Lotic Primary Producers

Abstract

Abstract Phytoplankton communities are usually sparse in smaller headwaters streams, limited by light and current. However, phytoplankton can be abundant and diverse in larger rivers and estuaries, with seeding from numerous sources along the river continuum, such as farm ponds, oxbow lakes, and drainage ditches. Phytoplankton-based food webs occur in many large rivers and estuaries. In large, nutrient-rich rivers nuisance and toxic blooms can form, especially in heavily regulated rivers; this can have severe impacts on river animals and human drinking-water users. The major microscopic primary producers in headwaters or middle-order streams are often periphytic microalgae, living on rocky substrata or macrophyte stems and leaves. This is an important food source to grazers, which supports fish and other vertebrates, mollusks, and crustaceans. Periphyton can also form nuisance blooms fueled by a constant nutrient source, overgrow macrophytes on occasion, and disrupt stream ecology and human usage.