Stable Isotope Analysis Reveals That Agricultural Habitat Provides an Important Dietary Component for Nonbreeding Dunlin

Although shorebirds spending the winter in temperate areas frequently use estuarine and supratidal (upland) feeding habitats, the relative contribution of each habitat to individual diets has not been directly quantified. We quantified the proportional use that Calidris alpina pacifica (Dunlin) made of estuarine vs. terrestrial farmland resources on the Fraser River Delta, British Columbia, using stable isotope analysis (δ13C, δ15N) of blood from 268 Dunlin over four winters, 1997 through 2000. We tested for individual, age, sex, morphological, seasonal, and weather-related differences in dietary sources. Based on single- (δ13C) and dual-isotope mixing models, the agricultural habitat contributed approximately 38% of Dunlin diet averaged over four winters, with the balance from intertidal flats. However, there was a wide variation among individuals in the extent of agricultural feeding, ranging from about 1% to 95% of diet. Younger birds had a significantly higher terrestrial contribution to diet (43%) than did adults (35%). We estimated that 6% of adults and 13% of juveniles were obtaining at least 75% of their diet from terrestrial sources. The isotope data provided no evidence for sex or overall body size effects on the proportion of diet that is terrestrial in origin. The use of agricultural habitat by Dunlin peaked in early January. Adult Dunlin obtained a greater proportion of their diet terrestrially during periods of lower temperatures and high precipitation, whereas no such relationship existed for juveniles. Seasonal variation in the use of agricultural habitat suggests that it is used more during energetically stressful periods. The terrestrial farmland zone appears to be consistently important as a habitat for juveniles, but for adults it may provide an alternative feeding site used as a buffer against starvation during periods of extreme weather. Loss or reduction of agricultural habitat adjacent to estuaries may negatively impact shorebird fitness, with juveniles disproportionately affected.

Agricultural Policy and Nest Success of Prairie Ducks in Canada and the United States

The Prairie Pothole Region of North America has been modified by agriculture during the past 100 yr, resulting in habitat loss, fragmentation, and degradation that have reduced the abundance and productivity of many wildlife species. The 1985 U.S. Farm Bill provided economic incentives to agriculture that are considered by many to be beneficial to nesting waterfowl and other wildlife. Canada has not experienced an equally comprehensive legislative initiative, which would seem to indicate that benefits to waterfowl in Canada should lag behind those in the United States. However, with the removal of some agricultural subsidies in Canada during the 1990s, the amount of perennial cover in the Canadian prairies increased to levels similar to those of the 1970s. Therefore, it is unclear whether and how the U.S. and Canadian prairies might differ with regard to habitat quality for nesting waterfowl. We used historical and contemporary data to compare temporal trends in duck nest success between the United States and Canada and to assess how mean nest success varied with proportion of cropland and wetland density. The data best supported models with nonlinear temporal trends that varied between the two countries and suggested that mean nest success in Canada declined from its high point in 1930s and remained below the long-term value of 0.16 until the end of the time series in 2005. Mean nest success in the United States also declined from its high point in the 1930s, but increased to above the long-term value of 0.25 during the early 2000s. Mean nest success varied negatively with proportion of cropland in both the United States and Canada. Mean nest success was positively correlated with pond density at Canadian sites, but showed only a weak association with pond density at U.S. sites. All models explained the low proportions of the variation in nest success, suggesting that unmeasured factors such as the abundance and identity of nest predators may have strong effects on nest success. Nonetheless, these results support earlier suggestions that agricultural policy that encourages permanent cover positively influences duck reproductive success. We also found that, for reasons that are not entirely clear, nest success for the same intensity of row cropping was generally higher in the United States than in Canada. Further research is required to elucidate the exact nature of the composition, size, and distribution of permanent cover that coincides with greater average nest success by dabbling ducks in the United States. In addition, the data suggest that the benefits that might accrue from increases in the amount of perennial cover in Canada would be better realized if these efforts are accompanied by strong measures to conserve wetlands.

Risk of Agricultural Practices and Habitat Change to Farmland Birds

Many common bird species have declined as a result of agricultural intensification and this could be mitigated by organic farming. We paired sites for habitat and geographical location on organic and nonorganic farms in Ontario, Canada to test a priori predictions of effects on birds overall, 9 guilds and 22 species in relation to candidate models for farming practices (13 variables), local habitat features (12 variables), or habitat features that influence susceptibility to predation. We found that: (1) Overall bird abundance, but not richness, was significantly (p < 0.05) higher on organic sites (mean 43.1 individuals per site) than nonorganic sites (35.8 individuals per site). Significantly more species of birds were observed for five guilds, including primary grassland birds, on organic vs. nonorganic sites. No guild had higher richness or abundance on nonorganic farms; (2) Farming practice models were the best (ΔAIC < 4) for abundance of birds overall, primary grassland bird richness, sallier aerial insectivore richness and abundance, and abundance of ground nesters; (3) Habitat models were the best for overall richness, Neotropical migrant abundance, richness and abundance of Ontario-USA-Mexico (short-distance) migrants and resident richness; (4) Predation models were the best for richness of secondary grassland birds and ground feeders; (5) A combination of variables from the model types were best for richness or abundance overall, 13 of 18 guilds (richness and abundance) and 16 of 22 species analyzed. Five of 10 farming practice variables (including herbicide use, organic farm type) and 9 of 13 habitat variables (including hedgerow length, proportion of hay) were significant in best models. Risk modeling indicated that herbicide use could decrease primary grassland birds by one species (35% decline from 3.4 to 2.3 species) per site. Organic farming could benefit species of conservation concern by 49% (an increase from 7.6 to 11.4 grassland birds). An addition of 63 m of hedgerow could increase abundance and richness of short distance migrants by 50% (3.0 to 4.8 and 1.3 to 2.0, respectively). Increasing the proportion of hay on nonorganic farms to 50% could increase abundance of primary grassland bird by 40% (6.7 to 9.4). Our results provide support for alternative farmland designs and agricultural management systems that could enhance select bird species in farmland.

Contributions of labile and resistant organic materials to the immobilization of inorganic soil N when used in the restoration of abandoned agricultural fields

We have examined the contributions sucrose and sawdust make to the net immobilization of inorganic soil N and assimilation of both C and N into microbial biomass when they are used as part of a restoration plan to promote the establishment of indigenous vegetation on abandoned agricultural fields on the Central Hungarian Plain. Both amendments led to net N immobilization. Sucrose addition also led to mobilization of N from the soil organic N pool and its immobilization into microbial biomass, whereas sawdust addition apparently immobilized soil N into a non-biomass compartment or a biomass component that was not detected by the conventional biomass N assay (CHCl3 fumigation and extraction). This suggests that the N was either cycled through the biomass, but not immobilized within it, or that it was immobilized in a protected biomass fraction different to the fraction into which N was immobilized in response to sucrose addition.

Microbial and biochemical soil quality indicators and their potential for differentiating areas under contrasting agricultural management regimes

The aim of this study was to examine interrelationships between functional biochemical and microbial indicators of soil quality, and their suitability to differentiate areas under contrasting agricultural management regimes. The study included five 0.8 ha areas on a sandy-loam soil which had received contrasting fertility and cropping regimes over a 5 year period. These were organically managed vegetable, vegetable -cereal and arable rotations, an organically managed grass clover ley, and a conventional cereal rotation. The organic areas had been converted from conventional cereal production 5 years prior to the start of the study. All of the biochemical analyses, including light fraction organic matter (LFOM) C and N, labile organic N (LON), dissolved organic N and water-soluble carbohydrates showed significant differences between the areas, although the nature of the relationships between the areas varied between the different parameters, and were not related to differences in total soil organic matter content. The clearest differences were seen in LFOM C and N and LON, which were higher in the organic arable area relative to the other areas. In the case of the biological parameters, there were differences between the areas for biomass-N, ATP, chitin content, and the ratios of ATP: biomass and basal respiration: biomass. For these parameters, the precise relationships between the areas varied. However, relative to the conventionally managed area, areas under organic management generally had lower biomass-N and higher ATP contents. Arbuscular mycorrhizal fungus colonization potential was extremely low in the conventional area relative to the organic areas. Further, metabolic diversity and microbial community level physiological profiles, determined by analysis of microbial community metabolism using Biolog GN plates and the activities of eight key nutrient cycling enzymes, grouped the organic areas together, but separated them from the conventional area. We conclude that microbial parameters are more effective and consistent indicators of management induced changes to soil quality than biochemical parameters, and that a variety of biochemical and microbial analyses should be used when considering the impact of management on soil quality. (C) 2004 Elsevier Ltd. All rights reserved.

The Phosphorus Indicators Tool: a simple model of diffuse P loss from agricultural land to water

The Phosphorus Indicators Tool provides a catchment-scale estimation of diffuse phosphorus (P) loss from agricultural land to surface waters using the most appropriate indicators of P loss. The Tool provides a framework that may be applied across the UK to estimate P loss, which is sensitive not only to land use and management but also to environmental factors such as climate, soil type and topography. The model complexity incorporated in the P Indicators Tool has been adapted to the level of detail in the available data and the need to reflect the impact of changes in agriculture. Currently, the Tool runs on an annual timestep and at a 1 km(2) grid scale. We demonstrate that the P Indicators Tool works in principle and that its modular structure provides a means of accounting for P loss from one layer to the next, and ultimately to receiving waters. Trial runs of the Tool suggest that modelled P delivery to water approximates measured water quality records. The transparency of the structure of the P Indicators Tool means that identification of poorly performing coefficients is possible, and further refinements of the Tool can be made to ensure it is better calibrated and subsequently validated against empirical data, as it becomes available.

Towards a nutrient export risk matrix approach to managing agricultural pollution at source

A generic Nutrient Export Risk Matrix (NERM) approach is presented. This provides advice to farmers and policy makers on good practice for reducing nutrient loss and is intended to persuade them to implement such measures. Combined with a range of nutrient transport modelling tools and field experiments, NERMs can play an important role in reducing nutrient export from agricultural land. The Phosphorus Export Risk Matrix (PERM) is presented as an example NERM. The PERM integrates hydrological understanding of runoff with a number of agronomic and policy factors into a clear problem-solving framework. This allows farmers and policy makers to visualise strategies for reducing phosphorus loss through proactive land management. The risk Of Pollution is assessed by a series of informed questions relating to farming intensity and practice. This information is combined with the concept of runoff management to point towards simple, practical remedial strategies which do not compromise farmers' ability to obtain sound economic returns from their crop and livestock.

Land use for England and Wales: evaluation of management options to support 'good ecological status' in surface freshwaters

This paper analyses historic records of agricultural land use and management for England and Wales from 1931 and 1991 and uses export coefficient modelling to hindcast the impact of these practices on the rates of diffuse nitrogen (N) and phosphorus (P) export to water bodies for each of the major geo-climatic regions of England and Wales. Key trends indicate the importance of animal agriculture as a contributor to the total diffuse agricultural nutrient loading on waters, and the need to bring these sources under control if conditions suitable for sustaining 'Good Ecological Status' under the Water Framework Directive are to be generated. The analysis highlights the importance of measuring changes in nutrient loading in relation to the catchment-specific baseline state for different water bodies. The approach is also used to forecast the likely impact of broad regional scale scenarios on nutrient export to waters and highlights the need to take sensitive land out of production, introduce ceilings on fertilizer use and stocking densities, and controls on agricultural practice in higher risk areas where intensive agriculture is combined with a low intrinsic nutrient retention capacity, although the uncertainties associated with the modelling applied at this scale should be taken into account in the interpretation of model output. The paper advocates the need for a two-tiered approach to nutrient management, combining broad regional policies with targeted management in high risk areas at the catchment and farm scale.

The role of uncomposted materials, composts, manures, and compost extracts in reducing pest and disease incidence and severity in sustainable temperate agricultural and horticultural crop production - A review

This review evaluates evidence of the impact of uncomposted plant residues, composts, manures, and liquid preparations made from composts (compost extracts and teas) on pest and disease incidence and severity in agricultural and horticultural crop production. Most reports on pest control using such organic amendments relate to tropical or and climates. The majority of recent work on the use of organic amendments for prevention and control of diseases relates to container-produced plants, particularly ornamentals. However, there is growing interest in the potential for using composts to prevent and control diseases in temperate agricultural and horticultural field crops and information concerning their use and effectiveness is slowly increasing. The impact of uncomposted plant residues, composts, manures, and compost extracts/teas on pests and diseases is discussed in relation to sustainable temperate field and protected cropping systems. The factors affecting efficacy or such organic amendments in preventing and controlling pests and disease are examined and the mechanisms through which control is achieved are described.

Mitigation of diffuse phosphorus pollution during rewetting of fen peat soils: A trans-European case study

Intensive cultivation of fen peat soils (Eutric Histosols) for agricultural purposes, started in Europe about 250 years ago, resulting in decreased soil fertility, increased oxidation of peat and corresponding CO2-emissions to the atmosphere, nutrient transfer to aquatic ecosystems and losses in the total area of the former native wetlands. To prevent these negative environmental effects set-aside programs and rewetting measures were promoted in recent years. Literature results and practical experiences showed that large scale rewetting of intensively used agricultural Histosols may result in the mobilisation of phosphorus (P), its transport to adjacent surface waters and an accelerated eutrophication risk. The paper summarises results from an international European Community sponsored research project and demonstrates how results obtained at different scales and from different scientific disciplines were compiled to derive a strategy to carry out rewetting measures. A decision support system (DSS) for a hydrologically sensitive area in the Droemling catchment in north-eastern Germany was developed and is presented as a tool to regulate rewetting in order to control P release. It is demonstrated that additional laboratory experiments to identify essential processes of P release during rewetting and the site-specific management of the water table, the involvement of specific knowledge and experience of the stakeholders are necessary to develop an applicable DSS. The presented DSS is practically used to prevent freshwater resources from diffuse P pollution.

An inventory of heavy metals inputs to agricultural soils in England and Wales

An inventory of heavy metal inputs (Zn, Cu, Ni, Pb, Cd, Cr, As and Hg) to agricultural soils in England and Wales in 2000 is presented, accounting for major sources including atmospheric deposition, sewage sludge, livestock manures, inorganic fertilisers and lime, agrochemicals, irrigation water, industrial by-product 'wastes' and composts. Across the whole agricultural land area, atmospheric deposition was the main source of most metals, ranging from 25 to 85% of total inputs. Livestock manures and sewage sludge were also important sources, responsible for an estimated 37-40 and 8-17% of total Zn and Cu inputs, respectively. However, at the individual field scale sewage sludge, livestock manures and industrial wastes could be the major source of many metals where these materials are applied. This work will assist in developing strategies for reducing heavy metal inputs to agricultural land and effectively targeting policies to protect soils from long-term heavy metal accumulation. (C) 2003 Elsevier Science B.V. All rights reserved.

Hydrological controls on soil redox dynamics in a peat-based, restored wetland

Increasing areas of altered wetland are being restored by re-flooding the soil. Evidence in the literature indicates that this practice can induce the redox-mediated release of soil nutrients, thereby increasing the risk of diffuse water pollution. However, for the sake of improving wedand management decisions, there is a need for more detailed studies of the underlying relationship between the hydrological and redox dynamics that explain this risk; this is particularly the case in agricultural peatlands that are commonly targeted for the creation of lowland wet grassland. A 12-month field study was conducted to evaluate the relationship between hydrological fluctuations and soil redox potential (Eh) in a nutrient-rich peat field (32 g N kg(-1) and 1100 mg P kg(-1) in the surface 0-30 cm soil) that had been restored as lowland wet grassland from intensive arable production. Field tensiometers were installed at the 30-, 60- and 90-cm soil depths, and Pt electrodes at the 10-, 30-, 60- and 90-cm depths, for daily logging of soil water tension and Eh, respectively. The values for soil water tension displayed a strong negative relationship (P < 0.001) with monthly dip well observations of water table height. Calculations of soil water potential from the logged tension values were used, therefore, to provide a detailed profile of field water level and, together with precipitation data, explained some of the variation in Eh. For example, during the summer, alternating periods of aerobism (Eh > 330 mV) in the surface, 0-10 cm layer of peat coincided with intense precipitation events. Redox potential throughout the 30-100 cm profile also fluctuated seasonally; indeed, at all depths Eh displayed a strong, negative relationship (P < 0.001) with water table height over the 12-month study period. However, Eh throughout the 30-100 cm profile remained relatively low (< 230 mV), indicating permanently reduced conditions that are associated with denitrification and reductive dissolution of Fe-bound P. The implications of these processes in the N- and P-rich peat for wetland plant diversity and water quality are discussed. (c) 2006 Elsevier B.V. All rights reserved.