Monitoring Mangrove Forest Degradation and Regeneration: Landsat Time Series Analysis of Moisture and Vegetation Indices at Rabigh Lagoon, Red Sea

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.

Sediment Metal Contamination, Bioavailability, and Oxidative Stress Response in Mangrove Avicennia marina in Central Red Sea

“…The Red Sea comprises about 135 km 2 area of mangroves distributed up to the northern boundary of mangroves at 28.207302 o N. The central Red Sea is in an arid environment possessing high temperature and sparse rainfall; the mean annual (sporadic) rainfall in the Jeddah region is 55 mm (Aljahdali et al, 2021a). Some mangrove habitats of the Saudi Arabian Red Sea develop as a narrow fringe that could support halophytes located along the shore and adjacent to sand flats that may sometimes be flooded (Almahasheer et al, 2016;Rasul and Stewart, 2018).…”

Environmental Factors Causing Stress in Avicennia marina Mangrove in Rabigh Lagoon Along the Red Sea: Based on a Multi-Approach Study

“…It takes 15 days on average for water to circulate the lagoon and the inflow rate is typically at 50 cm s −1 (Aljahdali et al, 2021). Strong evaporation led to an abrupt increase in salinity and temperature from S1 to S8 (Table 1).…”

“…Lagoons along the Red Sea are important transition systems providing essential socio-economic goods and services, such as shore protection, fisheries, carbon sequestration, etc. (Aljahdali and Alhassan, 2020a;Aljahdali et al, 2021). However, they possess extremely harsh conditions such as drought, high salinity and high temperature, which constitute an enormous challenge for mangroves.…”

“…Seawater from the Red Sea (25 ∼ 30 • C, salinity of 39‰) enters the Rabigh Lagoon through an open inlet (900 m wide and 2.5 m deep) as surface inflow. After circulating the lagoon, it exits in the form of subsurface flow (Figure 1B; Aljahdali and Alhassan, 2020a;Aljahdali et al, 2021). Strong evaporation substantially increases both water temperature and salinity along the inflow route.…”

“…Strong evaporation substantially increases both water temperature and salinity along the inflow route. The southern end receives sporadic runoffs through urban regions (Figure 1C), and is characterized by substantially higher organic matter and nutrient concentrations in sediments (Aljahdali et al, 2021). It is essential to understand how the stress in mangroves in Rabigh Lagoon responds to environmental factors as global warming could strengthen evaporation and elevate water temperature in the lagoon.…”