The Question

Date: Fri, 07 Nov 2008 10:53:52 -0500
From: Angel Dybas <ald68@cornell.edu>
Subject: Question regarding nutrient monitoring
To: Kris Stepenuck <kris.stepenuck@ces.uwex.edu>
Organization: Cornell Cooperative Extension

Hi Kris,

I tried to send out an email to the listserv last week, but I don't know if it went through. I'm looking for information on how groups are monitoring for nutrients. I may be taking over a water quality monitoring program that we have at Cornell Cooperative. In the past, they monitored nutrients four times a year using the LaMotte spectrophotometer that we have. Since nutrients are a huge problem in the estuary we're monitoring, I would like to monitor for nutrients more often, however, the spectrophotometer that we have is not giving accurate readings. I would like to know if spectrophotometers such as LaMotte or Hach are capable of getting results comparable to a laboratory. If you know of anyone that could provide some advice, it would be greatly appreciated.

Thanks,

Angel

Date: Fri, 07 Nov 2008 13:28:37 -0600
From: "Clay, David" <David.Clay@SDSTATE.EDU>
Subject: RE: [CSREESVolMon] Question regarding nutrient monitoring
To: Kris Stepenuck <kris.stepenuck@ces.uwex.edu>

My suggestion is to send you instrument in for recalibration and run appropriate standards.

David Clay, Director
Drought Center
SDSU
Brookings, SD 57007
605-688-5081
david.clay@sdstate.edu

Date: Fri, 07 Nov 2008 11:54:49 -0800
From: Bridget Hoover <Bridget.Hoover@noaa.gov>
Subject: RE: [CSREESVolMon] Question regarding nutrient monitoring

Hi Angel, most of our nutrient analysis is conducted by a certified lab, however, for a couple of programs we do use Hanna meters in the field for orthophosphate and ammonia. Both have shown good correlation with lab samples (with slight modifications to the manufacturer’s instruction and reagents). If you’d like more details I can provide them.

Bridget Hoover
Water Quality Protection Program Director
Monterey Bay National Marine Sanctuary
299 Foam Street
Monterey, CA 93940
B (831) 647-4217
F (831) 647-4250
www.montereybay.noaa.gov/

Date: Mon, 10 Nov 2008 10:01:24 -0600
From: Jay Gilbertson <edwdd@brookings.net>
Subject: Nutrient monitoring question
To: ald68@cornell.edu

Angel: Through the wonders of listserv, your question about nutrient monitoring made it to South Dakota. For several years now, we have been using a couple of HACH sprectophotometers (DR/4000 and DR/5000) to test for nitrate in well water and other samples. The particular test we use is one that does not require any additional sample manipulation, so it lends itself well to public outreach (www.eastdakota.org/NT.html). When we have checked our machine results against those from splits sent to our State Health laboratory, the results have been very good (for the both the project summarized at the website, and all subsequent tests). So far, we have really only had one sample exhibit a large deviation, and that is attributed to operator error (I had loaned the device out to a local soil conservation district, and they appear to have screwed up the math).

We have not tried measuring any other constituent, but I am reasonably confident that the results would be the same. We have been very satisfied with our HACH units (although at >$6,500 each, I would hope they work well!).

Jay P. Gilbertson, Manager
East Dakota Water Development District
132B Airport Avenue Brookings, South Dakota 57006
(605) 688-6741
edwdd@brookings.net

Date: Tue, 11 Nov 2008 09:02:54 -0500
From: Todd Walter <mtw5@cornell.edu>
Subject: Re: [Fwd: [CSREESVolMon] Question regarding nutrient monitoring]
To: Angel Dybas <ald68@cornell.edu>, "Brian K. Richards" <bkr2@cornell.edu>,
Larry Geohring <ldg5@cornell.edu>

Hello Angel,

Your question about monitoring nutrients was forwarded to me (among others). We do quite a bit of nutrient monitoring and might be able to help answer your questions. First, what is the objective of your monitoring (what do you want to see) and what nutrients are you interested in? Also, what are typical nutrient concentrations?

In general, you can get very good results with a wide range of approaches if the person doing the analysis is careful. The community science institute here in Tompkins County has one spectrophotometer and some burettes that make up the core of its analysis equipment and they generally get reliable numbers.

Peace,
Todd

Date: Sun, 16 Nov 2008 13:05:29 -0800 (PST)
From: Paul Mack <umrgrad@sbcglobal.net>
Subject: Re: [CSREESVolMon] Question regarding nutrient monitoring
To: ald68@cornell.edu

Angel,

Here are my 2 cents...

Hach spectrophotometers are respected and widely used in industry. We have had good reliability with our old Hach instrument in nutrient analysis, and it still can calibrate to standard solutions with an accuracy of 1%. Accuracy isn't so much a factor of the device itself rather than the skill of the operator using it. In good hands it will give results that are within the ballpark of a professional lab; in sloppy hands, it is useless. So, we try to use volunteers with job experience or education in science/engineering.

Professional laboratories are not always a gold standard by which you should compare your results: we once tried a side-by-side test with a local professional lab, but their results were so bad that we could draw no conclusion and it was a waste of money. That said, even two professional labs testing the exact same water sample will arrive at two slightly different results.

In your email, you question the validity of your test results and mention "nutrients are a huge problem in the estuary we're monitoring". If you mean that the nutrient concentration is known to be severe (such as in excess of 5 mg/L) in the estuary, then you must dilute the water sample prior to testing, and then multiply the spectrophotometer reading by the same factor to arrive at the final value. The amount of dilution is dependent on the estuary's nutrient concentration as well as your spectrophotometer's test range. Your spectrophotometer's manual specifies a different working range for each analyte; for example, it might specify "Range: 0 - 4.5 mg/L" for nitrate. If your estuary's actual nitrate concentration is 21 mg/L, then you would dilute the sample by 5x to bring it down to the spectrophotometer's range. Then, you would multiply the spectrophotometer reading by 5 to arrive at the final value.

Dilution should be done with laboratory-grade deionized/distilled water.


Paul Mack
Sierra Club - DuPage County, Illinois
http://www.illinois.sierraclub.org/rpg/watermonitorproj.htm

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