Abstract
Rabigh Lagoon, located on the eastern coast of the Red Sea, is an ecologically rich zone in Saudi Arabia, providing habitat to Avicennia marina mangrove trees. The environmental quality of the lagoon has been decaying since the 1990s mainly from sedimentation, road construction, and camel grazing. However, because of remedial measures, the mangrove communities have shown some degree of restoration. This study aims to monitor mangrove health of Rabigh Lagoon during the time it was under stress from road construction and after the road was demolished. For this purpose, time series of EVI (Enhanced Vegetation Index), MSAVI (Modified, Soil-Adjusted Vegetation Index), NDVI (Normalized Difference Vegetation Index), and NDMI (Normalized Difference Moisture Index) have been used as a proxy to plant biomass and indicator of forest disturbance and recovery. Long-term trend patterns, through linear, least square regression, were estimated using 30 m annual Landsat surface-reflectance-derived indices from 1986 to 2019. The outcome of this study showed (1) a positive trend over most of the study region during the evaluation period; (2) most trend slopes were gradual and weakly positive, implying subtle changes as opposed to abrupt changes; (3) all four indices divided the times series into three phases: degraded mangroves, slow recovery, and regenerated mangroves; (4) MSAVI performed best in capturing various trend patterns related to the greenness of vegetation; and (5) NDMI better identified forest disturbance and recovery in terms of water stress. Validating observed patterns using only the regression slope proved to be a challenge. Therefore, water quality parameters such as salinity, pH/dissolved oxygen should also be investigated to explain the calculated trends.
Highlights
Mangrove swamps are a common feature in coastal areas that are exposed to the daily fluctuation of tides
The number of pixels with significant positive trends was the highest for MSAVI (Figure 5b). This presents a good case for using MSAVI over regions with sparse vegetation since it can prevent the influence of background soil
The vegetation around Rabigh lagoon is dominated by mangrove trees [41]
Summary
Mangrove swamps are a common feature in coastal areas that are exposed to the daily fluctuation of tides. They are predominantly found in muddy substrate with low wave energy and hypersaline environment [1,2,3,4,5,6,7]. Mangroves serve as an important habitat for fish communities and other benthic flora and fauna [8]. They play a key role in shoreline protection and waste assimilation through the purification of marine water and surrounding air. Mangrove trees have shown great tolerance to low levels of dissolved oxygen in coastal environments [11,12,13,14]
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