Residual phosphorus in runoff from successional forest on abandoned agricultural land: 1. Biogeochemical and hydrological processes

Soluble reactive phosphorus (SRP)concentrations measured in runoff fromabandoned agricultural land now in forestsuccession in the northeastern United Stateswere significantly higher than expected fromundisturbed forest land. This finding differsfrom P uptake in hardwood forest successionfollowing natural disturbance. Fieldmonitoring of a 16.6 ha old-field regrowthforest stand in the Catskills Mountains, NewYork, USA demonstrated runoff SRP trendsincluding an early summer flush that could notbe explained by simple dilution. An assay ofoutflow sediment and biomass, flowpath sedimentand biomass, forest floor leaf litter andbiomass, and Bh horizon mineral soil indicatedthat surface litter from the regrowth forestprovided the most significant contribution tothe elevated SRP in runoff. It is posited thatmicrobial mineralization of residual organic Pin surface litter coupled with the transientprocess of SRP mobilization at the soil surfaceresulting from a rising saturated layerfollowed by dissolution in surface runoff mayelevate SRP to the range observed. MeasuredSRP concentrations remain lower than reportedvalues for crop or pastureland. The resultsreported represent an important deviation fromthe prevailing view that forest land does notcontribute to eutrophication (based on enhancedP uptake in forest succession); this is aconsequence of residual P from landabandonment – a widespread practice throughoutthe northeastern US and other regions.     

The effect of diversity and spatial arrangement on biomass of agricultural cultivars and native plant species

Various spatial arrangements can be found within natural grassland plant populations and communities. In contrast, spatial arrangement diversity is typically not observed in agroecosystems. Little is known about the influence of spatial arrangement on the productivity and success of agricultural or native plants. Such information is of interest to farmers who want to increase yield and restorationists working with native ecosystems. Agricultural and native plants were planted in two-way mixtures that included combinations of cultivars, species, genera, or functional groups. Each combination was arranged as a random mixture within rows, alternating rows of the different genotypes or species, and as alternating pairs of rows. Aboveground biomass was determined for each mixture component and compared to monoculture controls. Though plot composition had the most consistent influence on aboveground biomass, spatial arrangement appeared to have some influence among agricultural cultivars. Whether native or agricultural, biomass was greater for mixtures containing both a grass and a legume.     

Comparison of the hydrological characteristics of three small experimental holm oak forested catchments in NE Spain in relation to larger areas

Precipitation and streamflow have been measured in three small (0.04–0.52 km²) experimental catchments covered by dense holm oak (Quercus ilex L.) forests. Two of them are in the Prades mountains and one in the Montseny mountains (NE Spain). Here we test the hydrological representativeness of these catchments against the streamflow record at two nearby larger (34–60 km²) catchments, one from each massif. Comparisons of (i) annual streamflow, (ii) seasonal distribution of streamflow, and (iii) flow duration curves were made. At Prades, for the period of common record, mean annual precipitation was about 580 mm, and mean annual streamflow 44–81 mm at the two experimental catchments and 102 mm at the larger one. Most streamflow occurred during winter and spring in the three catchments. At Montseny, rainfall was higher, and mean annual streamflow was 495 mm in the experimental catchment, and 760 mm in the larger catchment, though these data were obtained in different periods in each catchment. Streamflow was roughly equal in autumn, winter and spring. At both sites flow duration curves were fairly similar in the small experimental catchments and the larger catchments. The higher streamflow at Montseny is reflected in its flow duration curves being well above those at Prades. The experimental catchments at Prades are thus fairly representative of the larger nearby catchment for the investigated hydrological characteristics. At Montseny, hydrological differences between the experimental catchment and the larger catchment are probably due to the higher mean altitude of the latter and to the non-overlapping periods of their streamflow records.     

Nitrogen export by surface runoff from a small agricultural watershed in southeast China: seasonal pattern and primary mechanism

The seasonal pattern and primary mechanism of nitrogen (N) export by surface runoff from the Wuchuan subwatershed (WCW), an agricultural upper watershed (1.88 km²) located in southeast China, were investigated based on extensive streamwater measurements in 2004–2005 under subtropical climatic conditions. The results disclosed a highly variable but strong linkage between hydrological and anthropogenic controls and N export. N export via surface runoff presented a significant seasonal pattern caused by changes in rainfall and watershed N input. Approximately 75% of the annual N export (67 kg ha⁻¹) was flushed by those storm runoff mainly occurred during the wet season (March through September). The WCW dataset of N concentrations and loads during both baseflow and stormflow implied an interactive effects of anthropogenetic N input and hydrology conditions: N export was flush-driven in late spring, summer and autumn (wet season), but highly related with soil N in winter and early spring. Compared to undisturbed watersheds under similar rainfall conditions, WCW exported a considerable amount of N due to intensive fertilizer application (a mean of 690 kg N ha⁻¹ year⁻¹, commonly as surface applications). This work provides a first characterization of a small agricultural Chinese catchment under subtropical climates and its associated N export behavior.     

Assessing freshwater ecotoxicity of agricultural products in life cycle assessment (LCA): a case study of wheat using French agricultural practices databases and USEtox model

Purpose  

A life cycle assessment (LCA) was conducted on winter wheat, based on real agricultural practices databases, on a sample divided into four production scenarios. The main objectives of this study are (1) to assess the environmental impact of winter wheat, using an LCA covering field practices, and the transport and storage of grain until it is sold to a miller; (2) to use the USEtox model (Rosenbaum et al. in Int J Life Cycle Assess 13:532–546, 2008) to assess the part of the total freshwater ecotoxicity impact due to pesticide use, its variability among plots, and to identify the active ingredients with the strongest impact; (3) and with the help of fungicide, insecticide, herbicide experts, to identify active ingredients to replace these high-impact pesticides and estimate the effect of such a substitution on total freshwater ecotoxicity.     

Assessing the impact of local habitat variables and landscape context on riparian birds in agricultural,urbanized, and native landscapes

Large tracts of natural habitat are being replaced by agriculture and urban sprawl in Mediterranean regions worldwide. We have limited knowledge about the effects of human activities on native species in these landscapes and which, if any, management practices might enhance the conservation of native biodiversity within them. Through a citizen volunteer bird-monitoring project, we compared bird abundance and species richness in northern Californian riparian zones surrounded by vineyards, urban areas, and natural areas. We assessed both local and landscape-level variables that may enhance native bird diversity in each land use type. We also demonstrate a new statistical approach, generalized estimating equations, to analyze highly variable data, such as that collected by volunteers. Avian abundance was highly correlated with both landscape context and local habitat variables, while avian richness was correlated with local habitat variables, specifically shrub richness, and percent of tree cover. In particular, shrub species richness has a strong positive correlation with riparian-preferring bird species. This suggests that active local management of riparian zones in human-dominated landscapes can increase our ability to retain native bird species in these areas.     

The impact of spatial structure on the accuracy of contour maps of small data sets

Spatial analysis of insect counts provides important information about how insect species respond to the heterogeneity of a given sampling space. Contour mapping is widely used to visualize spatial pest distribution patterns in anthropogenic environments, and in this study we outlined recommendations regarding semivariogram analysis of small data sets (N < 50). Second, we examined how contour maps based upon linear kriging were affected by the spatial structure of the given data set, as error estimation of contour maps appears to have received little attention in the entomological domain. We used weekly trap catches of the warehouse beetle, Trogoderma variabile, and the accuracy assessment was based upon data sets that had either a random spatial structure or were characterized by asymptotic spatial dependence. Asymptotic spatial dependence (typically described with a semivariogram analysis) means that trap catches at locations close to each other are more similar than trap catches at locations further apart. Trap catches were poorly predicted for data sets with a random spatial structure, while there was a significant correlation between observed and predicted trap catches for the spatially rearranged data sets. Therefore, for data sets with a random spatial structure we recommend visualization of the insect counts as scale-sized dots rather than as contour maps.     

Assessing the impacts of agricultural intensification on biodiversity: a British perspective

Agricultural intensification is best considered as the level of human appropriation of terrestrial net primary production. The global value is set to increase from 30%, increasing pressures on biodiversity. The pressures can be classified in terms of spatial scale, i.e. land cover, landscape management and crop management. Different lowland agricultural landscapes in Great Britain show differences among these pressures when habitat diversity and nutrient surplus are used as indicators. Eutrophication of plants was correlated to N surplus, and species richness of plants correlated with broad habitat diversity. Bird species diversity only correlated with habitat diversity when the diversity of different agricultural habitats was taken into account. The pressures of agricultural change may be reduced by minimizing loss of large habitats, minimizing permanent loss of agricultural land, maintaining habitat diversity in agricultural landscapes in order to provide ecosystem services, and minimizing pollution from nutrients and pesticides from the crops themselves. While these pressures could potentially be quantified using an internationally consistent set of indicators, their impacts would need to be assessed using a much larger number of locally applicable biodiversity indicators.     

Assessing potential desertification environmental impact in life cycle assessment. Part 2: agricultural case study in Spain and Argentina

Purpose

Land use in dry lands can result in a final stage where land is completely depleted or entirely degraded causing the desertification phenomenon. The first part (part 1) of this series of two articles proposed a methodology to include desertification in life cycle assessment (LCA). A set of variables to be measured in the life cycle inventory, characterization factors, and an impact assessment method for the life cycle impact assessment phase were proposed. This second part (part 2) aims at showing the application of the model proposed in part 1 on two case studies of agricultural activities.

Methods

The impact model proposed is applied to plots of land devoted to agricultural activities in two countries: Argentina and Spain. In the agricultural plots of Spain (1SP to 9SP), two crops were analyzed: winter wheat (Triticum aestivum) and rapeseed (RS, Brassica napus). Two crops were considered in the Argentinean case study: rapeseed (RS, B. napus) and digit grass (Digitaria eriantha) (10AR to 17AR). A bare soil state is considered in both countries as a reference state. Both case studies consider only the agricultural stage in the inventory of a complete life cycle assessment study. Both also consider only one impact category in life cycle environmental assessment: desertification impact due to land occupation.

Results and discussion

On the basis of the obtained results, it can be inferred that cultivating 1 ha of rapeseed and 1 ha of wheat has the same impact on the analyzed plots in Spain and improves the reference state conditions in 50 % of the cases. Moreover, rapeseed grown in Mendoza produces almost the same impact as in some of the Spanish plots. Normalized areas of plots could be useful to compare results in different regions of the world to avoid the influence of the area of occupation in results.

Conclusions

The proposed model implies a contribution of significant importance because so far there has not been an impact assessment tool for land use in dry lands within the LCA framework. The main strength of the proposed model is that it allows a simple way to quantify the desertification impact. Also, it is emphasized that the model can be adapted virtually without difficulty to the evaluation of all types of crops with different management practices in different regions in the life cycle impact assessment stage.     

Dissolved organic carbon concentrations in runoff from shallow heathland catchments: effects of frequent excessive leaching in summer and autumn

Transport and turnover of dissolved organic carbon (DOC) is important in the C cycle of organic soils. The concentration of DOC in soil water is buffered by adsorption to the soil matrix, and has been hypothesized to depend on the pool size of adsorbed DOC. We have studied the effect of frequent artificial excessive leaching events on concentration and flux of DOC in shallow, organic rich mountain soils. Assuming a constant Kd value for DOC adsorption to the soil matrix, we used these data to assess the change in the pool of adsorbed (or potential) DOC in the soil. The study involved manipulation of precipitation amount and frequency in summer and autumn in small, heathland catchments at Storgama, southern Norway. The shallow soils (16–34 cm deep on average) limit the possibility for changes in water flow paths during events. The mini-catchments range in size from 75 to 98 m². Our data show that after leaching of about 1.2 g DOC m⁻² the DOC concentration in runoff declines by approximately 50%. From this we conclude that the pool size of adsorbed potential DOC in the shallow soils at any time is of the order 2–3 g m⁻². Frequent episodes suggest that the replenishment rate, which depends on the decomposition rate of soil organic matter, is fast and the potential DOC pool could be fully restored probably within days during summer, but with some more time required in autumn, due to lower temperatures. Both pool size of potential DOC and replenishment rate are seasonally dependent. The pool of potential DOC, and thus the DOC concentration in discharge, is at their maximum in the growing season. However, under non-leaching conditions, the concentration of DOC in soil water and thus the pool size of potential DOC seems to level off, possibly due to conversion of DOC to less reversibly bound forms, or to further decomposition to CO₂.     

Assessing the impact of land-use change on soil C sequestration in agricultural soils by means of organic matter fractionation and stable C isotopes

Within the framework of the Kyoto Protocol, the potential mitigation of greenhouse gas emissions by terrestrial ecosystems has placed focus on carbon sequestration following afforestation of former arable land. Central to this soil C sequestration are the dynamics of soil organic matter (SOM). In North Eastern Italy, a mixed deciduous forest was planted on continuous maize field soil with a strong C₄ isotopic C signature 20 years ago. In addition, a continuous maize field and a relic of the original permanent grassland were maintained at the site, thus offering the opportunity to compare the impacts on soil C dynamics by conventional agriculture, afforestation and permanent grassland. Soil samples from the afforested, grassland and agricultured systems were separated in three aggregate size classes, and inter‐ vs. intra‐aggregate particulate organic matter was isolated. All fractions were analyzed for their C content and isotopic signature. The distinct ¹³C signature of the C derived from maize vegetation allowed the calculation of proportions of old vs. forest‐derived C of the physically defined fractions of the afforested soil. Long‐term agricultural use significantly decreased soil C content (?48%), in the top 10 cm, but not SOM aggregation, as compared to permanent grassland. After 20 years, afforestation increased the total amount of soil C by 23% and 6% in the 0–10 and in the 10–30 cm depth layer, respectively. Forest‐derived carbon contributed 43% and 31% to the total soil C storage in the afforested systems in the 0–10 and 10–30 cm depths, respectively. Furthermore, afforestation resulted in significant sequestration of new C and stabilization of old C in physically protected SOM fractions, associated with microaggregates (53–250 μm) and silt&clay (<53 μm).     

Hydrochemical modeling of coupled C and N cycling in high-elevation catchments: Importance of snow cover

Several ecosystems in the western US are already undergoing nitrogen (N)saturation, a condition where previously N limited ecosystems are no longer Nlimited. This state of N saturation leads to adverse impacts on terrestrialecology and water quality. Due to the complexities of terrestrialcarbon-nitrogen cycling, integrated hydrologic-biogeochemical modeling providesa tool to improve our understanding and discern between the impacts of changesin N deposition from changes in other ecosystem processes. A model ofbiogeochemical processing in alpine watersheds was developed and applied to theEmerald Lake watershed. Simulations of major terrestrial carbon and nitrogenpools and fluxes were adequate. The use of snow cover information to estimatesoil temperatures improved model simulations indicating that snow coverprocesses need to be incorporated into biogeochemical models of seasonally snowcovered areas. The model simulated mineral nitrogen processes well butsignificant changes in denitrification and dissolved organic nitrogen exportprocesses appear to be necessary. Ourresults also showed that variations in snow cover duration have more of animpact on mineral N export, plant uptake and mineralization than appearspossible due to changes in atmospheric deposition.     

Study on the removal of pesticide in agricultural run off by granular activated carbon

In this batch study, the adsorption of malathion by using granular activated carbon with different parameters due to the particle size, dosage of carbons, as well as the initial concentration of malathion was investigated. Batch tests were carried out to determine the potential and the effectiveness of granular activated carbon (GAC) in removal of pesticide in agricultural run off. The granular activated carbon; coconut shell and palm shells were used and analyzed as the adsorbent material. The Langmuir and Freundlich adsorption isotherms models were applied to describe the characteristics of adsorption behavior. Equilibrium data fitted well with the Langmuir model and Freundlich model with maximum adsorption capacity of 909.1 mg/g. The results indicate that the GAC could be used to effectively adsorb pesticide (malathion) from agricultural runoff.     

Estimation of nitrate removal by riparian wetlands and streams in agricultural catchments: effect of discharge and stream order

1. Assessment of the role of landscape structures such as buffers is a necessary prerequisite for the sustainable management of water resources in an agricultural setting. 2. We monitored nitrate concentrations during interstorm periods at the outlet of 16 subcatchments of different orders within a catchment of 378 km². We characterised stream network, wetlands, agricultural practices and land cover and identified their relationships with nitrate fluxes and concentrations. 3. Two main factors controlled annual nitrate fluxes: the agricultural nitrogen surplus and the nature of the system comprising the wetland zone and adjoining watercourses. In the latter case, nitrate fluxes were reduced in proportion to the surface area of the riparian wetland and the flowpath distance of fluxes in the stream network. At the scale of the order‐6 stream, 53% of annual nitrate flux during interstorm periods was removed during transfer via the wetland and the river, corresponding to 21.1 kg N ha^?1 per year. 4. The influence of the riparian wetland zone/watercourse system increased during periods of low water level, explaining up to 64% of nitrate concentration variation among locations within the river network, but only 9% during periods of high water level. 5. The buffering role was stronger at higher stream orders, and the dependence on stream order was more apparent at low water level, when we observed mean nitrate concentrations in the order‐6 stream that were 47% lower than observed in order‐2 or order‐3 streams.     

Tetracycline-inducible Expression Systems： New Strategies and Practices in the Transgenic Mouse Modeling

To accurately analyze the function of transgene(s)of interest in transgenic mice,and togenerate credible transgenic animal models for multifarious human diseases to precisely mimic human dis-ease states,it is critical to tightly regulate gene expression in the animals in a conditional manner.The abilityto turn gene expression on or off in the restricted cells or tissues at specific time permits unprecedentedflexibility in dissecting gene functions in health and disease.Pioneering studies in conditional transgene ex-pression have brought about the development of a wide variety of controlled gene expression systems,whichmeet this criterion.Among them,the tetracycline-controlled expression systems(e.g.Tet-off system andTet-on system)have been used extensively in vitro and in vivo.In recent years,some strategies derived fromtetracycline-inducible system alone,as well as the combined use of Tet-based systems and Cre/lox P switch-ing gene expression system,have been newly developed to allow more flexibility for exploring gene functionsin health and disease,and produce credible transgenic animal models for various human diseases.In thisreview these newly developed strategies are discussed.