Moving on up: can results from simple aquatic mesocosm experiments be applied across broad spatial scales?
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Spivak AC, Vanni MJ, Mette EM
chlorophyll, experimental design, mesocosm, Nutrients, scaling, 0.004 m3, 0.02 m3, 1 m3, 5 m3, 500 m3, USA
1. Aquatic ecologists use mesocosm experiments to understand mechanisms drivingecological processes. Comparisons across experiments, and extrapolations to larger scales,are complicated by the use of mesocosms with varying dimensions. We conducted amesocosm experiment over a volumetric scale spanning five orders of magnitude (from4 L to whole ponds) to determine the generality of algal responses to nutrient enrichment.Recognising that mesocosm dimensions may affect algal growth, we also manipulated theratio of mesocosm surface area to volume (SA : V) over two levels (high versus low). Weused mesocosm tanks of similar size and construction to those commonly used in aquaticexperiments to increase the generality of our results.2. Volume was generally a stronger determinant of algal responses than mesocosm shape(i.e. SA : V). However, the effects of both volume and shape on algae were weak andexplained a small portion of the variance in response variables. In addition, there was noconsistent, directional relationship (positive or neutral) between mesocosm volume andalgal abundance (estimated by chlorophyll concentration). Combined, our findings suggestthat results from small-scale experiments, examining the direct response of algae tonutrient enrichment, can probably be ‘moved on up’ and applied to larger, more naturalaquatic systems.3. Algal response to nutrient enrichment (e.g. nutrient use efficiency and effect size) variedstrongly with time. This underscores the importance of choosing an experimentaltimescale appropriate to the biological and? or ecological process of interest.4. We compared our results to those from a recent meta-analysis of nutrient-limitationstudies that included 359 freshwater pelagic experiments, spanning a wide range ofvolumetric and temporal scales. Similar findings between this experiment and the metaanalysisindicate that algal response to nutrient enrichment varies little across spatialscales. Therefore, it is probable that results from small-scale pelagic algal nutrientlimitationexperiments are relevant to large-scale processes, such as eutrophication.
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