The authors used Be and Al cosmogenic isotopes in sediments to

determine the rate of sediment supply to an arroyo in a semi-arid region.

With samples from varying grain sizes, depths, and from several different

landforms, they demonstrate that estimates of sediment supply rates

derived from physical measurements are reasonable; and that sufficient

sediment is produced within the basin to support a 1000-year sediment

cycle within the arroyo. Further, they test and verify the validity of

several assumptions key to this kind of study: first, that the arroyo

channel integrates the sediment from throughout the basin; that the basin

is in long-term steady-state; and that the nuclide abundance of the

sediment is independent of the sediment grain size for this small,

lithologically homogeneous basin.

The authors present in a mostly clear fashion a well-reasoned and

interesting study that succeeds in its goals. A list of references cited

is needed. The addition of one figure, accompanied by an explanation of

the spatial relationships between the categories of landforms they

sampled, will fill the papers one major deficit. In addition, several

minor changes in the text, figure captions, and figures themselves will

add to the clarity of the presentation.

I recommend this paper for publication with only the minor

revisions noted. These suggestions mostly concern grammar and punctuation,

and are noted on the manuscript. My comments for more important revisions

are provided below, and are referenced by number to their location of

concern in the manuscript.

Specific comments

Your reasoning for your categorization of the sampled landforms eludes me.

Id like to see a brief statement as to the typical arrangement of

landforms, their origin, and their contribution to the sediment cycle in

the basin; and a schematic figure showing the spatial relationship between

these landforms.

You need to explain why you use only one of the several erosion rates

shown in table 3. Otherwise it appears that you choose values to fit your

argument.

I dont understand where you get these estimates of maximum volume and

sediment export for the arroyo. These numbers need references or an

explanation for their derivation.

I dont see how the entire depositional history of the basin is mixed by

the arroyo channel. Wouldnt at least some of the sediment be exported

before channel mixing begins? Perhaps addressing comment #1 will make this

more clear.

Steady-state vs. steady state: Your use of the hyphen varies throughout

the paper. Choose to use it or not to use it, and then search/replace to

standardize all instances.

The caption to figure 8 needs rewording to improve the clarity of the

description of the figure. The arrows seem not to correlate with their

description in the caption.

Review of Clapp et al, "Rates of Sediment Supply to Arroyos from Upland Erosion Determined Using In Situ Produced Cosmogenic 10Be and 26Al."

This paper seeks to quantify the rates of upland erosion and sediment supply to the Arroyo Chavez basin in New Mexico using in situ-produced cosmogenic 10Be and 26Al. The rate of upland erosion (275 ± 65 g m-2 yr-1) and bedrock equivalent lowering rates (102 ± 24 m My-1) determined by the authors are in agreement with rates determined by other techniques. Clapp et al., also use the abundance of nuclides among different geomorphic compartments/reservoirs in the basin to verify key assumptions (posed by others but, which have yet to be field-tested) necessary for the determination of sediment generation rates and bedrock equivalent lowering rates using cosmogenic isotopes.

The strength of this paper is its thoroughness. The purpose, procedure, data, and conclusions are presented in a logical fashion and key concepts and explanations are separated into distinct sub-heading sections. The use of cosmogenic isotopes in the determination of erosion and sediment supply rates is presented so the non-expert can understand how and why cosmogenic isotopes work specifically for this experiment and for other similar studies. Many sentences are very long, but the use of numbering within the sentence helps in the flow and presentation of the assumptions, data, and interpretations. The illustrations/figures are generally straightforward and simple. I am still a little confused about what is explained in fig. 9.

This paper should be accepted for publication in its current form with only minor revisions necessary: typos and grammar (noted in the text), updating incomplete references, and possibly a few specific revisions to comments listed below.

1) I'm a little confused by this last sentence. Maybe it's just me, but I can't seem to see how it fits here in the abstract. I've looked back into the text a few times a have trouble finding anything about 'bedrock to soil conversion'.

2) I'm unfamiliar with 'mesa-slope topography' Is it a well-known landform? A schematic diagram of the mesa-slope topography and geology would help me in visualizing what you are explaining in Geomorphic Setting.

3) Here (page 5) you mention the depth of nuclide accumulation is <3 meters. On page 13 and page 18 (fig. 8) you mention it as 200cm/2m.

4) How do you come up with these estimates of sediment export? Did you somehow calculate the estimate of % sediment export, did someone else, or is it just a hypothetical value? This kind of hit me by surprise. You should mention this estimate of % sediment export and time of arroyo back-filling in the abstract.

5) Doesn't figure 4 (p.23) and Results listed on page 8 and 9 say that there are differences in the nuclide abundances between the two reservoirs (hillslope and bedrock)? Yet here you say there are 'no large' differences in the sediment reservoirs.

OF CLAPP ET AL, "RATES OF SEDIMENT SUPPLY....."

This paper presents the results of isotopic measurements made on sediment samples collected from a semi rid basin in New Mexico. The data are used to calculate erosion rates and to test the assumptions inherent in making these erosion rate calculations from sediment abundances.

Overall, this is a reasonable draft manuscript that is full of good data and interesting interpretations. It is currently incomplete and needs polish and completion before it will be ready for submission. It would have benefited greatly from a careful proofreading before circulation.

The results section will be much improved by just a wee bit of interpretation as the specific results are narrated. This will set context for the reader with the data nearby.

The ms would benefit from more explicit consideration of the finding that bare bedrock is supplying little sediment in comparison to rock buried by colluvium. The ms could spend a sentence or two more on the rate of sandstone erosion and comparison to sandstones elsewhere.

Figure captions are very rough and a bit to narrative. They need to be more succinct.

The manuscript could be improved by adding more detail (data) to the abstract. There are many missing references and places where the author has queried other authors -- these need to be cleaned up. Also, some spelling errors made it through presumed spell-checking. These need to be cleaned up before submission. Data are reported in places with many insignificant figures. A critical clean up is needed.

1. Abstract has many marks for glow and grammar. Needs a little more beef such as the number of measurements, proposed minimum cycling times....

2. The Puerco Basin must be larger than this! It took us days to fly over it...

3. Figure one needs some indication of scale in the caption!

4. This is a nice figure that will reproduce and reduce more easily if the font is changed to a san serif such as helvetica

5. Why is Gosse ref in here? All others are sediment? suggest delete.

6. The proper abbreviation for micrometers is um or mm. "m" all alone is meaningless.

7. See rearrangement for flow...

8. Problems with graphics I arroyo channel sediment box.

9. Paragraph break for clarity.

10. Just a little bit of concluding will really help the reader follow what you are doing here. See suggestions on ms.

11. Use of "X" is very confusing here....try a combo figure that keeps the data sets together but apart.

12. Mega yuck double negative....how about, "increase with depth"

13. Try to expunge the "our", too indicative of ownership.

14. Make active...We tested...using four samples...

15. This paragraph seems really redundant..suggest cut or shorten.

16. HOW!!!! there is no mention of how you did this, most importantly in terms of production rates that you used in eq. 1. This section needs to be much more explicit.

17. How is this value calculated? MUST JUSTIFY!

18. Arrows for rates don't line up well and are unclear. This whole figure is confusing. I think it needs a better explanation in the caption.

19. More important than what?????

20. Really, entire? How about 1000s of years...

REVIEWER FOUR

A critical review of "Rates of sediment supply to arroyos from upland and

erosion determined using in-situ produced cosmogenic 10Be and 26Al and

three strawmen" by Erik Clapp et. al.

Clapp et. al. use in-situ produced cosmogenic 10Be and 26Al to determine

the sediment generation to the Arroyo Chavez headwater basin from the

hillslopes and capping mesa, to investigate the validity of the assumption

that arroyo cycling has happened as frequently as several times in the

last millennia. The authors use a well defined system of "compartments"

such as hillslope colluvium, an alluvial fan, basin fill and stream

sediments to determine the residence times in each of these areas. The

result of this investigation supports the idea that arroyo cycling is

possible on the several hundred-time scale. A secondary, but no less

important result of their research, validates some assumptions that other

scientists have used but not proven, such as isotopic steady state,

erosional steady state, and independence of grain size.

The paper is well written except for a few confusing sentences and some

grammatical errors noted on the manuscript. Other suggestions for clarity

are noted below. The data set is complete and the author's interpretation

of the data set leave little doubt that about the quality of science. The

figures compliment the text well. The only suggestion is for Figure 9 to

include sample labels and to show the 90-cm shift that coincides with the

164 m/ Ma erosion rate curve.

I recommend that this paper be published after it address the minor

revisions noted and two more major elements. 1) What percentage of basin

fill is eroded in an arroyo cycle and what happens to the sediment that is

left behind? This is important due to the authors reliance on isotopic

concentrations, and the possibility of contamination from previous cycles.

2) Clarification on why the basin is in isotopic steady state even after

the authors state that sediment generation (and hence probably erosion

rates) have not been constant through out time (as indicated by the 90 cm

slug of sediment). But overall: Good science.

1) Should you start off with something likeCycles of arroyo incision and

backfilling have occurred. cause the way you start that sentence implies

that just incision is happening and the arroyo is getting deeper and

deeper and deeper.

2) Do we have a number rather than severalor even a minimum?

3) Is there another word for cut? It took me a few times to understand,

but I also understand you cannot just use channel because you mean the top

and not just the active channel. I don't know.

4) Is there anyway to quantify the carbonate like maybe a stage I

carbonate deposition? Some nerds might think this is important because

maybe this could tell them something about the age of the basin fill too.

5) If such a basin does not exist, then why do you say that A.C. is in

steady state in your abstract? Maybe you should think about rewording

this sentence or leaving it out.

6) Isotopic steady state: Is the whole message behind this assumption

thisIf the basin is in a steady state erosion and sediment transport,

then the isotopes are in steady state?

7) How can you show us that the erosion rates have been constant over the

103 years?

8) Why the extra sieving? Do we see the data? Is it important?

9) Which six and which 11? 6 x 3 = 18 and the other 11 = 29? What is

happening to your samples?

10) How many samples? 19? You mention 26 on page 3.

11) "All" sampleshow many is that now4?

12) Just a fleeting thought? When these things get reamed out, does all

of the basin fill get transported down to the Rio Puerco? You mentioned

that the Rio Puerco is filling again but Arroyo Chavez is not. So will AC

get the rest of the way reamed out or does much of the basin fill get

left behind? and if it does get left behind, what are the cosmogenic

signatures of the old basin fill? Although you do mention pieces of

evidence which you might want to put together such as outcrops at the

bottom of the cut, fast sed generation rates (less than detection limits)

maybe I am just getting ahead of myself and I should read the rest of your

paper first.

13) I don't think we need the background on what comos isos were used

for. but then again this is QR and probably not an audience with a

working knowledge of cosmos isos.

14) This reads like a conclusion section but saying you are going to do it

rather than you did it. can you make it more fun to read?

15) What is your erosion rate from just the bedrock samples? Unclear

what you are using to determine these lowering ratesyou should state what

samples are used to determine each lowering rate.

16) What about the rest of the basin fill? How much is left and what are

the abundances in this sediment? Do cut and fill events happen in the

sample place and remove same amount of sediment everytime?

17) Not completely true. You could have different initial concentrations

along with differnet combinations of erosion rates to get the constant

isotopic composition below 200 cm. Ok I just read the rest of the

paragraph. I have to read further before I comment like this.

18) do you want to make this number in the same units as the sediment

generation number (g m-2 y-2) to avoid confusion or at least put it in ()

19) label on graph or caption

20) show this on the figure

21) You just mentioned that you have different deposition rates now and

that says to me that you have different erosion rates and thus you are not

in isotopic steady state. What am I missing here?

Review of Clapp, Bierman, Pavich, and Caffee

This paper addresses the topic of Arroyo channel incision in the mid-west

through the analysis of cosmogenic nuclides. The study approached the

analysis of sediment budgeting within the Arroyo Chavez Basin in New

Mexico by first using sample analysis to verify that the assumptions

needed to estimate sediment budgeting were valid. This portion of the

paper specifically focuses on the assumptions of grain size independence

from isotope abundance, fluvial integration throughout the basin, and a

steady erosional/isotopic state. Once the assumptions have been verified,

the authors use a Sediment-Isotope model to determine the rates of

sediment generation and bedrock lowering throughout the canyon. The

resultant rates show that the Arroyo Chavez basin has been cycling through

cut and fill sequences approximately once every thousand years.

The paper has been written in a fashion that can guide a person who knows

little about cosmogenic isotopes through the details of the study. The

author thoroughly explains the reasoning behind the different models and

tests that were used, and how the isotopic compositions have been

produced. The description of isotopic steady state on page 6 is a good

example of the clarity with which the author has explained the basic

principles behind the study. The detailed explanations allowed me to

easily follow the papers content up to the presentation of results on page

8. Results and discussion, although well organized, were technically

written and it took me a long time get to a point where I understood what

was being discussed. I believe that a few organizational changes might aid

the reader through th more technical parts of the paper. For example,

discussing assumptions before the sediment generation and bedrock

lowering, instead of after, would explain how certain pieces of the

assumption validation process were important to the final outcome. I

think that would allow the reader to better follow why those assumptions

needed to be made and proved in order to get the final numbers regarding

sediment generation and bedrock lowering.

The figures and tables are excellent. They were visually clear, easy to

read, informative, and contributed greatly to the discussions in the text.

Considering the benefit of the figures to my overall understanding of the

paper, I think that additional references to figures and tables would be

useful. Many of the figures and tables are only referred to once in the

text, even though the data from that table or figure is discussed in more

than once place. The data appears to be strong, and correlates well with

the discussion of the assumptions and the final conclusions of the study.

My comments regarding specific areas of the text can be found in the

attached manuscript.

I recommend this paper for acceptance with minor edits. The cosmogenic

study provides an interesting and useful comparison to the previous

sediment budget studies performed in the same area (i.e Gellis 1998 and

Dethier 1988). As the author notes in the introduction, this isotopic

analysis of the Arroyo Chavez basin provides more information than

previous studies because of its immunity to the effects of small climate

variations, as well as its ability to determine the residence times of

sediment within different sediment reservoirs. The close correlation of

this studys data with that from Gellis and Dethier demonstrates that if

the assumptions of the sediment-isotope model can be verified, cosmogenic

isotopes can be used to accurately evaluate erosional processes within a

specific sedimentary basin. Hence, the methods of this study could be

applied to other basins for analysis.

Manuscript:

1. Which few millennia are you referring to? I found that confusing.

2. A figure or photo would be useful in the Geomorphic Setting section. A

small stratigraphic column would be useful, but even just a photo of a

typical hillslope within the canyon would be helpful.

3. The indicated sentence is awkward and needs to be reworded.

4. I had a difficult time making the connection between sample locations

indicated in Figure 2 and their corresponding descriptions on Table 1.

For example, it took me a while to figure out that samples 14.1, 14.2, and

14.3 were the same sample except sieved into different portions (I think

that was because the sieving wasnt mentioned until later). Also, a short

explanation about why you took the samples as you did would be useful.

For example, you could explain that different depth samples were taking in

order to verify the assumption that the arroyo was a steady state system.

5. I wasnt sure what the point of this paragraph was. A summary sentence

to connect it all together at the end of the paragraph might help.

6. I wasnt sure what figure 5 was representing, or why the analysis was

being done. Which assumption were you working on?

7. I think you could re-mention one of your figures here.

8. Maybe refer to Figure 6 again?