Factors Impacting the Prevalence of Foodborne Pathogens in Agricultural Water Sources in the Southeastern United States
Round 1
Reviewer 1 Report
In light of recent leafy green and other produce outbreaks associated with irrigation water and the implementation of the PSR, I believe this is a timely review and has merit for publication. The unique aspect of this manuscript is relating agricultural water sources to prevalence of foodborne pathogens and focusing on studies in the southeastern US. It would be beneficial if the authors could incorporate a section on methods of irrigation/sources of water in the southern US, highlighting the unique aspects of agricultural water within this particular region.
As for the organization of the manuscript, I would suggest that the manuscript would flow better as follows: 1) Introduction, 2) Microbial Quality of Agricultural Water Sources (and change header to Regulations, Guidelines and Microbial Quality Standards for Agricultural Water Sources), 3) Implications of Water Scarcity, 4) Microbial Indicators of Irrigation Water Contamination, 5) Irrigation Water as a Vehicle of Foodborne Pathogens, 6) Current Status of Knowledge-Factors Affecting the Prevalence of Foodborne Pathogens in Surface Waters in the Southeastern US, 7) Conclusions.
1) Introduction: The first three paragraphs in the introduction could be reduced as they are redundant (i.e. tighten the statements regarding fresh produce and public health risk and reword statements using the words “contamination” or “contaminated” to reduce redundancy). Additionally, the first two sentences of the last paragraph are too verbose and need to be stated differently. Introduce the topic of surface water and include types (i.e. ponds, lakes, etc) here. The authors reference surface water multiple times throughout the manuscript in different levels of detail and it would benefit the readers to introduce what surface water is in the introduction. Also, I feel it would be prudent to identify specifically which states the authors are considering the southeastern U.S. for reference.
2) Water Scarcity in the Southeastern U.S.: Move from section 2 to Section 3 and rename to Implications of Water Scarcity. Please make clear how water is scarce in the southeastern U.S. Include specific rainfall totals for at least the states the authors discuss in the review (i.e. Georgia, Tennessee, Florida, etc). Discuss drought in more detail (i.e. stats on increased occurrences within the southeastern US). Explain how hurricanes, floods, ice storms related to water scarcity. Perhaps title this section extreme weather events and water scarcity or move the extreme weather parts to Microbial Quality section? The authors mention reclaimed or recycled water, but do not go into detail as to what these waters entail, i.e. describe their use during times of water scarcity.
3) Irrigation Water as a Vehicle of Foodborne Pathogens: Move from section 3 to section 5. Please add more examples of recent outbreaks in produce traced to water. Perhaps use this section as the starting paragraph of section 6 (Current Status….).
4) Microbial Quality of Agricultural Water Sources: Move from section 4 to section 2 and change header to Regulations, Guidelines and Microbial Quality Standards for Agricultural Water Sources. The first paragraph of this section should include FSMA and PSR details (found in introductory section). Create a new section to include strategies to reduce microbial loads (paragraph 3) should be its own section toward the end of the review or perhaps in the conclusions. If it becomes its own section, expand mitigation examples (this would add tremendously to the review as these practices are emerging).
5) Microbial Indicators of Irrigation Water Contamination: Move from section 5 to section 4. This section should be discussed after Regulation and Microbial Quality Standards section.
6) Current Status of Knowledge-Factors Affecting the Prevalence of Foodborne Pathogens in Surface Waters in the Southeastern U.S.: This section is the most important of the review and is the authors’ strongest written section.
7) Conclusions: Change “6” to “7” in header.
Throughout the manuscript, the authors have a tendency to repeat sentences and thoughts as well as have run-on sentence structure. These instances need to be streamlined and the manuscript tightened.
This manuscript provides a timely and worthy topic for review. With extensive organizational changes and added content, the manuscript will be a well received contribution.
Author Response
Response to Reviewer 1 Comments
Point 1: In light of recent leafy green and other produce outbreaks associated with irrigation water and the implementation of the PSR, I believe this is a timely review and has merit for publication. The unique aspect of this manuscript is relating agricultural water sources to prevalence of foodborne pathogens and focusing on studies in the southeastern US. It would be beneficial if the authors could incorporate a section on methods of irrigation/sources of water in the southern US, highlighting the unique aspects of agricultural water within this particular region.
Response 1: Additional information regarding methods of irrigation and implications on produce contamination has been included in the second paragraph of the section “Water as a Vehicle for Foodborne Pathogen Transmission during Crop Production”.
Point 2: As for the organization of the manuscript, I would suggest that the manuscript would flow better as follows: 1) Introduction, 2) Microbial Quality of Agricultural Water Sources (and change header to Regulations, Guidelines and Microbial Quality Standards for Agricultural Water Sources), 3) Implications of Water Scarcity, 4) Microbial Indicators of Irrigation Water Contamination, 5) Irrigation Water as a Vehicle of Foodborne Pathogens, 6) Current Status of Knowledge-Factors Affecting the Prevalence of Foodborne Pathogens in Surface Waters in the Southeastern US, 7) Conclusions.
Response 2: Sections were reordered and renamed following the reviewer’s suggestions with additions and restructuring of sections as follow: 1) Introduction, 2) Water as a Vehicle for Foodborne Pathogen Transmission during Crop Production, 3) Regulations, Guidelines, and Microbial Quality Standards for Agricultural Water Sources, 4) Microbial Indicators of Irrigation Water Contamination, 6) 6. Current Status of Knowledge - Factors Affecting the Prevalence of Foodborne Pathogens in Surface Water in the Southeastern U.S.; 7) Strategies to Reduce Microbial Load in Agricultural Water Sources, 8) Conclusions.
Point 3: 1) Introduction: The first three paragraphs in the introduction could be reduced as they are redundant (i.e. tighten the statements regarding fresh produce and public health risk and reword statements using the words “contamination” or “contaminated” to reduce redundancy). Additionally, the first two sentences of the last paragraph are too verbose and need to be stated differently. Introduce the topic of surface water and include types (i.e. ponds, lakes, etc) here. The authors reference surface water multiple times throughout the manuscript in different levels of detail and it would benefit the readers to introduce what surface water is in the introduction. Also, I feel it would be prudent to identify specifically which states the authors are considering the southeastern U.S. for reference.
Response 3: Sentences were reordered, removed, or rephrased, and the two first paragraphs were combined to reduce redundancy.
More detail was added to surface water topic in the second paragraph.
States considered for the review were identified in the new section “Water as a Vehicle for Foodborne Pathogen Transmission during Crop Production”.
Point 4: 2) Water Scarcity in the Southeastern U.S.: Move from section 2 to Section 3 and rename to Implications of Water Scarcity. Please make clear how water is scarce in the southeastern U.S. Include specific rainfall totals for at least the states the authors discuss in the review (i.e. Georgia, Tennessee, Florida, etc). Discuss drought in more detail (i.e. stats on increased occurrences within the southeastern US). Explain how hurricanes, floods, ice storms related to water scarcity. Perhaps title this section extreme weather events and water scarcity or move the extreme weather parts to Microbial Quality section? The authors mention reclaimed or recycled water, but do not go into detail as to what these waters entail, i.e. describe their use during times of water scarcity
Response 4: The section “Water Scarcity in the Southeastern U.S.” has been relocated in the new section “Water as a Vehicle for Foodborne Pathogen Transmission during Crop Production”.
Additional information about climate, precipitation, water sources and the implications related to water scarcity have been included in the new section “Water as a Vehicle for Foodborne Pathogen Transmission during Crop Production”.
Point 5: 3) Irrigation Water as a Vehicle of Foodborne Pathogens: Move from section 3 to section 5. Please add more examples of recent outbreaks in produce traced to water. Perhaps use this section as the starting paragraph of section 6 (Current Status….).
Response 5: This paragraph was relocated to the first paragraph of the introduction section to call readers’ attention about the importance of investigating microbial water quality used for agriculture.
Additional examples of outbreaks related to contaminated water have been added to the first paragraph of the introduction section.
Point 6: 4) Microbial Quality of Agricultural Water Sources: Move from section 4 to section 2 and change header to Regulations, Guidelines and Microbial Quality Standards for Agricultural Water Sources. The first paragraph of this section should include FSMA and PSR details (found in introductory section). Create a new section to include strategies to reduce microbial loads (paragraph 3) should be its own section toward the end of the review or perhaps in the conclusions. If it becomes its own section, expand mitigation examples (this would add tremendously to the review as these practices are emerging).
Response 6: The title of the section was renamed according the reviewer’s suggestion.
Authors decided to introduce the section “Water as a Vehicle for Foodborne Pathogen Transmission during Crop Production” before the section “Regulations, Guidelines, and Microbial Quality Standards for Agricultural Water Sources” to provide background information about the states addressed in the review.
Additional information about FSMA and PSR were added in the first paragraph of the section “Regulations, Guidelines, and Microbial Quality Standards for Agricultural Water Source”.
According to reviewer’s suggestion, a new section called “Strategies to Reduce Microbial Load in Agricultural Water Sources” was created and more information was included before the conclusion section.
Point 7: 6) Current Status of Knowledge-Factors Affecting the Prevalence of Foodborne Pathogens in Surface Waters in the Southeastern U.S.: This section is the most important of the review and is the authors’
Response 7: No changes required.
Point 8: 7) Conclusions: Change “6” to “7” in header.
Response 8: Conclusion section was renumbered.
Point 9: Throughout the manuscript, the authors have a tendency to repeat sentences and thoughts as well as have run-on sentence structure. These instances need to be streamlined and the manuscript tightened.
Response 9: Sentences were reordered and rephrased, and words replaced clarity.
The manuscript has been proofread by two additional colleagues.
Point 10: This manuscript provides a timely and worthy topic for review. With extensive organizational changes and added content, the manuscript will be a well-received contribution.
Response 10: The authors appreciate your thoughtful contributions and suggestions to improve the quality of our manuscript.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Major comments
The authors mention on Page 5 of 16 that “Also, a clear relationship between microbial water quality and precipitation has been insufficiently determined,…..”. However, many studies around the world have demonstrated this relationship to be almost always positive; the authors also point out the same in most of the literature cited with a few exceptions. It would therefore be good to identify the reasons for those studies that did showed contrary results. Many factors could affect the correlation between precipitation and the detection or abundance of microbial species in surface waters. One very important factor would be the surrounding land use. It would therefore be beneficial if the authors could identify the factors around their cited studies as these could explain the variability. Also, the sampling regime (immediately after rainfall? Is the plume into the river sampled or is the sample collected after the plume? What part of the river is sampled – the edges or the centre or a cross section? How many samples are collected and how long after the rainfall? The depth of the river would affect resuspension and overall observed microbial counts could be affected. What method of analysis was used – culture-based or molecular based – sensitivity of method could play a role. Intensity of rainfall?). Thus, the authors may want to do some more findings that would help explain rainfall as a factor influencing microbial quality of irrigation water.
Regarding temperature, while the authors identify that there is a genera increase in microbial counts with an increase in temperature, this does not seem to be the case always, especially with some organisms like Campylobacter. If appropriate measures have to be designed, the reason for the observed dissimilarity between the studies need to be understood. Simply citing studies that have reported results is not sufficient. Campylobacter is listed in the WHO top priority foodborne pathogens. Their deviation from observed seasonal trends need to be explained to avoid potential health risks
Concerning wildlife, the authors give insufficient information on how these could impact irrigation water. As discussed in this section of the manuscript, examples given point to humans and domestic animals as well. Authors need to identify more studies that relate the influence of wildlife on water quality. The type of organisms that could originate from this source and the survival of these organism in the environment would be important.
In the Physicochemical parameters, temperature is the most important as this influences the other parameters as well. Again here, the authors need to discuss how these parameters affect the microbial quality. What should be expected when the pH or EC changes for example? What happens to the microbial diversity? What happens to the abundance of the organisms and why does this happen?
Minor comments
Page 3 of 16; Line 3: … cases of Salmonellosis…
Page 3 of 16; Line 8-9: …animal intrusion, and human waste, among other…(Delete the etc and correct spelling of intrusion)
Page 3 of 16; Line 16:… quality of water contacting…
Page 3 of 16; Line 8 (from bottom):… or inactivate the pathogen
Author Response
Response to Reviewer 2 Comments
Point 1: The authors mention on Page 5 of 16 that “Also, a clear relationship between microbial water quality and precipitation has been insufficiently determined,…..”. However, many studies around the world have demonstrated this relationship to be almost always positive; the authors also point out the same in most of the literature cited with a few exceptions. It would therefore be good to identify the reasons for those studies that did showed contrary results. Many factors could affect the correlation between precipitation and the detection or abundance of microbial species in surface waters. One very important factor would be the surrounding land use. It would therefore be beneficial if the authors could identify the factors around their cited studies as these could explain the variability. Also, the sampling regime (immediately after rainfall? Is the plume into the river sampled or is the sample collected after the plume? What part of the river is sampled – the edges or the centre or a cross section? How many samples are collected and how long after the rainfall? The depth of the river would affect resuspension and overall observed microbial counts could be affected. What method of analysis was used – culture-based or molecular based – sensitivity of method could play a role. Intensity of rainfall?). Thus, the authors may want to do some more findings that would help explain rainfall as a factor influencing microbial quality of irrigation water. 

Response 1:
The sentence “Also, a clear relationship between microbial water quality and precipitation has been insufficiently determined..”. was deleted and discussion regarding the relationship was added.
For those studies that had controversial results, more information was added to explain the discrepancies.
Information about the geographical location, land use, surrounding activities, sampling regime, location of sample collection, and other additional information that could contribute to a better understanding of the findings have been added for each specific area.
The number of samples collected is available in Table 1 for each study.
In addition, the subsection called “Wildlife” has been moved to the subsection “Rainfall” – Now called “Rainfall, Geographical Location, and Bacterial Source Tracking” to better address those three topics. Mention of molecular methods was made when utilized, but the majority of studies relied on culture-based methods.
Point 2: Regarding temperature, while the authors identify that there is a genera increase in microbial counts with an increase in temperature, this does not seem to be the case always, especially with some organisms like Campylobacter. If appropriate measures have to be designed, the reason for the observed dissimilarity between the studies need to be understood. Simply citing studies that have reported results is not sufficient. Campylobacter is listed in the WHO top priority foodborne pathogens. Their deviation from observed seasonal trends need to be explained to avoid potential health risks
Response 2: Additional information and explanation about discrepancies in the results related to C. jejuni prevalence and health impact have been included in the subsections “Rainfall, Geographical Location, and Bacterial Source Tracking” and “Temperature and Seasonality”.
Point 3: Concerning wildlife, the authors give insufficient information on how these could impact irrigation water. As discussed in this section of the manuscript, examples given point to humans and domestic animals as well. Authors need to identify more studies that relate the influence of wildlife on water quality. The type of organisms that could originate from this source and the survival of these organism in the environment would be important.
Response 3: Additional information regarding wildlife and the impact of manure on microbial water quality have been included in the subsection “Rainfall, Geographical Location, and Bacterial Source Tracking”.
Point 4: In the Physicochemical parameters, temperature is the most important as this influences the other parameters as well. Again here, the authors need to discuss how these parameters affect the microbial quality. What should be expected when the pH or EC changes for example? What happens to the microbial diversity? What happens to the abundance of the organisms and why does this happen?
Response 4: In fact, water physicochemical properties are highly dependent on the seasonality and temperature of the water sources. Additional information has been included regarding physicochemical properties of water and the prevalence of pathogenic bacteria. However, the complexity of the correlation between these factors and the prevalence of pathogenic microorganisms in water has been inadequately investigated in Southeastern U.S.
Point 5: Page 3 of 16; Line 3: … cases of Salmonellosis…
Response 5: Typo was corrected.
Point 6: Page 3 of 16; Line 8-9: …animal intrusion, and human waste, among other…(Delete the etc and correct spelling of intrusion)
Response 6: Typo was corrected.
Point 7: Page 3 of 16; Line 16: quality of water contacting…
Response 7: Typo was corrected.
Point 8: Page 3 of 16; Line 8 (from bottom): or inactivate the pathogen
Response 8: Typo was corrected.
Author Response File: Author Response.docx
Reviewer 3 Report
GENERAL COMMENTS
The authors demonstrate a thorough grasp of food pathogens and related federal policy and regulations. However, the discussion of human influences on water quality is inadequate in the manuscript. Factors including water temperature, precipitation events, and physiochemical properties (such as turbidity) are indeed very important. But as the authors note at the end of the article, there are numerous other variables involved. I suggest that a major variable (excluded by the authors) would be the presence of significant sources of microbial contaminants in the watershed that contributes to the surface water body (or source of irrigation water). It is extremely unlikely that the risks associated with surface water irrigation are uniform across all watersheds (or even across all watersheds hosting significant produce farms) in the southeastern United States.
Like all other states, to comply with section 303(d) of the Clean Water Act, Florida, Georgia, Alabama, and Tennessee compile biennial lists of surface waters that are impaired, or not supporting their designated uses, and the cause or source (turbidity, fecal coliform, nitrate, and others) of the impairment. Many states also provide (free of charge) GIS data sets that, for example, could be used to help investigate risks associated with drawing irrigation water from different surface water bodies. Many of the rivers noted by the authors are impaired rivers (e.g. some stretches of the Little River in Georgia are impaired due to fecal coliform) and so it would not be surprising to find microbial contamination in samples taken directly from those waters or from irrigation water drawn from those waters.
In addition to the authors’ work thus far on this manuscript on evaluating the general microbial risks associated with surface water irrigation, there are additional data that need to be considered: 1) location(s) of produce farms, 2) watershed(s) within which the farms exist, 3) what is known about water quality in the watershed(s), 4) whether there are major point sources of microbial contamination in the watershed(s), 5) whether there are major non-point sources of microbial contamination in the watershed, 6) land use (e.g. urban, agricultural, parks) and land cover (e.g. forest, grass, row crops…).
There is nothing wrong, per se, with the review constructed so far by the authors but it does not rise to the level of being novel or significantly different than other publications that examine microbial risk associated with irrigated agriculture, or than those that model risk of microbial contamination of surface waters.
It is therefore suggested that the authors reexamine their work to incorporate above suggestions (i.e. a fuller description of the conditions in watersheds and water resources that have been studied in the context of microbial contamination of produce) and possibly partner with another colleague who is well-versed in studying surface water contamination and/or GIS.
It is also unclear from the manuscript whether any selection criteria were used to choose articles reviewed and summarized in section 6 of this manuscript. For example, does the manuscript review all the articles published between 2010 and 2019 dealing with microbial contamination and irrigation in the southeastern United States, or some subset thereof? The Web of Science database, for example, has functions that allow one to select articles by keywords, authors, dates, geography, and other criteria.
INTRODUCTION
Page 1, 2nd paragraph: Agricultural production has increased overall in the United States. However, fresh produce is mainly grown in very specific locations or regions and the authors would do well to describe the distribution of produce, and how it has intensified in selected areas in the U.S. In part, the choice of which produce is grown where dictates the extent to which irrigation is necessary. The USDA National Agricultural Statistics Service provides high-level information that the authors could use to focus their attention in this article. There are not that many counties in the southeastern United States in which more than 1,000 acres are devoted to produce.
Page 2, 1st paragraph (continued from prev. page): It is true that surface water is more vulnerable to contamination. It is also true that surface-connected (or shallow) groundwater such as that found in alluvial aquifers along and beneath streams is nearly as vulnerable to contamination as surface water.
Page 2, 2nd paragraph: Is surface water really the source of contamination? Or, just like “irrigation water-see section 3 header), is water a vehicle for delivering microbes from their actual source (e.g. animal feeding operations or septic tanks) to food that is irrigated with the water?
SECTION 2: WATER SCARCITY…
It is true that agriculture is the largest consumer of water worldwide. But that is not close to the case in the United States as a whole-in the U.S. just over 1/3 of water use is for irrigation. The authors are encouraged to (again) consult the USGS Report: Estimated Use of Water in the United States in 2015 (which is cited later in the paper) as well as related USGS websites providing data on state-by-state water uses. The authors’ argument about stress on water resources in the SE U.S. driving increased reliance on surface waters or reclaimed wastewater would be stronger if specific numbers indicating such a trend were provided.
Somewhere in the manuscript the authors should more thoroughly describe the general climate and precipitation patterns in the SE United States. Annual average precipitation would often be adequate for crops; however, there is a good deal of monthly or seasonal variability as well as a good deal of variability around the annual average precipitation in the SE United States. It seems that water storage in stormwater ponds (with pervious bottoms for aquifer recharge) might be very important-such as was practiced traditionally for millennia in SE India (monsoon climate) and other regions.
SECTION 3: IRRIGATION WATER AS A VEHICLE
It is definitely the case that irrigation water has been associated with foodborne illness outbreaks involving several different microbial populations. However, the authors would do well to discuss these outbreaks in the context of the entire body of foodborne illness outbreaks-how important are irrigation-related foodborne pathogens compared to other sources/causes?
It is true that surface water is more vulnerable and is frequently contaminated. But surface water quality varies widely even within the SE United States. All the sources of contamination listed are valid, but not within every watershed, and not within the context of every farm that uses surface water for irrigation. The presence of contamination sources, proximity to contamination sources, and location within a watershed (e.g. upstream or downstream) compared to contamination sources are all very important.
Were withdrawals in Florida and North Carolina mostly groundwater? Surface water? Surface-influenced groundwater?
SECTION 4: MICROBIAL QUALITY…
Are there opportunities to ‘game the system’ within the MWQP-in other words, do producers get to choose all the dates on which samples are collected?
Line 10 in first paragraph-please reexamine the use of the word ‘generic’-this is probably a typo
Paragraph 2: can more be explained about differences in surface topography? Are all leafy greens with complex surface topography at greater risk of retaining microbial populations because water droplets are easily trapped on/in the surfaces?
Paragraph 2, 3rd to last line: the word “the” is missing before “pathogen”
Paragraph 3: if 2.5ppm chlorine can induce phytotoxicity, what is the optimal tradeoff (in ppm) between chlorine “kill action” and phytotoxicity? Is this known?
Chlorine also does not always fare well in the presence of turbidity and organic matter and (in drinking water) often forms carcinogenic compounds (trihalomethanes). It is unknown whether this would take place in irrigation water. Another drawback for UV (compared to chlorine) is that there is no residual disinfection effect.
SECTION 5: MICROBIAL INDICATORS…
Paragraph 1, line 6: but as the authors point out, E. coli species are naturally present in the environment…as are Salmonella. It might be good to just clearly state that in the first paragraph and then go on to explain why it is difficult to rely upon a single indicator for potential fecal contamination.
SECTION 6: CURRENT STATUS OF KNOWLEDGE
Sub-sections (5.1, 5.2…) are not numbered correctly in this section.
End of page 4/ beginning of page 5: was it only previous data or was it previous studies that were summarized?
Section 5.1 (6.1), 1st paragraph, line 4: this is the closest the authors get to noting the importance of proximity/location within a watershed relative to contaminant sources.
1st paragraph, last sentence: Agriculture is by far number one on the list of nonpoint sources of pollution, so the correlation between percentage of agricultural land and bacterial prevalence is neither unexpected nor interesting. It is unlikely that all forms of agriculture would contribute equally to microbial contamination, however.
3rd paragraph: The Suwanee River watershed may in fact be an ideal area to study, but should the authors provide information about the number and types of produce farms utilizing irrigation water from this source? A map of the watershed with important features or characteristics such as land use and locations of studies summarized by the authors might be helpful.
4th paragraph: is this greater (presumed) correlation (rather than impact?) important? Are the urban lakes used for irrigation? Is it possible that rainfall would not meaningfully impact microbial populations if the watershed is relatively undeveloped or did not contain good conduits for introducing microbes into surface waters?
Section 5.2 (6.2):
Does precipitation also vary seasonally?
Preventative measures—be specific-preventing surface water contamination? Preventing irrigation water contamination? Preventing food contamination? All three?
Higher microbial counts in warmer waters is expected. The finding of higher counts in spring in one watershed is probably worth investigating-how is this watershed different than the others?
Section 5.3 (6.3): the title (wildlife) is misleading—perhaps retitling the sub section “source tracking” would be more accurate.
The absence of any mention of poultry manure (either in stockpiles or spread on fields) or poultry mortality pits as a source of surface (and ground) water contamination is mystifying. There are hundreds of millions of broiler chickens raised in Alabama, Georgia, and Florida. See for example maps and data produced by the National Agricultural Statistics Service 2017 Census of Agriculture.
Section 5.4 (6.4), line 4: what is meant by “environmental conditions”
CONCLUSIONS-should this be numbered 7 (instead of 6)?
Would it be important to note that in general there are correlations between microbial quality and rainfall events as well as warmer temperatures, but that this relationship does not hold for all watersheds?
Author Response
Response to Reviewer 3 Comments
Point 1: The authors demonstrate a thorough grasp of food pathogens and related federal policy and regulations. However, the discussion of human influences on water quality is inadequate in the manuscript. Factors including water temperature, precipitation events, and physiochemical properties (such as turbidity) are indeed very important. But as the authors note at the end of the article, there are numerous other variables involved. I suggest that a major variable (excluded by the authors) would be the presence of significant sources of microbial contaminants in the watershed that contributes to the surface water body (or source of irrigation water). It is extremely unlikely that the risks associated with surface water irrigation are uniform across all watersheds (or even across all watersheds hosting significant produce farms) in the southeastern United States.
Response 1: Additional information about the watershed, land use, and surrounding activities were included to better address the topics discussed in the section “Current Status of Knowledge - Factors Affecting the Prevalence of Foodborne Pathogens in Surface Water in the Southeastern U.S.”
Point 2: Like all other states, to comply with section 303(d) of the Clean Water Act, Florida, Georgia, Alabama, and Tennessee compile biennial lists of surface waters that are impaired, or not supporting their designated uses, and the cause or source (turbidity, fecal coliform, nitrate, and others) of the impairment. Many states also provide (free of charge) GIS data sets that, for example, could be used to help investigate risks associated with drawing irrigation water from different surface water bodies. Many of the rivers noted by the authors are impaired rivers (e.g. some stretches of the Little River in Georgia are impaired due to fecal coliform) and so it would not be surprising to find microbial contamination in samples taken directly from those waters or from irrigation water drawn from those waters.
Response 2: The water sources cited on the manuscript have been checked and updated for this information according to the 303(d) list.
Point 3: In addition to the authors’ work thus far on this manuscript on evaluating the general microbial risks associated with surface water irrigation, there are additional data that need to be considered: 1) location(s) of produce farms, 2) watershed(s) within which the farms exist, 3) what is known about water quality in the watershed(s), 4) whether there are major point sources of microbial contamination in the watershed(s), 5) whether there are major non-point sources of microbial contamination in the watershed, 6) land use (e.g. urban, agricultural, parks) and land cover (e.g. forest, grass, row crops…).
Response 3: Information about the geographical location, land use, surrounding activities, sampling regime, location of sample collection, and other additional information that could contribute to a better understanding of the studies have been included for each specific area on the section “Current Status of Knowledge - Factors Affecting the Prevalence of Foodborne Pathogens in Surface Water in the Southeastern U.S.”
Point 4: There is nothing wrong, per se, with the review constructed so far by the authors but it does not rise to the level of being novel or significantly different than other publications that examine microbial risk associated with irrigated agriculture, or than those that model risk of microbial contamination of surface waters.
Response 4: No response required.
Point 5: It is therefore suggested that the authors reexamine their work to incorporate above suggestions (i.e. a fuller description of the conditions in watersheds and water resources that have been studied in the context of microbial contamination of produce) and possibly partner with another colleague who is well-versed in studying surface water contamination and/or GIS.
Response 5: A description of each watershed was included in the subsection “Rainfall, Geographical Location, and Bacterial Source Tracking”.
A collaboration with another specialist in the area of water management and vegetable production has been added to the manuscript to incorporate the required information from the Southeastern U.S.
Point 6: It is also unclear from the manuscript whether any selection criteria were used to choose articles reviewed and summarized in section 6 of this manuscript. For example, does the manuscript review all the articles published between 2010 and 2019 dealing with microbial contamination and irrigation in the southeastern United States, or some subset thereof? The Web of Science database, for example, has functions that allow one to select articles by keywords, authors, dates, geography, and other criteria.
Response 6: Articles selected on the section “Current Status of Knowledge - Factors Affecting the Prevalence of Foodborne Pathogens in Surface Water in the Southeastern U.S.” included peer-review publications that had investigated environmental factors and physicochemical aspects related to microbial contamination of agricultural water sources in the six states included in the Southeastern region of U.S. Databanks such as PubMed, Web of Science and Google Scholar were used to search and review peer-review articles using matching keywords such as: Salmonella, E. coli, Campylobacter jejuni, coliforms, irrigation water contamination, agricultural water, surface water, watershed, Florida, Georgia, Alabama, Tennessee, North Carolina, South Carolina, and other terms related to the review topic.
INTRODUCTION
Point 7: Page 1, 2nd paragraph: Agricultural production has increased overall in the United States. However, fresh produce is mainly grown in very specific locations or regions and the authors would do well to describe the distribution of produce, and how it has intensified in selected areas in the U.S. In part, the choice of which produce is grown where dictates the extent to which irrigation is necessary. The USDA National Agricultural Statistics Service provides high-level information that the authors could use to focus their attention in this article. There are not that many counties in the southeastern United States in which more than 1,000 acres are devoted to produce.
Response 7: Additional information about fresh produce in the southeastern U.S. has been included in first paragraph of the section “Water as a Vehicle for Foodborne Pathogen Transmission during Crop Production”. Also, Table 1 containing harvested area of produce in the southeastern U.S. has been added to the same section.
Point 8: Page 2, 1st paragraph (continued from prev. page): It is true that surface water is more vulnerable to contamination. It is also true that surface-connected (or shallow) groundwater such as that found in alluvial aquifers along and beneath streams is nearly as vulnerable to contamination as surface water.
Response 8: No changes were required. Authors added more information about the subject described on the section “Water as a Vehicle for Foodborne Pathogen Transmission during Crop Production”.
Point 9: Page 2, 2nd paragraph: Is surface water really the source of contamination? Or, just like “irrigation water-see section 3 header), is water a vehicle for delivering microbes from their actual source (e.g. animal feeding operations or septic tanks) to food that is irrigated with the water?
Response 9: The world “source” has been replaced for “vehicle” to avoid confusion.
SECTION 2: WATER SCARCITY…
Point 10: It is true that agriculture is the largest consumer of water worldwide. But that is not close to the case in the United States as a whole-in the U.S. just over 1/3 of water use is for irrigation. The authors are encouraged to (again) consult the USGS Report: Estimated Use of Water in the United States in 2015 (which is cited later in the paper) as well as related USGS websites providing data on state-by-state water uses. The authors’ argument about stress on water resources in the SE U.S. driving increased reliance on surface waters or reclaimed wastewater would be stronger if specific numbers indicating such a trend were provided.
Response 10: The section “Water Scarcity in the Southeastern U.S.” has been incorporated in the new section “Water as a Vehicle for Foodborne Pathogen Transmission during Crop Production”.
Additional information regarding the use of water for irrigation purpose on each state has been included to the section “Water as a Vehicle for Foodborne Pathogen Transmission during Crop Production” according to the USGS Report.
Point 11: Somewhere in the manuscript the authors should more thoroughly describe the general climate and precipitation patterns in the SE United States. Annual average precipitation would often be adequate for crops; however, there is a good deal of monthly or seasonal variability as well as a good deal of variability around the annual average precipitation in the SE United States. It seems that water storage in stormwater ponds (with pervious bottoms for aquifer recharge) might be very important-such as was practiced traditionally for millennia in SE India (monsoon climate) and other regions.
Response 11: Additional information about general climate and precipitation patterns in the southeastern U.S. has been included to the first paragraph of the section “Water as a Vehicle for Foodborne Pathogen Transmission during Crop Production” according to the USGS Report.
SECTION 3: IRRIGATION WATER AS A VEHICLE
Point 12: It is definitely the case that irrigation water has been associated with foodborne illness outbreaks involving several different microbial populations. However, the authors would do well to discuss these outbreaks in the context of the entire body of foodborne illness outbreaks-how important are irrigation-related foodborne pathogens compared to other sources/causes?
Response 12: The section “Irrigation Water as a Vehicle of Foodborne Pathogens” has been incorporated in the section “Water as a Vehicle for Foodborne Pathogen Transmission during Crop Production”.
More information about the importance of foodborne outbreaks and irrigation-related issues has been added to the first paragraph in the introduction section.
Point 13: It is true that surface water is more vulnerable and is frequently contaminated. But surface water quality varies widely even within the SE United States. All the sources of contamination listed are valid, but not within every watershed, and not within the context of every farm that uses surface water for irrigation. The presence of contamination sources, proximity to contamination sources, and location within a watershed (e.g. upstream or downstream) compared to contamination sources are all very important.
Response 13: Information about sampling location, land use, and surrounding activities have been included throughout the section “Current Status of Knowledge - Factors Affecting the Prevalence of Foodborne Pathogens in Surface Water in the Southeastern U.S.”
Point 14: Were withdrawals in Florida and North Carolina mostly groundwater? Surface water? Surface-influenced groundwater?
Response 14: Information about irrigation withdrawals were readdressed and additional information about water sources were included to the section “Water as a Vehicle for Foodborne Pathogen Transmission during Crop Production”.
SECTION 4: MICROBIAL QUALITY…
Point 15: Are there opportunities to ‘game the system’ within the MWQP-in other words, do producers get to choose all the dates on which samples are collected?
Response 15: The section “Microbial Quality of Agricultural Water Sources” has been renamed as “Regulations, Guidelines, and Microbial Quality Standards for Agricultural Water Sources”.
This is the main caveat when talking about microbial standards for agricultural water established by the FDA. Because timing of sample collection is left to the growers’ discretion, some individuals may improve and manipulate their MWQP by testing water sources at advantageous times, such as during periods of drought or late in the day when the water surface has been exposed to solar radiation for several hours, leading to results that may not be the most representative of the microbial water quality. This information has been added to the end of the first paragraph of the section “Regulations, Guidelines, and Microbial Quality Standards for Agricultural Water Sources”.
Point 16: Line 10 in first paragraph-please reexamine the use of the word ‘generic’-this is probably a typo
Response 16: Typo was corrected.
Point 17: Paragraph 2: can more be explained about differences in surface topography? Are all leafy greens with complex surface topography at greater risk of retaining microbial populations because water droplets are easily trapped on/in the surfaces?
Response 17: Additional information about surface topography and implications on microbial contamination of fresh produce has been included to the second paragraph of the section “Regulations, Guidelines, and Microbial Quality Standards for Agricultural Water Sources”.
Point 18: Paragraph 2, 3rd to last line: the word “the” is missing before “pathogen”
Response 18: The word “the” has been added before “pathogen”.
Point 19: Paragraph 3: if 2.5ppm chlorine can induce phytotoxicity, what is the optimal tradeoff (in ppm) between chlorine “kill action” and phytotoxicity? Is this known?
Response 19: Additional information about chlorine levels and the implications for produce production has been included in the first paragraph of the new section “Strategies to Reduce Microbial Load in Agricultural Water Sources”.
Point 20: Chlorine also does not always fare well in the presence of turbidity and organic matter and (in drinking water) often forms carcinogenic compounds (trihalomethanes). It is unknown whether this would take place in irrigation water. Another drawback for UV (compared to chlorine) is that there is no residual disinfection effect.
Response 20: Additional information about chlorine limitations and UV-C has been included in the last paragraph of the new section “Strategies to Reduce Microbial Load in Agricultural Water Sources”.
SECTION 5: MICROBIAL INDICATORS…
Point 21: Paragraph 1, line 6: but as the authors point out, E. coli species are naturally present in the environment…as are Salmonella. It might be good to just clearly state that in the first paragraph and then go on to explain why it is difficult to rely upon a single indicator for potential fecal contamination.
Response 21: Additional information clarifying the limitations on relying solely on a single microbial indicator for fecal contamination has been added at the beginning of the first paragraph in the section “Microbial Indicators of Irrigation Water Contamination”.
SECTION 6: CURRENT STATUS OF KNOWLEDGE
Point 22: Sub-sections (5.1, 5.2…) are not numbered correctly in this section.
Response 22: Subsections were correctly numbered.
Point 23: End of page 4/ beginning of page 5: was it only previous data or was it previous studies that were summarized?
Response 23: Table 1 contains the summary of previous studies that were addressed in the section “Current Status of Knowledge - Factors Affecting the Prevalence of Foodborne Pathogens in Surface Water in the Southeastern U.S.”
Point 24: Section 5.1 (6.1), 1st paragraph, line 4: this is the closest the authors get to noting the importance of proximity/location within a watershed relative to contaminant sources.
Response 25: Additional information about the surrounding activities has been added throughout the section “Current Status of Knowledge - Factors Affecting the Prevalence of Foodborne Pathogens in Surface Water in the Southeastern U.S.”
Point 25: 1st paragraph, last sentence: Agriculture is by far number one on the list of nonpoint sources of pollution, so the correlation between percentage of agricultural land and bacterial prevalence is neither unexpected nor interesting. It is unlikely that all forms of agriculture would contribute equally to microbial contamination, however.
Response 25: The sentence “Interestingly, the study also identified that the percentage of agricultural land surrounding the water source corresponded to the percentage of the bacterial prevalence” was deleted due to irrelevance to the topic.
Point 26: 3rd paragraph: The Suwanee River watershed may in fact be an ideal area to study, but should the authors provide information about the number and types of produce farms utilizing irrigation water from this source? A map of the watershed with important features or characteristics such as land use and locations of studies summarized by the authors might be helpful.
Response 26: Additional information about watershed activities on the surrounding area have been added throughout the subsections on the section “Current Status of Knowledge - Factors Affecting the Prevalence of Foodborne Pathogens in Surface Water in the Southeastern U.S.”
In addition, a figure (Figure 1) has been included in the manuscript to demonstrate and summarize the geographical location of the studies conducted in the southeastern U.S. that provided the exact location on the publication.
Point 27: 4th paragraph: is this greater (presumed) correlation (rather than impact?) important? Are the urban lakes used for irrigation? Is it possible that rainfall would not meaningfully impact microbial populations if the watershed is relatively undeveloped or did not contain good conduits for introducing microbes into surface waters?
Response 27: This reference was removed from the manuscript.
Section 5.2 (6.2):
Point 28: Does precipitation also vary seasonally?
Response 28: Precipitation patterns and climate in the southeastern U.S. were explained in more detail in the section “Use of Water and It Ways as a Vehicle of Foodborne Pathogens in Food Production on Southeastern U.S.”
Point 29: Preventative measures—be specific-preventing surface water contamination? Preventing irrigation water contamination? Preventing food contamination? All three?
Response 29: The sentence was rephrased for better clarification.
Point 30: Higher microbial counts in warmer waters is expected. The finding of higher counts in spring in one watershed is probably worth investigating-how is this watershed different than the others?
Response 30: Additional information and explanation regarding seasonal discrepancies, especially for C. jejuni, have been included throughout the sub-section “Rainfall, Geographical Location, and Bacterial Source Tracking” and “Temperature and Seasonality”.
Point 31: Section 5.3 (6.3): the title (wildlife) is misleading—perhaps retitling the sub section “source tracking” would be more accurate.
Response 31: Title has been changed to “Bacterial Source Tracking” as suggested and subsection was incorporated to the subsection “Rainfall” to better address these topics. The section is now called “Rainfall, Geographical Location, and Bacterial Source Tracking”
Point 32: The absence of any mention of poultry manure (either in stockpiles or spread on fields) or poultry mortality pits as a source of surface (and ground) water contamination is mystifying. There are hundreds of millions of broiler chickens raised in Alabama, Georgia, and Florida. See for example maps and data produced by the National Agricultural Statistics Service 2017 Census of Agriculture.
Response 32: Additional information regarding manure and microbial water contamination have been included in the first paragraph of the subsection “Rainfall, Geographical Location, and Bacterial Source Tracking”.
Point 33: Section 5.4 (6.4), line 4: what is meant by “environmental conditions”
Response 33: The words “environmental conditions” have been replaced by “solar radiation”.
Point 34: CONCLUSIONS-should this be numbered 7 (instead of 6)?
Response 34: Conclusion section has been renumbered.
Point 35: Would it be important to note that in general there are correlations between microbial quality and rainfall events as well as warmer temperatures, but that this relationship does not hold for all watersheds?
Response 35: Authors agree with the reviewer that the relationship between microbial quality, rainfall events, and warmer temperature apply to all watersheds. However, the topography of the watershed as well as land use and surrounding activities are different for each watershed. Those aspects may differently directly impact the correlation between microbial water quality and rainfall.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
Thank you for submitting the responses to the comments raised by the reviewers.
Author Response
The authors appreciate the comments and suggestions raised by the reviewer.
Reviewer 3 Report
The authors have done a thorough job of responding to comments and concerns about the originally submitted manuscript and should be commended for their diligent work that occasionally rises far above expectations, and for enlisting the assistance of a colleague who is obviously versed in the horticulture/water quality nexus. There are two remaining important issues (minor compared to the previous review):
Regarding the literature review-it is not yet clear whether the article includes all the relevant articles (based on the keywords and databases searched by the authors) or if there was any filtering or selecting done to include some articles and exclude others. This could easily be clarified by stating that the authors reviewed all the articles found using the specified keywords and databases (if that is the case).
In the section on water as a vehicle, it is worth noting that 1) even though groundwater may most typically be drawn from deep wells, there are undoubtedly cases in which irrigation water is drawn from shallow wells (in which case water quality may closely resemble that of surface water) and 2) even if wells are relatively deep, not all aquifers are protected. For example, the Floridian Aquifer system has unconfined, semiconfined, and confined areas. And there are overlying surficial aquifers (with often only sand between them and the surface)...and there are karst features as well. So even though water quality in the Floridian Aquifer system is still generally good, it is vulnerable and land use change coupled with increasing use/withdrawal of water may cause water quality problems in the future. See USGS Circular 1355 for details.
Author Response
Response to Reviewer 3 Comments
Point 1: Regarding the literature review-it is not yet clear whether the article includes all the relevant articles (based on the keywords and databases searched by the authors) or if there was any filtering or selecting done to include some articles and exclude others. This could easily be clarified by stating that the authors reviewed all the articles found using the specified keywords and databases (if that is the case).
Response 1: Additional information regarding the criteria used to include publications in the review for the review has been included in the first paragraph of the section “Current Status of Knowledge - Factors Affecting the Prevalence of Foodborne Pathogens in Surface Water in the Southeastern U.S.”
Point 2: In the section on water as a vehicle, it is worth noting that 1) even though groundwater may most typically be drawn from deep wells, there are undoubtedly cases in which irrigation water is drawn from shallow wells (in which case water quality may closely resemble that of surface water) and 2) even if wells are relatively deep, not all aquifers are protected. For example, the Floridian Aquifer system has unconfined, semiconfined, and confined areas. And there are overlying surficial aquifers (with often only sand between them and the surface)...and there are karst features as well. So even though water quality in the Floridian Aquifer system is still generally good, it is vulnerable and land use change coupled with increasing use/withdrawal of water may cause water quality problems in the future. See USGS Circular 1355 for details.
Response 2: Additional information regarding shallow wells and risks of contamination has been included in the last paragraph of the section “Water as a Vehicle for Foodborne Pathogen Transmission during Crop Production”.
Author Response File: Author Response.docx
