Abstract of PhD Thesis

Spatial and temporal fluxes of plant-nutrients in turlough soils

Sarah Kimberley, Trinity College Dublin (2008)

Turloughs are annually flooding karstic depressions which constitute ecologically important and geographically restricted ground-water dependent ecosystems, identified as priority habitats under the EU Habitats Directive.  Turlough conservation is also driven by the EU Water Framework Directive and there have been recent attempts to characterise the karst aquifers associated with turloughs, which are generally of a conduit or shallow epikarst nature.  Different types of karst aquifers are thought to influence turlough trophic status and ecological diversity.  The natural trophic status of turloughs is also thought to be influenced by the soil types present however the relationships between turlough karst aquifers, soil types and soil nutrient status are poorly understood.  Eutrophication constitutes one of the main threats to the quality of the turlough habitat and soil nutrient assessments are required to generate quantitative information on turlough trophic ranges. Soil property variability is well recognised, however information on the spatial and temporal variations of turlough soil nutrient related properties, and how these might influence plant community structure and sampling strategies for conservation assessment, is lacking.  The primary aim of this project was to contribute to a better understanding of turlough spatial and temporal soil nutrient dynamics and their associations with soil types, vegetation types, karst aquifer types and current turlough trophic assessments.

At the catchment scale, focus was placed on determining whether turloughs located within different types of karstic flow systems have contrasting soil nutrient properties. Four turloughs were selected for study from the conduit flow system associated with the Coole Garryland SAC, Co. Galway and four were selected from the shallow epikarst flow system within the East Burren SAC, Co. Clare. Soil types and nutrient related properties were described in the upper, middle and lower areas of each turlough. Mineral, moderately calcareous soils were associated with Coole Garryland whereas highly organic, highly calcareous soils were characteristic of the East Burren.  This variation in soil types was attributed to the contrasting parent materials, hydrology and hydrochemistry associated with the different types of karst aquifers within each catchment area.  The general N, P and K status of turloughs within the two catchments was low, which was in agreement with previous trophic assessments of turloughs as low nutrient habitats which are sensitive to enrichment.  High degrees of variation were generally associated with the turlough soil types characteristic of each catchment. Kilcolgan Series Rendzinas and Gleys were characteristic of Coole Garryland whereas Burren Series Rendzinas, Fen Peats, and Marls were characteristic of the East Burren.  Such variation presents challenges for making nutrient comparisons among turlough soils types and potentially for detecting true relationships between soil types, vegetation and hydrology. Soil nutrient conditions were found to be a secondary influence to degrees of wetness and associated soil alkalinities on the distributions of grass/forb dominated vegetation types and sedge dominated vegetation types.

At the within-turlough scale, more detailed investigations of the spatial patterns of plant-nutrient availablity, and their relation to soil type and flooding susceptibility, were conducted using gradient directed transects within two turloughs representative of each catchment.  High degrees of variation in plant-nutrient availability were associated with the turlough flooding gradients and spatial patterns were often not linked to soil type.  Different soil properties varied to different extents within different turloughs, indicating that accurate mean soil nutrients will be readily estimated for some properties more than others in different turloughs.

The temporal variations (monthly) in nutrient availability among common turlough soil types were also considered within selected turloughs representative of each catchment, along with the implications of temporal variations for making soil nutrient assessments of individual turloughs.  Mean nutrient assessments based on plant-available P consistently reflected an oligotrophic and ultra-oligotrophic nutrient status within Garryland and Knockaunroe respectively over the growing season whereas mean nutrient assessments based on plant-available N varied among sampling periods.  Overall, the results suggested that spatial and temporal fluxes of nutrients in turlough soils present challenges for making accurate soil nutrient assessments and for understanding turlough soil nutrient cycling, therefore highlighting the requirement for sampling strategies which cover the range of variation within the turlough basin.