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Restoration and water table control on peatlands to limit fire risk are national priorities in Indonesia. The present study was initiated at Padang Island, Sumatra, to increase understanding on peatland hydrology in the tropic. At the pilot site, water table and precipitation were monitored at different stations. The results show variation in water table depths (WTDs) over time and space due to spatial and temporal variability in rain intensity and drainage networks. In part of the island, large-scale drainage for plantations led to deep WTD (−1.8 m) and high WTD recession rates (up to 3.5 cm/day). Around villages, farm-scale drainages had a smaller impact with a lower recession rate (up to 1.8 cm/day) and shallow WTD, typically below −0.4 m, the threshold for sustainable peatland management in Indonesia. The recession rates levelled off at 1.0 cm/day near the drained forest/plantation and at 0.5 cm/day near the farm. Deeper layers had much lower specific yield (Sy), 0.1 at −1.5 m depth, compared with top peat soils with Sy up to 0.3. Proximity to drainages extended discharge flow to deeper layers. The results highlighted the severity of peatland drainage impact on most coastal zones of Padang Island, which have intensive drainage networks. HIGHLIGHTS High spatial and temporal variability of water table was observed in Padang Island.; The variability was partially driven by variation in land use and farm drainages.; Recession rate near pulp plantations remained high (0.01 m/day) at −1.5 m depth.

Subarctic ecohydrological processes are changing rapidly, but detailed and integrated ecohydrological investigations are not as widespread as necessary. We introduce an integrated research catchment site (Pallas) for atmosphere, ecosystems, and ecohydrology studies in subarctic conditions in Finland that can be used for a new set of comparative catchment investigations. The Pallas site provides unique observational data and high-intensity field measurement datasets over long periods. The infrastructure for atmosphere- to landscape-scale research in ecosystem processes in a subarctic landscape has recently been complemented with detailed ecohydrological measurements. We identify three dominant processes in subarctic ecohydrology: (a) strong seasonality drives ecohydrological regimes, (b) limited dynamic storage causes rapid stream response to water inputs (snowmelt and intensive storms), and (c) hydrological state of the system regulates catchment-scale dissolved carbon dynamics and greenhouse (GHG) fluxes. Surface water and groundwater interactions play an important role in regulating catchment-scale carbon balances and ecosystem respiration within subarctic peatlands, particularly their spatial variability in the landscape. Based on our observations from Pallas, we highlight key research gaps in subarctic ecohydrology and propose several ways forward. We also demonstrate that the Pallas catchment meets the need for sustaining and pushing the boundaries of critical long-term integrated ecohydrological research in high-latitude environments.

Key Points: • Land use such as agriculture and peat extraction alter the physical and hydraulic properties of the peat more strongly than other land uses • The top 30 cm peat depth was most affected by agriculture and peat extraction, as indicated by the bulk density, specific yield, and porosity values • The van Genuchten-Mualem soil water retention model was applied successfully to different layers of peat under different land use Undisturbed peatlands are effective carbon sinks and provide a variety of ecosystem services. However, anthropogenic disturbances, especially land drainage, strongly alter peat soil properties and jeopardize the benefits of peatlands. The effects of disturbances should therefore be assessed and predicted. To support accurate modeling, this study determined the physical and hydraulic properties of intact and disturbed peat samples collected from 59 sites (in total 3,073 samples) in Finland and Norway. The bulk density (BD), porosity, and specific yield (Sy) values obtained indicated that the top layer (0–30 cm depth) at agricultural and peat extraction sites was most affected by land use change. The BD in the top layer at agricultural, peat extraction, and forestry sites was 441%, 140%, and 92% higher, respectively, than that of intact peatlands. Porosity decreased with increased BD, but not linearly. Agricultural and peat extraction sites had the lowest saturated hydraulic conductivity, Sy, and porosity, and the highest BD of the land use options studied. The van Genuchten-Mualem (vGM) soil water retention curve (SWRC) and hydraulic conductivity (K) models proved to be applicable for the peat soils tested, providing values of SWRC, K, and vGM-parameters (α and n) for peat layers (top, middle and bottom) under different land uses. A decrease in peat soil water content of ≥10% reduced the unsaturated K values by two orders of magnitude. This unique data set can be used to improve hydrological modeling in peat-dominated catchments and for fuller integration of peat soils into large-scale hydrological models.

Catchment storage sustains ecologically important low flows in headwater systems. Understanding the factors controlling storage is essential in analysis of catchment vulnerability to global change. We calculated catchment storage and storage sensitivity of streamflow for 61 boreal headwater catchments in Finland. We also explored the connection between computed storage indices and low flow conditions. The relationships between selected climate, snow, and catchment characteristics and calculated storage properties and low flows were investigated, in order to assess the importance of different factors that render catchments vulnerable to climate and environmental change. We found that the most sensitive areas to climate change were located in the southern boreal coastal zone, with fine‐grained soils and agricultural areas. In contrast, catchments in the middle and northern boreal zone, with till and peatland soils and higher snow water equivalent values, were less sensitive under current conditions. In addition, we found a threshold at a snow to precipitation ratio of 0.35. Above that threshold, summer low flows were generally sensitive to changes in snow conditions, whereas below that threshold catchment characteristics gained importance and the sensitivity was more directly related to changes in temperature and timing of rainfall. These findings suggest that a warming climate will have pronounced impacts on hydrology and catchment sensitivity related to snow quantity and snow cover duration in certain snow to precipitation ratio zones. Moreover, land use activities had an impact on storage properties in agricultural and drained peatland areas, resulting in a negative effect on low flows.

In wetlands, the water budget is traditionally quantified by measuring the hydrologic components including precipitation, evapotranspiration and surface water-groundwater inflows and outflows. However, the reliability of measurements is often questioned due to the difficulty of rigorously monitoring all components of the water budget. Quantifying the rainfall event to water table response ratio is an alternative approach with minimal need for data commonly collected in peatland studies. However, the method has been used only in a limited number of biophysical settings including different microforms, hydroclimatic and hydrogeological settings. The objectives of this study are to quantify the reactivity of the water table to precipitation for different pristine peatlands located in different hydroclimatic conditions and to provide quantitative assessments of water storage of as many peatlands as possible. To do so, site-specific hourly water table and precipitation measurements was collected from northern peatlands worldwide. In total, data from more than 30 sites were retrieved from 8 research groups. For all peatlands, water-table depths varied between 80 cm below the peat surface and 10 cm above the peat surface. The results highlight that the hydrology of all peatlands is characterized by a shift from an environment that can store water to an environment that contributes to rapid outflow, and this is a uniform feature across sites. However, for peatlands with the lowest water storage capacities, this shift occurs during relatively moderate rainfall events (40 mm) or successive small rainfall events. Blanket peat bog best embodied this type of hydrological response. For peatlands with the highest water storage capacity, this shift occurs following multiple moderate to large precipitation events (40 mm – 80 mm) and it is strongly enhanced by the shift from high to low evaporative periods. The peatlands with the highest storage capacity are raised bogs with deep water-table. These conditions are best observed in peatlands located in geographical settings with high evaporation rates. Among all the peatlands, maximum water storage capacity for given rainfall events was equal to ≈150 mm. These analyses also confirm that the water table rise caused by precipitation events contain sufficient information to constrain water storage variations around monitored wells peatlands for a wide array of biophysical settings.

Spatiotemporal information on historical peatland drainage is needed to relate past land use to observed changes in catchment hydrology. Comprehensive knowledge of historical development of peatland management is largely unknown at the catchment scale. Aerial photos and light detection and ranging (LIDAR) data enlarge the possibilities for identifying past peatland drainage patterns. Here, our objectives are (1) to develop techniques for semiautomatically mapping the location of ditch networks in peat-dominated catchments using aerial photos and LIDAR data, and (2) to generate time series of drainage networks. Our approaches provide open-access techniques to systematically map ditches in peat-dominated catchments through time. We focused on the algorithm in such a way that we can identify the ditch networks from raw aerial images and LIDAR data based on the modification of multiple filters and number of threshold values. Such data are needed to relate spatiotemporal drainage patterns to observed changes in many northern rivers. We demonstrate our approach using data from the Simojoki River catchment (3,160 km²) in northern Finland. The catchment is dominated by forests and peatlands that were almost all drained after 1960. For two representative locations in cultivated peatland (downstream) and peatland forest (upstream) areas of the catchment; we found total ditch length density (km/km²), estimated from aerial images and LIDAR data based on our proposed algorithm, to have varied from 2% to 50% compared with the monitored ditch length available from the National Land survey of Finland (NLSF) in 2018. A different pattern of source variation in ditch network density was observed for whole-catchment estimates and for the available drained-peatland database from Natural Resources Institute Finland (LUKE). Despite such differences, no significant differences were found using the nonparametric Mann-Whitney U test with a 0.05 significance level based on the samples of pixel-identified ditches between (1) aerial images and NLSF vector files and (2) LIDAR data and NLSF vector files.

Snowmelt spring floods dominate the annual carbon flux in Arctic streams. However, climate change is altering their timing and magnitude due to changes in snow conditions, further altering the processes controlling the carbon cycle at the catchment scale. Current knowledge is limited by a lack of high-resolution data from Arctic areas. In this study we combine high-resolution biogeochemical-hydro-climatological variables with spectral wavelet analysis for new insights into carbon processes.This study was conducted during the snowmelt spring flood period in a sub-arctic headwater catchment in Pallas-Ylläs national park, Finland (68°02′N, 24°16′W). We collected in-stream dissolved organic carbon (DOC), carbon dioxide (C02), and terrestrial C02 flux alongside a suite of hydro-climatological variables measured at 30-minute intervals. Continuous wavelet transformations and wavelet coherence were produced to assess the relationship between hydro-climatological variables and carbon variables at different periodicities.Wavelet transforms indicated that the onset of snowmelt caused the development of significant diel periodicity for in-stream DOC, CO2 and terrestrial CO2 flux, while substantial periods of significant periodicity were observed at multiple day periodicities. Wavelet coherence analysis identified that DOC was consistently lead by flow and conductivity across daily and multiple daily scales suggesting that transport of carbon from the surface and shallow sub-surface pathways to the stream were the predominant processes controlling in-stream DOC. Interestingly for in-stream CO2, groundwater level showed periodic rather than consistent spectral coherence suggesting it is not a consistent control on CO2 in the spring flood. The strongest coherence for in-stream CO2 was with in-stream O2, which may suggest the importance of in-stream metabolism as a control on in-stream CO2 dynamics. Terrestrial CO2 fluxwas controlled by notably different processes than in-stream Carbon and linked strongest to climatological variables. Photosynthetically active radiation (PAR) showed the strongest relationship with CO2 terrestrial flux dynamics. Our study highlights the unique processes controlling different parts of the carbon cycle in a headwater arctic catchment during the snowmelt spring flood. We highlight in-stream DOC as particularly vulnerable to changes in spring flood magnitude and timing given the importance of snowmelt dominated transport processes to DOC flux. To identify future changes in the Arctic carbon cycle, wavelet analysis shows potential as tool to analyse changes in processes in high-resolution datasets.

Cycling of water quality constituents in lakes is affected by thermal stratification and homo-thermal conditions and other factors such as oligotrophication, eutrophication, and microbial activities. In addition, hydrological variability can cause greater differences in water residence time and cycling of constituents in man-made lakes (reservoirs) than in natural lakes. Thus, investigations are needed on vertical mixing of constituents in new impounded reservoirs, especially those constructed to supply domestic water. In this study, sampling campaigns were conducted in the Sabalan reservoir, Iran, to investigate vertical changes in constituent concentrations during the year in periods with thermal stratification and homo-thermal conditions. The results revealed incomplete mixing of constituents, even during cold months when the reservoir was homo-thermal. These conditions interacted to create a bottom-up regulated reservoir with sediment that released settled pollutants, impairing water quality in the Sabalan reservoir during both thermal stratification and homo-thermal conditions. Analysis of total nitrogen and total phosphorus concentrations revealed that the reservoir was eutrophic. External pollution loads, internal cycling of pollutants diffusing out from bottom sediments, reductions in inflow to the reservoir, and reservoir operations regulated vertical mixing and concentrations of constituents in the Sabalan reservoir throughout the year.

Fully integrated physically based hydrological modeling is an essential method for increasing hydrological understanding of groundwater‐surface water (GW‐SW) interactions in peatlands and for predicting anthropogenic impacts on these unique ecosystems. Modeling studies represent peat soil in a simplistic manner, as a homogeneous layer of uniform thickness, but field measurements consistently show pronounced spatial variability in peatlands. This study evaluated uncertainty in groundwater levels and exfiltration fluxes associated with the simplified representation of the peat soil layer. For transferability of the results, impacts of selected topographical and hydrogeological conceptual models on GW‐SW exchange fluxes were simulated in a hypothetical hillslope representing a typical aquifer‐mire transect. The results showed that peat soil layer geometry defined the simulated spatial GW‐SW exchange patterns and groundwater flow paths, whereas total groundwater exfiltration flux to the hillslope and groundwater level in the peatland were only subtly altered by different conceptual peat soil geometry models. GW‐SW interactions were further explored using different scenarios and dimensionless parameters for peat hydraulic conductivity and hillslope‐peatland system slope. The results indicated that accurate representation of physical peat soil properties and landscape topography is important when the main objective is to model spatial GW‐SW exchange. Groundwater level in virtual peatland was not greatly affected by groundwater drawdown in an adjacent aquifer, but the magnitude and spatial distribution of GW‐SW interactions was significantly altered. This means that commonly used groundwater depth observations near peat‐mineral soil interfaces and within peatlands may not be a suitable indicator for monitoring the hydrological state of groundwater‐dependent peatland ecosystems.

Optimal nutrient pollution monitoring and management in catchments requires an in-depth understanding of spatial and temporal factors controlling nutrient dynamics. Such an understanding can potentially be obtained by analysing stream concentration&ndash, discharge (C-Q) relationships for hysteresis behaviours and export regimes. Here, a classification scheme including nine different C-Q types was applied to a total of 87 Nordic streams draining mini-catchments (0.1&ndash, 65 km2). The classification applied is based on a combination of stream export behaviour (dilution, constant, enrichment) and hysteresis rotational pattern (clock-wise, no rotation, anti-clockwise). The scheme has been applied to an 8-year data series (2010&ndash, 2017) from small streams in Denmark, Sweden, and Finland on daily discharge and discrete nutrient concentrations, including nitrate (NO3&minus, ), total organic N (TON), dissolved reactive phosphorus (DRP), and particulate phosphorus (PP). The dominant nutrient export regimes were enrichment for NO3&minus, and constant for TON, DRP, and PP. Nutrient hysteresis patterns were primarily clockwise or no hysteresis. Similarities in types of C-Q relationships were investigated using Principal Component Analysis (PCA) considering effects of catchment size, land use, climate, and dominant soil type. The PCA analysis revealed that land use and air temperature were the dominant factors controlling nutrient C-Q types. Therefore, the nutrient export behaviour in streams draining Nordic mini-catchments seems to be dominantly controlled by their land use characteristics and, to a lesser extent, their climate.

The Zayanderud Basin is an important agricultural area in central Iran. In the Basin, irrigation consumes more than 90 percent of the water used, which threatens both the downstream historical city of Isfahan and the Gavkhuni Wetland reserve&mdash, the final recipient of the river water. To analyze impacts of land use changes and the occurrence of metrological and hydrological drought, we used groundwater data from 30 wells, the standardized precipitation index (SPI) and the streamflow drought index (SDI). Changes in the wetland were analyzed using normalized difference water index (NDWI) values and water mass depletion in the Basin was also assessed with gravity recovery and climate experiment (GRACE)-derived data. The results show that in 45 out of studied 50 years, the climate can be considered as normal in respect to mean precipitation amount, but hydrological droughts exist in more than half of the recorded years. The hydrological drought occurrence increased after the 1970s when large irrigation schemes were introduced. In recent decades, the flow rate reached zero in the downstream part of the Zayanderud River. NDWI values confirmed the severe drying of the Gavkhuni Wetland on several occasions, when compared to in situ data. The water mass depletion rate in the Basin is estimated to be 30 (&plusmn, 5) mm annually, groundwater exploitation has reached an average of 365 Mm3 annually, with a constant annual drop of 1 to 2.5 meters in the groundwater level annually. The results demonstrate the connection between groundwater and surface water resources management and highlight that groundwater depletion and the repeated occurrence of the Zayanderud River hydrological drought are directly related to human activities. The results can be used to assess sustainability of water management in the Basin.

Impacts of mining on water quality are a great concern in the Arctic region. This study evaluated the impact of pre-treated mine effluent on river water quality. The study was conducted along the Seurujoki River in sub-Arctic Finland, which is impacted by Kittila gold mine. The study analyzed water quality and hydrological data upstream and downstream of the mining area over an eight-year period, including a tailing dam leakage event in 2015. The analysis focused on water quality determinants such as electrical conductivity (EC), sulfate, antimony, manganese, and total nitrogen (Ntotal). Descriptive statistics on river water at four stations along the river corridor showed negative impacts of mining activities on the recipient water body. In order to find an indicator for water quality, correlation analysis between the water quality determinants was carried out. It identified EC as a good indicator for continuous water quality monitoring, especially to detect mining accidents such as partial failure of a tailings dam. The results showed increasing contaminant concentrations due to mining as more mine effluent was generated over time. A linear mixed model was developed to predict the coefficient of different elements affecting EC at river water monitoring stations impacted by mining effluents. The results provide new information on how to assess mining water impacts and plan future water quality monitoring.

The Arvandroud river (also known as Shatt-al-Arab) and its estuary have been degraded due to the changing river flow regime in the Tigris and Euphrates. This study assessed changes in flow from the major rivers and the impacts on the estuary. To assess the river flow changes, three major flow regime attributes were computed: timing (TIF), magnitude (MIF), and variability (VIF). By combining these indices, the total flow regime impact factor (IF) was scaled between 0 and 1, and classified into five groups: Low (0.80

Bed siltation can drastically alter the physical conditions of headwater streams and is therefore a stressor for stream ecosystems. We studied 32 headwater streams that represented near‐natural (reference; N = 11), sediment‐impacted (N = 12), or wood‐ (N = 4) or stone‐restored (N = 5) streams to quantify how extensive siltation and restoration with either large woody debris (LWD) or boulder structures influence transient storage conditions. We carried out repeated stream tracer experiments, field measurements of habitat characteristics, and numerical simulations to determine the effects of siltation and restoration on total transient storage. Compared with reference streams, impacted streams had a smaller storage zone cross‐sectional area (Aₛ/A) ratio and fraction of median travel time due to transient storage (F₂₀₀), whereas restored streams had transient storage conditions similar to near‐natural conditions. Both of the two restoration methods had positive but differing impacts on bed sediment and transient storage properties. The LWD restoration created diverse total transient storage conditions, whereas boulder restoration decreased fine sediment cover. Addition of both LWD and boulders could thus aid the recovery of headwater streams from excessive sediment input and increase transient storage and in‐stream habitat complexity.

Nutrient export from drained peatland has significant impacts on aquatic environments in Nordic catchments. Spatial information on variations in nutrient concentrations across different landscapes and land uses is needed to design measures for achieving the good ecological status of the EU Water Framework Directive. In this study we determined background concentrations in natural peatland-dominated streams and examined effects of peatland use practices on water quality in headwater catchments. We quantified sources for different elements by joint analysis of water chemistry, isotopes, and hydrology for 62 small catchments in North Ostrobothnia, Finland. Concentrations of nutrients and suspended solids were relatively high in catchments containing drained peatland. In particular, dissolved nitrogen and phosphorus concentrations were elevated during baseflow conditions when flow likely originated from deeper soil layers. Total concentrations of nutrients, suspended solids, and loss on ignition also showed elevated values, and changes in the ratio of dissolved and particulate forms, especially the C/N ratio, were observed. Past drainage had a stronger effect on organic matter and nutrients concentrations than local hydroclimate conditions. These results strongly indicate that current water protection methods are not sufficient to capture all seasonal variations in nutrient and suspended solid loads from drained peatland. Thus, more effort and actions are needed for water protection in such areas.

River regulation is challenging when there is diverse upstream and downstream interest, leading to regional and international conflict. However, quantifying the upstream-downstream flow regime changes and their causes are given less consideration in the river basin. In this study, we presented three new ratios for downstream-upstream low flow contribution (DUL), downstream-upstream high flow contribution ratio (DUH), and meteorological-hydrological drought ratio (MHD), for an integrated assessment of flow regime alteration across the river basin. To test the methods, we compared flow regime alteration upstream and downstream in the Ceyhan basin in central Turkey, which was significantly modified by agriculture between 1984 and 2018 (the irrigated area increased 2.8-fold, rainfed farming decreased by 67.6%). Our analysis revealed a clear change in the contribution of low and high flow seasons to annual flow in the last station of the river at Misis after 1984, but no considerable change in upstream tributaries. In the last decade (2005–2014) and the second half (1995–2014) of the study, the frequency of hydrological droughts increased, while meteorological droughts followed a stationary pattern. Evaluation of the impact of anthropogenic activities on river regime (by comparing flow regime characteristics after 1984 with those from 1975 to 1984 as post- and pre-impact periods) revealed low to incipient impact upstream (Hankoy, Karaahmet, and Kadirli river headwaters), severe impact below the Aslantas dam in the basin center, and moderate impact at the last station on the Ceyhan river. The new metrics provide supplementary information on the flow regime alteration in the basin and can be introduced as a novel quantitative measure to recognize the driving factor of droughts.

Peatlands worldwide are being threatened by intensive land use and drainage, which leads to soil subsidence. This has consequences for farming, especially on low-gradient cultivated peat-dominated lowlands with high flood risk. In this study, we combined historical soil elevation data and new lidar data to improve the estimation of subsidence and its consequences for lowland river systems. The results showed 202−349 mm subsidence within the last 24–51 years, with a mean rate of 5.15–9.47 mm y⁻¹ for riparian peatland on the west coast of Finland. The subsidence rate was partly explained by the depth of the organic soil layer (R² = 0.710, p > 0.05). The results also showed that increasing flooding of cultivated fields is mainly due to soil subsidence, not to increased flooding occurrence in river systems. The area flooded annually was found to increase by 101–194 % for the last 24–51 years, due to soil subsidence near rivers. Generalization of the results to catchment scale indicated an increase in the annual flood zone of 45 % in cultivated fields in one of two study catchments (Siikajoki river basin). These results demonstrate the value of using historical data to study soil subsidence and confirm that the risk of flooding increases in cultivated organic lowlands due to intensive drainage and subsidence. New management strategies, such as peatland rewetting, restoration, and paludiculture, should be considered in future land use plans to reduce subsidence and provide new income streams for farmers.

The natural flow regime of rivers has been strongly altered world-wide, resulting in ecosystem degradation and lakes drying up, especially in arid and semi-arid regions. Determining whether this is due mainly to climate change or to water withdrawal for direct human use (e.g. irrigation) is difficult, particularly for saline lake basins where hydrology data are scarce. In this study, we developed an approach for assessing climate and land use change impacts based on river flow records for headwater and lowland reaches of rivers, using the case of Lake Urmia basin, in north-westen Iran. Flow regimes at upstream and downstream stations were studied before and after major dam construction and irrigation projects. Data from 57 stations were used to establish five different time intervals representing 10 different land use development periods (scenarios) for upstream (not impacted) and downstream (impacted) systems. An existing river impact (RI) index was used to assess changes in three main characteristics of flow (magnitude, timing and, intra-annual variability). The results showed that irrigation was by far the main driving force for river flow regime changes in the lake basin. All stations close to the lake and on adjacent plains showed significantly higher impacts of land use change than headwaters. As headwaters are relatively unaffected by agriculture, the non-significant changes observed in headwater flow regimes indicate a minor effect of climate change on river flows in the region. The benefit of the method developed is clear interpretation of results based on river flow records, which is useful in communicating land use and climate change information to decision makers and lake restoration planners.

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.

Organic matter and nutrient export from drained peatlands is affected by complex hydrological and biogeochemical interactions. Here, partial least squares regression (PLSR) was used to relate various soil and catchment characteristics to variations in chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) concentrations in runoff. Peat core samples and water quality data were collected from 15 peat extraction sites in Finland. PLSR models constructed by cross-validation and variable selection routines predicted 92, 88, and 95% of the variation in mean COD, TN, and TP concentration in runoff, respectively. The results showed that variations in COD were mainly related to net production (temperature and water-extractable dissolved organic carbon (DOC)), hydrology (topographical relief), and solubility of dissolved organic matter (peat sulfur (S) and calcium (Ca) concentrations). Negative correlations for peat S and runoff COD indicated that acidity from oxidation of organic S stored in peat may be an important mechanism suppressing organic matter leaching. Moreover, runoff COD was associated with peat aluminum (Al), P, and sodium (Na) concentrations. Hydrological controls on TN and COD were similar (i.e., related to topography), whereas degree of humification, bulk density, and water-extractable COD and Al provided additional explanations for TN concentration. Variations in runoff TP concentration were attributed to erosion of particulate P, as indicated by a positive correlation with suspended sediment concentration (SSC), and factors associated with metal-humic complexation and P adsorption (peat Al, water-extractable P, and water-extractable iron (Fe)).

The characteristics of groundwater systems and groundwater contamination in Finland, Norway and Iceland are presented, as they relate to outbreaks of disease. Disparities among the Nordic countries in the approach to providing safe drinking water from groundwater are discussed, and recommendations are given for the future. Groundwater recharge is typically high in autumn or winter months or after snowmelt in the coldest regions. Most inland aquifers are unconfined and therefore vulnerable to pollution, but they are often without much anthropogenic influence and the water quality is good. In coastal zones, previously emplaced marine sediments may confine and protect aquifers to some extent. However, the water quality in these aquifers is highly variable, as the coastal regions are also most influenced by agriculture, sea-water intrusion and urban settlements resulting in challenging conditions for water abstraction and supply. Groundwater is typically extracted from Quaternary deposits for small and medium municipalities, from bedrock for single households, and from surface water for the largest cities, except for Iceland, which relies almost entirely on groundwater for public supply. Managed aquifer recharge, with or without prior water treatment, is widely used in Finland to extend present groundwater resources. Especially at small utilities, groundwater is often supplied without treatment. Despite generally good water quality, microbial contamination has occurred, principally by norovirus and Campylobacter, with larger outbreaks resulting from sewage contamination, cross-connections into drinking water supplies, heavy rainfall events, and ingress of polluted surface water to groundwater.

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.

In arid regions, the construction of dams has led to an increase in irrigated agriculture, resulting in the desiccation of vulnerable lakes and wetlands. In many arid mountainous regions, such as in the Middle East, upstream dams typically feed rivers that flow into lowland terminal (closed) lakes or wetlands. The release of water for environmental purposes is a widely recognised option for reducing such impacts. The present study used monthly hydrological data from the Kor river in southern Iran, its main reservoirs and data above and below the Korbal irrigation system. The Kor river is a major source for feeding the Bakhtegan and Tashk lakes, which have recently started to disappear. An analysis of the water resource system before the dam construction (before 1973) showed that the monthly lake inflow depended on available water in river above the irrigation system (for eight months) and, during the irrigation season, water consumed for irrigation as well (for four months). However, in the post-development period (after 1997), the flow rate to the lake depended almost entirely on the Korbal irrigation system, except during some winter months when little irrigation was needed. Environment flow release has not been effective as it has led to greater water availability in the river, which results in more water being consumed for irrigation, as demonstrated here. To overcome this management mismatch, a new environmental flow release strategy (regime) was designed in which water is released from the upstream reservoirs during periods of low irrigation demand (e.g. winter months).

The Bakhtegan catchment, an important agricultural region in south-western Iran, has suffered groundwater depletion in recent years. As groundwater is considered the main source of fresh water in the catchment, especially for agriculture, monitoring groundwater responses to irrigation is important. Gravity Recovery and Climate Experiment (GRACE) satellite data can help determine water mass changes in catchments and assess water volume changes. In this study, we compared GRACE-derived water mass data against groundwater volume variations measured in situ. We also assessed the efficiency of GRACE-derived data in catchments smaller than the 200,000 km2 recommended area when using GRACE. For the study period (January 2002 through December 2011), the GRACE data showed a 7.6 mm annual decline in groundwater level, with a total volume loss of 2.6 km3 during the period. The in situ monthly measurements of groundwater level showed an average depletion of 10 m in catchment aquifers during the study period. This depletion rate was supported by the recorded decrease in precipitation volume, especially in the post-drought period after 2007. These results demonstrate that GRACE can be useful tool for monitoring groundwater depletion in arid catchments.

Managed aquifer recharge (MAR) structure is widely used to expand groundwater resources. In arid regions with flash flooding, MAR can also be used as a flood control structure to decrease peak discharge of rivers. In this paper, we present a method for quantifying the role of MAR in head water systems and assess its impact on the total water balance in a river basin. The method is based on rainfall-runoff modeling, reservoir flood routing, recharge analysis and river flow analysis. For the case selected, Kamal Abad MAR in Lake Maharlou basin in southern Iran, we analyzed changes in the downstream river regime using two scenarios (with MAR and without MAR) with different return periods. The results revealed a significant impact of MAR on river flow in terms of changes in flow timing, magnitude and variability. With MAR, the ephemeral river studied became disconnected from the main stream, albeit, whereas the case without MAR, floods with return period higher than 10 years would be connected to the downstream. Even though, MAR structures are useful in arid and semi-arid climates for irrigation water supply, their placing and designing need more attention. The developed method can be used to assess the impacts of MAR on river flow and find the best location for it to make the connection of the ephemeral river and downstream river, an issue which has not received much attention in hydrological research.

Water management in arid basins often lacks sufficient hydro-climatological data because, e.g., rain gauges are typically absent at high elevations and inflow to ungauged areas around large closed lakes is difficult to estimate. We sought to improve precipitation and runoff estimation in an arid basin (Lake Urmia, Iran) using methods involving assimilation of satellite-based data. We estimated precipitation using interpolation of rain gauge data by kriging, downscaling the Tropical Rainfall Measuring Mission (TRMM), and cokriging interpolation of in-situ records with Remote Sensing (RS)-based data. Using RS-based data application in estimations gave more precise results, by compensating for lack of data at high elevations. Cokriging interpolation of rain gauges by TRMM and Digitized Elevation Model (DEM) gave 4&ndash, 9 mm lower Root Mean Square Error (RMSE) in different years compared with kriging. Downscaling TRMM improved its accuracy by 14 mm. Using the most accurate precipitation result, we modeled annual direct runoff with Kennessey and Soil Conservation Service Curve Number (SCS-CN) models. These models use land use, permeability, and slope data. In runoff modeling, Kennessey gave higher accuracy. Calibrating Kennessey reduced the Normalized RMSE (NRMSE) from 1 in the standard model to 0.44. Direct runoff coefficient map by 1 km spatial resolution was generated by calibrated Kennessey. Validation by the closest gauges to the lake gave a NRMSE of 0.41 which approved the accuracy of modeling.

Cultivated peatlands under drainage practices contribute significant carbon losses from agricultural sector in the Nordic countries. In this research, we developed the BASGRA-BGC model coupled with hydrological, soil carbon decomposition and methane modules to simulate the dynamic of water table level (WTL), carbon dioxide (CO2) and methane (CH4) emissions for cultivated peatlands. The field measurements from four experimental sites in Finland, Denmark and Norway were used to validate the predictive skills of this novel model under different WTL management practices, climatic conditions and soil properties. Compared with daily observations, the model performed well in terms of RMSE (Root Mean Square Error; 0.06–0.11 m, 1.22–2.43 gC/m2/day, and 0.002–0.330 kgC/ha/day for WTL, CO2 and CH4, respectively), NRMSE (Normalized Root Mean Square Error; 10.3–18.3%, 13.0–18.6%, 15.3–21.9%) and Pearson's r (Pearson correlation coefficient; 0.60–0.91, 0.76–0.88, 0.33–0.80). The daily/seasonal variabilities were therefore captured and the aggregated results corresponded well with annual estimations. We further provided an example on the model's potential use in improving the WTL management to mitigate CO2 and CH4 emissions while maintaining grass production. At all study sites, the simulated WTLs and carbon decomposition rates showed a significant negative correlation. Therefore, controlling WTL could effectively reduce carbon losses. However, given the highly diverse carbon decomposition rates within individual WTLs, adding indicators (e.g. soil moisture and peat quality) would improve our capacity to assess the effectiveness of specific mitigation practices such as WTL control and rewetting.

River regulation and climate change are two major causes of river regime alteration that are difficult to separate, and thus the individual effect of each is not always clear. To demonstrate the relative effect of regulation practices and observed climate change, we present results from a spatio-temporal study of two adjacent rivers in Northern Europe, the Kemijoki (regulated) and the Tornionjoki (pristine), with similar climate and catchment conditions. Spatial and temporal analysis was performed using daily hydrologic data from 11 gauging stations on these rivers. Flow regime alteration analysis showed that both rivers had altered significantly on a daily scale, but that there were low impacts on flow regime on a monthly scale. Daily variation in natural stream flow regime for time period of 2001–2015 was altered in both rivers when compared to the discharge during 1952–1966, but the degree of hydrologic alteration (DHA) of daily flow values for the winter months was significantly higher in the case of the regulated Kemijoki river. For river Tornionjoki, changes and variations related to climate seems to be the reason for the observed flow regime change with increased mean monthly flow for August and December. An increase in annual maximum and decrease in minimum flows was also observed in Tornionjoki, these changes however were smaller than overall changes in the regulated river Kemijoki. Based on the degree of alteration (Indicators of Hydrologic Alteration (IHA) analysis), both climate change and regulation operations affected the river regimes. About 50% of total change in observed range variability approach (RVA) in the river Kemijoki was estimated to result from regulation practices. This was confirmed by analysing data from Ounasjoki which is the pristine tributary of Kemijoki. The extent of alteration in both rivers was dependent on the spatial position of the gauging station within the river network. The impact of regulation on downstream reaches of the regulated river decreased with the increase in catchment area around that part of the river. Thus integrating daily and monthly flow data from varied spatial location on a river network, offers a useful tool for analysing flow regime conditions.

In a study on northern treatment wetlands, we examined whether P adsorption capacity remained high, with maintained P retention, after almost 20 years of loading. We also examined the most important processes for the treatment wetlands as a long-term P sink and analysed peat and water quality in the peat soils of the wetland. We tested P adsorption capacity by comparing batch test results with peat P and pore water PO 4 -P concentrations. The results showed that P adsorption capacity in the treatment wetland did not change in a 12-year period according to batch testing but the maximum sorption capacity may have been reached, although P retention level remained high after almost 20 years of wetland use. Phosphorus accumulation through peat accretion as a long-term sink was only of minor importance for P retention (0.5–7%). The main retention mechanisms for P in runoff in the wetlands were found to be filtration, sedimentation and precipitation with metals. Iron (Fe) accumulation in the surface peat indicated that its origin was peat extraction runoff. Thus long-term P retention depends on the hydrogeological setting and the quality of the water, which depends on the source. Calculations based on inlet/outlet loads from treatment wetlands may not always provide a reliable estimate of long-term P retention due to occasional P release from Fe under anaerobic conditions. Therefore new sites or sites experiencing problems with P retention should be sampled to determine the balance between peat P content and pore water PO 4 -P concentration and the availability of metals for precipitation.

Pristine peat soils are characterized by large porosity, low density and large water and organic matter contents. Drainage and management practices change peat properties by oxidation, compaction and mineral matter additions. This study examined differences in physical properties (hydraulic conductivity, water retention curve, bulk density, porosity, von Post degree of decomposition) in soil profiles of two peatland forests, a cultivated peatland, a peat extraction area and two pristine mires originally within the same peatland area. Soil hydraulic conductivity of the drained sites (median hydraulic conductivities: 3.3 × 10−5 m/s, 2.9 × 10−8 m/s and 8.5 × 10−8 m/s for the forests, the cultivated site and the peat extraction area, respectively) was predicted better by land use option than by soil physical parameters. Detailed physical measurements were accompanied by monitoring of the water levels between drains. The model ‘DRAINMOD’ was used to assess the hydrology and the rapid fluctuations seen in groundwater depths. Hydraulic conductivity values needed to match the simulation of observed depth to groundwater data were an order of magnitude greater than those determined in field measurements, suggesting that macropore flow was an important pathway at the study sites. The rapid response of depth to groundwater during rainfall events indicated a small effective porosity and this was supported by the small measured values of drainable porosity. This study highlighted the potential role of land use and macropore flow in controlling water table fluctuation and related processes in peat soils.

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.

Despite the fundamental role of river flow in determining the structure and function of lotic ecosystems, few studies have directly related features of the natural flow regime to variation in stream invertebrate assemblage composition. We classified 240 near-pristine, snowmelt-dominated Finnish streams into hydrological river types. We assessed the relationship of these types with benthic macroinvertebrate assemblage structure and examined the relative importance of hydrological variables, local-habitat variables, and geographical location in predicting variation in assemblage structure. We used a hydrological model to obtain site-specific daily discharges for a 30-y period (1981–2010) and calculated 223 flow indices based on flow index modeling tools. We used a combination of principal component and cluster analysis to classify the sites into 6 distinct hydrological types that were separated mainly by geographical location and catchment-size-related factors. Nonmetric multidimensional scaling and multire...

The Bakhtegan catchment, an important agricultural region in south-western Iran, has suffered groundwater depletion in recent years. As groundwater is considered the main source of fresh water in the catchment, especially for agriculture, monitoring groundwater responses to irrigation is important. Gravity Recovery and Climate Experiment (GRACE) satellite data can help determine water mass changes in catchments and assess water volume changes, but have been under-used to date in water resources management. In this study, we compared GRACE-derived water mass data against groundwater volume variations measured in situ. We also assessed the efficiency of GRACE-derived data in catchments smaller than the 200,000 km2 recommended area when using GRACE. For the study period (January 2002 through December 2011), the GRACE data showed a 7.6 mm annual decline in groundwater level, with a total volume loss of 2.6 km3 during the period. The in situ monthly measurements of groundwater level showed an average depletion of 10 m in catchment aquifers during the study period. This depletion rate was supported by the recorded decrease in precipitation volume, especially in the post-drought period after 2007. These results demonstrate that GRACE can be useful in groundwater resources management of catchments facing groundwater depletion and increasing water demand.

A stable isotope study of 67 kettle lakes and ponds situated on an esker aquifer (90 km2) in northern Finland was carried out in the summer of 2013 to determine the role of groundwater inflow in groundwater-dependent lakes. Distinct seasonal fluctuations in the δ18O and δ2H values of lakes are the result of seasonal ice cover prohibiting evaporation during the winter. An isotope mass balance approach was used to calculate the inflow-to-evaporation ratios (ITOT/E) of all 67 lakes during the summer of 2013 when the isotopic compositions of the lakes were approaching a steady-state. The normalised relative humidity needed in this approach came from assuming a terminal lake situation for one of the lakes showing the highest isotope enrichment. Since evaporation rates were derived independently of any mass balance considerations, it was possible to determine the total inflow (ITOT) and mean turnover time (MTT) of the lakes. Furthermore, the groundwater seepage rates of those lakes revealing no visible surface inflow were calculated. Here, a quantitative measure was introduced for the dependence of a lake on groundwater (G index) that is defined as the percentage contribution of groundwater inflow to the total inflow of water to the given lake. The G index values of the lakes studied ranged from 27.8–95.0%, revealing large differences in groundwater dependency among the lakes. This study shows the effectiveness of applying an isotope mass balance approach to quantify the groundwater reliance of lakes situated in a relatively small area with similar climatic conditions.

With climate warming, snowmelt and runoff will occur more frequently during winter months. For efficient removal of runoff loads, water pollution protection methods such as constructed wetlands must also function during winter runoff periods. This study evaluated the purification efficiency and function of constructed wetlands in treating peat extraction runoff in all seasons, using collected data on inflow and outflow concentrations and wetland properties from 14 treatment wetlands in Finland. The runoff water flows partly on top of the peat layer as surface flow and partly as horizontal subsurface flow. In three of these wetlands, seasonal ground frost depth was also observed in two winter periods. In winter, the surface peat in constructed wetlands was mostly frozen (0–42 cm depth) but in some parts of the wetland the water flowed as overland or near-surface flow. Chemical oxygen demand (COD Mn ) and ammonium nitrogen (NH 4 -N) purification efficiency varied seasonally, with NH 4 -N purification efficiency being highest during the warm summer period and COD Mn purification efficiency being lowest during summer and winter. For other water quality parameters (N tot , P tot , PO 4 -P, Fe, and SS), no influence of season was noted.

Summary Springs are unique ecosystems, but in many cases they are severely threatened and there is an urgent need for better spring management and conservation. To this end, we studied water quality and quantity in springs in Oulanka National Park, north-east Finland. Multivariate statistical methods were employed to relate spring water quality and quantity to hydrogeology and land use of the spring capture zone. This revealed that most springs studied were affected by locally atypical dolostone–limestone bedrock, resulting in high calcium, pH, and alkalinity values. Using Ward’s hierarchical clustering, the springs were grouped into four clusters based on their water chemistry. One cluster consisted of springs affected by past small-scale agriculture, whereas other clusters were affected by the variable bedrock, e.g., springs only 1 km from the dolostone–limestone bedrock area were beyond its calcium-rich impact zone. According to a random forest model, the best predictors of spring water chemistry were spring altitude and the stable hydrogen isotope ratio of the water (δ2H). Thus stable water isotopes could be widely applicable for boreal spring management. They may also provide a rough estimate of groundwater flow route (i.e., whether it is mainly local or regional), which largely determines the chemical characteristics of spring water. Our approach could be applied in other boreal regions and at larger spatial scales for improved classification of springs and for better targeted spring management.

Vast regions of the northern hemisphere are exposed to snowfall and seasonal frost. This has large effects on spatiotemporal distribution of infiltration and groundwater recharge processes as well ...

Purification efficiency of a treatment wetland for a peat extraction area in Northern Finland was studied March–October 2012. The focus was on the snowmelt season, with inflow and outflow sampled twice a day. All samples were analysed for stable isotopes of water and various water quality parameters. The wetland inflow and outflow were continuously monitored which in combination of precipitation and evaporation data allowed to study the effect of direct precipitation (dilution) and evaporation (enrichment) on the wetland water balance and water quality. The evaporated water volume was approximately 20% of the inflow on days with small inflows, whereas the proportion of precipitation was more variable. Negative correlations between hydraulic load and water quality at the outlet were found, whereas evaporation, precipitation from/to wetland had a negligible impact on outlet water quality. The observation year was rainier than normal, which complicated application of isotope techniques as the evaporation signal was weak. However, the heavy rain provided ample data on wetland performance under different flow conditions. The wetland reduced concentrations of e.g. suspended solids, phosphate-phosphorus, ammonium and iron, but reduction rate of other dissolved nutrients and organic carbon was low or negative. The observed retention of suspended solids load (28% during snowmelt, 61% during the whole observation period) shows that treatment wetlands can reduce the environmental impact of peat extraction areas.

A key question in environmental flow (EF) allocation from reservoirs is the annual distribution of flow. Flow release from reservoirs can be partly supplemented or compensated for by natural runoff from the downstream (residual) part of the catchment. Here we present a new hydrological approach to estimate the optimal intra-annual flow regime for EF which also considers water inflow from the downstream residual sub-catchment. First, the standard intra-annual regimes at downstream target points are defined for reference. This annual hydrograph is then divided into two main parts: a variable hydrograph (related to upstream of the reservoir and the point of EF release) and a residual hydrograph (associated with downstream catchment runoff). Based on the magnitude of the residual hydrograph, the allocated EF is estimated by optimization. This method provides a first estimate of the intra-annual EF regime based on hydrological data, but biological, geomorphological, and other effective components can also be included in the optimization procedure. To test the method, the intra-annual EF regime was estimated for four different points of the Kor river in southern Iran. The results showed that the best fit between the EF regime and the natural river regime at the reference point depended on the magnitude of allocated flow and the allocation site in the catchment.

Atmospheric circulation generally influences regional climate variability and thereby controls catchment hydrology and consequently transport of elements in natural riverine systems. This study examined dependencies between total organic carbon (TOC) variability in the River Oulujoki (Finland) during 1963–2011 and prominent atmospheric circulation patterns (ACPs), which manifest natural climatic conditions over Finland and control hydrological processes in the river catchment. North Atlantic Oscillation, Scandinavia, East Atlantic and East Atlantic/West Russia patterns were statistically significant ACPs affecting variations in TOC export at River Oulujoki lower basin area. In the River Oulujoki, TOC export was largely controlled by changes in TOC fluxes generated from tributaries of river and near areas to its main channel. Besides, runoff from Lake Oulujarvi slightly influenced TOC export variability in the River Oulujoki. Understanding such responses of TOC fluxes to ACPs is a useful tool for sustainable water resources planning and management on regional and local scales.

In the Boreal region, anticline eskers aquifers are recharged in upland hillslopes and water discharges in the surrounding lowlands. Organic peat soils often confine the aquifer discharge area and drainage of these confining peat layers can decrease the flow resistance in the peat soil, which may cause unintentional groundwater level drawdown. This poses a risk to groundwater bodies and their good water status in the Boreal region. To increase awareness of the risk areas and to assess potential areas for drainage restoration, a model based on geographical information systems (GIS) was developed to predict the locations of high groundwater discharge. The output of the model is a map highlighting the potential areas where groundwater is more likely to discharge. The model output was validated with stream flow data collected from two eskers located in Finland. The developed GIS model is recommended as a tool to delineate groundwater protection areas where drainage of the peat soil should not be allowed and for assessing areas where such drainage networks could be restored to protect vulnerable groundwater systems.

A combination of driving forces are increasing pressure on local, national, and regional water supplies needed for irrigation, energy production, industrial uses, domestic purposes, and the environment. In many parts of Europe groundwater quantity, and in particular quality, have come under sever degradation and water levels have decreased resulting in negative environmental impacts. Rapid improvements in the economy of the eastern European block of countries and uncertainties with regard to freshwater availability create challenges for water managers. At the same time, climate change adds a new level of uncertainty with regard to freshwater supplies. In this research we build and calibrate an integrated hydrological model of Europe using the Soil and Water Assessment Tool (SWAT) program. Different components of water resources are simulated and crop yield and water quality are considered at the Hydrological Response Unit (HRU) level. The water resources are quantified at subbasin level with monthly time intervals. Leaching of nitrate into groundwater is also simulated at a finer spatial level (HRU). The use of large-scale, high-resolution water resources models enables consistent and comprehensive examination of integrated system behavior through physically-based, data-driven simulation. In this article we discuss issues with data availability, calibration of large-scale distributed models, and outline procedures for model calibration and uncertainty analysis. The calibrated model and results provide information support to the European Water Framework Directive and lay the basis for further assessment of the impact of climate change on water availability and quality. The approach and methods developed are general and can be applied to any large region around the world., Journal of Hydrology, 524, ISSN:0022-1694, ISSN:1879-2707

Summary Water resources management is moving towards integration, where groundwater (GW), surface water (SW) and related aquatic ecosystems are considered one management unit. Because of this paradigm shift, more information and new tools are needed to understand the ecologically relevant fluxes (water, heat, solutes) at the GW–SW interface. This study estimated the magnitude, temporal variability and spatial distribution of water fluxes at the GW–SW interface using a fully integrated hydrological modelling code (HydroGeoSphere). The model domain comprised a hydrologically complex esker aquifer in Northern Finland with interconnected lakes, streams and wetlands. The model was calibrated in steady state for soil hydraulic conductivity and anisotropy and it reproduced the hydraulic head and stream baseflow distribution throughout the aquifer in both transient and steady state modes. In a novel analysis, model outputs were compared with the locations and magnitude of GW discharge to lakes estimated using field techniques. Spatial occurrence of GW–lake interaction was interpreted from airborne thermal infrared imaging. The observed GW inflow locations coincided well with model nodes showing positive exchange flux between surface and subsurface domains. Order of magnitude of simulated GW inflow to lakes showed good agreement with flux values calculated with a stable water isotope technique. Finally, time series of GW inflow, extracted as model output, showed moderate annual variability and demonstrated different interannual inflow changes in seepage and drainage lakes of the aquifer. Overall, this study demonstrated the ability of a fully integrated numerical model to reproduce observed GW–SW exchange processes in a complex unconfined aquifer system. The model-based estimates obtained for GW influx magnitude and spatial distribution, along with information on GW quality can be used to estimate ecologically relevant fluxes in future water resources management.

Lake water level regimes are influenced by climate, hydrology and land use. Intensive land use has led to a decline in lake levels in many regions, with direct impacts on lake hydrology, ecology and ecosystem services. This study examined the role of climate and river flow regime in controlling lake regimes using three different lakes with different hydraulic characteristics (volume-inflow ratio, CIR). The regime changes in the lakes were determined for five different river inflows and five different climate patterns (hot-arid, tropical, moderate, cold-arid, cold-wet), giving 75 different combinations of governing factors in lake hydrology. The input data were scaled to unify them for lake comparisons. By considering the historical lake volume fluctuations, the duration (number of months) of lake volume in different ‘wetness’ regimes from ‘dry’ to ‘wet’ was used to develop a new index for lake regime characterisation, ‘Degree of Lake Wetness’ (DLW). DLW is presented as two indices: DLW1, providing a measure of lake filling percentage based on observed values and lake geometry, and DLW2, providing an index for lake regimes based on historical fluctuation patterns. These indices were used to classify lake types based on their historical time series for variable climate and river inflow. The lake response time to changes in hydrology or climate was evaluated. Both DLW1 and DLW2 were sensitive to climate and hydrological changes. The results showed that lake level in high CIR systems depends on climate, whereas in systems with low CIR it depends more on river regime.

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.

Treatment wetlands are considered best management practice as they can remove nitrogen, phosphorus and suspended solids from peat extraction or forestry runoff. Treatment wetlands are established on intact or formerly drained peatlands after restoration of the site hydrology by ditch blocking or other methods. However, drainage changes the physical properties of peat, so the hydraulic and hydrological conditions in peatlands may change. Consequently, treatment wetlands constructed on drained areas may have short residence times, resulting in poor purification results. This study determined the hydrological and hydraulic characteristics of treatment wetlands constructed on drained peatlands by studying peat hydraulic conductivity and water distribution in 20 different wetlands in Finland. Four wetlands were studied in more detail using tracer tests, water balance and continuous groundwater measurements. More than 50% of the drained treatment wetlands studied had a lower active flow depth layer (only 10 or 20 cm) with higher hydraulic conductivity ( K ) than normally found in pristine peatlands. At 25% of the sites, K was high at all depths investigated (down to 60–70 cm). At several sites, the water was unequally distributed across the wetland surface, indicating that only part of the wetland was being used for purification. The residence time, as determined by tracer tests, varied significantly between sites. These results indicate that past drainage still influences the hydraulics of treatment wetlands.