The quantities of nitrogen, phosphorus, and other biologically useful nutrients are the primary determinants of a water body's TSI. Nutrients such as nitrogen and phosphorus tend to be limiting resources in standing water bodies, so increased concentrations tend to result in increased plant growth, followed by corollary increases in subsequent trophic levels.[lower-alpha 1] Consequently, trophic index may sometimes be used to make a rough estimate of biological condition of water bodies.[2]