Papers dealing with charophytes biomass are not numerous worldwide, and methods to measure that attribute are more or less standard.

Two boat-based and one in-water sampling method were used by Rodusky et al. (2005) to collect submersed aquatic macrophytes (SAV) as part of a long term monitoring program in Lake Okeechobee, Florida, U. S.A. The boat-based methods consisted of a ponar dredge used only to collect Chara, and an oyster tongs-like apparatus to collect all other SAV. The in­water method involved use of a 0.5 m2 PVC quadrat frame deployed by a diver. Comparison of the three methods above showed no consistent pattern to the significant differences found in sampling precision between the three sampling methods, regardless of the geographical location, sediment type, SAV species or density.

To estimate charophytes biomass, the quadrat method is the most used one. According to the method, first a quadrate shall be delimited in the field, e. g. a 25 cm2 (Westlake 1965, 1971; Krebs 1989). Within this quadrat, a 5 cm diameter (area 19.7 cm2) and 50 cm tall PVC tube is inserted. Tube wall must be perforated throughout the first basal 25 cm to allow water circulation and the gathering of the plants.

Once collected, material must be stored in glass vials (e. g. 50 ml volume) and taken to the laboratory. In the laboratory, charophytes must be gently washed and if necessary scrapped with a very soft brush to remove other algal material and sediments adhered to the plants. After washed and/or scrapped, the excess water must be dried with some paper towel and finally placed in a porcelain melter.

For the analytic procedure, the charophyte material must be calcinated at 550°C during 1 hour, then cooled in a desiccator and weighted using an analytical scale to have P0. Immediately after, plants must be taken to an aerated oven at 65-70°C until no further weight change is observed for quantification of its dry weight (P1), and after 1 hour calcination at 550°C for determination of its ash dry weight (P2) (Hunter 1976). Determination of the ash free dry mass (AFDM) (Рз) is done using the mathematics Рз = (P1 — P0) — (P2 — P0). If total phosphorus (TP) is required, Strickland & Parsons (1965) method is to be used, i. e. the calcinated material is washed with 25 ml of HCl 1N, crushed and heated in a water-bath for 1 hour. After cooling, samples are diluted with 50-250 ml deionized water depending on the amount of calcinated material.

Palmer & Reid (2010) proposed a method they called ‘invention’ for the production of macroalgae to provide a sustained, economical source of biomass that may be used in various end-uses processes, including energy production. Their method provides specific combinations of macroalgae types, saltwater growth media compositions, and open pond water containers that resulted in biomass production beyond what may occur naturally without the required manipulation. Specifically, macroalgae that produce an exosqueleton in the presence of brackish water (e. g. stoneworths) have been found to provide excellent biomass production of at least 10 metric tons and up to 200 metric tons per acre per year under their method conditions.

Total phosphorus concentration is determined using a spectrophotometer. Another possibility for TP determination is by the molybdenum blue colorimetric method (Murphy & Riley 1962) after digestion with K2S2O8 in an autoclave at 120°C for 30 minutes (APHA 1995). Total nitrogen (TN) can be determined using spectrophotometry, based on the Koeofell colorimetric method. Calcium and magnesium can also be determined using a spectrophotometer, however, based on the Calmagite colorimetric method.