Hysteresis effects in organic matter turnover in a tropical floodplain during a flood cycle

Tropical inland waters are increasingly recognized for their role in the global carbon cycle, but uncertainty about the effects of such systems on the transported organic matter remains. The seasonal interactions between river, floodplain, and vegetation result in highly dynamic systems, which can exhibit markedly different biogeochemical patterns throughout a flood cycle. In this study, we determined rates and governing processes of organic matter turnover. Multi-probes in the Barotse Plains, a pristine floodplain in the Upper Zambezi River (Zambia), provided a high-resolution data set over the course of a hydrological cycle. The concentrations of oxygen, carbon dioxide, dissolved organic carbon, and suspended particulate matter in the main channel showed clear hysteresis trends with expanding and receding water on the floodplain. Lower oxygen and suspended matter concentrations prevailed at longer travel times of water in the floodplain, while carbon dioxide and dissolved organic carbon concentrations were higher when the water spent more time on the floodplain. Maxima of particulate loads occurred before highest water levels, whereas the maximum in dissolved organic carbon load occurred during the transition of flooding and flood recession. Degradation of terrestrial organic matter occurred mainly on the floodplain at increased floodplain residence times. Our data suggest that floodplains become more intense hotspots at prolonged travel time of the flood pulse over the floodplain.ISSN:0168-2563ISSN:1573-515

Relationship between inferred penetration depth and the hydrophobicity (log K_ow) of the PAHs.

<p>K_ow = Concentration in octanol phase/Concentration in aqueous phase. The K_ow values for the PAHs were retrieved from <a href="http://www.env.gov.bc.ca/wat/wq/BCguidelines/pahs/pahs-01.htm" target="_blank">http://www.env.gov.bc.ca/wat/wq/BCguidelines/pahs/pahs-01.htm</a>.</p

Hysteresis effects in organic matter turnover in a tropical floodplain during a flood cycle

Tropical inland waters are increasingly recognized for their role in the global carbon cycle, but uncertainty about the effects of such systems on the transported organic matter remains. The seasonal interactions between river, floodplain, and vegetation result in highly dynamic systems, which can exhibit markedly different biogeochemical patterns throughout a flood cycle. In this study, we determined rates and governing processes of organic matter turnover. Multi-probes in the Barotse Plains, a pristine floodplain in the Upper Zambezi River (Zambia), provided a high-resolution data set over the course of a hydrological cycle. The concentrations of oxygen, carbon dioxide, dissolved organic carbon, and suspended particulate matter in the main channel showed clear hysteresis trends with expanding and receding water on the floodplain. Lower oxygen and suspended matter concentrations prevailed at longer travel times of water in the floodplain, while carbon dioxide and dissolved organic carbon concentrations were higher when the water spent more time on the floodplain. Maxima of particulate loads occurred before highest water levels, whereas the maximum in dissolved organic carbon load occurred during the transition of flooding and flood recession. Degradation of terrestrial organic matter occurred mainly on the floodplain at increased floodplain residence times. Our data suggest that floodplains become more intense hotspots at prolonged travel time of the flood pulse over the floodplain.ISSN:0168-2563ISSN:1573-515

Calculated penetration depths for oil concentrations and PAH measured in our Short-Column Experiment one in the presence of Corexit.

<p>Depths were extrapolated from the of PAH concentrations in the sediment sections assuming an exponential trend. Anthracene data did not allow calculation of a trend due to large scatter of data.</p

Setup of the Short-Column Experiment.

<p>Clean seawater, crude oil dispersed by sonication, or crude oil dispersed by Corexit and sonication were flushed through the sand columns by gravity. The effluent of the columns was collected as a time series in 4 vials each.</p

Results from the in-situ chamber incubations.

<p>Left pane: chamber experiment 1. No dispersant was applied. Right pane: Results from chamber experiment 2. The DOC measurements were less sensitive than the fluorescence measurements and included all dissolved organic carbon. Error bars depict standard error.</p

PAH concentrations in seawater after the addition of oil or oil and Corexit.

<p>PAH concentrations were measured in the seawater 24 h after the addition of Deepwater Horizon Crude oil or addition of the same amount of oil with Corexit. Note logarithmic Y-axis scaling.</p

Composition of the percolating water in the Short- and Long-Column Experiments.

<p>The long columns were subsequently flushed with an additional 300 mL of clean artificial seawater (in parenthesis).</p

Cumulative release of acenaphthylene and chrysene as a function of the volume of water released from the columns.

<p>Triangles indicate the first experiment, circles the duplicate. The white symbols represent the control experiments, the grey symbols the experiments with oil (treatment I), and the orange symbols the experiments with oil and dispersant (treatment II).</p