Ari Laurén

Trends in hydrometeorological conditions and stream water organic carbon in boreal forested catchments

Temporal trends in stream water total organic carbon (TOC) concentration and export were studied in 8 forested headwater catchments situated in eastern Finland. The Seasonal Kendall test was conducted to identify the trends and a mixed model regression analysis was used to describe how catchment characteristics and hydrometeorological variables (e.g. precipitation, air and stream water temperatures, and atmospheric deposition) related to the variation in the concentration and export of stream water TOC. The 8 catchments varied in size from 29 to 494 ha and in the proportion of peatland they contained, from 8 to 70%. Runoff and TOC concentration were monitored for 15-29 years (1979-2006). Trends and variation in TOC levels were analysed from annual and seasonal time series. Mean annual TOC concentration increased significantly in seven of the eight catchments. The trends were the strongest in spring and most apparent during the last decade of the study period. The slopes of the trends were generally smaller than the variation in TOC concentration between years and seasons and between catchments. The annual TOC export showed no clear trends and values were largely determined by the temporal variability in runoff. Annual runoff showed a decreasing trend in two of the eight catchments. Mean annual air and stream water temperatures showed increasing trends, most clearly seen in the summer and autumn series. According to our modeling results, stream water temperature, precipitation and peatland percentage were the most important variables explaining annual and most seasonal TOC concentrations. The atmospheric deposition of SO4, NH4, and NO3 decreased significantly over the study period, but no significant link with TOC concentration was found. Precipitation was the main hydrometeorological driver of the TOC export. We concluded that stream water TOC concentrations and exports are mainly driven by catchment characteristics and hydrometeorological factors rather than trends in atmospheric acid deposition.

Is the Water Footprint an Appropriate Tool for Forestry and Forest Products: The Fennoscandian Case

The water footprint by the Water Footprint Network (WF) is an ambitious tool for measuring human appropriation and promoting sustainable use of fresh water. Using recent case studies and examples from water-abundant Fennoscandia, we consider whether it is an appropriate tool for evaluating the water use of forestry and forest-based products. We show that aggregating catchment level water consumption over a product life cycle does not consider fresh water as a renewable resource and is inconsistent with the principles of the hydrologic cycle. Currently, the WF assumes that all evapotranspiration (ET) from forests is a human appropriation of water although ET from managed forests in Fennoscandia is indistinguishable from that of unmanaged forests. We suggest that ET should not be included in the water footprint of rain-fed forestry and forest-based products. Tools for sustainable water management should always contextualize water use and water impacts with local water availability and environmental sensitivity.

Iron concentrations are increasing in surface waters from forested headwater catchments in Eastern Finland

Observations of increased water colour have been made in lakes and rivers all across the northern mid-latitudes of Europe and North America, particularly during the last 10-20 yr. This water browning or brownification has been attributed to the increased organic carbon concentrations due to climate change and decreased acid atmospheric deposition. Given that iron (Fe) may also increase water colour, the contribution of Fe to water brownification has received small attention. Our aim was to study the temporal trends of Fe in forested headwater catchments in eastern Finland, where an increasing air temperature and total organic carbon (TOC) trend had been observed in an earlier study. We found a statistically significant increasing trend also in stream water Fe concentrations and a strong correlation between the trends of TOC and Fe. The average increase in TOC and Fe concentrations between 1995 and 2006 was 0.5 mg l(-1) yr(-1) (2.5%), and 34.6 μ gl(-1) yr(-1) (3.5%), respectively. These results indicate that the increased water colour or brownification in Northern Europe may not only be due to increased concentrations of organic matter but also increased concentrations of Fe. The change in precipitation and temperature conditions, particularly during late autumn and early winter periods, appeared to be the main environmental factor behind increasing Fe trends. The strong correlation between the trends of Fe and TOC indicated that the increased Fe-organic matter complexation is the mechanism behind increasing Fe trends, but further research is needed to assess the chemical forms of increased Fe that coupled with increased TOC concentrations would enhance water brownification.

Effects of increased forest productivity and warmer climates on carbon sequestration, run-off water quality and accumulation of dead wood in a boreal landscape: A modelling study

Abstract Forest productivity is expected to increase in the future owing to the use of genetically improved plant material and climate warming. Increased productivity will lead to shorter optimum rotation lengths and larger annual clear-cut areas. This study explored the likely effects of increased forest production and a warmer climate in 15 scenarios (five productivity levels and three climate conditions) on: (1) wood production, (2) carbon sequestration, (3) water quality, and (4) amounts of coarse woody debris (CWD). The effects were simulated using a set of ecosystem models incorporating the same climate and management scenarios in a hypothetical managed boreal forest landscape. Under the assumption that increased productivity is coupled to a proportional decrease in rotation length, the outputs at the landscape-level scale were briefly as follows. In each simulated climate scenario, increased productivity resulted in increases in above- and below-ground carbon sequestration, and reduced CWD accumulation, but did not have significant effects on dissolved total nitrogen (DTN) loads in run-off water. In addition, at every simulated productivity level, a warmer climate led to reductions in carbon sequestration below ground and amounts of CWD, but increases in DTN contents in run-off water. Reasons for these trends are identified and explained.

Hydraulic Properties of Mor Layers in Finland

Mor, which is the most common humus form in Finnish forests, is an important interface between the mineral soil and the atmosphere through which hydraulic processes, e.g. infiltration and evaporation, take place. Hydraulic properties, i.e. water-retention characteristics and the unsaturated hydraulic conductivity K ( ) in the mor layers of low-fertility (CT) Scots pine ( Pinus sylvestris L.) sites and medium-fertility (MT) Norway spruce ( Picea abies (L.) Karst.) sites were measured on undisturbed samples. Samples were collected from four clusters, each of which contained 3-5 stands of CT and MT sites. Water retention and K ( ) were slightly higher on MT than on CT sites. With a decrease in matric potential ( ) from -4 to -60 kPa, the mean K decreased from 8.8 2 10 -3 to 1.4 2 10 -6 m d -1 and from 6.9 2 10 -3 to 4.9 2 10 -7 m d -1 at the MT and CT sites, respectively. The main source of variation both in water retention characteristics and K ( ), was the spatial heterogeneity within a stand. K ( ) did not differ statistically between stands or between clusters within either of the site types studied.

Water protection and buffer zones: How much does it cost to reduce nitrogen load in a forest cutting?

Abstract Uncut buffer zones between clear-cuttings and water bodies can reduce export of nutrients to surface waters, but decrease in harvested stock volume result in losses of income for the landowner. Thinning in the buffer zones increases the income, but the effect of thinning on nutrient export is not well known. The FEMMA ecosystem model was applied to simulate nitrogen (N) export from a catchment with clear-cuttings and buffer zones. FEMMA is a spatially semi-distributed model calculating water and nitrogen fluxes in a scale of head-water catchments. The calibrated FEMMA model was applied to produce scenarios with different thinning intensities in buffer zones of varying dimensions. Reductions in N export achieved with buffer zones were computed for a 5-year period following the cutting. The economic current value of the stand left in the buffer zone represented an opportunity cost of the buffer zone. The unit cost of N reduction (€kg−1 N reduced) calculated from these simulations ranged from €219 to €1578 kg−1 N. A similar reduction in N export could be achieved with different combinations of buffer zone dimension and thinning intensity, but the unit costs of N reduction differed remarkably. The results indicate that cost-effective water protection can be achieved when the dimension of buffer zone and the intensity of thinning are optimized. Experimental research is warranted to verify these simulation results.

Impacts of logging residue and stump removal on nitrogen export to a stream: A modelling approach

Abstract The use of forest chips for energy can decrease net carbon emissions to the atmosphere, but harvesting logging residues and stumps may have adverse effects on the environment, including changes in nutrient export to water-bodies. The aim of this study was, with the aid of a computer model, to simulate the effects of logging residue and stump removal on nitrogen (N) export from a clear-cut area to a stream. A spatially semi-distributed FEMMA ecosystem model (tool for Forestry Environmental Management) was used to simulate N export from a catchment subject to clear-cutting and four different scenarios of logging residue and stump removal. These scenarios were compared with a conventional clear-cutting scenario, where the logging residues were left on site. Simulations suggested that the logging residue recovery does not decrease N export to the stream. In the model this was explained by a decrease in microbial immobilization, which in the case of conventional clear-cutting reduces net release of N in decomposition and mitigates the export of N. The decrease in immobilization is directly related to the removal of the woody debris from the site. Simulations suggested that harvesting of logging residues in low atmospheric N-deposition areas is not an effective strategy for reducing N loads in water-bodies.

Thermal and Aeration Properties of Mor Layers in Finland

Thermal conductivity (K T), air permeability (K a) and relative diffusivity of oxygen (ratio of oxygen diffusion coefficient in the soil to the oxygen diffusion coefficient in free air, D/D 0) were measured from undisturbed mor samples taken from low-fertility (CT) Scots pine (Pinus sylvestris L.) sites and medium-fertility (MT) Norway spruce (Picea abies (L.) Karst.) sites. K T

Restoration of nutrient-rich forestry-drained peatlands poses a risk for high exports of dissolved organic carbon, nitrogen, and phosphorus

Restoration impact of forestry-drained peatlands on runoff water quality and dissolved organic carbon (DOC) and nutrient export was studied. Eight catchments were included: three mesotrophic (one undrained control, two treatments), two ombrotrophic (one drained control, one treatment) and three oligotrophic catchments (one undrained control, two treatments). Three calibration years and four post-restoration years were included in the data from seven catchments, for which runoff was recorded. For one mesotrophic treatment catchment only one year of pre-restoration and two years of post-restoration water quality data is reported. Restoration was done by filling in and damming the ditches. Water samples were collected monthly-biweekly during the snow-free period; runoff was recorded continuously during the same period. Water quality was estimated for winter using ratios derived from external data. Runoff for non-recorded periods were estimated using the FEMMA model. A high impact on DOC, nitrogen (N) and phosphorus (P) was observed in the mesotrophic catchments, and mostly no significant impact in the nutrient-poor catchments. The DOC load from one catchment exceeded 1000kg (restored-ha)-1 in the first year; increase of DOC concentration from 50 to 250mgl-1 was observed in the other mesotrophic treatment catchment. Impact on total nitrogen export of over 30kg (restored-ha)-1 was observed in one fertile catchment during the first year. An impact of over 5kg (restored-ha)-1 on ammonium export was observed in one year in the mesotrophic catchment. Impact on P export from the mesotrophic catchment was nearly 5kg P (restored-ha)-1 in the first year. The results imply that restoration of nutrient-rich forestry-drained peatlands poses significant risk for at least short term elevated loads degrading the water quality in receiving water bodies. Restoration of nutrient-poor peatlands poses a minor risk in comparison. Research is needed regarding the factors behind these risks and how to mitigate them.

Nitrogen and Carbon Dynamics and the Role of Enchytraeid Worms in Decomposition of L, F and H Layers of Boreal Mor

Decomposition of organic material releases carbon dioxide (CO2) into the atmosphere, and dissolved organic carbon (DOC), dissolved organic nitrogen (DON) and ammonium (NH4–N) into soil water. Each of the decomposition products contributes differently to overall export of carbon (C) and nitrogen (N) to water courses. Our aim was to study the quantity and composition of the released C and N as affected by the organic material and soil fauna, represented by enchytraeid worms. We measured the release rate of carbon dioxide, and calculated the release rates for DOC and dissolved N in soil from repeated measurements of DOC and N pools during laboratory incubation of litter (L), fermented (F) and humus (H) layers of boreal forest mor. The intermediate decomposition products, DOC and DON, were characterised according to the molecule size. The release rate of the decomposition products was higher for fresh than for old organic material. The majority of N and C were released as NH4–N and CO2, respectively. The amount of extractable organic N in soil decreased by time but DON increased. Enchytraeids stimulated N mineralisation and the release of large molecule size DOC, particularly in L layer. The results suggest that organic N in extractable form biodegrades effectively, and that soil fauna have an important role in the decomposition. The results were interpreted from the water quality point of view and the implications of the results to modelling of decomposition and export of DOC and dissolved N to recipient water bodies are discussed. In the modelling context, the novelty of the study is the description of the intermediate decomposition products and the division of the dissolved organic compounds into low molecular weight and high molecular weight fractions.