Carbon Footprint of Lamb and Wool Production at Farm Gate and the Regional Scale in Southern Patagonia

Round 1

Reviewer 1 Report

• Generally speaking, an interesting article. A few things needs to be clarified throughout the article
  • Please be very clear about what geographic areas - region of Patagonia, province of Santa Cruz etc. eg line 41 & line 95-105 – if this study only covers the Santa Cruz province in the Southern Patagonian region, please be clear about this.
  • Functional unit – as this study is for a cradle-to-processor gate, normally you would report the CF for the entire supply chain, and then break it down into subsets eg on-farm, transport, processor. The current presentation of figures is very confusing, and a CF of 12-1-38.5 kg CO_2-eq/ kg live weight lamb meat – is it live weight, or lamb meat, they are not the same. And does the 3.31kg refer to the additional CO_2-eq emissions from processing? It must be very clear about exactly what kg lamb you are referring to – are you talking about carcase weight or a retail ready product (ie bone-in) ie how is the meat exported?

Please make sure you use kg CO_2-eq and other SI units eg kg (not Kg) and make a general check for editorial issues (eg Table 4 – fam gate, overgazed)

Line 13 – “the Patagonian region” Line 14 – ruminant livestock are the main problem Line 19 – as per general comment, it would be more useful to report the CF of the whole system, then discuss the on-farm contribution Line 21 – it would be useful to make it obvious what % transport contributed to the overall CF, rather than stating the unit as it is Line 27 – replace powerful with significant Line 28 – missing some text after ranged?

Line 40 - The introduction should cover other LCAs of lamb and wool production – it is included in the discussion section so should be introduced here Line 41 – make references consistent eg steppe grasslands or steppe ecosystem – are grasslands and steppe the same thing? How does this relate to the 5 ecosystems discussed later? Line 43-44 – why the sudden mention of Santa Cruz? Is this the same as Southern Patagonia? Please make it clearer exactly how all these geographic areas relate to one another,  Line 48 – what are the regular evaluations? Financial? Productivity? Line 62-65 – speciality – do you mean life-time grass fed? Similarly, is the CF about marketing, or do you need a CF to export into certain markets? Line 80 – are all the variables independent? It is much more likely that some of the variables are actually dependent. Line 80-82 – not clear how the hypothesis can be that grazing effects CF when it isn’t included as a variable – need to include a comment that different grassland condition are considered. Also make it clear whether the CF includes changes in soil carbon. Line 84 – constrains or promotes grassland production?

Line 89-94 – how were the farms categorised as good ecological condition or overgrazed? Was it based on the stocking rate from the data you obtained from farms, or something else? Please provide a reference or explain how the reported numbers were calculated. Line 92 – is ANPP the same as NPP in table3? Just use one term consistently Line 90 – can a summary of the number of farms in each ecosystem be provided, even if just in the supplementary material. It is a bit difficult to tell from Figure 1 B and D Line 95 105 – Does “cold temperature region” refer to the whole Southern Patagonia region, or just the Andes Mountains? Please make it absolutely clear if the multiple uses of the term region refer to Southern Patagonia, or in fact to the ecosystems? Line 100 – variations in precipitation are mentioned, are there other variations which are relevant? Fig 1C – transport routes? Fig 1 D – white could be used instead of the light grey. Line 123-4 – please rewrite Table 1 – Outputs – are these both per year? Line 135 – what are extensionists? Are they lease hold farmers? Feedlots? Line 168 – what do you mean by manure management? It is because it is extensive production, there is no stockpiling of manure so it is assumed to degrade aerobically in the field? Or does this mean that no emissions from manure were included in the analysis? Line 177-183 – if this was assumed data, where was it taken from (please provide a reference)? Or was this calculated from the primary data from the 63 ranches? Fig 2 – needs an arrow for DMI from ecosystem to Livestock – perhaps make livestock box a bit separate + include flow from excreta to ecosystem? Why does F-Erosion have double arrow? Consider labelling Figures 2a and 2b. What do the numbers in the second diagram refer to? What is Estancia? Key – please revise, couple of errors (C leached from top soil, voc from soil, carbon leaving the farm as products, remove second Rh Line 202 – did you assume the same fuel economy for the wool transport? Line 207 – mention that Comodoro is in neighbouring province Chubut Line 208 – metric tons? Line 204-219 - it should be stated whether the product is exported as chilled or frozen product? And as whole carcasses, sides or boxed products (ie boxed product, there should be some packaging in the inventory, so probably not)? The meat yields should be specified somewhere, even if only in an appendix (is live weight to hot standard carcase weight = dressing yield, chiller losses, retail yield (cold carcase to bone-in retail). Are any skins from the meat processing plant sent to the wool processing industry? What assumptions are made about methane emissions from wastewater treatment from processing? Or is it excluded from the study? How are byproducts dealt with? Are any emissions allocated to them, or is system expansion used? eg tallow, meal, skins, manure, paunch, boiler ash, nutrient content in wastewater, biomethane from wastewater etc System boundaries – if the product is exported, why doesn’t the analysis include transport to the point of export? Or at least state where it is and why it wasn’t included Table 2 – it would be useful if the energy consumption was reported in consistent units, to enable comparison with other studies eg MJ or GJ, rather than MWh, m3 natural gas and L diesel, or at least include the conversion factors included as a note in the table. Line 223 – fitted? Or developed? Line 225 – Needs a bit more discussion of how the CF was calculated from the farm data eg was the data from the two grazing intensities extrapolated to each region? Line 226 – how were the 32 variables selected? Why weren’t some metrics relating to animal productivity used, such as lambing %, kg/meat or wool produced per hectare per year? Number of lambs reared per ewe mated/ lamb growth rates (as per line 425) Table 3 – NPP – gC (not grC)? Spell out m.a.s.l Line 239 – remove “among these uncorrelated variables” because it is not clear that they aren’t independent/ uncorrelated Line 244 & 248 – is this referring to the calculated values from the farm data vs the modelled value from the region model? Line 247 – what database?   Line 250 – spell out the acronym ANOVA Line 255 – consider replacing mask with screening criteria Line 259 – first Line 258 – 262 – this seems like quite a complicated procedure, couldn’t the transport distances have been included with each ranches other inventory data? Line 264-266 – seems a bit repetitive? Line 277 – quantity of pixels for the whole province? Does this mean the land area of the province was split evenly between the 2 categories?

Line 283 – keep figures consistent with Abstract. As per previous comment, the CF contributed by processing was 3.3 kg, not the CF after processing, as per previous comments. Line 333 – west-southwest Line 346 – as per previous comment, are they independent? Some of these correlations could have nothing to do with the CF, they could simply be that they would correlate anyway. Figure 5 & 6 – consider using L, M, H on graph instead of A, B and C. Line (366-377) + (385-399) – consider moving to Supplementary material Figure 7 & 8 – include that it is cradle to processor gate somewhere in title

Line 419 – grazing intensity-past management ? What does this mean? Line 420 –CF (not CD), what is meant by harsh environmental conditions (low/high temperature?) Line 429 – 436 – this is the first time you have mentioned biodiversity, you should include it in the introduction if you want to include it here Line 484-486 – this belongs in section 4.1 Line 509-511 – please provide a reference Lines 533+ – some of this text should be moved to the introduction? Might be worthwhile looking at Ogilvy, S., Gardner, M., Mallawaarachichi, T., Schirmer, J., Brown, K., Heagney, E. (2018) NESP-EP: Farm profitability and biodiversity project final report. Canberra Australia for some information on similar systems in Australia.

Author Response

"Please see the attachment."

Author Response File: Author Response.pdf

Reviewer 2 Report

The study aims to compute the carbon footprint (CF) of the sheep production system located in the Southern Patagonia area, from the production of lambs and wool in the farm to the transport of the outputs to the industrial sites to their industrial processing. Moreover, the authors tested the correlation of different topographic, climatic and vegetation variables on the CF classes of the lamb and wool, and performed the upscale of the farm-gate CF to the entire study are using a multiple regression model.

The study interestingly focus on expanding CF analysis on the supply-chain point of view and on a geographical point of view, connecting the CF analysis to the local ecosystems of the study area, thus reporting information usable to test mitigation options in the future.

 

Broad comments

Aims

The authors had the purpose to respond to five different demands: 1) what are the CF of sheep meat and wool in the study area; 2) upscale the farm-gate CF including also the contribution due to the transport of sheep and raw wool to the industrial processing and that due to the industrial processing; 3) upscale CF to the regional level by using a step-wise multi regression model based on topographic, climatic and vegetational variables; 4) test the hypothesis that CF is more sensitive to stocking rate (as indicator of grazing) than other explanatory variables; 5) test the hypothesis that CF is lower when the environmental conditions (rainfall, temperature, topography) constrain grassland production.

Objectives no. 1-3 is well established and the results reported answered the relative demands.

About objective no.4, the study reports the mean CF of each ecosystem split between overgrazed and good grassland conditions, on one hand, and the correlation of the classes of CF with different topographic, climatic and vegetational variables. However, no clear answer to the hypothesis is reported. Please, make clear if “farm level CF is more sensitive to the effects of grazing (stocking rates) than the other potential explanatory variables such as transportation distances and emissions resulting from industrial processing”.

About objective no. 5., no information to formulate this hypothesis is reported in the introduction section. Please add a paragraph in the introduction section about the factors affecting grassland production, in particular about the variables then reported in the results (i.e., mean annual temperature, rainfall, slope, NDVI, NPP).

 

Material and methods

The study involved 63 farms, located in 5 ecosystems of Southern Patagonia and characterized by two different grassland status (“overgrazed” and “good”). Although the authors report in figure 1 the characteristics of the study area and the location of the farms, the experimental design is not totally clear. Please add the information of the distributions of the farm in the “ecosystem” variable and in the “grassland status” variable. Moreover, a short table with data about mean annual temperature, mean rainfall, mean scope, NDVI and ANPP per ecosystem would be useful to understand the results.

The section 2.2 (“footprint calculation at farm level”) presents the materials and methods used to calculate CF result, which type of gases the authors took into account and what production phases they considered. Usually, CF calculation follows the recommendations of the ISO standard 14040 (ISO, 2006), thus separating the goal and scope definition, life cycle inventory, life cycle impact assessment and interpretation. To make the reading more clear, the use of this four points would be useful.

In particular: 1) please state very well what type of inputs (e.g., off-farm feedstuffs?) and phases are included in the CF computation, 2) report in a table the emission factors and equations used to compute the CF, with relative references.

 

Among the emission factors, either enteric methane or nitrous oxide volatized from animal excreta at pasture are fixed factors (per head or per hectare). As these emissions constitute a great part of the farm-gate total GHGs emission, it is fundamental to state the limit of the study, explaining why the authors did not use Tier 2 or 3 levels of emission calculation. For example, data about diet characterises and nitrogen animal input-output flow could help to have an idea from where the values “2.45-7.62 kg N₂O/ha/y” derived.

About the carbon emission related to the soil, different fluxes (autotrophic and heterotrophic respiration, plant photosynthesis) are considered. In literature, a substantial equilibrium in C-soil fluxes is reached in 20-30 years from the shift from arable crop to grassland. The paper is not clear in the C net fluxes from the soil calculated in the study, if it is calculated at farm level or ecosystem level (good vs overgrazed grassland), what is the mean value of C net flux and mean value of the single contributions. Please give precise information on C fluxes (C lost to atmosphere due to soil respiration, - as CO₂ or CH₄, C lost due to animal respiration, C fixed by plant, C leach into deeper soil levels, C input due to animal excreta). This also because most of LCA study cut off CO₂ due to animal respiration and CO₂ fixed by plant because of its recirculation in C global biogeochemical cycle.

Reading about the CF in the different stages (farm, transport, industrial processing) and the modelling on regional level of these CF, it is not always clear what CF is involved. Using different name (e.g, CF_FARM if considering only CF at the farm-gate) could make the lecture clearer.

 

Results

Because of the consideration of all the processes from animal rearing to transport to industrial process, reporting the CF of lamb meat per unit of carcass as well as per unit of live weigh could give insights on the loss due to carcass yield.

The study aims to compute the CF of sheep sector from farm to transport to industrial processing. As only ranges of value for the three single phases are reported, a whole CF value lacks. Please add the mean value and range of the whole CF per 1 kg lamb live weight and 1 kg wool from cradle to industrial processing gate.

 

Discussion

In the section, the discussion of the results about what variable explained better the CFs of lamb LW and wool is short and authors did not do deep considerations about this point of the aims. Please add one-two paragraph to discuss these results.

Correctly, the authors discuss the consequences of the results found about the relation between CF and grassland productivity, showing the research gap and the trade-offs in the land sparing vs land sharing issue. As the study involved an extensive and grassland-based livestock system, I ask if result of CF per m² or ha could be reported, because of land is an important trait of this type of livestock system.

The study focus also on the contribution of C fluxes from and to soil and discuss the possibility to have notable negative CO₂-eq fluxes in the system. However, the discussion of the limits of this option (saturation of the C stocking capacity of the soil) lacks. Please, add a section to discuss results also in this point of view.

 

Conclusions

At the state, conclusions are too general and not linked with the paper. Please insert the answers to the different issue arisen in the objectives.

 

Specific comments

Abstract

Line 15 delete “related”

Line 22 check the unit of measure

Line 23 CO₂-eq

Line 30. NDVI is not stated

 

Introduction

Lines 44-45. The sentence is not clear. I suggest: “Extensive livestock production systems in Southern Patagonia, based on low input level and natural areas, are dominant,….”

Lines 53-58. Before introducing grassland management effect, add a sentence to explain the contribution of the grassland-based livestock production to the total GHGs emission of livestock sector.

Line 53. The sentences is clear but not well written. I suggest to change in “ Grassland management can determine whether extensive livestock systems could be a net sink or a source of GHGs”.

Lines 56-57 Shift the sentence before line 54, to improve the issue flow.

Lines 62-65. The sentences are not well linked with the previous sentences. I suggest to report that CF could be useful for different purposes, then listing the advantages and possible uses.

Line 73 Environmental-minded

Materials and methods

Line 87 ranches or sheep farm? Be consistent throughout the paper

Lines 147-149. Use the characterization factors derived from Myhre et al. 2013 (V IPCC assessment report) instead of IPCC, 2006. Consequently, update the results of carbon footprint.

Lines 161-173. Please give here (or in Results), the mean value and the range of the emission (positive if C is emitted to the atmosphere, negative if the soil is a net sink of C) about C fluxes from soil.

Line 194 please delete “Rh=”

Line 195 “NO₂ + CH₄= C content of manure left in the ecosystem (kg C/ha/yr)” is not reported in the figure

Line 220. The table reports the range of values, not the mean. Please add a column with the mean value of the variables.

Lines 247-251 Authors stated to have tested the CF model performing a calibration using the same database (observed vs modelled) and simple and two way Anova considering ecosystem classification an land use intensity (= grassland condition of overgrazed vs good?). Please report the results of these analysis.

Line 256 ELE was not stated as abbreviation before (only in the table 3). Please explain the abbreviation also in the test. In the same way, the other abbreviations reported, throughout the paper.

 

Results

Lines 283 As the functional unit was 1 kg lamb live weight, substitute “lamb meat” with “lamb live weight”. Check throughout the paper.

Line 299. Check if the unit kg CO₂-eq /kg product/km is correct. Is it kg Co2-eq/kg product?

Line 309 CO₂-eq. Check the subscript in the chemical formulas throughout the paper

Lines 336-337 the 5^th aim of the paper was to test the hypothesis that “CF would be lowest where the physical environmental conditions (moisture, temperature, topography) constrains grasslands production”. Reading the 336-337 lines and knowing from literature that CF was lower where grassland is more productive, I think that the real hypothesis to test is “CF would be lowest where the physical environmental conditions (moisture, temperature, topography) ARE NOT constrainED grasslands production”, isn’t it?

Lines 366-393. Technically, all the abbreviations are stated only in table 3, whereas each figure and table should be self-explanatory . Consequently, reading what the data are showing is difficult. Please modify.

Discussion

Line 420 CFs instead of CDs

Line 459. The sentence is incomplete. Please complete.

Line 478. “processing in processing plant” makes the sentence difficult. Please reformulate

Lines 508-511. The discussion of the different options to abate enteric methane could be long; moreover, no consensus exists on one option because of all have different side-effects to be taken into account. I would not cite one option as better than others. The citation [52] is dated and focussed on cattle, and more recent reviews could be used.

Line 532 life cycle, not lifecycle. Please, correct.

Line 533. No abbreviation at the beginning of the sentence.

Lines 555-557. The sentence could be split in two shorter ones.

 

Table 1. Add a column with the mean values of the variables

Table 4 add lines with the mean values for each ecosystem, beyond the mean value for overgrazed and good grassland condition within each ecosystem. Add a line with mean value of CF for all the database, for lamb LW and wool.

Figures 3 and 4. ELE is not stated

Figure 5 and 6. It is difficult to read the axis of the different images, what type of values they represent. Please modify.

 

 

Author Response

Please see the attachment

Author Response File: Author Response.pdf