Recovery targets and timescales for Lough Neagh and other lakes.

The framework, model and methods of Nürnberg were applied and evaluated in Lough Neagh and 19 other lakes in order to establish inflow phosphorus concentrations that support target lake values. Supporting concentrations, in the absence of an internal load, were derived and the effect of uncertainty in the model retention coefficient was relatively small, ±11-20 % in Lough Neagh and an average (n = 17) of ±9.7 % in the other lakes. There was further support for the model and methods from an independent estimate of the net internal load in Lough Neagh (13 % difference) and from another model in the other lakes (Supporting concentrations, which should be lower, were by an average of 11 mg P m-3). In the framework, steady state with the phosphorus load is assumed, but, based on a generic lake model, is not likely if the hydraulic residence time>0.5-0.8 yr and should lead to a decrease in phosphorus retention, which was found during three periods in Lough Neagh. Based on a compilation of internal load recovery times from 23 lakes in the literature, it could take between 8 and 20 years for lakes with an internal load to approach their targets.

Timescale of reduction of long-term phosphorus release from sediment in lakes.

It is important for lake management and policy to estimate the timescale of recovery from long-term P release from sediment after a reduction in the external load. To provide a scientific basis for this, a condensed model was elaborated, applied and evaluated in four lakes. The model is based on first order kinetics, with an overall rate constant composed of the rate of diagenesis of labile P (kd,2) and rate of burial of P (kb) below an active sediment layer. Using the variation of P fractions in dated sediment cores, kd,2 varied from 0.0155 to 0.383 yr-1, kb from 0.0184 to 0.073 yr-1 and the overall rate constant from 0.0230 to 0.446 yr-1. The active layer depths, 8 to 29 cm, and kd,2 values are within the ranges found by others. The time for a 75% reduction (t75) of labile P in the active layer is 60 years in Lough Melvin, 3 in Ramor, 33 in Sheelin and 41 in Neagh, although P release is only important in Ramor and Neagh. Combining the kd,2 values with other estimates (mean 0.0981 yr-1, median 0.0426; n=14) produces a t75 value of less than 14 and 33 years. A review of other models indicates a timescale of one to two decades and from lake monitoring also of one to two decades. It is desirable to estimate the timescale directly in all lakes if sediment P release is important, but, generally, it should take between one and three decades.

Assessing lake ecological status across a trophic gradient through environmental and biological variables.

The Water Framework Directive was widely welcomed because it sought to integrate chemical and biological elements of aquatic ecosystems to achieve 'good ecological status', reflecting at most slight anthropogenic impact. However, implementation has been criticised because of the failure to adequately integrate these elements and assess status of the whole ecosystem. In this study, a suite of environmental and biotic variables was measured to assess their relative importance as predictors of lake status for 50 lakes in the north of the island of Ireland. Total Phosphorus (TP) had a strong effect on taxon biomasses and ecological quality ratios (EQR) for most taxa, as expected, but other environmental variables, such as pH, water colour and spatial location, were also important. Most variance in mean EQR, the average of the taxon values, was predicted by five environmental variables (chlorophyll a, TP, population density, water colour and elevation) and whether (alien) cyprinid fish were present. Oligotrophic lakes with cyprinid fish had lower mean EQRs than cyprinid-free lakes, indicating the importance of recording species introductions when assessing lake status. Strong evidence for bottom-up effects was also detected, and cyprinids probably influenced trophic structure by increasing nutrient release from the sediment rather than by top-down effects. Phytoplankton biomass, fish biomasses, and the percentage of predatory fish, increased with TP. Our results further emphasize the need to adopt a more integrated approach when assessing lake status.

Metal to phosphorus stoichiometries for freshwater phytoplankton in three remote lakes.

Simultaneous measurements of changes in phytoplankton biomass and the metal and phosphorus (P) content of cells have been captured to attest to metal to P stoichiometries for freshwater phytoplankton. Three Scottish lakes that had received high, medium or low metal contamination from the atmosphere were selected for study. Phytoplankton cells were collected and Inductively Coupled Plasma-Mass Spectrometry was used to measure their lead (Pb), cadmium (Cd), mercury (Hg), copper (Cu), zinc (Zn), nickel (Ni), chromium (Cr), manganese (Mn), cobalt (Co) and P content. Increased phytoplankton growth in the lakes resulted in significant algae growth dilution of the mass-specific Pb, Cd, Hg, Cu, Ni and Cr in the phytoplankton. Changes in the phytoplankton cell count and their Hg, Pb, Cd, Cu, Mn, Co, Ni and Cr concentrations showed the process of algae bloom dilution to be subject to exponential decay, which accelerated in the order of Mn < Cu < Ni < Pb and Cd < Cr and Hg < Co. This indicated a metabolic and detoxification mechanism was involved in the active selection of metals. For the first time simultaneous measurements of metals and P stoichiometry in freshwater phytoplankton are reported. The mean metal to P stoichiometry generated was (C106P1N16)1000Pb0.019Hg0.00004Cu0.013Cd0.005Cr0.2Co0.0008Mn0.2Ni0.012 based on field measurements and the Redfield average C, N and P stoichiometry of (CH2O)106(NH3)16H3PO4.

The Applicability of the Distribution Coefficient, KD, Based on Non-Aggregated Particulate Samples from Lakes with Low Suspended Solids Concentrations.

Separate phases of metal partitioning behaviour in freshwater lakes that receive varying degrees of atmospheric contamination and have low concentrations of suspended solids were investigated to determine the applicability of the distribution coefficient, KD. Concentrations of Pb, Ni, Co, Cu, Cd, Cr, Hg and Mn were determined using a combination of filtration methods, bulk sample collection and digestion and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Phytoplankton biomass, suspended solids concentrations and the organic content of the sediment were also analysed. By distinguishing between the phytoplankton and (inorganic) lake sediment, transient variations in KD were observed. Suspended solids concentrations over the 6-month sampling campaign showed no correlation with the KD (n = 15 for each metal, p > 0.05) for Mn (r2 = 0.0063), Cu (r2 = 0.0002, Cr (r2 = 0.021), Ni (r2 = 0.0023), Cd (r2 = 0.00001), Co (r2 = 0.096), Hg (r2 = 0.116) or Pb (r2 = 0.164). The results implied that colloidal matter had less opportunity to increase the dissolved (filter passing) fraction, which inhibited the spurious lowering of KD. The findings conform to the increasingly documented theory that the use of KD in modelling may mask true information on metal partitioning behaviour. The root mean square error of prediction between the directly measured total metal concentrations and those modelled based on the separate phase fractions were ± 3.40, 0.06, 0.02, 0.03, 0.44, 484.31, 80.97 and 0.1 µg/L for Pb, Cd, Mn, Cu, Hg, Ni, Cr and Co respectively. The magnitude of error suggests that the separate phase models for Mn and Cu can be used in distribution or partitioning models for these metals in lake water.

An assessment of toxicity in profundal lake sediment due to deposition of heavy metals and persistent organic pollutants from the atmosphere.

A Tier I Sediment Ecological Risk Assessment of profundal lake sediment contaminated by diffuse pollution of heavy metals and POPs deposited from the atmosphere was completed. The concentrations of seven heavy metals and four groups of POPs (OCs, PCBs, PAHs, PBDEs) were determined in the profundal sediment of ten lakes in the United Kingdom and two sediment toxicity tests completed (chironomid survival and emergence and cladoceran survival and reproduction). The results showed that around half the lakes are at least moderately contaminated by Pb, Zn, Cd, As and PAHs deposited from the atmosphere and the toxicity quotient suggests that the contaminants of concern are Pb, As and PAHs, and not the other metals nor OCs and PCBs. There was toxicity in the sediment of four of the lakes. The Probable Effect Concentration Quotient values indicated that metals in the sediments of Scoat Tarn, Agden Reservoir and Llyn Llagi were likely to be responsible for the laboratory toxicity found in these lakes, with PAHs also contributing in Agden Reservoir.

Developing an optimal river typology for biological elements within the Water Framework Directive.

The Water Framework Directive requires a river classification based on environmental variables (a typology) to be created as a structure for reporting ecological status. A single permutation procedure, utilising the same variables repeatedly but with different categorical divisions, enabled both the choice of variables and the boundary divisions for these variables to be optimised simultaneously in the development of the typology. This, in addition to a data set which appropriately combined different biological elements, enabled a typology to be developed which was far more effective than a System A, CCA-derived or expert opinion-based typology in segregating communities. This optimal typology could be used to improve the performance of ecological quality assessment methods.

The 20th century whole-basin trophic history of an inter-drumlin lake in an agricultural catchment.

Eight 1-m sediment cores were extracted from across the basin of Friary Lough, a 5.4-ha eutrophic lake in a wholly grassland agricultural catchment in Co. Tyrone, Northern Ireland. Sedimentary TP, diatom inferred TP, Ca, Na, Fe, Mn, loss-on-ignition (LOI), dry weight and density were determined in the core profiles. Core dating and correlation gave a 210Pb, 137Cs and 241Am chronology from 1906 to 1995 and enabled a whole-basin estimate of chemical and sediment accumulation rate over the 20th Century. The major changes for all parameters occurred after c. 1946. Sediment accumulation rate was most influenced by organic matter accumulations, probably of planktonic origin, and increasing after c. 1946. Inorganic sediment accumulation rate was found to be largely unchanging through the century at 10 t km(-2) yr(-1) when expressed as catchment exports. All chemical accumulation rate changes occurred after c. 1946. Total phosphorus accumulation rate, however, was found to be the only chemical to be increasing throughout the epilimnion and hypolimnion areas of the sedimentary basin at an average of 22.5 mg m(-2) yr(-1) between 1946 and 1995. The other chemical parameters showed increasing accumulation rates after c. 1946 in the epilimnion part of the basin only. Interpreted in terms of whole-basin sedimentation and catchment export processes over time, it is suggested that diffuse TP inputs are independent of sediment inputs. This corresponds to hydrochemical models that suggest soluble P as the primary fraction that is lost from grassland catchments. The increase in sedimentary TP accumulation rate, and DI-TP concentration, are also explained with regard to current models that suggest increases in runoff P concentrations from elevated soil P concentrations. Increases in eplimnion chemical and sediment accumulation rate after c. 1946 may be due to local erosion that has limited impact on lake basin sedimentation.

The historical record of PAH, PCB, trace metal and fly-ash particle deposition at a remote lake in north-west Scotland.

Sediment cores taken from the deep basin of Loch Coire nan Arr in north-west Scotland were dated using 210Pb calibrated spheroidal carbonaceous particle (SCP) profiles and analysed for trace metals, polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). These data show that the site is one of the least contaminated by atmospheric pollution in the UK. Peak concentrations of PAHs were found to be equivalent to background values at sites in the English Lake District. The date of concentration maxima for SCP, PCB and some metals were in agreement with previously published polychlorinated dibenzo-p-dioxin/polychlorinated dibenzofuran (PCDD/F) data suggesting long-range industrial sources. The date of individual PAH concentration maxima were earlier, but concomitant with each other, possibly suggesting the influence of a local source. Comparison with remote European mountain lakes shows Loch Coire nan Arr to be one of the least contaminated sites in Europe with respect to PCBs, but more contaminated with respect to PAHs.