Southwestern Ireland Research Articles

The last ice sheet in Western Scotland during Greenland Interstade 1: Integrating the onshore and offshore records

Sedimentary sequences deposited by the decaying marine margin of the British–Irish Ice Sheet (BIIS) record isostatic depression and successive ice sheet retreat towards centres of ice dispersion. Radiocarbon dating by accelerator mass spectrometry (AMS) of in situ marine microfaunas that are commonly associated with these sequences constrain the timing of glacial and sea level fluctuations during the last deglaciation, enabling us to evaluate the dynamics of the BIIS and its response to North Atlantic climate change. Here we use our radiocarbon-dated stratigraphy to define six major glacial and sea level events since the Last Glacial Maximum. (1) Initial deglaciation may have occurred ⩾18.3 kyr 14C BP along the northwestern Irish coast, in agreement with a deglacial age of ∼22 36Cl kyr BP for southwestern Ireland. Ice retreated to inland centres and areas of transverse moraine began to form across the north Irish lowlands. (2) Channels cut into glaciomarine deglacial sediments along the western Irish Sea coast are graded to below present sea level, identifying a fall of relative sea level (RSL) in response to isostatic emergence of the coast. (3) Marine mud that rapidly infilled these channels records an abrupt rise in global sea level of 10–15 m ∼16.7 14C kyr BP that flooded the Irish Sea coast and may have triggered deglaciation of a marine-based margin in Donegal Bay. (4) Intertidal boulder pavements in Dundalk Bay indicate that RSL ∼15.0 14C kyr BP was similar to present. (5) A major readvance of all sectors of the BIIS occurred between 14 and 15 kyr 14C BP which overprinted subglacial transverse moraines and delivered a substantial sediment flux to tidewater ice sheet margins. This event, the Killard Point Stadial, indicates that the BIIS participated in Heinrich event 1. (6) Subsequent deposition of marine muds on drumlins 12.7 14C kyr BP indicates isostatic depression and attendant high RSL resulting from the Killard Point readvance. These events identify a dynamic BIIS during the last deglaciation, as well as significant changes in RSL that reflect a combination of isostatic loading and eustatic changes in global sea level.

Decadal-scale changes in the shallow subtidal benthos of an Irish marine reserve

Abstract Long-term annual monitoring of rocky intertidal and shallow subtidal shores of an Irish sea lough (1990–2010) documented major regime shifts in the past decade. When population densities of the purple urchin Paracentrotus lividus plummeted in Lough Hyne Marine Reserve in southwestern Ireland, the warm-water fucalean alga Cystoseira foeniculacea and ephemeral algae proliferated shortly after. We discuss the possible influences of release from herbivory and climate change on this algal proliferation, which blanketed the benthos. Smothering of the benthos led to high levels of shallow subtidal anoxia. Furthermore, the invasive fucalean alga Sargassum muticum has made repeated incursions into the reserve. Although being reduced by persistent eradication efforts (2003–2011), Sargassum is spreading within the lough. Limited seawater flushing and propagule dispersal within the lough and eutrophication in coastal waters may have contributed to community-level changes. Whether the regime change is cyclical (contingent on re-establishment of urchins within the lough and continued eradication of S. muticum) or irreversible (the result of critical transitions) remains unclear.

The role of pressure solution seam and joint assemblages in the formation of strike-slip and thrust faults in a compressive tectonic setting; The Variscan of south-western Ireland

The Ross Sandstone in County Clare, Ireland, was deformed by an approximately north-south compression during the end-Carboniferous Variscan orogeny. The initial assemblage consists of mutually abutting orthogonal arrays of 170° oriented set 1 joints/veins (JVs) and approximately 75° oriented set 1 pressure solution seams (PSSs) formed under the same stress conditions. Orientations of splay JVs and PSSs (set 2) suggest a clockwise remote stress rotation of about 35° responsible for the contemporaneous shearing of the set 1 arrays. Among these nearly orthogonal strike-slip faults, the prominent set is sub-parallel to set 1 JVs. These faults are formed by the linkage of en-echelon segments with broad damage zones responsible for right-lateral offsets of hundreds of meters. Thrust faults with up to 30 m of offset initiate within shale horizons and follow either the PSSs in the sandstones or high-angle shales within tilted sequences. Within the large thrust fault zones, compartmentalised blocks of rocks are bounded by thrust faults segments with various dip angles. Strike-slip and thrust faults are contemporaneous and owe their existence to initial weaknesses in the form of JVs and PSSs rather than by switching relative stress magnitudes and orientations associated with Andersonian models of faults and related stress orientations.

Gap-filling techniques for the annual sums of nitrous oxide fluxes

The full accounting of greenhouse gas emissions is only possible when the three key contributors (CO2, CH4 and N2O) are continuously measured throughout the observation period. While some field techniques such as eddy covariance or automatic closed chamber measurements have attempted near-continuous observations, it is always beyond the control of the experimentalist to ensure perfect continuity. Therefore, the final time series of fluxes will inevitably have periods without reliable values (i.e., gaps) and will need to be gap-filled. While there is abundant literature on methodologies for gap-filling CO2 fluxes, there is no literature on the gap-filling methods for trace gases such as nitrous oxide. We investigate three general approaches for gap-filling nitrous oxide time series: linear extrapolation, moving average and look-up tables. A five-year time-series of eddy-covariance measurements from an intensive grassland site in South-Western Ireland was used as an example. The amount of gaps varied significantly from year to year. The single-year look-up table technique produced consistently good results even when long gaps were present in the time series. In some years, the simpler annual extrapolation technique performed equally well. It is essential that this work be extended with more complex methods, and that methods in this paper are further evaluated under different environmental conditions. We believe that these methods and analysis could also be applied to other trace gas gap-filling (e.g., CH4) which have similar intermittent patterns of emission.

Molecular phylogeography of the microturbellarian Monocelis lineata (Platyhelminthes: Proseriata) in the North-East Atlantic

Monocelis lineata is a complex of cryptic species (three in the Mediterranean and one in the Atlantic) widespread in midlittoral habitats. Throughout the range, populations with or without an ocular pigmented shield are found. We investigated the genetic structure of the North-East Atlantic populations with the aim of shedding light on their phylogeography and reconstructing possible patterns of recolonization after the Wurmian glaciation. Fourteen samples were investigated using cytochrome c oxidase subunit I (COI) and 13 by inter-simple sequence repeats (ISSRs). COI did not exhibit a clear pattern of decreased genetic diversity along a latitudinal gradient. Populations from Ferrol (Spain), Doolin (Ireland), and Helsingor (Denmark) showed a higher genetic variability, whereas a reduction in the number of haplotypes was found at the northernmost edge of the distribution and in northern Ireland and Scotland. Two genetically differentiated areas (southern Europe and south-western Ireland versus northern Atlantic) were revealed by ISSR data. The results obtained provided evidence of three refugia (Iberian Peninsula, south-western Ireland, and North Sea), and the occurrence of secondary contacts that shaped the genetic variability of some of the populations examined. Two different recolonization pathways of north-western Europe during the post-Wurmian glaciations have been detected. Furthermore, ISSR analysis provided evidence of genetic divergence among populations with and without pigmented eyespot, suggesting the action of ecological differentiation. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 117–135.

The expansion of the house mouse into north‐western Europe

The western house mouse Mus musculus domesticus is a human commensal, and as such, its phylogeography relates to historical human settlement patterns and movements. We investigate the phylogeography of house mice in northern France and the British Isles (particularly Ireland and the Scottish islands) using microsatellite data and mitochondrial (mt) control region sequences from modern and museum material, placing these in a Europe-wide context. The majority of mtDNA sequences from northern France belong to a clade widespread across the British mainland and Germany, supporting an earlier suggestion that this clade distribution represents colonization by house mice in the Iron Age. The presence of the clade in south-western Ireland indicates possible Iron Age colonization there as well. However, the majority of the Irish sequences belong to a clade elsewhere associated with Norwegian Viking activity, and likely represent the main wave of house mouse colonization of Ireland, arriving from the Scottish islands during the Viking period and linked to urbanization. The St Kilda sequences (from 100-year-old museum samples of the extinct form ‘Mus muralis’ of Barrett-Hamilton) and sequences from South Uist and Lewis also belong to this clade. The clustering of populations shown by the microsatellite data is distinctly different from the mtDNA phylogeny, with populations grouping by geographic proximity, possibly reflecting the genetic effects of secondary colonization. When the mtDNA sequence data are placed in a Europe-wide context, it is clear that the distributions of the two prevalent clades from the vicinity of the British Isles are essentially limited to north-western Europe. These two clades show no evidence of expansion through central Europe, and may therefore reflect maritime colonization.

Energy fluxes and evaporation mechanisms in an Atlantic blanket bog in southwestern Ireland

Water and energy fluxes control the development of northern peatlands and influence their carbon budget. Blanket bogs are peatlands that occur in temperate maritime regions where precipitation is much greater than evapotranspiration (ET). In this paper, five years (October 2002–September 2007) of ET and energy fluxes derived from eddy‐covariance measurements were analyzed in the context of the predicted climate change for Ireland. Monthly ET at the Glencar Atlantic blanket bog varied little, ranging between a minimum of 12 mm month−1 and a maximum of 56 mm month−1 over the five years, resulting in an annual ET average of 394 mm, with typical highest daily values of 2.5–3.0 mm. Compared to other peatland types, Glencar had lower summer ET and a lower ET/potential ET ratio, despite having higher precipitation and water table. The ET was limited not only by the low vapor pressure deficit and cool summer temperatures but also by the low cover of vascular plants and mosses (essential for transpiration). The energy budget was similar to other peatland types in terms of net radiation and sensible heat fluxes, but had lower latent and higher ground heat fluxes. A comparison among the five years suggests that the predicted climate change (greater winter precipitation, lower summer precipitation, and higher all year round temperatures) will probably increase winter ET, while the summer energy flux patterns will not be profoundly affected. However, if the frequency of summer rain events should diminish, the moss component of these ecosystems may become water stressed, ultimately leading to lower evapotranspiration.

A simple short range model for the prediction of harmful algal events in the bays of southwestern Ireland

A simple model is described which predicts harmful algal events in the bays of southwestern Ireland. Fundamental to the model is the physical forcing of circulation in these bays in summer. The predominant hydrographic feature at this time is a wind-driven two-layer oscillatory flow acting in a thermally stratified water column. This mechanism exchanges substantial proportions of the bays' volumes, and harmful algal events arise with the associated transport of harmful populations into them. The model is therefore based on the criterion that wind-driven water exchanges result in exchanges of phytoplankton, which, if the time of year is correct, result in toxic events. Utilising Bantry Bay as an example, hindcasting showed that the model has a high degree of success using a wind index based on the sequence of winds that results in water exchange. The model was implemented by estimating indices from the five-day weather forecast, and trialled in 2005. Results were published on the web in real time, during which a predicted water exchange event in mid-June was accompanied by an influx of Dinophysis acuminata into Bantry Bay with an associated contamination of shellfish with Diarrheic Shellfish Poisoning toxins.

Short term dynamics of planktonic foraminiferal sedimentation in the Porcupine Seabight

Modern planktonic foraminifera collected with a sediment trap, and subfossil assemblages from surface sediments from the Galway Mound in the Porcupine Seabight off southwestern Ireland, (northeastern Atlantic), were studied in order to investigate recent assemblage variations. The sediment trap operated fromApril to August 2004 with a sampling interval of eight days and covered the spring bloom and early summer. Ten different species were recorded. Globorotalia hirsuta, Turborotalita quinqueloba and Globigerinita glutinata appeared predominately in spring. Eogloboquadrina incompta, Globigerina bulloides and Globorotalia inflata were abundant in spring and summer. Highest foraminiferal tests flux occurred in June. The faunal composition was similar to subfossil assemblages from surface sediments, but the species proportions were different. This contrast wasmainly driven by the subtropical species G. hirsuta, which was frequent in 2004 but rare in surface sediment samples and in earlier plankton collections obtained from the southern Porcupine Seabight during the 1990s. The individual weight of deposited foraminifera is mainly influenced by the spring bloom, as indicated by sea-surface chlorophyll-a data. The top three-ranked species, G. hirsuta, N. incompta and G. bulloides, contributed 87 % to the foraminiferal carbonate flux at Galway Mound.

Seasonal variation of DOC concentration and annual loss of DOC from an Atlantic blanket bog in South Western Ireland

This paper represents the first continuous dissolved organic carbon (DOC) record, measured in a stream draining an Atlantic blanket bog in South West Ireland for the calendar year 2007. At 30-min intervals, the DOC concentration was automatically measured using an in-stream spectroanalyser whose variation compared well with laboratory analysed samples taken by a 24-bottle auto-sampler. The concentration of DOC ranged from 2.7 to 11.5 mg L−1 with higher values during the summer and lower values during the winter. A simple linear regression model of DOC concentration versus air temperature of the previous day was found, suggesting that temperature more than discharge was controlling the DOC concentration in the stream. The change in DOC concentration with storm events showed two patterns: (1) in the colder period: the DOC concentration seemed to be independent of changes in stream flow; (2) in the warmer period: the DOC concentration was found to rise with increases in stream flow on some occasions and to decrease with increasing stream flow on other occasions. The annual export of DOC for 2007 was 14.1 (±1.5) g C m−2. This value was calculated using stream discharge data that were determined by continuously recorded measurements of stream height. The flux of DOC calculated with the 30-min sampling was compared with that calculated based on lower sampling frequencies. We found that sampling frequency of weekly or monthly were adequate to calculate the annual flux of DOC in our study site in 2007.

Vegetation and environmental variation in an Atlantic blanket bog in South-western Ireland

A vegetation survey was carried out in a relatively intact Atlantic blanket bog in Southwest Ireland to study the vegetation patterns in relation to environmental variation, and to quantify the effect of artificial and natural borders on compositional variation. The data were analysed using canonical correspondence analysis. In terms of both vegetation and water chemistry, the study site can be categorized as typical of Atlantic blanket bogs in the maritime regions of North-western Europe. The distribution of plant species was explained mainly by depth of the water table. The distribution of bryophytes was secondarily explained by the pH of the bog water, while the distribution of vascular plants was secondarily explained by concentrations of ammonia. The vegetation distribution exhibited little variation between the central sector of the peatland and its disturbed edges (hill-grazing and restoration areas), but a substantial variation was observed between the area along a natural edge (stream) and the areas close to the other peatland borders or centre. Similarly, the internal variation within each sector (centre, hill-grazing edge and restoration area edge) was small, but substantial vegetation variation was observed within the area located along the stream. The area along the stream was associated with relatively deep water table, shallow peat depth, high water colour, pH and NH4+ concentrations, and low Cl− concentrations in the bog water. Our results suggest the existence of strong centre-natural margin gradients, as in raised bogs, and indicate that human or animal disturbance do not give rise to the marked transition zones that often characterize natural margins of mire systems. This indicates that even small areas and remnants of Atlantic blanket bogs are worthy of conservation and that their conservation value would benefit from the inclusion of sectors close to the natural peatland borders, which would increase the plant biodiversity of the conserved area.

Fine-spatial Paleoecological Investigations Towards Reconstructing Late Holocene Environmental Change, Landscape Evolution, and Farming Activity in Barrees, Beara Peninsula, Southwestern Ireland

Long-term environmental change and human impact have been reconstructed at fine spatial and temporal resolutions in an archaeologically rich, and floristically interesting, part of southwestern Ireland, namely the Beara peninsula, County Cork. Detailed pollen and macrofossil analyses, and radiocarbon dating have been carried out on several short peat monoliths, and on a peat core and a lake core from small basins. Landscape evolution, vegetation dynamics, and farming activity from the end of the Neolithic (c. 2500 B.C.) to the present day, i.e., the period of greatest human impact in southwestern Ireland, have been reconstructed. While significant opening-up of the landscape began relatively early in the Bronze Age (between c. 2400–2100 B.C.), the main woodland clearances took place in the later Bronze Age (beginning c. 1400 B.C. and continuing into the Iron Age, i.e., to c. 400 B.C.). In the mid- and later Iron Age, there was considerable fine-scale spatial variation, with activity being concentrated mainly in the uplands (at c. 200 m asl) and at lower elevations. Radiocarbon dating and pollen evidence show that the linear stone-wall system, now partly obscured by shallow peat, was laid out towards the end of the Iron Age (c. A.D. 400) in the context of a largely open landscape. While the initial foci of bog growth appear to relate to the late Neolithic/beginning of the Bronze Age, widespread development of blanket bog was essentially a phenomenon of the late 1st/early 2nd millennium A.D. It was probably favoured by wetter and cooler conditions during the Little Ice Age. Detailed records are presented for the filmy ferns, Hymenophyllum tunbrigense, H. wilsonii, and Trichomanes speciosum, and also Myrica and Ulex, both shrubs with pronounced, oceanic distribution patterns.

Aggregation in the Tick Ixodes ricinus (Acari: Ixodidae): Use and Reuse of Questing Vantage Points

Ongoing work in oak woods in Killarney National Park in southwestern Ireland is focusing on the factors influencing the fine-scale aggregated distribution of Ixodes ricinus L. (Acari: Ixodidae) on the ground. The extent of reuse of stems of vegetation as questing points by adult ticks was determined by paint-marking stems on which ticks were found, counting and removing these ticks, and subsequently reexamining the same stems for ticks on two further occasions. Overall, an estimated 2,967 stems in 123 separate rush plants (Juncus effusus L.) were examined. Statistical analysis of the data demonstrated a highly significant reoccupancy by ticks of stems previously and recently used. Furthermore, it is shown that the extent of stem reuse by ticks is significantly and positively correlated with the numbers of ticks originally observed on those stems. Although other factors may be involved in generating clumping of ticks, the results are compatible with the proposition that aggregation of I. ricinus on the ground is pheromone-mediated. The findings are discussed in relation to what is known about the powers of lateral movement of I. ricinus on the ground and the possible implications for the performance of tick traps.

Bantry Bay, County Cork, a Fortified Maritime Landscape

Coastal fortification is an important component of the maritime cultural landscape, charged with the protection of settlements and the repulsion of hostile parties. Bantry Bay in southwestern Ireland features a range of martial monuments, ranging from medieval castle sites to 19th-century gun emplacements, within an outstanding maritime landscape. The monuments display great continuity in siting, often at vantage points overlooking sheltered anchorages and bays, reflecting the importance of maritime communication in the region. Their evolution and proliferation show the contemporary military trends as well as the wider political and economic concerns of a society in conflict.

Dietary Analysis of Sympatric Arctic Char and Brown Trout in Lough Muckross, South-Western Ireland

Stable isotope analysis was used to examine dietary separation between sympatric Arctic char (Salvelinus alpinus (L.)) and brown trout (Salmo trutta) in Lough Muckross, Co. Kerry, and to test the applicability of the interactive segregation hypothesis to observed trophic relationships. Gut contents showed both species fed seasonally on similar prey. Stable isotopes indicated the long-term nature of the similarity in feeding relationships, with results providing no support for the interactive segregation hypothesis as used to explain dietary differences between the species in Scandinavian lakes. Feeding and capture patterns indicative of differences in habitat use were consistent with the MacArthur niche compression hypothesis, with differences in temperature preferences for both species providing a plausible mechanism for observed habitat separation. IRELAND

Henry Pelham's Lost Grand Jury Map of Kerry (c.1800): A Newly Found Derivative

The ‘South Division of the County of Kerry’ (GSI FS 1.2.001) is a copy of the southern half of a lost late eighteenth / early nineteenth century map of County Kerry, in southwestern Ireland. Geological annotations on the map are traced to specific episodes (c.1820, 1838 and 1844) in the unofficial geological survey of Ireland conducted by Richard (later Sir Richard) Griffith between 1811 and 1855. The Griffith provenance of the map is part of the evidence used to identify the ‘South Division of the County of Kerry’ as a derivative of the now lost Grand Jury map of Kerry made by the American émigré artist and cartographer Henry Pelham. Dr Jean B. Archer was formerly a geologist in the Geological Survey of Ireland.

A Y-Chromosome Signature of Hegemony in Gaelic Ireland

Seventeen-marker simple tandem repeat genetic analysis of Irish Y chromosomes reveals a previously unnoted modal haplotype that peaks in frequency in the northwestern part of the island. It shows a significant association with surnames purported to have descended from the most important and enduring dynasty of early medieval Ireland, the Ui Neill. This suggests that such phylogenetic predominance is a biological record of past hegemony and supports the veracity of semimythological early genealogies. The fact that about one in five males sampled in northwestern Ireland is likely a patrilineal descendent of a single early medieval ancestor is a powerful illustration of the potential link between prolificacy and power and of how Y-chromosome phylogeography can be influenced by social selection.

AMS 14C dating of deglacial events in the Irish Sea Basin and other sectors of the British–Irish ice sheet

Sedimentary sequences deposited by the decaying marine margin of the British–Irish Ice Sheet (BIIS) record isostatic depression and successive ice sheet retreat towards centres of ice dispersion. Radiocarbon dating by accelerator mass spectrometry (AMS) of in situ marine microfaunas that are commonly associated with these sequences constrain the timing of glacial and sea level fluctuations during the last deglaciation, enabling us to evaluate the dynamics of the BIIS and its response to North Atlantic climate change. Here we use our radiocarbon-dated stratigraphy to define six major glacial and sea level events since the Last Glacial Maximum. (1) Initial deglaciation may have occurred ⩾18.3 kyr 14C BP along the northwestern Irish coast, in agreement with a deglacial age of ∼22 36Cl kyr BP for southwestern Ireland. Ice retreated to inland centres and areas of transverse moraine began to form across the north Irish lowlands. (2) Channels cut into glaciomarine deglacial sediments along the western Irish Sea coast are graded to below present sea level, identifying a fall of relative sea level (RSL) in response to isostatic emergence of the coast. (3) Marine mud that rapidly infilled these channels records an abrupt rise in global sea level of 10–15 m ∼16.7 14C kyr BP that flooded the Irish Sea coast and may have triggered deglaciation of a marine-based margin in Donegal Bay. (4) Intertidal boulder pavements in Dundalk Bay indicate that RSL ∼15.0 14C kyr BP was similar to present. (5) A major readvance of all sectors of the BIIS occurred between 14 and 15 kyr 14C BP which overprinted subglacial transverse moraines and delivered a substantial sediment flux to tidewater ice sheet margins. This event, the Killard Point Stadial, indicates that the BIIS participated in Heinrich event 1. (6) Subsequent deposition of marine muds on drumlins 12.7 14C kyr BP indicates isostatic depression and attendant high RSL resulting from the Killard Point readvance. These events identify a dynamic BIIS during the last deglaciation, as well as significant changes in RSL that reflect a combination of isostatic loading and eustatic changes in global sea level.

Relative Influences of Catchment Geology, Land Use and in-Stream Habitat on Brown Trout Populations in South-Western Ireland

Salmonid populations were sampled in 36 streams, at altitudes between 10m and 200m, in counties Cork and Kerry, south-western Ireland. The catchment land use ranged from open moorland and rough pasture/improved grassland to afforested sites with varying levels of catchment afforestation, mostly coniferous but with some patches of mixed coniferous and deciduous trees. The main geology types within the region were slate, Old Red Sandstone and limestone. Study sites were electrofished, and the density, biomass, age structure and condition of salmonid populations were assessed. A range of in-stream riparian and catchment environmental variables were measured, and the data were analysed using stepwise multiple regression to identify the most influential environmental factors affecting trout metrics following principle component analysis. The majority of salmonids were trout (86%), and mean trout density ranged from 0.662 fish mto 0.984 fish m-2 for all sites, irrespective of catchment geology. Trout condition did not differ significantly with level of catchment afforestation or geology, with the exception of limestone with high catchment afforestation. At sites with underlying limestone, trout condition decreased with increased catchment afforestation. River habitat structure was identified as the most important variable influencing trout density and biomass, irrespective of geology and water chemistry.

Relative Influences of Catchment Geology, Land Use and In-Stream Habitat on Brown Trout Populations in South-Western Ireland

Salmonid populations were sampled in 36 streams, at altitudes between 100m and 200m, in counties Cork and Kerry, south-western Ireland. The catchment land use ranged from open moorland and rough pasture/improved grassland to afforested sites with varying levels of catchment afforestation, mostly coniferous but with some patches of mixed coniferous and deciduous trees. The main geology types within the region were slate, Old Red Sandstone and limestone. Study sites were electrofished, and the density, biomass, age structure and condition of salmonid populations were assessed. A range of in-stream riparian and catchment environmental variables were measured, and the data were analysed using stepwise multiple regression to identify the most influential environmental factors affecting trout metrics following principle component analysis. The majority of salmonids were trout (86%), and mean trout density ranged from 0.662 fish m⁻² to 0.984 fish m⁻² for all sites, irrespective of catchment geology. Trout condition did not differ significantly with level of catchment afforestation or geology, with the exception of limestone with high catchment afforestation. At sites with underlying limestone, trout condition decreased with increased catchment afforestation. River habitat structure was identified as the most important variable influencing trout density and biomass, irrespective of geology and water chemistry.