Kaldy JE, Brown CA, Pacella SR

Carbon limitation in response to nutrient loading in an eelgrass mesocosm: influence of water residence time

Eelgrass is a cornerstone of healthy estuaries, providing essential fish habitat and as a sentinel species for assessing nutrient impacts. Both temperature and nutrients stimulate photosynthesis. Anthropogenically increased photosynthesis, due to warming and nutrient loading, can reduce CO2 availability in the water column and lead to eelgrass loss due to a “negative carbon balance”. Consequently, plants die because their metabolism requires more carbon than is available in the water for photosynthesis or from stored reserves. Previous studies have suggested nitrate toxicity as a mechanism of mortality; here we provide an alternative explanation — extreme CO2 limitation. We suggest multiple physiological pathways that can contribute to negative carbon balance in eelgrass and highlight how water replacement rates may influence these responses.

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