Abstract
The effect of shrimp pond effluent discharges on the mangrove forest in Khung Krabaen Bay (KKB), eastern Thailand, was assessed by comparing the nitrogen content (%N) and stable nitrogen isotope (δ15N) of mangrove leaves and sediments with those in a natural mangrove forest in Ranong, southern Thailand. At the KKB site, the mean %N and mean δ15N value of mangrove leaves were 1.73±0.16% and 5.19±0.77‰, respectively, while in the mangrove sediment, %N was 0.20±0.02% and 5.21±0.88‰ for δ15N. At the Ranong site, the mean %N and mean δ15N values of mangrove leaves were 1.18±0.18% and 3.71±0.43‰, respectively, while in the mangrove sediment, values were 0.12±0.02% and 3.74±0.27‰, respectively. The %N and δ15N values of both leaves and sediments at the KKB site were significantly higher than those at the Ranong site (P < 0.01). The mean %N and mean δ15N values of shrimp feeds were 6.72±0.19% and 7.37±0.90‰, respectively. The mean δ15N of shrimp feeds was significantly higher than those of mangrove leaves and sediments (P < 0.01). Thus, high %N and δ15N in mangrove leaves and sediments at the KKB site were most probably due to the assimilation of 15N-enriched dissolved inorganic nitrogen from shrimp pond effluent. These results showed that mangrove forests are effective areas for trapping inorganic nitrogen from anthropogenic nitrogen inputs.
