Evaluating the significance of benthic regeneration of phosphorus in Oneida Lake

Background/Question/Methods

Oneida Lake is a large, shallow, mesotrophic lake with an average depth of 6.8m. Nutrient loading the lake declined in the 1980s with water clarity and chlorophyll concentrations declining after the arrival of zebra mussels in 1992.  However, a sequence of bluegreen algae blooms still characterized the late summer – early fall period. The goal of this study was to determine the significance of benthic regeneration of phosphorus (P) in Oneida Lake. In order to determine the importance of benthic regeneration of P, the P loading of three streams (Oneida, Chittenango, and Fish Creek) were measured throughout the summer of 2015. Profiles of dissolved oxygen and temperature as well as P concentrations at 2 and 10 m depth were measured at one standard station.  To examine phosphorus regeneration on a finer scale, an incubation experiment was conducted using benthic chambers containing ~5cm of substrate overlain by ~20cm of water collected from a location approximately 0.1km offshore with a depth of 8m.  The chambers were incubated at 21^oC in a water bath for 48 hours with dissolved oxygen (DO) and soluble reactive phosphorus (SRP) samples being taken at 3, 6, 12, and 24 hours. 

Results/Conclusions

The period from June 24^th to July 27^rd was chosen because it coincided with a period of stratification occurring from July 2^nd to the 24^th. On July 13^th the dissolved oxygen was below 4mgl^-`below a depth of 8 m and between July 16^th and 21^st the concentration of SRP increased from 4.66 to 26.61μgl^-1 at 10m and at that concentration there would be approximately 1711kg of SRP released from sediments below 10m. In comparison between June 26^th and July 2^nd there was a period of high discharge from streams with visibly high sediment loads. During this time SRP concentrations in the streams ranged from 6.67 to 9.77μgl^-1 which resulted in 530 kg of SRP loading to the lake from the inflowing streams. Over five days the benthic sediments increased in concentration and total SRP loading over two times that of the tributaries over an entire week. In the benthic chambers DO declined linearly at a rate of 0.12 μgl^-1 hr^-1. This data shows that it is possible to get a large release of P from benthic sediment without completely anoxic conditions and that the polymictic nature of Oneida Lake periodically mixes large amount of P into the water column.