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A semi-natural community known locally as Culm grassland in Devon and N. E. Cornwall is under threat from agricultural improvement, abandonment and inappropriate management In the last fifty years 87% of the original area has been lost. Further loss may be prevented by an examination of the factors that influence the plant community and how they may be manipulated by management. Thus the research described in this thesis addressed the soil conditions and the plant communities, with particular reference to phosphorus cycling. In 1992 a preliminary characterisation of soil nutrient and water conditions, and species composition was conducted on a pristine Culm grassland, an improved grassland and a formerly abandoned Culm grassland. A significant elevation in soil extractable phosphorus was found in mid-April in response to fertiliser applications on the improved grassland. Similarities with previous research and an absence of a similar pattern in mineral nitrogen prompted a detailed investigation of phosphorus dynamics in 1993. A better indication of plant 'available' P was found by removing soil solution directly using novel methods of centrifuging and suction cups. Environmental conditions were highly influential. Low concentrations of P in suction cup solutions on Culm grassland indicated that Culm species may remove P at very low concentrations. An investigation of the above-ground biomass found that the uptake of P was highest in M. caerulea. M. Caerulea also influenced the return of P to the soil via organic matter through the production and subsequent breakdown of large quantities of litter. Additions of P to turfs caused a perturbation by enhancing the uptake of P by M. caerulea and increasing P fixation. The data was employed to produce a schematic model of the Culm grassland which identified input and outputs, storage compartments and transfers within the P cycle. This contributed towards making management recommendations for a range of Culm grassland communities which may be maintained, improved or recreated.

Phytoplankton constitute the main algal biomass in pelagic ecosystems and, therefore, play a fundamental role in the functioning of the marine trophic web. Information on long-term trends in marine phytoplankton may help to distinguish between biological responses to natural oscillations in climate and global warming, and to evaluate possible regional effects of eutrophication. The aim of this work was to contribute to the general understanding of how phytoplankton are spatio-temporally structured at the large-scale. To achieve this aim, the Continuous Plankton Recorder (CPR) survey data were used to identify the dominant large-scale spatial patterns of phytoplankton in north-western European continental shelf waters. Spatial patterns have been described in relation to their variability in time (seasonal and decadal). Finally, fluctuations of phytoplankton in space and time are described in relation to changes in the environment of the North Atlantic. The analysis included approximately 70,000 samples taken between 1960-1995. The large-scale, spatio-temporal patterns ranged from the meso to the macro-scale (50-10,000 km) and from months to decades. The structure of the thesis follows a progression from the seasonal to the inter-annual scale and from phytoplankton biomass to the phytoplankton community. Particular emphasis is placed on a broad overview of the long-term changes in marine phytoplankton and interpreting anomalous phytoplankton values. Overall, the results suggest that the environment plays a fundamental role in structuring the phytoplankton from the seasonal scale to the decadal scale. The seasonal spatial evolution of phytoplankton shows close associations to the hydrography of the north-east Atlantic, from the overall biomass to the timing and ending of the seasonal growth period. At larger-scales, atmospheric forcing (principally governed by the North Atlantic Oscillation index) has a dominant effect on decadal variability of phytoplankton populations in the north-east Atlantic. Although there is considerable regional variability in the long-term trends in phytoplankton biomass and community structure, underlying patterns emerged to reveal common trends. During the last decade, there has been a considerable increase in phytoplankton bion1ass in most regions (particularly the North Sea) and an increase in the dominance of dinoflagellates amongst the phytoplankton community, while the opposite pattern was observed for the northern oceanic area of the north-east Atlantic. These different spatial responses show similar patterns to changes in the decadal variability of sea-surface temperature influenced by the North Atlantic Oscillation index. While atmospheric variability plays a key role in the overall long-term and regional patterns of phytoplankton, oceanic influences on the North Sea ecosystem have been underestimated in the past. The anomalous phytoplankton biomass values, and large community shifts in the North Sea, are associated with episodic hydrographic events seen during the late 1970s/early 1980s and the late 1980s/early 1990s. It is suggested that these hydrographic events conspire to produce anomalous ocean climate conditions in the North Sea which persist for a number of years and are significant enough to alter the overall ecology of the North Sea.

The aim of this thesis was to evaluate the use of a meiofaunal copepod as a test species for assessing the developmental and reproductive effects of toxicants relevant to freshwater ecosystems. The harpacticoid copepod Bryocamptus zschokkei was chosen as a candidate test species as it possesses several attributes (widespread distribution, small size and fast development times) that are considered pre-requisites for toxicity test organisms, and has previously been shown to be a sensitive component of the stream community to contaminant exposure. Prior to conducting toxicity tests with B. zschokkei, studies were performed to evaluate the effects of water hardness and food quality on the development and reproduction of this copepod. These data were then used to define optimal culture conditions. Bryocamptus zschokkei was insensitive to water hardness at <150 mg 1ˉ¹ (as CaCO3), reflecting its range of tolerance in the field and suggesting the potential for toxicity testing across a range of hardness levels. Food quality affected development and reproduction: beech leaves (Fagus sylvatica L.), conditioned for 2 weeks supported optimal overall development to adult and reproduction of B. zschokkei and were chosen for use in subsequent culturing and testing regimes. Development and reproduction assays for assessing the effects of environmental parameters on B. zschokkei were combined to produce the first full life-cycle toxicity test for a freshwater copepod. This life-cycle test was relatively quick (6 weeks at 20°C) and is highly reproducible. The effects of three reference chemicals, the trace metal zinc, the pesticide lindane, and the moulting hormone 20-hydroxyecdysone (20-HE), were measured using this toxicity test. There was no effect of 20-HE (0-269 µg 1ˉ¹) on the life cycle of B, zschokkei. Bryocamptus zschokkei was, however, relatively sensitive to zinc and lindane compared with other freshwater crustaceans although sensitivity depended on the chemical and the duration of exposure. A model of ‘equiproportional development' was used to aid interpretation of the mechanism of toxicity of lindane, which was found to act by significantly prolonging the development time to adult. Reproductive endpoints (numbers of eggs and nauplii per female) were the most sensitive measure of zinc and lindane exposure, with lowest observed effect concentrations (LOEC) of 0.48 mg Zn 1ˉ¹ and 32 fig lindane 1ˉ¹, respectively. An increase in abortion frequency, observed for these contaminants, may have potential as a biomarker of stress for this copepod. In conclusion, it is proposed that toxicity tests with B. zschokkei should be included in contaminant assessment procedures for freshwater systems as they would increase the choice and ecological relevance of current testing regimes.

The cereal aphids Rhopalosiphum padi (L.) and Sitobion a venae (F.) cause spread of Barley Yellow Dwarf Virus in autumn sown crops over the winter. Control is achieved by correctly timed insecticide applications, commonly synthetic pyrethroids. Polyphagous predators contribute to the natural control of these aphids. A field investigation into the effects of deltamethrin on polyphagous predators,using barriered plots, showed that natural control may be reduced due to the reduction in numbers of predators over the winter. Also, spring populations, which limit the growth of summer populations of aphids, may be reduced as larvae are most affected. The field dispersal of apterous R. padi was simulated in a computer simulation model based on changes in distribution along crop rows, and found to be between 0.6 - 1.3 m day. Analysis of leaves, using ELISA, confirmed spread of virus in the crop, with a maximum in January. A damage code based on symptom expression in the crop was devised, but was of use only as a guide to infection. Dispersal was observed by release of apterous R. padi in the centre of nineteen 1m² experimental plots of wheat. Dispersal showed a step-like relationship with mean daily temperature and an "activity threshold" at 7-9° C. Dispersal rates were much less than those obtained from commercial fields, possibly due to density-dependent mortality. Experiments in controlled environment rooms showed that apterae moved greater distances at temperatures above the "activity threshold", but other factors were involved. Observation of individual R. padi showed that apterae were capable of walking ∅.7m hour at 11°± 2°C. The implications of all the results on improving forecasting and integrated control of cereal aphids and BYDV are discussed.

In order to investigate the biogeochemistry of aquatic ecosystems, a quantitative understanding of primary production and the temporal and spatial distribution of nutrients is necessary. This thesis describes the development of a submersible FI based nutrient sensor for the in situ determination of nitrate in estuarine and coastal waters. Chapter One describes the role of nitrogen in the global and marine nitrogen cycles and provides an overview of laboratory and in situ methods for its determination. Chapter Two describes the key parameters for a field instrument and culminates with the overall design specification for the system. Chapter Three describes in detail the design, build and optimisation of the key individual components of the system, e.g. sample delivery system, injection valve, reduction column, reaction column, flowcell, on-board control system and the housing of the complete integrated system. Chapter Four describes the optimisation and analytical performance of the FI instalment prior to field trials. The key operational parameters such as flowcell path length, injection volume and detector response were investigated. LOD, reproducibility and linear range were determined and the control programme for the onboard computer is reported. For example, a LOD of 0.01 Nitrate-N, a linear range of 0-140 | iM Nitrate-N and a reproducibility of ± 5 % were achieved. Chapter Five describes the field experiments where the FI system was initially used as a bench instrument and compared to a laboratory FI method which had been validated by participation in two interlaboratory exercises and for nitrate in river and sea water. The first submersed deployments involved the optimisation of the system operational characteristics and developing the field techniques. The final part of this chapter describes the weekly field studies of Barn Pool in Plymouth Sound using the submersed nutrient sensor for a period of two months. The operation and performance of the submersed sensor was assessed against an air segmented continuous flow analyser during a Land Ocean Interaction Study (LOIS) North Sea cruise aboard the RVS Challenger. The results from this exercise and the relevant salinity and turbidity measurements are presented in Chapter Six.

Biological monitoring techniques, selected to cover increasing levels of biological organisation (cellular, individual, population and community), were compared and contrasted to determine the relative sensitivities of these approaches to heavy metal contammation. The study was centred on the Fal Estuary in Cornwall, an ideal experimental field site-with well documented heavy metal contamination resulting firom the long-term discharge of waste from a local tin mine. Five creeks leadmg from the estuary differ dramatically in the concentrations of heavy metals in the sediments, but little in natural environmental variables (sediment granulometry, salinity etc.). The contaminant induced damage was evaluated at the cellular level in Mytilus edulis by the Neutral Red Assay to detect lysosomal membrane damage. Parameters of the energy budget of this species were determined to estmiate 'Scope for Growth' of mdividuals. along with a Larval Survival assay to estabUsh their reproductive and developmental success. At the population level. Cohort Growth studies were undertaken using the polychaete Nephtys hombergi. At the community level, data firom an extensive three year survey of benthic macrofauna structure were analysed. In addition to investigating biological parameters, contammant levels in sedunent and tissue were determuied using Atomic Absorption Spectrommetry. All techniques, except the population level, detected the extreme pollution of the most contaminated creek, Restronguet, but did not accurately reflect the known metal gradient. However, community studies established distinct macrofaunal assemblages between both sites and years. Techniques were compared and validated in a novel approach using the program BIOENV, with the multivariate analysis package PRIMER (Plymouth Routines in Multivariate Ecological Research). The cellular assay correlated reasonably well agamst the heavy metal levels, the larval survival assay correlated well to the community structure. However, the community structure approach was the most sensitive and relevant monitoring method to determme the long-term contamination of the Fal Estuary.

Long-term physical, chemical and biological monitoring (May 1990 to November 1994) was conducted in order to quantify water and sediment quality changes arising from the impoundment of Sutton Harbour, Plymouth (UK). Spore tracer studies revealed that 95 % water renewal times increased from 45 h to 72 h after impoundment. Semi-diurnal (tidal) salinity variations of circa 5 x10ˉ³ were observed, revealing a mechanism which shunts contaminated estuarine water into the harbour during flood tides. Salinity typically varied from 17 x 10ˉ³ to 34 x 10ˉ³ seasonally, and exhibited strong inverse correlations with total oxidised nitrogen and orthophosphate, demonstrating the riverine source of dissolved nutrients. These varied seasonally in concentration by 2 to 3 orders of magnitude. Impoundment restricted the flux of riverborne nutrients but greater retention of brackish bottom waters produced a stronger concentration gradient, resulting in possible nutrient storage by diffusion into the porewaters. Sewage outfalls and sediments were the main sources of ammonium. Following impoundment, the evidence suggests that a balance between nutrients from reduced external (riverine) fluxes and increased internal (porewater) fluxes has developed. Phytoplankton blooms were regular but short-lived features in summer, and continued after impoundment. Sewage contamination, with faecal coliform bacteria occasionally exceeding 30,000 cfu 100 mtˉ¹, improved unequivocally after impoundment, but stricter controls on internal sources are required. The permanently anoxic harbour sediments, consisting mainly of silt, contained Cd (1.8 µg gˉ¹), Cu (160 µg gˉ¹), Hg (1.2 µg gˉ¹), Pb (200 µg gˉ¹) and Zn (290 µg gˉ¹) in the <63 µm fraction. Sedimentary Cu, Pb and Zn concentrations increased during the monitoring period. The benthic macrofauna consists mainly of polychaete worms, with species diversity decreasing during construction, and then attaining a new, impoverished equilibrium after impoundment. Multivariate analysis revealed changes in community structure involving loss of sensitive taxa and appearance of opportunists. The ecological impact of impoundment was minimal, in that the harbour ecosystem was able to withstand the imposed environmental stresses. The management strategy adopted will ensure that water and sediment quality are maintained in Sutton Harbour; recommendations equally applicable to future harbour impoundment projects.

Growth and reproductive potential of the turkey-wing mussel in Bermuda was assessed following field studies, the determination of nutrient storage sites and nutrient use during periods of reproduction, and seasonal fluctuations in the scope for growth index. Larval and post-larval development were also described and were typical of the family Arcidae. Furthermore, post-larval production, by controlled laboratory rearing, was suggested as a useful tool for enhancement of stocks for this species. Both preliminary field and laboratory studies indicated slow shell growth of the species throughout its life cycle. Temperature minima recorded during the winter months were suggested to have a negative effect on growth of Area zebra in the field. Gonadal development, expressed as gonadic index (dry gonad weight/empty shell weight x100) and confirmed by histological analyses, indicated a &quot;rest&quot; period during the winter months. The reproductive cycle was assessed and two well-defined spawning seasons, early summer (June) and autumn (September), were determined. The metabolic processes occurring prior to the summer spawning period were regulated by a glycogen-based metabolism with the pedal muscle as main storage organ. Processes regulating the second reproductive activity are characterized by a direct reliance on ingested food, favoured by high environmental temperature and food supply. Calorific values pointed to a low storage of nutrient. The adaptability of the turkey-wing mussel to low food supply was demonstrated by its response to laboratory-induced starvation, expressed as the molar ratio of oxygen consumed to ammonia excretion (O/N). Temperature played a significant role in the responses of the physiological variables in scope for growth (SFG) affecting most crucially clearance rate, hence energy inake. The inherently high growth efficiency (K2) determined for A. zebra in Bermuda, and determination of temperature as the key causal agent of its scope for growth, suggests the limitation of the Bermuda environment to the growth and reproduction of the species.

Marine zooplankton play an important role in the transfer of CO2 from the atmosphere/ocean system to deeper waters and the sediments. They also provide food for much of the world's fish stocks and in some areas of the ocean depleted of nutrients they sustain phytoplankton growth by recycling nutrients. They therefore have a profound effect on the carbon cycle and upon life in the oceans. There is a perceived lack of information about global distributions of zooplankton needed to validate ecosystems dynamics models, and the traditional methods of survey are inadequate to provide this information. There is a need to develop new technologies for the large scale survey of zooplankton, which should provide data either suitable for quick and easy subsequent processing, or better still, processed in real time. New technologies for large scale zooplankton survey fall into three main categories: acoustic, optical and video. No single method is capable of providing continuous real time data at the level of detail required. A combination of two of the new technologies (optical and video) has the potential to provide broad scale data on abundance, size and species distributions of zooplankton routinely, reliably, rapidly and economically. Such a combined method has been developed in this study. The optical plankton counter (OPC) is a fairly well established instrument in marine and freshwater zooplankton survey. A novel application of the benchtop version of this instrument (OPC-IL) for real time data gathering at sea over ocean basin scales has been developed in this study. A new automated video zooplankton analyser (ViZA) has been designed and developed to operate together with the OPC-IL. The two devices are eventually to be deployed in tandem on the Undulating Oceanographic Recorder (UOR) for large scale ocean survey of zooplankton. During the initial development of the system, the two devices are used in benchtop flow through mode using the ship's uncontaminated sea water supply. The devices have been deployed on four major oceanographic cruises in the North and South Atlantic, covering almost 40,000 km. of transect. Used in benchtop mode, it has been shown that the OPC can simply and reliably survey thousands of kilometres of ocean surface waters for zooplankton abundance and size distribution in the size range 250|im. to 11.314 mm. in real time. The ViZA system can add the dimension of shape to the OPC size data, and provide supporting data on size distributions and abundance. Sampling rate in oligotrophic waters, and image quality problems are two main limitations to current ViZA performance which must be addressed, but where sufficient abundance exists and good quality images are obtained, the initial version of the ViZA system is shown to be able reliably to classify zooplankton to six major groups. The four deployments have shown that data on zooplankton distributions on oceanic scales can be obtained without the delays and prohibitive costs associated with sample analysis for traditional sampling methods. The results of these deployments are presented, together with an assessment of the performance of the system and proposals for improvements to meet the requirements specified before a fiill in-situ system is deployed.