Driving factors of phytoplankton trace metal concentrations and distribution along anthropogenically-impacted estuaries of southern Taiwan

Abstract

Phytoplankton are key marine components in global primary productivity and ocean biogeochemistry. However, anthropogenic activities impact phytoplankton through toxic metal dispersion—threatening the food web with increased metal bioaccumulation. This study assessed the phytoplankton trace metal concentrations, distribution, and relationship with community structure. Environmental parameters (temperature, salinity, pH, dissolved oxygen, biological oxygen demand, suspended solids, chlorophyll-a, ammonium, nitrate, nitrite, phosphate, silicate, total phosphorus) and phytoplankton were collected in southern Taiwan; from five transects (estuaries; T1–T5), composed of estuarine (Es) and offshore (Os) sites. This study respectively used size and density fractionation to accurately measure phytoplankton trace metals. Results showed that anthropogenically-impacted rivers and marine outfall discharges drive community structure and phytoplankton trace metal distribution. Among sites, T3–T5Es differed in its environmental characteristics. Significant differences on environmental characteristics and trace metals in phytoplankton were found between transects—indicating higher anthropogenic impacts in T3 (Dianbao–Houjin estuary) and T4 (Kaohsiung Harbor estuary). Phytoplankton trace metals follows an order of Fe >> Mn > Cr > Cu > Ni > Co > As > Pb > Hg. Metals in estuarine phytoplankton were higher compared offshore, but not significantly different (p > 0.05), highlighting the role of marine outfalls in offshore pollutant diffusion. Phytoplankton metal distribution showed a distinct spatial gradient between agriculture- and industry-associated areas. Significantly high Cr bioaccumulation factor (BCF > 100) were also found in transects T2 and T4. Overall, this study presents an accurate trace metal data and BCF in phytoplankton of southern Taiwan. Further, insights on the potential relationship between phytoplankton community structure and trace metal concentrations are presented – with nutrients mainly impacting phytoplankton community, initiating a ripple effect which likely favored blooming of metal-tolerant species (high dominance) – increasing the trace metal bioaccumulation.