Drought Phase Research Articles

Small-scale patterns of plant functional types and soil features within Mediterranean temporary ponds

Temporary ponds (TPs) are shallow water bodies characterized by alternating phases of drought and flooding. They exhibit a small-scale zonation with a central belt (CB), an intermediate belt, and an outer belt (OB). Starting from the hypothesis that plant assemblage composition is affected by the position within TPs, our aims were to define the small-scale patterns of plant functional types, soil evolution, and soil physicochemical properties and to analyze their relationships and how they were affected by pond characteristics (i.e., elevation, substratum, total size, belt size, maximum water depth, and hydroperiod). Our results pointed out that patterns of plant functional types and soil evolution followed the position within the pond, soil physicochemical properties were weakly affected, and there was a relationship between plant functional types, soil small-scale patterns, and pond characteristics. Principal component analysis showed a positive correlation of Alfisols with CB, aquatic and amphibious species, maximum water depth, and hydroperiod, and of Entisols with OB and terrestrial species. A combined microtopography–hydrology effect was the primary factor controlling soil evolution and plant functional type patterns. As a consequence, modification in topographic shape and/or hydrologic parameters could alter TP environments. The results provide information for management strategies as an answer to the concerns surrounding continued worldwide TP decline.

Carbon dynamics of eucalypt seedlings exposed to progressive drought in elevated [CO2] and elevated temperature

Elevated [CO2] and temperature may alter the drought responses of tree seedling growth, photosynthesis, respiration and total non-structural carbohydrate (TNC) status depending on drought intensity and duration. Few studies have addressed these important climatic interactions or their consequences. We grew Eucalyptus globulus Labill. seedlings in two [CO2] concentrations (400 and 640 μl l(-1)) and two temperatures (28/17 and 32/21 °C) (day/night) in a sun-lit glasshouse, and grew them in well-watered conditions or exposed them to two drought treatments having undergone different previous water conditions (i.e., rewatered drought and sustained drought). Progressive drought in both drought treatments led to similar limitations in growth, photosynthesis and respiration, but reductions in TNC concentration were not observed. Elevated [CO2] ameliorated the impact of the drought during the moderate drought phase (i.e., Day 63 to Day 79) by increasing photosynthesis and enhancing leaf and whole-plant TNC content. In contrast, elevated temperature exacerbated the impact of the drought during the moderate drought phase by reducing photosynthesis, increasing leaf respiration and decreasing whole-plant TNC content. Extreme drought (i.e., Day 79 to Day 103) eliminated [CO2] and temperature effects on plant growth, photosynthesis and respiration. The combined effects of elevated [CO2] and elevated temperature on moderate drought stressed seedlings were reduced with progressive drought, with no sustained effects on growth despite greater whole-plant TNC content.

Relación entre las características pluviométricas y los niveles de residuos de insecticidas organoclorados en un curso fluvial

The concentrations of organochlorine insecticide residues was investigated during four well defined periods in samples of water from the River Almar (province of Salamanca, Spain). These periods coincides with a phase of drought, gentle rain after the drought, strong rains after the drought and heavy rains. It is seen that solubilization and drag from de basin are very small during the dry phase, increase during the phase of heavy rains, continue to rise during the gentle post-drought phase and reach a maximum during the strong rains post-drought. Among the organochlorine pesticides, lindane was always outstanding in its behaviour; this is noteworthy in that it is the only pesticide whose use is permitted by Spanish legislation.

Plant functional group composition modifies the effects of precipitation change on grassland ecosystem function.

Temperate grassland ecosystems face a future of precipitation change, which can alter community composition and ecosystem functions through reduced soil moisture and waterlogging. There is evidence that functionally diverse plant communities contain a wider range of water use and resource capture strategies, resulting in greater resistance of ecosystem function to precipitation change. To investigate this interaction between composition and precipitation change we performed a field experiment for three years in successional grassland in southern England. This consisted of two treatments. The first, precipitation change, simulated end of century predictions, and consisted of a summer drought phase alongside winter rainfall addition. The second, functional group identity, divided the plant community into three groups based on their functional traits- broadly described as perennials, caespitose grasses and annuals- and removed these groups in a factorial design. Ecosystem functions related to C, N and water cycling were measured regularly. Effects of functional groupidentity were apparent, with the dominant trend being that process rates were higher under control conditions where a range of perennial species were present. E.g. litter decomposition rates were significantly higher in plots containing several perennial species, the group with the highest average leaf N content. Process rates were also very strongly affected by the precipitation change treatmentwhen perennial plant species were dominant, but not where the community contained a high abundance of annual species and caespitose grasses. This contrasting response could be attributable to differing rooting patterns (shallower structures under annual plants, and deeper roots under perennials) and faster nutrient uptake in annuals compared to perennials. Our results indicate that precipitation change will have a smaller effect on key process rates in grasslandscontaining a range of perennial and annual species, and that maintaining the presence of key functional groups should be a crucial consideration in future grassland management.

Characteristics of extreme droughts inferred from tree-ring data in the Qilian Mountains, 1700−2005

Severe droughts were evaluated using a tree-ring network of 12 chronologies (1700−2005) from the Qilian Mountains on the northeastern Tibetan Plateau. A total of 98 drought years, including 78 moderate, 15 severe, and 5 extreme events, were identified for the past 306 yr. Following the starting year of a drought phase, drought commonly continued for 1 to 2 yr. The spatial patterns of moisture conditions in central and eastern China corresponding to 19 major drought years during the period 1700−2000 were grouped into 3 clusters, with one particular pattern showing droughts of nation-wide impact (i.e. 1721, 1928 and 1966). Drought events became more frequent during the 20th century. Moreover, the multi-year event during the late 1920s and early 1930s was the longest in the past 306 yr. As shown by the tree-ring data, this extreme drought event occurred first in the western Qilian Mountains, and then progressed gradually toward the central and eastern parts of the area, culminating in 1928. Comparison with historical documents demonstrates that the climatic information imbedded in the tree-ring network can provide quantitative measures of drought severity and fill the gaps where historical documents are lacking and/or incomplete.

Development and lithogenesis of the palustrine and calcrete deposits of the Dibdibba Alluvial Fan, Kuwait

A model is proposed for the development of the Quaternary palustrine carbonate–calcrete association, which occurs as hard crust capping low hills at a distal flood plain of Al Dibdibba alluvial fan located at southwestern Kuwait. Field occurrence, detailed petrographic investigation and geochemical analysis revealed that a single cycle of groundwater calcrete with vertical gradational maturity pattern was developed. This represents a continuous sedimentological cycle during which flood sheet conditions prevailed with intermittent periods of humid and arid conditions. Subsequently, calcitic micrite was continuously precipitated from small, shallow, local, isolated and short lived ponds fringed by freshwater marshes with abundant charophyte meadows. The latter were developed as a result of flooding scattered depressions by groundwater supersaturated with respect to calcite due to rise of groundwater table. The deposition of two facies of carbonate muds, namely; biomicrite and pelintraclasts skeletal micrites was followed by a drought phase which witnessed desiccation of the fresh water ponds and significant drop in groundwater level. A sequence of pedogenic and diagenetic processes acted on the deposited carbonate muds are manifested by: (a) desiccation cracks, (b) micrite neomorphism, (c) infilling of root burrows and some cracks by aeolian siliciclastics, (d) karstification, (e) marmorization, (f) calcretization of root burrow infill and development of pseudo-rhizocrete, (g) calcite cementation and mineral authigenesis, and (h) silcretization. These processes are responsible for the development of hard palustrine carbonate crust. At the advent of aridity, the whole system of Al Dibdibba alluvial fan was subjected to deflation. This resulted in reversing the paleotopography of the hard crusted palustrine depressions into carbonate capped domal hills.

Comparing water-vegetative indices for rice ( Oryza sativa L.)–wheat ( Triticum aestivum L.) drought assessment

Drought indices (DI) are an useful tool for assessing different sectarian droughts. Standardized Precipitation Index (SPI) has been used worldwide to assess/monitor the onset, active phase, cessation and severity of drought. Normalized Difference Vegetation Index (NDVI) provides a comprehensive vegetation dynamics, which directly linked with rainfall received in a particular region. Indo-Gangetic Region (IGR), providing employment and livelihood to tens of millions of rural families directly or indirectly and rice ( Oryza sativa L.)–wheat ( Triticum aestivum L.) (RW) system of the Indo-Gangetic Plains (IGP) contributes 80% of the total cereal production and is critical to food security of the region. This study tries to verify the applicability of water-vegetative indices viz., SPI, Rainfall Index (RI) and NDVI for drought assessment of rice–wheat system productivity over IGR-India. The relationship between monsoon rainfall and NDVI shows that at around 1100 mm rainfall, the NDVI reached saturation point and no further significant increase in NDVI with increase of rainfall is noticed. Even though, there was a positive correlation of seasonal monsoon rainfall and average NDVI, conflicting results are noticed between monthly distribution of rainfall and monthly anomaly of NDVI over IGR States. It is noticed that June dif NDVI (actual NDVI–mean NDVI) contributes more to rice productivity followed by July. However, the combined effect of June, July and August, explains 15% of the variation of Kharif Rice Productivity Index (KRPI). As far as wheat is concerned, statistically significant relation was found between Wheat Productivity Index (WPI) and anomaly NDVI during December–March. This explains 35% of the variability in WPI.

Trophic functioning of the St. Lucia estuarine lake during a drought phase assessed using stable isotopes

The St. Lucia Estuary is Africa’s largest estuarine system and is currently experiencing the stress of prolonged freshwater deprivation, manifested by extremely low water levels and hypersalinity. These unprecedented conditions have raised questions regarding the trophic functioning of the ecosystem. Despite the substantial amount of research previously undertaken within this system, no studies of food web structure and function have yet been documented. This study therefore aimed to examine the food web structure of the St. Lucia estuary system through the use of carbon and nitrogen stable isotope analysis. Analysis of carbon isotope ratios indicates that benthic carbon sources are most utilised at sites with low water levels and generally higher salinity (Catalina Bay, Charter’s Creek). Conversely, the estuarine region of the mouth and Narrows, with its elevated water levels and lower salinity, still sustains a viable pelagic food web. Analysis of δ 15N ratios indicates that the number of trophic transfers (food chain length) might be related to water levels. Overall, the study provides a greater understanding of the ecological processes of this complex estuarine lake, which may allow for future comparisons of trophic functioning under drought and normal/wet conditions to be made.

Microalgal productivity in an estuarine lake during a drought cycle: The St. Lucia Estuary, South Africa

The St. Lucia estuarine lake on the north coast of KwaZulu-Natal, South Africa, is one of the largest estuarine systems in Africa and of unique importance for the adjacent marine and terrestrial ecosystems. The area regularly experiences periods of drought, resulting in hypersaline conditions in its shallow lakes and the closure of the estuarine mouth. This study aimed to assess the primary production rates of phytoplankton and microphytobenthos throughout an annual cycle of this drought phase. Primary production rates were assessed at representative sites, namely the Mouth, Narrows, South and North Lakes from June 2006 to May 2007. Because of the drought, the salinity gradient from the mouth to the head of the estuary was reversed by comparison to estuarine systems with a steady freshwater inflow and regular marine exchange. In March 2007, during the study, the mouth opened as a result of rough seas, and the marine influence broke the existing reversed gradient, producing a marine salinity throughout the system. Microphytobenthic primary productivity varied between 0 and 34 mg C m −2 h −1 and showed strong correlations with salinity, DIN:DIP ratios and irradiance. Benthic productivity was high across the system after breaching of the mouth. Pelagic primary productivity (between 0 and 180 mg C m −2 h −1), showed a correlation with temperature and irradiance and was highest across the system in February 2007 when the mouth was still closed. There was no significant correlation between production rates and biomass (chl-a) in either the benthic or pelagic habitats. The negative correlation between DIN:DIP ratio and benthic primary productivity indicated that phosphorus was the limiting nutrient. This study shows that salinity, along with seasonally dependent parameters such as temperature and irradiance, correlates with the rate of microalgal production. Hence, in these shallow lakes, the largest primary productivity can occur in either the pelagic or benthic subsystems, depending on prevailing conditions at the time.

Identification of drought-tolerant plants for roadside greening—An evaluation of chlorophyll fluorescence as an indicator to screen for drought tolerance

Drought is a major limitation to plant growth and development so the identification of suitable screening techniques and quantifiable traits associated with drought tolerance can potentially help reduce the impact of water deficit on plant replacement needs and allow for remedial action where necessary to be undertaken. Twelve species of flowering plants ( Excocecaria cochinensis Lour., Russelia equisetiformis Schlecht. & Cham., Lantana montevedensis (Spreng.) Briq., Phyllanthus cochinchinensis (Lour.) Spreng., Evolvulus pilosus Syne., Talinum triangulare (Jacq.) Willd., Coreopsis grandiflora Hogg ex Sweet, Chlorophytum cosmosum (Thunb.) Jacques., Elephantopus scaber L., Periscaria hydropiper (L.) Spach., Stenotaphrum secundatum (Walter.) Kuntze. and Tradescantia pendula (Schnizl.) Hunt.) commonly planted along streets and roads for aesthetic purposes were examined here using the chlorophyll fluorescence ratio ( F v/ F m – a measure of photochemical efficiency) and digital image analysis of green foliage coverage. Both have been confirmed to be reliable indicators in the identification of drought tolerant and susceptible species. Plants were initially allowed to establish for 60 days under adequate irrigation following containerization (establishment phase). This was followed by another 60 days of drought (drought phase). For the last 60 days of the experiment, plants were re-watered and allowed to recover (recovery phase). Based on fluctuations in photochemical efficiency over the different phases, five species were identified as susceptible to drought whilst another five were considered to have the ability to resist water stress and two were identified as drought intermediate species – exhibiting reduced sensitivity to drought conditions where a decline in values of F v/ F m were only observed in the recovery phase. One of the drought intermediate species ( T. triangulare) exhibited little to no relationship between chlorophyll fluorescence and soil moisture content. Plants were deemed drought tolerant through stable F v/ F m values and lower leaf senescence as recorded by a greater extent of green foliage at the end of the drought and recovery phase. The identification of drought tolerant and susceptible species was further confirmed through regression analysis of F v/ F m and soil moisture content where linear relationships were observed between leaf chlorophyll fluorescence and soil moisture for most of the plants examined in this study. Results of this study strongly suggest that evaluation of whole shrubs using chlorophyll fluorescence is capable of providing a means to identifying the susceptibility of plants to water stress.

Meteorological and water quality changes in Lake Trasimeno (Umbria, Italy) during the last fifty years

This paper illustrates the results of an analysis performed on historical data of the main meteorological and water quality variables collected during the last fifty years in the basin of Lake Trasimeno, a shallow lake subjected to important water level fluctuations. The results reveal a significant increase of the annual mean of minimum and maximum air temperature, water temperature and solar radiation, and a significant reduction of precipitation and cloud cover, which have mostly occurred during the last twenty years. The decadal rate of warming observed in the last twenty years for air temperature (0.33 °C decade-1) is consistent with the estimate reported by the IPCC for the land-surface temperature in the Northern Hemisphere, whereas the surface water temperature in Lake Trasimeno shows a more marked increase (0.65 °C decade-1), comparable to that observed in other lakes of Mediterranean areas. On a monthly scale, the most significant variations are observed in late-spring and early summer months for temperature and solar irradiation, and in winter and spring months for rainfall, which result in an appreciable modification of the seasonal progression. The alterations of the thermal and hydrological balance of the lake have caused a progressive lowering of the water level and the emergence of evaporative conditions. As a consequence of the drought, a progressive accumulation of dissolved salts (3.5 106 kg y-1) is observed, which is partially explained by meteoric loading. The analysis also shows that an increase in the total alkalinity has occurred during the main drought phases of the last forty years, which has been shown to be consistent with what expected on the basis of the changes in the ionic composition of the waters. With decreasing water levels, a strong reduction in water transparency has also been observed, which does not appear to be connected with a change in the trophic state of the lake, but rather with the increase of suspended solids from bottom sediments, in agreement with the predictions based on resuspension models in shallow waters. On putting the results into the future scenario of climate change, an accelerating drought and progressive worsening of the water quality can be predicted for Lake Trasimeno in the near future.

Ciliados (Protozoa) de sedimentos secos de una charca temporaria de la Argentina

Temporary ponds represent special environments that are inhabited by organisms adapted to changingenvironmental conditions. Ciliates are able to survive complete loss of water in these transient habitats through cyst formation. However, ciliates from the Neotropical region in general have been poorly studied with modern techniques. The main goal of this study is to describe the ciliates in dried sediments of a temporary pond from Buenos Aires Province, Argentina, through sampling efforts that were performed 2003-2005. Soil samples were obtained during drought phases and rewetted in laboratory to establish raw and enriched cultures. Ciliates were then studied both in vivo and after impregnation with protargol. In this study, we present 4 new records for Argentina (Gonostomum affine (Stein, 1859) Sterki, 1878, Stylonychia bifaria (Stokes, 1887) Berger, 1999, Pleurotricha lanceolata (Ehrenberg, 1835) Stein, 1859, Meseres corlissi Petz and Foissner, 1992), 1 for South America (Blepharisma americanum (Suzuki, 1954) Hirshfi eld, Isquith and Bhandary, 1965), and 2 for the Neotropical Realm (Gonostomum strenuum (Engelmann, 1862) Sterki, 1878, Stylonychia lemnae Ammermann and Schlegel, 1983).

Effect of ploidy levels on the activities of Δ1-pyrroline-5-carboxylate synthetase, superoxide dismutase and peroxidase in Cenchrus species grown under water stress

The effects of ploidy levels on the activities of delta(1)-pyrroline-5-carboxylate synthetase (P5CS; EC not assigned), superoxide dismutase (SOD; EC 1.15.1.1) and guaiacol peroxidase (POX; EC 1.11.1.7), as well as malondialdehyde (MDA) and proline contents were studied in two months old plants of Cenchrus species. The Cenchrus species represent three ploidy levels: diploid, tetraploid, hexaploid and two life spans: annual and perennial. Plants were subjected to water stress for 2, 4, 6 and 8 d by withholding water under glasshouse conditions. Although the levels of proline increased with the magnitude of water stress, the P5CS activity did not show a corresponding increase in all species. Peroxidase and superoxide dismutase activities showed an increase or steady state in the early phase of drought and then declined with the further increase in the magnitude of water stress, indicating differing behaviors of species towards drought tolerance. Under drought, diploid Cenchrus species had a higher POX activity, MDA accumulation and lower proline content than tetraploid species. Lower POX and higher P5CS activities and proline contents, however, were observed in hexaploid and tetraploid species. Taken together, our findings suggest that diploid species have a less efficient antioxidant system to scavenge reactive oxygen species than tetra and hexaploid Cenchrus. This may result in a corresponding variability in growth and persistence under natural grasslands. The study also paves the way for investigations on the molecular events associated with drought in Cenchrus species differing in ploidy and life span.

Dynamics of redox processes in a minerotrophic fen exposed to a water table manipulation

Climate change studies foresee substantial changes in precipitation patterns in northern temperate regions, including an increased frequency of drought and intense rain events. To elucidate the impact of drying and rewetting on redox processes in peatlands we conducted a field scale manipulation experiment, tracing the below ground dynamics of dissolved inorganic carbon (DIC), methane (CH 4), and electron acceptors in a minerotrophic fen. On three treatment plots, a drought phase of ~ 4 weeks was initiated by means of a drainage system and a mountable roof. Subsequently we simulated a heavy rainfall by irrigation, which raised the water table by 20–35 cm. Three plots served as control. Solute electron acceptor concentrations increased during drought and decreased after rewetting, consistent with treatment and weather. Changes in solid phase electron acceptor contents were not detected. Drought induced aeration regenerated electron acceptors and suppressed methanogenic activity. This suppressive effect persisted during and some 1–4 weeks after rewetting, dependent on depth. Hydrogen- and acetate-dependent iron and sulfate reduction were thermodynamically viable processes in the peat as their energy gain exceeded the threshold for microbial metabolism of − 23 kJ mol − 1 . Hydrogenotrophic methanogenesis was apparently thermodynamically inhibited in most of the peat, but proceeded presumably in microenvironments. In the uppermost peat layers, partly above the water table level, iron and sulfate reduction and occasionally methanogenesis overlapped and aeration was limited. Thus, in these layers reductive processes could partly proceed even during drought. As all processes, including methanogenesis, responded quickly to wetting events, the microbial community seemed to be well adapted to fluctuating redox conditions. This study demonstrated that the dense and highly decomposed material could still provide anaerobic habitats for microorganisms during drought and the depth distribution of redox processes was quite insensitive towards the water table manipulations, presumably due to formation of microenvironments.

Glacial to Holocene climate changes in the SE Pacific. The Raraku Lake sedimentary record (Easter Island, 27°S)

Easter Island (SE Pacific, 27°S) provides a unique opportunity to reconstruct past climate changes in the South Pacific region based on terrestrial archives. Although the general climate evolution of the south Pacific since the Last Glacial Maximum (LGM) is coherent with terrestrial records in southern South America and Polynesia, the details of the dynamics of the shifting Westerlies, the South Pacific Convergence Zone and the South Pacific Anticyclone during the glacial–interglacial transition and the Holocene, and the large scale controls on precipitation in tropical and extratropical regions remain elusive. Here we present a high-resolution reconstruction of lake dynamics, watershed processes and paleohydrology for the last 34 000 cal yrs BP based on a sedimentological and geochemical multiproxy study of 8 cores from the Raraku Lake sediments constrained by 22 AMS radiocarbon dates. This multicore strategy has reconstructed the sedimentary architecture of the lake infilling and provided a stratigraphic framework to integrate and correlate previous core and vegetation studies conducted in the lake. High lake levels and clastic input dominated sedimentation in Raraku Lake between 34 and 28 cal kyr BP. Sedimentological and geochemical evidences support previously reported pollen data showing a relatively open forest and a cold and relatively humid climate during the Glacial period. Between 28 and 17.3 cal kyr BP, including the LGM period, colder conditions contributed to a reduction of the tree coverage in the island. The coherent climate patterns in subtropical and mid latitudes of Chile and Eastern Island for the LGM (more humid conditions) suggest stronger influence of the Antarctic circumpolar current and an enhancement of the Westerlies. The end of Glacial Period occurred at 17.3 cal kyr BP and was characterized by a sharp decrease in lake level conducive to the development of major flood events and erosion of littoral sediments. Deglaciation (Termination 1) between 17.3 and 12.5 cal kyr BP was characterized by an increase in lake productivity, a decrease in the terrigenous input and a rapid lake level recovery, inaugurating a period of intermediate lake levels, dominance of organic deposition and algal lamination. The timing and duration of deglaciation events in Easter Island broadly agree with other mid- and low-latitude circum South Pacific terrestrial records. The transition to the Holocene was characterized by lower lake levels. The lake level dropped during the early Holocene (ca 9.5 cal kyr BP) and swamp and shallow lake conditions dominated till mid Holocene, partially favored by the infilling of the lacustrine basin. During the mid- to late-Holocene drought phases led to periods of persistent low water table, subaerial exposure and erosion, generating a sedimentary hiatus in the Raraku sequence, from 4.2 to 0.8 cal kyr BP. The presence of this dry mid Holocene phase, also identified in low Andean latitudes and in Patagonian mid latitudes, suggests that the shift of storm tracks caused by changes in the austral summer insolation or forced by “El Niño-like” dominant conditions have occurred at a regional scale. The palm deforestation of the Easter Island, attributed to the human impact could have started earlier, during the 4.2–0.8 cal kyr BP sedimentary gap. Our paleoclimatic data provides insights about the climate scenarios that could favor the arrival of the Polynesian people to the island. If it occurred at ca AD 800 it coincided with the warmer conditions of the Medieval Climate Anomaly, whereas if it took place at ca AD 1300 it was favored by enhanced westerlies at the onset of the Little Ice Age. Changes in land uses (farming, intensive cattle) during the last century had a large impact in the hydrology and limnology (eutrophication) of the lake.

Examination of Antioxidative System’s Responses in the Different Phases of Drought Stress and During Recovery in Desert Plant Reaumuria soongorica (Pall.) Maxim

The aim of this study was to test the protective roles of superoxide dismutases (SODs), guaiacol peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) against oxidative damage and their activities in different phases of the dry down process in Reaumuria soongorica (Pall.) Maxim. leaves. Drought stress was imposed during 100 consecutive days and rewatering after 16, 72, and 100 days. The concentration of hydrogen peroxide (H(2)O(2)), malondialdehyde, and SODs activities were elevated significantly with progressing drought stress. POD and CAT activities increased markedly in the early phase of drought and decreased significantly with further drought stress continuation, and POD activity was unable to recover after rewatering. Ascorbate, reduced glutathione, APX, and GR activities declined in the initial stages of drought process, elevated significantly with further increasing water deficit progression and recovered after rewatering. These results indicate that: (1) iron SODs-removing superoxide anion is very effective during the whole drought stress; (2) CAT scavenges H(2)O(2) in the early phase of drought and enzymes of ascorbate-glutathione cycle scavenge H(2)O(2) in further increasing drought stress; and (3) POD does not contribute to protect against oxidative damage caused by H(2)O(2) under drought stress.

Impact of short-term climatic events on latest Pliocene land settings and communities in Central Italy (Upper Valdarno basin)

The Upper Valdarno (Italy) Plio-Pleistocene continental deposits record the latest uniform subtropical humid conditions and the successive climatic signature of glacial/interglacial cycling. The palynological and sedimentological analyses on the Poggio Rosso alluvial plain sediments reveal two major climatic fluctuations correlated to a glacial/interglacial cycle just before the Plio-Pleistocene boundary. The glacial phase, indicated by the expansion of herbs as well as by ephemeral streams associated with calcareous palaeosols, extends from the base of the succession and culminates close to an impressive mammalian bone accumulation dated at 1.87 Ma. The associated increasing aridity had severe consequences on the faunal communities, inducing the migration of open plain dwellers and the trapping of other residents around a few residual shrinking water bodies. A cooperative Pachycrocuta brevirostris clan acted as regulator of game populations debilitated by drought. Previous research indicates that hyenas were also the major bone accumulators. The following moister and warmer interglacial phase ca 1.83 Ma is documented by arboreal taxa and hydromorphic palaeosols in a floodplain crossed by migrating, perennial, sinuous streams. The Climatic Amplitude Method calculated mean annual temperatures around 12.5–14 °C and mean annual precipitation around 800 mm, with a minimum of 400 mm during the glacial phase and 15/16–19 °C and 750–1200 mm during the interglacial phase. The reconstruction reveals higher mean annual temperatures and precipitation during the interglacial as compared to the present-day climate. During the glacial, conditions were similar to today's in all but lower precipitation values were reached during the acme drought phase just above the fossiliferous bed. Poggio Rosso documents the ecological consequences the buildup of the Apennine chain had under the effects of the latest Pliocene global climatic changes. It therefore represents one of the first signals of the patchiness that, since then, gradually increased leading to the eventual habitat fragmentation typical of the late Pleistocene landscapes.

A 4500-year proxy climate record from peatlands in the North of Ireland: the identification of widespread summer ‘drought phases’?

Mid-to-late Holocene high-resolution testate amoebae-derived water table reconstructions from two peatlands in the North of Ireland are presented. The proxy climate records are dated and correlated using a combination of AMS 14C dating, spheroidal carbonaceous particles and tephrochronology. The reconstructions start prior to the Hekla 4 tephra isochron (2395–2279 BC) and thus span the last ∼4500 years. The records are compiled by the process of tuning within chronological errors, standardisation and stacking. Comparisons are made to existing palaeoclimate records from peatlands in Northern Britain and Ireland and the compiled lake-level record for mid-latitude Europe. Four coherent dry phases are identified in the records at ca 1150–800 BC, 320 BC–AD 150, AD 250–470 and AD 1850–2000. Recent research has shown that peat-derived water table reconstructions reflect summer water deficit and therefore the dry phases are interpreted as periods with a higher frequency and/or greater magnitudes of summer drought. These ‘drought phases’ occur during periods of relatively low 14C production, which may add support to the hypothesis of persistent solar forcing of climate change during the Holocene. Any relationship with the North Atlantic stacked drift ice record is less clear.

Community structure of epibenthic meiofauna in the St. Lucia Estuarine Lake (South Africa) during a drought phase

The St. Lucia Estuary is Africa's largest estuarine system. It is a major component of the iSimangaliso (formerly Greater St. Lucia) Wetland Park, which was declared a World Heritage Site in 1999. The system has been severely affected by drought conditions which have culminated in the mouth of the system being cut off from the Indian Ocean since June 2002, for a period of almost five years. This study aimed to document the dynamics of meiofauna of the system during a drought phase, since (1) the effects of droughts on estuaries are poorly documented and understood and (2) because studies of meiofauna have never been undertaken in this system before. Meiofauna samples as well as physico-chemical data were collected at representative sites in February, April, August and October 2005. The drought had a major effect on the estuary, resulting in the development of hypersaline conditions (maximum 126 at Hells Gate), and to the complete evaporation of pelagic habitats, especially in the northern regions. The meiofauna of the St. Lucia Estuary was statistically separated into two distinct spatial clusters under drought conditions. The first cluster comprised sites in the Narrows and the southern region of South Lake, while the second comprised sites in the northern regions of South Lake and False Bay. Meiofauna of cluster 1, which was least affected by the drought, comprised nematodes, polychaetes, copepods, amphipods and ostracods, all of which accounted for 97% of meiofauna in this cluster. Cluster 2 on the other hand, which was more severely affected by the drought, was dominated by nematodes and copepods, which cumulatively contributed 97% to meiofauna in this group. Taxonomic richness and diversity of meiofauna were positively correlated with water depth, while abundance was inversely correlated with water temperature. The major effects of low water levels on the meiofauna of the system occurred through a negative impact on diversity and taxonomic richness, resulting in assemblages dominated by taxa most physiologically suited to such conditions. Secondly, at the peak of the drought, there was discontinuous water flow in the St. Lucia Estuary, resulting in parts of the northern and southern regions of the system being fragmented. This could have prevented the spread of meiofaunal taxa between the different basins of the system, and also explains the spatial separation of meiofauna into distinct clusters within the estuary.

Effect of introduced species and habitat alteration on the occurrence and distribution of euryhaline fishes in fresh- and brackish-water habitats on Aruba, Bonaire and Curaçao (South Caribbean)

We conducted an ichthyological survey during the dry season of 2006 on the semi-arid islands of Aruba, Bonaire and Curaçao to provide information on species composition, richness and distribution in natural and non-natural aquatic habitats. The dry season species assemblages (N = 9 species) comprised less species than the wet seasons, and these data refine our knowledge of the indigenous fish fauna and its refuge localities during phases of drought and ensuing high salinity. A hierarchical cluster analysis reveals that the three islands have different species compositions with Curaçao being the most diverse, probably due to its having the most habitats and freshwaters present throughout the year. Species richness was unrelated to salinity and species diversity was highest in canalised streams. In the dry season fewer amphidromous species are present than in the wet season. We found no significant effect of human-induced changes on the presence or absence of fish species in the Netherlands Antilles. The presence of exotic species (including Xiphophorus helleri on Aruba, a first record for this island, and Oreochromis mossambicus and Poecilia reticulata occurring on all three islands) did not have a clear effect on the presence of indigenous species, nor did human alteration of the habitats have an influence on the occurrence of fish species.