Towards a strategy for the conservation of the freshwater pearl mussel Margaritifera margaritifera in County Donegal, Ireland

This study attempts to identify the habitat requirements of the pearl mussel Margaritifea margaritifera in County Donegal, in north west Ireland, an area with little urban, industrial or intensive agricultural development. No mussels occur in rivers where calcium and conductivity levels are high or where the substratum is predominantly bedrock or fine sediment but it was not possible to distinguish clearly between mussel and non-mussel sites on the basis of ordination analysis. However, rivers which still support mussels and rivers with historical records of mussels are loosely grouped. Rivers which formerly supported mussels but lack living M. margaritifera appear to have suitable habitat for mussels; pearl fishing is the most likely reason for the extinction of these mussel populations. Where population densities are high, for example in locations on the rivers Eske, Clady and Owenea, conservation may necessitate the establishment of reserves. The prospect for the successful reintroduction of mussels into former mussel rivers such as the Finn and Eany Water, where suitable habitat exists and water quality is high, is very good.

Energy levels, radiative rates and electron impact excitation rates for transitions in He-like Cl XVI, K XVIII, Ca XIX and Sc XX.

We report calculations of energy levels, radiative rates and electron impact excitation cross
sections and rates for transitions in He-like Cl XVI, K XVIII, Ca XIX and Sc XX. The grasp
(general-purpose relativistic atomic structure package) is adopted for calculating energy levels
and radiative rates. To determine the collision strengths and subsequently the excitation rates,
the Dirac atomic R-matrix code (darc) is used. Oscillator strengths, radiative rates and line
strengths are reported for all E1, E2, M1 and M2 transitions among the lowest 49 levels of
each ion. Collision strengths are averaged over a Maxwellian velocity distribution and the
effective collision strengths obtained listed over a wide temperature range up to 107.4 K.
Comparisons are made with similar data obtained from the flexible atomic code (fac) to
highlight the importance of resonances, included in calculations with darc, in the
determination of effective collision strengths. Discrepancies between the collision strengths
from darc and fac, particularly for forbidden transitions, are also discussed. Additionally,
theoretical lifetimes are listed for all the 49 levels of the above four ions.