Nutrients and River Ecosystems

Abstract

Abstract Streams and rivers carry nutrients (nitrogen [N] and phosphorus [P]) and transform nutrients, and in turn the nutrients strongly impact the growth and composition of bacteria, phytoplankton, benthic microalgae, macroalgae, and macrophyte vegetation. N exists in organic and inorganic forms and has complex cycles and “spirals” between dissolved inorganic ammonium and nitrate, and labile and refractory organic forms, which also can be dissolved or structurally part of organisms. P is either inorganic or organic, with less complex cycling, but critical as well. Too much N or P (or N and P) causes algal blooms and oxygen demands, and high N inorganic concentrations can be toxic. Sources of nutrients are discussed, as is how and why N or P (or both) can limit (or stimulate) the growth of phytoplankton to bloom conditions. The various concentrations of N and P that characterize eutrophic, mesotrophic, and oligotrophic waters is discussed in regulatory and nonregulatory situations.