B.S. Gimeno

Nitrogen critical loads and management alternatives for N-impacted ecosystems in California

Empirical critical loads for N deposition effects and maps showing areas projected to be in exceedance of the critical load (CL) are given for seven major vegetation types in California. Thirty-five percent of the land area for these vegetation types (99,639 km(2)) is estimated to be in excess of the N CL. Low CL values (3-8 kg N ha(-1) yr(-1)) were determined for mixed conifer forests, chaparral and oak woodlands due to highly N-sensitive biota (lichens) and N-poor or low biomass vegetation in the case of coastal sage scrub (CSS), annual grassland, and desert scrub vegetation. At these N deposition critical loads the latter three ecosystem types are at risk of major vegetation type change because N enrichment favors invasion by exotic annual grasses. Fifty-four and forty-four percent of the area for CSS and grasslands are in exceedance of the CL for invasive grasses, while 53 and 41% of the chaparral and oak woodland areas are in exceedance of the CL for impacts on epiphytic lichen communities. Approximately 30% of the desert (based on invasive grasses and increased fire risk) and mixed conifer forest (based on lichen community changes) areas are in exceedance of the CL. These ecosystems are generally located further from emissions sources than many grasslands or CSS areas. By comparison, only 3-15% of the forested and chaparral land areas are estimated to be in exceedance of the NO(3)(-) leaching CL. The CL for incipient N saturation in mixed conifer forest catchments was 17 kg N ha(-1) yr(-1). In 10% of the CL exceedance areas for all seven vegetation types combined, the CL is exceeded by at least 10 kg N ha(-1) yr(-1), and in 27% of the exceedance areas the CL is exceeded by at least 5 kg N ha(-1) yr(-1). Management strategies for mitigating the effects of excess N are based on reducing N emissions and reducing site N capital through approaches such as biomass removal and prescribed fire or control of invasive grasses by mowing, selective herbicides, weeding or domestic animal grazing. Ultimately, decreases in N deposition are needed for long-term ecosystem protection and sustainability, and this is the only strategy that will protect epiphytic lichen communities.

Empirical and simulated critical loads for nitrogen deposition in California mixed conifer forests

Empirical critical loads (CL) for N deposition were determined from changes in epiphytic lichen communities, elevated NO(3)(-) leaching in streamwater, and reduced fine root biomass in ponderosa pine (Pinus ponderosa Dougl. ex Laws.) at sites with varying N deposition. The CL for lichen community impacts of 3.1 kg ha(-1) year(-1) is expected to protect all components of the forest ecosystem from the adverse effects of N deposition. Much of the western Sierra Nevada is above the lichen-based CL, showing significant changes in lichen indicator groups. The empirical N deposition threshold and that simulated by the DayCent model for enhanced NO(3)(-)leaching were 17 kg N ha(-1) year(-1). DayCent estimated that elevated NO(3)(-) leaching in the San Bernardino Mountains began in the late 1950s. Critical values for litter C:N (34.1), ponderosa pine foliar N (1.1%), and N concentrations (1.0%) in the lichen Letharia vulpina ((L.) Hue) are indicative of CL exceedance.

Evidence of ozone-induced adverse effects on crops in the Mediterranean region

Abstract The impacts of ambient ozone pollution on crops in the Mediterranean countries have been recorded regularly in the so-called “grey literature” of UN/ECE Workshop Reports for the Convention on Long-range Transboundary Air Pollution, and less frequently in the peer-reviewed literature. This short communication reviews such records and shows that ambient ozone episodes have been reported to cause visible injury on 24 agricultural and horticultural crops grown in commercial fields including three of the most important crops in the region (wheat, maize, and grapevine). On one occasion, the damage was so extensive that complete crop loss occurred in commercial glasshouses of Butterhead lettuce in one area of Greece. Experiments with open-top chambers have indicated that ambient ozone caused 17–39% yield loss in crops such as wheat, bean, watermelon and tomato. The applicability of the long-term critical level of ozone described by Fuhrer et al. (Environ. Pollut. 97 (1997) 91) for the Mediterranean areas is also considered.

An international cooperative programme indicates the widespread occurrence of ozone injury on crops

The UN/ECE ICP-Vegetation 1 routinely investigates the effects of ambient ozone pollution on crops throughout Europe. Each year, a series of co-ordinated ambient air experiments are conducted over a large area of Europe and a range of crop species are observed for the occurrence of injury following ozone episodes. In 1995 and 1996, ozone injury was observed at sites throughout Europe from United Kingdom (Nottingham) to the Russian Federation (Moscow) and from Sweden (Ostad) to Italy (Naples). The only site participating in the ICP-Vegetation where it was not observed was that at Finland (Jokioinen). Injury was identified on subterranean and white clover, French bean, soybean, tomato, and watermelon at one or more sites. Injury was also detected in gardens and on crops growing in commercial fields. Two short-term critical levels which incorporate ozone dose and air saturation vapour pressure deficit (VPD) were derived from the 1995 data. These were (i) an AOT40 2 of 200 ppb.h over 5 days when mean VPD (0930‐1630 h) is below 1.5 kPa and (ii) an AOT40 of 500 ppb.h over 5 days when mean VPD (0930‐1630 h) is above 1.5 kPa. In general, the 1996 data supported these critical levels although injury did occur on two occasions when the AOT40 was less than 50 ppb.h, and the VPD was less than 0.6 kPa. Thus, ICP-Vegetation experiments have shown that ozone injury can occur over much of Europe and that plants are most at risk in conditions of high atmospheric humidity. ©2000 Elsevier Science B.V. All rights reserved.

Effects of ozone concentrations on biogenic volatile organic compounds emission in the Mediterranean region

Abstract Measurements of air volatile organic compounds (VOCs) and ozone concentrations in different rural sites of Catalonia (NE Spain) were conducted during 1995 and 1996, and the effects of ozone concentrations on biogenic emissions of Mediterranean plants were studied in open top chambers. A significant positive relationship was found between tropospheric ozone and VOC concentrations, which followed seasonal (maximum in early summer and minimum in early winter) and geographical (slightly larger concentrations in interior than in coastal sites) patterns. Results in the open top chambers fumigation experiments showed species-specific responses. There was no significant effect of ozone on VOCs and terpene emission by Aleppo pines, Pinus halepensis L., but there was an order of magnitude increase in VOC emission with increasing tropospheric ozone concentrations (plus 40 nl L −1 ) in tomatoes, Solanum lycopersicum L. var. Tiny Tim. This response of tomato plants thus opens the possibility of a positive feedback for tropospheric ozone formation.

Agriculture-induced increase in nitrate concentrations in stream waters of a large Mediterranean catchment over 25 years (1981―2005)

Anthropogenic activities influence past and present nitrate levels recorded in European stream waters, posing a threat to aquatic biota and human beings. Scarce information on temporal trends of nitrate concentration and its causes is available for Mediterranean catchments. This study presents the evolution of nitrate concentrations over 25 years in stream waters of the Ebro River Basin (Spain), a large Mediterranean catchment involving 85,566 km(2). Nitrate concentration increased with time in 46% of the 65 sites involved in the study. Agricultural cover of 30 hydrologically independent sub-catchments was the main land use related to nitrate concentration (R(2)=0.69). Throughout the 25 year-period, the sites showing increased nitrate concentrations with time (trend sites) also presented an enhanced influence of agricultural cover on nitrate concentrations along the time frame of the study. As a result of these temporal changes, at the end of the studied period nitrate concentrations in stream waters responded similarly to agricultural cover in both trend and non-trend sites, showing non significant differences in the slope of the resultant regression models. At this time, agricultural cover explained 82% of the variability found in nitrate levels. If these trends remain unchanged, in 2015 many of the water bodies considered in this study would not comply with the requirements of the European Union Water Framework Directive (WFD). Therefore management decisions, mainly associated to agricultural practices, should be implemented as soon as possible at the catchment level to meet WFD objectives.

Biomonitoring ozone phytotoxicity in eastern Spain

High ozone (O3) levels have been recorded in eastern Spain. A project was developed to identify the areas of elevated O3 and determine if these levels were above critical concentrations for plant damage. Thus, a network of bioindicators was established in two Autonomous Communities of Spain: Catalunya (31.930 km2) and Valencia (23.305 km2) to assess O3 phytotoxicity. Three tobacco cultivars, (Bel-W3, Bel-C and Bel-B) were used during the 1994 growing season in both Regions. In Catalunya the highest O3 phytotoxicity was recorded in coastal areas, while the phytotoxicity decreased as plants were grown further in-land. A lower O3 phytotoxicity was observed in coastal sites of the Valencia Autonomous Community, compared to Catalunya, although the O3 injury was observed downwind from Valencia city in the most resistant cultivar Bel-B. The results in the Valencian Community were difficult to interpret, since plant viruses were widely distributed, not only in indicator plants, but also in commercial crops grown in the area. The analysis of O3 concentrations, meteorological parameters and visible injury at the Catalan sites showed that high relative humidity levels could favour O3 phytotoxicity. Therefore, the interactions between O3 exposure and environmental conditions on plant response should be further studied for the establishment of sound critical levels.

The Relative Sensitivity of Different Mediterranean Plant Species to Ozone Exposure

An experimental study was performed in open-top chambers to assess the relative O3-sensitivity of the following Mediterranean woody plants: Quercus ilex ssp. ilex, Quercus ilex ssp. ballota, Olea europaea ssp. sylvestris, Ceratonia siliqua and Arbutus unedo. Assessment of O3 ‘sensitivity’ was based on the development of O3-induced visible injury and the extent of the reduction in relative growth rate induced by O3. Two-year-old seedlings were exposed in open-top chambers to charcoal filtered air (CFA), Non-filtered air (NFA) or Non-filtered air supplied with 40 ppb O3 from 09:00 to 18:00 hours (NFA+40). No clear relationships were found between the development of visible injury and effects on plant growth or accumulated biomass. Olea europea ssp. sylvestris and Quercus ilex ssp. ballota appeared to be the most O3-sensitive tree species screened; a ten month exposure to ambient O3 levels (AOT40 = 12.4 ppm.h) caused reductions in height and/or stem growth. Further research is needed to characterise the physiological, biochemical and anatomical characteristics that may underlie the ‘sensitivity’ of certain Mediterranean species to O3

Sensitivity analysis of a parameterization of the stomatal component of the DO3SE model for Quercus ilex to estimate ozone fluxes

A sensitivity analysis of a proposed parameterization of the stomatal conductance (g(s)) module of the European ozone deposition model (DO(3)SE) for Quercus ilex was performed. The performance of the model was tested against measured g(s) in the field at three sites in Spain. The best fit of the model was found for those sites, or during those periods, facing no or mild stress conditions, but a worse performance was found under severe drought or temperature stress, mostly occurring at continental sites. The best performance was obtained when both f(phen) and f(SWP) were included. A local parameterization accounting for the lower temperatures recorded in winter and the higher water shortage at the continental sites resulted in a better performance of the model. The overall results indicate that two different parameterizations of the model are needed, one for marine-influenced sites and another one for continental sites.

Results from the UN/ECE ICP-crops indicate the extent of exceedance of the critical levels of ozone in Europe

The experiments of the United Nations/Economic Commission for Europe (UN/ECE) International Cooperative Programme on effects of air pollution and other stresses on crops and non-wood plants (ICP-Crops) are designed to investigate the effects of ambient ozone pollution on crops and non-wood plants. Each year, participants from approximately 17 European countries conduct a series of coordinated experiments to determine which species develop visible injury following ozone episodes and whether the biomass or yield of sensitive species is reduced. In 1993, ozone injury was only seen at two thirds of sites but in 1994 injury was detected at almost all sites. This coincides with generally higher ozone concentrations measured in that year. Injury was seen on crops including subterranean clover (Trifolium subterraneum L.), white clover (Trifolium repens L.), bean (Phaseolus vulgaris L.), tomato (Lycopersicon esculentum), soybean (Glycine max), watermelon (Citrullus lanatus) and tobacco (Nicotiana tabacum L.) at experimental sites and in some cases, in commercial fields. The application of ethylenediurea (EDU) to some crop species reduced the level of visible injury. At some sites, the yield of EDU-treated bean plants was greater than that of untreated plants where the critical level of ozone for yield reduction was exceeded. Preliminary analysis of ozone concentrations in the days preceding injury indicated a sequential ozone concentration effect. The results are discussed in relation to Level I and Level II mapping of exceedance of the short- and long-term critical levels for ozone.