Interactions of trace metals with phytoplankton and zooplankton in Lough Neagh, Northern Ireland

Abstract

A modified marine automated McLane Remote Access Sampler (RAS) was tested in two lakes in comparison with grab samples taken with a Ruttner sampler. All samples for total phosphorus, suspended solids and chlorophyll a fell within calculated 95% confidence intervals when compared with the parallel grab samples. There was no significant difference in the variation of cell length of phytoplankton for Cyanobacteria (p=0.09), Chlorophyta (p=0.06), and Dinophyta (p=0.27). Both RAS and grab sample concentrations measured for Cu, Pb and Cd were within or below the limit of detection of the analytical method.

For the first time trace metal concentrations in phytoplankton and zooplankton in Lough Neagh are reported. Average concentrations in phytoplankton for Cu, Pb, Cd, Mn and Fe during 2003 were 275 ± 227, 2.2 ± 1.0, 2.3 ± 1.7, 1.4 ± 1.1 and 16.4 ± 11.4 μgig dry weight (n = 10) respectively. Average concentrations in phytoplankton for Cu, Pb, Cd, Mn and Fe during 2004 were 66.5 ± 36.3, 4.9 ± 2.7, 1.1 ± 1.1, 2.5 ± 1.4, and 51.7 ± 17.3 μgig dry weight (n = 12) respectively. Copper concentrations in phytoplankton show highly significant correlations with zooplankton copper concentrations in both sampling campaigns with r2 values of 0.81 (p=0.001) and 0.60 (p=0.003). Fe, Mn and Cd in the 2003 sampling campaign show significant correlations between phytoplankton and zooplankton with respective r2 values of 0.86 (p=0.0001), 0.71 (p=0.004) and 0.45 (p=0.043). Calculated biomagnification factor scores (BMF) would suggest that zooplankton in Lough Neagh accumulate a significant proportion of their copper requirements from their diet.

Calculations show that phytoplankton and zooplankton can accumulate as much as 25.3 and 99.6 kg of Cu respectively in the water column in Lough Neagh. Accumulation of copper between phytoplankton, zooplankton, particulate and the aqueous phase, shows that zooplankton partition the greatest portion of metal during both campaigns with 48% and 35% of copper in 2003 and 2004 respectively.

The average sedimentation rate measured in Lough Neagh during the sampling campaign in 2003 was 37.5 g m-2 d-1 (n = 5) whilst during the 2004 sampling campaign it was 51.6 g m-2 d- 1 (n = 6).

Metal fluxes calculated from sediment trap material show correlations with suspended solids varied significantly between both years. In 2003, no significant positive correlations were established between Cu, Pb, Cd, Mn and Fe flux and suspended solids, with r2 values of 0.10, 0.38, 0.06, 0.16 and 0.16. In 2004, Si!:,'11ificant positive correlations were established for all metals with r2 values of 0.65 (p=0.053), 0.72 (p=0.033), 0.40 (p=0.177), 0.73 (p=0.030), and 0.55 (p=0.091).

Date of Award	2004
Original language	English