Artificial Regulation of Water Level and Its Effect on Aquatic Macrophyte Distribution in Taihu Lake

Management of water levels for flood control, water quality, and water safety purposes has become a priority for many lakes worldwide. However, the effects of water level management on the distribution and composition of aquatic vegetation has received little attention. Relevant studies have used either limited short-term or discrete long-term data and thus are either narrowly applicable or easily confounded by the effects of other environmental factors. We developed classification tree models using ground surveys combined with 52 remotely sensed images (15–30 m resolution) to map the distributions of two groups of aquatic vegetation in Taihu Lake, China from 1989–2010. Type 1 vegetation included emergent, floating, and floating-leaf plants, whereas Type 2 consisted of submerged vegetation. We sought to identify both inter- and intra-annual dynamics of water level and corresponding dynamics in the aquatic vegetation. Water levels in the ten-year period from 2000–2010 were 0.06–0.21 m lower from July to September (wet season) and 0.22–0.27 m higher from December to March (dry season) than in the 1989–1999 period. Average intra-annual variation (CVa) decreased from 10.21% in 1989–1999 to 5.41% in 2000–2010. The areas of both Type 1 and Type 2 vegetation increased substantially in 2000–2010 relative to 1989–1999. Neither annual average water level nor CVa influenced aquatic vegetation area, but water level from January to March had significant positive and negative correlations, respectively, with areas of Type 1 and Type 2 vegetation. Our findings revealed problems with the current management of water levels in Taihu Lake. To restore Taihu Lake to its original state of submerged vegetation dominance, water levels in the dry season should be lowered to better approximate natural conditions and reinstate the high variability (i.e., greater extremes) that was present historically.

[1]  C. Wright,et al.  Improved wetland remote sensing in Yellowstone National Park using classification trees to combine TM imagery and ancillary environmental data , 2007 .

[2]  Guofeng Wu,et al.  Concurrent monitoring of vessels and water turbidity enhances the strength of evidence in remotely sensed dredging impact assessment. , 2007, Water research.

[3]  R. Lawrence,et al.  Mapping wetlands and riparian areas using Landsat ETM+ imagery and decision-tree-based models , 2006, Wetlands.

[4]  Stacy L. Ozesmi,et al.  Satellite remote sensing of wetlands , 2002, Wetlands Ecology and Management.

[5]  László G.-Tóth,et al.  Ecological effects of water-level fluctuations in lakes: an urgent issue , 2008, Hydrobiologia.

[6]  Brigitte Poulin,et al.  Wetland monitoring using classification trees and SPOT-5 seasonal time series , 2010 .

[7]  J. Paillisson,et al.  Can small water level fluctuations affect the biomass of Nymphaea alba in large lakes , 2006 .

[8]  B. Lundén,et al.  Assessment of changes in the seagrass-dominated submerged vegetation of tropical Chwaka Bay (Zanzibar) using satellite remote sensing , 2006 .

[9]  Jin Xiangcan,et al.  The community features of aquatic plants and its influence factors of lakeside zone in the north of Lake Taihu , 2007 .

[10]  Patricia Rodríguez,et al.  Water level as the main driver of the alternation between a free-floating plant and a phytoplankton dominated state: a long-term study in a floodplain lake , 2011, Aquatic Sciences.

[11]  H. Xue,et al.  Experiment of emergent macrophytes growing in contaminated sludge: implication for sediment purification and lake restoration. , 2010 .

[12]  K. Bjorndal,et al.  Historical Overfishing and the Recent Collapse of Coastal Ecosystems , 2001, Science.

[13]  David W. Schindler,et al.  Recent advances in the understanding and management of eutrophication , 2006 .

[14]  Paul Whitehead,et al.  Flow controls on lowland river macrophytes: a review. , 2008, The Science of the total environment.

[15]  M. Scheffer,et al.  Strong growth limitation of a floating plant (Lemna gibba) by the submerged macrophyte (Elodea nuttallii) under laboratory conditions , 2010 .

[16]  Qin Boqiang.  Progress and prospect on the eco-environmental research of Lake Taihu , 2009 .

[17]  K. Moore,et al.  Chesapeake Bay: An Unprecedented Decline in Submerged Aquatic Vegetation , 1983, Science.

[18]  M. Bauer,et al.  Application of Landsat imagery to regional-scale assessments of lake clarity. , 2002, Water research.

[19]  Kumud Acharya,et al.  Modeling impacts of Yangtze River water transfer on water ages in Lake Taihu, China , 2011 .

[20]  Dehua Zhao,et al.  Remote sensing of aquatic vegetation distribution in Taihu Lake using an improved classification tree with modified thresholds. , 2012, Journal of environmental management.

[21]  M. Scheffer,et al.  Floating plant dominance as a stable state , 2003, Proceedings of the National Academy of Sciences of the United States of America.

[22]  M. Scheffer,et al.  Alternative equilibria in shallow lakes. , 1993, Trends in ecology & evolution.

[23]  Kingsley W. Dixon,et al.  Dormancy, germination and seed bank storage: a study in support of ex situ conservation of macrophytes of southwest Australian temporary pools , 2010 .

[24]  Gu Xiao-hong,et al.  Aquatic macrophytes in East Lake Taihu and its interaction with water environment , 2008 .

[25]  P. Chavez.  Image-Based Atmospheric Corrections - Revisited and Improved , 1996 .

[26]  P. Chambers,et al.  Global diversity of aquatic macrophytes in freshwater , 2007, Hydrobiologia.

[27]  Ronghua Ma,et al.  Detecting Aquatic Vegetation Changes in Taihu Lake, China Using Multi-temporal Satellite Imagery , 2008, Sensors.

[28]  Han Olff,et al.  Positive Feedbacks in Seagrass Ecosystems – Evidence from Large-Scale Empirical Data , 2011, PloS one.

[29]  B. Qin,et al.  The contribution of phytoplankton degradation to chromophoric dissolved organic matter (CDOM) in eutrophic shallow lakes: field and experimental evidence. , 2009, Water research.

[30]  Min Yang,et al.  Taihu Lake Not to Blame for Wuxi's Woes , 2008, Science.

[31]  Boqiang Qin,et al.  Lake eutrophication: Control countermeasures and recycling exploitation , 2009 .

[32]  Michael J. Fogarty,et al.  Integrated ecosystem assessments , 2008 .

[33]  Xu Dong,et al.  Changes in physicochemical and biological factors during regime shifts in a restoration demonstration of macrophytes in a small hypereutrophic Chinese lake , 2010 .

[34]  Marten Scheffer,et al.  Succession of aquatic vegetation driven by reduced water‐level fluctuations in floodplain lakes , 2005 .

[35]  M. Scheffer,et al.  Water-level fluctuations affect macrophyte richness in floodplain lakes , 2005, Hydrobiologia.

[36]  J. Paillisson,et al.  Water level fluctuations for managing excessive plant biomass in shallow lakes , 2011 .

[37]  Dehua Zhao,et al.  Estimation of water clarity in Taihu Lake and surrounding rivers using Landsat imagery , 2011 .

[38]  Katherine E. Mills,et al.  Integrated Ecosystem Assessment: Lake Ontario Water Management , 2008, PloS one.

[39]  E. H. Nes,et al.  Managed water levels and the expansion of emergent vegetation along a lakeshore , 2004 .

[40]  L. Lesack,et al.  The influence of water transparency on the distribution and abundance of macrophytes among lakes of the Mackenzie Delta, Western Canadian Arctic , 2002 .

[41]  Zhu Guangwei.  Eutrophic status and causing factors for a large, shallow and subtropical Lake Taihu, China , 2008 .

[42]  J. Otahel,et al.  Spatio-temporal changes in land cover and aquatic macrophytes of the Danube floodplain lake , 2011 .

[43]  P. Carvalho,et al.  Effects of an exotic invasive macrophyte (tropical signalgrass) on native plant community composition, species richness and functional diversity , 2010 .

[44]  Jiang Nan.  RS-based Dynamic Monitoring of Lake Area and Enclosure Culture in East Taihu Lake , 2005 .

[45]  Patricia Chow-Fraser,et al.  Use of IKONOS Imagery to Map Coastal Wetlands of Georgian Bay , 2007 .

[46]  A. Lorenz,et al.  Macrophytes respond to reach‐scale river restorations , 2012 .

[47]  Weiping Hu,et al.  [Spatial distribution characteristics and ecological significance of alkaline phosphatase in water column of Taihu Lake]. , 2009, Huan jing ke xue= Huanjing kexue.

[48]  Gu Xiao.  Evolution of community structure of aquatic macrophytes in East Taihu Lake and its wetlands , 2005 .

[49]  Gang Pan,et al.  In-lake algal bloom removal and submerged vegetation restoration using modified local soils , 2011 .

[50]  S. Carpenter,et al.  Catastrophic shifts in ecosystems , 2001, Nature.

[51]  Andy Hector,et al.  Competition for Light Causes Plant Biodiversity Loss After Eutrophication , 2009, Science.

[52]  G. Andersson,et al.  Long‐term pattern of alternative stable states in two shallow eutrophic lakes , 1993 .

[53]  P. Chow-Fraser,et al.  Mapping Floating and Emergent Aquatic Vegetation in Coastal Wetlands of Eastern Georgian Bay, Lake Huron, Canada , 2010, Wetlands.

[54]  Weiping Hu,et al.  Impacts of the Yangtze River water transfer on the restoration of Lake Taihu , 2008 .

[55]  K. Havens.  Submerged aquatic vegetation correlations with depth and light attenuating materials in a shallow subtropical lake , 2003, Hydrobiologia.

[56]  E Brown de Colstoun,et al.  National Park vegetation mapping using multitemporal Landsat 7 data and a decision tree classifier , 2003 .

[57]  Lucie Guo,et al.  Doing Battle With the Green Monster of Taihu Lake , 2007, Science.