May 2010 Documents for Stakeholder Advisory Committee Review

• Roughly half of all California land is owned and managed by the Federal Government. Much of it is managed for lumber and mineral production and habitat purposes. It supports grazing animals, large forests and grasslands, and extensive chaparral communities. It seems to me these systems should be given more prominence in the assessment. Privately owned forestlands should also be included.

• Increasing incidence of fires in forest, grassland, and chaparral systems oxidize sequestered nitrogen. Certainly they produce nitrogen based salts that run off or are leached into rivers streams and lakes. I don’t know enough about the biology or chemistry to know whether or not wild fires are significant contributors to atmospheric components of the nitrogen cycle in California, but they could be. For example, a quick web search shows nitrate radicals are measurable in the atmosphere.

• Nitrogen is sequestered in animal tissue. Approximately 3% of human body mass is N. California has a population of about 38 million people. Assuming an average body weight of 45 kg (about half the average of adult males) (I don’t know if this is a good assumption or not.), then the human population is sequestering about 51 thousand metric tons of N per year. That’s increasing at a rate of about 1%/yr.

    There are about 8 million dogs and 9 million cats in California. A similar calculation to that above would show smaller but meaningful amounts of N sequestered in domestic animal tissue.

    As markets change, numbers of cows, cattle, sheep, chickens, turkeys, etc also fluctuate affecting the storage of N. For example, A sell off of dairy cows for slaughter will result in a spike in the release of N into the system.

    If one takes into account wildlife numbers, too, the total impact of N sequestered in animate tissue may be large.

• Much work needs to be done on the impacts of urban nitrogen flow. It is my understanding that over the past three or four decades the N component in wastewater runoff has been reduced dramatically. (This is not to say that the remaining ammonia component may still not cause damage to the environment.) Nearly all of the nitrogen in the urban human waste stream is captured in sewage sludge (biosolids) 30% of which is deposited in land fills, 50% applied to farmland (the latter is a controversial activity), and around 10% is exported. I don’t know what happens to the remaining 10%. Somewhere near 800 thousand dry tons are produced a year. N content is variable from 1 to 5% or so, so 8 to 40 thousand tons of N are processed annually through the sludge system. .

   
• Large amounts of commercial fertilizers are applied to urban landscapes and are largely unreported. Overuse is very likely. (An indicator of the importance of urban fertilizer use is that Municipal Water District in Southern California estimates 80% of its water is used for landscaping). Urban horticulture is an important component of nitrogen input, storage and waste. Check out the garden section of Home Depot or Lowe's or even the local Ace Hardware store to get an idea of urban fertilizer use. The contribution of urban horticulture to N in urban runoff might be important.

• The roughly 8 million domestic dogs and 9 million domestic cats in California consume substantial amounts of commercially produced feed. The yearly excretion of nitrogen by these animals is not so noticeable because of the way it is distributed (unless you step in it), but it is still meaningful. A conservative estimate , assuming .05 kg of waste per cat per day and 0.1 kg per dog, is about 1.25 metric tons/day (about 400 metric tons/year) of nitrogen rich animal food is consumed and equivalent waste deposited in the urban environment. A reasonable guess is that about 10 thousand metric tons of N contained in dog/cat waste are spread across the urban landscape each year. How this contributes to N runoff into, say, San Francisco Bay would be an interesting question.

• Imports and exports of food make the whole problem complex. Colorado beef, Iowa pork, and Arkansas chicken contribute to California’s urban nitrogen input.

• Who knows where the byproducts used in the production of domestic animal food come from.

• As urban areas expand population controls on ungulates – deer, feral swine, etc. are reduced. Increased nitrogen rich waste appears where it may be unwanted.

Al, we respond to you point by point:

1) (Federal Gov't land) The main reason to focus on agriculture is that the vast majority of new N inputs is related to agricultural systems. The statewide N budget does take into account inputs and losses to natural lands as well.

2)(Increasing fire incidence) Fires can volatilize large amounts of nitrogen in natural systems. In drier areas of the state they can be the major N loss pathway. While they are not a significant source of NOx, we should do a proper accounting to document total N losses from fires in California.

3)(8 million dogs and cats) One aspect not addressed in the mass balance so far that will be included in the assessment is the stocks of nitrogen. The N content of all of the animals is dwarfed by the N in vegetation which is once again orders of magnitude smaller than soil N stock.

4) (Urban nitrogen flow) There are some areas that have recently moved to upgrade wastewater treatment particularly in the South Bay, the Santa Ana watershed, and the Inland Empire in part because there is no location to discharge N and in part for water recycling. However, the majority of sewage is still discharged directly into the ocean with little N treatment. Our estimate is 35 thousand tonnes of N in biosolids most of which is land applied, but this is a small fraction of the human waste stream. About an equal amount is sent to the landfill, although this includes non-food waste as well. The vast majority of N in the waste stream is in dissolved portion of wastewater.

5) (Landscape fertilizer application) Turfgrass fertilization is a big mystery as there are very few reliable estimates of N application rates. The literature suggests an average of 100 lbs N/acre for other parts of the country, but there are no comparable data for California. Given the 3 million or so acres of turfgrass at 100 lbs/acre and you get 150,000 tons of N. The fate of N in turfgrass is also not clear. Most clippings are sent to the landfill in California, and there is a large potential for N storage in turf soils, especially for the first 30 years. Turf is excellent at preventing leaching of N, but there is some potential for runoff because of improper irrigation or during precipitation events. However, any runoff should be included in the river discharge numbers.

6) (Dog and cat feed) Our estimate is around 20 thousand metric tonnes of dog and cat waste produced statewide. The assumption is that most cat waste (from fed animals) would go to the landfill with the kitty litter. For dogs, as with humans, most of the N is in the urine, which is largely added to soils. It is certainly a potential source for N in urban runoff (as well as pathogens), but it appears to be relatively small compared to human waste inputs or fertilizer.
  
7) (Inputs and exports) At the statewide level, we don’t make any assumptions about what people are eating. We can tally up all the N produced in the food in the state and the food N demand to estimate the need to move food around. We know that California exports many commodities out of the state such as almonds and lettuce. We know that California imports grain corn. We know that California both imports and exports wheat. From a mass balance perspective it doesn’t matter where the food comes from although for other reasons it is interesting to know.

8) (Byproducts) Who even knows what the byproducts are that go into pet food? This industry, like many others, has recently consolidated and it is very hard to get information about what is in pet food. There are national surveys by the Census of Manufacturing that report what goes into pet food. For the mass balance it doesn’t actually matter what the pet food consists of except whether it is from California or not. There is probably some import of grain for pet food, but I would assume that most of the byproducts are not economical to transport.

9) (Ungulates) We have been assuming that most wild animals throughout the state are excreting N in approximately the same locations where they are eating so that there is no net movement of N in or out. Unlike people and their pets which are eating food that was brought in from elsewhere.

Wildfires and controlled burns may not contribute significantly to the overall N budget but they are very important sources of elevated NOx and VOC which leads in many cases to elevated ozone concentrations. This is problem in particular for the San Joaquin Valley and presumably the Sacramento Valley because these elevated concentrations impact human health and lead to increased exceedances of the 8 hr ozone standard.

As I’ve suggested in the interview and during recent discussions with Sonja and Todd -- based on my review of the summary documents, the project seems largely conceptual and academic, focused on data collection, and creating frameworks and/or models to organize large amounts of data. While I recognize the importance of data collection and clarification in this field, it’s not clear what t extensive body of data is going to be used for, and where this is leading… ie, whether and how that data will be used effectively. I would be delighted to see this whole project to address problems, identify effective and practical solutions -- in terms of developing and spreading the use of farming practices (and/or policies) to avoid/prevent and/or mitigate nitrogen pollution and effectively develop sustainable approaches that enable sufficient nutrients for economical crop production while minimizing negative impacts from nitrogen. It seems like this project COULD be a great opportunity for ASI to pursue research and participatory education/outreach that advances and increases the adoption of more sustainable systems approaches to soil nutrient management and erosion control -- eg, nitrogen-fixing cover crops, crop rotations, intercropping, green manures, hedgerows/habitat conservation, effective nutrient management systems for dairies, and other unusual/innovative approaches, such as breeding of legume crops that have greater capacity to fix nitrogen. There are many producers in California who are providing good examples of such innovations…and making a difference… They are probably a small minority, but I believe it would make sense to analyze, document, learn lessons from those approaches, and work on actions to increase their adoption. . In other words, I hope that the project has a more explicit goal of using data in some effective way for solving pressing problems and increasing advances in this field. (If this project is only intended to collect data for the purpose of creating a large data bank -- ie, as a modeling exercise, then I’m not sure if it makes sense for me to participate actively.)

Ann:
One of the roles of our practices fellow is to examine current management practices to see which ones might increase nitrogen use efficiency and reduce pollution. He will also be examining tradeoffs between reduced nitrogen application and other cropping considerations such as yield and product quality. This analysis will provide a storehouse of information for producers and decision makers to use while implementing management on their fields.

My primary concern is that the diagram of the N-system shown on p. 1 fails to accurately depict the processes whereby the N-cycle is anthropogenically impacted, leading to what is often referred to as the nitrogen cascade. In particular, there is a functional disconnect when moving from the Nitrogen Stocks and Flows compartment to the Ecosystem Services compartment. Leaching, deposition, runoff, sewage discharge, etc. are depicted as drivers of ecosystem services. There needs to be a distinction between ecosystem services and the degradation of ecosystem services.

So of course it is true that a very high level of agricultural productivity confers important social benefits, particularly when we look at the fruit, nuts, and vegetables produced in CA and their inherent health benefits. But the other components listed as Ecosystem Services are in fact being disrupted/degraded by the forces identified under Direct Drivers in the model.

The same point applies to the link between Ecosystem Services and Human Well-Being. Are we achieving Health and nutrition, Economic prosperity, and Social equity from the current processes of N-cycle disruption? Yes, we are to one extent or another but we need a comparable compartment that also makes explicit the negative impact of the current system on human health, most of which occurs as a result of inhalation of ozone and PM 2.5 (ammonium nitrate), our primary secondary air contaminants, that are outcomes of fossil fuel combustion, agricultural production, sewage, etc.

In a similar vein, on the bottom of p. 3 the point is made that a decision was made to leave fossil fuel-related impacts on the atmoshere out of the model, because of the large fraction of emissions that do not interact with California ecosystems, and are not deposited in the state. In fact, there are considerable health impacts from inhalation by humans of these N-compounds and significant crop losses from ozone exposure. I understand that the center of gravity of the model (and this larger project) is cropland and N-use for crops and livestock production, but speaking for an air quality regulatory agency, it is important to work from a comprehensive model that is capable of depicting land, water, and atmospheric impacts from N-cycle disruption as equally important elements of a larger whole.

David:
We do believe that the direct drivers portion of the Conceptual Framework depicts human-caused changes in the nitrogen cycle, which then cascade through biological systems (nitrogen stocks and flows) and have impact on ecosystem services, which then impact human well-being.

The conceptual framework does represent both positive and negative effects of N on the flows of ecosystem services. For instance, the arrow from N stocks and flows to Ecosystem services does not imply that an increase in sewage discharge results in an increase in fish catch. The effect is in fact probably the opposite. However, if this is unclear we shall endeavor to make the framework more portray this link more explicitly without unnecessarily complicating the graphic.

Additionally, we should be clearer in distinguishing the decisions we need to make for the mass balance accounting and the health impacts of air pollution. In terms of accounting at the statewide level, we track N when it becomes incorporated or is removed from the land surface. So we can estimate inputs of fossil fuel related NOx and NH3 production as well as emissions of NOx and NH3 from natural sources (mostly soils and manure) to come up with the total input to the atmosphere. We can estimate the total deposition of oxidized and reduced nitrogen. By difference (assuming a zero or small background concentration of reactive N in the atmosphere) we can estimate export of N from California’s atmosphere to points downwind. Within the state, there are certainly areas where NOx, ozone, and PM 2.5 concentrations are very high with serious human health impacts and we will discuss those in other portions of the assessment. For example, we will include information on trends in the days exceeding air quality standards. If there are other datasets on atmospheric N concentrations, that help tell the N story, then it would be great to hear about them.

in assessing the trade-offs between reduced N applications and other cropping considerations farm profitability must be considered.

The framework needs to address the cost of unequal regulation on CAlifornia farmers and the impact on profitability. You may well achieve a better nitrogen balance at the expense of production agriculture. You will simply export your nitrogen problems outside the borders of the state.

Tim:
Our economic analysis will take this into account as this is one of the key questions asked by our stakeholders.
 

I appreciate the insightful comments from the Stakeholders submitted thus far. It is evident that the quantification of N flows is extremely complex and it is much easier to calculate the imputs than the losses. When looking at the Mass Balance Table, the quantification of the loss data is limited and will require further research and/or modeling to fill in the blanks. The suggested solution to calculating the losses does not give me comfort as to their accuracy. Also, the diffulty of differentiating between the various sources of N in the river (sewage vs ag or urban runoff) is mentioned. The Nitrogen Cycle graph suggests that the conclusions will be based on a view from 30,000 feet.

As a farmer I am hoping that the conclusions from this study will provide me with a road map to adapt my farming operation to more carefully manage nitrogen. However, I am concerned that the data generated will lack the specificity necessary for me to identify my contribution to nitrogen pollution and will cause the regulators to adopt rules and regulations based on the results of the project which may or may not improve the environment. The results should provide the farmer with a clear message so that he can adopt BMPs to either mitigate any nitrogen pollution and/or develop sustainable practices.

Thank you for undertaking a very complex project.

Don:
We are doing an analysis of practices across a range of crops that will hopefully provide producers with the guidelines to implement BMPs. As we are continually told by our stakeholders each farm is different and not all practices work for all farmers, but the goal of the analysis of practices across a range of systems is to provide farmers with some tools and a clear picture of the tradeoffs of specific management practices.

My comments focus on the Mass Balance section. There is a statement that, "a mass balance is an efficient and scientifically rigorous method to track the flows of N in a defined area." That statement is then contradicted by observations on the difficulty of actually making those measurements. I would argue that the statement and a subsequent one about ascertaining the validity of N flow estimate is further compromised in reference to nitrous oxide emissions. To quote from the document, "nitrous oxide (N2O) emissions from cropland soils can be estimated using an emission factor calculated from the predictable relationship of N2O to fertilization rates (which is the approach used in most current emissions inventories). The flow calculated using an emission factor can be compared to the N2O
emissions scaled up from measurements of actual cropland soils; that is, we can multiply the
measured emissions from representative areas of cropland by the total area of cropland". These measurements are in the formative stages and are immensely complex. We have little knowledge of what N2O emission occur from the 350 plus crops grown in CA under a range of soil, irrigation, rotation, tillage, etc conditions. I would argue likewise for losses from nitrate leaching and through biological processes. That is one of the limitation of doing an N balance. We lack much in the ways of studies and field measurements that are needed for scientifically valid conclusions about quantities.

Rather than emphasizing quantification of losses, I would identify the potential magnitude of the loses more qualitatively. We know California is losing a tremendous amount of nitrogen and that there is much inefficiency in the system. Importantly there is also "mal-distribution" of nitrogen. The dairies have way too much. But both dry and liquid manure are difficult to transport and hard to use because much of the N is in the organic form (pathogens are also a concern). Additionally we are not taking advantage of growing legumes and winter cover crops, but for important reasons. Those are some of the topics that would be useful to emphasize, perhaps in a later paper. I understand that the document is looking at the issues more at the 30,000 foot level but it misses important details because of it. But I very much appreciate the effort.

The comments from the other stakeholders are indeed interesting and stimulating -- representing a wide range of perspectives and expertise that raise a number of important issues and questions. As intended, this assessment process is bringing us to grips with what we thought we knew but really do not fully understand.

An example of this adds to the comment by Allen Dusalt about nitrous oxide emissions: for California crops and conditions we cannot simply predict emissions from established estimates. To be more specific, work underway in almonds is showing actual nitrous oxide emissions are substantially less (e.g., one order of magnitude to orders of magnitude) than emissions predicted by estimates.

My concern about the statement in the white paper about a reliable method not existing to distinguish N coming from sewage discharge from N coming from ag and urban runoff was further heightened when I read of two new studies that point to Sacramento’s wastewater having negative impacts on the declining fish populations in the Delta.

One study by Patricia Gilbert of the University of Maryland focuses on the problems with increased ammonia in Sacramento wastewater disrupting algae production in the Delta thus rippling up the food chain to compromise fish species.

Ammonia is a byproduct of urine and feces and is not removed by Sacramento’s wastewater treatment plant, which employs a secondary treatment. Her results show that the decline in the Delta food chain correlates directly with an increase in ammonia in the Sacramento River linked o the capital region's population growth.

The city’s sanitation district does not agree and believes further analysis needs to be done on the water flow and diversions.

The second study by Inge Werner, a toxicologist at UC Davis, indicates threatened Delta smelt may be harmed by exposure to ammonia at levels below federal limits.
She found that the amount of ammonia in the river was not enough to kill smelt in short-term exposures and that the wastewater was more toxic to larval smelt than ammonia by itself, suggesting something else it contains makes the exposure worse for smelt or amplifies ammonia's toxic effect.

These studies emphasize not only the complexity of N differentiation but also what happens when it combines or is exposed to other products and processes. Allen mentioned in his comment above about the 350 (I would say 400) commodities grown in the widely varying ecosystems of our state. We will need to be vigilant in this N review to not simplify this incredibly intricate cycle in an effort to reach a conclusion.

It is quite helpful to read these excellent comments, which reflect some of the things that CCOF and others raised earlier this week, when members members of the California Climate and Agriculture Network (Cal CAN) to which CCOF belongs met with ASI staff. My technical expertise straggles way behind everyone else's, but I represent end user stakeholders who just need excellent research to be translated into tangible actions that they can implement in their farming and processing practices. I'm concerned that the document for review doesn't completely capture that N isn't just a stand-alone issues for farmers, it's part of an extremely complex system. I look forward to the meeting in June where I can learn more from the other stakeholders.

This is a response to Allen, Cynthia, Claudia, and Bob's comments from the ASI California Nitrogen Assessment team.

Allen:
This point is well taken that a mass balance is only as good as the data going in to the calculations. Our goal is to come up with a best estimate for each value but also document the uncertainties in each nitrogen flow. The example of N2O is a good one for understanding the difference between the field-level view and the 30,000-foot view. We are certainly not able to predict what the N2O emissions from a particular crop under the range of management practices that Allen mentions. However, based on the preliminary data from California, along a with much larger global database, we can bracket what a reasonable estimate of N2O emissions would be for all the cropland in the state and determine if this is a major loss pathway for nitrogen. But we agree that there is certainly a lot of work that needs to be done to understand where N2O emissions are higher or lower than the averages.

We agree that there are many inefficiencies related to N use and feel that these should become apparent in the mass balance calculations. The use of specific practices to increase efficiencies will be addressed as well, but not in the mass balance section.

Cynthia:
he main goal of the mass balance is to get a broader understanding of the relative magnitude of the various sources of nitrogen inputs to the state. Because it is so mobile and reactive, nitrogen can easily cause problems far from the original locations where it was used or created. However, we agree that it is important to consider localized problems of excessive N in addition to the statewide view. In addition to the Delta broadly, there are other places like the Stockton Deep Water Ship Channel or streams in the San Bernardino Mountains that are experiencing problems due to excess nitrogen. We don’t mean to suggest that is impossible to separate sources (sewage, animal waste, fertilizer, atmospheric deposition, etc), or that we can simplify all of the complexities of agricultural decisions. At the statewide level we can get a big picture view of the sources and losses, but then we have to dive in to the details to look at mass balances for different land use types or at smaller spatial scales like watersheds or groundwater basins and examine how different management strategies may affect mass balances.

Claudia:
The California Nitrogen Assessment will be conducting an analysis that looks at a suite of practices that farmers will be able to implement in order to better manage nitrogen. This is not captured in the mass balance, but will be captured in the other parts of the assessment.

Bob:
While Allan is correct that we cannot accurately predict emissions at the field level, the purpose of the mass balance is to get as close as we can on the one hand, and to analyze and explain the uncertainty around those numbers and what that uncertainty means, on the other hand.
We certainly welcome any unpublished data available to add to our collection of existing N2O measurements. As of right now there are 6 published studies with field measurements of N2O, 5 of which are in Yolo County. We recognize that we are not at the level yet to predict N2O emissions from any particular field. However, the limited data that we have suggest that on average N2O emissions in California are strongly related to fertilizer application rate just as in the rest of the world. There are plenty of uncertainties in the field measurements considering the number of possible combinations of crops/soil types/fertilization practices, irrigation practices/etc. but the goal of the mass balance to bracket the range of likely N2O (as well as other gases which are even less frequently measured) emissions.

You could perhaps add some factor(s) to include labor or labor saving as a direct driver (this may be included in management practices). Farmers might add more N during first application because they will be too busy to be able to make a second pass later as a side dress.

Additionally, big Ag business and Farm Bill influences should be captured somewhere (they may be implicit in some categories).

Also, wildlife habitat as an additional ecosystem service

Belinda:
The opportunity cost of labor, as well as of other non-fertilizer inputs clearly affects farm management choices. These effects of input costs are implicit in the categories “Farm management” for both animal and crop systems. Machinery use, irrigation water etc…are important inputs too. In addition, the distinction between hired farm labor and family farm labor is also something to take into account. We agree that all could affect N choices in some cases. Certainly, small farms may be particularly constrained by the time of the farmer depending variations across seasons, leading to excess nitrogen application in some cases.

We certainly have in mind farm bill policy and the influence of various stakeholder groups (farmers, agribusiness, environmentalists, etc…) under the category “Social, political and economic factors” of “indirect drivers”.

Wildlife welfare is indeed important enough for the public that it would should be added to the shortlist of ecosystem services provided in the Ecosystem Service box. Thank you for spotting this omission.

We note that agricultural imports are considered as an input to California but do not find agricultural exports accounted for as a loss. If the boundary is going to be the state lines it would seem that N exports in products shipped out of state should be credited as a loss pathway. Agricultural products are shown in the Conceptual Framework, but do not seem to be included in the mass balance.
Nitrogen as nitrate in groundwater is a particular concern for dairy farms and various practices and investigations are proceeding to control N discharges to groundwater. There are areas of the state where groundwater has elevated levels of nitrate, and it is relatively easy to assume that it is of dairy origin. There are significant other areas that are equally high in nitrate, but historically have not had dairy farms. An important point to make is that research to assist in doing a better job of source determination will be critical in effectively understanding the roles of various contributors to CA N flow.
As urban wastewater treatment plants are prohibited from discharging into water courses of the state, increased competition for the land base necessary for disposal of wastewater by irrigation is bound to occur.
We note a statement in the mass balance discussion that NOx and NH3 “affect air quality and respiratory health.” It should be noted that ambient levels of NH3 are generally far below levels where they might be harmful on their own, even close to manure storage facilities. The risk is in enclosed spaces. Additionally, there are differences depending on location. In the South Coast air basin control of NH3 is indeed part of their particulate control strategy, but in the San Joaquin the targeted element is NOx. We should probably be careful not to make too broad of assertions lest we inadvertently lead the thought process down an inappropriate path.
We have attempted to quantify N2O releases from furrow irrigated corn plantings using an EPA approved flux chamber. We can only state that our efforts were wildly unsuccessful. Allen’s point is well-taken.
As is Cynthia’s regarding ammonia releases by urban plants. If a dairy farm released a similar amount, they would be subject to enforcement action.

Paul:
Agricultural exports are counted as a loss but since they are less than imports the overall net change positive. If this was unclear we will aim to remedy that.

We are looking to find the best available science to understand the hydrology of flows of nitrate into groundwater across the state.

We are also analyzing the best available knowledge of the public health community to understand the linkages between NOx and NH3 and air quality and respiratory health.

While it is true that N2O emissions are difficult to measure, we are able to get within a measure of accuracy and will reflect that knowledge and the uncertainty around it in our assessment.

My comments are the following:

1) on the mass balance of nitrogen subheading in the third paragraph, it says that "we don't always have a reliable method to differentiate between the various sources of" N. This is true, although there are a number of scientists that have been looking at doing just that through a combination of tracers, age dating, and isotope analysis through Lawrence Livermore and USGS. So it is not that this is impossible, it is just expensive and time consuming as I understand it. Of course some areas are more complicated than others as well.

2) I am interested in how you plan to "investigate whether there are particular local and regional hotspots of N which threaten both ecosystem and human health."

3) In the "How N Flows are Calculated" section, on the Inputs, I see (6) "dissolved N in groundwaer pumped for irrigation and drinking water" as also a loss in the sense that it is moving N from deeper in the aquifer to the surface where it may be taken up by crops or released into the atmosphere or denitrified in the soil, etc. In fact, one way of "treating" or "cleaning up" nitrate contaminated groundwater is to "pump and treat," which is essentially what this is describing. So I am not sure that that fits but I think that is not entirely captured here as is.

4) on the mass balance table, I am not entirely clear on how you got the numbers for fertilizer application and synthetic N chemicals and what the differentiation is. Is synthetic fertilizer included in fertilizer? Also, where did you get the number for groundwater pumping. And again, I feel there should be numbers on the input and potentially losses as well, although I am not sure exactly how to fact the different dynamics in (see comment above).

Laurel:

1) Laurel sums up the issue quite nicely. There are cases where the limitation is the cost and time to collect and analyze and interpret the samples while in other cases the interpretation is much more difficult.

2) There will be two approaches to the hotspot issue. The first, is a qualitative approach compiling information from the literature where nitrogen excess of some sort is a problem. So that areas with contaminated groundwater, poor air quality, high N deposition, eutrophication, etc. can be identified. The second approach is more quantitative. We will begin with a gridded landcover map of the state. A mass balance can be done for each grid cell and we can estimate the total amount of N flowing through a point in space and partition the fate of the N inputs as gas losses or leaching losses.

3) Because anything below the root zone is considered out of the study area, N in recharge is a loss and N in extracted water is a new input (along with the N dissolved in water pumped out of the Delta by the CVP and SWP because the Delta pumps are pumping water that has already been “lost” by the rivers based on our boundaries). For groundwater extraction, we are assuming that the nitrate is not removed prior to the agricultural or municipal water use . For the statewide mass balance, we do not need to distinguish the fate of the N, but for the grid based mass balance we will have to apportion groundwater pumping on the landscape. We are assuming the N extracted in the groundwater is not treated in any way prior to use.

4) All synthetic fertilizer starts as ammonia, which is all imported to California. There is the production of other fertilizers in California from ammonia as well as the import of other types of fertilizer produced elsewhere. Ammonia is also the primary starting point for other synthetic chemicals besides fertilizer such as resins, plastics, and explosives. There are national, but not California specific numbers for these other synthetic N uses. So we can scale by the population of California to estimate the amount of non-fertilizer synthetic N. We have lumped fertilizer use with other synthetic N chemicals, but the latter are about 5% of the total. The assumption is that most of these synthetic chemicals are stored in the urban landscape or end up in the landfill.

Thank you for the opportunity to comment on these documents.

Procedurally, some description of the intended audience and use of documents for review could be useful. I'm assuming these are primarily intended for outreach to agricultural and environmental interests, policy-makers, and the interested public. For that purpose, I think the graphics are visually appealing and the text readable, with minor defects such as in Para 2, line 7 (delete "the" in "...or the there are...").

My primary concern is that these documents do not convey a strong message regarding why anyone should care about this issue, though I believe there's a fair degree of consensus in the scientific community that, globally, human activities have seriously disrupted the nitrogen cycle. The draft Nitrogen Cycle graphic does specify some environmental endpoints, but I would suggest taking that a step further and monetizing or otherwise quantifying the damage to human health and ecosystem services attributable to reactive nitrogen in the environment (as well as its positive value for food production). I note the earlier comments about the complexity of quantifying stocks and flows for a rigorous mass balance and recognize that economic valuation of ecosystem service effects adds another layer of complexity, but I think the explanatory value would be worth the effort.

Don:
The communications and outreach team for the assessment is working to create materials that help the general public and non-specialty audiences understand the nitrogen cycle and the issues around the disruption of this cycle. These include interactive graphics of the nitrogen cycle, slide shows that explain how nitrogen moves through natural systems and its impacts, video interviews with expert scientists and farmers, etc.

One of the challenges in this communications project involves the fact that the entry point for public interest is usually related to issues of human health – this is what people care about the most. However, this is one of the areas where there is considerable amount of scientific uncertainty related to where the nitrogen is coming from and what is the true extent of the health impacts. We are working to be sensitive to this uncertainty in our communications while not undercutting the importance of nitrogen pollution’s impacts on the environment and human health.

Your suggestion about monetizing and quantifying damage is well-taken. Changes in Ecosystem Services affect human wellbeing both positively and negatively. The arrow from the ES box to the Human wellbeing box simply represents an effect and not the sign (+ or -) of the effect. We propose to measure the magnitude of these effects.