Duration Of Dry Period Research Articles

Linking local ecological outcomes with basin-wide water planning: a case study of Yanga National Park, an important Australian inland forested wetland

Maintaining and restoring the ecological integrity of floodplains remains a priority for many Australian federal and state government agencies. The Murray-Darling Basin Authority (MDBA) introduced the Proposed Basin Plan 2012, the Australian government’s latest basin-scale water planning instrument to promote a healthy, working river system. The proposal seeks to limit surface water (consumptive) use to 10 873 GL year-1 on a long-term average. The controversy prompted by this proposed reduction has underscored a need for rigorous and transparent modelling of ecological benefits. In this paper, we investigate the likely ecological outcomes of the proposal for Yanga National Park, one of the most significant environmental assets in the Murray-Darling Basin, using a decision support system. Our results indicate that the proposal will increase the inundation extent with a 33% (or 7000 ha) increase in median flood. The increase in inundation would improve the hydrological conditions in most wetlands in terms of the frequency and duration of events and inter-flood dry periods and enhance the habitat quality for a range of biota, though benefits are not distributed evenly across the wetland.Editor D. Koutsoyiannis; Guest editor M. AcremanCitation Wen, L. and Saintilan, N., 2014. Linking local ecological outcomes with basin-wide water planning: a case study of Yanga National Park, an important Australian inland forested wetland. Hydrological Sciences Journal, 59 (3–4), 904–915.

Trends and variability in extreme precipitation indices over Maghreb countries

Abstract. Maghreb countries are highly vulnerable to extreme hydrological events, such as floods and droughts, driven by the strong variability of precipitation. While several studies have analyzed the presence of trends in precipitation records for the Euro-Mediterranean basin, this study provides a regional assessment of trends on its southernmost shores. A database of 22 stations located in Algeria, Morocco and Tunisia with between 33 and 59 yr of daily precipitation records is considered. The change points and trends are analyzed for eleven climate indices, describing several features of the precipitation regime. The issue of conducting multiple hypothesis tests is addressed through the implementation of a false discovery rate procedure. The spatial and interannual variability of the precipitation indices at the different stations are analyzed and compared with large-scale atmospheric circulation patterns, including the North Atlantic Oscillation (NAO), western Mediterranean Oscillation (WEMO), Mediterranean Oscillation (MO) and El Niño–Southern Oscillation (ENSO). Results show a strong tendency towards a decrease of precipitation totals and wet days together with an increase in the duration of dry periods, mainly for Morocco and western Algeria. On the other hand, only a few significant trends are detected for heavy precipitation indices. The NAO and MO patterns are well correlated with precipitation indices describing precipitation amounts, the number of dry days and the length of wet and dry periods, whereas heavy precipitation indices exhibit a strong spatial variability and are only moderately correlated with large-scale atmospheric circulation patterns.

Monitoring of land use change impact on stormwater runoff and pollutant loading estimation in Yongin watershed Korea

This study investigates the preliminary assessment of land use changes and their specific effects on hydrological characteristics and stormwater quality in Yongin watershed. Two experimental catchment sites comprising of mix land uses including urban and construction areas were monitored and tested for major stormwater quality parameters. It was observed that dry field, paddy field, forest, and ground cover were changed to bare land about 61, 96, 13, and 9%, respectively, at Site 1 from June 2011 to December 2011 due to construction activities for new development. The findings indicate that increase in bare soil resulted in reduction of stormwater runoff. Overall pollutograph shape for the entire stormwater events for most of the water quality parameters showed multiple peaks of equivalent magnitude, reflecting the rainfall intensity distribution. A wide range of Event mean concentrations (EMCs) for individual runoff event was measured for each water quality constituent based on the flow rate and concentration data. These wide EMC distributions did not show relationship with antecedent dry period, rainfall intensity, and runoff duration due to continuous modifications in monitoring sites. Pollutant loading at Site 2 was higher as compared to Site 1 because of the urban area impact and the difference of catchment area.

Changes in the Duration of European Wet and Dry Spells during the Last 60 Years

AbstractDaily rain gauge data over Europe for the period from 1950 to 2009 were used to analyze changes in the duration of wet and dry spells. The duration of wet spells exhibits a statistically significant growth over northern Europe and central European Russia, which is especially pronounced in winter when the mean duration of wet periods increased by 15%–20%. In summer wet spells become shorter over Scandinavia and northern Russia. The duration of dry spells decreases over Scandinavia and southern Europe in both winter and summer. For the discrimination between the roles of a changing number of wet days and of a regrouping of wet and dry days for the duration of the period, the authors suggest a fractional truncated geometric distribution. The changing numbers of wet days cannot explain the long-term variability in the duration of wet and dry periods. The observed changes are mainly due to the regrouping of wet and dry days. The tendencies in duration of wet and dry spells have been analyzed for a number of European areas. Over the Netherlands both wet and dry periods are extended in length during the cold and the warm season. A simultaneous shortening of wet and dry periods is found in southern Scandinavia in summer. Over France and central southern Europe during both winter and summer and over the Scandinavian Atlantic coast in summer, opposite tendencies in the duration of wet and dry spells were identified. Potential mechanisms that might be responsible for the changing durations of wet and dry periods and further perspectives are discussed.

Differences in desiccation tolerance do not explain altitudinal distribution patterns of tropical bryophytes

Bryophyte biomass and diversity vary strongly with altitude in the tropics. Low abundance and low species numbers in lowland rain forests are most likely due to reduced diurnal activity times combined with high nocturnal respiration rates at high temperatures. This may exclude many montane species from the warm lowlands. However, an alternative hypothesis explains the observed pattern, namely a limited desiccation tolerance of montane species, precipitation being more concentrated but less frequent in most lowland forests compared to montane cloud forests. To test this hypothesis, we studied the desiccation tolerance of four montane and four lowland bryophyte species. The effects of prolonged drought were quantified with chlorophyll fluorescence (Fv/Fm) and the extent of electrolyte leakage. Both montane and lowland species survived dry periods of ≧80 days, which far exceeds the duration of dry periods in the wet lowland tropics. We can thus exclude intolerance to long dry spells as an explaination for the absence of the tested montane species in the lowlands. We should continue to focus on other mechanisms to explain the altitudinal gradient of bryophyte abundance and diversity in the tropics, in order to understand this pattern, as well as to predict future trends under climatic warming.

Flow intermittency alters longitudinal patterns of invertebrate diversity and assemblage composition in an arid‐land stream network

Summary1. Temporary streams comprise a large proportion of the total length of most stream networks, and the great majority of arid‐land stream networks, so it is important to understand their contribution to biotic diversity at both local and landscape scales.2. In late winter 2010, we sampled invertebrate assemblages in 12 reaches of a large arid‐land stream network (including perennial and intermittent headwaters, intermittent middle reaches and perennial rivers) in south‐east Arizona, U.S.A. Intermittent reaches had then been flowing for c. 60 days, following a dry period of more than 450 days. We sampled a subset of the perennial study reaches three more times between 2009 and 2011. Since intermittent reaches were dry during these additional sampling periods, we used assemblage data from two other intermittent streams in the study network (sampled in 2004–05 and 2010) to explore interannual variability in intermittent stream assemblage composition.3. Invertebrate richness was lowest in intermittent reaches, despite their often being connected to species‐rich perennial reaches. The assemblages of these intermittent reaches were not simply a subset of the species in perennial streams, but rather were dominated by a suite of stoneflies, blackflies and midges with adaptations to intermittency (e.g. egg and/or larval diapause). On average, 86% of individuals in these samples were specialists or exclusive to intermittent streams. Predators were 7–14 times more abundant in perennial than in intermittent reaches.4. Despite being separated by long distances (12–25 km) and having very different physical characteristics, the assemblages of perennial headwaters and rivers were more similar to one another than to intervening intermittent reaches, emphasising the prime importance of local hydrology in this system.5. The duration and recurrence intervals of dry periods, and the relative importance of dispersal from perennial refuges, probably influence the magnitude of biological differences between neighbouring perennial and temporary streams. Although perennial headwaters supported the highest diversity of invertebrates, intermittent reaches supported a number of unique or locally rare species and as such contribute to regional species diversity and should be included in conservation planning.

Is there any predictor for tinnitus outcome in different types of otologic surgery?

Our objective was to determine the effect of different types of otologic surgeries on tinnitus symptoms. Our study consisted of 63 patients who were operated between January and June 2011. Variables such as age, sex, presence of systemic diseases, location and size of the perforation, duration of dry period, type of otological surgery, peroperative presence of cholesteatoma, timpanosclerotic plaques and ossicular chain discontinuity were evaluated. Audiologic evaluation by pure tone audiometry and assessment of THI scores were conducted before surgery and 12 weeks after surgery. There was a very significant difference between preoperative and postoperative mean THI scores (p < 0.01). There was no significant effect of presence of ossicular discontinuity, cholesteatoma, tympanosclerotic plaques, type of surgery or duration of symptoms on the difference of preoperative and postoperative THI scores (p > 0.05). There was a significant positive relationship between audiological gain and THI scores (r = 0.355, p < 0.01). In our study, we investigated the relationship between many types of otological surgeries including some preoperative and peroperative pathological findings and tinnitus. As a result, we found that postoperative audiologic gain is an important factor determining outcome of tinnitus in these types of otological surgeries.

Statistical analysis of inter-arrival times of rainfall events for Italian Sub-Alpine and Mediterranean areas

Abstract. In this work a set of time-series of inter-arrival times of rainfall events, at daily scale, was analysed, with the aim to verify the issue of increasing duration of dry periods. The set consists of 12 time-series recorded at rain gauges in 1926–2005, six of them belong to an Italian Sub-Alpine area (Piedmont) and six to a Mediterranean one (Sicily). In order to overcome the problem related to limited sample size for high values of inter-arrival times, the discrete probability polylog-series distribution was used to fit the empirical data from partial (20 yr) time-series. Moreover, a simple qualitative trend analysis was applied to some high quantiles of inter-arrival times as well as to the average extent of rain clusters. The preliminary analysis seems to confirm the issue of increasing duration of dry periods for both environments, which is limited to the ''cold'' season.

Analyses of a long‐term, high‐resolution radar rainfall data set for the Baltimore metropolitan region

We introduce a long‐term, high‐resolution radar rainfall data set for the Baltimore metropolitan area covering the 10‐yr period from 2000–2009. Rainfall fields are developed at 15 min time interval and 1 km horizontal resolution for a 17,000‐km2 region centered on the Baltimore metropolitan area. The Hydro‐NEXRAD system is used as a platform for generating radar rainfall fields. We utilize the high‐resolution, 10‐yr data set to characterize striking spatial heterogeneities in rainfall for the Baltimore metropolitan region, both in terms of mean rainfall and rainfall extremes. The role of complex terrain (associated with urbanization, the Chesapeake Bay, and mountainous terrain) in controlling spatial heterogeneities of rainfall climatology for the Baltimore study region is discussed. We also characterize the seasonal and diurnal variation of rainfall over the study region using the 10‐yr rainfall data set, with particular focus on the diurnal variation of rainfall during the warm season. High‐resolution rainfall fields are especially useful for examining the distribution of rainfall from a drainage basin perspective, as illustrated through analyses of basin‐averaged rainfall rate for basins of contrasting drainage area and analyses of the duration of dry periods for small urban watersheds. Analyses and methodologies used to develop the long‐term Baltimore rainfall data set are broadly applicable to other regions of the United States and in settings around the world with long‐term, high‐quality radar data sets.

Atmospheric fate of non-volatile and ionizable compounds

A modified version of the Multimedia Activity Model for Ionics MAMI, including two-layered atmosphere, air–water interface partitioning, intermittent rainfall and variable cloud coverage was developed to simulate the atmospheric fate of ten low volatility or ionizable organic chemicals. Probabilistic simulations describing the uncertainty of substance and environmental input properties were run to evaluate the impact of atmospheric parameters, ionization and air–water (or air–ice) interface enrichment. The rate of degradation and the concentration of OH radicals, the duration of dry and wet periods, and the parameters describing air–water partitioning ( K AW and temperature) and ionization (p K a and pH) are the key parameters determining the potential for long range transport. Wet deposition is an important removal process, but its efficiency is limited, primarily by the duration of the dry period between precipitation events. Given the underlying model assumptions, the presence of clouds contributes to the higher persistence in the troposphere because of the capacity of cloud water to accumulate and transport non-volatile (e.g. 2,4-D) and surface-active chemicals (e.g. PFOA). This limits the efficiency of wet deposition from the troposphere enhancing long-range transport.

Climate Change and Crop Vulnerability in Nigeria

In Nigeria, food insecurity remains problematic due to dislocations in the agricultural productivity pathways. Food preferences and utilization patterns are skewed in favor of crop-based staples, which availability in quantity and quality, depend on the aggregate crop output. Unfavorable environmental conditions such as caused by climate change would create some level of vulnerability of the crops and thus have implication on food security. Two components of the Agricultural Value Chain, production and storage, appear to be most responsive to changes in environments with production being the most vulnerable since all the activities involved in the process of production occur in the fields and are weather -dependent. Climate change – directed irregularities or deviation from the normal seasonal patterns such as onset and duration of wet and dry periods, short and prolonged dry spells clearly manifest in various levels of crop vulnerability. It would therefore appear that a sustainable crop-based agricultural system can only be achieved where crop vulnerability is considerably minimized. If climate change effects can be incorporated in the design and implementation of national development programs right away, it will help to reduce vulnerability, stabilize food production and better secure livelihoods. The ecosystem approach with crop rotations, bioorganic fertilizers (e.g., from legumes) and biological pest controls, improves soil health and water retention, increases fertile top soil, reduces soil erosion and maintains productivity over the long term.Key words: vulnerability, climate change, crop productivity.

Tropical Street Trees and Climate Uncertainty in Southeast Asia

Urban trees are a critical quality of life element in rapidly growing cities in tropical climates. Tropical trees are found in a wide variety of habitats governed largely by the presence and duration of monsoonal dry periods. Tropical cities can serve as a proxy for climate change impacts of elevated carbon dioxide (CO2), urban heat island, and drought-prone root zones on successful urban trees. Understanding the native habitats of species successful as tropical urban trees can yield insights into the potential climate impact on those habitats. Species from equatorial and montane wet forests where drought stress is not a limiting factor are not used as urban trees in cities with monsoonal dry climates such as Bangkok and Bangalore. Absence of trees from a wet habitat in tropical cities in monsoonal climates is consistent with model and empirical studies suggesting wet evergreen species are vulnerable to projected climates changes such as lower rainfall and increased temperatures. However, monsoonal dry forest species appear to have wider environmental tolerances and are successful urban trees in cities with equatorial wet climates such as Singapore as well as cities with monsoonal climates such as Bangkok and Bangalore. In cities with monsoonal dry climates, deciduous tree species are more common than dry evergreen species. Although dry deciduous species generally have better floral displays, their prevalence may in part be the result of greater tolerance of urban heat islands and drought in cities; this would be consistent with modeled habitat gains at the expense of dry evergreen species in native forest stands under projected higher temperatures from climate change. Ecological models may also point to selection of more heat- and drought-tolerant species for tropical cities under projected climate change.

Regional drought over the UK and changes in the future

Summary This paper develops tools to assess regional drought events based on limited periods of record and applies them to regional climate model output to examine potential future changes in drought due to increased greenhouse gases. The drought metric was defined as a monthly time series of standardized 12-month precipitation accumulations. Regional drought events were characterised by determining the severity, area, duration and frequency of dry periods. In order to improve statistical inference of drought events, a drought generator was adopted to synthesis a large number of events trained on the available data. In nearly all cases, the drought generator produces synthetic events with drought characteristics statistically indistinguishable from the training data. Severity–Area–Frequency (SAF) curves and Area–Probability (Area–P) curves could then be constructed from the synthetic data to determine the return period of a drought event of a given severity covering a given area. These techniques were applied to observations and to output from the Hadley Centre regional climate model (HadRM3). HadRM3, when driven by climate reanalysis data, has good correlation with the observed drought metric. HadRM3 also captures the timing of observed dry periods but not the relative seriousness of any particular period. Natural variability is large with regional drought characteristics highly dependent on the time period covered by the training data. Although the synthetic drought characteristics of HadRM3 generally overlap with the observed natural variability; the model slightly overestimates the area of observed drought; underestimate its frequency; and underestimate the severity at any given area. HadRM3 projections of changes in drought characteristics over the second half of the 21st century under increased atmospheric greenhouse gases hint at an increase in the severity of drought. However, any changes are not readily distinguishable from natural variability or projection uncertainty. Therefore it is not yet possible to robustly predict changes in UK meteorological droughts arising from increased greenhouse gasses.

Statistical Modeling of the Monthly Palmer Drought Severity Index

This paper presents a new approach for the modeling of dry period interarrival times. The new model targets dry period interarrival times directly and uses a combination of the empirical model and results from extreme-value theory to achieve good fits. Existing approaches initially model dry period duration and successive wet period duration, then get a model for dry period interarrival times as a by-product. We perform a statistical study and analyze various duration characteristics of dry and wet periods based on monthly Palmer drought severity indices for climate divisions in the United States. Data from the states of Nebraska, Nevada, Arizona, and Florida are used to show that previous models are often inadequate. We also estimate return periods showing that our proposed approach for modeling dry period interarrival times is necessary and that designs and actuarial calculations based on the results produced by fitting previously published models would be severely flawed.

Short communication: The effect of dry period duration and dietary energy density in early lactation on the rennet gelation properties of milk

This study was carried out to examine the effects of decreasing the dry period (DP) duration and altering the energy density of the diet during early lactation on the rheological characteristics of milk. Forty mature Holstein-Friesian cows were used in a completely randomized design with a 2 × 2 factorial arrangement of treatments. Cows were randomly assigned to 1 of 2 dry period treatments and 1 of 2 nutritional treatments. The DP treatments were continuous milking (CM) or an 8-wk standard dry period (SDP), and the nutritional treatments were a standard energy diet (SE) or a high energy diet (HE). Actual DP lengths were 6.3±1.7 d and 62.1±1.9 d for cows on the CM and SDP treatments, respectively. Milk samples were collected at 2, 6, and 10 wk postpartum. The concentrations of fat, protein, and lactose were determined in each sample. The rennet gelation properties were measured at 31°C using dynamic low-amplitude strain oscillatory rheometry. The following parameters were obtained from the resultant elastic shear modulus (G′): gelation time, maximum curd firming rate, and gel strength. Reducing the DP duration from 62 to 6 d resulted in increases in milk protein concentration (31.8 vs. 34.7 g/kg), maximum curd firming rate (2.58 vs. 3.60 Pa/min), and gel strength (69.4 vs. 90.5Pa). Increasing the dietary energy density decreased percentage milk fat (43.1 vs. 37.7 g/kg) but otherwise had no effect. Gel strength was correlated with maximum curd firming rate (r=0.99), and both variables were correlated with milk protein concentration (r=0.71 and r=0.73, respectively). The results indicate that decreasing the duration of the DP increased milk protein concentration and improved the rennet gelation properties of milk, but that dietary energy density had little effect.

The effect of dry period duration and dietary energy density on milk production, bioenergetic status, and postpartum ovarian function in Holstein-Friesian dairy cows

Following parturition, it is typical for dairy cows to enter a period of negative energy balance and body condition loss to support mammary milk synthesis; this is associated with compromised reproductive performance. Alternative management strategies during the prepartum (dry) and early postpartum periods may ameliorate this loss. Forty mature Holstein-Friesian cows were assigned to 1 of 2 dry period treatments [standard 8-wk dry period (SDP) or no planned dry period (NDP)] and 1 of 2 dietary energy density treatments [standard TMR (STMR) or high-quality TMR (HTMR)]. Milk yield during wk 1 to 12 postpartum was reduced in cows assigned to the NDP treatment. Energy balance and body condition score (BCS) during wk 1 to 4 postpartum were increased in cows assigned to the NDP treatment compared with the cows assigned to the SDP treatment, and BCS increased from wk 5 to 12 postpartum in the NDP cows compared with the SDP cows. During the first 12wk postpartum, cows assigned to the HTMR diet had greater milk yield and reduced milk fat concentration compared with the cows assigned the STMR diet. The BCS was greater from wk 5 to 12 postpartum in HTMR cows compared with STMR cows. During the period from wk −3 to +3 relative to parturition, circulating concentrations of insulin, glucose, and IGF-I were greater in cows in the NDP treatment compared with cows in the SDP treatment. Cows assigned to the HTMR diet had greater circulating insulin and glucose concentrations compared with the STMR cows from wk −3 to +3 relative to parturition. The first postpartum ovulation occurred earlier for cows in the NDP treatment compared with cows in the SDP treatment (16.9 vs. 24.8 d postpartum. Cows assigned to the STMR diet tended to have a higher conception rate to first service compared with cows assigned to the HTMR diet. Energy balance and metabolic status can be improved by either eliminating the dry period or by feeding a higher energy diet, but effects on the reproductive axis appear to be different.

A 1000‐year record of dry conditions in the eastern Canadian prairies reconstructed from oxygen and carbon isotope measurements on Lake Winnipeg sediment organics

AbstractA short sediment core (162 cm), covering the period AD 920–1999, was sampled from the south basin of Lake Winnipeg for a suite of multi‐proxy analyses leading towards a detailed characterisation of the recent millennial lake environment and hydroclimate of southern Manitoba, Canada. Information on the frequency and duration of major dry periods in southern Manitoba, in light of the changes that are likely to occur as a result of an increasingly warming atmosphere, is of specific interest in this study. Intervals of relatively enriched lake sediment cellulose oxygen isotope values (δ18Ocellulose) were found to occur from AD 1180 to 1230 (error range: AD 1104–1231 to 1160–1280), 1610–1640 (error range: AD 1571–1634 to 1603–1662), 1670–1720 (error range: AD 1643–1697 to 1692–1738) and 1750–1780 (error range: AD 1724–1766 to 1756–1794). Regional water balance, inferred from calculated Lake Winnipeg water oxygen isotope values (δ18Oinf‐lw), suggest that the ratio of lake evaporation to catchment input may have been 25–40% higher during these isotopically distinct periods. Associated with the enriched δ18Ocellulose intervals are some depleted carbon isotope values associated with more abundantly preserved sediment organic matter (δ13COM). These suggest reduced microbial oxidation of terrestrially derived organic matter and/or subdued lake productivity during periods of minimised input of nutrients from the catchment area. With reference to other corroborating evidence, it is suggested that the AD 1180–1230, 1610–1640, 1670–1720 and 1750–1780 intervals represent four distinctly drier periods (droughts) in southern Manitoba, Canada. Additionally, lower‐magnitude and duration dry periods may have also occurred from 1320 to 1340 (error range: AD 1257–1363), 1530–1540 (error range: AD 1490–1565 to 1498–1572) and 1570–1580 (error range: AD 1531–1599 to 1539–1606). Copyright © 2009 John Wiley &amp; Sons, Ltd.

Variation of Dry Days Since Last Rain (DDSLR) as a measure of dryness along a Mediterranean – Arid transect

Dry periods between rainstorms control the soil moisture conditions, and are the antecedent conditions for various geomorphological, hydrological and ecological processes. An annual distribution of dry condition, based on the Dry Days Since Last Rain (DDSLR) approach is presented, showing the duration and timing of dry periods for various daily rainfall thresholds and probabilities. Daily rainfall data from five stations along a climatic transect in Israel, extending from the Judean Mountains, which have a Mediterranean climate, to the Dead Sea arid region were studied. The results show that DDSLR values increased with increasing aridity. At a 0.1 mm rainfall threshold, the DDSLR values were similar along this transect. However, at higher daily thresholds, differences among different locations along the transect, become more noticeable.

Southern African Biological Soil Crusts are Ubiquitous and Highly Diverse in Drylands, Being Restricted by Rainfall Frequency

Biological soil crusts (BSCs) are found in all dryland regions of the world, including the polar regions. They are also known to occur in the southern African region. Although there were a number of case studies on BSCs from that region, we did not know if they are a normal part of the vegetation cover or just a phenomenon that occasionally occurs here and there. In order to investigate diversity, distribution patterns, and the driving factors of both, we followed a random sampling system of observatories along a transect, stretching from the Namibian-Angolan border down south to the Cape Peninsula, covering seven different major biomes. Biological soil crusts were found to occur in six out of seven biomes. Despite the fact that soil-dwelling algae occurred in the Fynbos biome, crust formation was not observed for hitherto unknown reasons. Seven BSC types were distinguished on the basis of morphology and taxonomic composition: three of them were cyanobacteria-dominated, one with additional chlorolichens, two with bryophytes, one hypolithic type restricted to quartz gravel pavements, and the unique lichen fields of the Namib Desert. Besides 29 green algal species in 21 genera, one heterokont alga, 12 cyanolichens, 14 chlorolichens, two genera of liverworts, and three genera of mosses, these crusts are positioned among the most diverse BSCs worldwide mainly because of the unusual high cyanobacterial species richness comprising 58 species in 21 genera. They contribute considerably to the biodiversity of arid and semi-arid bioregions. Taxonomic diversity of cyanobacteria was significantly higher in the winter rain zone than in the summer rain zone (54 versus 32 species). The soil photosynthetic biomass (chlorophylla/m2), the carbon content of the soil and the number of BSC types were significantly higher in the winter rain zone (U27, 29=215.0, p=0.004 [chla]; U21, 21=135.0, p=0.031 [C]; U27, 29=261.5, p=0.028 [BSC types]; excluding the fog-dominated Namib biome). The winter rain zone is characterized by a lower precipitation amount, but a higher rain frequency with the number of rainy days more evenly distributed over the year. The dry period is significantly shorter per year in the winter rain zone (U8, 9=5.0, p=0.003). We conclude that rain frequency and duration of dry periods rather than the precipitation amount is the main factor for BSC growth and succession. Nitrogen content of the soils along the transect was generally very low and correlated with soil carbon content. There was a weak trend that an increasing proportion of silt and clay (<0.63 mm) in the soil is associated with higher values of BSC chlorophyll content (Pearson correlation coefficient=0.314, p=0.237). Furthermore, we found a significant positive correlation between silt and clay and the number of BSC types (Pearson correlation coefficient=0.519, p=0.039), suggesting that fine grain-size promotes BSC succession and their biomass content. Lichens and bryophytes occurred in BSCs with lower disturbance frequencies (e.g. trampling) only. Crust thickness and chlorophyll content increased significantly from crusts of the early successional type to the late successional crust types. From our results, we conclude that BSCs are a normal and frequent element of the vegetation in arid and semi-arid southwestern Africa, and that rain frequency and duration of dry periods rather than the precipitation amount are the key factors for the development, differentiation and composition of BSCs.

Evaluation of prognostic factors and middle ear risk index in tympanoplasty

The aim of this study was to examine the role of the prognostic factors and middle ear risk index on the success of tympanoplasty. Case series. The charts of 231 patients who underwent tympanoplasty operations between 2002 and 2007 were reviewed. Prognostic factors such as age, sex, presence of systemic diseases, location and size of perforation, duration of dry period, presence of myringosclerosis, presence of septal and conchal pathology, operation type, and status of the opposite ear and middle ear risk index were investigated. The overall success rate was 74.4%. Multivariate analysis was carried out on significant prognostic factors to obtain independent variables and yielded the following results (95% CI): size of the perforation (<50%) (OR:8.11), healthy opposite ear (OR:5.64), more than 3 months dry period (OR:2.21), absence of myringosclerosis (OR:4.01) and low middle ear risk index (OR:87.1). Size of the perforation(<50%), healthy opposite ear, absence of myringosclerosis, more than 3 months dry period, and low middle ear risk index were found to be significant independent prognostic factors.