Browsing by Subject "fosfori"

In this study, the goal was to determine which nutrient, phosphorus or nitrogen, limits the phytoplankton growth at the Vanajavesi freshwater site. The aims were to detect spatial and temporal changes and find out if the wastewater treatment plant (hereafter, WWTP) located by the study site affects the nutrient concentrations and the limiting nutrient. The reliability of determining limiting nutrient by bioassays and measuring the phytoplankton response to different treatments as fluorescence was also evaluated. The study was conducted because knowledge of nutrient limitation is essential when allocating resources to reduce nutrient loading and planning other remediation practices in eutrophicated waterbodies. According to the EU Water Framework Directive, all waterbodies in the EU must be in a good ecological status by the year 2027. This goal is yet to be achieved in Vanajavesi; the ecological status of the river Vanajanreitti is poor and that of lake Vanajanselkä is moderate. The samples for bioassays were taken from five different locations. Three sampling sites were in the river and two by the lake. Based on the direction which the water flows, one of the sampling sites was before the outlet from the WWTP and the rest after it. The bioassays were carried out with the water and natural phytoplankton community taken from the study site. The experiment was conducted five times: in November, March, May, July and August. The temperature and light conditions in the incubation room were set to mimic those in Vanajavesi at each given time. Part of the preparations was to filter out the zooplankton using 50 μm plankton net. There were four different treatments: control without nutrient additions, nitrogen addition, phosphorus addition and nitrogen and phosphorus additions. Fluorescence from the 2 litre incubation bottles was measured every 1-3 days during each experiment. Chlorophyll a was determined in laboratory before and after the experiments. Nutrient concentrations were also determined before each experiment. Small seasonal and temporal changes were observed in the nutrient concentrations and the limiting nutrient. These changes were most likely due to changing seasons, effluent from the WWTP and denitrification at lake Vanajanselkä. Phosphorus limited phytoplankton growth year around at all places. At the end of the summer also nitrogen was limiting. In July co-limitation was detected in all sampling sites. In situations of co-limitation there was either no secondary limiting nutrient, or it was phosphorus. Only once, in August at the sampling point before the outlet from the WWTP, was the secondary limiting nutrient nitrogen. On average the nutrient concentrations were higher in the river than in the lake. Chlorophyll a concentrations and some nutrient concentrations were higher after the WWTP. However, no significant negative impact due to WWTP could be detected, especially at lake Vanajanselkä and the WWTP did not result in a change from phosphorus limitation to nitrogen limitation. Bioassays and the phytoplankton yield measured with a fluorometer was a reliable way of determining the limiting nutrient. Chlorophyll a concentrations verified the fluorescence results. The probe used in this study measured only the fluorescence of chlorophyll a. Even more accurate result of the phytoplankton biomass would have been obtained with a probe that measures also the fluorescence of phycocyanin, the photosynthetic pigment in cyanobacteria, because cyanobacteria has less chlorophyll a than other phytoplankton groups. As Vanajavesi is phosphorus limited or co-limited by phosphorus and nitrogen year around, reductions in phosphorus loading will likely improve the water quality. The main source of phosphorus to Vanajavesi is the nutrient loading from agricultural practises on the drainage basin. Efficient management of this diffuse loading will cause the phytoplankton biomass, especially the biomass of harmful cyanobacteria, to decrease. Nitrogen-fixing cyanobacteria is not dependent on the nitrogen concentrations in the water column, but the concentration of phosphorus. Significantly reducing the phosphorus loading is a prerequisite for the Vanajanreitti and Vanajavesi to be in a good ecological status by the year 2027.

Human-induced nutrient enrichment has led to eutrophication, which is globally a severe environmental problem in aquatic ecosystems. Eutrophication has a variety of deteriorating effects on marine ecosystems in the form of e.g., cyanobacterial blooms, bottom water hypoxia and anoxia, as well as increased fish and benthos mortality. The Baltic Sea is especially prone to eutrophication due to the combined effects of restricted water exchange and extensive nutrient loads. Nutrient enrichment reinforces primary production which further enhances organic matter remineralisation in the sediment – water interface, leading to oxygen depletion in the bottom waters. Decreased oxygen concentrations on the seafloor can lead to the release of phosphorus bound to reducible iron oxides. The so-called ‘vicious circle’ of internal loading is formed through the further enhanced nutrient release from the sediments into the water column due to the reduced bottom water conditions resulting from increased supply of organic matter into the system. However, the processes controlling phosphorus transport from land to sea through the ‘coastal filter’ remain poorly understood. In this study, sediments from Paimionlahti estuary were examined for phosphorus content and bulk elemental composition. Sedimentary phosphorus contents were determined through chemical extractions. The extracted fractions of phosphorus (P) include Fe oxide bound P (Fe-P), authigenic apatite P (Ca-P I), detrital apatite P (Ca-P II), and organic P (org-P). The fraction of Fe-P dominated in the upper sediment layers in most sites, whereas more unreactive fractions associated with P burial remained constant through sediment depth. The generally unreactive forms of P illustrated increasing trends towards open sea areas, partly explained by changes in the overall sediment composition as well as by potential differences in environmental conditions among sampling sites. The highest amounts of Fe-P were recorded in sites with the highest sediment accumulation. The results demonstrate that P from rivers is transformed and processed in the coastal zone, delaying its transport to the open sea.