No Project associated with this Finding

Periphyton assemblages from the nearshore environment of the west
(California) side of Lake Tahoe, were analyzed to determine their taxonomic
composition and community structure across habitats and seasons. Lake
Tahoe is the second deepest lake in the US and an iconic oligotrophic subalpine
lake with remarkable transparency. It has experienced o"shore cultural
eutrophication since the 1960s with observations of nuisance nearshore algal
growth since the mid 2000s attributed to anthropogenic stressors. Samplings
from November 2019–September 2020 provide useful snapshots against
which older monitoring may be# contextualized. A voucher flora, complete
with descriptions, photo-documentation and referencing to species concepts
employed, was created as a method of providing reproducible identification
and enumeration of algal species, and more seamless reconciliation of detailed
taxonomic data with future monitoring projects. The eulittoral zone (0–2 m)
is seasonally dominated by elongate araphid (Synedra, Ulnaria) and stalked or
entubed diatoms (Gomphonema, Cymbella, Encyonema). The sublittoral zone
(>2 m) is dominated by a nitrogen-fixing Epithemia-cyanobacteria assemblage
with less seasonal changes in dominance and composition that expanded
to impinge on the 2 m depths of the eulittoral zone in the Fall. Sublittoral
epipsammic samples, despite their proximity to rocks, had a very distinct
diatom composition and high species dominance, similar to what was seen
in the Fall eulittoral samples, with high numbers of Staurosirella chains and
small biraphid diatoms. The deeper samples at 30 and 50 m contained high
numbers of live Epithemia, and indicate a thriving sublittoral assemblage at
these greater depths, but with less biomass. The 2019–20 data show many
of the same diatom taxa observed in the 1970’s and 1980’s but with changes
in species dominance. Notably, there was less of the green alga Mougeotia,
when compared to the 1970’s data, and a higher dominance by nitrogen fixing
Epithemia in the sublittoral zone, persisting year-round. These new data show
roughly double the algal species biodiversity that had been documented previously in the Lake Tahoe nearshore, and is largely attributed to the methods employed. Adopting these new methods in future monitoring e"orts should
improve harmonization of taxonomic data and help advance our knowledge
of the contributions to nearshore cultural eutrophication.