Peatland degradation: The relationship between raised bog hydrology and normalized difference vegetation index

Peatlands are recognized as important landscape elements and their disturbance, followed by the loss of their ecohydrological functions, leads to falling water tables and degradation. Sometimes, the shortage of hydrological monitoring data impedes the detection of degrading peatland areas. The application of cost-effective remote sensing methods for assessment of humidity conditions permits monitoring of a large area and longer periods of time. Therefore, in this study, we assessed the links between hydrological parameters and the normalized difference vegetation index (NDVI) as well as identifying spatio-temporal patterns in the condition of raised bog vegetation, according to NDVI, in the epkeliai raised bog, a semipristine peatland in south-eastern Lithuania. Time series of NDVI (2000-2018) were obtained from the moderate resolution imaging spectroradiometer and compared with field measurements. A strong positive correlation between NDVI and water table depth was found. Moderate (for the whole raised bog) and strong (for control subbasin) positive correlations between NDVIavg and annual minimum flow over 30 and 7 days were found. This confirms that NDVI could be treated as an appropriate indicator, showing the degradation processes of the raised bog ecosystem and could be applied in its management. Analysis of the interannual NDVIavg variation confirmed the prevalence of stable favourable conditions during the growing season with a slight decrease in NDVImax over last 4 years. Meanwhile, analysis of spatial NDVI variation revealed obvious spatial patterns where possible degradation processes tend to appear.