|dc.description.abstract||The purpose of this study was to develop a classifi cation
scheme for l ake trophic status based on the relative abundance of
l ake sediment diatom trophic indicator species.
A total of 600 diatom frustules were counted from the surface
sediments of e a ch of 30 lakes selected to repr e seni~ a continuum
from u.lt ra-oligotrophic t,o fairly eutrophic but not hype r-'
Published autecological information was used to determine the
trophic indicator status of each of the s pecies. A quotieht was
derived by dividing the s um of all the e utrophic indicator
species by the sum of all oligotrophic indicai.-:.or species. Oligo'-
mesotrophic. mesotrophic and meso-eutrophic species were added to
both the numerator and denomina tor. Five categories of diatom
i.nferred trophic status were recognized : ultra-oligotrophic -
0'-0.2:3, oligotrophic::: 0.24-0 . 70, mesotrophic :: 0.'71 -0.99,
meso-elxtrophic :: 1. 00-1. '78 and eutrophic:: 1.. 79-2. 43. But only
three of these (oligotrophic:: 0-0.69, mesotrophic ::: 0 . 70'-1.69 j
and eutrophic:: 1.70-2.50) proved usef ul.
The present study of the relationship between diatom inferred
trophic status and the literature-derived trophic status of SO
lake s (which were purposely chosen to represent a broad spectrum
of lakes in Canada) indicated that: 1) Based on diatom species
(assemblages ) it is possible to segregate the lakes from which.
th",)se diatoms were taken into three basic categories : o ligotrophic, mesotrophic and eutrophic lake types. ~~) It was not
possible t,o separate meso-eutrophic and o l igo-mesotrophic lakes
f rom mesotrophic l akes as the the degree of overlap betwee n the
diat,om species in these lake types was extremely high. 3) Ha d
mo r e ul tra-oligotroph,ic lakes been sampled it might have been
possible to more a ccurately s eparate them f rom oligotrophic
Jakes. 4 ) Had. more humic lakes been sampled in this s tudy I f eel
it would have been possible to identify a unique diatom
a ssemblage which would h a ve chara cterized t his lake type .
Re gression analyses were performed using the aforementioned
diatom inferred trophic index as a f unction of 1) log Sec chi
transparency (r = - 0.70) 2) total phosphorus (r = 0. 77 ) and 3)
chlorophyll-a (r = 0.74). Once e ach of these rel ationships had
been established , it was possible to infer paleotrophic
(downcore) changes in an oligotrophic lake (Barbara Lake) and in
a eutrophic lake (Chemung Lake) .
Barbara Llake was dominated by oligotrophic s pecies and
remained oligotrophic throughout the 200-·year history r epresented
by i t s 32 em long sediment core. Chemung Lake is currently
dominated. by eutrophic species but went through a mesotrophic
st,age which was associated with a rise in the water level of the
lake followi n g dam construction in its watershed in the early
1.900 J ::;. This was followed by its reversion to it,s present day
eutrophic stage (dominated by eutrophic species) possibly as a
r esult of shallowing process which can be attributed to " silting'
up" of the reservoir and the invasion of the l ake by Myriophyllum spjcatum (Eurasian milfoil) i n the 1970's . In addition, nutrient
.:r':l.ch run"'offwhich resulted from increased human a.ctivities
associated with cottage development along its shores has
contribut ed to its eutrophication. There is some evidence that
the rat,e o :f its prog ressive eutrophication has declined during
the last decade. This was correlated with legislation enacted in
the 60's and 70's in Ontario which was aimed at reducing nutrient
loading from cottages.||en_US