Effects of Tropical Cyclone Passage on Plankton Community Respiration in a Phosphate-Limited Freshwater Ecosystem

Abstract

Plankton community respiration (CR) in aquatic ecosystems varies with environmental factors, which could be altered during tropical cyclones (TCs). A potential increase in CR resulting from the effects of TCs is generally understudied. Here, we examined the relationship between plankton CR and environmental factors, including during TC-affected periods, in a phosphate-limited freshwater ecosystem. We conducted an intensive in situ sampling in Fei-Tsui Reservoir (FTR) from January 2010 to December 2015 during TC periods and non-TC periods. Our results showed a consistent temporal pattern that plankton CR increased between March to October and declined between November to February. These changes in plankton CR, primarily supported by bacterial biomass, were positively influenced by euphotic depth-averaged temperature. The CR also significantly increased with euphotic depth-averaged NO₂-concentrations and decreased with euphotic depth-averaged NO₃-concentrations. These results indicated that these factors typically influenced CR dynamics in the FTR. During TC periods, plankton CR was increased further due to a higher and ideal euphotic depth-averaged temperature (23-27°C) and increased supply of limiting nutrient resources via stream runoff. Overall, this study showed that a TC positively influences plankton CR by creating favorable water conditions. Notably, with a higher frequency of intense TCs projected for the Western North Pacific in most climate change scenarios, the impact of TCs on CR may increase in the near future.

Keywords: Bacterial biomass; Oligotrophic lake; Plankton; Total community respiration; Typhoon.

Fig. 1.

Map of the study area, including (a) Taiwan’s geographical location, (b) Fei-Tsui Reservoir, and (c) the dam site.

Fig. 2.

Timeseries and boxplot displaying differences in euphotic depth-averaged plankton community respiration in tropical cyclone (TC) and nonTC periods in the Fei-Tsui Reservoir from January 2010 to December 2015. The euphotic depth spans from 0–20 m on average. Each bar represents individual sampling. Different bar colors indicate the TC and Non-TC periods. periods. The p-value estimated by the Mann-Whitney U test is shown.

Fig. 3.

Relationships between euphotic depth-averaged plankton community respiration versus (a) euphotic depth-averaged temperature, (b) dissolved oxygen (DO), (c) dissolved organic carbon (DOC), (d) NO₂^-, (e) NO₃^-, and (f) PO₄³-concentrations in the Fei-Tsui Reservoir from January 2010 to December 2015. The euphotic depth spans from 0–20 m on average. Black and white circles represent tropical cyclone (TC) and non-TC periods, respectively. Estimated R2 and p-values by simple linear regression analysis are shown. The solid line indicates a significant relationship (p ≤ 0.001) and the broken line indicates no significant relationship (p > 0.05).

Fig. 4.

Relationships between euphotic depth-averaged plankton community respiration versus (a) euphotic depth-averaged bacterial biomass, (b) chlorophyll a, and (c) log10 0–50 m depth-averaged small zooplankton biomass in the Fei-Tsui Reservoir from January 2010 to December 2015. The euphotic depth spans from 0–20 m on average. Black and white circles represent tropical cyclone (TC) and non-TC periods, respectively. The correlation coefficient (r) and p-values estimated by Pearson’s correlation test are shown.

Fig. 5.

Relationships between euphotic depth-averaged plankton community respiration versus (a) euphotic depth-averaged temperature during tropical cyclone (TC) periods and non-TC periods (all datasets and May–November dataset) and (b) precipitation during TC periods in the Fei-Tsui Reservoir. The euphotic depth spans from 0–20 m on average. Black and white circles represent TC and non-TC periods, respectively. Estimated R2 and p-values by simple linear regression analysis are shown. The solid line indicates a significant relationship (p ≤ 0.05).

Fig. 6.

Boxplots comparing (a) precipitation, (b) euphotic depth-averaged dissolved organic carbon (DOC), (c) NO₂^-, (d) NO₃^-, (e) PO₄³-concentrations between tropical cyclone (TC) periods and non-TC periods using the May–November dataset. The euphotic depth spans from 0–20 m on average. Estimated p-values by the Mann-Whitney U test are shown.