|
We have just concluded a 5 year study of the potential of microfossils (foraminifera, diatoms, ostracods, palynomorphs) to document human impacts in New Zealand estuaries. We have investigated the effects of historical and existing sewage disposal, stormwater run-off, oyster and mussel farming and human-introduced marine invasive species (chord grass and Asian mussels). Other impacts such as dairy effluent, tip leachate, dockyards and marinas in coastal settings have also been examined.
Determining how the current condition of an estuarine ecosystem relates to its pre-impact state is difficult. While monitoring the concentration of trace metals, sediments, coliform bacteria and other pollutants is useful it does not document the relative status of the soft-sediment biota. The only biological clues preserved in late Holocene sediment cores come from the hard-parts of a small portion of the original biota. The macrofaunal record is not easily investigated using coring techniques and is at best patchy. For remedial initiatives to be at all effective it is important to "see" what historic changes have occurred to the pre-impact communities.
Once an age model has been established, any changes in the benthic microfossils can be related to pre-human (pre 1200 AD), Polynesian (1200-1840), early European (1840-1950) and late European (post 1950) phases. For example, in New Zealand, changes in salinity, and probably pH, are commonly marked following early European deforestation and late European urbanisation. The development of a salinity proxy based on foraminiferal census data has been an important contribution. This paper summarises the methodologies and outcomes of our investigations which can serve as the basis for future research documenting other impacted estuaries and any restoration efforts.
|
