Use of wetland buffer areas to reduce nitrogen transport from forested catchments: Retention capacity, emissions of N2O and CH4 and vegetation composition dynamics

The use of buffer areas in forested catchments has been actively researched during the last 15 years; but until now, the research has mainly concentrated on the reduction of sediment and phosphorus loads, instead of nitrogen (N). The aim of this thesis was to examine the use of wetland buffer areas to reduce the nitrogen transport in forested catchments and to investigate the environmental impacts involved in their use. Besides the retention capacity, particular attention was paid to the main factors contributing to the N retention, the potential for increased N2O emissions after large N loading, the effects of peatland restoration for use as buffer areas on CH4 emissions, as well as the vegetation composition dynamics induced by the use of peatlands as buffer areas. To study the capacity of buffer areas to reduce N transport in forested catchments, we first used large artificial loadings of N, and then studied the capacity of buffer areas to reduce ammonium (NH4-N) export originating from ditch network maintenance areas in forested catchments. The potential for increased N2O emissions were studied using the closed chamber technique and a large artificial N loading at five buffer areas. Sampling for CH4 emissions and methane-cycling microbial populations were done on three restored buffer areas and on three buffers constructed on natural peatlands. Vegetation composition dynamics was studied at three buffer areas between 1996 and 2009. Wetland buffer areas were efficient in retaining inorganic N from inflow. The key factors contributing to the retention were the size and the length of the buffer, the hydrological loading and the rate of nutrient loading. Our results show that although the N2O emissions may increase temporarily to very high levels after a large N loading into the buffer area, the buffer areas in forested catchments should be viewed as insignificant sources of N2O. CH4 fluxes were substantially higher from buffers constructed on natural peatlands than from the restored buffer areas, probably because of the slow recovery of methanogens after restoration. The use of peatlands as buffer areas was followed by clear changes in plant species composition and the largest changes occurred in the upstream parts of the buffer areas and the wet lawn-level surfaces, where the contact between the vegetation and the through-flow waters was closer than for the downstream parts and dry hummock sites. The changes in the plant species composition may be an undesired phenomenon especially in the case of the mires representing endangered mire site types, and therefore the construction of new buffer areas should be primarily directed into drained peatland areas.

Valikoiva muuttoliike Uudellamaalla

This thesis explores selective migration in Greater Helsinki region from the perspective of counterurbanisation. The aim of the study is to research whether the migration is selective by migrants age, education, income level or the rate of employment and to study any regional patterns formed by the selectivity. In the Helsinki region recent migratory developments have been shifting the areas of net migration gain away from the city of Helsinki to municipalities farther off on the former countryside. There has been discussion about Helsinki s decaying tax revenue base and whether the city s housing policy has contributed to the exodus of wealthier households. The central question of the discussion is one of selective migration: which municipalities succeed in capturing the most favourable migrants and which will lose in the competition. Selective migration means that region s in-migrants and out-migrants significantly differ from each other demographically, socially and economically. Sometimes selectivity is also understood as some individuals greater propensity to migrate than others but the proper notion for this would be differential migration. In Finnish parlance these two concepts have tended to get mixed up. The data of the study covers the total migration of the 34 municipalities of Uusimaa provinces during the years 2001 to 2003. The data was produced by Statistics Finland. Two new methods of representing the selectivity of migration as a whole were constructed during the study. Both methods look at the proportions of favourably selected migrants in regions inward and outward migrant flow. A large share in the inward flow and a small share in the outward flow is good for region s economy and demography. The first method calculates the differences of the proportions of favourably selected four migrant groups and sums the differences up. The other ranks the same proportions between regions giving value 1 to the largest proportion in inward flow and 34 to the smallest, and respectively in outward flow the smallest proportion gets value 1 and the largest 34. The total sum of the ranks or differences in proportions represents region s selectivity of migration. The results show that migration is indeed selective in the Greater Helsinki region. There also seems to be a spatial pattern centred around the Helsinki metropolitan region. The municipalities surrounding the four central communes are generally better of than those farther away. Not only these eight municipalities of the so called capital region benefit from the selective migration, but the favourable structure of migration extends to some of the small municipalities farther away. Some municipalities situated along the main northbound railway line are not coming through as well as other municipalities of the capital region. The selectivity of migration in Greater Helsinki region shows signs of counter-urbanisation. People look for suburban or small-town lifestyle no longer from Espoo or Vantaa, the neighbouring municipalities to Helsinki, but from the municipalities surrounding these two or even farther off. This kind of pattern in selective migration leads to unbalanced development in population structure and tax revenue base in the region. Migration to outskirts of the urban area also leads to urban sprawl and fragmentation of the urban structure: these issues have ecological implications. Selective migration should be studied more. Also the concept itself needs clearer definition and so do the methods to study the selectivity of migration.

Elämää keskustassa ja kaupunkiseudun reunoilla. Urbaani ja jälkiesikaupungillinen elämäntyyli asumisen valinnoissa ja arkiliikkumisessa Helsingin seudulla.

The lifestyles of people living in single-family housing areas on the outskirts of the Greater Helsinki Region (GHR) are different from those living in inner city area. The urban structure of the GHR is concentrated in the capital on the one hand, and spread out across the outskirts on the other. Socioeconomic spatial divisions are evident as well-paid and educated residents move to the inner city or the single-family house dominated suburban neighbourhoods depending on their housing preferences and life situations. The following thesis explores how these lifestyles have emerged through the housing choices and daily mobility of the residents living in the new single-family housing areas on the outskirts of the GHR and the inner city. The study shows that, when it comes to lifestyles, residents on the outskirts of the region have different housing preferences and daily mobility patterns when compared with their inner city counterparts. Based on five different case study areas my results show that these differences are related to residents values, preferences and attitudes towards the neighbourhood, on the one hand, and limited by urban structure on the other. This also confirms earlier theoretical analyses and findings from the GHR. Residents who moved to the outskirts of Greater Helsinki Region and the apartment buildings of the inner city were similar in the basic elements of their housing preferences: they sought a safe and peaceful neighbourhood close to the natural environment. However, where housing choices, daily mobility and activities vary different lifestyles develop in both the outskirts and the inner city. More specifically, lifestyles in the city apartment blocks were inherently urban. Liveliness and highest order facilities were appreciated and daily mobility patterns were supported by diverse modes of transportation for the purposes of work, shopping and leisure time. On the outskirts, by contrast, lifestyles were largely post-suburban and child-friendliness appreciated. Due to the heterachical urban structure, daily mobility was more car-dependent since work, shopping and free time activities of the residents are more spread around the region. The urban structure frames the daily mobility on the outskirts of the region, but this is not to say that short local trips replace longer regional ones. This comparative case study was carried out in the single-family housing areas of Sundsberg in Kirkkonummi, Landbo in Helsinki and Ylästö in Vantaa, as well as in the inner city apartment building areas of Punavuori and Katajanokka in Helsinki. The data is comprised of residential surveys, interviews, and statistics and GIS data sets that illustrate regional daily mobility, socio-economic structure and vis-à-vis housing stock.