Long-Term Dynamics of Chlorophyll-a Concentration and Its Response to Human and Natural Factors in Lake Taihu Based on MODIS Data

Abstract

Chlorophyll-a plays an essential biochemical role in the eutrophication process, and is widely considered an important water quality indicator for assessing human activity’s effects on aquatic ecosystems. Herein, 20 years of moderate resolution imaging spectroradiometer (MODIS) data were applied to investigate the spatiotemporal patterns and trends of chlorophyll-a concentration (Chla) in the eutrophic Lake Taihu, based on a new empirical model. The validated results suggested that our developed model presented appreciable performance in estimating Chla, with a root mean square error (MAPE) of 12.95 μg/L and mean absolute percentage error (RMSE) of 29.98%. Long-term MODIS observations suggested that the Chla of Lake Taihu experienced an overall increasing trend and significant spatiotemporal heterogeneity during 2002–2021. A driving factor analysis indicated that precipitation and air temperature had a significant impact on the monthly dynamics of Chla, while chemical fertilizer consumption, municipal wastewater, industrial sewage, precipitation, and air temperature were important driving factors and together explained more than 81% of the long-term dynamics of Chla. This study provides a 20 year recorded dataset of Chla for inland waters, offering new insights for future precise eutrophication control and efficient water resource management.

Retrievals of Chlorophyll-a from GOCI and GOCI-II Data in Optically Complex Lakes

“…Due to the decreasing water temperature and increasing wind speed [48], the mean Chla in Lake Taihu in 2018 significantly decreased. Influenced by the rising temperature in 2019, the mean Chla in Lake Taihu also increased [49], which is consistent with the variation trend in the frequency of algal blooms proposed by Xue (2022) [41].…”

Monitoring Chlorophyll-a Concentration Variation in Fish Ponds from 2013 to 2022 in the Guangdong-Hong Kong-Macao Greater Bay Area, China

“…It is evident that Chl-a concentration exhibits noticeable seasonal variations, peaking in summer (56.7 µg•L −1 ) and reaching its lowest in winter ( 43 Additionally, the fluctuation of Chl-a concentration in fish ponds is more pronounced than in natural lakes. For instance, Cao et al examined the changes of Chl-a concentration in Taihu Lake from 1984 to 2019, revealing that the summer average Chl-a concentration was the highest (24.9 ± 6.9 µg•L −1 ), while the winter average was the lowest (20.9 ± 63.6 µg•L −1 ) [16], with a difference of only 4 µg•L −1 between summer and winter. Deng et al analyzed the seasonal variations of phytoplankton in Lake Taihu over twenty years, and found that Chl-a concentration is slightly higher in summer than that in winter [46].…”

“…Our results revealed significant spatiotemporal variations in Chl-a concentration in fish ponds in the GBA, including interannual, seasonal, and spatial patterns. Environmental changes [49,50], climate changes [14], and human activities [5,16,17] are the primary driving forces of these changes, with temperature potentially exerting the most significant natural influence. To delve deeper into these dynamics, we calculated the water temperature of fish ponds for four seasons from 2013 to 2022, deriving the average over the decade.…”

“…Remarkably, over 90% of the world's inland water bodies are smaller than <0.01 km 2 , excluding very small (<0.001 km 2 in area) fish ponds, totaling approximately Remote Sens. 2024, 16, 2033 2 of 26 3.2 billion in number, and covering an area of approximately 800,000 km 2 [3]. Understanding their cumulative impact on global water environmental changes necessitates further intensive studies [3].…”

“…Chlorophyll-a (Chl-a) is a crucial photosynthetic pigment produced by algae during photosynthesis, making it an effective indicator for monitoring water eutrophication [13]. In recent years, factors such as climate change [14] and excessive aquaculture activities resulting from human activities [15][16][17] have led to elevated eutrophication [18][19][20]. Consequently, there has been a proliferation of algae in inland water bodies, leading to an increase in Chl-a concentration [21,22].…”