Next they estimated the macrophyte biomass in each lake from the 

 area covered by macrophytes and the macrophyte density in kg of 

 wet biomass per square meter. This permitted calculation of the kg 

 of P contained in macrophyte biomass in each lake and the amount of 

 P that would be released to the water column assuming 100% death 

 and decomposition of the macrophytes. Dividing this mass of P by 

 the lake volume yielded a concentration that when added to water 

 column total P produced an estimate of the potential total P content 

 of the water column (WCP). This approach provided more realistic 

 estimates of trophic state for lakes such as Fairview in Orange Co., 

 which appeared oligotrophic based on water-column nutrients and 

 Chi a, but contained a large standing crop of macrophytes. The 

 estimate of total water-column P content brought this lake to the 

 eutrophic range, which was edaphically consistent with other lakes in 

 the same physiographic region. Recent evidence shows that water- 

 column P concentration in Lake Fairview has increased to the 

 predicted WCP level because of macrophyte removal by grass carp 

 (Canfield pers. comm.). Canfield et al. (1983a) noted that the same 

 approach may be used with N for lakes that are N-limited. 



Macrophytes and the Lake Ecosystem 

 Despite the emphasis on water-column nutrients and 

 phytoplankton biomass to characterize lake trophic state, 

 macrophytes are responsible for a substantial amount of the primary 

 production that occurs in many lakes. This is especially the case in 

 Florida because the shallow depths of Florida lakes, the high amounts 

 of insolation and the long growing season are conditions that support 



