Journal
JOURNAL OF FRESHWATER ECOLOGY
Volume 30, Issue 1, Pages 5-24Publisher
TAYLOR & FRANCIS INC
DOI: 10.1080/02705060.2014.994047
Keywords
eutrophication; Lake Taihu; nitrogen; nutrient management; phytoplankton; cyanobacterial blooms; phosphorus
Funding
- US National Science Foundation [ENG/CBET 0826819]
- INSPIRE Program [1230543]
- Dimensions of Biodiversity Program [DEB 1240851]
- National Science Foundation of China [41230744]
- Natural Science Foundation of Jiangsu Province [BK2012895]
- External Cooperation Program of Chinese Academy of Sciences [GJHZ1214]
- Direct For Biological Sciences
- Division Of Environmental Biology [1240851] Funding Source: National Science Foundation
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Rapidly increasing urban, agricultural, and industrial growth in the Taihu basin during the past four decades has led to accelerated nitrogen (N) and phosphorus (P) loading to the lake. This has caused the lake to shift from oligo-mesotrophic to hypertrophic conditions, symptomized by toxic cyanobacterial blooms, dominated by the non-N-2 fixing genus Microcystis. From 2008 to 2013, a series of in situ microcosm and mesocosm nutrient addition bioassays were conducted that were focused on the heavily polluted northern region (i.e., Meiliang Bay) and other lake locations. Bioassays showed that phytoplankton production, as chlorophyll a and photopigments diagnostic of major phytoplankton groups, was controlled by P inputs from spring to early summer, while N played a more dominant controlling role in summer-fall. In most cases, combined N and P additions promoted maximum growth. This pattern proved true for both the highly eutrophic northern region and the less-eutrophic central and southern regions. Cyanobacteria, chlorophytes, and cryptophytes all showed the strongest positive responses to N and N+P enrichment during the summer bloom period, while diatoms were the least abundant then and just moderately stimulated by nutrient additions. Cyanobacteria failed to selectively respond to P inputs during the summer bloom period, contradicting the paradigm that selective P enrichment will favor them, especially the N-2-fixing genera. Rather, Microcystis-dominated blooms remained N-limited during summer months and were not replaced by N-2-fixing genera, indicating that internal N and P regeneration of previously loaded nutrients must be sustaining blooms. Successful 'de-eutrophication' of Taihu will require reductions of both N and P inputs in all lake regions in order to control blooms and counter the legacy of several decades of nutrient over-enrichment.
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