Metal induced variations of TEP sticking properties in the southwestern lagoon of New Caledonia

Variations of the sticking properties of transparent exopolymeric particles (TEP) were investigated by studying the interactions between latex beads and TEP precursors collected along a gradient of increasing metal concentrations. For each sampling station, a suspension of TEP and beads was prepared and the formation of mixed aggregates was monitored under increasing turbulence intensities. The number of TEP-attached beads scaled with TEP size and was highest in the stations near the coral reef, and decreased towards anthropogenically-impacted stations. The combined study at successive levels of turbulence revealed that the TEP pool at a given station was composed of particles with heterogeneous physico-chemical properties. TEP stickiness, estimated at low turbulence intensity from the exponential decrease in particle concentrations in the 5-7 µm size range, increased continuously from the bay to the open ocean station, from 0.05 to 0.71. The role of metals in regulating TEP sticking properties was investigated by monitoring changes in TEP-beads interactions after addition of metals to solutions of TEP precursors. Addition of metals resulted in a strong decrease of the number of TEP-attached beads, suggesting that high metal concentrations induce a reduction of TEP sticking properties. Potential implications for vertical flux in the lagoon are discussed, considering estimates of naturally occurring turbulence regime, particle concentrations, and TEP turnover rates. This study suggests that the low physico-chemical reactivity of TEP in metal-impacted areas may result in a decoupling between coagulation and sedimentation rates, implying enhanced retention time and recycling.