Pond Study CSS version


        In hyper-eutrophic ponds with abundant nutrients scums of filamentous green algae often become obvious near the water surface. These floating clouds of metaphyton originate on sediment, rock or macrophyte surfaces, from which they become disengaged and rise to the surface (Fig. 33). Because of the high density of algal cells within the clouds of metaphyton, access to light and nutrients for many individuals may be poor, and the scums probably start to decompose soon after they appear. Constant replenishment from below, however, may result in the continued presence of metaphyton during much of the summer (Lembi, 1988).

Fig. 33  Metaphyton at the surface of a pond, showing columns to filamentous algae buoyed upward by oxygen bubbles.

        Abundances of metaphyton are compared to phytoplankton abundances in the 13 target ponds based on samples taken in July in Figure 34. Of the 5 ponds with especially high overall algal biomass, two (BR, WA) had large quantities of metaphyton while three Fig. 33. Metaphyton at the surface of a pond, showing columns to filamentous algae buoyed upward by oxygen bubbles. 44 (GF, HH, HW) had high phytoplankton densities but little metaphyton. The overall effect of total P on metaphyton biomass was not as strong as for the phytoplankton (Fig. 35).

Fig. 34  Biomass of phytoplankton vs. metaphyton in 13 ponds in July


Fig. 35  Relationship between total phosphorus and metaphyton biomass in 13 ponds during July.

        Some examples of filamentous green algae and filamentous blue-green algae responsible for scum formation in southeast Pennsylvania are shown in Figure 36a-b.

Fig. 36a  Major kinds of unbranched metaphyton-forming algae.


Fig. 36b  Major kinds of branched or reticulate (net-like) metaphyton-forming algae.

        Many other species of algae may be attached or intertwined with the green algal filaments, and may constitute the principal food for metaphyton-associated invertebrates. Both the algae and invertebrates associated with scums of metaphyton differ from those present in the plankton and in/on the sediments. In effect, metaphyton clouds are unique communities within the larger pond ecosystem.