Effects of Feral Pig (Sus scrofa) Exclusion on Enterococci in Runoff from the Forested Headwaters of a Hawaiian Watershed

Abstract

The role feral pigs (Sus scrofa) as a source of fecal contamination in Pacific Island ecosystems is not well understood. This study investigated the effects of feral pigs on enterococci (ENT) in runoff and soils of a Hawaiian forest. Seven sites were established with paired fenced/unfenced runoff plots in the Manoa watershed. Runoff was collected monthly from these plots after rain events from June 2008 to April 2009; soil ENT at each plot were also quantified. ENT in runoff were highly variable ranging from below the detection limit to >4.38 log 10 most probable number (MPN) 100 mL −1 . A repeated measures ANOVA found no overall fencing effects. This ANOVA did reveal a month by site interaction, indicating that while ENT in runoff were the highest in the wet season, this was not consistent across all sites. Soil ENT ranged from 14 to 511 MPN g −1 and differed among sites but not between fencing treatments. The only variables that were significantly correlated to ENT in runoff were runoff volume and soil ENT; slope, throughfall, soil moisture, bare soil cover, and total suspended solids in runoff were not correlated with ENT. While concentrations of ENT in runoff were highly variable across the months and sites, these forested headwaters did serve as sources of ENT to downstream ecosystems throughout the year. To minimize effects on human health, we recommend that public authorities employ greater warnings (i.e., signage) at streams and beaches in the lower reaches of this and other forested Hawaiian watersheds that are frequently used by both residents and tourists.

Soil and hydrological responses to wild pig (Sus scofa) exclusion from native and strawberry guava (Psidium cattleianum)-invaded tropical montane wet forests

“…In line with this interpretation, while no differences in runoff volume or soil erosion 407 were observed during the first two large rainfall events (December 2012 and February 2013), we 408 did observe greater soil erosion in unfenced native forest plots during the last two events 409 (November 2013 and December 2013), possibly a function of increased differences in bare soil 410 between plots (Singer et al, 1984). Using a similar setup of paired runoff plots on O'ahu Island, 411 Dunkell et al (2011b) found no significant fencing effect on runoff within the first year of plot 412 establishment. By contrast, after seven years of soil recovery, Vtorov (1993) found that soil 413 porosity outside of a pig enclosure was more than three-fold higher than within the enclosure.…”

“…In addition to their effect on infiltration and runoff, ungulates impact runoff water quality 76 by introducing pathogenic bacteria (Pavlov et al, 1992). Fecal indicator bacteria (FIB), such as 77 Escherichia coli and enterococci, are commonly used to assess fecal contamination in soils 78 (Dunkell et al, 2011b) and water (Strauch et al, 2014). Tropical soils support the growth of 79 pathogenic bacteria and their erosion can be a source of contamination to surface waters 80 (Hardina and Fujioka, 1991).…”

Climate Change and Land Use Drivers of Fecal Bacteria in Tropical Hawaiian Rivers

“…Using a space‐for‐time model system to examine the consequences of forecasted shifts in climate (decreasing MAR, increasing number of dry days) in Hawaii, we found that stream FIB increased with decreasing MAR (H1); FIB yield increased more rapidly with 24‐h rainfall in lower‐MAR watersheds (H2); and reducing % forest cover or increasing urbanization resulted in increased levels of bacteria (H3). In native tropical soils, wildlife feces augments naturally occurring bacteria, contributing to the contamination of surface waters via runoff (Dunkell et al, 2011; Fujioka et al, 1998), and it remains unclear how this influences FIB in tropical rivers or the potential for climate change to alter bacteria loading. Whereas in temperate climates drainage from septic tanks and cesspools, pasturelands, and urban runoff contribute to the bacterial loading of surface waters in deforested and urbanized watersheds (Crowther et al, 2002; Hathaway et al, 2010), few studies have quantified such impacts in the tropics or whether climate change and LULCC interact to increase contamination relative to their independent effects.…”

“…Additionally, in Hawaii the use of cesspools/septic systems, the accumulation of livestock/wildlife feces, and erosion due to deforestation drive nonpoint source runoff, impairing water quality (Viau et al, 2011a). Wildlife have the potential to substantially alter the bacterial loads of surface waters (Strauch, 2011), especially feral pigs, whose behavior (e.g., rooting and wallowing) further increases sediment and bacterial inputs (Dunkell et al, 2011). …”

Microbes in beach sands: integrating environment, ecology and public health

“…Landscape factors within the watershed can influence fecal indicator bacteria concentrations in source waters and at beaches, e.g. forested headwaters can be a source of fecal indicator bacteria to bathing waters downstream in subtropical and temperate environments (Byappanahalli et al 2003a; Dunkell et al 2011; Flood et al 2011; Frenzel and Couvillion 2002; Fujioka et al 1988; Mallin et al 2000; Whitman et al 2006). Several studies have shown that the degree of urbanization within a watershed is the strongest predictor of fecal indicator abundance, although not necessarily indicative of human fecal pollution (Flood et al 2011), because impervious surfaces can concentrate runoff laden with fecal indicators from numerous sources.…”