Estimates of the biological production of entire lake fish communities were collected from the published literature on lakes covering a wide range of geographic areas and trophic status. Correlation analysis shows that fish production is uncorrected with the morphoedaphic index (p > 0.05) but closely correlated with annual phytoplankton production (r2 = 0.79), mean total phosphorus concentration (r2 = 0.67), and annual average fish standing stock (r2 = 0.67). Empirically derived regression equations are presented and compared with previous models based on catch and yield data. Analysis of these equations suggests that conversion of phytoplankton into fish production is 100 times more efficient in oligotrophic lakes than hyper-eutrophic ones, but that a much lower fraction of fish production can be channeled to sustainable yield in oligotrophic lakes. Sustained yields were frequently as little as 10% of the annual community fish production.
The relationship between epiphyton biomass and water column total phosphorus concentration (TP) was studied in macrophyte beds in 11 lakes covering a wide range of trophic status (TP = 5.8–72.8 μg∙L−1). Phosphorus concentration was a poor predictor of epiphyton biomass when considered alone. Our data do not agree with previous studies that found that epiphyton biomass increased continuously with TP. Instead, we found a very weak, nonlinear relationship between TP and epiphyton biomass, where epiphyton biomass increased up to TP≈39 μg∙L−1, and decreased at higher TP. Season and sampling depth accounted for significantly more variation in epiphyton biomass than did TP. Epiphyton biomass increased with depth in oligotrophic lakes but decreased with depth in eutrophic lakes. Seven common species of macrophytes of differing architecture developed significantly different epiphyton biomass. Macrophytes with flexible, ribbon-like leaves supported lower epiphyton biomass than species of broad-leaved or whorled architecture. The effect of host type on epiphyton algae biomass was not, however, as great as the influence of environmental variables.
Macrophyte beds in 11 lakes of differing trophic conditions were sampled intensively to examine the influence of macrophyte abundance and composition, epiphyton biomass, phytoplankton concentration, and water depth on the abundance of phytophilous invertebrates. Numerical abundance and biomass of phytofaunal taxa were only weakly correlated. Phytofauna biomass ranged from 17 to 270 mg dry mass∙g macrophyte dry mass−1(1–29 g dry mass∙m−2) among the macrophyte beds. Multiple regression analysis showed that total phytofaunal biomass was positively correlated with the biomass of the three primary producers in the littoral zone: macrophytes, epiphyton, and phytoplankton. Phytofauna biomasses in deeper macrophyte beds or near the water surface were lower than those found in shallower water or near the sediment surface. Correlations of phytofauna biomass with macrophytes, epiphyton, and depth varied somewhat among phytofaunal taxa. The phytofauna biomass was often dominated by chironomid larvae, but gastropods, water mites, and oligochaetes were also important components of the phytofauna biomass. Small crustaceans such as cladocerans and copepods frequently were numerically dominant but usually composed only a small fraction of the biomass. Preference of various invertebrate taxonomic groups for particular species of aquatic macrophyte was slight.
The maximum depth of macrophyte colonization and depth distribution of macrophyte biomass were assessed over 3 years, in late summer, at six sites in the St. Lawrence River and two sites in the Ottawa River (Lake des Deux Montagnes). Maximum depth of submerged plant colonization could be predicted from the light extinction coefficient (r2 = 0.82) and Secchi disk depth (r2 = 0.80). The aboveground and total biomass of macrophytes were related to a variety of environmental variables as follows in descending order of importance: exposure to wind and waves, plant growth forms, water depth, and light intensity. Together, these variables accounted for 67 and 74% of sampling variability of aboveground and total biomass, respectively. These environmental variables were used to elaborate hierarchical predictive models of aboveground and total biomass of emergent and submerged macrophytes. The empirical relationship that links St. Lawrence River and Ottawa River aquatic plants to environmental variables may eventually allow us to forecast wetland response to changes in water levels and water clarity resulting from climate variability and (or) discharge regulation.
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