3.1 Environmental gradient based on water quality
The averaged environmental parameters in the PCA analysis reflected a
water quality trend from TM6 (SFB) to MM5 (TPC) (Figure 1, Table S1).
The seven environmental parameters varied between sites. Nitrogen
(nitrite and nitrate) and salinity have a greater contribution to the
variation in TPC whilst ammonia and phosphorus to LCC. Overall, PC1
explained most of the variation observed (79.6 %) among sites and this
was consistent with the geographic distribution, supporting the
occurrence of a pollution gradient along Tolo Harbour (Figure 1). Based
on the environmental data, sites were categorized into three relative
pollution levels along the Tolo Harbour Channel (SFB as highly polluted,
LCC as moderately polluted, and TPC as low polluted site).