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. 2014 Feb 15;79(1-2):114-22.
doi: 10.1016/j.marpolbul.2013.12.029. Epub 2014 Jan 4.

Microbial release from seeded beach sediments during wave conditions

Matthew C Phillips  1 , Zhixuan Feng  2 , Laura J Vogel  1 , Ad J H M Reniers  2 , Brian K Haus  2 , Amber A Enns  1 , Yifan Zhang  1 , David B Hernandez  1 , Helena M Solo-Gabriele  3
Affiliations

Microbial release from seeded beach sediments during wave conditions

Matthew C Phillips et al. Mar Pollut Bull. .

Abstract

Beach sands can sustain indigenous and introduced populations of enterococci. The objective of this study was to evaluate wave action in promoting the release of introduced bacteria. To accomplish this objective this study developed a method to assess attachment and identified conditions under which introduced bacteria are integrated into the sand. A new "shearing assay" showed that attachment of the introduced spike mimicked that of the natural sand when the spike was allowed to integrate into the sand for 24h at room temperature at a sand moisture content of 20%. Experiments in a wave flume showed that waves were capable of releasing about 60% of the total bacteria added. This suggests that for the range of wave conditions evaluated (height: 1.9-10.5 cm, period:1-2.7s), waves were incapable of releasing all of the bacteria. Further study is needed to evaluate bacteria attachment mechanisms.

Keywords: Attachment; Beach sand; Enterococci; Wave flume; Waves.

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Figures

Figure 1
Figure 1. Methods development
Approach for developing the method for seeding the sand with enterococci, points where shearing assay was used, and conceptual approach for wave flume evaluation.
Figure 2
Figure 2. Development of sand seeding method
A, Seeded sand (at a 20% moisture content and subject to overnight incubation (41°C) and at room temperature (20 °C) was most conducive to bacterial growth. B, this growth was not significantly retarded by the addition of dye into the sand. C, in testing this seeded sand with the shearing assay there was no significant difference in the percentage of bacteria released from the seeded sand, seeded sand with dye and the natural sand taken from NMDB(p=0.62). All error bars correspond to one standard deviation.
Figure 3
Figure 3. Beach base and the locations of water and sediment samples
The horizontal reference point for the water samples corresponds to the top of the beach base. Dotted lines across the top of the beach base represent sampling transects where initial and final samples of the background sand were collected. The shaded box shows the 20 cm wide strip of seeded sand. Water sample location B was always taken from above the strip of seeded sand. The seeded sand was placed in predetermined locations along the sloping beach to simulate wave interactions with the sediment on the beach.
Figure 4
Figure 4. Concentrations of dye versus levels of enterococci
Concentration of dye generally tracks the levels of ENT in the water for the first 6 minutes of waves. r=0.49, p<0.001
Figure 5
Figure 5. Percentage release of total enterococci released from the sand, normalized by the total number of released enterococci in the first 6 minutes
In this experiment ENT were observed to have a linear release from the sand as shown by the data points on the graph. The time “−2” represents the sampling before the initiation of waves but after the seeded sand had been fully inundated with water. The percent was calculated as the total number of bacteria released in the first 6 minutes, divided by the total number of bacteria released at 2-minute intervals.
Figure 6
Figure 6. Gross release of enterococci for the entire 30-minute trial
Contours of enterococci concentrations (unit of color bar scale: CFU/100 mL) in the flume water using linear interpolation between sampling locations. The magenta triangles on the right of each panel illustrate the water sampling locations. Red arrows indicate locations of seeded sand strip. The magenta line in the “no wave” control trial shows the location of waterline.
Figure 7
Figure 7. Percent released for wave flume trials and percent released for corresponding shearing assays
A. The percent released is similar between the shearing assay and wave flume for all trials. Mean is displayed as an X on each box. There was no statistical difference between the two data sets (p=0.6) B. Dotted line represents a theoretical 1:1 relationship between the percent released in the wave flume and percent released in the shearing assay. The solid line represents the linear regression for the observed relationship. The linear regression from the data is not statistically dissimilar from a 1:1 ratio and fits this theoretical 1:1 linear regression (r=0.52, p=0.08). The percentages released from sand during the wave flume and shearing assay are correlated (r=0.63, p=0.037).
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