Diurnal changes of cyanobacteria blooms in Taihu Lake as derived from GOCI observations

Abstract

Using frequent and long‐term measurements (eight times per day, 2011 to present) from a geostationary satellite sensor (Geostationary Ocean Color Imager, GOCI), this study investigates diurnal changes of cyanobacterium Microcystis aeruginosa blooms (near‐surface high concentrations or surface scums) in Taihu Lake, from which vertical migration patterns could be inferred. After proper atmospheric correction, a cyanobacterial index algorithm is used to quantify equivalent surface cyanobacterial density (σ, 0–100%) at both pixel and synoptic scales from each cloud‐free image, followed by analysis of diurnal changing patterns of σ at both scales. Three typical diurnal changing patterns are identified from all images, which show distinctive and different seasonality from the long‐term statistics. Spatial distributions of the “hotspot” regions where diurnal changes are most often observed have also been established. While the seasonality of the three patterns appears to be a result of seasonality in both temperature and light availability, large blooms only occur 1 d after major wind events. Based on several lines of evidence, we hypothesize that the diurnal changes of such observed surface bloom patterns are likely a result of vertical migration rather than horizontal dissipation/aggregation of cyanobacteria. The mean migration speeds inferred from either a simple model or a radiative transfer model (< 0.03 cm s−1 or < 1 m h−1) are consistent with those reported earlier from laboratory measurements for certain cyanobacteria colony sizes. Complete understanding of the three types of diurnal patterns and direct validation of the hypothesis, however, require further investigations from field measurements.

Assessment of the Number of Valid Observations and Diurnal Changes in Chl-a for GOCI: Highlights for Geostationary Ocean Color Missions

“…(2) The insufficient number of valid Chl-a retrievals in these regions, where effective atmospheric correction (AC) procedures are difficult to implement because of extreme turbidity-enhanced signals in the AC bands (i.e., near-infrared), constitutes a limitation [ 50 , 51 , 52 ]. Indeed, geostationary observations boast unique advantages in studying coastal and inland waters, where the short-term dynamics of optical properties should be remarkable due to various factors, including tide forcing, winds and waves, surface runoff and diurnal vertical migrations of algae [ 5 , 6 , 7 ].…”

“…Real geostationary measurements from GOCI have been used to demonstrate its advantages over coastal oceans by tracking the diurnal changes in the sediment plumes of riverine estuaries [ 6 , 22 ], documenting the short-term spatial and vertical redistributions of harmful algal blooms [ 5 , 7 , 23 ], and detecting the continuous evolution of internal waves [ 24 ], etc. In the open ocean, however, the optical characteristics of the water column have commonly been considered diurnally invariant; this assumption has even been applied to determine the accuracy of the GOCI ocean color products [ 25 ].…”

“…For example, the first geostationary ocean color imager (GOCI, data available since 2011), operated by the Korea Institute of Ocean Science & Technology, has demonstrated its unique contributions in capturing the diurnal changes of red tides, turbidity plumes, water quality and ocean surface current, etc. [5][6][7][8][9][10][11][12], given its temporal resolution of eight hourly observations per day. Although they have coarse spectral and spatial resolutions, geostationary meteorological satellites (such as the Himawari-8 from the Japan Meteorological Agency and the Geostationary Operational Environmental Satellite (GOES) from NOAA) boast high observational frequencies (tens of minutes), allowing them to detect, for example, the short-term dynamics of floating algae [13][14][15].…”

Oxidative Stress and Antioxidant Responses of Phormidium ambiguum and Microcystis aeruginosa Under Diurnally Varying Light Conditions

“…To establish a presence in an ecosystem, cyanobacteria require temperature and light-intensity conditions within suitable ranges, which can vary between cyanobacterial species [27,29,30]. Under preferable environmental conditions for most cyanobacteria, such as tropical and subtropical conditions, temperature factors do not show significant diurnal variation [31]. However, the light conditions certainly change, regardless of the geological location.…”

A Remote Sensing Algorithm of Column-Integrated Algal Biomass Covering Algal Bloom Conditions in a Shallow Eutrophic Lake

“…For instance, the bloom area has been observed to double even within 6 h in the East China Sea from Geo-stationary Ocean Color Imager (GOCI) observation [11]. Neither algal growth rate nor environmental conditions would allow bloom areas to expand at such a rapid pace, indicating that vertical migration of algae is a likely cause [46]. Thus, column integrated algal biomass is considered to be a more robust indicator of eutrophication.Empirical estimation of heterogeneous column-integrated algal biomass is often conducted using in situ measurements, such as the vertical profile of Chl-a.…”