Please use this identifier to cite or link to this item: http://hdl.handle.net/1946/27539
Geothermal energy utilization in Iceland is a growing industry in order to fulfil constantly growing energy demand. One of Iceland’s geothermal power plant is located in NE-Iceland, the 60 MW Krafla geothermal Power Plant, which currently utilizes energy from 18 boreholes. The primary objective of this study was to investigate possible effects from the effluent from a geothermal energy utilization on the aquatic ecosystem in the stream Hlíðardalslækur. I studied both spatial and temporal variations in the benthic algae and Cyanobacteria assemblages in three geothermally spring-fed streams in the Krafla geothermal area. The diversity and density of invertebrates within the same sites were also studied in September 2015 and January 2016. Periphyton accrual responses to four different nutrient enrichments were also tested in the fall of 2015.
Algae and Cyanobacteria assemblage varied significantly between sampling sites in regards to dominating genera, density and diversity. Relatively high periphyton densities characterized upstream reaches from the power plant, along with the numbers of genera and diversity being relatively high as well. Endosymbiotic diatoms (i.e. N2-fixing genera such as Epithemia and Rhopalodia) and non-N2-fixing diatoms (Caloneis, Nitzschia and Navicula) characterized the algae communities, along with the presence of Chlorophyta (Stigeoclonium and Klebsormidium). The N2-fixing Cyanobacteria, mainly Anabaena, grew spatially upstream, mainly on cobbles near the stream banks. Invertebrates were in low densities and their diversity was also rather poor. The periphyton accrual was significantly increased by adding nitrogen to the streams. There were significant changes in the algae and Cyanobacteria assemblage downstream to the power plant where microbial mats covered the stream bottom. These mats consisted only of heterocystous (N2-fixing) and non-heterocystous Cyanobacteria, as neither diatoms nor green algae seemed to thrive in that habitat. N2-fixing genera, Anabaena and Calothrix, characterized the downstream site closest to the power plant, along with the non-N2-fixing genera of Phormidium and Lyngbya. Significantly lower diversity was at sites where the microbial mats had colonized. However, densities and biomass were high. The density of invertebrates was low at the downstream site, closest to the power station with Chironomidae and other Diptera the only taxa present. Phosphorous addition increased biomass significantly and nitrogen had no effects. In general, the effects from the geothermal power plants effluent appear to be highly localized. At a site some three kilometers downstream from the power plant, numbers of taxa and diversity had increased significantly, although biomass and density usually decreased. N2-fixing diatoms and the N2-fixing genera of Anabaena were in high abundance and partly dominated the streams bottom. At the same site, Chlorophyta (e.g. Stigeoclonium and Microspora) had reappeared. The density of invertebrates were much higher at this site than it was closer to the power plant. Neither nitrogen nor phosphorous increased the periphyton accrual at this downstream site. The algal and cyanobacterial biomass along with the diversity were significantly higher at the reference site in comparison to the remaining sites, with site KR1-6 as an exception. The assemblage was mainly dominated by non-N2-fixing diatoms (e.g. Melosira and Rhoicosphenia) and various species of Navicula. The highest density of invertebrates was at the reference site. Nutrient enrichment had no significant effect on the periphyton accrual, which may indicate that the reference site constantly gains nutrients from its nearby source. Generally, algal and cyanobacterial density and biomass differed between seasons, as highest values occurred in late summer, July and September 2015. The temporal differences were also present for the invertebrates, in which density was significantly higher in September in comparison to density in January.