Lough Neagh Research Articles

Seasonal variation in egg size and density of crustacean zooplankton in Lough Neagh, Northern Ireland

Seasonal variation in egg size and density of crustacean zooplankton in Lough Neagh, Northern Ireland

Chironomidae in Lough Neagh, Northern Ireland

Chironomidae in Lough Neagh, Northern Ireland

Silica and diatom growth in Lough Neagh: the importance of internal recycling

1. Lough Neagh is a large eutrophic lake with a high dissolved silica (SiO2) concentration arising from the basaltic rock in parts of the catchment and the normal winter maximum concentration is over 8 mg L−1. Based on frequent observations between 1974 and 1997, the annual cycles of SiO2 input, uptake and release are explored. 2. Large spring blooms of the planktonic diatoms Aulacoseira subarctica Haworth and Stephanodiscus astraea occur every year and are terminated by SiO2 depletion. Although there are periods when one diatom species has dominated the other, over the period as a whole, the two diatoms appear to be in a stable coexistence. 3. A model of the effect of river inputs on lake concentration shows that without SiO2 release from the sediment, the maximum spring dissolved SiO2 concentration (and hence diatom crop) would be only about one‐third of that actually observed. 4. It is concluded that within‐lake processes play a large role and are potentially more variable than catchment processes in determining the available SiO2 in Lough Neagh. 5. The role of benthic animals, especially Chironomus anthracinus, in the sediment SiO2 release process is discussed. Field data suggest the SiO2 release rate is highly sensitive to temperature, but this could be partly caused by an interaction between temperature and animal activity.

Silica and diatom growth in Lough Neagh: the importance of internal recycling

Silica and diatom growth in Lough Neagh: the importance of internal recycling

The random redistribution of sediment by wind in a lake

The total sedimentation rate was measured fortnightly for a year in a large shallow lake (Lough Neagh, Northern Ireland, surface area 383 km2, mean depth 8.9 m) at five sites using 10 sediment traps. The total sedimentation rate included both primary and secondary sedimentation. As the annual average total sedimentation rate, 53.2 ± 44.1 g m−2 d−1, is more than 25 times the primary value, secondary sedimentation due to wind‐induced resuspension is very important. The average of the largest 30% of wave mixed layer (WML) values, a function of wind speed and effective fetch, strongly correlates with the total sedimentation rate (r2 values of 0.69 and 0.98 at two westerly sites) at most of the sites. As the WML value approaches the water depth, then the orbital motion of the waves and the associated turbulence cause sediment disturbance and resuspension. Changing WML values, then, provide a basis to describe the "random redistribution" (RR) of sediment in lakes and these resuspension events can occur as frequently as 2–3 times every two weeks. This study provides, for the first time, clear results and a description of the process of RR of sediment in a lake, particularly the link between wind and sediment resuspension.

Monodiamesa ekmani (Diptera: Choronomidae) in Lough Neagh, Northern Ireland

ABSTRACT The larval habitat of Monodiamesa ekmani Brundin in Lough Neagh. Northern Ireland is shallow water. ≤5m depth, on a sandy substrate. Within that habitat, larval distribution is affected by the degree of disturbance of the sediment due to wave action. Larvae are most abundant generally at 4m depth, where disturbance is low throughout the year. In an area of sand bars, larvae are more abundant in the bar troughs than on the crests at times of high disturbance, but they are more evenly spread through the area in the summer when disturbance is less frequent. The life cycle appears to be of one year's duration, with emergence in May-June.

THE IRISH SEA REGION: WHY THE GENERAL LACK OF EXPLORATION SUCCESS?

With the exception of the prolific East Irish Sea Basin, there have been no hydrocarbon discoveries to date in the other basins in the Irish Sea region. Excellent reservoirs, viable seals and structural traps have been identified in all the basins, suggesting that other factors have prevented the accumulation or preservation of oil and gas. The lack of exploration success in the Larne ‐ Lough Neagh, Solway and Peel, Kish Bank and Central Irish Sea Basins is attributed to a combination of poor preservation of regional source rocks, unfavourable timing of hydrocarbon migration and trap formation and, locally, a lack of seal integrity. Inversion episodes during latest Carboniferous, Late Jurassic‐Early Cretaceous and Early Tertiary times were critical in preventing the optimum conditions necessary for the generation and preservation of oil and gas in these basins.

Operating experiences of a treatment plant designed for biological nutrient removal by pilot trials and mathematical modelling

An existing rendering plant wastewater treatment facility had to be up-graded to comply with new more stringent discharge consent standards. The rendering plant processes slaughterhouse waste materials to produce animal feed additives. The wastewater contains biodegradable organic substances, mainly organic acids and ammonia. The treated effluent is discharged to an adjacent river which feeds into nearby Lough Neagh. The revised consent standards required the removal of ammonia and new reduced standards for total-N and total-P are pending. The site trials indicated influent levels of BOD 1500–5000 mg/l and ammonia 250–750 mg/l. The discharge requirements were 20 mg/l BOD and 10 mg/l ammonia. The pilot trial results were tested against a mathematical model to verify the suitability of the treatment process and predict performance under full-scale conditions. An activated sludge plant with anoxic stage was constructed to provide nitrification-denitrification with phosphate removal by post-precipitation. This paper focuses on a comparison of predicted performance with the actual performance over an extended period.

Ice-flow stages and glacial bedforms in north central Ireland: a record of rapid environmental change during the last glacial termination

Satellite imagery is a useful tool to assess large-scale (>10 3 km 2 ) geological patterns. Satellite imagery of north central Ireland shows cross-cut and overprinted subglacial bedform patterns. Bedform lineations, supported by sedimentary evidence, are used to reconstruct four ice-flow stages (named A-D) during the termination of the last (Devensian) glaciation (22 000–13 000 radiocarbon ( 14 C) years BP ). Flow stage A relates to southwesterly flow of Scottish ice across eastern Ireland. Flow stage B, during the last glacial maximum (c. 25 000–22 000 14 C years BP), records southeasterly ice-flow from dispersal centres in northern parts of Ireland. Transverse subglacial ridges (Rogen moraines) formed during stage B are the largest area of this ridge type in western Europe. Flow stage C records erosional headcutting in the Rogen moraine field and sediment streamlining (drumlinization) by ice streams drawn into the Irish Sea Basin. This flow stage is constrained by AMS radiocarbon dates from marine microfaunas to around 14 500 14 C years BP. Flow stage D records drumlinization from an inland centre in the Lough Neagh Basin. Overall bedform patterns can be used to reconstruct ice mass history and evaluate controls on ice activity, including millennial-scale changes in amphi-North Atlantic climate. Field evidence of bedform relationships also casts doubt on current concepts of drumlinization and the role of pervasive sediment deformation in glacial systems.

Parasitism and epibiosis in native and non‐native gammarids in freshwater in Ireland

The introduced amphipod crustaceans Gammarus pulex and G. tigrinus are displacing the native G. ducheni celticus in a number of freshwater sites in Northern Ireland. We investigated parasite and epibiont infection in populations in the Rivet Lagan and Lough Neagh where both native and invading species occur. Prevalence of the four parasites and epibionts observed was higher in the native G. d. celticus than in the invading amphipods at both field sites. In Lough Neagh. G. d. celticus individuals suffered higher burdens of the rotifer Embata parasitica and the protozoan Epistylis in comparison with the invading species. These patterns may reflect host specificity by the parasites or may result from different susceptibilities of the native and invading host species. We consider the influence of parasitism on host invasions and resulting species distributions.

Observations on the spatial and temporal variation in the phosphorus status of lakes in the British Isles

Abstract. An examination of total phosphorus (TP) concentrations from 902 lakes in England, Scotland and Northern Ireland (NI), suggest that only Scottish lakes have a high percentage (73%) of oligotrophic waters (TP<10 μg PI‐1). The TP status of upland lakes in NI was greater than Scottish lakes particularly if lake catchments were afforested. Although lowland lakes in NI drain a predominately non‐urbanized landscape, 38% of lakes below 100 m had TP concentrations > 100 μg PI‐1 and only 29% <35 μg PI‐1. English lakes tended to have higher TP concentrations (70% > 101 μg PI‐1) which may reflect P inputs from sewage treatment works (STWs) although lakes draining agricultural catchments frequently produced high TP concentrations. Between 1985 and 1995, annual point source TP inputs to Loch Leven, Scotland, declined by 8 tonnes P or 40% of the 1985 TP loadings to the Loch. As point source inputs were proportionally richer in dissolved molybdate reactive phosphorus (MRP) than diffuse inputs, the MRP loading was reduced by 46%. From 1974 to 1995, TP concentrations in Lough Neagh (NI) increased despite reduced TP inputs from STWs. Partitioning of annual TP loadings from two major inflowing rivers to Lough Neagh, showed river MRP loadings from non‐point sources had been increasing at annual rates of 1.9 and 2.3 kg P km‐2. The remaining non‐MRP river loadings had not been influenced by lower TP loads from STWs and showed no tendency to increase with time. Insufficient data is available from other lake systems in the British Isles to judge whether the increase in non‐point source MRP loadings observed in the Lough Neagh catchment has been repeated elsewhere.

Predicting the spring algal biomass in Lough Neagh using time series analysis

1. Lough Neagh is a large eutrophic lake covering 387 km2 with a mean depth of 8.9 m. It is an important natural resource, being the largest single source of potable water for Belfast, Northern Ireland.2. This report examines the causes of the year‐to‐year variation in the April–June (spring) algal biomass, measured as chlorophyll a, for the period 1974–92.3. The spring chlorophyll a declined following the introduction of a phosphorus (P) reduction programme at major sewage treatment works in 1981. However, since 1990 the chlorophyll a concentrations in the spring have increased.4. Time series methodology was employed to develop a model which explained 76% of the annual variation in spring chlorophyll a concentrations.5. The independent variables used in the multiple regression model were the previous year’s spring chlorophyll a concentration, soluble reactive P inputs for April–June and the particulate P concentration in the Lough during the previous summer.

Synonymy of shape Proteocephalus pollanicola Gresson, 1952 (Cestoda: Proteocephalidae), a parasite of pollan, shape Coregonus autumnalis pollan, with shape P. exiguus La Rue, 1911

The systematic status of the tapeworm Proteocephalus pollanicola Gresson, 1952, a parasite of pollan Coregonus autumnalis pollan Thompson, was evaluated on the basis of freshly collected material from the type-locality (Lough Neagh, Northern Ireland). Comparison of morphological, biometrical and DNA data (RAPD method) from P. pollanicola and from P. exiguus La Rue, 1911, a very common parasite of coregonid fish, did not find any substantial differences between them to confirm the validity of P. pollanicola. Accordingly, P. pollanicola is considered to be a synonym of P. exiguus, a widely distributed parasite in the Holarctic.

Getting the Picture: On Dermot Seymour’s Painting the Russians Will Water Their Horses on the Shores of Lough Neagh

Getting the Picture: On Dermot Seymour’s Painting the Russians Will Water Their Horses on the Shores of Lough Neagh

Dissimilatory nitrate reduction in anaerobic sediments leading to river nitrite accumulation

Recent studies on Northern Ireland rivers have shown that summer nitrite (NO(inf2)(sup-)) concentrations greatly exceed the European Union guideline of 3 (mu)g of N liter(sup-1) for rivers supporting salmonid fisheries. In fast-flowing aerobic small streams, NO(inf2)(sup-) is thought to originate from nitrification, due to the retardation of Nitrobacter strains by the presence of free ammonia. Multiple regression analyses of NO(inf2)(sup-) concentrations against water quality variables of the six major rivers of the Lough Neagh catchment in Northern Ireland, however, suggested that the high NO(inf2)(sup-) concentrations found in the summer under warm, slow-flow conditions may result from the reduction of NO(inf3)(sup-). This hypothesis was supported by field observations of weekly changes in N species. Here, reduction of NO(inf3)(sup-) was observed to occur simultaneously with elevation of NO(inf2)(sup-) levels and subsequently NH(inf4)(sup+) levels, indicating that dissimilatory NO(inf3)(sup-) reduction to NH(inf4)(sup+) (DNRA) performed by fermentative bacteria (e.g., Aeromonas and Vibrio spp.) is responsible for NO(inf2)(sup-) accumulation in these large rivers. Mechanistic studies in which (sup15)N-labelled NO(inf3)(sup-) in sediment extracts was used provided further support for this hypothesis. Maximal concentrations of NO(inf2)(sup-) accumulation (up to 1.4 mg of N liter(sup-1)) were found in sediments deeper than 6 cm associated with a high concentration of metabolizable carbon and anaerobic conditions. The (sup15)N enrichment of the NO(inf2)(sup-) was comparable to that of the NO(inf3)(sup-) pool, indicating that the NO(inf2)(sup-) was predominantly NO(inf3)(sup-) derived. There is evidence which suggests that the high NO(inf2)(sup-) concentrations observed arose from the inhibition of the DNRA NO(inf2)(sup-) reductase system by NO(inf3)(sup-).

Tectonic evolution of the Larne Basin

Abstract The Larne Basin lies in the Midland Valley terrane between Northern Ireland and SW Scotland. A proportion of the basin lies onshore Northern Ireland, with an offshore continuation into the North Channel seaway. The basin is orientated NE-SW, and the sedimentary basin fill thickens to the west. Extensional faults in the south of the basin dip generally to the east, those in the north to the northwest. Preserved sediments range in age from Carboniferous to Tertiary, but are predominantly Permo-Triassic. Integration of seismic interpretations, well data and outcrop fault and fracture measurements has revealed a number of Mesozoic and Cenozoic tectonic events. Late Carboniferous N-S compression was followed by a major phase of regional early Permian ENE-WSW/NE-SW extension. ENE-WSW extension followed in the late Triassic and early Jurassic with post-early Jurassic to late Cretaceous minor subsidence and uplift resulting in a major erosional unconformity between the Lower Lias and Upper Cretaceous Greensand and Chalk. Early Tertiary (Palaeocene) uplift and NE-SW extension led to extensive basalt extrusion, and later NW-SE to NNE-SSW extension and faulting resulted in the deposition of the Upper Oligocene Lough Neagh Clays in the neighbouring Lough Neagh Basin. The late Tertiary (Miocene) saw a phase of compression, leading to uplift and erosion. AFTA® analyses of Permian and Triassic samples indicate c. 450 m of Tertiary uplift and erosion. Sonic velocity analysis of the Mercia Mudstone Group and Sherwood Sandstone Group suggests uplift of 0.5–1.1 km, possibly reflecting maximum burial at an earlier? Jurassic time.

Post-Invasion Amphipod Communities of Lough Neagh, Northern Ireland: Influences of Habitat Selection and Mutual Predation

1. Lough Neagh, Northern Ireland, has been invaded by three non-indigenous amphipod species this century; the North American Gammarus tigrinus and Crangonyx pseudogracilis, plus the European G. pulex. These species have come into contact with the sole native Lough species, G. duebeni celticus. 2. The Lough and its associated rivers were surveyed in 1993-94 and a selection of sites re-sampled the following year. The distributions, relative abundances and habitat utilization patterns of the four amphipod species were determined. All single and mixed species combinations of the four species were found. Gammarus pulex and G. d. celticus are ubiquitous in their habitat selection; however, the former species is replacing the latter. Gammarus tigrinus occurs in deep, mid-Lough areas and, to a limited extent, colonizes sheltered, vegetated shores. Crangonyx pseudogracilis has a fragmented distribution, but utilizes a variety of habitats. 3. Considering those habitat types utilized by all four species, evidence was found for species interactions from field data. First, although both North American species have much greater reproductive outputs, their mean densities were significantly lower than the mean densities of both G. d. celticus and G. pulex. Secondly, the mean density of total Gammarus was significantly higher where C. pseudogracilis was absent compared to where it was present. Thirdly, re-sampling at selected sites in 1994-95 revealed that G. tigrinus and C. pseudogracilis had disappeared from areas dominated by the other two Gammarus species. 4. Since differential mutual predation has been linked to the replacement of G. d. celticus by G. pulex in Irish rivers, predatory interactions among all other combinations of the four species of Lough Neagh were investigated. Male G. d. celticus and G. pulex preyed significantly more frequently on moulted female G. tigrinus than did male G. tigrinus in reciprocal interactions. Predatory/survival abilities may be influenced by body size (G. d. celticus > G. pulex > G. tigrinus). However, G. tigrinus preyed on female G. d. celticus significantly more frequently than on female G. pulex. 5. All three Gammarus species preyed heavily on the smaller C. pseudogracilis, with G. pulex the most severe predator, followed by G. d. celticus and then G. tigrinus. Such predation occurred regardless of the moult state of victims, and frequencies of predation were particularly high on reproductive females. Thus, high rates of Gammarus predation may explain the limited invasion success of C. pseudogracilis. 6. The dynamic nature of Lough Neagh's amphipod communities appears to arise from a combination of overlapping habitat utilization, differential predation and episodes of local immigration/exclusion. Species diversity, and probably biomass, have increased following the introductions, which are likely to have significant effects on other species and at other trophic levels.

Lough Neagh: The ecology of a multipurpose water resource (R. B. Wood and R. V. Smith [eds.

Lough Neagh: The ecology of a multipurpose water resource (R. B. Wood and R. V. Smith [eds.

Reproductive behaviour in Chironomus anthracinus (Diptera: Chironomidae), with a consideration of the evolution of swarming

Reproductive behaviour in Chironomus anthracinus Zetterstedt (Diptera: Chironomidae), one of the most ubiquitous species in cold‐temperate lakes of Northern Europe, was investigated in Lough Neagh, Northern Ireland. Aerial swarming is an indispensable part of mating in this species. It has been recognized that adults, emerging from offshore, travel to inshore resting sites for physical/sexual maturation, before gathering at lake margins to form swarms. After copulation, females immediately travel back to open‐water sites (up to 1000m offshore—the longest oviposition flight recorded for a chironomid species) for oviposition. Protandry was evident and sex ratios were completely reversed in the near‐shore swarming site and the offshore oviposition site. A sequence of mating behaviour was clarified, involving an initial grasp, landing, an end‐to‐end position, and separation. There was a high incidence of homosexual (male‐male) grasps, indicating that grasping is initiated with a fairly crude cue, and many (heterosexual) grasps failed to proceed to a correct mating position. This resulted in an estimation of only one out of eight grasps resulting in a proper copulation. More egg masses were found in the surface water farther offshore, together with spent females. An egg mass contained c. 1000 eggs and hatching occurred within one month of oviposition.Sexual differences in the pattern of reproductive migration between the emergence/oviposition site offshore, the inland resting site, and the near‐shore swarming site, and the modes of mating and mating success achieved, together point to a possibility that the conspicuous swarming behaviour in this species may have evolved primarily through mate selection on the part of females. A swarm occurring at the end of the males’ lives serves as an efficient mechanism for females to select the best‐quality mate, while males have no other strategy than to participate vigorously in a swarm if they are to attain a reproductive success with choosy females. Thus, two sexes apparently adopt different strategies in their reproductive life: males spend their energy in swarming, while females pass through the swarm site with a quick but guaranteed reward and spend their remaining energy in reaching offshore sites with muddy substrata which provide the best chance of survival for the offspring.

The boat from Lough Neagh

The boat from Lough Neagh