Landscape factors in material transport from rural catchments in Estonia
Käesoleva väitekirja tulemuseks olid uudsed järeldused Eesti valglate toitainevoogudest, eriti mis puudutab süsinikuühendite ärakande inten¬siivis¬tumise seost kliimamuutustega. Samuti analüüsib käesolev töö luha ja mineraalmaa vahelisi ökotone seni vähe käsitletud maastiku geokeemilisest aspektist. Esimesena lahkab väitekiri 21. sajandi algusaastate põllumajanduse taastumise järel toimuvat toitainete väljakande tõusu Eestis. Kokkuvõttes on inimtegevusel olnud toitainete ärakandele Eestis soovimatuid mõjusid.The present work was a field-based investigation of ecosystem processes that drive the transport of nitrogen, phosphorus and organic carbon in Estonian agricultural landscapes backed up by a literature review. The results of the review led to the conclusion that nitrogen is often determined by factors of agriculture and soil characteristics, especially moisture, controlling denitrification. Phosphorus transport were found stronger in connection with physical factors, especially flow conduits and barriers. The field-investigated riparian mire – upland redox barriers in the soil were found to be marked by corresponding vegetation boundaries in the studied Estonian till plain. Such ecotones can be observed in aerial and satellite imagery at the footslopes, revealing redox barriers and related hot spots in agricultural landscapes. Man-made drainage removes redox barriers and corresponding ecotones, making the landscape uniform and therefore vulnerable to disturbances, such as floods and droughts. The ecotones may represent functional boundaries for delineating wetlands and planning the sustainable use of agricultural landscapes. The rise of nutrient runoff from the Porijõgi and its sub-catchments during the 1997–2009 period was caused by the magnification of water discharges in the last two years and the re-intensification of agricultural land-use, although the recovery of nutrient flows fell remarkably short of expectations, probably owing to catchment retention. Export of organic carbon compounds in Estonian streams increased in the years 1992–2007, in spite of a general decrease in water discharges during that period. The main drivers of the increased dissolution of peat were the extremely low water tables deepened by man-made drainage, as revealed by close correlations with rising trends in droughts. It can be concluded that human activities have altered the matter discharges in Estonian agricultural landscapes in rather undesired ways.