Factors affecting N immobilisation/mineralisation kinetics for cellulose-, glucose- and straw-amended sandy soils

The kinetics of N immobilisation/mineralisation for cellulose-, glucose- and straw-amended sandy soils were investigated in a series of laboratory incubations. Three Scottish soils expected to exhibit a range of biological activity were used: a loamy sand, intensively cropped horticultural soil subject to large inputs of inorganic fertilisers and pesticides (Balmalcolm - pH 7.2, organic matter 3.3%); a sandy loam soil highly enriched with organic manures and used for organic vegetable production (Strathmiglo - pH 7.1, organic matter 7.3%); and a loamy sand soil of low fertility in a zero-grazing, low intensity organic ley-arable rotation (Aldrochty pH 6.0, organic matter 5.0%). Incubations of soils with 1,000 mg cellulose-C kg^-1 soil at 8°C, showed peak N immobilisation of 71Lj, 92Lj and 65ᆣ mg N g^-1 added C for the Balmalcolm (after 34 days), Strathmiglo (after 34 days) and Aldrochty soils (after 63 days). The N remineralisation by the end of the incubation (>300 days) was 0, 50 and 22 mg N g^-1 cellulose-C in the Balmalcolm, Strathmiglo soil and Aldrochty soils, respectively. Only about 30% of the N immobilisation could be explained by soil microbial biomass N accumulation (much less than expected from model simulations). The C/N ratio of the extra microbial biomass was quite wide (19). Bacterial, protozoan and nematode biomass accounted for only 18%, 0.1% and 0.5% of the extra C immobilisation, respectively. These data suggest that fungal biomass growth and deposition of recalcitrant fungal metabolites are the main sinks for the N immobilised. With 1,000 mg glucose-C kg ^-1 added to the Balmalcolm soil, about 75 mg N g^-1 added C were immobilised after 6 days. Under less well aerated conditions at 15°C, immobilisation of only 10-20 mg N g^-1 added cellulose C took place in 2-4 weeks, but soluble organic C increased greatly. The N remineralised after 4-6 weeks.     

Slurry acceptance mapping of Northern Ireland for run-off risk assessment

Using geographic information system techniques, hydrology of soil types (HOST) classes were combined with slope, rockiness, flood hazard and soil moisture deficit classes within a risk matrix to produce a slurry acceptance map for Northern Ireland (NI) on a 50 m grid. Moreover, due to the whole territory of NI being designated as a nitrate vulnerable zone, a nitrates action programme is to be implemented across the region in the near future and this is likely to restrict slurry applications to the growing season. To assess the risk classes associated with slurry applications during the growing season, an additional slurry acceptance map for NI was created in which the HOST factor was excluded from the analysis. The maps created showed that, for the period January–December, the majority (80%) of agricultural soils in NI were in the severe risk category following application of 50 m³ ha^?1 of slurry. However, this proportion was reduced to only 29% when the same volume of slurry was applied during the growing season, when the soils were not saturated and significant rainfall was not received in the period immediately after slurry application.     

Predicting freshwater critical loads from national data on geology,soils and land use

Using information on geology, soils and land use, a map has been generated for Great Britain which indicates five classes of sensitivity of surface waters to acidification. This map has been used for designing sampling strategies for mapping critical loads of acidity for freshwaters. This paper evaluates the freshwater sensitivity map using a data set of water chemistry collected as part of the UK critical loads programme. Discriminant analysis was used to predict five critical load classes from information on geology and soil sensitivity for freshwater sites. This showed geology and soil information can correctly predict approximately 50% of all critical loads classes. In addition, 77% of sites fall within one critical loads class of that predicted. Predictions may be improved by including other variables eg altitude and geographical location. Differences between lake, stream and reservoir sites are also examined. Ranges of critical loads values were determined for each of the five classes of surface water sensitivity. While a trend in critical load values was evident between classes, there was significant overlap. A simplified sensitivity map with only three classes related more closely to critical loads values. The paper demonstrates the usefulness of the surface water sensitivity map for assessing acidification at a national scale, but highlights the difficulties of predicting critical loads for individual sensitive catchments using national data.     

Liming the acid lake Hovvatn,Norway: A whole-ecosystem study

Hovvatn, a 1-km² chronically-acidified lake in southernmost Norway, was treated with 200 tonne of powdered limestone in March 1981. An additional 40 tonne were added to a 0.046 km² pond (Pollen) draining into Hovvatn. The lakes were stocked with brown trout in June 1981 and in each subsequent year. At ice-out pH rose from 4.4 to 6.3 (Hovvatn) and 7.5 (Pollen), Ca and alkalinity increased, and total Al decreased by 120 μg L^?1. None of the other major ions exhibited significant changes in concentration. Total organic Cand Pincreased after liming. The phytoplankton community was dominated by chrysophytes and did not change significantly following liming. The zooplankton community was typical of acid lakes prior to liming. There was a clear succession in species dominance following treatment, although no new species immigrated to the lakes. Zoobenthos changed from a community characterized by low abundance and reduced number of species to increased abundances of oligochaetes, mayflies and chironomids. Hovvatn and Pollen were barren of fish prior to stocking. The stocked fish showed remarkably high growth rate during the first years. Liming apparently improved conditions for zoobenthos, enhancing the processing of fine detritus which in turn resulted in elevated levels of TOC and P in the lakewaters during the first year after liming. The “oligotrophication” process typical of acid lakes was temporarily reversed by liming. The interactions between groups of organisms in Hovvatn and Pollen indicates that many years are required before a new steady-state can be attained following liming.     

Gallic acid metabolites are markers of black tea intake in humans

Gallic acid is one of the main phenolic components of black tea. The objective of this study was to identify urinary gallic acid metabolites with potential for use as markers of black tea intake. In an initial study, nine compounds, assessed by using gas chromatography-mass spectrometry, were found to increase in concentration in urine after 3 cups of black tea over 3 h. A subsequent study employed a controlled crossover design in which 10 subjects consumed 5 cups per day of black tea or water for 4 weeks in random order. Twenty-four hour urine samples were collected at the end of each period. Of the 9 candidate compounds identified in the initial study, only 3 were present at higher concentrations in urine of all 10 subjects during tea-drinking in comparison to water-drinking periods. These compounds were identified as 4-O-methylgallic acid, 3-O-methylgallic acid, and 3, 4-O-dimethylgallic acid, all methyl ether derivatives of gallic acid. It is suggested that these compounds have the potential to be used as markers of black tea intake.     

The Boreray sheep of ST Kilda,outer hebrides,Scotland: The natural history of a feral population

The Boreray sheep have survived for 50 years without interference by man and maintain high density on rich maritime pastures heavily manured by seabirds. They are a blackface breed obtained from a cross between old Scottish shortwool and early blackface sheep. There is a population of about 400 on about 55 ha of pasture and the rams and ewes (with lamb and yearling rams) run in separate groups. The survival of rams is poor compared with ewes with an adult sex-ratio of about 10 ewes to 1 ram. Numbers of sheep fluctuate between 330 and 460 without causing sheet erosion, landslipping and disruption of the vegetation. The conservation plan for Boreray rests on continued non-interference with the sheep and no sheep should be introduced to the island.     

Growth and Metal Accumulation of Mycorrhizal Sorghum Exposed to Elevated Copper and Zinc

Arbuscular mycorrhizal fungi (AMF) alter heavy metal acquisition by higher plants and may alter plant response to soil-contaminating heavy metals. Two communities comprised of Glomus intraradices and G. spurcum were investigated for their influence on copper (Cu) and zinc (Zn) resistance of Sorghum bicolor. One community was isolated from a Cu- and Zn-contaminated soil (AMF-C) and one consisted of isolates from non-contaminated soil (AMF-NC). Non-mycorrhizal (NM) sorghum plants were also included. The two community ecotypes differed in their capacity to protect sorghum from Cu and Zn toxicity and exhibited differential metal uptake into hyphae and altered heavy metal uptake by roots and translocation to plant shoots. AMF-C reduced Cu acquisition under elevated Cu conditions, but increased Cu uptake and translocation by sorghum under normal Cu conditions, patterns not exhibited by AMF-NC or NM plants. Hyphae of both fungal ecotypes accumulated high concentrations of Cu under Cu exposure. AMF-C exhibited elevated hyphal Zn accumulation and stimulated Zn uptake and translocation in sorghum plants compared to AMF-NC and NM plants. Differences in metal resistance between fungal treatments and between mycorrhizal and non-mycorrhizal plants were not related to differences in nutrient relations. The enhanced Cu resistance of sorghum and altered patterns of Cu and Zn translocation to shoots facilitated by AMF isolated from the metal-contaminated soil highlight the potential for metal-adapted AMF to increase the phytoremediation potential of mycotrophic plants on metal-contaminated environments.     

Effects of ozone on calcareous grassland communities

A system of 16 open-top chambers was used to investigate the effects of a range of ozone concentrations typical of those found in southern Britain on the species composition of calcareous grassland communities. Two experimental approaches were adopted: the first involved the use of artificial communities of species typical of calcareous grasslands, whilst the second involved semi-natural chalk grassland swards transplanted from the field. Elevated ozone had little effect on total biomass of the artificial communities, but did significantly alter the species composition. The proportion of forbs decreased linearly with increased ozone exposure above 40ppb. Species composition was stable in the transplanted swards receiving filtered air, whilst there was a shift towards what appeared to be a more calcareous grassland community in the swards treated with higher ozone exposures. Thus, both experiments provide evidence that ambient levels of ozone in southern Britain can cause changes in species composition of semi-natural calcareous grassland communities.