Scaling-up in estuaries: The Feasibility of using small scale results to draw large scale conclusions

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Title: Scaling-up in estuaries: The Feasibility of using small scale results to draw large scale conclusions
Author: Scheiner, Christopher
Abstract: Estuarine ecosystems are dynamic, heterogeneous ecosystems that are increasingly impacted by human activities, particularly excess nutrient loading and the resulting eutrophication. Much of the descriptive research investigating large-scale eutrophication is performed using field surveys and small-scale, manipulative microcosm experiments. To investigate confounding effects of scale and heterogeneity, we conducted a large-scale field survey of benthic conditions in West Falmouth Harbor (WFH), Cape Cod, Massachusetts, and compared our results to those observed in microcosm studies that utilized sediments and macrofauna from WFH. We used geographic information systems to estimate field condition heterogeneity and design an appropriate sampling strategy, and geostatistical interpolation methods to construct a dataset for the whole estuary based on our disparate sampling stations. Macroinvertebrate distribution was patchy, with somewhat lower densities than were used in experiments. The range of oxygen consumption rates (field 1.1-5.4; microcosm 1.0-9.3 mmol m-2 h-1) and benthic chlorophyll a (field 16-218; microcosm 30-263 mg m-2) were loosely comparable between field and microcosms. Porewater ammonium was higher in the microcosms (field 0-84; microcosm 28-1690 μM), particularly in experimental treatments without animals. The presence of macroinvertebrates in microcosms, especially the sipunculan Phascolopsis gouldii, resulted in better agreement, implying that the degree to which biological conditions approximate reality dictates how closely physico-chemical conditions follow suit. Measures of water depth and seagrass presence compared well to independent surveys, suggesting that sampling methods were adequate. Root mean square errors of the interpolated surfaces were large for most sampled conditions; increasing sampling resolution and adjusting sample collection strategies to account for macroinvertebrate habitat preferences should result in more accurate predictions. Our results have important implications for studies in soft-bottom estuaries, as they validate the use of microcosms to evaluate the relationship between patterns of species distribution and the ensuing system-level processes.
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Date: 2011-05-13

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