Stimulation of Saginaw Bay charophyte photosynthesis by phosphorus

Like many other benthic algae, charophytes can attain high abundance in shallow waters, thereby affecting benthic ecology and nutrient cycling, and their subsequent death, detachment, and shoreline deposition contribute to beach fouling within the Laurentian Great Lakes. In-situ nutrient enrichment experiments and stoichiometric analyses have shown that other types of Great Lakes benthic algae are frequently phosphorus (P)-limited, but comparable information is lacking for charophytes. This study coupled short-term P enrichment of charophytes collected from inner Saginaw Bay with fluorometric estimates of algal photosynthesis to assess potential nutrient limitation. Benthic irradiance at the experimental sites was frequently sufficient to saturate charophyte photosynthesis, and charophyte photosynthesis was stimulated by experimental P enrichment, suggesting that these algae were P-limited under natural conditions. Reduction of P loading may be an effective charophyte control measure, even in relatively light-poor and nutrient-rich areas of the Great Lakes.