Abstract
Wetlands are one of the most biologically productive ecosystems. Wetland ecosystem services, ranging from provision of food security to climate change mitigation, are enormous, far outweighing those of dryland ecosystems per hectare. However, land use change and water regulation infrastructure have reduced connectivity in many river systems and with floodplain and estuarine wetlands. Mangrove forests are critical communities for carbon uptake and storage, pollution control and detoxification, and regulation of natural hazards. Although the clearing of mangroves in Australia is strictly regulated, Great Barrier Reef catchments have suffered landscape modifications and hydrological alterations that can kill mangroves. We used remote sensing datasets to investigate land cover change and both intra- and inter-annual seasonality in mangrove forests in a large estuarine region of Central Queensland, Australia, which encompasses a national park and Ramsar Wetland, and is adjacent to the Great Barrier Reef World Heritage site. We built a time series using spectral, auxiliary, and phenology variables with Landsat surface reflectance products, accessed in Google Earth Engine. Two land cover classes were generated (mangrove versus non-mangrove) in a Random Forest classification. Mangroves decreased by 1480 hectares (−2.31%) from 2009 to 2019. The overall classification accuracies and Kappa coefficient for 2008–2010 and 2018–2020 land cover maps were 95% and 95%, respectively. Using an NDVI-based time series we examined intra- and inter-annual seasonality with linear and harmonic regression models, and second with TIMESAT metrics of mangrove forests in three sections of our study region. Our findings suggest a relationship between mangrove growth phenology along with precipitation anomalies and severe tropical cyclone occurrence over the time series. The detection of responses to extreme events is important to improve understanding of the connections between climate, extreme weather events, and biodiversity in estuarine and mangrove ecosystems.
Highlights
Coastal and estuarine ecosystems are valued for their ecosystem services, coastal protection, as a nursery for fish, and carbon sequestration [1,2]
The aim of this research is to quantify how coastal mangrove forests have spatially and temporally changed in a decadal period (2009–2019) within estuarine catchments of the Great Barrier Reef and to explore the seasonality, climate responses, and variability of mangroves through a dense time series of satellite images in Central Queensland, Australia. Both biotic and abiotic factors constrain the phenological trajectory of a mangrove forest, e.g., regional climate, seawater and soil salinity, latitude, and local vegetation interactions, and these can vary across different locations and years
We demonstrated an operational method to (1) map mangrove forests in Central Queensland, Australia using an normalized difference vegetation index (NDVI) time series, which was built in Google Earth Engine (GEE)
Summary
Coastal and estuarine ecosystems are valued for their ecosystem services, coastal protection, as a nursery for fish, and carbon sequestration [1,2]. Mangrove forests are an important part of tropical estuarine ecosystems and considered integral to the emerging blue carbon economy. Blue carbon consists of carbon that is stored, sequestered, or released from coastal vegetation ecosystems [3]. Human interference leading to widespread degradation and deforestation has caused a decline in mangrove cover and biomass. Carbon emissions from global mangrove loss is estimated to be. Emissions from the global transportation sector are projected to rise to 11,900 Tg CO2 eq by 2100 [5]. The rate of mangrove loss has decreased substantially since the 1990s, from ~2% to
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