Enhancing growth of mangrove seedlings in the environmentally extreme Arabian Gulf using treated sewage sludge

The response of mangrove (Avicennia marina) seedlings to treated (wet) sludge from a sewage treatment plant (STP) was tested in a randomized block design experiment at a tree nursery on Mubarraz Island in the Arabian Gulf. The growth response of seedlings to half-strength and full-strength STP sludge was monitored over 103 days and compared with the response to freshwater, seawater and half-strength seawater treatments. Sludge treatments resulted in significantly greater plant growth, leaf number, leaf biomass and root biomass than the other treatments did. The positive effect of STP sludge on seedling growth is attributed to enhanced levels of total nitrogen (8.9 ± 0.1 mg l^-1) and total phosphorus (7.8 ± 0.2 mg l^-1) in the sludge and its low salinity. These results suggest that sludge from sewage treatment plants may be beneficially used in mangrove nurseries and plantations in this arid region, where soils are nutrient-poor and fresh water is scarce.