Transport och upptag av makronäringsämnen i ytvatten : Vilka faktorer påverkar transport och upptag av makronäringsämnen i ett mindre avrinningsområde?

Sammanfattning: The availability of nutrients is the foundation of our ecosystems both on land and in the sea. The processes that control the surplus of nutrients and the biogeochemical cycle are linked to several important environmental issues and therefore important to know. At present, there is an excess of nutrients in our waters, mainly due to anthropogenic activities such as agriculture, emissions from operations or forestry. The abundance of nutrients leads to an overproduction of plant and zooplankton, which in turn creates problems such as oxygen deprivation, impaired depth of vision, changes in species composition and thus also changes in the structure of ecosystems. This study aims to increase the knowledge of which factors affect how nutrients are transported from land to sea. The focus is on the transport and uptake of macronutrients in a smaller catchment area with little anthropogenic influence. The study is based on analytical results from sampling surface water in the Forsmark area located on the coast of Uppland. The starting point has been to investigate how the availability of dissolved nitrogen, phosphorus, carbon and silicon differs in Lake Bolundsfjärden, its inflow and outflow, as well as which key factors control the mobility and transport of nutrients in the catchment area.  The study has been carried out by analysing data from previous samplings in the area. The sampling has been carried out by SKB (Svensk kärnbränslehantering AB) for approximately 20 years as part of their research on nuclear fuel disposal. Relevant parameters from the sampling results were compiled and have been statistically analyzed through Spearman's correlation tests as well as Wilcoxon signed ranked tests. The key factors that have a major impact on the uptake and transport of nutrients are temperature, alkalinity, and pH. These parameters are part of the biogeochemical cycle and vary with the seasons of a temperate climate. Silicon, nitrogen and phosphorus co-vary with several seasonal parameters, while the DOC content in surface water is only indirectly affected by the seasons mainly in the form of precipitation and snowmelt.  Over the past two decades, the annual nutrient flow has remained relatively stable for phosphorus and silicon, while nitrogen and DOC show rising trends, a likely explanation being ongoing climate change with more extreme weather.