(1) The hypothesis underlying this research is that the bioavailability and toxicity of Al at neutral pH are dependent on its chemical form. Different compounds of Al may therefore have differential effects. The aim of the research presented in this thesis was to use the freshwater snail Lymnaea stagnalis (L.) to examine the effect of different Al compounds on water concentrations, bioaccumulation, behaviour and neuronal activity. Silicon is known to limit availability and ameliorate toxicity of AI. A further aim was therefore to investigate any changes in the response to Al in the presence of Si. (2) When Al was added as Al nitrate or Al lactate, Al water concentrations fell over 48 hours, probably as a result of hydroxyprecipitation. The presence of L. stagnalis caused a further reduction in Al water concentrations, even when loss of Al as a result of accumulation by the snails was taken into account. This increase in loss is suggested to be due to the presence of extracellular mucopolysaccharides secreted by the snails. Snails exposed to Al nitrate or Al lactate for 48 hours significantly accumulated AI. The gut is suggested to be the main route of uptake of Al and with snails accumulating Al as a result of ingesting insoluble AI. When Al was added as Al maltol, Al water concentrations remained high and accumulation by the snails was reduced. This suggests reduced bioavailability of Al when bound to maltol. The presence of Si increased the rate of loss of Al from the water column; however, this effect was masked in the presence of snails. The presence of Si had no significant effect on accumulation of Al by L. stagnalis. (3) Changes in the behaviour of L. stagnalis in response to exposure to Al nitrate, Al lactate and Al maltol (500 Jlgr1 ) were investigated. Depression of feeding behaviour and behavioural state score were observed after 2 to 14 days of continuous exposure, regardless of the form of AI. However, there was some evidence to suggest differences in the timing of behavioural changes depending on the Al compound to which snails were exposed. In some experiments behavioural changes in response to Al maltol occurred later than those in response to the other Al compounds. Differences in timing may be due to differences in bioavailability. The presence of Si ameliorated the toxic effects of Al on behaviour, although the concentration of Si was found to be critical. Concentrations of Si above 100 JlM protected against the toxic effects of Al on behaviour while concentrations below 100 JlM did not. (4) The effects of different Al compounds on the electrophysiological properties of an identified neuron (right parietal dorsal 1; RPD I) in the isolated CNS of L. stagnalis were examined. Extracellular addition of Al chloride or Al lactate (100 JlM) had marked and long lasting effects which included an increase or induction of irregular firing activity in the form of action potentials fired singly or in bursts. There was also an increase in the frequency and amplitude of synaptic inputs. These effects were accompanied by a slow depolarisation and changes in action potential shape and size. Extracellular addition of Al maltol (100 JlM) caused no significant changes. These differential effects are suggested to be due to differences in the bioavailability of the Al compounds. The presence of Si had no ameliorative effect on the electrophysiological changes produced in RPD 1 in response to Al lactate. (5) The results obtained in this study support the hypothesis that different Al compounds have differential effects. The results are discussed in relation to previous studies on Al toxicity and, in particular, to studies on the solution chemistry of the Al compounds used.

There has been increasing interest in combining proxy records from raised mire and floodplain ecosystems in order to provide greater clarity concerning Holocene climate and environment change. However, there are a number of questions still to be addressed concerning this approach. Perhaps most pertinent is that there has been limited research as to how these systems interact and react to change in a local landscape context. For instance, do ecosystems register events such as increased wetness in a synchronous manner and to what extent do they experience different thresholds? It has become increasingly apparent that chronologically aligning these records is challenging. This study provides a palaeoenvironmental reconstruction across a transect from raised mire to floodplain, using the Humberhead Levels in South Yorkshire as a case study. Coleoptera and pollen were used as environmental indicators, while multiple fraction dating and Bayesian modelling were used to produce age-depth models. These results were compared with previous research undertaken in the region in order to explore wider environmental signals. Floodplain-peat development (c. 8000-3000 cal BC) was intrinsically linked to rising sea-levels, causing base-levels to rise, leading to plaudification and the formation of rheotrophic mire-peat communities, from at least c. 5000 cal BC. The mire communities reached ombrotrophy by c. 2800 cal BC and were no-longer influenced by base-level flow. Consequently, the floodplain and mire ecosystems stopped registering synchronous episodes of change, such as increased wetness. Although the floodplain and lagg fen ecosystems continued to experience similar changes, they also recorded a number of asynchronous hydrological events. These systems may have experienced different thresholds. That floodplain, mire and lagg fen communities do not always register similar or simultaneous environmental changes highlights that more caution should be taken when combining different datasets in order to infer wider regional reconstructions.

In England and Wales, eutrophication, physical habitat modification and water abstraction have been identified by the Environment Agency as the most significant stressors preventing freshwaters from reaching Good Ecological Status. A similar pattern has emerged across the European Union. These stressors often exist in combination; however understanding of their ecological impact has tended to be based on the spatial pattern of individual stressors. This thesis investigates relationships between multiple stressors and standard river macroinvcl1ebratc community metrics. A general framework using linear multilevel (or mixed effects) models is developed, allowing integrated analysis of selected historical monitoring datasets which have hierarchical and spatial-temporal structure. Multi-model inference is used to define multiple partial relationships, including interaction terms (describing synergistic I antagonistic effects), without over-fitting or neglecting tapering effects. Initially, partial relationships are demonstrated with seasonal antecedent high and low flows. A cross-level interaction term is used to deduce that compared to more natural channels, the macroinvertebrate community in more resectioned channels appears more sensitive to antecedent low flow. Furthermore, there is the suggestion that although macroinvertebrates in lowland rivers arc more sensitive to low flow and extent of channel resectioning separately. together these may have. a greater •effect in upland rivers. For a series of Chalk stream sites, supra-seasonal drought is shown to be associated with incremental ecological decline, and there is a particular partial relationship between the autumn community and summer flows two years prior to sampling. Trampling of the channel/banks by livestock (poaching) was also associated with lower metric scores. Spatial associations between stressors and reference-corrected WFD monitoring metrics are shown to exist: arable and improved grassland cover in the nearby landscape, phosphorus (SRP) concentration in the water and extent of channel/bank resectioning (negative). A positive relationship between the metrics and riparian woody vegetation exists both in space and through time. In general, partial relationships could be estimated despite the inevitable co-occurrence of these stressors. The negative effects of arable land cover may have reduced since 1990, and there was a suggestion of greater sensitivity to SRP in upland rivers. Although the results are statistical associations and would benefit from testing in a more experimental manner, they are relatively robust given certain caveats. They have implications for the management of stressors as part of Water Framework Directive (WFD) Programmes of Measures. Impacts of water abstraction must be considered in the light of channel modification and climate (drought status). Whilst it makes sense to focus on ameliorating eutrophication when it is dominant, addressing land management stressors, including riparian and channel habitat would still be needed to achieve WFD goals. The study demonstrates the wealth of knowlcdge that can be gained from existing monitoring datasets using analytical techniques which respect the structure of the data. However an overly risk-based monitoring approach may compromise our capability to extract this knowledge. This study provides a basis for future work, needed to address potential non-linear responses, interactions of habitat modification and supra-seasonal drought, response of individual taxa and generalisation to other biological quality elements.

Temperature and light are key determinants of microalgal specific growth rates (μ) and hence also influence aquatic ecosystem dynamics. Despite this importance there is no clear consensus on the functions that should be used to model the effects of these environmental variables on within- and across-species microalgal growth rates. Therefore examining the biological basis and statistical fits of existing functions, and deriving new ones, comprise the main objective of this thesis. Using quantile regression, and information theory I have compared existing functions and derived new ones that describe microalgal maximum specific growth rates (μmax) in response to temperature, photon-flux density (PFD), daylength, and PFD, and daylength combined. The main findings are outlined in (i) to (v), below, (i) A comparison of the μmax temperature function derived here to the function of Eppley (1972), suggested that the Eppley curve intercept is too low and that models that incorporate the Eppley function may underestimate primary production by ~ 30%. (ii) My non-linear general model of microalgal growth in response to daylength will be useful in comparative studies to normalise growth rates to a standard daylength.

Availability of iron in an aquatic system is governed by the concentrations present within the catchment and prevailing environmental conditions. Iron is characterised by low solubility at circumneutral pH. Conversion of ferric iron, into soluble ferrous iron, requires a reduction in pH and redox potential. Research to date has tended to focus upon acid mine drainage, where anthropogenic activity initiates extreme acidity and the liberation of mobile iron. In instances of naturally occurring deposition, the acidity is derived from ecological processes, such as organic decay, respiration and natural acids. Once in the soluble form, iron is vulnerable to rainfall induced transport into receiving waterbodies. Precipitation of iron, from the water onto the streambed, takes place when pH increases downstream and conditions become increasingly oxidised. Interaction between iron-water and deposit concentrations was explored across the Antrim Plateau and Sperrin Mountains, in Northern Ireland. Basalt and brown earths dominate the Antrim Plateau, whereas the Sperrin Mountain soils are composed of peat underlain by schist. Significant relationships existed between water and deposit concentrations across both localities. Concentrations of deposit iron were consistently less in the Antrim Plateau, due to lower levels of iron in the water, as a consequence of variance in soil and rock type. In the Sperrin Mountains, eight streams were sampled monthly for one year, over a range of high to low iron sites. Seasonal variation in rainfall influenced iron concentrations in the water. The solubility of iron within streams in the Sperrin Mountains is predominantly controlled by pH. Dissolved oxygen was less influential owing to the hydrodynamics of upland stream networks, which are generally fast flowing and well oxygenated. The occurrence of iron deposition is therefore dependent upon the concentration of iron in the water and the pH of the waterbody. Composition of deposit material present on stone and tile substrates was analysed. Metal concentrations increased with increasing deposit density. A strong association also existed between deposit iron and organic matter concentration. Chlorophyll a concentrations increased with increasing deposit density, up to a critical point, after which they began to decline as deposit density continued to rise. Autotrophic index values behaved negatively with chlorophyll a concentration and positively with deposit organic matter and iron. The density of deposit material present within streams has a strong influence upon both the abundance of algae and invertebrate community structure. Deposit iron concentrations in excess of 1.0 mg cm-2 had a deleterious effect upon chlorophyll a concentration. Invertebrate numbers were also detrimentally affected by elevated concentrations of iron. Species composition was principally controlled by the density of deposit iron, which influenced algal abundance and controlled community structure in relation to feeding habit. The accumulation of deposit iron alters stream ecosystem functioning and facilitates the transition from autotrophy to heterotrophy. Key attributes of stream ecology are, therefore, altered by iron deposition as a result of food web simplification.

The overall aim of this thesis was to assess the effects of changes in low flows on biotic indicators of environmental quality on chalk streams in the context of water trading. Water trading is likely to go ahead in England in the upcoming years with little assessment of the likely impacts on the freshwater environment and subsequently the ecosystem services provided. Using the river Nar in Norfolk (UK) as a case study, a method using habitat models and data collection was used to investigate this. The methods were derived into three research questions: Firstly data collected in the field and EA data were used to investigate the impact of low flows on the three indicator species: Fish (brown trout), Macrophytes (Crowfoot) and benthic macro-invertebrate (Mayfly) (RQ1). Secondly hydraulic and habitat models (Flood modeller, TUFLOW, CASiMiR) were built to show how flows affected habitat availability (RQ2). Finally a trading model was developed by a team at Manchester University to show how water trading influences flow. These flow scenarios were run through the habitat models to show how water trading affects the habitat availability of the indicator species (RQ3). The results showed how the indicator species are generally more affected by the antecedent flow conditions as opposed to the daily flows. Furthermore the difference in habitat between the typologies was highlighted during the first research question where the fen reach generally provided poorer habitat than the chalk reach. A key finding in RQ1 was that brown trout numbers increase when BMI have better quality and therefore when the brown trout have more food sources. This led onto a key area of research which investigated the interconnectedness of species. It was found that in order to use habitat models to fully assess habitat availability, not only do the hydraulic components need to be addressed but a species’ biotic dependants i.e. food sources and refugia also need to be taken into account. RQ2 described a novel approach to do this and showed how spawning brown trout’s habitat availability changes when their biotic dependants are included. Finally RQ3 showed how water trading does affect habitat availability but the small impact should be weighed up against the benefits to water resources. Three main conclusions could be drawn from this research; firstly how there is a site specific nature of habitats and management should reflect these differences, secondly there is much uncertainty around habitat model and finally water trading does not impact habitat availability if HOF is activated. These findings and methods can be taken forward with the increase in water trading in England which would enable environmentally efficient water trades whilst being beneficial to effective water resource management.

No description available.

In chalk streams, Gammarus pulex is an abundant macroinvertebrate shredder that egests cohesive, cylindrical faecal pellets. The size and mass of faecal pellets influences their transport and utilisation in aquatic ecosystems, and are determined both by body size and diet in Gammarus. The number of Gammarus faecal pellets in sediments in the River Chess (a chalk stream and my field study site) varied over time, with the highest numbers found in Autumn and the lowest numbers found in Summer. Faecal pellet numbers did not vary spatially between different habitat types within the river. Gammarus faecal pellets are bound together by exopolymer substances, and also initially by a peritrophic membrane. Their breakdown is complex and involves changes to the size of organic matter particles within the pellet (which become larger over time), and is primarily mediated by bacteria internal to the pellets themselves. Although changes occur to the pellet during breakdown, the overall structure of the pellet is maintained for long periods, and Gammarus faecal pellets are relatively stable structures which have the potential to store organic matter in the environment. Organic materials in Gammarus faecal pellets are utilised by bacteria and other micro organisms as a substrate, bacterial numbers peaking soon after pellet egestion, and microbial respiration rates of faecal pellets are maintained at relatively high rates. Invertebrates also consume Gammarus faecal pellets, either to gain nutrition from the microbial communities there, or directly from organic matter within the pellets. Gammarus faecal pellets are likely to be an important ecological component of chalk streams, transforming, retaining and recycling organic matter (especially allochthonous materials) so that it can be utilised by other organisms in the ecosystem.

Increased human demands upon water resources and growing uncertainty surrounding climate change have focused attention on the need to determine environmental flows (e-flows) to protect and sustain river ecosystems. Internationally there have been several advances but within England an anthropocentric approach to water resources management has led to polices that set minimum flows founded in fear of water shortage. By exploring the history of flow management in England and its influence on current practice, and by introducing the concept of ‘ecological drought’ as a basis for managing future flows, this thesis makes two valuable contributions to the e-flows debate. It also explores the influence of George Baxter who more than 50 years ago proposed that compensation flows below dams could be varied to meet the seasonal ecological requirements without reducing water supplies. In this thesis, hydrological assessments are made of watercourses spanning the ‘natural – heavily modified’ continuum located across the River Trent and Great Ouse catchments of central England, using a dataset of 48 stations and approximately 1000 station-years. Analyses highlight a variety of ‘ecological drought’ responses, in magnitude, timing and duration, with extreme low flows being rarely observed on all watercourses in the same year. This suggests e-flow determinations at the local, sub-catchment, scale would have benefits for environmental protection and water supply. A variety of potential e-flow metrics are examined and Baxter’s hypothesis tested. It is shown that supporting flows during the key ecological periods of spring and autumn, while sustaining current levels of abstraction, would risk degradation of the rivers through the increased frequency and duration of extreme low flows. Finally, the thesis examines practical issues impacting on any future e-flows policies relating to climate change and hydrometry.

Freshwater ecosystems are currently amongst the most threatened habitats due to high levels of anthropogenic stress and increasing efforts are required to monitor their status and assess aquatic biodiversity. Biomonitoring, which is the systematic measurement of the responses of aquatic biota to environmental stressors, is used to evaluate ecosystem status. Macroinvertebrates are commonly used organisms for ecosystem assessment, due to their numerous biomonitoring qualities, which qualify them as ecological indicators. Traditional taxonomy-based monitoring is labour intensive, which limits the throughput, and is often inefficient in providing species level identification, which limits the accuracy of detections. The introduction of molecular based methods for biomonitoring, especially when coupled with High Throughput Sequencing (HTS) applications, offers a step change in ecosystem monitoring. Here I tested the utility of DNA based applications for increasing the efficiency of freshwater ecosystem biomonitoring, using benthic macroinvertebrates as a target group. For the first part of this work, I used DNA barcoding of the Cytochrome Oxidase Subunit I (COI), from individual specimens, to populate a barcode reference library for 94 species of Trichoptera, Gastropoda and Chironomidae from the UK. Then, I used High Throughput Sequencing (HTS) methods to characterise diversity from complex environmental samples. First, I used metabarcoding of aqueous environmental DNA (eDNA) and community invertebrate samples (Chironomidae pupal exuviae), collected on regular intervals throughout a year, to identify diversity levels and temporal patterns of community variation on ecosystem-wide and group specific scales. Finally, I used a structured design of mock macroinvertebrate communities, of known biomass content, to perform a comparison between PCR-based metabarcoding of the COI gene and PCR-free shotgun sequencing of mitochondrial genomes (mito-metagenomics), and evaluate their efficiency for accurate characterisation of biomass content of bulk samples. Overall, HTS has demonstrated great potential for advancing biomonitoring efforts, allowing ecosystem scale diversity detection from non-invasive types of samples, such as eDNA, whilst moving into mito-metagenomic work could improve the field even further by improving quantitative abundance results on the community composition level.