Contraction,fragmentation and expansion dynamics determine nutrient availability in a Mediterranean forest stream |
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| Authors: | D von Schiller V Acuña D Graeber E Martí M Ribot S Sabater X Timoner K Tockner |
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| Institution: | 1.Leibniz-Institute of Freshwater Ecology and Inland Fisheries,Berlin,Germany;2.Catalan Institute for Water Research,Girona,Spain;3.Department of Freshwater Ecology,National Environmental Research Institute,Silkeborg,Denmark;4.Biogeodynamics and Biodiversity Group,Centre for Advanced Studies of Blanes, CSIC,Blanes,Spain;5.Institute of Aquatic Ecology,University of Girona,Girona,Spain |
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| Abstract: | Temporary streams are a dominant surface water type in the Mediterranean region. As a consequence of their hydrologic regime,
these ecosystems contract and fragment as they dry, and expand after rewetting. Global change leads to a rapid increase in
the extent of temporary streams, and more and more permanent streams are turning temporary. Consequently, there is an urgent
need to better understand the effects of flow intermittency on the biogeochemistry and ecology of stream ecosystems. Our aim
was to investigate how stream nutrient availability varied in relation to ecosystem contraction, fragmentation and expansion
due to hydrologic drying and rewetting. We quantified the temporal and spatial changes in dissolved nitrogen (N) and phosphorus
(P) concentrations along a reach of a temporary Mediterranean forest stream during an entire contraction–fragmentation–expansion
hydrologic cycle. We observed marked temporal changes in N and P concentrations, in the proportion of organic and inorganic
forms as well as in stoichiometric ratios, reflecting shifts in the relative importance of in-stream nutrient processing and
external nutrient sources. In addition, the spatial heterogeneity of N and P concentrations and their ratios increased substantially
with ecosystem fragmentation, reflecting the high relevance of in-stream processes when advective transport was lost. Overall,
changes were more pronounced for N than for P. This study emphasizes the significance of flow intermittency in regulating
stream nutrient availability and its implications for temporary stream management. Moreover, our results point to potential
biogeochemical responses of these ecosystems in more temperate regions under future water scarcity scenarios. |
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