Effects of cooling water discharge on the structure and dynamics of epilithic algal communities in the northern Baltic

Abstract

The Forsmark Biotest Basin is a shallow coastal ecosystem that receives brackish cooling-water discharge from a nuclear power plant. The effects of the discharge on epilithic algal communities were investigated by analysing samples taken every third week throughout one year at 11 sites differentially affected by temperature and/or flow rate enhancement. Community variation was summarized in a canonical correspondence analysis (CCA) of species abundances as a function of site and date. The temperature increase favoured blue-green algae at the expense of red and brown algae. Blue-green algae were however abundant in summer in stagnant water, whether heated or not, and some red and brown algae became abundant in winter in heated sites with flowing water. Green algae and diatoms increased in biomass in the heated sites, but not in relative cover-abundance. The absence of ice and snow cover at sites with heated and/or flowing water caused autumn species to persist into winter, because of the higher light intensity (compared with natural conditions) and the absence of the mechanical abrasion by ice. The thermal discharge lowered species diversity (Shannon-Weaver index) both in summer and winter at sites with flowing water, but not at sites with quiescent or stagnant water. CCA showed alternate periods of stability and rapid change within the seasonal cycle. Individual species were placed according to their optimum; red and brown algae in winter/spring, green algae in spring/summer, blue-green algae in summer, and diatoms at various times. Exceptions to this pattern were species endo-or epiphytic on species of a different group. Analysis of the effects of temperature, flow rate and ice cover on the seasonal pattern of particular species showed that different species respond in individualistic ways to different combinations of these environmental variables. Introductionprevent an ice cover from forming in areas where this would normally occur. The elimination of ice Power stations that use cooling water to discharge and snow cover makes more light available during waste thermal energy modify the aquatic environwinter, and removes the usual mechanical abradment in their discharge area by increasing water ing effect of the ice. Each of these environmental temperature and flow rate. The faster flow can changes has the potential to affect the composialso increase nutrient supply, and the combition, structure and dynamics of aquatic econation of increased temperature and flow rate can systems.

Summer disease inParazoanthus axinellae(Schmidt, 1862) (Cnidaria, Zoanthidea)

“…Regarding cyanobacteria, massive blooms are generally related to nutrient enrichment, but a temperature increase was also reported as a factor enhancing mat development (Tison et al 1981;Whitton & Potts 1982;Snoejis & Prentice 1989). In our case, the increase in sea water temperature was concomitant to the development of cyanobacterial mats.…”

Warming leads to higher species turnover in a coastal ecosystem

“…One sample was fixed with 70% ethanol and later used for the preparation of permanent slides for diatom identification. The total % cover of the phytobenthos was estimated on a 1–9 cover scale (Snoeijs & Prentice, 1989), separating cover 76–100% (9), 51–75% (8), 26–50% (7), 11–25% (6), 6–10% (5), 1–5% (4) and < 1% (1–3). In the latter category, score 3 was given for more than 10 individuals present, 2 for 6–10 individuals, and 1 for 1–5 individuals.…”

“…This temporal flume comprises anomalies from 0 to + 9 °C, thus comprising the entire range of future temperature predictions for the next century (IPCC, 2007). The impacts of temperature and other environmental factors on the community composition of each of the three functional groups were previously published by Snoeijs & Prentice (1989) and Snoeijs (1989a, b). However, none of these studies addressed the consequences of warming for species richness and species turnover.…”

Photosynthesis, carbon uptake and antioxidant defence in two coexisting filamentous green algae under different stress conditions

“…They cause nuisance blooms in lakes and shallow marine areas when general conditions for algal growth become favourable, e.g. by increased nutrient availability (Kamer et al 2001, Gordillo et al 2003 or increased water temperature (Snoeijs & Prentice 1989). In a wide ecological sense, these shortlived, fast-growing easy colonisers are classified as r-strategists.…”