Articles containing the keyword 'water table'

Five ploughed research areas from Finnish Norther Karelia were selected for comparison studies of plough ridges and untouched soil. Measurements were made at a depth of 10 cm in sample plots on both mineral and paludified mineral soil and peatland parts of these areas. In summer 1987 daily soil water matric potential was measured using tensiometers, and volumetric soil moisture content and density were determined from soil samples at two dates during the summer. Water characteristics of the core samples were also determined. On paludified mineral and peat soils the water table depth from the soil surface was measured.

The results indicated that in plough ridges matric potential was lowest. Plough ridges were also seen to dry and wet faster and to a greater degree than untouched soils. In untouched soils, soil water relations and aeration were not affected by the distance to the furrow. The effect of the plough ridge was smallest on peatland, where there was a good capillary connection from plough ridge to the ground water, if the ditches were not very effective. The soil in the ridges did not dry too much to restrict seedling growth. The untouched surface soil in poorly drained peat and paludified minear soil was, at least in a rainy growing season, often and also for long times so wet that 10% minimum air space required for good seedling root growth was not available.

The PDF includes an abstract in English.

• Mannerkoski, E-mail: hm@mm.unknown
• Möttönen, E-mail: vm@mm.unknown

The study discusses the amplitude of the simultaneous groundwater table fluctuations in different parts of pine mires, and factors influencing it. The assumption generally used in hydrological computations that the simultaneous vertical fluctuation in the groundwater table in different parts of mires are equal does not hold good in detail. Numerous cases were detected where the fluctuation at one place did not correspond to that at another site to a statistically significant degree. The main reason for the unequal fluctuation at the different sites seems to be the difference in the microtopography and in the hydraulic conductivity between the sites.

The PDF includes a summary in Finnish.

• Kurimo, E-mail: hk@mm.unknown

Altitude fluctuation of mire surface proportional to that of the groundwater table is presented for three virgin pine mires in Eastern Finland during the growing season 1982. The average amplitude of the surface fluctuation was found to be dependent on the period representing a certain type of weather, being limited to a certain maximum. The average amplitude of the surface fluctuation ranged from 18 to 45 mm; each of the mires followed a fluctuation scale of its own.

The daily fluctuation rates were low, generally 0.5–1 mm. No sudden fluctuation peaks occurred. Regularities in the surface fluctuation were caused by the duration of the period representing continuous sinking or rise of the groundwater table, and magnitude of it. The daily rate of the surface fluctuation related to that of the groundwater table was smaller in the beginning of such period than at the end of the same period. The one-directional rise or sinking of the altitude of the mire surface according to the groundwater table fluctuation is responsible for the autocorrelation of the long-term regression data.

The PDF includes a summary in Finnish.

• Kurimo, E-mail: hk@mm.unknown

The paper describes the results obtained from an investigation into the effect of ditch spacing, ditch depth and furrowing on ground water table and on development of a Scots pine (Pinus sylvestris L.) plantation on open small-sedge bog in Central Finland (60° 50’ N; 24° 20’ E), drained in 1967. The area was planted in 1968 with 2+1 Scots pine transplants, and fertilized with Y fertilizer for peat soils. The seedlings were measured in 1972.

The depth of the ground water table was greater, the narrower the ditch spacing. The water furrows shortened the duration of the high ground water and lowered the ground water table particularly in the case of ineffective drainage. The narrower the ditch spacing within the blocks, the higher were the young trees. On the other hand, the differences in the height of the trees between the ditch spacings were eliminated by the effect of the furrows.

The PDF includes a summary in English.

• Päivänen, E-mail: jp@mm.unknown

The aim of the present study was to increase the knowledge of the anaerobic conditions prevailing in virgin peat soils of different kinds, and on the fluctuation of the aerobic limit. Silver rod method was used to indicate anaerobic conditions and to locate the aerobic limit. The material included 18 peatland sample plots on treeless bogs, in pine bogs and in spruce swamps in Southern Finland. Observations of the discoloration of the silver rods and measurements of ground water level were made from 8 June to 13 August 1968.

The results show that the location of the aerobic limit is dependent of the depth of the ground water table, and usually lies 5–15 cm above the ground water table. Down to 10–20 cm below the aerobic limit, where it reaches maximum, the rate of decomposition of sulfurous organic matter is positively correlated with the distance from the aerobic limit. Deeper it gradually decreases, and in the depth of 25–35 cm no hydrogen sulphide seems to be released.

In the forested peatland types the volume of the growing stock and the increment were dependent on the depth of the aerobic limit only when nutrient content and pH of the peat was more or less constant. Where the aerobic limit was close to the ground surface but the nutrient contents were relatively high, the volume of the growing stock may be comparatively high. Birch (Betula sp.), better than the conifers, is able to stand conditions poor in oxygen. The growing stock was poor in sites where the aerobic limit was near the ground surface, but the nitrogen and phosphorus contents were high, or vice versa. Consequently, aerobic limit is of great importance as an indicator of site quality.

The PDF includes a summary in English.

• Lähde, E-mail: el@mm.unknown

The present investigation revealed that the influence of a forest cover on the water economy of the soil is very great in Finland. Cutting of the forest gave cause to a rise of the ground water table, which, when clear-cutting is in question, reached a magnitude of 20–40 cm. The water supplies of the soil increased 40–60 mm. In the winter, too, the ground water remaind at a lower level in the forest than in opening, however, the difference is rather small. Thinnings had same kind of effect as clear-cuttings, but the influence of even heavy thinnings was still relatively small.

The water supplies of the soil after felling decreased mainly due to the decrease in the interception in the canopy. When the water table is at the same level in the forest and in opening, evapotranspiration might be greater in the forest than in openings. However, when the water level is during the growing season considerably lower in the forest than in an opening, the evapotranspiration is strongly decreased in the forest, which means that more water is evaporated and transpirated from the opening than from the forest. Because the water table is at a higher level in the opening than in the forest, runoff from clear-cut areas has exceeded that from the forest. This means that the influence of felling on the water economy of the soil is actually even greater than indicated in this work.

The results mean that the influence of the forest cover makes up that of drainage. This affects the need for maintenance of ditches. On the other hand, the final cutting will rise the ground water strongly.

The PDF includes a summary in English.

• Heikurainen, E-mail: lh@mm.unknown

The present study deals with correlation between level of ground water table and water content of peat in peatlands drained for forestry. The results have been obtained partly from field studies and partly from experiments in the laboratory.

Both the field and laboratory experiments proved that a close rectilinear correlation exists between the level of the ground water table and the water content of surface peat. A given change in the level of the ground water table corresponds to a smaller change in the water content the deeper the peat layer examined is situated. The change in the water content in the surface layer (0–20 cm) in the cases studied was of such a magnitude that a change of 10 cm in the level of the ground water table corresponded to a change of about 5 volume per cent. In deeper layers the change was smaller. The state of equilibrium regulating the water content of the peat is relatively stable. It is possible that the so-called optimum drainage of a peatland for each tree species can be theoretically determined on the basis of the correlation between the water content of peat and the level of ground water table.

The method used in the study, the repeated weighing of peat samples in their original place, has proved to be very useful and decisively better than the method based on one-time samples. The experiment also indicate that the correlation can be determined with laboratory experiments.

• Heikurainen, E-mail: lh@mm.unknown
• Päivänen, E-mail: jp@mm.unknown
• Sarasto, E-mail: js@mm.unknown

Result of a survey of soils supporting forest plantations in Wisconsin in the United States indicated a close correlation between the levels of fertility of non-phreatic, coarse-textured soils and the growth of red pine (Pinus resinosa Roezl) stands aged from 15 to 32. This relationship, however was not observed in plantations established on deep-gley soils, underlain at a depth of 3–9 fl by ground water.

The survey encountered 20 red pine plantations on soils underlain by a deep ground water table accessible to tree roots thorough their contact with gley horizon or with extended capillary fringe. The average growth of the stands was 80 cubic feet/acre (5.6 m³/ha) at the age of 22 years. Thus, mensuration analysis suggested that the soils are the choice grounds for forestry enterprise. However, the analysis of soil samples showed that in many instances the soils are extremely low in mineral colloids, organic matter and nutrients. Many of the sites would be regarded as critically deficient in nitrogen, phosphorus and potassium.

The following hypothesis are suggested to explain this discrepancy:

a) The moisture content of coarse-textured non-phreatic soils remain near the wilting point during a large apart of the growing season with subsequent reduction of transpiration and uptake of nutrients. If a capillary fringe provides a supply of water for the root system, trees may derive an adequate supply of salts and exchangeable ions from comparatively infertile substrata.

b) The suitably located ground water provides adequate aeration of the surface soil layers which is not impeded by capillary fringe, increasing activity of mycorrhiza, and a mycotrophic uptake of nutrients from unweathered minerals.

c) The above effects of natural subirrigation should change the concept of soil fertility based on mere chemical analysis. The time during which the roots are engaged in active absorption appears to be of equal importance as the concentration of nutrients in available form.

The PDF includes a summary in Finnish.

• Wilde, E-mail: sw@mm.unknown
• Iyer, E-mail: ji@mm.unknown

Lowering of the ground water table is caused by decrease in the amount of water because of evapotranspiration. Evapotranspiration of a forest is determined by converting a lowering of the ground water table into a decrease in the amount of water. This paper describes a method to determine the transpiration of tree stands and ground vegetation as well as total evaporation on a Finnish drained peatland, which ground water table was relatively high, by measuring the level of the ground water table.

It was shown that in drained peatlands with relatively high ground water level, the ground water table fell during the day between about 9 a.m. and 6 p.m., and remain at approximately same level during rest of the day. The fall of ground water table was caused by transpiration of the trees and ground vegetation, and could be over 20 mm. Thus, measuring the daily lowering of ground water table can be used to estimate transpiration of the trees. When the method is applied to measuring the total evaporation of longer periods of time, also rainfall, interception, stand rainfall and stemflow have to be measured. The method is applicable only on sites with relatively high ground water level.

The PDF includes a summary in Finnish.

• Heikurainen, E-mail: lh@mm.unknown

Soil respiration readings are reported for three ameliorated peatland sites of different types, covering a period of four years, during which the sites were drained and treated with various fertilizers. Respiration is shown to increase exponentially with temperature, varying mostly in the range 100–500 mg CO² m^-2 h^-1. The changes in soil respiration followed those in surface temperature with a time-lag of approximately 3–3.5 hours. At one site, where the groundwater table dropped by about 0.5 m after ditching, soil respiration increased 2.5-fold within a few weeks, whereas at the other two sites both the fall in the groundwater table and the resultant changes in soil respiration were small.

The fertilizers tested were slow-dissolving PK, fast-dissolving PK, wood ash, slow-dissolving PK + urea, slow-dissolving PK + Nitroform (urea formaldehyde) and slow-dissolving PK + urea + a micro-element mixture. Application of fast-dissolving PK + urea led to a rapid increase in soil respiration at the site poorest in nutrients, and slow-dissolving PK to a slow increase in respiration. The greatest, steady increase of all was achieved by treatment with ash. At the sites with a higher natural nutrient content the application of fertilizers usually led to a decline in soil respiration lasting 1–2 years, after which the initial level was normally regained. Treatment with micro-elements caused an initial fall in soil respiration values in all three biotopes, followed by a pronounced increase.

The PDF includes a summary in Finnish.

• Silvola, E-mail: js@mm.unknown
• Välijoki, E-mail: jv@mm.unknown
• Aaltonen, E-mail: ha@mm.unknown

The present study deals with the ground water table in the soil of drained peatlands and with the technique used for its determination. The terms depth and height of the ground water table are defined in the paper. Because of the fact that the surface of peatlands moves under the influence of a great number of different factors, the depth of the ground water table and the height of the ground water table are not parallel concepts. The present paper concentrates on the depth of the ground water table.

Observations on the depth of the ground water table in the sample plots in 1966-67 and 1968-69 show that the maximum of the late summer usually exceeds that of the early spring, and that the minimum occurring in the period of snow melting is more clearly discernible than that of the fall. Great differences occur in the depths of the ground water table in different sample plots. These differences are due to the specific properties of the peat of different peat layers, which are expressed in terms of the ground water coefficient. The duration of the depth of the ground water table proved to be a useful way to express the long-term changes.

Four kinds of short-term fluctuations in the ground water table were observed: a) the ground water table falls during the night hours, although the rate of falling is slower than in daytime, b) the ground water table rests at the same depth during the night, whereas during the day it clearly falls, c) the descent of the ground water table is similar throughout the whole 24-hour period, d) the ground water table rises during the night hours and falls in daytime. Occurrence of these types are discussed. Typical short-term fluctuation is the fall due to evaporation in the daytime.

The third part of the paper discusses the techniques used to measure the changes in ground water table.

The PDF includes a summary in English.

• Heikurainen, E-mail: lh@mm.unknown

The aim of this study was to assess the effect of cutting of different intensities on the hydrology of drained peatland. The study concerned with measuring changes in the ground water level, throughfall, and snow cover, and specially runoff. This study focused on the phenomena that occur during the growing season. Seven sample plots were measured in an area in Central Finland which had been drained about 50 years earlier and had Scots pine (Pinus sylvestris L.) stand of uniform age.

To survey the hydrological effects of cuttings, 20%, 40% and 60% of the stand volume was removed in thinnings. In addition, one sample plot was clear-cut. During the first two years after cutting the interception diminished, and throughfall increased by 7% for the 20% thinning, by 8% for the 40% thinning and by 12% for the 60% thinning. Clear cutting increased the throughfall by 29%. The thinnings increased the depth of the snow cover the more the heavier the thinning.

Even the lightest thinning raised the ground water table, but the difference between 20% and 40% thinning was not marked. Cuttings increased runoff the greater the heavier the cutting. The hydrological changes of fellings were detrimental for the site. However, there was a marked change only between the 40% and 60% thinnings. Fertilization had a favourable effect on the hydrology of the peatland by increasing the depth of ground water table, and decreasing the throughfall.

The PDF includes a summary in Finnish.

• Heikurainen, E-mail: lh@mm.unknown

The aim of the present study was to collect information on biological activity in the topmost 30 cm peat layer in certain natural and drained peatlands of different fertility, covered by different stands.

The results showed that if the ground water table in peatland sites is located in the immediate vicinity of the ground surface (about 5-10 cm in depth), conditions are reducing, and often even anaerobic, up to the ground surface. By means of drainage the aerobic limit can be dropped to a greater depth. This will occur because of the aerobic limit closely follows the fluctuation of the ground water table.

Although, by means of drainage, the aerobic limit can be lowered to more than 50 cm in depth, rains are followed by a rise of a ground water table and the aerobic limit; hereby a change from oxidizing to reducing conditions takes place. Only by keeping the ground water table and the aerobic limit constantly at the depth of more than 50 cm is it possible to obtain oxidizing conditions in the topmost 20-30 cm peat layer. The anaerobic conditions prevent the tree roots penetrating deeper in the peat.

In reducing conditions cellulose decomposition as well as carbon dioxide release from peat samples is slower than in oxidizing conditions. The rate of cellulose decomposition, however, is essentially dependent on the nitrogen content and the acidity of the peat.

• Lähde, E-mail: el@mm.unknown

We used a process-based hydrological model SUSI to improve guidelines for ditch network maintenance (DNM) operations on drained peatland forests. SUSI takes daily weather data, ditch depth, strip width, peat properties, and forest stand characteristics as input and calculates daily water table depth (WTD) at different distances from ditch. The study focuses on Scots pine (Pinus sylvestris L.) dominated stands which are the most common subjects of DNM. Based on a literature survey, and consideration of the tradeoffs between forest growth and detrimental environmental impacts, long term median July–August WTD of 0.35 m was chosen as a target WTD. The results showed that ditch depths required to reach such WTD depends strongly on climatic locations, stand volume, ditch spacing, and peat thickness and type. In typical ditch cleaning areas in Finland with parallel ditches placed about 40 m apart and tree stand volumes exceeding 45 m³ ha^–1, 0.3–0.8 m deep ditches were generally sufficient to lower WTD to the targeted depth of 0.35 m. These are significantly shallower ditch depths than generally recommended in operational forestry. The main collector ditch should be naturally somewhat deeper to permit water outflow. Our study brings a firmer basis on environmentally sound forestry on drained peatlands.

• Hökkä, Natural Resources Institute Finland (Luke), Natural resources, Latokartanonkaari 9, P.O. Box 2, FI-00791 Helsinki, Finland E-mail: hannu.hokka@luke.fi
• Laurén, University of Eastern Finland, Faculty of Science and Forestry, School of Forest Sciences, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: ari.lauren@uef.fi
• Stenberg, Natural Resources Institute Finland (Luke), Natural resources, Latokartanonkaari 9, P.O. Box 2, FI-00791 Helsinki, Finland E-mail: leena.stenberg@luke.fi
• Launiainen, Natural Resources Institute Finland (Luke), Bioeconomy and environment, Latokartanonkaari 9, P.O. Box 2, FI-00791 Helsinki, Finland E-mail: samuli.launiainen@luke.fi
• Leppä, Natural Resources Institute Finland (Luke), Bioeconomy and environment, Latokartanonkaari 9, P.O. Box 2, FI-00791 Helsinki, Finland E-mail: kersti.leppa@luke.fi
• Nieminen, Natural Resources Institute Finland (Luke), Natural resources, Latokartanonkaari 9, P.O. Box 2, FI-00791 Helsinki, Finland E-mail: mika.nieminen@luke.fi

The amount of water in peat soil is one factor affecting its bearing capacity, which is a crucial aspect in planning peatland timber harvesting operations. We studied the influence of weather variables on the variation of drained peatland growing season water conditions, here the ground water table depth (WTD). WTD was manually monitored four times in 2014 and three times in 2015 in 10–30 sample plots located in four drained peatland forests in south-western Finland. For each peatland, precipitation and evapotranspiration were calculated from the records of the nearest Finnish Meteorological Institute field stations covering periods from one day to four weeks preceding the WTD monitoring date. A mixed linear model was constructed to investigate the impact of the weather parameters on WTD. Precipitation of the previous four–week period was the most important explanatory variable. The four-week evapotranspiration amount was interacting with the Julian day showing a greater effect in late summer. Other variables influencing WTD were stand volume within the three-metre radius sample plot and distance from nearest ditch. Our results show the potential of weather parameters, specifically that of the previous four-week precipitation and evapotranspiration, for predicting drained peatland water table depth variation and subsequently, the possibility to develop a more general empirical model to assist planning of harvesting operations on drained peatlands.

• Hökkä, Natural Resources Institute Finland (Luke), Management and Production of Renewable Resources, Paavo Havaksen tie 3, FI-90014 Oulun yliopisto, Finland E-mail: hannu.hokka@luke.fi
• Uusitalo, Natural Resources Institute Finland (Luke), Green Technology, Kaironiementie 15, FI-39700 Parkano, Finland E-mail: jori.uusitalo@luke.fi
• Lindeman, Natural Resources Institute Finland (Luke), Green Technology, Kaironiementie 15, FI-39700 Parkano, Finland E-mail: harri.lindeman@luke.fi
• Ala-Ilomäki, Natural Resources Institute Finland (Luke), Green Technology, Jokiniemenkuja 1, FI-01370 Vantaa, Finland E-mail: jari.ala-ilomaki@luke.fi

At sites with either peat or mineral soils in large areas of boreal forests, high soil-water contents hamper tree growth and drainage can significantly increase growth. Hence, areas covering about 15 × 10⁶ ha of northern peatlands and wet mineral soils have been drained for forestry purposes. Usually ditches gradually deteriorate, thus reducing their functionality as drains, and ditch-network maintenance (DNM) might be needed to maintain stand growth rates enabled by the original ditching. This article reviews current knowledge on establishing the need for DNM in boreal forest stands, subsequent growth responses, and the financial outcome of the activity. The issues covered in the review are: (i) ditching, changes in ditches over time and the need for DNM; (ii) interactions between soil water and both stand properties and stand management; (iii) ground-water level (GWL) and tree growth responses to DNM; and (iv) financial viability of DNM. Conclusions about the current understanding of issues related to DNM are drawn and implications for DNM in practice are summarized. Finally, gaps in knowledge are identified and research needs are suggested.

• Sikström, The Forestry Research Institute of Sweden (Skogforsk), Uppsala Science Park, SE-751 83 Uppsala, Sweden E-mail: ulf.sikstrom@skogforsk.se
• Hökkä, Natural Resources Institute Finland (Luke), Management and Production of Renewable Resources, P.O. Box 16, FI-96301 Rovaniemi, Finland E-mail: hannu.hokka@luke.fi