Suo - Abstracts of Vol. 52, 2001

Runoff water from 75 Finnish ditch networks was sampled for chemical analysis in 1990-1992. In total, 2815 samples were analyzed. Higher mean and median concentrations of total dissolved phosphorus were observed than reported earlier. Except for phosphorus, concentration of most elements increased with increasing site fertility. No clear relationship between phosphorus concentration and the site characteristics could be detected. The median concentration of suspended solids in runoff water from old ditch networks was as low as 2.4 mg l-1.

Key words: ditch networks, peatland forests, water quality

The effects of ditch network maintenance on runoff water quality was studied at 23 sites in different parts of Finland. The study included a calibration period of 1–3 years before maintaining the ditches and six years after. No observations were made during winter. After ditch maintenance, which involves either cleaning of old ditches and/or digging of complementary new ditches, the concentrations of suspended solids in runoff water increased immediately. At sites where the ditches cut into fine-textured subsoil, runoff continued to have increased suspended solids concentrations throughout the whole six-year period. However, if the bottom of the ditches consisted of coarse mineral subsoil or peat, the annual mean concentration of suspended solids returned to pre-treatment levels in 5–6 years. Concentrations of mineral nitrogen, especially NH4-N, increased while the concentration of organic nitrogen decreased after ditch network maintenance. These changes persisted for the whole six-year period. The overall effect of these changes resulted in a slight lowering of total dissolved nitrogen concentrations. With the exception of a few sites, runoff water pH increased after ditch maintenance and remained high during the 6-year period. Concentrations of DOC decreased at all sites after ditch maintenance and was still at a low level after six years. Concentrations of base cations (Ca, Mg, K, Na) increased significantly after ditch maintenance and were still high after six years. High concentrations of Al and Fe immediately after the digging operations were observed in a few sites. Concentration of total dissolved P did not change much and tended to decrease rather than increase.

Key words: ditch maintenance, peatland, runoff quality

This study aimed at finding out the effects of maintaining ditch systems by ditch cleaning and complementary ditching on volume growth of drained Scots pine (Pinus sylvestris L.) stands. Volume growth during the first ten post-treatment years was increased by 0.16 m3 ha–1 a–1 after ditch cleaning, 0.36 m3 ha–1 a–1 after complementary ditching, and 0.48 m3 ha–1 a–1 after the combined treatment. The average growth reactions during the second five-year period were considerably higher than during the first one. No drastic reductions in stand growth, however, occurred in the untreated plots during the post-treatment period of ten years.

Key words: complementary ditching, ditch cleaning, forest drainage, peatland, Pinus sylvestris L., tree stand, volume growth

Kite aerial photography (KAP) involves the use of large kites to lift camera rigs 50–150 m above the ground. Various types of radio-controlled, single- and dual-camera systems may be employed to acquire images in visible and near-infrared portions of the spectrum. KAP has many advantages for peatland research, including: high portability, rapid setup and operation, small crew, range of suitable weather and site conditions, high-resolution images, and low cost of equipment and operation. On this basis, KAP could be utilized for multitemporal imagery throughout the growing season and from year to year to document study sites. Kite aerial photography at Endla Nature Reserve in Estonia demonstrates the potential of this method for acquiring useful images in vertical and oblique orientations. Sun glint in oblique views (toward the sun) can highlight the presence of water bodies regardless of water depth or turbidity. Color-infrared KAP would be especially useful for separating different types of vegetation cover and water bodies in peat bogs. Kite aerial photography could represent one level of observation in a multistage and multitemporal approach that involves ground study, conventional aerial photographs, and satellite imagery.

Key words: Estonia, kite aerial photography, peatland, remote sensing

Relationships between the peat nutrient concentrations and the degree of humification, the ground vegetation and the botanical composition of the peat were studied on an afforested, originally treeless mire with a wide nitrogen gradient. The afforestation was carried out in 1971 using spot sowing and spot fertilisation. A broadcast fertilisation experiment that involved six replicates with four treatments, (i) a control, (ii) PK (rock phosphate and KCl), (iii) PK+ B, Cu and (iiii) wood ash was established in 1981–82. The surface peat layers were sampled for nutrient analyses in 1995 and for peat type determinations in 1997. The ground vegetation was inventoried in 1995. In 1995, the peat total nitrogen concentration varied from 8.7 to 29.1 mg g–1 in the 0–5 cm peat layer. The total nitrogen, phosphorus and iron concentrations and the degree of humification in the peat were all positively correlated with the proportion of Carex components and with each other. The frequency of Sphagnum mosses correlated negatively but that of forest mosses positively with the peat total nitrogen concentration. Broadcast fertilisation with wood ash increased the concentrations of phosphorus, potassium, calcium, magnesium, manganese, boron, copper and zinc especially in the 0–5 cm peat layer but did not affect other peat properties or the ground vegetation.

Keywords: nitrogen, mineral nutrients, peat component, degree of humification, Carex, Sphagnum, forest mosses

An important topic among peat producers, nature conservationists and scientists is the reuse of approximately 50 000 hectares of peat production areas which will be abandoned in next ten years. Depending on the soil properties, thickness of the remained peat, geomorphology of the soil and bedrock and ground water characteristics, there are many options to choose from. The most typical reuse of those areas has been afforestration, but depending on the soil properties, the land is suitable also for agriculture of various forms, such as cereal, potato, strawberry or cranberry farming to name but a few. In lake poor areas, such as Southern Ostrobothnia, the areas can be transformed to lakes for recreation or bird hunting purposes. The most important thing is to do something since without care; these areas will transform themselves into useless bushland. The reuse is great environmental issue, but also an economical issue for distant peat producing regions of Finland. Reuse of peat production areas was discussed in a mire seminar held on February 2, 2001 in Jalasjärvi, Southern Ostrobothnia, Finland. This report briefly outlines the topics discussed in the seminar. Geological Survey of Finland has been carrying out pilot-projects, in which the soil and ground water properties of several peat production areas are surveyed by using GPS receivers and ground penetrating radar in order to find out most suitable use. The results and possible choices of reuse are visualised using GIS enabling decision making. Construction of lakes is considered important in lake-poor areas for balancing the discharge, for migrating birds and for recreation hunting. For afforestration, the large, flat peat production areas with extreme wind and illumination conditions are difficult areas, since lot of fertilizers are needed and the thin peat layer is easily burned by sun and blown away by wind. The areas are very suitable for organic farming in a way that no fertilizers have been added to the soil after the last ice age. In environmental sense, the most important principles are protection of water resources and hydrology, increasing the biodiversity and creation of sink for greenhouse gases. In order to do this, the only choices are afforestration or reintroduction of mires. However, it is also essential that infrastructure constructed for peat production (roads, ditches and electricity) could be of use after peat is lifted.

Northern wetlands are an important source of the greenhouse gas CH₄. We studied CH₄ turnover in an oligotrophic mire near the Yenisej River in West Siberia in July 1996. CH₄ emissions were determined using closed chambers. CH4 production and CH4 oxidation potentials were estimated from flask incubations. Mean CH₄ emissions from lawn and mudbottoms were 117±19 mg m^–2 d^–1 (SE; n=47). CH₄ concentrations, CH₄ production and CH₄ oxidation potentials in lawn samples were high, indicating that CH₄ oxidation might be important in controlling CH₄ emissions from this mire. Ridges showed low values in all parameters including CH₄ emissions. The area-weighted estimate for the mire was 80 mg m^–2 d^–1, which makes this an area of medium to high CH₄ emission. For the surrounding pine forest soil, a CH₄ sink of about –1 mg m^–2 d^–1 was estimated, a value similar to that in other boreal forest soils. The area-weighted estimate for ca. 360 km² of mire and forest around the site was a CH₄ emission of at least 25 mg CH₄ m^–2 d^–1 during summertime.

Keywords: CH₄ emission, CH₄ oxidation, CH₄ production, Siberia

In Finland there are approximately one million hectares of nitrogen-rich drained mires which may suffer from deficiency of potassium (and phosphorus). These site types are originally wet sedge fens with thick peat layers. The degree of deficiency of mineral nutrients varies, but it is propable that fertilizing with potassium and phosphorus would improve growth in most cases. This kind of fertilization which aims at rebalancing available nutrient stores for trees is called “repairing fertilization”. However, it is almost impossible to say when there is a question of repairing fertilization or normal fertilization meant to improve growth. This study introduced the assessment of repairing fertilization plan simultaneously with different methods to determine the need of such a fertilization. Earlier instructions emphasize visible potassium and phosphorus deficiency symptoms or needle analyses. However, these methods alone do not provide enough information to reliably determine the need of fertilization. For example the limit of severe potassium deficiency in Norway spruce needle analysis is 5.2 mg g-1 while visible deficiency symptoms will not be apparent until the value drops down to 4.0 mg g-1. In other words spruce may suffer from severe potassium deficiency long before it can be seen by human eyes. The problem of needle analysis is commonly it‘s reliability as needles are collected only from 5–10 trees per site.

The results indicate that determining the need of repairing fertilization should be based on both the mire site type (sedge fens) and the thickness of the peat layer (over 0.4–0.5 meter). Determining the need of repairing fertilization on drained mires should not be solely based on the needle analysis and visible potassium deficiency symptoms as the case has been so far.