## 2 Materials and Methods
### Determination of Biovolume  
To express plankton community data within the framework of total biomass, it is necessary to estimate the relative contributions made to total community biomass by the taxonomic groups identified through nucleic acid sequencing. It has become common practice to estimate cell biovolumes through the application of geometric shapes and there are numerous literature sources recommending geometric shape assignment [20; 21; 22; 23; 24; 25; 26]. As detailed measurement required for the use of complex shapes is not part of the existing data, it was decided to base these calculations on the simplest geometric shape(s) possible using existing taxonomic data bases. It was decided that even a slight overestimation of biovolume was acceptable because taxa cell sizes vary greatly in estuarine systems due to environmental conditions. Overall dimensions have been compiled for 986 taxa found in the Chesapeake Bay Program Monitoring data. Currently there are 21 shapes employed in the standardized Chesapeake Bay List (Table 1). There are four notable simplifications to shape codes over [PERSON] et al. [23] recommended the shape. All taxa in the genera of _Amphora_, _Auricula_, _Cymbella_, _Encyonema_, _Hemidiscus_, _Rhopalodia_, where the recommended geometric shape is symbolloid were simplified to ellipsesoids. Shapes for the taxa of the genera _Actinastrum_ and _Ankistrodesmus_ were simplified to prolated sphere from cylinder+ 2 cones. Species in the genera of _Chatetoreceros_ were estimated as cylinder, the recommended shape is elliptical prism but dimensions were unavailable to use the correct shape. Taxa in the genus _Chattonella_ were estimated using a shape of a cone plus half sphere. The conversion of biovolume to carbon was based on protocol and equation from [PERSON] [27]. For all phytoplankton other than diatoms; the following equation was used to convert biovolume to a carbon estimate:  
\[\text{Log}_{10}\text{ C}=(0.886\times\text{log}_{10}\text{ (TV)})-0.46\]  
where:  
\[\text{TV}=\text{Total Cell Biovolume in cubic microns}\]  
\[\text{C}=\text{Cell Carbon Value in pictogram per cell}\]  
For all diatoms, it is necessary to correct plasma volume for the cell vacuole, and then a conversion to carbon may be made. The cell cytoplasmic layer is calculated as the ratio of total cell surface area to area to total cell volume. (Table 1)Cell plasma volume was then calculated using an equation from [PERSON] [27]. Plasma Volume = (Surface Area, \(\mu\)M\({}^{2}\)) (Cytoplasmic Layer Thickness) + (0.1 \(\times\) Total Cell Volume, \(\mu\)M\({}^{3}\))  
Then the following equations are used to convert plasma volume to a carbon estimate:  
Equation to calculate phytoplankton carbon for diatoms where the ratio of cell surface area to cell volume is \(<\)0.9:  
\[\text{Log}_{10}\text{ C}=0.892\times\text{log}_{10}\text{ (PV)}-0.61\]  
Equation to calculate phytoplankton carbon for diatoms where the ratio of cell surface area to cell volume is \(>\)0.9:  
\[\text{Log}_{10}\text{ C}=0.758\times\text{log}_{10}\text{ (PV)}-0.422\]  
where:  
\[\text{PV}=\text{Total Cell Plasma in Cubic Microns}\]  
\[\text{TV}=\text{Total Cell Biovolume in pictogram per cell}\]  
\[\text{C}=\text{Cell Carbon Value in pictogram per cell}\]  
This left approximately 405 taxa either without dimensions or having carbon values calculated but the dimensions necessary to make a carbon estimate independently of the data generating lab. For 71 of these taxa, biovolumes and surface areas were derived by computing a mean of all carbon value for all the taxa in the genus, family or group. These taxa have assigned method designations of FAMILY_AVE, GENUS_AVE, or GROUP_AVE. For all the remaining 332 taxa, the provided carbon value was accepted as best available and a biovolume was back calculated using the appropriate equations from [PERSON] [27]. In all cases where diatom biovolumes were back calculated, the plasma volume was assumed to equal to Total Cell volume. (method codes: CBP_EST_T1 and CBP_EST_TB).