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991.
The OSPAR Eutrophication Strategy requires assessment of eutrophication to be based on the ecological consequences of nutrient
enrichment and not just on nutrient enrichment alone, i.e. finding reliable evidence for accelerated growth of algae and higher
forms of plant life caused by anthropogenic nutrient enrichment, leading to undesirable disturbance. Fully flushed marine
waters of England and Wales (salinity >30) were assessed against OSPAR’s harmonised criteria of nutrient concentration and
ratios, chlorophyll concentrations, phytoplankton indicator species, macrophytes, dissolved oxygen (DO) levels, incidence
of fish kills and changes in the zoobenthos, using region specific thresholds. None of the thirteen assessment areas, including
six nutrient enriched areas, exhibited evidence for undesirable disturbance. This paper details the methods and the overall
outcome of the assessment. It presents evidence that undesirable disturbance caused by nutrient enrichment was not detected
in English and Welsh marine waters assessed under the OSPAR procedure. The main reasons for the lack of eutrophication problems,
such as the underwater light climate limiting the accelerated growth of algae, which might otherwise result from nutrient
enrichment, are discussed. 相似文献
992.
993.
994.
Spatial variability in nutrient concentration and biofilm nutrient limitation in an urban watershed 总被引:1,自引:0,他引:1
Nutrient enrichment threatens river ecosystem health in urban watersheds, but the influence of urbanization on spatial variation
in nutrient concentrations and nutrient limitation of biofilm activity are infrequently measured simultaneously. In summer
2009, we used synoptic sampling to measure spatial patterns of nitrate (NO3
−), ammonium (NH4
+), and soluble reactive phosphorus (SRP) concentration, flux, and instantaneous yield throughout the Bronx River watershed
within New York City and adjacent suburbs. We also quantified biofilm response to addition of NO3
−, phosphate (PO4
3−), and NO3
− + PO4
3− on organic and inorganic surfaces in the river mainstem and tributaries. Longitudinal variation in NO3
− was low and related to impervious surface cover across sub-watersheds, but spatial variation in NH4
+ and SRP was higher and unrelated to sub-watershed land-use. Biofilm respiration on organic surfaces was frequently limited
by PO4
3− or NO3
− + PO4
3−, while primary production on organic and inorganic surfaces was nutrient-limited at just one site. Infrequent NO3
− limitation and low spatial variability of NO3
− throughout the watershed suggested saturation of biological N demand. For P, both higher biological demand and point-sources
contributed to greater spatial variability. Finally, a comparison of our data to synoptic studies of forested, temperate watersheds
showed lower spatial variation of N and P in urban watersheds. Reduced spatial variation in nutrients as a result of biological
saturation may represent an overlooked effect of urbanization on watershed ecology, and may influence urban stream biota and
downstream environments. 相似文献
995.
Nitrogen export by surface runoff from a small agricultural watershed in southeast China: seasonal pattern and primary mechanism 总被引:1,自引:0,他引:1
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. 相似文献
996.
Gunnar W. Schade Sheena J. Solomon Ebba Dellwik Kim Pilegaard Annette Ladstätter-Weissenmayer 《Biogeochemistry》2011,106(3):337-355
In-canopy mixing ratio gradients and above-canopy fluxes of several volatile organic compounds (VOCs) were measured using
a commercial proton transfer reaction mass spectrometer (PTR-MS) in a European beech (Fagus sylvatica) forest in Denmark. Fluxes of methanol were bidirectional: Emission occurred during both day and night with highest fluxes
(0.2 mg C m−2 h−1) during a warm period; deposition occurred dominantly at daytime. Confirming previous branch-level measurements on beech,
the forest’s monoterpene emissions (0–0.5 mg C m−2 h−1), and in-canopy mixing ratios showed a diurnal cycle consistent with light-dependent emissions; a result contrasting temperature-only
driven emissions of most conifer species. Also emitted was acetone, but only at ambient temperatures exceeding 20°C. Slow
deposition dominated at lower temperatures. Our in-canopy gradient measurements contrast with earlier results from tropical
and pine forest ecosystems in that they did not show this beech ecosystem to be a strong sink for oxygenated VOCs (OVOCs).
Instead, their gradients were flat and only small deposition velocities (<0.2 cm s−1) were observed to the onsite soil. However, as methanol soil uptake was consistent and possibly related to soil moisture,
more measurements are needed to evaluate its soil sink strength. In turn, as canopy scale fluxes are net fluxes with stomatal
emissions from photosynthesizing leaves potentially affecting non-stomatal oxygenated VOC uptake, only independent, controlled
laboratory experiments may be successful in separating gross fluxes. 相似文献
997.
Sébastien Gogo Fatima Laggoun-Défarge Frédéric Delarue Nathalie Lottier 《Biogeochemistry》2011,106(1):53-69
Peatlands act as a sink of carbon (C) through the accumulation of dead remains of plants. Under global changes triggered by
human activities, it is not only the sink capacity of peatland that is in danger, but also the C already stored. Invasion
of Sphagnum peatlands, mainly by Molinia caerulea and Betula spp, is a growing preoccupation. This study aims to assess the extent of the influence of this invasion on the biochemical
characteristics of the peat. Elemental analysis, sugar and Rock–Eval pyrolysis parameters were measured in 50 cm profiles
collected in invaded and intact plots. The results show that oxygen index ratios (OICO2/OICO) can be used to detect new C substrate injection as invading plants have a lower ratio than Sphagnum spp and Sphagnum peat. Total hemicellulosic sugar contents and organic matter (OM) degradation indices (R400, PPI) suggest that the invading
plants promote a faster OM decomposition probably through a faster degradability and a relatively higher nutrient content
of their litter. Differences in terms of nutrient status between areas of the peatland are suggested to be of great importance
in determining the extent of OM transformation likely due to stoichiometric constraints. 相似文献
998.
Luís Vázquez Rosario Panadero Vicente Dacal Francisco Javier Pato Ceferino López Pablo Díaz María Sol Arias Gonzalo Fernández Pablo Díez-Baños Patrocinio Morrondo 《Experimental & applied acarology》2011,53(4):399-409
During the 2007 and 2008 hunting seasons (April–October) the skin of 367 roe deer (Capreolus capreolus L.), hunted in different preserves from Galicia (Northwestern Spain), were examined for ticks (Acari: Ixodidae). The overall
prevalence of infestation by ticks was 83.1%. The predominant species was Ixodes ricinus (83.1%), whereas a single Dermacentor marginatus specimen appeared in one roe deer. All developmental stages of I. ricinus were found parasitizing roe deer, the adults being the most frequent (82.2%), followed by nymphs (45.6%) and larvae (27.2%).
The mean intensity of infestation by I. ricinus was 43.2 ± 49.85; most of them were adults (30.7 ± 31.64) and in a lesser extend nymphs (16.9 ± 24.74) and larvae (10.7 ± 29.90).
Ixodes ricinus was present all over the study with percentages that oscillated between 100% in spring and 57.4% in autumn. CHAID algorithm
showed the sex of roe deer as the most influential factor in tick prevalence, followed by the climatic area. The different
developmental stages of I. ricinus were more frequent in males than in females, and the prevalence of adults and larvae were higher in roe deer from coastal
areas than in those from mountainous and central areas, whereas nymphs were more frequent in mountainous areas. Host age and
density were not determinants for tick infestation. Our results confirm that roe deer are important hosts for I. ricinus in northwestern Spain, serving as a vehicle for the geographic distribution of these ticks. 相似文献
999.
Lander Baeten Gorik Verstraeten Pieter De Frenne Margot Vanhellemont Karen Wuyts Martin Hermy Kris Verheyen 《Plant Ecology》2011,212(5):901-909
The colonization rates of understorey plants into forests growing on former agricultural land differ remarkably among species.
Different dispersal and recruitment largely account for the contrasting colonization rates, but different effects of the soil
legacies of former agricultural land use on plant performance may also play a role. Seven herbaceous forest species were sampled
in paired post-agricultural and ancient forest stands to study whether land-use history has an effect on the aboveground nutrient
concentrations (N, P and N:P ratios) and biomass of forest herbs and, if so, whether slow and fast colonizing species respond
differently. Results showed that P concentrations were significantly affected by former land use with higher concentrations
in the post-agricultural stands. N concentrations were unaffected and N:P ratios were significantly higher in the ancient
stands. Nutrient concentrations varied considerably among species, but the variation was unrelated to their colonization capacity.
Six out of the seven species had higher biomass in the post-agricultural stands relative to the ancient stands, and the degree
to which the species increased biomass was positively related to their colonization capacity, i.e., the fast colonizing species
showed the strongest increase. Such differential responses to past land use may contribute to the contrasting colonization
capacity of forest plants. Land-use history thus affected both the nutrient concentrations and biomass of forest herbs, and
only the biomass response was related to colonization capacity. 相似文献
1000.
Since the 1950s, agricultural intensification has affected the structure and functioning of ecological systems including wet
grasslands. Our study site, a wet grassland near Třeboň, Czech Republic, was historically a sedge meadow, but increased nutrient
additions, a long-lasting flood in 2002 and changed mowing patterns resulted in domination by Phalaris arundinacea. The aim of the study was to determine how different nutrient conditions may affect plant structure and production in a wet
grassland used for hay production. Species composition and percent cover were determined from line intercepts. Aboveground
biomass was harvested six times each in 2007 and 2008 and primary production then calculated. Ingrowth core bags were used
to determine belowground production. Aboveground production was two times greater in the high nutrient versus the low nutrient
area in both years, while belowground production was very similar. The high nutrient area was still dominated by P. arundinacea, but Carex gracilis was now a co-dominant in the low nutrient area. However, other factors, such as water level and mowing regime, may interact
with nutrient level to govern wet grassland structure and function. 相似文献