Spatio-Temporal Variability of Aquatic Vegetation in Taihu Lake over the Past 30 Years

Dehua Zhao,Ying Cai,Hao Jiang,Shuqing An,Delin Xu,Meiting Lv,Jose Luis Balcazar

doi:10.1371/journal.pone.0066365

Abstract

It is often difficult to track the spatio-temporal variability of vegetation distribution in lakes because of the technological limitations associated with mapping using traditional field surveys as well as the lack of a unified field survey protocol. Using a series of Landsat remote sensing images (i.e. MSS, TM and ETM+), we mapped the composition and distribution area of emergent, floating-leaf and submerged macrophytes in Taihu Lake, China, at approximate five-year intervals over the past 30 years in order to quantify the spatio-temporal dynamics of the aquatic vegetation. Our results indicated that the total area of aquatic vegetation increased from 187.5 km2 in 1981 to 485.0 km2 in 2005 and then suddenly decreased to 341.3 km2 in 2010. Similarly, submerged vegetation increased from 127.0 km2 in 1981 to 366.5 km2 in 2005, and then decreased to 163.3 km2. Floating-leaf vegetation increased continuously through the study period in both area occupied (12.9 km2 in 1981 to 146.2 km2 in 2010) and percentage of the total vegetation (6.88% in 1981 to 42.8% in 2010). In terms of spatial distribution, the aquatic vegetation in Taihu Lake has spread gradually from the East Bay to the surrounding areas. The proportion of vegetation in the East Bay relative to that in the entire lake has decreased continuously from 62.3% in 1981, to 31.1% in 2005 and then to 21.8% in 2010. Our findings have suggested that drastic changes have taken place over the past 30 years in the spatial pattern of aquatic vegetation as well as both its relative composition and the amount of area it occupies.

Highlights

With the rapid development of the Chinese economy since the ‘‘reform and opening-up’’ policy was implemented in 1978, human activities have placed a growing stress on the country’s freshwater lakes, which are extremely vulnerable to natural and anthropogenic disturbance [1,2,3]
Because of the substantial spatial variation in the aquatic environments of Taihu Lake, we divided the lake into six sections (Fig. 1): I, Meiliang Bay and Zhushan Bay, the most polluted area in the lake [17]; II, Gonghu Bay, through which large amounts of water have been flushed into the lake from the Yangtze River since 2001 [18,19]; III, the eastern coastal areas that represent the traditional distribution area of aquatic vegetation; IV, the east bay, where most of the activities related to fisheries production are focused; V, the central area and the west coastal areas, which occupy 58.8% of the lake; VI, the southeast section, which connects the central area and the east bay
3.1 Spatio-temporal Dynamics of Distribution Area We used the classification tree (CT) models developed in this study to map emergent, floating-leaf and submerged vegetation in 1981, 1984, 1989, 1995, 2000, 2005 and 2010 (Fig. 3)

Summary

Introduction

With the rapid development of the Chinese economy since the ‘‘reform and opening-up’’ policy was implemented in 1978, human activities have placed a growing stress on the country’s freshwater lakes, which are extremely vulnerable to natural and anthropogenic disturbance [1,2,3]. Since the 1978 policy changes, the Taihu Lake catchment has experienced rapid socio-economic development. Concurrent with the rapid socio-economic development, the aquatic ecosystem of Taihu Lake has degraded appallingly [11,12,13], with the degradation being widely attributed to eutrophication and human activities such as flood control projects and wetland reclamation [11], and the distribution and community structure of aquatic macrophytes have clearly changed [14,15]

Methods

Results

Conclusion