Kurth Perttu

Salix vegetation filters for purification of waters and soils

Abstract During recent years it has become obvious that it is both environmentally and economically appropriate to use vegetation filters of short rotation willows ( Salix spp.) to purify waters and soils. Swedish and Polish experiences of vegetation filter efficiencies have been demonstrated in several laboratory, field lysimeter and full-scale experiments. However, there are still many questions to be answered; for example, how the uptake and allocation mechanisms of heavy metals and recalcitrant organic constituents function, or which maximum doses are possible in a particular situation without any risk of leaching losses. During the past two decades of integrated research in Sweden on plant nutrition it has been demonstrated that willows have the capacity for efficient uptake both of macro and micro nutrients, which is reflected in their high productivity. This paper presents results on how vegetation filter stands of willow, irrigated with municipal wastewater, can function as purification plants while at the same time producing fuel wood. This two-fold utilisation benefits both the environment (e.g. with less air pollution from wood compared with fossil fuels) and the economy (by combining wastewater treatment and fuelwood production). Treatment plants for wastewater purification using various types of vegetation filters have been used both in Poland and Sweden. The Polish experience has been in three sites, namely the Wroclaw experiment, the Zoo at Oliwa near Gdansk, and Turwia near Poznan. In Sweden both nutrient and heavy metal uptake have been followed incorporating the whole process chain from establishment, cultivation and harvesting of the wastewater-irrigated willows to the utilisation of the wood in heating plants.

Economics of using municipal wastewater irrigation of willow coppice crops

Abstract Until now, treatment of municipal wastewater in Sweden has mainly consisted of removal of phosphorus and easily biodegradable organic substances. Most of the nitrogen has been released in the water phase to the recipients. The recently introduced legal requirements to remove also nitrogen have encouraged the recirculation approach, meaning that, before chemical phosphorus precipitation, municipal wastewater can be used as an adequate nutrient resource for biomass production. The general aim of this paper is to illustrate a realistic way of handling and utilising this resource in a recirculation system, applying a combination of waste water treatment and biomass production. The economic calculations (based on nitrogen, which is a topical problem at the treatment plants) show that the costs for a conventional technical system for removal of nitrogen and phosphorus in wastewater (70–180 SEK (kgN) −1 ) (1 USD = 6.70 SEK) can allow a good margin for investment, operation and management of an irrigation system for wastewater treatment in willow cultivation. The calculations show that treatment costs in willow cultivations vary depending on type of system and size. Nitrogen application rate also has a major impact on costs.

Environmental justification for short-rotation forestry in Sweden

Abstract Short rotation forestry in its present context deals mainly with willows and to some extent with alders and poplars. The aim of this paper is to present and discuss which direct and indirect environmental factors that are improved in such a way that there is a clear justification for promoting growth and use of short-rotation forestry in Sweden. It is clear that willow cultivation promotes biodiversity, if established and managed correctly, compared with conventional agriculture and forestry. Its capacity to efficiently take up nutrients and heavy metals (including cadmium) is shown in several experiments. In this respect, willow can be used as a vegetation filter for wastewater treatment instead of conventional treatment plants. Calculations have shown that the economy of such filters is more favourable than that of conventional plants, at least for societies up to 2000 person equivalents (pe). SRF crops, used for heating purposes, are carbon dioxide neutral and also reduce many of the air-polluting components compared with fossil fuels. The conclusion, therefore, must be that there are several justifications for growing and using SRF, not least as substitution for fossil fuels.

Environmental and hygienic aspects of willow coppice in Sweden

Willow coppice of various Salix spp. has been shown to be a good alternative to fossil fuels both environmentally and economically. Willow stands have also been shown to be adaptable as vegetation filters in order to purify waters and soils. The purification efficiency of willow vegetation filters has been demonstrated in several countries, e.g. Sweden, Poland, Denmark, and Estonia. However, there are still many questions to be answered: for example, what are the mechanisms behind the uptake and allocation of heavy metals and recalcitrant organic constituents, which maximum doses are possible in a particular situation without risks for leakage, and how are hygienic aspects influenced when using vegetation filters. The aim of this paper is to point out some relevant facts concerning willow coppice in general and willow vegetation filters in particular. More specifically, the paper presents and discusses the direct and indirect factors that are improved in such a way that there is a clear benefit of short-rotation forestry. For example, willow cultivations enhance biodiversity compared with conventional agricultural crops and monospecific conifer plantations. They have a pronounced capacity to take up nutrients and heavy metals (including cadmium). The economy is favourable regardless whether the coppice is used as biofuel or as a vegetation filter. The conclusion is that the growing and use of willow coppice is beneficial for the environment and may come to play an important role in a society based on recycling principles.

Effects of nutrient supply and soil cadmium concentration on cadmium removal by willow

Abstract This investigation studied the effect of an increased biomass production as a result of fertilization and an elevated Cd concentration in the topsoil on concentration and amount of Cd in two clones of Salix (81090 and 78183). The experiment was conducted over a three year period using 200-dm 3 lysimeters filled with clay soil. A liquid fertilizer containing all essential macro- and micronutrients in balanced proportions by weight was applied at two rates according to growth. The lower rate corresponded to 0, 20 and 20 kg N ha −1 during years 1, 2 and 3, respectively, while the higher rate was 30, 60 and 60 kg N ha −1 for the same period. The Cd levels in the topsoil were an initial content of 0.3 mg Cd (kg dw soil) −1 and 0.6 mg Cd (kg dw soil) −1 after addition of CdSO 4 . Biomass production increased significantly due to fertilization. In general, this increase in biomass resulted in a higher Cd amount in the stem. However, the magnitude was small and only statistically significant in some cases, mainly because increased biomass also resulted in a lowered Cd concentration due to an effect of biological dilution. Addition of Cd to the topsoil resulted in higher Cd concentrations and total Cd amounts (concentration×biomass) in the Salix plants. In most cases the increase in total stem Cd amount was 40–80% of the increase in soil Cd concentration, although a directly proportional increase was observed occasionally. Clone 81090 had higher concentrations and total amounts of Cd in the stems than clone 78183, while clone 78183 produced more stem biomass. The leaves had the highest Cd concentrations, but the total amounts of Cd were largest in the stems.

Transport and retention of bacteriophages in two types of willow-cropped lysimeters.

Abstract Irrigation and fertilization of short‐rotation willow coppice with wastewater is a new way of reusing wastewater in Sweden. To evaluate the possible impact of viruses on groundwater quality, the transport and retention of the bacteriophage Salmonella Typhimurium type 28B were studied in two types of willow‐cropped field lysimeters containing clay or sand soil. Phages were applied to the soil surface and moderate irrigation was done daily under field‐like conditions. In the clay, soil rapid transport of bacteriophages was recorded with breakthrough at 1,2‐m depth after 2–24 hours indicating macropore flow through the soil. Phage transport through the sand soil varied considerably, but was in general much slower and the phage retention much higher compared with the clay soil. The willow plants were not found to facilitate phage leaching. Instead, the results indicate the presence of phage retaining processes in the rhizosphere.

Model for Energy Exchange of a Pine Forest Canopy

ABSTRACT The CANOPY model describes energy exchange in a sparse pine forest stand at Jadraas, central Sweden in order to evaluate simple formulas for regional forest evapotranspiration. It incorporates latent and sensible heat exchange, long- and shortwave radiation balance, heat conduction and storage in trees and ground, and interception of precipitaion and dew. Self-sustained modules for different parts of the system are connected through the main program. This program structure enables each process to be studied separately, incorporation of various degrees of interaction, and direct comparison of different theories for the various processes. Required driving variables, given with a resolution of an hour or less, are global radiation, atmospheric longwave radiation, air temperature, relative humidity, wind speed, and precipitation. Simulation results indicate that penetration of shortwave radiation is more governed by gaps in the canopy than by reflection and transmission properties of the crowns. Evapotranspiration is almost fully determined by the surface (i.e., stomatal) resistance. This resistance is successfully predicted as a function of global radiation and vapour pressure deficit using a semiempirical equation with physiological basis. The aerodynamic regime of the forest is important only in the case of dew or precipitation. A successful prediction of interception is therefore necessary. Additional index words : Evaporation, interception, latent heat flow, longwave radiation, sensible heat flow, shortwave radiation, stomatal resistance, transpiration.

Simple calculation of extinction coefficient of forest stands

Abstract A method to determine the extinction coefficient without extensive radiation measurements is proposed. The crown density, which is a necessary parameter for estimation of sun path length within the canopy, is determined by the use of an instrument similar to the Cajanus cylinder. Sky obscuration factors (SOF) at different solar elevations are estimated from fish-eye photographs. The photographs are also used to determine the relative amount of completely transparent and completely opaque parts of the canopy. Combination of the results from these investigations makes it possible to calculate the extinction coefficient. The calculations are tested against measurements of short-wave radiation above and below a Scots pine canopy. For a sparse stand such as this, the calculations are quite sensitive to the determination of SOF. At ground level 35% of the radiation comes through the obstructed part of the canopy when the solar elevation is 45°.

Spatial variation in above-ground growth in unevenly wastewater-irrigated willow Salix viminalis plantations

Abstract In several Swedish wastewater treatment plants, an improved level of water treatment has been achieved through irrigation of short-rotation willow ( Salix viminalis ) coppice (SRWC) with secondary or tertiary treated wastewater. The spatial variation in above-ground growth in two unevenly wastewater-irrigated SRWC fields in southernmost Sweden was measured during 3 consecutive years. Wastewater was distributed on the soil surface through pipes with emitters spaced at distances varying from 10 to 21 m. During the first year of irrigation, a very marked gradient in growth developed, with stools (i.e. resprouted stubs) standing within 2 m of wastewater emitters growing several times faster than those standing 5 m or more away. This situation prevailed after three growing seasons with wastewater irrigation, indicating that any redistribution of plant roots towards the emitters was insufficient for a spatial levelling of the growth. We conclude that, in order to promote growth and fully utilize the treatment potential of SRWC, wastewater should be applied fairly evenly, i.e. through emitters at spacings of less than 5 m.

Ecological, biological balances and conservation

The scientific work within the activity “ecological/biological balances and conservation” is summarised in this report. The aims of the activity during its existence between 1992 and 1994 have been to: i) arrange a workshop and publish the presentations on the environmental aspects of energy forest cultivations, ii) perform joint scientific work together with the activity group on “biological disposal of wastewaters and sludges”, that is closely related to environmental problems, and iii) produce ecological guidelines concerning energy forestry, suitable for advisers and farmers dealing with bioenergy problems. The most important results from the workshop were the environmental benefits from energy forestry when compared with intensive agriculture and forestry. Energy forestry has positive influence on the carbon balances, nutrient recycling, and soil sustainability. The effects are also positive on the natural flora and fauna, which in most cases are enriched when compared with agricultural crops. From the joint efforts of the two activities the main result was a study tour, conference and workshop, concentrating on biological purification systems. The most promising system seems to be the vegetation filters of short rotation coppice. The report on ecological guidelines contains a number of ideas and recommendations for establishment, management and harvesting of energy forests in an environmentally acceptable way. It gives also advice on how to locate the stands to minimise the risk of nutrient leakage from arable land.