Temporal–spatial variations of chlorophyll a and primary production in Meiliang Bay, Lake Taihu, China from 1995 to 2003

Abstract

There are few long-term data sets on primary production in a lake, which can be used to validate the output from a production model. To address this need, we determined the temporal–spatial variations of chlorophyll a (Chl a) and primary production (PPeu), based on the vertically generalized production model (VGPM) by using 742 samplings at seven sites in Meiliang Bay in Lake Taihu from 1995 to 2003. An empirical model estimating primary production (PPin) was used to validate VGPM PPeu and the dominant factors controlling PP were determined. Markedly higher Chl a and PPeu values were recorded in Meiliang Bay in 1996 and 1997 than in other years and a marked decrease in Chl a and PPeu was found between 2001 and 2003. Peaks of Chl a typically appeared in summer (June–August) and minima occurred in winter (January). The highest daily mean PPeu usually occurred in summer (June); the exception was at site 1, where peak daily mean PPeu occurred in spring (April). The lowest daily mean PPeu was recorded in winter (January). In Meiliang Bay, 43.0% of annual PP occurred in only 3 months, from June to August. The relative difference of maximum and minimum PPeu was markedly larger than the corresponding difference in Chl a. Levels of both Chl a and PPeu were markedly decreased from the inner to the outer areas of Meiliang Bay; the highest annual integrated PPeu was found at site 1, close to the inflow of the River Liangxi and this level was 1.85 and 2.14 times higher than at sites 3 and 6, respectively, that were located in outer Meiliang Bay. The estimated daily mean PPeu variation closely matched with that of the Chl a concentration, implying that Chl a concentration can account for the considerable variation of PP. The annual integrated PPeu of the euphotic zone in Meiliang Bay ranged from 3.44 � 10 4 tC year -1 to 8.59 � 10 4 tC year -1 with an overall mean of 5.65 � 10 4 tC year -1 . A significant positive linear relationship was found between VGPM PPeu and empirical model PPin [PPin ¼ 0.826 (+0.015)PPeu þ 272.0 (+25.0), r 2 ¼ 0.80, n ¼ 742, P , 0.0001]. By considering the effect of water temperature, photosynthetically active radiation and photoperiod on PP, the VGPM- generated PPeu more accurately captured monthly variations than did the empirical model that only included Chl a concentration.