PATTERNS IN ALGAL RECRUITMENT FROM SEDIMENT TO WATER IN A DIMICTIC, EUTROPHIC LAKE

In the large, dimictic, and highly productive Lake Mendota (Wisconsin, USA), the recruitment rates from sediment to water were determined for some characteristic and dominating algal species during a 1-yr cycle. Quantifying recruitment in relation to abundance in the water on a whole-lake basis revealed that recruitment usually accounted for less than 1% of the total standing stock of each species per day, indicating that recruitment may not be an important population variable in Lake Mendota, but may instead function as an inoculum for future growth in the water column. The recruitment of Cryptomonas erosa and Ceratium hirundinella showed a dephasing among sites, suggesting that algae on the sediment surface rise into the water column in response to some depth-related cue. With the exception of one recruitment period for Aphanizomenon, no recruitment was recorded below the thermocline during the stratification period, indicating that a variable associated with stratified conditions affected algal movements from the hypolimnion to the euphotic zone. We argue that the understanding of recruitment patterns from sediment to water is a key factor in managing algal blooms in highly productive lakes.