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Potential effects of elevated atmospheric carbon dioxide on benthic autotrophs and consumers in stream ecosystems: a test using experimental stream mesocosms
Author(s) -
HARGRAVE CHAD W.,
GARY KAITLEN P.,
ROSADO SAMIR K.
Publication year - 2009
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/j.1365-2486.2009.01897.x
Subject(s) - mesocosm , benthic zone , carbon dioxide , environmental science , ecosystem , environmental chemistry , autotroph , ecology , trophic level , algae , biomass (ecology) , carbon dioxide in earth's atmosphere , chemistry , biology , genetics , bacteria
Elevated atmospheric carbon dioxide ( e CO 2 ) has been shown to have a variety of ecosystem‐level effects in terrestrial systems, but few studies have examined how e CO 2 might affect aquatic habitats. This limits broad generalizations about the effects of a changing climate across biomes. To broaden this generalization, we used free air CO 2 enrichment to compare effects of e CO 2 (i.e., double ambient ∼720 ppm) relative to ambient CO 2 ( a CO 2 ∼360 ppm) on several ecosystem properties and functions in large, outdoor, experimental mesocosms that mimicked shallow sand‐bottom prairie streams. In general, we showed that e CO 2 had strong bottom‐up effects on stream autotrophs, which moved through the food web and indirectly affected consumer trophic levels. These general effects were likely mediated by differential CO 2 limitation between the e CO 2 and a CO 2 treatments. For example, we found that e CO 2 decreased water‐column pH and increased dissolved CO 2 in the mesocosms, reducing CO 2 ‐limitation at times of intense primary production (PP). At these times, PP of benthic algae was about two times greater in the e CO 2 treatment than a CO 2 treatment. Elevated PP enhanced the rate of carbon assimilation relative to nutrient uptake, which reduced algae quality in the e CO 2 treatment. We predicted that reduced algae quality would negatively affect benthic invertebrates. However, density, biomass and average individual size of benthic invertebrates increased in the e CO 2 treatment relative to a CO 2 treatment. This suggested that total PP was a more important regulator of secondary production than food quality in our experiment. This study broadens generalizations about ecosystem‐level effects of a changing climate by providing some of the first evidence that the global increase in atmospheric CO 2 might affect autotrophs and consumers in small stream ecosystems throughout the southern Great Plains and Gulf Coastal slope of North America.