Developing a Protocol for Sampling Irrigation Water for Salmonella

Monitoring and regulation of irrigation water is becoming commonplace since agriculture is an important user of our limited water resources. Use of surface water impoundments for catching precipitation are an excellent method of sustainability of irrigation water sources, but the quality of these water sources must be established to ensure microbiological safety of the crops being irrigated with the waters. Sampling protocols used to achieve this objective vary greatly in number of samples collected, timing and frequency of samples collected, sampling location, holding times prior to analysis, assay organism, and other factors. Furthermore, bacteria populations are not uniformly distributed throughout surface water bodies and concentrations fluctuate based on a variety of factors including temperature, solar radiation and precipitation. Other factors, like the multitude of sources of fecal contamination, effects of environmental factors on the various sources/types of microorganisms and transport mechanisms which transfer the organisms to water bodies, contribute to increase these issues.

A uniform system of sample collection and laboratory analysis based on sound science are essential for the adequate assessment of the safety of irrigation water used in production of fresh vegetables and fruit crops. For this reason, the proposed research will provide guidance for growers on water sampling methods to maximize the ability to detect bacterial contamination in surface water irrigation sources. In addition, the water sampling protocol developed in this study will provide a science-based method for collecting samples that can be documented as part of a water quality program to minimize risks of produce contamination.

Camilla samplingThe primary goal of this project is to develop a producer-friendly sampling protocol which reflects Salmonella concentrations at the irrigation system intake.  The intake is usually 3 to 7 m from the bank and at a depth of 1 to 2 m and is the ideal place to collect a sample if we are interested in capturing the water pumped to the irrigation system.  Collecting samples at the intake typically requires a boat, specialized sampling equipment, and time all of which make it difficult for vegetable producers to collect samples during the growing season.  We will achieve the primary goal by addressing the following objectives.

Compare different strategies for collecting water samples from the bank of the irrigation pond to samples collected from the intake of the irrigation system.
Assess whether indicator bacteria such as E. coli adequately represent Salmonella concentrations in irrigation ponds.
Assess the interaction between water quality parameters (nutrients, dissolved oxygen, etc.) and Salmonella and E. coli concentrations.

The study area is characterized by a higher human infection and environmental incidence of Salmonella than other areas of the United States. It is located within the Suwannee River watershed and lies in the heart of a mixed produce agricultural production area that is characterized by well-drained soils and by dense dendritic stream networks with forested riparian buffers along streams.

Camilla in labThis project will utilize data collected from ten irrigation ponds which are currently being sampled monthly for analysis. The study proposed here will focus on a subset of these ponds: four ponds which have had the highest and most frequently detected concentrations of Salmonella and one pond with low frequency and detection to be used in the study being proposed. The pond with low detection will be included to more closely examine possibility for fluctuations of Salmonella which might be captured using a more sensitive sampling protocol.

Benefits to the Industry

In southern Georgia and in other parts of the southeastern United States, 1st, 2nd, and 3rd order streams are damned to create irrigation water reservoirs which are typically referred to as irrigation ponds (map at bottom left).  These ponds are an important feature of the region’s agroecosystem and contain fish, amphibians, and reptiles and are also frequently used by birds and mammals.  Consequently it is very important the vegetable growers characterize the water quality of ponds used to irrigate fresh produce.  This 2-year project will develop sampling protocols which will allow vegetable growers to accurately assess the quality of their surface irrigation water.  The results from this project will be leveraged by the results from companion studies which will give us a comprehensive assessment of potential sources and concentrations of Salmonella in these ponds.