Hello Dr. Scott Tiegs

Benthotorch sound too good superficially, as hours of analyses can be done in minutes as the company proclaims. However, based on the chlorophyll fluorescence, only certain groups of benthic microflora such as Chlorophyceae, Bacillariophyceae and Cyanophyceae etc can be estimated but to an ecologists, here lies the demerit. What about the genera and the species. Unless a sample can be ascertained at least up to the genus level, it does not hold any significant ecological data and in my belief the instrument fails to decipher the taxa up to the genus level. I haven't used it and it will not be wise to comment on the merits or demerits of the instrument. However, I just stated the apparent shortcoming of the instrument which came to my mind.

The following link may help shed light on the issue in a more academic manner <

Article Application of a spectrofluorimetric tool (bbe BenthoTorch) ...

I sincerely hope this helps.

Thanking you,

Dr. Abhishek Mukherjee

In my opinion, it may still be a good tool to estimate benthic productivity as chlorophyll a concentration.

I was planning to use one for field work last summer, but gave up because of problems with the battery. It couldn't hold a charge, so was more or less useless unless plugged in to the mains. It had recently been serviced, so there should have been no problem. I would be interested to hear if others have had similar experiences. As for when it does work - it seems to work best on standardised substrates with a mid-successional biofilm community. If you have blooms of filamentous algae, I would not use this instrument.

Hi Scott,

we have been working with Benthotorch for 6 years and we think it is a useful and reliable instrument, at least in our river typology (Alpine streams) where periphyton is never so thick. We never did any test to verify if the benthic chlorophyll a measured with standard methods lead to the same values of that measured with benthotorch, but in literature you can find some work about that.

In general, we think that also standard methods for benthic chlorophyll a have many limits:

- Is impossible to measure with precision the scraped area;

- How can you be sure you have scraped in the correct way and you have really removed all the periphyton? (limits due to subjectivity in the scraping and in the conformation of cobbles: when crevices are present, is very difficult to reach periphyton in it!)

- If you use a brush to scrape, how can you be sure if some periphyton remains within it?

Benthotorch overcomes these limits.

However, recently we received critics from a couple of reviewers concerning the use of benthotoch, ‘casue in their opinion the instrument is not precise and detects only the chl a of the upper layers of the biofilm.

This was confirmed in some papers, for instance:

https://www.researchgate.net/publication/276094486_Preliminary_evaluation_of_an_in_vivo_fluorometer_to_quantify_algal_periphyton_biomass_and_community_composition

in which the authors found correlation between standard methods and benthotorch up to 4 microgram/cm2. So probably if you work on thick periphyton, this is not exactly the best instrument you can choose. In our Alpine streams, we think it works well!

Concerning the battery problems, Francis, we had the same problem 2 years ago. We call the assistance and they changed the battery and gave us a new charger. Now it seems to work.

I hope our experience can be useful!

Best regards, Elisa

Thanks All,

For your insights onto this tool. I think I'll go ahead and purchase one since it seems to me sufficient for my needs.

Best,

Scott

Hi Scott, others,

I would like to share my thoughts. Due to some concerns me and my colleagues J. Aroviita and S.M. Karjalainen had last year, I tested two BenthoTorch devices in laboratory conditions at the Finnish Environment Institute. I had, in total, four cultivated samples containing cyanobacteria (phycoerythrin and phycocyanin), green algae and diatoms (one sample containing only one species). I wanted to test whether the devices correctly identify the organism group and whether the devices provide identical information. Also I compared how the total measured biomass correlated with a-chlorophyll determined by traditional laboratory methods.

The tested devices had troubles identifying the correct organism group when the samples contained a diatom species and a cyanobacterial species (phycoerythrin). For the first case, the devices erroneously reported green algae in addition to diatoms (the error was small for one of the devices, but for the other device, the magnitude of error was quite large). For the second case, both of the devices reported diatoms in addition to the phycoerythrin-containing cyanobacteria.

The total biomass reported by the devices was well correlated with a-chlorophyll content analyzed in the lab.

These somewhat varying results that I got with two devices can be due to several things (although the devices have been stored and treated similarly), but it is a good idea to be a bit cautious when using the biomass estimation of cyanobacteria, green algae and diatoms separately in e.g. statistical analyses or decision making. I found the estimation of total biomass to be rather reliable though. No method is perfect, and when keeping in mind the strengths and weaknesses of these types of devices, they can be useful tools. Remember to clean the device/lens properly! :)

Best regards,

Annika

Hi Scott et al.,

We have had generally okay results with a benthotorch but only after we learned to be pretty constrained in how we apply it. One major issue that we found is that the benthotorch underestimates standing stocks on rocks that are taken from full sun. My grad student wrote a paper about this (A cautionary tale for in situ fluorometric measurement of stream chlorophyll a: Influences of light and periphyton biomass in Freshwater Science last year) in which they found that you needed to have the rocks held out of the stream for 15 to 30 minutes before you get reliable numbers. The company was pretty unpleasant to work with when we brought up this issue with them. There are also potential issues with self-shading when standing stocks are high such that you get underestimates of the Chl a. We have found that it works well on tiles and on NDS glass frits and that is where we use it most. As long as you pull your rocks out of the stream and cover them for a bit or if you do your sampling in shaded streams or early in the day before the streams have had full sun on them, they work okay for natural substrates. Overall, we found that being able to take a high number of replicates makes it a useful tool for comparison within and among sites/treatments and it's probably worth getting for that. But, it is not as good if you are relying on it for a highly accurate measure of Chl a.

Hi Scott,

I was the graduate student working with Dana Warren using the BenthoTorch. In addition to the points Dana mentioned (shading rocks is really important) it is also important to develop stream-specific relationships between benthotorch measured Chl a and traditional lab-measured Chl a - you can not assume the relationship between BT-Chl a and Lab-Chl a to be 1:1. We have had some streams where this is the case but others where the slope deviates strongly from 1 and the y-intercept is well above 0. I would highly recommend putting in the time to build your own relationships that are specific to the sites/streams you are working in. This can add a lot of time and avoiding lab methods is one of the reasons to buy a BenthoTorch, but in my opinion, it is worth the extra effort to ensure accurate results.

Let me know if you have any questions - happy to help out.

Matt

Hi Scott Tiegs , hi Francis J. Burdon ! Same as you Franck, we had some troubles with the battery when needed. We sent it for repair, and after one month or two (if I remember well), it came back just fine. We used it on standardised substrates, and it was fine for the comparison work we made (see Seasonal variations overwhelm temperature effects on microbial processes in headwater streams: insights from a temperate thermal spring, in Aquatic sciences, 2019).

Hi All,

I received my benthotorch and it seems to function well, except that I can only get about 10 or so readings before the battery becomes exhausted. Is this the sort of battery problem that others experienced? Alice Gossiaux Francis J. Burdon

Best,

Scott

Hi Scott,

in my experience the battery problems started 3-4 years after we bought it. In the beginning we were able to perform measures even for 2-3 hours/per day with no problems and with no recharge.

10 readings is really nothing...

best regards,

elisa

To continue the discussion on the merits of this tool - the battery issues which made using the Benthotorch in the field untenable for our recent CROSSLINK fieldwork might be solved with a new power cable. However, there remains lingering doubts about its effectiveness in different conditions. Echenique-Subiabre et al. (2016) report that "Correlations between chlorophyll-a measured using the BenthoTorch and spectrophotometry were higher for thin (2 mm) biofilms (r2 = 0.58 and 0.27 respectively; p