> For the complete documentation index, see [llms.txt](https://swatplus.gitbook.io/io-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://swatplus.gitbook.io/io-docs/theoretical-documentation/section-7-main-channel-processes/in-stream-nutrient-processes/algae/algal-growth.md).

# Algal Growth

Growth and decay of algae/chlorophyll $$a$$ is calculated as a function of the growth rate, the respiration rate, the settling rate and the amount of algae present in the stream. The change in algal biomass for a given day is:

$$\Delta algae=((\mu \_a*algae)-(\rho\_a*algae)-(\frac{\sigma\_1}{depth}\*algae))\*TT$$                             7:3.1.2

where $$\Delta algae$$ is the change in algal biomass concentration (mg alg/L), $$\mu\_a$$ is the local specific growth rate of algae (day$$^{-1}$$ or hr$$^{-1}$$), $$\rho\_a$$ is the local respiration or death rate of algae (day$$^{-1}$$ or hr$$^{-1}$$), $$\sigma\_1$$ is the local settling rate for algae (m/day or m/hr), $$depth$$ is the depth of water in the channel (m), $$algae$$ is the algal biomass concentration at the beginning of the day (mg alg/L), and $$TT$$ is the flow travel time in the reach segment (day or hr). The calculation of depth and travel time are reviewed in Chapter 7:1.