Mineralization of dissolved organic phosphorus from a shallow eutrophic lake

Release of soluble reactive phosphorus (SRP) from dissolved organic phosphorus (DOP), concentrated by reverse osmosis of water samples from Lough Neagh Northern Ireland, was measured in the presence of enzymes and cultures of lake water bacteria in a basal liquid medium adjusted to the pH of lake water (7.6). No hydrolysis of unfractionated DOP was observed in the presence of alkaline phosphatase but a combination of alkaline phosphatase and phosphodiesterase mineralized 14% of DOP in a 30 day incubation period at 15 °C. A similar amount of mineralization was attained by phytase. Phytase induced the same degree of mineralization in a range of DOP fractions varying from MW > 100 000 to c. 500. A mixed culture of lake water bacteria mineralized 12% of unfractionated DOP. Single cultures of lake water bacteria displayed low mineralizing activity (mean of 49 cultures = 5% DOP hydrolysed). Results indicate that DOP from Lough Neagh in the above molecular weight range is predominantly recalcitrant to bacterial mineralization under natural lake conditions.     

The rates of sediment-water exchange of oxygen and sediment bioturbation in Lough Neagh,Northern Ireland

Oxygen is transported 30 mm into the sediment at an 8 m depth site in eutrophic Lough Neagh by the irrigational activities of the benthic fauna. Faunal activity also mixes the upper 20 mm of sediment. Sediment oxygen uptake rate, redox potential-depth profile and the chlorophylla concentration were measured in the upper sediment layers from February to November 1979. Chlorophylla input to the sediment, following the Spring phytoplankton maximum, remained in the 0–1 cm sediment layer but did cause the redox potential profile to change from one with potentials around 400 mV in the upper 50 mm to one with a strong gradient over the 0–30 mm region. The start of benthic faunal activity in May caused the chlorophylla to be mixed into the 1–2 cm layer and also caused oxygen to be transported into the sediment at a rate sufficient to change the redox potential back to its initial state. The biodiffusion coefficient for solids in the upper 20 mm was estimated to be 6 × 10⁻⁸ cm² s⁻¹. Oxygen transport in the pore, waters of the upper sediment layers was considered to be best described as advection, caused by the irrigational activities of the benthic fauna.     

The Nitrogen Cycle in Lough Neagh,N. Ireland 1975 to 1987

Results from thirteen years of weekly observations are presented on the nitrogen cycle in Lough Neagh. The data comprised catchment and atmospheric inputs, output via the outflow and calculated losses by sedimentation and denitrification. Nitrate-nitrogen in the rivers is the dominant input fraction and the nitrate loading has increased over the period observed. 52 % of the input N sediments to the lake bottom, but 65 % of this is lost by denitrification. In spite of increasing nitrogen inputs, the summer soluble nitrate concentrations have decreased due to uptake by a perpetual crop of the cyanobacterium Oscillatoria agardhii GOMONT .     

Implications of temporal and spatial variability in Paracentrotus lividus populations to the associated commercial coastal fishery

Analysis of population structure and behaviour of a semi-enclosed and theoretically non-fished population of the echinoid Paracentrotus lividus at Lough Hyne marine nature reserve, Co. Cork, Ireland, showed distinct variability. Aspects of the behavioural variability in this species have significant consequences for the natural fishery harvest potential of this species. Whether or not, when and where individuals migrate to the upper surfaces of rocks varies on a local and regional scale as well as seasonally. The effect of this is apparent changes in (a) the population structure, (b) the population size and (c) the population centres of abundance. The population structure and size of the Lough Hyne population has changed substantially, as have those on a larger spatial scale, although the causative agents are debatable. Such changes are the result of large-scale mortality of adults and failure of cohort recruitment. Despite the undeniable pressures of overfishing at many localities, it seems likely there is a strong `natural' and possibly predictable element to the variability in P. lividus population size and structure. For the restoration and sustainable harvest of Irish P. lividus aspects of its behavioural ecology need to be taken more closely into consideration.     

A freshwater‐feeding Lampetra fluviatilis L. population in Lough Neagh, Northern Ireland

Pollan Coregonus autumnalis , caught in the fresh waters of Lough Neagh, Northern Ireland, were scarred by river lamprey Lampetra fluviatilis and adult river lamprey were found for much of the year with full guts, indicating a freshwater‐feeding population.     

A sponge diversity centre within a marine ‘island’

The exposed and gulf-stream warmed south-west coast of Ireland has a Lusitanean fauna composed of elements of the colder waters to the north and east, and others from the warmer Mediterranean Sea. Lough Hyne, a small marine body, is unusual on this coast in being very sheltered, but also in being characterised by many different niches within a small space (1 km²). Sponges are particularly abundant, morphologically varied and more than 100 species have been described. Species diversity was measured at 6 m intervals on vertical and inclined profiles (to a maximum of 30 m) at six sites, spanning a range of flow rate and sedimentation regimes. Diversity, richness, evenness and density varied significantly with both flow regime and depth, but was much lower on the surrounding Atlantic coast. Four different sponge communities were differentiated on the basis of sponge species assemblages which correlated with different environmental conditions. At sites of turbulent and fast flow conditions, sponge diversity and richness were lowest, with the highest values being found at the sites of moderate and high sedimentation. Significant differences were observed in all four ecological variables with respect to substratum angle with the exception of the site experiencing the most turbulent flow conditions. Lough Hyne was found to possess the second highest sponge species diversity (H=3.626) and richness (77 species) of all available figures from temperate, polar and tropical areas (of similar sized sampling area). The uniqueness, diversity and species composition of the sponge community at this location suggests Lough Hyne is, biologically, a marine island within the island of Ireland.     

Determination of zooplankton dietary shift following a zebra mussel invasion, as indicated by stable isotope analysis

1. Freshwaters with established zebra mussel populations typically exhibit reduced chlorophyll a concentrations, but the subsequent impacts upon zooplankton are varied. We hypothesised that in an invaded system with less phytoplankton but available allochthonous subsidy, zooplankton may utilise greater proportions of allochthonous matter and that this could be traced by analysis of stable carbon and nitrogen isotopes. 2. We used archived zooplankton samples which had been consistently preserved and which spanned the invasion period of an Irish lake, Lough Erne. Increasing reliance upon allochthonous resources would be reflected in an increase in zooplankton δ¹³C away from phytoplankton which is relatively ¹³C‐depleted in humic‐stained L. Erne. 3. Analysis of a series of monthly samples (1992–96, 1999–2003) revealed significant ¹³C‐enrichment of mixed zooplankton, Eudiaptomus gracilis and Mysis relicta post‐zebra mussel invasion; δ¹³C values approached ?27‰ typical of terrestrial organic matter during spring and autumn. Changes in zooplankton elemental composition also suggested a switch to a lower quality diet. However, analysis of zooplankton δ¹³C from an annual, single‐point (June) time series spanning 28 years (1977–2004) suggested that when phytoplankton was sufficiently abundant, zooplankton used this resource and their δ¹³C remained relatively constant around ?32‰. Post‐invasion enrichment of mysid δ¹⁵N may reflect a shift towards carnivory, but planktonic prey abundance was reduced and a subsequent loss of body condition could result in the same isotopic changes. 4. Our results indicate that in L. Erne, when phytoplankton was reduced by zebra mussel filtering, zooplankton assimilated more from allochthonous matter, and potentially sustained a higher population than would otherwise be possible. Thus, zebra mussel impact on foodweb structure and function is likely to be different in lakes subject to varying subsidy levels.     

Preliminary results on phosphorus reduction in Lough Neagh - Assessing the effect against a background of change

Lough Neagh is a large (387 km²), shallow (mean depth 8.9 m) eutrophic lake. The phosphorus budget is described in order to illustrate that 75% of the particulate phosphorus input sediments to the bottom and that there is little retention of SRP in the lake. 54% of the SRP loading comes from sewage works and this is being reduced by phosphorus reduction at the major sewage works. There has been a downturn in the maximum algal crops, particularly of blue-green algae. However, there is an underlying upward trend in SRP loading and the paper stresses the importance of analysing trends in nutrient budgets to get an accurate evaluation of reduction strategies.     

Chlorophyll‐a concentrations and macroinvertebrate declines coincide with the collapse of overwintering diving duck populations in a large eutrophic lake

相似文献   

A comparative study of Alexandrium tamarense cyst distribution in Belfast Lough

Alexandrium tamarense is a cyst-forming dinoflagellate that can cause toxicity in shellfish. Belfast Lough, in northeast Ireland, has experienced toxicity events due to the presence of A. tamarense, which are monitored because of shellfish farms in the Lough. Since 1992 anthropogenic influences on the Lough have changed with the introduction of a ‘fast cat’ ferry service and an increase in mussel farming. In 2002 Belfast Lough was surveyed for A. tamarense cyst distribution in the sediments and the results are compared to a previous cyst survey carried out in the Lough in 1992. Cyst numbers were generally lower in 2002 than in 1992 (t-test, P < 0.01). The highest concentration found in 2002 was 1058 cysts g^?1 dry sediment compared with 3330 in 1992. Although sediment disturbance increased in the period between the surveys and plays a role in cyst distribution, A. tamarense cysts are still present in the seabed of the Lough. These cysts remain an important repository of inoculating cells for A. tamarense blooms that have not been removed by the recent anthropogenic activity in the Lough and therefore the requirement for monitoring remains. Comparisons between cyst counts per volume of wet sediment and per weight of dry sediment were carried out, and although the first is needed for ecological studies allowing a deeper analysis, it is also recommended that cyst counts per dry weight of sediment are always reported for wider comparative purposes.