Characteristic differences of the sediment under four mangrove species in Nansha Wetland, Guangzhou

Objective To compare the sediment characteristics under exotic mangrove species (Sonneratia apetala, Laguncularia racemosa) and native mangrove species (Aegiceras corniculatum, Acrostichum aureum), so as to better understand the potential ecological impacts of exotic species on the wetland environment.

Method The temperature, pH, redox potential (Eh), conductivity, contents of organic matter and nutrients (N, P, K), and texture of sediments under these four species in Nansha Wetland, Guangzhou were measured by using in situ measurement instruments and the common analysis methods of soil.

Result The sediment temperatures of exotic species (S. apetala 15.59 ℃, L. racemosa 16.85 ℃) were higher compared to native species(A. corniculatum 15.18 ℃, A. aureum 15.06 ℃). The sediment pH of exotic species(S. apetala 6.97, L. racemosa 6.54) were lower compared to native species (A. corniculatum 7.21, A.aureum 7.09). The sediment Eh of L. racemosa (30.16 mV) was significantly higher compared to other three species (S. apetala -5.02 mV, A. corniculatum -11.99 mV, A. aureum -4.85 mV). The contents of organic matter in the sediments under exotic species(S. apetala 8.41%, L. racemosa 8.75%)were significantly lower compared to native species (A. corniculatum 10.22%, A.aureum 10.25%). The sediment under S. apetala was sandy clay loam, which could be related to its significantly low effective K content since the sediments under other three species were all loamy clay.

Conclusion There are evident differences in the ecological factors of sediments between extotic and native mangroves. Fast growing of exotic mangroves may accelarate the decomposition of organic matter in sediments and cycling of substances, and therefore lead to changes in sediment characteristics.