Microbes in Beach Sands: Integrating Environment, Ecology and Public Health.

Beach sand is a habitat that supports many microbes, including viruses, bacteria, fungi and protozoa (micropsammon). The apparently inhospitable conditions of beach sand environments belie the thriving communities found there. Physical factors, such as water availability and protection from insolation; biological factors, such as competition, predation, and biofilm formation; and nutrient availability all contribute to the characteristics of the micropsammon. Sand microbial communities include autochthonous species/phylotypes indigenous to the environment. Allochthonous microbes, including fecal indicator bacteria (FIB) and waterborne pathogens, are deposited via waves, runoff, air, or animals. The fate of these microbes ranges from death, to transient persistence and/or replication, to establishment of thriving populations (naturalization) and integration in the autochthonous community. Transport of the micropsammon within the habitat occurs both horizontally across the beach, and vertically from the sand surface and ground water table, as well as at various scales including interstitial flow within sand pores, sediment transport for particle-associated microbes, and the large-scale processes of wave action and terrestrial runoff. The concept of beach sand as a microbial habitat and reservoir of FIB and pathogens has begun to influence our thinking about human health effects associated with sand exposure and recreational water use. A variety of pathogens have been reported from beach sands, and recent epidemiology studies have found some evidence of health risks associated with sand exposure. Persistent or replicating populations of FIB and enteric pathogens have consequences for watershed/beach management strategies and regulatory standards for safe beaches. This review summarizes our understanding of the community structure, ecology, fate, transport, and public health implications of microbes in beach sand. It concludes with recommendations for future work in this vastly under-studied area.

Anthropogenic impacts on a bedrock aquifer at the village scale.

This study focuses on assessing groundwater potability in a highly complex and heterogeneous fractured bedrock aquifer having variable overburden cover. Eight monitoring wells were installed in a privately serviced lakeside village, and groundwater was routinely sampled over a 2-year timeframe for concentration analysis of nitrate, fecal indicator bacteria, stable isotopes, and a total of 41 pharmaceutical compounds. While pollutant concentrations remained low throughout the study, the presence of fecal indicator bacteria and pharmaceuticals was noted at least once (but not always consistently) in most sampling intervals. An interpretation based on the integration of chemical, bacterial, and site characterization datasets suggests that: (1) the fracture network is complex and heterogeneous with limited vertical connectivity; (2) existing pathways are sufficient for the quick and widespread migration of surface contaminants to depth; (3) anthropogenic contaminants from both septic systems and agriculture are likely sourced in the surrounding uplands where overburden is thin; and (4) fecal contamination, as observed over the long term, is ubiquitous at the village scale. Groundwater quality is continually changing in this hydrogeologic environment and the determination of potability on the larger scale is not likely to be adequately captured with infrequent domestic well sampling (i.e., voluntary annual sampling by homeowners).

An Excel macro for generating trilinear plots.

This computer note describes a method for creating trilinear plots in Microsoft Excel. Macros have been created in MS Excel's internal language: Visual Basic for Applications (VBA). A simple form has been set up to allow the user to input data from an Excel worksheet. The VBA macro is used to convert the triangular data (which consist of three columns of percentage data) into X-Y data. The macro then generates the axes, labels, and grid for the trilinear plot. The X-Y data are plotted as scatter data in Excel. By providing this macro in Excel, users can create trilinear plots in a quick, inexpensive manner.

Animating ground water levels with Excel.

This note describes the use of Microsoft Excel macros (programs written in Excel's internal language, Visual Basic for Applications) to create simple onscreen animations of transient ground water data within Excel. Compared to many specialized visualization software packages, the use of Excel macros is much cheaper, much simpler, and can rapidly be learned. The Excel macro can also be used to create individual GIF files for each animation frame. This series of frames can then be used to create an AVI video file using any of a number of graphics packages, such as Corel PhotoPaint. The technique is demonstrated through a macro that animates changes in the elevation of a water table along a transect over several years.