Relationships between structure and function in streams contrasting in temperature

Abstract

Summary 1. We studied 10 first‐order Icelandic streams differing in geothermal influence in separate catchments. Summer temperature (August–September) ranged between 6 and 23 °C. 2. Macroinvertebrate evenness and species overlap decreased significantly with temperature whereas taxon richness showed no response. In total, 35 macroinvertebrate species were found with Chironomidae the dominant taxonomic group. Macroinvertebrate density increased significantly with temperature. Dominant species in the warm streams were Lymnaea peregra and Simulium vittatum. Algal biomass, macrophyte cover and richness were unrelated to temperature. Densities of trout (Salmo trutta), the only fish species present, reflected habitat conditions and to a lesser degree temperature. 3. Density of filter‐feeders increased significantly with temperature whereas scraper density, the other dominant functional feeding group, was unrelated to temperature. Stable isotope analysis revealed a positive relationship between δ15N and temperature across several trophic levels. No pattern was found with regard to δ13C and temperature. 4. Leaf litter decomposition in both fine and coarse mesh leaf bags were significantly correlated to temperature. In coarse mesh leaf packs breakdown rates were almost doubled compared with fine mesh, ranging between 0.5 and 1.3 g DW 28 days−1. Nutrient diffusion substrates showed that the streams were primarily nitrogen limited across the temperature gradient while a significant additional effect of phosphorous was found with increasing temperature. 5. Structural and functional attributes gave complementary information which all indicated a change with temperature similar to what is found in moderately polluted streams. Our results therefore suggest that lotic ecosystems could be degraded by global warming.

Effect of experimental and seasonal warming on litter decomposition in a temperate stream

“…This stimulation was expected since the activities of most temperate fungi and invertebrate species are stimulated by warming within the temperature range observed (Azevedo-Pereira et al 2006;Dang et al 2009;Ferreira and Chauvet 2011a, b). This stimulation is also in agreement with metabolic theory (Brown et al 2004) and with studies where litter was incubated along natural thermal gradients (Irons et al 1994;Fabre and Chauvet 1998;Swan and Palmer 2004;Friberg et al 2009;Boyero et al 2011b). Although an increase in water temperature by 10°C is over that expected for temperate woodland streams solely due to global warming (IPCC (Intergovernmental Panel on Climate Change) 2007; Morrill et al 2005), increases of this magnitude may occur under global-warming scenarios that include removal of riparian vegetation, water abstraction, or warm-water discharge from power plants (Poff and Mathews 1986;Stefan and Sinokrot 1993).…”

“…Water temperature of streams and rivers is expected to follow this increase by rising 0.6-1.0°C for each degree of increase in air temperature (Morrill et al 2005). This increase in water temperature might have strong effects on biotic communities and ecological processes (Hogg and Williams 1996;Friberg et al 2009), since species distribution, phenology, and biological activities are temperature-dependent (Parmesan and Yohe 2003;Brown et al 2004).…”

“…Correlative studies have found a positive relationship between decomposition rates of litter incubated along elevation (Fabre and Chauvet 1998), latitudinal (Irons et al 1994;Boyero et al 2011b), or geothermal gradients (Friberg et al 2009). Studies under different seasonal thermal regimes have also reported faster litter decomposition in warmer seasons (Swan and Palmer 2004;Ferreira et al 2006).…”

“…Studies under different seasonal thermal regimes have also reported faster litter decomposition in warmer seasons (Swan and Palmer 2004;Ferreira et al 2006). However, the relative sensitivity to temperature of microbial-driven and invertebrate-driven litter decomposition has rarely been discussed (but see Irons et al 1994;Friberg et al 2009;Boyero et al 2011b), despite the possibility that the two groups have distinct sensitivities to temperature (Boyero et al 2011b). In this study, we assessed the effects of experimental (*3°C) and seasonal warming (monthly mean temperature: 6-16°C) on oak leaf litter decomposition, and on the relative contributions of microbes and invertebrates to this process, in a small temperate mountain stream.…”

Longitudinal patterns of periphyton biomass in Qinghai–Tibetan Plateau streams: An indicator of pasture degradation?

“…Most of the existing research results showed that nutrient availability (Larned, 2010;Mulholland and Webster, 2010;Guariento et al, 2011;Drake et al, 2012), temperature (Friberg et al, 2009;Demars et al, 2011;Gudmundsdottir et al, 2011) and light (Fanta et al, 2010;Hill et al, 2011;Ohta et al, 2011;Stephens et al, 2012) were the factors restricting the abundance of stream periphyton. With respect to nutrient availability, no unified conclusions are recognized to date, although much research has been conducted in the past.…”