Response of the photosynthetic activity and biomass of the phytoplankton community to increasing nutrients during cyanobacterial blooms in Meiliang Bay, Lake Taihu

Abstract

Nutrient enrichment facilitates algal outbreaks in eutrophic shallow lakes. To further understand the influence of various inorganic nutrient forms on cyanobacterial blooms, a nitrate (NO 3 ), ammonium (NH 4 ), and orthophosphate (PO 4 ) amendment experiment was conducted in a large shallow lake of China (Lake Taihu) during summer. The results showed that the photosynthetic performance of phytoplankton responded more positively to phosphorus (P) than nitrogen (N), and NH 4 addition stimulated higher algal photosynthetic activities in P-enriched waters. Individual inorganic N or PO 4 addition significantly activated cyanobacteria and green algae. Meanwhile, the N plus P amendment promoted higher biomass of the planktonic microbial community, and the dual addition of NH 4 + PO 4 yielded the highest chlorophyll a concentration. NH 4 additions provisionally promoted higher green algae than cyanobacteria biomass in the beginning, while cyanobacteria dominated again with increasing NH 4 :PO 4 ratios. These results revealed that increasing ammonium would enhance the increase in phytoplankton biomass in advance and prolong the duration of algal blooms. Hence, based on the control of P loading, the reduction in external inorganic N focusing on ammonium sources (such as ammonia N fertilizer) at the watershed scale would help to alleviate eutrophication and cyanobacterial blooms over the long term in Lake Taihu. • Practitioner points• Ammonium addition stimulated higher algal photosynthetic activities in P-enriched waters. • Individual inorganic N or PO 4 addition significantly activated cyanobacteria and green algae. • The dual addition of NH 4 + PO 4 yielded the highest chlorophyll a concentration. • Increasing NH 4 would enhance the increase in phytoplankton biomass in advance and prolong the duration of cyanobacterial blooms.

Allelopathic Potential of the Cyanotoxins Microcystin-LR and Cylindrospermopsin on Green Algae

“…As a result of these changes, the ratio between the mainly represented taxonomic groups of algae and cyanobacteria, forming the phytoplankton in freshwater basins, has also changed in recent years. It has been reported that cyanobacteria are a dominant group in many water bodies [ 56 , 57 , 58 , 59 , 60 , 61 ]. In some water bodies, there is even a displacement of the Chlorophyta, which traditionally occupy the first place in the phytoplankton of freshwater basins, by representatives of cyanobacteria [ 57 , 60 , 62 ].…”

“…It has been reported that cyanobacteria are a dominant group in many water bodies [ 56 , 57 , 58 , 59 , 60 , 61 ]. In some water bodies, there is even a displacement of the Chlorophyta, which traditionally occupy the first place in the phytoplankton of freshwater basins, by representatives of cyanobacteria [ 57 , 60 , 62 ]. In all cases, however, the representatives of these groups of phytoplankton interact with each other and cyanobacteria always have an advantage.…”

Automatic Detection of Algal Blooms Using Sentinel-2 MSI and Landsat OLI Images

“…It is a shallow inland eutrophic lake with a maximum depth of 2.6 m and average depth of 1.9 m [57][58][59][60]. It is a drinking water source for more than 40 million people and plays an important role in aquaculture, tourism and flood control [8,58,59]. However, the large population, urbanization, industrial development, intensive agriculture and tourism activities caused hypereutrophic and experienced algal blooms in Lake Taihu since 1990s [61][62][63].…”

“…where Pi is the standardized reflectance of one pixel on a single band (Figure 2), Pj is one of the eight spatial neighbors of Pi (Figure 2), Wij is the spatial weight (Figure 2), and n is the number of spatial neighbours (8). Ii is the Local Moran's index that refers to the spatial association between a given pixel (Pi) and its spatial lag variable (∑ ) which was calculated using the spatial neighbors and their corresponding spatial weight.…”

Effects of Environmental Concentrations of Total Phosphorus on the Plankton Community Structure and Function in a Microcosm Study

“…Species capable of forming harmful algal blooms can reduce the photosynthetic capacity of coexisting algae by releasing allelochemicals after 10 d of exposure [ 30 ]. In addition, a large amount of N and P can also promote the photosynthesis of algae, which may prolong the duration of algal bloom and cause harm to the aquatic ecosystem [ 31 , 32 ]. The pH can be used as an indirect physicochemical proxy of photosynthesis, because the algae blooms may consume CO 2 faster through photosynthesis than what can be replaced by diffusion and ecosystem respiration.…”