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

Abstract

Potential shifts in rainfall driven by climate change are anticipated to affect watershed processes (e.g., soil moisture, runoff, stream flow), yet few model systems exist in the tropics to test hypotheses about how these processes may respond to these shifts. We used a sequence of nine watersheds on Hawaii Island spanning 3000 mm (7500-4500 mm) of mean annual rainfall (MAR) to investigate the effects of short-term (24-h) and long-term (MAR) rainfall on three fecal indicator bacteria (FIB) (enterococci, total coliforms, and ). All sample sites were in native Ohia dominated forest above 600 m in elevation. Additional samples were collected just above sea level where the predominant land cover is pasture and agriculture, permitting the additional study of interactions between land use across the MAR gradient. We found that declines in MAR significantly amplified concentrations of all three FIB and that FIB yield increased more rapidly with 24-h rainfall in low-MAR watersheds than in high-MAR watersheds. Because storm frequency decreases with declining MAR, the rate of change in water potential affects microbial growth, whereas increased rainfall intensity dislodges more soil and bacteria as runoff compared with water-logged soils of high-MAR watersheds. As expected, declines in % forest cover and increased urbanization increased FIB. Taken together, shifts in rainfall may alter bacterial inputs to tropical streams, with land use change also affecting water quality in streams and near-shore environments.

Modeling the Impact of Land Use Change on Basin‐scale Transfer of Fecal Indicator Bacteria: SWAT Model Performance

“…Changes in surface runoff can lead to variations in sediment and bacteria loads, as shown by several authors (Boithias et al, 2016; Ribolzi et al, 2016; Strauch, 2017), but few studies have physically simulated the chain of processes in a tropical watershed, which are listed in Table 4. This study found that the amount of precipitation was the most significant factor controlling FIB transport, as also mentioned in previous studies (Goto and Yan, 2011; Strauch et al, 2014). Figure 4 summarizes the stages of simulated bacteria transport processes.…”

Significance of beach geomorphology on fecal indicator bacteria levels

“…Canal presence was not significantly associated with exceedance levels; however, when comparing rivers and canals together, their combined significance despite distance from sampling point suggests an association with FIB contributions. Rivers and canals have potential to carry significant amounts of FIB from runoff accumulating from the inland areas (Nevers et al 2007, Byappanahalli et al 2010, Vergougstraete et al 2015) This includes influences from agricultural and urban land-uses, both of which are associated with elevated FIB levels (Strauch et al 2014, Walters et al 2011). In addition to land use, studies have also shown that riverbank sediments carry and eventually release significant amounts of FIB from their banks (Desmarais et al 2002, Brinkmeyer et al 2015).…”

Influence of Climate Extremes and Land Use on Fecal Contamination of Shallow Tubewells in Bangladesh

“…24, 25 Among the few studies on groundwater, the emphasis has been on groundwater resources. It is very rare to find a study that examines the combined effects of climate and land use on groundwater quality.…”