Harmful algal blooms cause beach shutdowns and affect drinking water. In Oneida Lake, the largest lake within New York State, these effects are harmful to the local economy. With increased global temperatures and eutrophication, the number of blooms occurring each year is on the rise, primarily of cyanophytes. To better understand these cyanobacteria blooms, we conducted three studies in 2018 to (1) understand the contribution of benthic algae to the water column, (2) to investigate limiting nutrients, and (3) to study algae diel distribution patterns. The first study sampled benthic algae emergence using algal recruitment traps that were placed in the sediment by SCUBA. The second study was conducted using a FluoroProbe to take profiles of the water column to identify what cyanobacteria concentrations were in the water column and whether a diel vertical migration was occurring. The third study used nutrient enrichments by phosphorus and different nitrogen components in a factorial experiment to investigate which nutrient was limiting for algal blooms in Oneida Lake.
Results/Conclusions
By sampling algal communities emerging from the benthos, we observed that at shallower depths (~4m) green algae dominated emergent communities, while at deeper depths (~6-10m) emergence was dominated by cyanobacteria. Though the average depth of Oneida lake is 6.7m, cyanobacteria emerging from the benthos is not a sizable contribution to algal production but may function as an inoculation of the water column. Though cyanobacteria did not demonstrate any migration patterns, both diatoms and green algae surfaced in the morning and moved deeper at sundown, with diatoms stratifying about a meter below other algal group. The enrichment study indicated that phosphorus is the limiting nutrient in Oneida Lake, which explains why storms that disturbed the benthos and input phosphorus into the water column are often followed by algal blooms. To understand triggers of HABs in Oneida Lake, we need to quantify relative contributions of phosphorus from different sources (internal vs external loading) and to elucidate physical conditions that influence the emergence of benthic algae into the water column.