The aquatic plant community of a lake is full of complex interactions that contribute to the overall health of an aquatic ecosystem. Every level of the aquatic food chain from bacteria and invertebrates to fish and waterfowl are dependent upon aquatic plants to some degree for their survival (Engel, 1985; Wetzel, 2001). Photosynthesis and respiration are important in maintaining clear waters (Engel, 1990). Aquatic plants stabilize sediments and absorb wave action which in turn prevents turbidity caused by suspended sediments. Light penetration, excess nutrients from run-off, wave action and lake morphometry all affect the plant community of the littoral zone (Barko 1988; Duarte and Kalff, 1986). The importance of aquatic plants in an aquatic ecosystem creates the need to study the diversity, density and distribution of the aquatic plant community as well as an examination of the factors impacting the plant community.

Re-establishment of persistent native submersed macrophyte populations in shallow systems is often complicated by invasions of nonnative canopy-forming species and eutrophic conditions that result in light limitation of growth. Exotic invasive species can often outcompete natives for light and nutrients, resulting in declines or complete elimination of desirable species populations over time (Madsen et al. 1991). However, efforts to control exotic macrophyte species may not improve growth conditions for native submersed macrophyte restoration if excessive cyanobacterial blooms maintain high light attenuation (James 2010). Additional management that targets reduction in algal biomass may be required in order to improve underwater light condition for native macrophyte growth and persistence. Since phosphorus (P) is generally regarded as the nutrient that limits algal growth, strategies to control P offer the most sustainable approach to improving algalinduced light attenuation in aquatic systems.

Submersed macrophytes play an important structuring role in biological community dynamics and water quality conditions of aquatic ecosystems (Jeppesen et al. 1998). Submersed macrophyte communities promote increased light penetration and water clarity by dampening wave shear stress and stabilizing flocculent sediment from resuspension (Barko and James 1998). They also provide refugia for young fish and habitat for a diversity of invertebrates. These interactions and feedbacks foster a fishery dominated by piscivores, increased grazing pressure on pelagic phytoplankton, and high transparency; features that are desirable both from an ecosystem perspective and for aesthetic and recreational reasons.

High phosphorus (P) flux from bottom sediments represents an important source in Half Moon Lake (Eau Claire, Wisconsin) that needs to be controlled in order to drive the system toward P-limitation of algal growth and improve underwater light condition for restoration of native submersed macrophytes. An aluminum (Al) sulfate-sodium aluminate (buffered alum) application represents an effective management technique for binding P in sediment and reducing flux into the water column for algal uptake in soft water lakes. The objectives of this technical document are to estimate the buffered alum dosage required to inactivate ~ 90% of the iron-bound P in the upper 5 cm sediment layer in Half Moon Lake.

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ACEI-058-09