation properties for hydraulic analyses. The field investigations were conducted in a two-stage channel containing five differently vegetated test reaches established to represent conditions from bare soil to grasses and ∼1 m tall willows. Comparing TLS to manual cross-sectional and vegetation surveys brought new insight into the reliability of TLS as a method to determine the vegetation characteristics and floodplain ground level for different seasons and variable vegetation cover. The detected ground level had a mean absolute error (MAE) of 2–14 cm in the grassy test reaches with 50 cm window size. In spring the reach-averaged MAE was 4 cm and increased to 8 cm for the late growing season. For the densely vegetated test reaches, increasing the point cloud density from 50,000 pts/m2 did not considerably improve the ground-level estimate. For deriving spa...

© 2014, Springer Science+Business Media Dordrecht. We developed and applied a computational model for simulating unsteady flow in a drainage network of a boreal forested peatland site. The input to the model was the hourly runoff produced by a hydrological model. The simulations of the flow in the ditch network were performed using an iterative procedure for solving the Saint-Venant equations that govern the flow in each of the network channels. These equations were solved separately for each ditch branch, and the flow depths at the junctions were corrected using the method of characteristics. The model was applied to the drainage network of a peatland catchment in Eastern Finland over a period of 15 months. Because flow resistance in the ditches depended strongly on flow conditions, flow resistance (Manning’s n) was introduced as a function of discharge. The model was calibrated and validated against field data and the simulation results were further applied to assess erosion risk. The highest risk of erosion occurred during long lasting flows induced by snowmelt at ditch sections with a steep slope and a large upstream area. These model results can aid in the design and siting of water protection measures within the drained area.

One of the water quality management practices in forested catchments is to construct wetland buffers between managed areas and recipient water courses. Wetland buffers can be constructed simply by routing runoff from forested areas to natural peatlands and wetlands, or by rewetting lower sections of drained peatlands by filling in or blocking the drainage ditches. The use of natural and restored wetland buffers for reducing nutrient and sediment export from forested catchments, particularly catchments dominated by forestry-drained peatlands, has been studied actively in Finland during the last 15 years. The studies have shown highly variable retention capacity for wetland buffers with different site characteristics and under different environmental conditions. In favorable conditions, high amounts of sediments and adhered mineral elements may be deposited within peat and surface vegetation of the buffer. Dissolved nutrients can be retained biologically into plant and microbial biomasses and chemically into peat. In contrast, nitrogen can also be lost into the atmosphere in gaseous form. In this literature review, we summarize the results of the experiments established on natural and restored wetland buffers in forested catchments in Finland to clarify the different processes and factors controlling their nutrient and sediment retention capacity. We also discuss the limitations and possible negative consequences of using wetland buffers for managing water quality in forested catchments.

The purpose of this article is to model the influence of land use on catchment runoff. The modeling is based on the sub-division of the catchment into smaller units by generation of the so-called “hydrologically similar units” (HSU) or “patch types“. HSUs aggregate areas of hydrologically similar behavior, e.g., land use, soil, slope, and vegetation. Each HSU is represented using a cross-section called a “characteristic profile“. For the calculation of the water balance of the characteristic profiles, a mathematical treatment of the key partitions of the hydrograph response was developed. The characteristic profile is the largest unit that can be handled mathematically still maintaining the idea of a hydrologically similar regime. An agricultural characteristic profile is a cross-section between two parallel open ditches or sub-surface drains. For forest areas the characteristic profile is called hillslope and the length of the hillslope can vary from few meters up to hundreds of meters. The total runoff from the characteristic profiles is an input to a channel network. In the present model, the channel processes are described using the geomorphologic instantaneous unit hydrograph (GIUH). The proposed hydrological model was tested in the Lestijoki catchment (1290 km 2 ) located in western Finland. The catchment was subdivided into 25 characteristic profiles with parameters fixed to typical values measured in Finnish conditions. The model calibration was carried out for the GIUH parameters using measured every-day river flow. The coefficient of determination was 0.74 for a 2 -y calibration period, and 0.70 for a 3 -y testing period. The model represented well the extent of variable contributing areas, which was the main reason for the non-linear behavior of the catchment response.

Despite the crucial role of snow in the hydrological cycle in cold climate conditions, monitoring studies of urban snow quality often lack discussions about the relevance of snow in the catchment-scale runoff management. In this study, measurements of snow quality were conducted at two residential catchments in Espoo, Finland, simultaneously with continuous runoff measurements. The results of the snow quality were used to produce catchment-scale estimates of areal snow mass loads (SML). Based on the results, urbanization reduced areal snow water equivalent but increased pollutant accumulation in snow: SMLs in a medium-density residential catchment were two- to four-fold higher in comparison with a low-density residential catchment. The main sources of pollutants were related to vehicular traffic and road maintenance, but also pet excrement increased concentrations to a high level. Ploughed snow can contain 50% of the areal pollutant mass stored in snow despite its small surface area within a catchment.

The objective of this study was to compare approaches to modeling surface runoff due to summer and autumn storms on a cultivated field. The data consisted of measurements performed every 15 minutes during rainfall-surface runoff events in 1993. A transfer function model was formulated using measured rainfall or rainfall excess as an input and surface runoff as an output. The physical models were based on the kinematic wave approximation of the Saint Venant equations. Surface runoff was assumed to flow first as an overland flow on a level field and second in rills. The results showed that the transfer function model using rainfall excess as an input, and the implicitly solved rill flow model performed the best with respect to the fitness coefficients, which denoted the efficiency of the model. The testing of the models using fixed parameter combinations indicated that an event based parameter estimation was not applicable in verifying the models to changing conditions.

Riparian forests (RF) growing along streams, rivers and lakes comprise more than 2% of the forest area in the Nordic countries (considering a 10 m wide zone from the water body). They have special ecological functions in the landscape. They receive water and nutrients from the upslope areas, are important habitats for biodiversity, have large soil carbon stores, but may emit more greenhouse gases (GHG) than the uplands. In this article, we present a review of the environmental services related to water protection, terrestrial biodiversity, carbon storage and greenhouse gas dynamics provided by RF in the Nordic countries. We discuss the benefits and trade-offs when leaving the RF as a buffer against the impacts from upland forest management, in particular the impacts of clear cutting. Forest buffers are effective in protecting water quality and aquatic life, and have positive effects on terrestrial biodiversity, particularly when broader than 40 m, whereas the effect on the greenhouse gas exchange is unclear.

In Finland nearly 6 million hectares of peatlands are drained for forestry purposes. Ditch network maintenance in the drained peatlands, i.e. cleaning old ditches or digging complementary ditches, deteriorates surface water quality by increasing the export of dissolved elements and suspended solids (SS). Effect of ditch network maintenance on the export of SS, dissolved organic carbon (DOC), and dissolved nitrogen (N), phosphorous (P), iron (Fe), aluminum (Al) and manganese (Mn) was studied in nine pairs of treated and control (no maintenance) catchments located in southern and central Finland. In this study we extended the paired catchment approach by combining data from several catchments and identifying the treatment effect on SS and element loads from the entire dataset. Following the method of Laurén et al. (2009) we identified how uncertainty in correlation between treatment and control catchments during pre-treatment period is reflected in the estimated treatment effect on SS and element loads. In the experiment, the export of SS increased significantly for the four year study period following the ditch network maintenance and Al export increased for one year. The export of N, P and Fe was not significantly changed and DOC and Mn export decreased after the ditch maintenance operation.

Seloste artikkelista: Nieminen, M., Ahti, E., Koivusalo, H., Mattson, T., Sarkkola, S. & Lauren, A. / Export of suspended solids and dissolved elements from peatland areas after ditch network maintenance in south-central Finland. Silva Fennica 44 (2010) : 1, 39-49.

The automatic monitoring station was established to the forested catchment in Eastern Finland. The ground water level was situated approximately 0.5 m below the lowest one of the three dielectric coefficient probe. There were three dielectric coefficient probes (CS615; Campbell Sci, UK) at three different depths (0.25 m, 0.6 m, 0.8 m). Data collecting was happened with CR10X datalogger (Campbell Sci, UK). The ground water level was measured by PDCR1830 (Druck, UK) from the nearest ground water pipe. The main aim of this study was to investigate how the rising ground water table effects to the measured soil dielectric coefficients and how transpiration and evapotranspiration are seen in measured dielectric coefficient and ground water level. The main result was that how well dielectric coefficient follows changes of ground water level. The transpiration of trees had an effect both dielectric coefficient (i.e. soil moisture) and ground water level. It looked like that transpiration ends at the beginning of September; because of the pumping effect of capillary increase disappear. And the ground water level is stable after the beginning of October, which means that evapotranspiration have been ended in that time.

Urbanization and associated increase of imperviousness alters the hydrological cycle of urbanizing catchments. Low Impact Development (LID) tools have been developed and applied to mitigate these hydrological impacts. Hydrological models are one way to evaluate the performance of LID tools before their implementation. As these tools represent small-scale hydrological processes, hydrological models used in assessment require a high spatial and temporal resolution in their process descriptions. Both flow and rainfall data at high recording frequencies (e.g. 1 min) are usually not available for large urban catchments and detail in spatial data for surface description has to be complemented through on-site observations. Thus, the assessment of LID performance for large urban areas has to overcome these constraints. Previous studies provide suggestions to overcome the lack of flow data for model calibration through parameter regionalization. Recently presented methods for reductions in spatial resolution while maintaining a detailed surface description provide a feasible way to characterize large urban catchments for LID performance assessment. However, rainfall data at high temporal and spatial resolution remains a key element for hydrological model applications in urban areas. The authors evaluated the impact of spatial and temporal rainfall variability on model performance using the Stormwater Management Model (SWMM) and high-resolution parameterizations of three urban catchments in combination with two rain gauges. While the distance between rain station and catchment did not affect model parameters the authors found a reduction in model efficiency with an increasing rain station distance from the catchment.