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Ratio between algal biomass and chlorophyll a

Sun, 11/09/2003 - 2:51pm — jrbloom
The variable ACHLA is the ratio between algae (as dry weight organic matter) and chlorophyll a. A value for ACHLA of 145 is suggested in the W2 manual. In the Spokane example the value was set to 130 (ACHLA) for phytoplankton and 65 for periphyton (ECHLA). In the EPA publication Rates, Constants, and Kinetics ... (2nd Ed., Bowie, et al., 1985) two values are presented for the percent of dry weight total phytoplankton that is chlorophyll a. These are 2 and 5-10 percent. Based on these values, ACHLA would be in the range of 10 to 50. These seems rather low. Can anyone suggest any good references for these values? [addsig]
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Water Quality
Wed, 11/12/2003 - 7:29am — Tom

Jim, On page 315 of the Rates, Constants, and Kinetics....., the C/chl a ratios are stated to range from 20 to 100. Since the model uses OM rather than C, this translates into a range of from about 40 to 220. The value of 145, which falls pretty much in the middle, is based on a default C/chl a ratio of 65, using the default C/OM ratio of 0.45. What page(s) are the numbers that you are referring to located? Tom[addsig]
Thu, 11/13/2003 - 11:47am — jrbloom

Tom I like the approach of using the C/Chlra ratios as an intermediary, since so little data is available for OM/Chlra (data on C/Chlra ratio is on page 286 of Rates, Constants, and Kinetics..., 2nd Ed.). I couldn't find the reference you refered to on p. 315 of R,C,K. I did find similar on p. 289 (2nd Edition), where studies show ranges for C/Chlra for total phytoplankton of 50-100, 25-112, and 10-100. Are you looking at the same edition as I am? Regarding ratios for periphyton, Oregon DEQ, to my knowledge, has only performed one detailed study in which both periphyton organic matter, as mg/m^2 Ash free dry weight of algae, and mg/m^2 periphyton chlorophyll a were collected. Sampling was performed at 8 stations on the upper Grande Ronde River in eastern Oregon. At each station, 5 rock scraping subsamples and 5 Surber artificial substrate samples were collected. Resultant ratios of OM (AFDW) to Chlra are as follows rock min 128 rock median 227 rock max 403 serber min 158 serber median 441 serber max 1083 These ratios may represent the high end, since much that is refered to in the lab report as "Ash free dry weight of algae" may consist of other organic matter besides photosynthetically active algae. Thanks for your help Jim[addsig]
Tue, 06/02/2009 - 2:41pm — Ranjan

Should a factor of 1,000 be accounted for ACHLA in v 3.6? The manual requires units of mg algae/ug chla.
Fri, 06/05/2009 - 9:45am — chris

Hi Ranjan, The units for ACHLA have changed for version 3.6. Since the units are now mg algae/ug chl a, the values will be a factor of 1000 different than those of version 3.5. chris
Wed, 06/17/2009 - 4:36pm — Ranjan

Chris, If I want units of g/m3 (mg/L) in the opt files, should I set the multiplier in the graph.npt file for Chl-A to 0.001? E.g., ACHLA = 0.145 in the w2_con.npt file, and the chl-A line in graph.net is: ....................CDNAME................... FMTCD CDMULT CDMIN CDMAX CDPLTC Chlorophyll a, g/m^3 (g10.3) 0.001 -5.0 145.0 OFF
Tue, 06/23/2009 - 12:10pm — chris

Ranjan, Yes...the multiplier should be set to 0.001. chris
Sat, 12/18/2010 - 9:38am — Oliver_O

Hi Chris, I am using W2 version 3.5 and I would like to know what the units are for the output values of Chlorophyll? The settings in my graph.npt file are: ....................CDNAME................... FMTCD CDMULT CDMIN CDMAX CDPLTC # Chlorophyll a, mg/m^3 (F10.3) 1.0 -5.0 145.0 OFF 14 I am not sure but I think the output values are given in micrograms/L. Is this correct? Thanks Oliver
Fri, 07/09/2010 - 2:08pm — Nancy

I would like to know if the same applies for ECHLA. The manual has a default value of 145 in the page C-170, but the preprocessor states a maximum of 0.80. Thank you.
Sun, 07/11/2010 - 6:32pm — chris

Hi Nancy, I looked in the code and the input coefficient ECHLA isn't actually used at the moment so it's value doesn't matter. Epiphyton are simulated in units of dry weight density (g/m^3) and are output by the model in units of g/m^2. Chris