The relationship of modern plant remains to water depth in alkaline lakes in New England, USA

Abstract

Paleohydrologists sometimes use macrofossils of aquatic vascular plants as one of several independent lines of evidence to infer changes in past lake-levels. Typically, this usage relies on an assumption that the seeds of aquatic species are not dispersed far from the source plants. The water depth over the coring site at the time the seeds were deposited is inferred from the water depth at which the species generally grows today. We determined the water depths at which particular plant-remain types are deposited, and tested whether they can be used successfully as proxy evidence for lake level. The results should aid the interpretation of fossil seeds in paleohydrological studies. A total of 189 surface sediment samples from 13 lakes in Maine and Massachusetts were examined for plant remains, and vegetation was surveyed in the immediate vicinity of each sediment sampling-site. The seeds of some taxa were found in sediment from water-depth ranges much broader than those in which living plants occur. However, in combination, even plant-remain types with broad depth ranges can be used effectively to reconstruct water depth. Presence of plant-remain types can be used to infer water depth regardless of abundance. Test samples indicate that inferring water depth from plant remains works well for shallow, alkaline lakes in New England.