Multivariate Analyses of Water Quality Dynamics Over Four Decades in the Barataria Basin, Mississippi Delta

Round 1

Reviewer 1 Report

interesting analysis of datasets which enables a long-term examination of the water quality in an estuary that has seen tremendous anthropogenic disturbance over the last century.

This is an important study, which is highly relevant to estuarine restoration efforts both in terms of restoring hydrology within estuaries and in preventing tidal wetland loss via diversions of sediment (and NUTRIENT rich) river inputs.

There are some editorial needs in terms of writing style. there are several places where paragraph topic sentences need to be modified.

THe discussion lacks an analysis of TSI.  What do the scores obtained here mean in comparison to other locations?

 

I need to attach my edited pdf for the authors.

Comments for author File: Comments.pdf

Author Response

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Reviewer 2 Report

156-159:  The data were log normalized for the ANOVAs, that’s good. 

159: the data are presented as the normal metric.  Presumably this means that the data were back-transformed.  If the data are asymmetric, shouldn’t the geometric means be presented?  Depending on the skewness, the geometric mean is usually a much better measure of central tendency than a simple arithmetic mean.  

Fig 2: Why are only 3 forms of nitrogen presented?  Surely ammonium is important at some of these stations. 

310:  clarify top ones.  Highest scores?  Uppermost stations?   If Fig. 2 it looks like the post-diversion TIN is lower downstream than pre-diversion TIN.  How do you explain this? This seems to be inconsistent with item g.   Please plot the geometric means.  I think it is acceptable to plot the SEs computed from arithmetic means around the geo means as long as you indicate what you have done.  You can’t calculate a SE on a geo mean, but you can calculate 95% Cis. 

364:  Mean concentrations, meaning arithmetic mean concentrations?  In general, arithmetic means are misleading when the data are skewed.  I would correct this.

366:  Here is mention of ammonium.  It is lower than NO3 in drainage from a swamp, which surprises me.  It is lower also in ag runoff, which is not surprising, but it is still the same order of magnitude as the low end of NO3.  This is not a criticism, just a comment, but it would be good to include a time series graphic along with the rest, unless it is essentially a flat line. 

Table 1:  does TIN include ammonium?

372:  insensitivity of drainage to what?  Insensitivity of nutrient concentration to changes in drainage.

378 The result of these studies – maybe add [12, 22,24] to indicate what studies you are referring to.

390:  NO3 was non-conservatively reduced. What does this mean?  Maybe uptake/loss was greater than can be accounted for by dilution?  This paragraph is contradictory.  It leads by saying that deterioration in WQ in the upper basin was due to ag runoff and canals that bypass wetlands, and it concludes by saying that inorganic nutrients were rapidly reduced. 

What effect if any is the dilution from GOM tidal waters or lateral inputs along the flow path that would lower concentrations?

The major conclusion is that there has been no evidence of deterioration of water quality in this basin after the diversion.  That is important and is supported by the statistics.  The PCA plots are a nice touch.  Can you make the arrow heads in the Seaton and pre-diversion plots the same size as the post diversion plot? 

411:  became

 

Author Response

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Reviewer 3 Report

The authors investigated the dynamics change of water quality collected from 1977 -1978 and 1994-2016 dataset in Barataria Basin. For this objective, they used ANOVA and PCA for examining three datasets before and after division periods which allowed us to analyze the relationship between parameters and its water quality deterioration. The authors concluded that the water quality of the upper-basin and low-basin affected by concentration of nutrients and clear water. From this view point, the manuscript represents an interesting and useful input. Following concerns must be faced before being usable for publication.

1. Line 203, 204, ug/L à µg/L.
2. Line 347, please provide more details regarding how to estimate TSI scores and Table 3 4-variables and 5-variables data.
3. In discussion section 4, Line 349-406, authors must provide more faithful representation regarding the water quality of the low-basin affected by division water.

Author Response

Reviewer#3

Line 203, 204: ug/L à µg/L.

Response: This correction has been made.

 

Line 347: please provide more details regarding how to estimate TSI scores and Table 3 4-variables and 5-variables data.

Response: More detail has been added to the text regarding the TSI scores and associated Tables.

 

In discussion section 4, Line 349-406: authors must provide more faithful representation regarding the water quality of the low-basin affected by division water.

Response:  We think that the reviewer means diverted water. In general, the levels of nutrients are lowered to levels of the lower basin by the time water flows south of Lake Salvador. Nitrate in diverted river water from the Davis Pond diversion is reduced to ambient levels by the time river water flows into eastern Lake Salvador.

Round 2

Reviewer 3 Report

Accept, no more comments.