Short-term Environmental Changes Research Articles

Photosynthesis of Lettuce Exposed to Different Short Term Light Qualities

The objectives of this study were to investigate the effect of short-term changes in the spectral environment on photosynthesis. Lettuce (Lactuca sativa) plant were grown under red-greenblue (RGB) light-emitting diodes (LEDs) for 23 d and then given 24-h exposure to red (R), redgreen (RG), or red-blue (RB) LEDs. Photosynthetic rates (Pn) were measured before the 24-h exposure, after 24-h exposure, and 24 h after returning to the original RGB lighting. Temporary changes in spectral quality affectedPn. The effects of the different light treatments onPnreversed after returning to the initial light source. This study showed thatPnwas responsive to spectral quality in the short-term and is not directly coupled to stomatal conductance.

Short-term environmental changes in Lake Morenito (41°S, 71°W, Patagonia, Argentina) from the analysis of sub-fossil chironomids

1.A short sediment core from Lake Morenito was studied to assess the impact of environmental changes on chironomid communities occurring during the last ca 100 yr. 2.Lake Morenito (41°S, 71°W) is located 20 km west of the city of Bariloche, in northern Patagonia, Argentina. Before 1960, this lake was a branch of Lake Moreno; by that time, an artificial dam closed the system, establishing the new lake. Another human disturbance that took place during the time span of the core was the introduction of salmonids to the area ca 1910. 3.The most important natural events that occurred in the area during the last 100 yr were related to volcanic episodes. One of them, occured in Chile in 1960 affecting the Argentinian side, coincided with the dam's construction. 4.Changes in the chironomid community were recorded by studying the sub-fossil remains (the chitinized head capsule of the larvae) present in the sedimentary sequence. The results show that volcanic tephra layers deposited along the core led to a sharp instantaneous drop in the diversity and abundance of chironomid assemblages. Human activities are also associated with a change in chironomid community composition. 5.Chironomus reached its maximum abundance values in 1910 and 1960. The organic matter content also increased at the same time. The increase of Chironomus after 1910 is clearly related to an increase in the trophic status of the lake. However, owing to the synchronicity of events in 1960, i.e. the volcanic event and the dam's construction, it is difficult to establish whether the change in the chironomid assemblage was in response to an increase in trophic enrichment, to natural disturbance, or both. Copyright © 2004 John Wiley & Sons, Ltd.

A record of long- and short-term environmental and climatic change during OAE3: La Luna Formation, Late Cretaceous (Santonian–early Campanian), Venezuela

The La Luna Formation was deposited under anoxic/dysoxic conditions in a tropical epicontinental sea on the northwest South America margin. Sedimentological, micropaleontological and geochemical evidence provides insights into factors that influenced the sedimentation and controlled the accumulation of organic-rich deposits at decimeter and meter scales during the youngest of the Cretaceous oceanic anoxic events (OAE). The La Luna Formation consists of an alternation of black marlstones interbedded with black limestones and black marly limestones. The benthic foraminifera assemblages indicate sedimentation in the upper neritic to upper bathyal environment. These rocks contain large amounts of organic matter. It is interpreted that a combination of warm global and rainy climate and the presence of bathymetric barriers caused poor circulation and low rates of water column ventilation during a high sea level in the early Santonian leading to the preservation of carbon-rich deposits in this region. During the late Santonian, a cooling-trend in global climate increased wind strength and upwelling; this change probably reduced runoff causing a weakening of the pycnocline and destabilized the stratification in the water column providing a progressive increase in oxygen in the water column and on the sea floor and a decrease in total organic carbon preservation in a shallower basin. These changes and the establishment of full mid- and deep-water exchange in response to the deepening and widening of the Equatorial Atlantic Gateway could have been important mechanisms for ending the epeiric sea anoxia. Changes through time in the vanadium–nickel fraction, planktonic and benthic foraminifera assemblages, productivity proxy elements, and lithological characteristics support this model. Superimposed on the general trend, variations in calcium carbonate and total organic carbon percentages at the scale of tens of centimeters reveal high frequency cyclic variations, which apparently correspond to the main frequencies of orbital forcing. This cyclicity is interpreted as a primary depositional signal and is the result of orbital-controlled fluctuations in terrigenous dilution and variations in oxygen concentration at the base of the water column. Variations in the intensity of upwelling can be observed, but they did not control the cyclicity.

Critical salinity, sensitivity, and commitment of salinity-mediated carbonic anhydrase induction in the gills of two euryhaline species of decapod crustaceans

Two euryhaline species of decapod crustaceans, Carcinus maenas and Callinectes sapidus, were subjected to a series of acute low-salinity challenges, and changes in carbonic anhydrase (CA) activity in the gills were monitored in order to characterize the nature of salinity-sensitive CA induction. CA activity is uniformly low in all gills of both species at high salinity, but at a critical salinity of 27 ppt, CA induction occurs in the posterior, ion-transporting gills, with CA activity approximately doubling. This salinity occurs right at, or slightly above, the point at which these species make the transition from osmoconformity to osmoregulation. The regulatory mechanism that controls the levels of CA expression after the initial induction has occurred is also very sensitive. Changes in CA activity occur in response to changes in salinity as small as 20 milliosmoles. CA induction only occurs after a critical minimum amount of time of exposure to low salinity (48-72 hr in C. maenas and 12 hr in C. sapidus), but once induction is begun, it continues regardless of subsequent salinity changes. The timing is most likely due to the time it takes for changes in gene expression and resultant increases in CA mRNA to occur in response to low-salinity exposure, and the delay in CA induction could be an adaptation to avoid making metabolically expensive responses to potentially short-term environmental changes.

Land–sea correlations for the last glaciation inferred from a pollen and dinocyst record from the portuguese margin

Pollen and dinoflagellate cyst assemblages from Core SU 81-18 recovered off Portugal (37°46′N, 10°11′W; 3135-m water depth) have been used to document the short-term environmental changes that occurred in southwest Europe since 25,000 yr B.P. The relationship between the oceanic and continental environments has been further examined by the use of other marine proxies (coarse sedimentary fraction, foraminifera) and by comparison with proximal land pollen records. Heinrich 2 (H2) and Heinrich 1 (H1) events were the most extreme parts of the highly variable last glacial period, with the maximum extension of dry steppe on land and the occurrence of cool and dilute waters at the core site. Our study shows that H1 and H2 are divided in two distinct phases: one with Neogloboquadrina pachyderma left coiling associated with the maximum input of ice rafted debris, reflecting the in situ release of icebergs and the occurrence of cool and dilute seawater at the core site; the other with dinoflagellate cysts of subpolar affinity, Bitectatodinium tepikiense, reflecting a seasonal control marked by warm summer SST and cold winter SST.

Carbon flux through the microbial community in a temperate sea during summer: role of bacterial metabolism

The carbon flux through bacterioplankton under oligotrophic conditions was studied during summer in the southern Bay of Biscay. An episode of coastal upwelling during our study allowed us to look at how bacterial metabolism responded to short-term environmental changes. Gross primary production (GPP) was significantly higher after the upwelling pulse; however, micro- bial respiration (R) exceeded the organic carbon fixation by primary producers (R > GPP), resulting in net heterotrophic balance during summer (net community production (NCP) < 0). Heterotrophic bac- teria were the major contributors to bulk community respiration, accounting for 70% of the total respiration. The variability in both bacterial respiration and plankton respiration was largely attrib- utable to differences in the dissolved organic carbon (DOC) concentration. The ratio of bacterial bio- mass to total phytoplankton biomass decreased after the upwelling pulse, whereas the bacterial pro- duction to primary production ratio increased as the productivity of the system increased. Bacterial production was always significantly lower than bacterial respiration, giving rise to a bacterial growth efficiency (BGE) lower than 10%. BGE responded to changes in phytoplankton production, increas- ing as the system became more productive. Short-term variations in the structure of the water column may have an important impact on bacterial processes within this oligotrophic system.

Sulphur release from flood lava eruptions in the Veidivötn, Grímsvötn and Katla volcanic systems, Iceland

Abstract Emissions of SO 2 by volcanic eruptions have been shown to be important for short-term environmental and climate changes. Stratospheric sulphur mass-loading by explosive silicic eruption is commonly considered to be the principal forcing factor for these changes. The SO 2 emissions from basaltic flood lava eruptions have not featured strongly in the discussions on volcano-climate interactions, notwithstanding the fact that basaltic magma is typically richer in sulphur (by a factor of two to four), than silicic magmas, as well as the evidence of widespread atmospheric impact associated with historical flood lava eruption. Fourteen Holocene flood lava eruptions are known from the Veidivötn, Grímsvötn, and Katla volcanic systems of the Eastern Volcanic Zone in South Iceland, which include the three largest of its kind in Iceland; the 1783–1784 Laki, 934–40 Eldgjá, and c. 8600 years BP Thjórsá events. We present new data on the sulphur content in melt inclusions from the Veidivötn system and use this information, along with existing inclusion data from the Grímsvötn and Katla volcanic systems, to establish an empirical method for estimating the sulphur mass release from these basaltic flood lava eruptions. The results show that these eruptions released a total of c. 700 Mt SO 2 into the atmosphere in four 600- to 850-year-long eruption periods. During each period, between 98 and 328 Mt SO 2 were emitted into the atmosphere, and the mass loadings from individual eruptions ranged from 5 to 210 Mt SO 2 . These flood lava eruptions are likely to have resulted in widespread atmospheric perturbations and, by analogy with the 1783–1784 Laki eruption, the effects of the largest eruptions may have been felt on a hemispheric scale.

ESR dating of a subfossil shell from Couve Island, Ubatuba, Brazil

The occurrence of subfossil material in bottom sediments of Couve Island, Ubatuba region, São Paulo State, is confirmed. The analyzed material consists of a bivalve shell that was dated by the electron spin resonance technique. By the additive irradiation method an archaeological absorbed dose of (25±5) Gy was obtained and calibration with other dating works in the same area allows the inference of an age of (25±5)×10 2 years. The importance of this finding and its paleoecological implications could contribute to elucidating the nature of short-term environmental changes in the Brazilian coastline during the Holocene, as well as becoming an important tool to the understanding of the distribution and biological aspects of the bivalve fauna.

A new laboratory method for monitoring deep-water coral polyp behaviour

Deep-water corals are found along the oceanic margins world-wide and in the north east Atlantic the most abundant species is Lophelia pertusa (L.). There is now growing evidence that deep-water reefs formed by such species are coming under increasing pressures from resource exploitation, principally deep-sea trawling and hydrocarbon exploration. Here a novel and unobtrusive method of recording deep-water coral behaviour in the laboratory is described using time-lapse video to record silhouettes of the polyps under infrared illumination. The polyps of L. pertusa behaved asynchronously and did not show any clear diurnal patterns over a three-day observation period. Conceptually, sessile benthic suspension feeders appear to be vulnerable to smothering by sediments disturbed by bottom trawls or sub-seabed drilling. This method allows deep-water coral polyp behaviour to be continuously monitored in the laboratory and, therefore, the responses of coral polyps to environmental perturbations such as sedimentation can be recorded. Further work is necessary to resolve the sensitivity of deep-water corals to short-term environmental change and the combined approach of in situ monitoring and subsequent laboratory experimentation has great potential to address these issues.

Rapid (10-yr) recovery of terrestrial productivity in a simulation study of the terminal Cretaceous impact event

Investigations of short-term (up to 10 3 yr) environmental change across the Cretaceous–Tertiary boundary provide evidence for reduced temperatures, consistent with the injection of debris and sulphate aerosols into the upper atmosphere by a large impact event. Concomitant with this was a postulated massive addition of CO 2 to the atmospheric carbon reservoir by impact vaporisation of the Chicxulub carbonate platform. Taken together, a high CO 2 but low irradiance environment would have created unusual conditions for the operation of the terrestrial biosphere. Here, we have evaluated this environmental influence on terrestrial ecosystems using a process-based dynamic global vegetation model forced with post-impact global climates, derived by modification of the GENESIS atmospheric climate model simulation for the latest Cretaceous. Our results suggest that terrestrial primary productivity initially collapsed and then recovered to pre-impact levels within a decade. Global terrestrial carbon storage in vegetation biomass exhibited a similar collapse but complete recovery took place on a 60–80 yr timescale. The recovery of both terrestrial net primary productivity and vegetation biomass was largely mediated by the high CO 2 concentration stimulating ecosystem photosynthetic productivity in the warm low latitudes. An apparently rapid recovery of terrestrial ecosystem function stands in marked contrast to the situation for the marine realm, where the organic carbon flux to the deep ocean was suppressed for up to 3 million years.

Short-term environmental change in a Jurassic lagoon deduced from geochemical trends in aragonite bivalve shells

The Bathonian age Inverbrora Member of the Brora Coal Formation, northern Scotland, was deposited in a predominantly fresh- water coastal lagoon setting. However, two prominent shell beds within the mostly argillaceous succession have been interpreted as resulting from temporary inundation of marine water and establishment of brackish conditions. The ensuing lagoon hydrology and paleoenvironment were investigated by measuring stable isotopic (δ18O and δ13C) and trace element (Mg, Sr, Mn, Ba) variations within five exceptionally well preserved aragonite shells of the bivalve Isognomon murchisoni . Transects were sampled across the visible growth banding with a resolution of 0.25−0.15 mm for stable isotopes, and 0.05 mm for trace elements. Oxygen and carbon isotope data define a broadly covariant trend (δ18O between +0.4‰ and −4.8‰ Peedee belemnite [PDB]; δ13C between +2.2‰ and −0.7‰ PDB) that supports a variably brackish-water setting with slight seasonal evaporation. Absolute trace element values vary from shell to shell but show consistent patterns of covariation. Profiles of Mg/Ca across shell layers display multiple sharp, episodic minima that are coincident with peaks in Sr/Ca and Ba/Ca. This is interpreted as documenting inundation of the restricted, brackish-water lagoon by relatively cooler seawater, leading to a temporary increase in metabolic activity of the bivalves. Less frequent minima in Mg/Ca, Sr/Ca, δ18O, and δ13C record fresh-water influx and dramatic salinity reduction in the lagoon. Bivalve metabolic efficiency was decreased, and in some cases breaks in shell growth occurred. This study shows that in hydrodynamically complex settings, trace element variation in bivalve shells can provide a detailed record of short-term environmental change.

Short-term variation and long-term changes in the oceanographic environment and zooplankton community in the vicinity of a sub-Antarctic archipelago

Mesozooplankton community structure in the vicinity of the Prince Edward Islands (PEIs) was investigated during six surveys conducted in late austral summer (April/May) from 1996 to 1999. Zooplankton samples were collected by oblique tows using a Bongo net fitted with 300-μm mesh. Surface temperature, average temperature and chlorophyll a were measured in conjunction with each net tow. The positions of the Sub-Antarctic Front (SAF) and the Antarctic Polar Front (APF), in relation to the islands, were determined by CTD and/or XBT transects to the west of the islands (upstream). Both fronts were characterized by a high degree of latitudinal variation. Changes in position of the fronts occurred rapidly, the SAF moving up to ∼120 km in a 2-week period. Consequently, the oceanographic environment in the vicinity of the PEIs was subject to a high degree of intra- and inter-survey variation. The positions of the SAF and APF appeared to have a significant impact on phytoplankton biomass in the vicinity of the PEIs, possibly through the alteration of local oceanographic flow dynamics. Water retention over the island shelf in 1996, associated with location of the SAF far to the north of the PEIs, corresponded to enhanced chlorophyll-a concentrations (∼1.54 mg m−3). Conversely, when the fronts were close to the islands, as in 1997 and 1999, higher current velocity limited water retention and chlorophyll-a concentrations in the inter-island region were relatively low (∼0.4 mg m−3). Cluster analyses showed that, in many instances, there was greater similarity among zooplankton communities from different surveys than among communities within surveys, indicating that short-term variability exceeded inter-annual variability. The population structure of the copepod Calanus simillimus indicated that there was inter-annual variation in the timing of the biological season. Differences in the population structure of species, and consequently their contribution to abundance and biomass, may therefore have been an important contributor to inter-annual variation in community structure. Evidence is provided of a long-term southward shift in the position of the SAF. It is postulated that this may affect the PEIs by increasing the proportion of allochthonous energy input, because the PEIs now lie in the path of the front, altering the tropho-dynamics of the island ecosystem. Lower mesozooplankton biomass associated with warmer sub-Antarctic water may have important negative consequences for higher trophic levels that depend on mesozooplankton for food.

Dynamics in the News Coverage of Minorities: The Case of the Arab Citizens of Israel

Most previous research in communication has looked at media coverage of minorities as a mostly static process in which journalists continually produce the same news stories. This article proposes a more dynamic approach that explains how such coverage can change over time and circumstance, and examines two factors that can alter the ways in which the news media cover minorities: short-term changes in the sociopolitical environment and changes in editorial policies. The case study looks at the Arab citizens of Israel. The findings demonstrate two changes that had an influence on the extremely negative portrayal of this minority in the Israeli media. The first was rooted in political changes during the election year 1992, when the Rabin government depended on the Arab parties to stay in power. The second variation was linked to the editorial policies of an elitist newspaper that set up alternative structures and routines for ongoing coverage of the Arab minority.

Collembolan community organization and its temporal predictability

Summary Long-term investigations on Collembola in Russian forests revealed that both stable and fluctuating communities can exist in natural ecosystems. Stable collembolan communities are characteristic of mesic moisture conditions, whilst fluctuating communities are typical of either xeric or hygric habitats. Stable communities are determined by between-year constancy in species and ecological structures, though other characteristics (for instance, total collembolan abundance or number of species) can vary. Stability of collembolan communities is externally stimulated by the constancy of environmental conditions or by their cyclic changing. Stable collembolan communities are best suited for the bioindication of long-term anthropogenic impacts on natural ecosystems, whereas fluctuating communities better reflect short-term environmental changes. A temporal predictability is possible only for stable communities.

Cautionary Tales: Adaptation and the Global Poor

Many who study global change, particularly from industrialized countries, are optimistic about the capacity of agriculture to successfully adapt to climate change. This optimism is based on historic trends in yield increases, on the spread of cropping systems far beyond their traditional agroecological boundaries, and the inherent flexibility of systems of international trade. Analysis of the success (or in rare cases, failure) of adaptation is by analogy—either to analogous socioeconomic or technological change or to short term environmental change. Such studies have been limited to industrialized countries.

A late Holocene record of environmental changes from coastal wetlands: Abel Tasman National Park, New Zealand

article size, organic content, loss on ignition (LOI), geochemistry, radiocarbon and 137Cs analyses were carried out on paired cores taken from Wainui, Totaranui and Awaroa Inlets, Abel Tasman National Park. A 1700 year record of long- and short-term environmental changes was produced representing a sedimentary and geochemical sequence from tidal flat to mature salt marsh. The sequence is punctuated by a series of short-term environmental changes, namely tsunami, establishment of salt marsh, and European settlement. Long-term environmental changes include fluctuating accretion rates and relative sea level rise. Tsunami “signatures” include: (i) a peak in fines, (ii) contemporaneous or “delayed” peak in organic content and/or LOI, (iii) contemporaneous peaks in Fe and/or S, (iv) dilution of anthropogenic contaminants, and (v) visible change in the sediments. Ruptures of the Wellington and West Wairarapa Faults are considered to be the tsunamigenic sources. Pre-European sediment accretion rates in Abel Tasman National Park range from 0.5 to 1.7 mm/a, with post-European settlement rates increasing to 1.6–2.7 mm/a. In the past 30 years, rates have increased to 2.3–3.3 mm/a. The component of relative sea level rise is estimated to be about 1.3–2.2 mm/a which compares favourably with the nearest tidal records from Wellington.

Stickstoff- und Kohlenhydratspeicherung in Rhizomen von Phragmites australis ( Cav.) Trin. ex Steudel an unterschiedlichen aquatischen Standorten oberbayerischer Seen

Nitrogen and carbohydrate utilization in Phragmites australis rhizomes was investigated under natural conditions at 10 sites in 5 lakes in Upper Bavaria over a period of two years. Nitrate and ammonium of surface and interstitial water was determined. The results indicate that conditions of habitat and environment, such as climate and fluctuation of water level, lead to different adaptations of reed. These parameters had an effect on the storage of nitrogen and carbohydrate. The reed stands exposed to high water level during spring and summer have a high carbohydrate content in the rhizomes. A positive correlation was shown between the aboveground biomass and the content of storaged carbohydrates during the vegetation period. No relationship could be demonstrated between the nitrogen availability of the habitats and the type of storage of carbohydrates and nitrogen. The nitrogen content in the rhizomes can be used as an indicator of the ability of reed stands to produce new secondary shoots after shoot loss. The differently established reed genotypes are not able to compensate short-term environmental changes, such as growing leisure problems and higher shoot loss by the increasing appearance of waterfowl, from their reserve storage.

Desertification and drylands development: what can be done?

By analysing the concept of desertification and the evolution of its definitions, five main themes were selected. The perception of the causes of desertification has shifted from blaming colonization to climate change and finally to the traditional land-use systems. In the 1960s in Africa, the trend was to attribute land degradation to sectorial development during colonization. During the 1970s, essentially because of UNEP efforts, middle-term climate changes and short-term droughts were considered as causes of desertification, while distinguishing meteorological, hydrological, edaphic and agricultural droughts. The consensus view of the last decades now is that desertification is primarily human induced: among them the effects of traditional indigenous land management and of imported exogenous land management can be distinguished. To separate climate-induced, short-term environmental changes from land degradation induced by human activities is impossible. What can be achieved in drylands? It is obviously erroneous to propose dry ecosystem development on the model of highly mechanized developed countries. Drylands development requires much more input, leading to accelerated waste production. It cannot follow the same scheme as in temperate or in wet-tropical ecosystems. They need higher investment and risk more irreversible land degradation. The drylands are financial sinks. Rehabilitation of the environment together with demographic control should have priority. Finally, preference should be given to small projects of irrigation rather than huge complex plans. © 1998 John Wiley & Sons, Ltd.

Effects of a Short-term Environmental Change on a Brackish-water Polychaete Community

. Aquatina lake is a brackish basin, connected with the Adriatic Sea along the mast of Apulia (Italy), with a mean salinity of 26%. The abundance and biomass of fifteen polychaete species were recorded by monthly samples in a pilot area of the lake from February 1989 to February 1990. Naineris laevigata was dominant, both in number of individuals and biomass. During 1990, obstruction of freshwater inflow to the lake caused an increase in salinity up to 4O%, followed by some changes in the polychaete community. Noromasrus hiericeus became dominant, and the abundances of the other species decreased except for Naineris laevipru. Salinity assumed normal values after three months, but community responded slowly becauie the massive presence of N. latericeus inhibited the recovery of other species. An abiotic disturbance, followed by a biotic disturbance, altered the structure of the polychaete community.

Changes in loblolly pine root growth potential from September to April

Loblolly pine (Pinustaeda L.) 1 + 0 seedlings were periodically hand lifted from a Virginia nursery to determine how root growth potential (RGP) varied between September and April. Several seedling characteristics, RGP, and shoot phenology were recorded for each lift date in 1983–1984 and 1984–1985. An attempt was made to relate RGP variation to changes in the nursery environment and to shoot phenology. Root growth potential variation was consistent between years and was more closely related to shoot phenological changes than to short-term environmental changes. During the development of dormancy, RGP was low, RGP increased when shoot activity resumed during the RGP tests (late winter, early spring), and declined as active shoot elongation began in the nursery. When RGP was low, elongation of existing lateral roots primarily contributed to the new root systems, but as seedling metabolism increased in the late winter, new root initiation also contributed to new root systems. Absolute differences in RGP between years may be related to the fibrosity of seedling root systems.