Evaluating the influences of harvesting activity and eutrophication on loss of aquatic vegetations in Taihu Lake, China

Juhua Luo,Ruiliang Pu,Hongtao Duan,Ronghua Ma,Zhigang Mao,Yuan Zeng,Linsheng Huang,Qitao Xiao

doi:10.1016/j.jag.2019.102038

Abstract

A rapid degradation of aquatic vegetations in Taihu Lake has roused a wide attention in recent years. Giving large-scale harvesting activity on aquatic vegetation since 2012, whether water eutrophication or the human harvest activity induced the degradation remains controversial and unclear. In this study, based on Landsat and HJ-CCD data acquired from 1984 to 2016 and a 12-year field observation (2005–2016) of water quality, a method was proposed to quantitatively assess impacts of harvesting activity and water quality change on degradations of both floating-leaved aquatic vegetation (FAV) and submerged aquatic vegetation (SAV) in Taihu Lake. First, areas of FAV and SAV covers from 1984 to 2016 in Taihu Lake were mapped using the satellite data, and then the mapped areas were modified to those on a reference date by using phenological curves of FAV and SAV covers. Next, correlations between water quality data and FAV and SAV covers were analyzed by using Pearson correlation analysis based on the data before implementing the human harvesting activity (i.e., before 2012), and multiple general linear models were established based on the selected water quality variables with p-value <0.01 for estimating covers of FAV and SAV from 2012 to 2016. Finally, based on the predicted areas of FAV and SAV covers by the models and the modified areas mapped from satellite data, the influences of water eutrophication and the human harvesting activity on the degradation of FAV and SAV covers were quantitatively assessed. The results indicated that (1) FAV cover exhibited a significant increase from 1984 to 2011 and then a rapid decrease, while SAV cover increased significantly before 2003 and then obviously declined; (2) water level (WL) and total nitrogen (TN) showed significantly negative correlations with FAV and SAV covers, while secchi disk depth (SDD) and SDD/WL had significantly positive correlations with FAV and SAV covers; (3) the human harvesting activity made a major contribution to the loss of FAV cover, and the degradation of SAV cover was mainly due to an increased lake eutrophication and deteriorated underwater light environment. The findings derived from this study could offer a guidance for Taihu Lake ecological restoration and effective management.

Highlights

Submerged aquatic vegetation (SAV) and floating-leaved aquatic vegetation (FAV) are the two main types of aquatic vegetation in most shallow lakes
The results indicated that (1) FAV cover exhibited a significant increase from 1984 to 2011 and a rapid decrease, while SAV cover increased significantly before 2003 and obviously declined; (2) water level (WL) and total nitrogen (TN) showed significantly negative correlations with FAV and SAV covers, while secchi disk depth (SDD) and SDD/WL had significantly positive correlations with FAV and SAV covers; (3) the human harvesting activity made a major contribution to the loss of FAV cover, and the degradation of SAV cover was mainly due to an increased lake eutrophication and deteriorated underwater light environment
Over the period of 33 years, SAV experienced some changes, and the change patterns were different among three regions, which might be summarizes as follows. i) In region A, as shown in Fig. 5a, SAV appeared in 1991, increased to the peak around 2003 and decreased with a large fluctuation while FAV slightly increased before 2014 and decrease. ii) In region B, as shown in Fig. 5b, the modified cover area of SAV fluctuated between 1 km2 and 5 km2 from 1984 to 1992; and SAV reached two peaks in 2003 and 2011, decreased dramatically from 104.50 km2 in 2011 to 23 km2 in 2016 (Fig.5b)

Summary

Introduction

Submerged aquatic vegetation (SAV) and floating-leaved aquatic vegetation (FAV) are the two main types of aquatic vegetation in most shallow lakes. Rapid expansion of FAV may have a potential of causing disturbances to biodiversity, nutrient cycling, and aquatic life habitat and even an adverse shift in shallow lakes from a clear-water plant-dominated state to a turbid algae-dominated state. This is because FAV with large leaf area floating on the water surface will block the light into the water, which may induce a rapid degradation of SAV and the death of aquatic animal living on SAV due to

Methods

Results

Discussion

Conclusion