Marine sulfide – bearing sediments that oxidize when in contact with oxygen and leach outelements in high concentrations to small watercourses have been a problem for many years allover the world especially around the Bothnian Bay. The purpose of this study was to furtherinvestigate the sulfur mineralogy present in acid sulfate soils in the area of Luleå, Sweden. Asecondary aim was to see if elements leach out and accumulate in an acid sulfate soil closer tothe recipient. Samples were taken in two profiles (one oxidized and one waterlogged) fromfour sites (sites A-D) and were analyzed for whole rock geochemistry. Two sites were furtherinvestigated for mineralogy in polished samples with an optical microscope, Ramanspectroscopy and SEM-EDS. Each profile consisted of three layers: oxidation zone, transitionzone and reduced zone. The oxidation zone above the groundwater table was light grey withbrown iron hydroxide staining. Parts that lied under the water table were dark grey-black within general strong odor (“rotten eggs”) due to its sulfur content. It was usually straightforwardto distinguish and separate the layers from each other directly in the field, however in somecases pH was needed for confirmation.A general feature of investigated polished samples is the presence of abundant framboidalpyrites that are common in reduced marine sediments. The transition zone was formed in suboxicconditions and this feature is reflected by the mineralogy. Many morphologies of theframboidal pyrite were observed in this layer and signs of both dissolution and formationoccur. In the sample from site C one could observe elemental sulfur in form of large (up to 50μm) euhedral crystals. In the samples with pH<4, no sulfides occur as they have been replacedby jarosite (site B). Site C lacks these sulfur-bearing hydroxides which is thought to be due toa sulfur concentration of <0.2 %. Sulfur shows extensive leaching at most sites but at site B andD1, it accumulates in the transition zone. Elements like cobalt (Co), nickel (Ni) and zinc (Zn)are leached out or are accumulated further down in the profile. Elements that could have beentransported and have accumulated in the waterlogged profiles are Co, Ni, Zn and chromium(Cr) and in some profiles also copper (Cu) and vanadium (V). / Coastal watercourses in Bottenviken: Method development and ecological restoration- A cross-border Swedish-Finnish cooperation project

The aim of this report was to investigate the potential effects of sulfide oxidation in sediments of an arctic lake, N Luossajärvi, induced by lowered water level. Lake water, potentially contaminated by metals, was pumped into a mine tailings impoundment. The water quality in the receiving water was evaluated to see if the drainage have had an effect on the water quality. Six sediment profiles were sampled. Each profile were divided into 5 cm sections and analyzed for major elements and trace metals. Water chemistry were analyzed at six sites. As, Ni and Cu had high concentrations within undrained sediments, where As levels were classified as highly contaminated (> 27 mg kg-1 dw). Trace metals had strong statistical correlation to each other indicating a common source. The PCA analyzes performed suggests that trace metals are controlled by a common factor and drained sediments showed two additional factors controlling the variance of metals. Water chemistry had overall good status, but As, Cd, Ni and Cu exceeded natural background values. Historical data on the other hand showed no statistical difference from measured values. No effects on water quality could therefore be seen after draining of the lake, proposing high precipitation of metals within the tailing or that metals is still prevailing in the drained sediments. Metal mobility were seen within the drained sediments, where only As and Cd were presumed connected to chemical weathering and where erosion and soil properties seems to be responsible for most metal mobility.