15 



Methods for Reconstructing Historical Macrophyte Communities 

 Historical macrophyte presence has been traditionally 

 determined from lake sediments by methods that do not yield 

 quantitative estimates of standing crop. Macrophyte presence has 

 been assessed historically from macrophyte remains, pollen and 

 seeds that are found in lake sediment. Davis (1985) studied 

 historical macrophyte presence in upper Chesapeake Bay and 

 summarized many of the biological and diagenetic factors that 

 obscure accurate reconstruction of former macrophyte communities. 

 Seed preservation is poor in some taxa (e.g. Vallisneria and 

 Potamogeton) and seed dispersal is poor in others (e.g. 

 Myriophyllum) leading to under-representation of these taxa in 

 sediments. Pollen and seed production is variable among species of 

 macrophytes (Yeo 1966, Birks 1980), and plants producing larger 

 quantities of these may be over-represented in the sedimentary 

 record. Seeds and pollen also may be unreliable indicators of 

 macrophyte standing crop because a large number of species 

 reproduce vegetatively by budding, fragmentation and by plants 

 arising from stolons and rhizomes (Tarver et al. 1979). 



Seed representation in the sedimentary record may be affected 

 by differential transport and palatability (Birks 1980). Birks (1973) 

 and Watts (1978) have shown that seed dispersal is often localized 

 for macrophyte taxa. Dispersal patterns, therefore, can cause a high 

 degree of spatial variability of macrophyte indicators in lake 

 sediment. Sampling from many littoral sediment cores is required to 

 obtain a reliable reconstruction of macrophyte history. 



