Decadal monitoring reveals an increase in Vibrio spp. concentrations in the Neuse River Estuary, North Carolina, USA

Abstract

A decade long study was conducted to investigate the ecological, biological, and temporal conditions that affect concentrations of Vibrio spp. bacteria in a well-studied lagoonal estuary. Water samples collected from the Neuse River Estuary in eastern North Carolina from 2004-2014 (with additional follow-up samples from Fall of 2018) were analyzed to determine Vibrio spp. concentrations, as well as the concentrations of inorganic and organic nutrients, fecal indicator bacteria, phytoplankton biomass, and a wide range of other physio-chemical estuarine parameters. A significant increase in Vibrio spp. was observed to occur in the estuary over the examined period. Strikingly, over this long duration study period, this statistically significant increase in total culturable Vibrio spp. concentrations does not appear to be correlated with changes in salinity, temperature, or dissolved oxygen, the three most commonly cited influential factors that predict estuarine Vibrio spp. abundance. Furthermore, shorter term (~3 years) data on specific Vibrio species (V. vulnificus and V. parahaemolyticus)show that while Vibrio spp. are increasing overall as a genus, the numbers of some key potentially pathogenic species are decreasing as a part of the total population, further supporting the concept that quantification of the entire genus is not a worthwhile use of resources toward predicting levels of specific potentially pathogenic species of public health concern. The significant increase in this concentration of Vibrio spp. in the studied estuary appears to be related to nitrogen and carbon in the system, indicating a continued need for further research.

Fig 1. Study region with ModMon sampling stations.

Fig 2. 12 month mean of log Vibrio spp. at station 70S.

Each 12-month period is from June–May. Labels indicate the year that the 12-month period began.

Fig 3. Vibrio spp. concentrations at each sampling date for station 70S.

Line is the linear regression of the data (r² = 0.20, p<0.0001).

Fig 4. Seasonal ARIMA model (1,1,1)(1,1,1) of mean monthly log Vibrio spp. data at station 70S.

Dots are actual measurements, red line represents modeled abundance, and blue lines are the 95% confidence interval.

Fig 5. Monthly six-year average of Vibrio spp. observed during the first (black line), middle (tan line), and last (red line) six years of study duration at station 70S.

Error bars are standard error of the mean.

Fig 6. 10-year monthly average Vibrio spp. abundance (symbols) and 3-month moving average (lines) during the study (blue line), and 2 (yellow line) and 5 (red line) years beyond the study.

Error bars are standard error of the means.

Fig 7. Vibrio spp. (black squares), V. vulnificus (red triangles), and V. parahaemolyticus (blue stars) concentrations at each sampling date for the last four years of study at station 70S.

Lines are the linear regression of the data for V. vulnificus (red line, r² = 0.1, p<0.05), V. parahaemolyticus (blue line, p>0.05) and Vibrio spp. (black line, p>0.05). Non-detectable samples were removed from this analysis.

Fig 8. Linear regression of water temperature and log Vibrio spp. concentration at station 70S.

Regression line = p<0.05 r² = 0.214.

Fig 9. Water temperature at station 70S in the Neuse River Estuary during each sampling date.

Slope of regression line is not significantly different than zero (p>0.05).

Fig 10. Non-linear regression of salinity and log Vibrio concentration at station 70S.

Regression line = p<0.05 r² = 0.246.

Fig 11. Linear regression of salinity and log Vibrio concentration at all stations and depths (N = 2120).

Regression line = p<0.05 r² = 0.23.

Fig 12. Salinity of station 70S over the course of the study.

Red line is LogNormal fit to data, r² = 0.165.

Fig 13. Palmer Drought Severity Index for the Neuse River Estuary during the course of the study.

Scale is reversed with negative (dry) values being the topmost part of the graph. Colors added to aid in visualization of drought index severity.

Fig 14. Linear regression of Vibrio abundance to NOX at station 70S.

Regression line is p<0.05, r² = 0.31.

Fig 15. Nitrate and nitrite at station 70S over the course of study.

Gauss non-linear fit to data (red line), r² = 0.19.

Fig 16. Regression of dissolved inorganic carbon and log Vibrio concentration at Station 70S.

Red regression line is significant (p<0.05, r² = 0.37).

Fig 17. Dissolved inorganic carbon at station 70S recorded during the duration of the study.

The slope of the linear fit of data (red line) is significantly different from zero (p<0.05, r² = 0.12).