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Shallow lakes have a tendency to settle into turbid or clear-water states, the latter having lower concentrations of total phosphorus (TP). However, how P-cycling is affected by and perhaps contributes to maintaining the different states is not well understood, in part because quantifying the processes involved by traditional methods is difficult. To elucidate these processes, we conducted experiments using 32 P-PO 4 as a tracer on samples collected from the unrestored, unvegetated sections of Huizhou West Lake where turbid water prevails as well as the restored, clear-water, macrophyte-rich waters of the lake. We measured PO 4 uptake rates, 32 P-PO 4 accumulation by various plankton size-fractions (picoplankton (0.2-2 μm), nanoplankton (2-20 μm) and microplankton (>20 μm)) as well as release rates of 32 P-PO 4 by labelled plankton. Our results revealed slow PO 4 uptake in the turbid state due to low PO 4 concentration, slow recycling of the high particulate P, and high levels of particulate 32 P which may allow for continuous high growth and biomass of phytoplankton. In contrast, in the clear water state, the uptake of PO 4 was rapid due to a higher PO 4 concentration, the recycling rates of particulate 32 P were high and the levels of particulate 32 P were low, potentially constraining the phytoplankton growth. A greater proportion of particulate 32 P was in the microplankton fraction in clear waters, suggesting that grazing by microplankton may play an important role in the rapid P recycling in clear-waters. Our results provide some evidence for a reinforcement of the turbid conditions (low recycling rate) when the lake is in a turbid state and vice versa when in the clear water state. The results add new knowledge to the understanding of P cycling in shallow lakes and illustrate the utility of using P-kinetics in contrasting states in plankton communities., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020. Published by Elsevier B.V.)

It has been shown that the main drivers of the dynamics of cladoceran and copepod abundances can be predators (fish), the quantity and/or quality of food in terms of the contents of eicosapentaenoic acid, phosphorus and nitrogen in the seston under eutrophic conditions. In experimental mesocosms under eutrophic conditions, we found that, fish did not affect the quantity and quality of food resources for crustaceans. In the second half of experiments, however, dominance shifted from copepods to cladocerans. This was due to the improvement of the food quality for cladocerans in terms of the carbon-to-phosphorus ratio in the seston rather than to fish predation. Under eutrophic conditions, fish reduced the biomass of both cladocerans and copepods without changing the ratio between them. [ABSTRACT FROM AUTHOR]