Abstract
River floodplains are among the most dynamic and diverse ecosystems on the planet. They are at risk of degradation due to river regulation and climate change. Environmental water has been delivered to floodplains to maintain environmental health by mimicking natural floods. It is important to understand the long-term effects of environmental water to floodplain vegetation to support its management. This study used Normalized Differences Vegetation index (NDVI) from the 30-year Landsat datasets of the Hattah Lakes floodplain in Australia to investigate the drivers of vegetation dynamics. We developed generalized additive mixed models (GAMM) to model responses of vegetation to environmental water, natural floods, precipitation, temperature, and distance to water across multiple spatial and temporal scales. We found the effect of environmental water on floodplain vegetation to be quite different from that of natural floods in both space and time. Vegetation in most areas of Hattah Lakes will respond to natural floods within one month of flooding, while positive responses to environmental water occur 1 to 3 months after inundation and are more restricted spatially. For environmental water planning, managers need to be aware of these differences. The implementation of new infrastructure to transport or retain environmental water on floodplains needs to be planned carefully, with continuous monitoring of rainfall and natural floods. Whilst environmental floods do not mimic the effect of natural floods, they do provide some positive benefits that can partially offset effects of reduced natural floods.
Highlights
River floodplains are among the most diverse, dynamic and vulnerable ecosystems on the earth [1]
To address this research gap, this paper focuses on modelling vegetation response to environmental water based on 30-year Landsat datasets in Hattah Lakes, Australia
The mean Normalized Differences Vegetation index (NDVI) value of Grassy riverine forest, which are mainly River Red Gum forests, is higher than other classes. This type of vegetation occurs along Chalka creek, through which environmental water is delivered to the water bodies in Hattah Lakes
Summary
River floodplains are among the most diverse, dynamic and vulnerable ecosystems on the earth [1]. They are important to ecology and the economy because of the ecosystem services they provide, including water purification, biodiversity, sediment retention, carbon sequestration, and tourism [2,3,4,5]. They are at risk of degradation and destruction due to increasing human populations, river regulation and climate change [3,6]. Anthropogenic influences on river systems combined with the ‘Millennium Drought’ from 1997 to 2009 led to severe declines in vegetation condition across the floodplains of the Murray-Darling
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