Response of a shallow-water sediment system to warming

Christian Alsterberg, Stefan Hulth and Kristina Sundbäck

Limnol. Oceanogr., 56(6), 2011, 2147-2160 | DOI: 10.4319/lo.2011.56.6.2147

ABSTRACT: Effects of predicted global warming (+4°C) on the structure and function of a temperate shallow-water sediment system were studied for 1.5 months during spring (March–April), using intact sediment in a flow-through system under close to natural light conditions. Although significant effects from temperature were observed during the entire experimental period, many were rather moderate and probably a combination of both direct and indirect effects. With the exception of an earlier development of floating microalgal mats at raised temperature, dividing the autotrophic compartment into a benthic and pelagic part, autotrophic variables, such as oxygen production, biomass, and species composition of benthic microalgae did not respond to warming. However, uptake of nutrients did increase, strengthening the role of shallow-water sediments as sinks for inorganic nutrients in spring. As hypothesized, heterotrophic variables (bacterial production, meiofaunal biomass, and dark fluxes of oxygen and total alkalinity) responded more clearly to warming than did autotrophic variables. Warming is generally hypothesized to push ecosystems towards heterotrophy, but there was no support for this in the present study. Although community respiration and anaerobic mineralization increased, the system remained highly autotrophic during the entire experiment due to the photosynthetic activity of benthic microalgae. The presence of a well-developed benthic microalgal community, already in early spring, appeared to moderate the temperature response. It therefore seems that, in spring, benthic microalgae dampen ecological consequences of global warming in illuminated sediment systems by maintaining the system net autotrophic.

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