Publication Date:
2018-03-07
Description:
As part of the NOAA/ROPME/MSRC sponsored assessment of the coast of Saudi Arabia, heavily impacted by the large oil spills of the 1991 Gulf War, we measured benthic community respiration (R) and primary production (P) rates in shallow subtidal basins near heavily oiled coastlines. Study sites were located in zones predicted to be basins of maximum deposition of any oiled sediments likely to wash off the adjacent coast and in reference bays predicted to be clean and unaffected. We measured oxygen exchange using in situ benthic respirometers and analysed petroleum hydrocarbon (PHC) levels in the near surface sediments at five stations. We concentrated our efforts in mud habitats to complement related studies in seagrass habitats. Measured community R rates ranged from a low of 700 μM m2 h−1 in coarse sand sediments with total organic carbon content (TOC) of only 0.16% of dry wt to the highest rate of 2184 μm m−2 h−1 in finer mud-sand habitats with 0.39% TOC. All measured rates were in the range of literature values for shallow marine sediments at temperatures of 17 to 19°C. Sediment oil content was 13–540 μg g−1 dry wt by ultraviolet fluorescence (UVF) analysis and 0.5–103 μg g−1 by gas chromatography (GC). Benthic P rates, calculated as light minus dark changes in dissolved oxygen, ranged from a low of 1162 μm m−2 h−1 at the most heavily oiled site to a high of 5216 μm m−2 h−1 at less oiled sites. While a weak inverse relationship between benthic P and sediment oil content was not significant statistically due to the small number of samples, a significant inverse relationship was found between the ratio of production to respiration (P/R) and the total petroleum content of the sediments by UVF. The effect appears to be driven more by differences in production than an effect on respiration which showed little relationship with either oil content or productivity. We conclude that within 1 year after the oil grounded on the intertidal sands of Saudi Arabia, the levels of oil in subtidal benthic sediments had decreased in most habitats to levels that did not show community stress by our oxygen measurements. Rather, long term damage to benthic subtidal habitats was limited only to enclosed bays adjacent to the most heavily oiled coastlines. Preliminary estimates of yearly P converted to carbon units indicates that the shallow mud sediments of the Gulf are at least as productive as most oligotrophic water columns. Since benthic habitats covered by seagrass, algae beds or coral reefs are likely to have even higher production rates, we conclude that benthic processes contribute significantly to the overall carbon flux in the Gulf ecosystem.
Type:
Article
,
PeerReviewed
Format:
text
DOI:
10.1016/0025-326X(93)90025-F
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