Photosynthesis in some British coastal waters may be inhibited by zinc pollution

Abstract

RIVER drainage from mineral-bearing and industrialised regions has produced elevated concentrations of heavy metals in several parts of the coastal waters around the UK, including Liverpool Bay^1,2, Cardigan Bay¹, the Bristol Channel^1–3, off the mouth of the River Tees⁴ and in the Firth of Clyde⁵. Little attention has been paid, however, to the possibility that the presence of the metals might be affecting the planktonic marine life of these sea areas. Phytoplankton represent the basic food resource on which the majority of marine animals and fish directly or indirectly depend, and it is thus conceivable that inhibition of their growth by toxic metals could have repercussions throughout the local marine food webs. We are investigating the role of trace quantities of both biologically beneficial and toxic substances in regulating the ‘quality’ of seawater, that is, its capacity to support and maintain, through photosynthesis, the production of living matter from the inorganic nutrients present in the water. As part of this research programme, we have examined how carbon fixation rates in natural populations of phytoplankton are affected by zinc concentrations encompassing those observed in the areas mentioned. Although zinc is a component of many enzyme systems⁶ and therefore essential for the growth of phytoplankton⁷, it becomes toxic if present greatly in excess of their basic requirements. We report here data which suggest that phytoplankton growth could be depressed by the zinc concentrations present in some British coastal waters.