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.
The bioavailability of sediment bound contaminants in lentic (Hamilton Harbour, Lake Ontario) and lotic (Detroit River connecting Lakes St. Clair and Erie) environments were assessed by a battery of multi-trophic tests using laboratory grown organisms. Hamilton Harbour is a hyper-eutrophic and highly contaminated environment due to extensive urban and industrial growth, while the Detroit River has been implicated as a major source of contaminants to Lake Erie. An array of sites across Hamilton Harbour and the Detroit River were selected, including the mouth of the Rouge River as well as the Trenton Channel--the contaminated western arm of the Detroit River. Multi-trophic acute assays were conducted using Daphnia magna, Hyalella azteca, Diporeia hoyi, and Lumbriculus variegatus. While the tests were consistent in determining the most toxic hot spots, variability existed in the sensitivities of test organisms to discriminate among less contaminated sites. The most toxic sediment in the Detroit River was at the mouth of the Rouge River, while the site in Windermere Basin in Hamilton harbour was found to be deleterious. The results indicated that the toxicity in a lotic ecosystem such as the Detroit River was caused by both the bottom sediments and the mobile seston component which contributed to the water-borne toxicity. Conversely, lentic and undisturbed ecosystems such as Hamilton Harbour contain much of their toxic component in the bottom sediments and not in the overlying water column. The multi-trophic battery of test approach adopted in our study appears to be effective in detecting and discriminating differential sensitivities of sediment bound contaminants in both lentic and lotic ecosystems. This battery of tests approach needs continued modification, development, and improvement to keep the assays up-to-date, sensitive, cost effective and adaptable in discriminating complex mixtures of sediment bound contaminants found in natural ecosystems.
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