World Flux Data Set 2016
The World Flux Data Set contains a total of 49 variables (14 categorical and 35 numeric) including sediment-water fluxes of oxygen, ammonium, nitrite, nitrate plus nitrite, nitrate, dissolved inorganic phosphorus and dissolved silica (DSi) as well as sample location, date of measurement, measurement techniques, and a variety of water column and sediment characteristics (see Metadata Table 2 for full description). There were very few studies that contained data for all of these variables; most had 30 to 70% of all variables available. In addition to the general criteria indicated above, we only included data sets in our analysis that reported sampling location, literature source, date of measurement, light conditions at the sediment surface, description of the measurement technique (i.e., intact cores or in-situ chambers), stirring method, core or chamber area, and at least one sediment-water flux measurement for one of the analytes of interest. Most studies reported fluxes of several analytes for multiple time periods during a year and additional values for water column and sediment conditions. In a limited number of cases, the minimum data needed for inclusion in the data set were not reported in the paper containing the sediment flux data. In these cases we were able to obtain the required data by contacting authors or we were able to find other papers containing the needed data. The current data set contains 2879 lines of data and is also made available on the web (www.gonzo.cbl.umces.edu).
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We examined papers from 80 different journals. We included data from a several technical reports and dissertations but our focus was on the peer-reviewed literature. We examined a total of 480 documents and were able to extract net sediment flux and associated environmental data for 167 different ecosystems and distinctly different parts of large ecosystems (e.g., low, mid, and high salinity zones of Chesapeake Bay were counted as three sites). After initial inspection of sediment-water flux data from peer-reviewed publications we made a number of decisions regarding criteria for inclusion in the database and subsequent analyses. First, we only included flux measurements made using intact sediment cores or in-situ chambers with incubations taking place either in-situ, on shipboard or in a laboratory setting; flux estimates derived from digenetic models based on pore water nutrient concentration gradients were not included. Second, only flux measurements made in the dark were included. We also did not include flux data if macrophytic plants (e.g., seagrasses or macroalgae) were contained in the incubation chamber. In addition, our data set was limited to sites with water depths less than 100 m to focus on estuarine and coastal systems. We did include data from a few deeper sites for comparative purposes, and because a few of these were also of historical and pioneering interest.