Populations of A. aquaticus and A. meridianus in Rutland Water, England, were sampled sequentially at monthly intervals from November 1979 to November 1981. The population densities of A. aquaticus ranged from 3758.7 m-2 to 238.8 m-2. A. meridianus was only present in the south arm where densities ranged from 999.9 m-2 to 42.9 m-2. The densities in the south arm followed divergent patterns during the study; A. aquaticus increased while A. meridianus decreased. Ovigerous females were present from early spring to late summer, giving rise to spring and autumn cohorts. A. aquaticus was most abundant on an algal substrate (Cladophora glomerata), and in the 'littoral' (< 2m depth), while A. meridianus occurred most frequently in the mud-detritus substrate. Respiration rates were determined at 4°, 10° and 16°C. The two Asellus species had similar rates of respiration, except at 16°C, where A. aquaticus showed a slightly higher rate of respiration than A. meridianus. Consumption, assimilation and faecal production rates on both decayed sycamore leaves and Cladophora were determined gravimetrically. For both species, the consumption and assimilation of decayed sycamore leaves were higher than those of Cladophora and increased with temperature for both species. The consumption and assimilation rates of Cladophora were rather higher in A. aquaticus than in A. meridianus. The annual population energy budget (KJ m-2) for A. aquaticus (mean biomass 15.086) was: consumption 705.8, production 48.0, respiration 132.3, and faeces 525.5. The significance of these energy values, and the ecological efficiencies calculated from them, are discussed in relation to previous reports. Both laboratory and field investigations of predation by invertebrates (using serological techniques) suggest that the intensities of predation on both Asellus species were severe. Intensities vary according to the predatory species, their abundance, and the time of the year. Further, these studies indicate that predation on A. meridianus is proportionally much greater than that on A. aquaticus, by a factor of 2.75.

Continuous, low intensity mixing using a perforated pipe system prevented a lowland, eutrophic reservoir - Staunton Harold - from stratifying in 1982 and 1983. Environmental variables were measured and related to the responses of individual phytoplankton species and assemblages. These responses were compared to those from Staunton Harold during a year when natural mixing occurred (1981) and Foremark - a nearby, eutrophic reservoir - which was allowed to stratify in all three years. Diatoms and small Chlorophytes had higher growth rates under mixed conditions whilst colonial Chlorophytes and filamentous Cyanobacteria were favoured by stable water columns. Stratification of phytoplankton communities did occur during mixed years when water column stability was high and/or motile species were present. Nutrient availability and the stability of the water column were found to be the dominant factors affecting the seasonal changes in assemblages. Artificial mixing and a lowering in the stability of the water column in Staunton Harold during 1982 and 1983 did not have major effects upon the periodicity but the perturbations caused by changes in stability could be explained using a matrix whose axes were these dominant factors. It was also shown that populations of phytoplankton which were mixed throughout the water column were able to tolerate wide ranges of underwater irradiance whilst stratified populations became light-shade adapted. This difference in the photosynthetic physiologies led to the mixed populations having a lower assimilation number and assimilation rates at higher intensties. The stratified populations had a higher assimilation number and assimilation rates at higher irradiances. Phytoplankton sedimentation was measured in both reservoirs but no differences were found under stratified and mixed conditions. Although phytoplankton assimilation was lowered by mixing, the mean total biomass was lower in one year of continuous mixing (1982) and higher in another (1983) when compared to the mean biomass in the naturally mixed year and those in Foremark.

<p> To investigate how biogeochemical processes affect the concentrations and fluxes of dissolved organic matter (DOM) in forested watersheds, I studied the quantity and quality of DOM at the Arbutus Lake Watershed, Adirondack Park (NY, USA). First, to understand the biogeochemical changes of DOM for surface waters in the watershed, I studied spatial and temporal patterns of the quantity (bioavailable/refractory concentrations) and quality (&delta;¹³C, aromaticity, and low (LMW; &lt; 1kDa) and high molecular weight (HMW; > 1kDa) of dissolved organic carbon (DOC), nitrogen (DON), and sulfur (DOS). DOC and DON constituents passing through a wetland were composed of highly refractory, aromatic HMW components compared to upland streams. DOS was dominated by the refractory, LMW form. I developed a &ldquo;bioavailability-molecular size model&rdquo; showing the refractoriness of the LMW DOS compared to the HMW DOC and DON. </p><p> Second, to evaluate how a lake nested in a forested watershed affects the dynamics of DOC and DON, I analyzed a mass balance of DOC, DON and dissolved inorganic nitrogen (DIN) from 2000 to 2009. Annual DOC and DON mass balances were strikingly uncoupled, and Arbutus Lake generally acted as a sink for DOC. But a periodic source for DON was observed, indicating that internal recycling between DIN and DON might be important in affecting DON concentrations in this oligo-mesotrophic lake. </p><p> Third, isotopic signatures of DOS in the inlet catchment of the Watershed revealed that the incorporation of reduced S (e.g., SH-) derived from bacterial dissimilatory sulfate reduction contributed to generating DOS in ground and surface waters. These results provide new information on mechanisms for geochemical DOS formation in forested catchments. </p><p> Last, to better understand isotopic changes in DOS, three isotopic pretreatment methods for sulfate widely used were compared. I found an excellent agreement of the &delta;³⁴S-sulfate values among the three methods. However, some differences were observed in the &delta;¹⁸O-sulfate values associated with possible O contamination before isotopic measurements. </p><p> Overall, my studies highlighted novel approaches comparing sources and transformation of three elemental DOM fractions of DOC, DON, and DOS along various watershed components and a lake nested forested watersheds.</p>

The effect of hydrography onthe planktonic community structure and secondary production of an area offthewest coast of the Isle ofMan was investigated in 1993. This region is subject to stratification in summer (May to September), the boundary between mixed and stratified water masses being marked bytheManx West Coast front (MWC). Acoastal front was also occasionally present, separating the mixed water mass from coastal water. Large interannual variability inthe strength of the stratification was apparent between 1993 and 1994. There were large seasonal changes in nutrient concentrations, with maximal concentrations inthe winter months. Nutrient depletion of theupper layer of thewater column in summer was apparent. Phytoplankton spatial distribution was strongly related to the physical structure of the area and higher fluorescence was measured during thegreater stratification in 1994. Abundances were initially highest inthe surface layers of the water column, though inlate summer were highest at the thermocline. Thetiming of the spring bloom was variable. Aseasonal succession of phytoplankton species was observed. The winter phytoplankton assemblage was dominated bylarge benthic and chain diatoms and the summer assemblage byRhizosolenia species. Agreater number of dinoflagellates were present inthe stratified area. The zooplankton assemblage was dominated bythe copepod species Pseudocalanus elongatus, Acartia clausi, Temora longicomis and Oithona simtlts, peak abundances occurring inJuly. No spatial variation was evident inzooplankton densities and composition except for ichthyoplankton densities, which were greater inshore. No spatial differences were noted incopepod grazing rates, eggproduction rates or chemical composition. However, seasonal and interspecific differences were considerable, with ingestion rates highest during the spring bloom and grazing impact greatest during the summer. Copepods grazed only a small proportion of the chlorophyll a inthe water column. Maximum rates of egg production occurred in April, prior to the spring phytoplankton bloom, butwere also high in the summer. Interspecific differences inthe numbers of eggs produced bycopepods and intheir seasonal production patterns were large. Only a small portion of the populations were producing eggs at anyonetime. This individual variability was attributed to the age structure of the population. Copepods were consuming enough algae to cover the energetic costs of reproduction. A. clausi and T. longicornis had the highest rates of grazing and egg production. T. longtcomis actually had the greatest impact onthe ecosystem, despite being far less abundant than the other copepod species. High mortality inthejuvenile stages was hypothesised as the reason for its low adult abundances. Protein was the major chemical constituent of the zooplankton, then lipids with carbohydrates only forming a small percentage of the dry weight. The amount of each of these components peaked inthe summer, their relative percentage varying seasonally. The stratified site, being the deepest, had the highest standing stocks of plankton. It was calculated that copepod stocks and productivity were generally high enough to support the observed densities of ichthyoplankton in the region.

No description available.

In Vietnam, wetlands have generally been perceived as wastelands. Large wetland areas were altered for agriculture, especially in the Mekong Delta, where rice production is a top priority for national food security and export Drainage of wetlands for agriculture has resulted in severe acid water pollution and degradation of wetland ecosystems where a native species Melaleuca cajuputi once dominated. The native Melaleuca forest provides many values for both people and environment. Rehabilitation of the Melaleuca forest faces policy conflicts for development programmes, immediate problems of poverty and lack of appropriate technical information. Poverty affects 15-20% of the population of the Delta, with many people landless and exploiting natural resources for their main income. This study examines the scientific basis for integration of the environmental and socioeconomic functions of Melaleuca into farming systems and trials a model to achieve this end. The effects of the Melaleuca ecosystem on surface water quality have been identified. Where rainwater passing through the Melaleuca canopy is temporarily acidified, the effect is greater on contact with the trunk than the leaves. Annually, Melaleuca adds 7-12 ton/ha litter to the ground. Litter decomposition led to a pH increase, and a reduction in Fe, Al, and SO4 concentration in surface water. Soil layers contribute to a pH increase under submerged conditions by reducing H' concentration, and soil micro-organisms decreased Fe concentration in acid water. Living Melaleuca and Eleocharis undergrowth significantly reduced Al and S04. concentration in acid water. These experimental results justified the establishment of an agro-forestry trial where Melaleuca forest was integrated with rice cultivation at a farm scale. In this trial Melaleuca land acts as a reservoir to keep flood water to irrigate the rice land, and improves quality of acidic drainage water from the rice land for irrigation. Farmers participated for the duration of three rice crops. The new combination of Melaleuca and rice crop management was linked with the indigenous knowledge of local people in its implementation. This has lead to the trial being readily adapted to field conditions. Specifically, one hectare of Melaleuca land can hold enough water to irrigate 1.5 hectares of rice land, whilst it can improve acidic water drained from 3 hectares of rice land. Farmers have no difficulty in the planting of Melaleuca, but they need information relating to rice crop management Melaleuca plantation provides more profit than the rice crop. The farmer needs to invest only once at the time of crop planting and can harvest after seven to eight years. They can also manage up to 70% of the crop profit at the harvesting time in terms of their own labour. For rice production, the farmer needs to invest in every crop over three to four months, and in terms of their own labour, they can manage only 30% of the crop profit, which is strongly dependent on the market. Thus, integrated agro-forestry based on the combination of Melaleuca forest with rice allows farmers to balance between short-term and long-term income while improving also environmental quality and biodiversity conservation

It has been suggested that pollutant nitrogen inputs adversely influence the response of heathland plants to certain climatic and biotic stresses. One specific hypothesis being that elevated nitrogen deposition may reduce drought tolerance in heathland vegetation. However, there is little evidence from field studies that this is the case. The aims of this research project have been firstly to establish the effects of increased nitrogen inputs upon plant water relations in certain dwarf heathland shrubs under winter and summer drought conditions. Secondly, to contribute to the understanding of how changes in plant water relations caused by increased inputs of nitrogen affects the growth, physiological perfonnance and consequent long tenn survival of heath land plant communities. Experimental field work was carried out at an existing upland site in Clwyd, North Wales near Ruabon from July 1995 to April 1999. Experimental work with potted plants was carried out in the glasshouse at Crewe, Octoberl995 to June 1997. A lowland field site at Budworth Common in Cheshire, consisting of twenty, 2 x 1 metre plots in a replicated random block layout was established by the author during March 1996, remaining a site of investigation until December 1998. At both the upland and lowland field sites the vegetation was dominated by Calluna vulgaris (L.) Hull. At Ruabon a twelve month study of shoot relative water contents in relation to soil moisture deficits was carried out on a monthly basis. Visible frost injury was surveyed and recorded each spring (April 1996 to April 1999). At Budworth Common (summer 1997), following 12 months of nitrogen applications (0, 20, 60 and 120 kg N ha-1yr-1 (NH4N03» a protracted period of drought was imposed on field plots by the use of drought shelters, these covered the whole of each plot.Comparisons were drawn between watered and droughted plants in the field. This was carried out by applying the equivalent summer rainfall for Budworth Common to one half (1m2) of every treatment plot and droughting the other half (1m2). Nitrogen treatments were continued at fortnightly intervals throughout. Budworth Common was used to study the impacts of elevated nitrogen and drought for a five month period from May to September 1997. Intensive experimental field work over the drought period recorded: weekly measurements of soil moisture deficits, shoot water potentials and shoot extension growth. Measurements of shoot relative water contents and infra red gas analysis were taken, the flowering period was recorded. During the post drought year (summer 1998) a spontaneous outbreak of Lochmaea suturalis (heather beetle) in the field plots showed the beetles to have a preference for high N treated Calluna. An increase in the competitive grass species Deschampsia jlexuosa was seen in droughted plots during summer 1998, particularly the high N treatments. As a result of experimental work carried out both in the field and laboratory this study has shown that elevated nitrogen does have detrimental impacts on the drought tolerance of certain heathland plants. Field work results compared positively with those obtained from the pot experiment. A higher incidence of visible frost and drought damage was recorded in high nitrogen plots. Lower soil moistures were recorded in high nitrogen plots. Measurements of shoot water potentials revealed that high nitrogen treatments under drought conditions exhibited more negative values than did low nitrogen plants. High nitrogen increased the number of early opening flowers under conditions of full water but in plants receiving high nitrogen and drought flowering was delayed. This study increases the understanding of the impacts of elevated nitrogen inputs on the water relations of heathland plants.

No description available.

No description available.

No description available.