Environmental management and conservation of Ireland’s small marl lakes and their crayfish populations

  • Raymond Wilson

Student thesis: Doctoral Thesis


Oligotrophic marl lakes have exceptional water clarity and are rare habitats for associated species but are also susceptible to deterioration because of nutrient enrichment. This thesis aimed to determine the current status and cause of eutrophication at the Magheraveely/Kilroosky Marl Loughs SAC (Northern Ireland, UK), investigate mitigation measures, estimate groundwater influx, and assess the population status of co-designated and endangered white-clawed crayfish Austropotamobius pallipes.

The surveyed nine lakes failed EU Water Framework Directive nutrient standards. During thermal stratification anoxic hypolimnia resulted in sediment Phosphorus (P) release that maintained the current trophic status.

In extrapolations from measurements on sediment cores from Kilroosky Lough, sediment in hypoxia contributed 0.022 mg P L−1 to the whole-lake concentration. Sediment P release decreased by 59 % with aeration and by 60 % after removing the upper 10 cm sediment. CaNO3 dosing supressed P release at water NO3 concentrations above 5.6 mg L−1.

Groundwater discharge was measured with a RAD7 radon detector customised to process 16 L water samples. A 222Rn mass balance estimated annual groundwater contributions between 40 % and 160 % of lake volume and between 15 % and 62 % of total water input depending on site.

Trapping surveys and mark-recapture surveys mapped crayfish presence and assessed population size. There was substantial abundance in two lakes and low-level presence in two lakes with one first record. Resampling with a Monte Carlo method investigated the relationship between survey effort and variability of catch per unit effort (CPUE). Even high trapping efforts yielded CPUE results with an excess of 20 % relative standard deviation. Therefore, an assessment of conservation targets requires surveys with a measure of uncertainty.

Lake restoration and survival of crayfish populations need mitigation of surface water P transfers and inhibition of sediment P release e.g., by CaNO3 dosing to stabilise marl lake self-cleaning mechanisms.
Date of AwardJun 2023
Original languageEnglish
SponsorsDepartment of Agriculture, Environment and Rural Affairs Northern Ireland
SupervisorJoerg Arnscheidt (Supervisor), Yvonne McElarney (Supervisor), Frances Lucy (Supervisor), Chris Mc Gonigle (Supervisor) & James Dooley (Supervisor)


  • Lake sediments
  • Phosphorus release
  • Eutrophication
  • In-lake remediation
  • Calcium nitrate dosing
  • Radon
  • Radon-222
  • Groundwater quantification
  • White-clawed crayfish
  • Austropotamobius pallipes
  • Trapping surveys
  • Magheraveely
  • Kilroosky Lough

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