From sand to sludge: how lakes are changing in a rapidly fixating
coastal dune system
Abstract
Western European coastal dune landscapes are naturally dynamic and ever
changing. However, in the past 100 years coastal dunes have become more
stable and encroached by sand-fixating grasses and shrubby vegetation.
The drivers of these changes are primarily due to human exploitation
with deliberate planting for coastal protection and nitrogen deposition,
mainly from agricultural sources. The effects of these changes on
terrestrial plant communities in dune landscapes are well documented;
they are becoming more homogenous and species poor especially due to the
loss of specialized pioneer species. However, much less is known about
the effects on the aquatic plant communities in the dune landscape. Here
we studied the composition of plant communities in 38 shallow dune lakes
in Northwest Denmark, with the aim to identify the effect of
stabilization and vegetation encroachment on the aquatic plant
communities. Fine benthic and dissolved organic matter (FBOM and DOC)
along with lake type (permanent/temporary) was among the main
explanatory factors for specialized dune lake plant communities.
Isoetids and low-growing plant communities were negatively impacted by
increasing amounts of FBOM and DOC, the latter being more pronounced in
permanent lakes. At the same time, elevated amounts of organic matter
led to an increase of emergent and amphibian plant communities. Stable
isotope analysis suggested that the main source of organic matter was
allochthonous, possibly resulting from a buildup of organic matter in
the catchment of each lake. These results suggest that coastal dune
fixation and vegetation encroachment affect plant communities in a
similar manner to terrestrial communities, leading to a loss of rare and
low-growing dune lake plant species specialists and a favoring of more
common and competitive species.