Periods Of High Rainfall Research Articles

Response of reptiles to weed-control and native plant restoration in an arid, grass-invaded landscape

Introduced grasses are a major threat to dryland ecosystems world-wide because of their ability to transform plant communities and change fire regimes. These structural and functional shifts are often assumed to impact wildlife but this has rarely been measured directly. Likewise, evaluation of weed removal programs rarely considers benefits to fauna, thereby limiting information that could inform management decisions. We used an experimental approach to test the impacts of removing invasive buffel grass (Cenchrus ciliaris), a globally significant invader of dryland systems, on reptiles, a prominent component of the Australian desert fauna. A combination of mechanical and herbicide treatment was applied to replicate plots in areas that had been invaded for at least two decades and changes to ground cover and plant and reptile assemblages were monitored over six years and compared to still-invaded control plots. Following treatment, native plants re-established without the need for reseeding or planting, especially during a period of high rainfall, when positive effects on reptiles also became apparent. The abundance and species richness of reptiles increased at all plots during the mesic period, but less so in control plots, and remained higher at treated plots thereafter, although this was only significant at some times. Post-treatment 27 of 36 species were captured more frequently in treated plots and only four species, all with very low captures, were captured more often in invaded control plots. This consistent trend among species suggests negative impacts of buffel grass on reptiles are likely caused by broad factors such as reduced prey or habitat diversity. Together with concurrent research at the same sites, our results provide experimental evidence that removing buffel grass from heavily invaded areas, even at small scales, benefits a variety of native flora and fauna. Until landscape-scale options are available, restoration of smaller areas within buffel-invaded landscapes can help to preserve native seed banks and adult plants, reduce fire impacts, and provide patches of favourable habitat for fauna. The creation of ‘islands’ of restored native vegetation deserves further consideration as an effective intervention that could help to achieve short and long-term conservation goals in grass-invaded dryland ecosystems.

The variation and controls of mean transit times in Australian headwater catchments

AbstractDetermining mean transit times in headwater catchments is critical for understanding catchment functioning and understanding their responses to changes in landuse or climate. Determining whether mean transit times (MTTs) correlate with drainage density, slope angle, area, or land cover permits a better understanding of the controls on water flow through catchments and allows first‐order predictions of MTTs in other catchments to be made. This study assesses whether there are identifiable controls on MTTs determined using 3H in headwater catchments of southeast Australia. Despite MTTs at baseflow varying from a few years to >100 years, it was difficult to predict MTTs using single or groups of readily‐measured catchment attributes. The lack of readily‐identifiable correlations hampers the prediction of MTTs in adjacent catchments even where these have similar geology, land use, and topography. The long MTTs of the Australian headwater catchments are probably in part due to the catchments having high storage volumes in deeply‐weathered regolith, combined with low recharge rates due to high evapotranspiration. However, the difficulty in estimating storage volumes at the catchment scale hampers the use of this parameter to estimate MTTs. The runoff coefficient (the fraction of rainfall exported via the stream) is probably also controlled by evapotranspiration and recharge rates. Correlations between the runoff coefficient and MTTs in individual catchments allow predictions of MTTs in nearby catchments to be made. MTTs are shorter in high rainfall periods as the catchments wet up and shallow water stores are mobilized. Despite the contribution of younger water, the major ion geochemistry in individual catchments commonly does not correlate with MTTs, probably reflecting heterogeneous reactions and varying degrees of evapotranspiration. Documenting MTTs in catchments with high storage volumes and/or low recharge rates elsewhere is important for understanding MTTs in diverse environments.

Uncarina roeosliana Rauh ontomorphogenesis in early stages of development

The aim. To find out the morphology of the seeds and the features of its germination and to study the development of Uncarina roeoesliana Rauh (Pedaliaceae) plants in the early stages of ontogeny in connection with the problem of a seed germination and their cultivation under introduction.Materials and methods. The latent and pregenerative periods of the ontomorphogenesis of Uncarina roeoesliana plants under growing conditions in the protected soils of the Botanical garden named after acad. O.V. Fomin were investigated. Biomorphological, introducting, histological methods were used in this work.Results. A method of accelerating the germination of freshly harvested seeds has been developed. Uncarina roeoesliana seeds are large (about 7x5 mm), mostly wide-triangular, brown in colour with little-noticed wing around the perimeter of the seed. The dorsal side forms folds, the hem is on the micropillary part of the seed. The periclinal walls are convex and often with papillae. The embryo is large, occupies most of the seed, the endosperm has a lot of lipids, which is typical for the representative of the same family Sesamum indicum L. The presence of papillae probably contributes to the moisture accumulation to increase the enzymatic activity when the seeds are swell. All of these features of seed germination are consistent with the environmental conditions of Uncarina's natural habitats: high temperatures, low rainfall and significant dry periods. Probably the plants of this species belong to macrobiotics, that is, they can retain seed germination for a long time. The germination is aboveground. During the 24 weeks of development, the plants reach the virginal stage of development: they form radish roots, 5-6 pairs of leaves, of which only two pairs remain in the young plants at this stage, and a thickened basal part of the stem .Conclusions. Comparing Uncarina roeoesliana with other caudiciform plants, we can conclude that this plant has a high potential for survival in arid conditions due to the ability of seeds to germinate only in conditions of considerable moisture and the ability of the plant to accumulate moisture in the basal part of the stem and in fleshy roots. In this case, the plant is adapted to exist both in the mode of a dormancy and in the mode of an active growth, but in the latter case only in the presence of sufficient moisture in the soil

Sustainability of groundwater through community-driven distributed recharge: An analysis of arguments for water scarce regions of semi-arid India

Study Region: Semi-Arid Regions of Marathawada, Vidarbha and Saurashtra in IndiaStudy Focus: To understand and evaluate the impact of Managed Aquifer Recharge (MAR) efforts.New Hydrological Insights for the Region: Since 1990, the Saurashtra region of Gujarat, India witnessed a massive community-based distributed groundwater recharge movement, initially catalyzed by NGOs and later supported by the government. The region has witnessed visible improvement in groundwater resources during recent years, which was attributed by some researchers to the recharge movement. A competing hypothesis holds that improvement in groundwater levels in Saurashtra are a result more due to a succession of good rainfall years during 2001–2014, aided by transfer of surface water from a big dam on Narmada River, rather than the distributed recharge movement. We develop and implement a 2-way test of these competing hypotheses: First, we compare groundwater recharge patterns in Saurashtra during a recent period of high rainfall years with a similar period before the onset of the recharge movement; second, for both these high rainfall periods, we also compare groundwater recharge patterns in two other comparable aquifer and terrain regions, viz., Vidarbha and Marathawada in Maharastra, which did not experience recharge movement on the same scale as Saurashtra did. Our results support the hypothesis that the community supported distributed recharge movement is the key to improved groundwater recharge in Saurashtra during 2004-09.

Partitioning the influence of hydrodynamics-induced physical variables and nutrients on phytoplankton assemblages in a shallow tropical reservoir (Koka, Ethiopia)

Ecological processes, population dynamics and species interactions in shallow lakes and reservoirs are affected by seasonal and inter-annual fluctuations in rainfall and runoff. The present study aimed to explore the relationship between riverine runoff and phytoplankton community structure in Koka Reservoir, Ethiopia. Onsite measurements and collection of water samples and phytoplankton were performed at monthly intervals from January to August 2016 at three sampling sites along a stretch of the reservoir running from the river mouth to center and the outlet (dam). The results showed the decline in phytoplankton biomass at the river mouth site. The decline was particularly noticeable during the period of high rainfall and runoff compared to that of the low water period. This was associated with the hydrodynamics-induced high turbidity and reduced euphotic depth. Our results implied that phytoplankton community structure was strongly influenced by flood pulse. The results suggest that river flow and watershed management have the potential to be used more widely as an aquatic resources management option in small and medium-sized lakes and reservoirs.

Hurricanes, El Ni\xf1o and harmful algal blooms in two sub-tropical Florida estuaries: Direct and indirect impacts

Future increases in the intensity of hurricanes and El Niño periods predicted by climate change models have focused attention on their role in stimulating harmful algal blooms (HABs). A series of hurricanes that recently impacted Florida (USA) provided a unique opportunity to explore the relationships between hurricanes, El Niño and HABs in two Florida estuaries subject to repeated intense ecosystem disruptive HABs, the Indian River Lagoon and the St. Lucie Estuary. The roles that hurricanes and El Niño play in contributing to HAB events are examined in the context of key structural and functional features of each estuary and their watersheds, including morphology, water residence time and hydrology, such as the influence of Lake Okeechobee discharges into the St. Lucie Estuary. The most direct impact was the increase in rainfall associated with hurricanes and El Niño, resulting in enhanced nutrient loads which drive HABs in the Indian River Lagoon and Lake Okeechobee. Major HABs in Lake Okeechobee also present an indirect threat of freshwater HAB blooms in the St. Lucie Estuary via mandated discharges from the lake into the estuary during high rainfall periods. Conversely, during the absence of HABs in Lake Okeechobee, short water residence times produced by discharges into the St. Lucie Estuary can result in lower bloom intensities.

Hydroclimate influences on modern pollen rain of upland southeastern Amazonia

For accurate interpretations of palaeopalynological data, it is important to understand the influence of the current vegetation composition and characteristics on the formation of the palynological assemblage recorded in artificial or natural pollen traps. Therefore, in this study, modern pollen rain was characterized using artificial pollen traps under different ecological conditions and climatic seasons in Trilha da Mata Lake, Carajás North Ridge, southeastern Amazonia. The collection of pollen rain data comprises the total period from September 2015 to August 2016. There were two periods of low rainfall (September to December 2015 and May to August 2016) and one period of high rainfall (January to April 2016). The first two periods were represented by a predominance of canga vegetation pollen relative to forest pollen. Under dry conditions, the associations among the taxa Aparisthmium/Alchornea, Myrcia and Bellucia dichotoma were considered important for forest ecosystems, while those among Pleroma, Hyptis parkeri, Borreria and Perama carajensis were considered important for canga ecosystems. Under wet conditions, the forests were well represented by Schefflera, Anthurium lindmanianum, Pseudopiptadenia suaveolens and Glycydendron, and the most represented canga vegetation in the pollen rain were Poaceae undif., Miconia, M. acutistipula var. ferrea and Psychotria. Aparisthmium/Alchornea and Poaceae undif. Aparisthmium/Alchornea was related to periods of low water availability, and Poaceae undif. was associated with marshy or flooded environments. Thus, an increase in the influx of Poaceae undif. pollen grains was determined by variations in the extension of flooded areas, indicating an increase in the amount of rainfall and not the opposite case. Thus, future studies on vegetation reconstruction must consider modern pollen assemblages to precisely determine paleoenvironmental and paleoclimate conditions during sediment deposition.

Using non-systematically collected data to evaluate the conservation status of elusive species: a case study on Australia’s Oenpelli python

Abstract ContextSpecies conservation assessments require information on distribution, habitat requirements and population demography and trends. Uncertain conservation assessments limit effective planning and may lead to poor management decisions. Top-order predators generally receive considerable attention from ecologists and conservation biologists, with the notable exception of large pythons and boas. They are typically elusive and have low population densities, posing challenges for ecological research and monitoring. Ecological and demographic data are lacking for most large snake species and are generally inadequate to properly assess conservation status or to evaluate their broader ecological roles. The Oenpelli python (Simalia oenpelliensis) is Australia’s second-longest snake species, but remains one of the least-known of the world’s pythons. AimsWe sought to use non-systematically collected data from multiple sources to evaluate Oenpelli python population trends and habitat associations, and to assess its conservation status. MethodsWe identified a priori biases in data and evaluated their influences on environmental models and temporal variability in reporting patterns. We then used these findings to assess the conservation status of this species, identify knowledge gaps, and refine future survey and monitoring methods. Key resultsOenpelli python records were strongly associated with monsoon rainforest, sandstone outcrops and perennial streams, irrespective of detection biases. Total area of occupancy was estimated to be 19252km2. Detection patterns were strongly seasonal and associated with periods of low rainfall and low moonlight, informing better-targeted survey and monitoring methods with improved sensitivity. ConclusionsOenpelli pythons have a highly fragmented distribution owing to their strong association with monsoon rainforest. This habitat is likely to provide more food resources and refuge from high temperatures than are the surrounding savanna woodlands. Detection probability should improve by surveying Oenpelli pythons in September on moonless nights and following periods of high rainfall. Taking a precautionary approach, the Oenpelli python qualifies as Vulnerable under IUCN criteria, supporting its current Red List and Northern Territory Government status. ImplicationsNon-systematically collected data on poorly known species can be used to improve conservation assessments where there may otherwise be high uncertainty. The present study also highlighted the paucity of ecological knowledge of large iconic snake species globally.

Edible Mushrooms of Ecuador: consumption, myths and implications for conservation

Background: Ecuador is divided into three geographical regions: Amazon, Coast and Mountains, on which one having its own empirical knowledge and traditions in relation to their natural environments. Studies about traditional knowledge of macrofungi were initially carried out in the Brazilian Amazon and later in Colombia, Guyana and Venezuela. In Ecuador few studies have been published. Thus, the aim of this study is to investigate many ethnomycological data of the edible mushrooms used by several ethnic Ecuadorian groups, discussing the meanings of species’ vernacular names and related myths.Methods: The ethnomycological data of the edible mushrooms were collected in 13 indigenous communities of Ecuador during periods of high rainfall from 2002 to 2016, with interviews and forums. Additionally, the fungal specimens were collected, and voucher deposited at Herbarium QAP.Results: Thirty-seven edible species of macrofungi were identified and some of them are discussed in relation to aspects like local peoples’ mythologies, habits or tradition, their preparation for consumption and myths. Thus, this research added new several ethnomycological data and helped to understand the mycophagous behavior in Ecuador.Conclusions: These studies should continue in order to prevent ethnobiological loss caused by the degradation of the environment in which these people live, causing a loss of the biodiversity. In addition, biological conservation of these ecosystems is urgent since many natural resources are used for these indigenous communities as food consumptions.Key words: Amazonia, biodiversity, Coast, Fungi, Páramos, South America

Seroprevalence of Rift valley fever in South African domestic and wild suids (1999–2016)

Rift valley fever (RVF) is a vector-borne viral disease of domestic ruminants, camels and man, characterized by widespread abortions and neonatal deaths in animals, and flu-like symptoms, which can progress to hepatitis and encephalitis in humans. The disease is endemic in Africa, Saudi Arabia and Yemen, and outbreaks occur after periods of high rainfall, or in environments supporting the proliferation of RVF virus (RVFV)-infected mosquito vectors. The domestic and wild animal maintenance hosts of RVFV, which may serve as sources of virus during inter-epidemic periods (IEPs) and contribute to occurrence of sporadic outbreaks, remain unknown, although reports indicate that the African buffalo (Syncerus caffer) may play a role. Due to the close proximity of the habitats of domestic pigs and warthogs to those of known domestic and wild ruminant RVFV maintenance hosts respectively, our study investigated their possible role in the epidemiology of RVF in South Africa by evaluating RVFV exposure and seroconversion in suids. A total of 107 warthog and 3,984 domestic pig sera from 2 and all 9 provinces of South Africa, respectively, were screened for presence of RVFV neutralizing antibodies using the virus neutralization test (VNT). Sero-positivity rates of 1.87% (95% CI: 0.01%-6.9%) and 0.68% (95% CI: 0.49%-1.04%) were observed for warthogs and domestic pigs, respectively, but true prevalence rates, taking test sensitivity and specificity into account, were lower for both groups. There was a strong association between the results of the two groups (χ2 =0.75, p=.38), and differences in prevalence between the epidemic and IEPs were non-significant for all suid samples tested (p>.05). This study, which provides the first evidence of probable exposure and infection of South African domestic pigs and warthogs to RVFV, indicates that further investigations are warranted, to fully clarify the role of suids in the epidemiology of RVF.

Assessment of Spatial Variability and Temporal Dynamics of Dissolved Organic Matter (DOM) at Lower Kinabatangan River Catchment, Sabah.

The spatial and temporal variability of dissolved organic matter (DOM) characteristics and surface water quality in the Lower Kinabatangan River Catchment were determined between October 2015 and May 2016. The objectives of this study were: (i) to distinguish the DOM absorption characteristics and physicochemical quality of surface water draining from different types of land use: oil palm plantation (OP), secondary forest (SF) and semi-natural vegetation (SV); and to examine its temporal variations during dry and wet periods. The collected physicochemical parameters data was analysed and classified based on the Malaysian National Water Quality Standard (NWQS). Findings indicated all the parameters fall into Class I, except for pH, total suspended solids (TSS) and concentration dissolved oxygen (DO). Linear discriminant analysis has been applied to distinguished the physico-chemical and absorption DOM properties data into mutually-exclusive spatial and temporal groups. Interestingly, the pH, DO and total nitrogen values were exhibited as dominant parameters at SV during both low and high rainfall periods. The dominance of these parameters suggested that the spatially and temporally varied water quality were influenced by both natural processes (e.g precipitation rate) and anthropogenic factor (e.g land use change). Whereas, both absorption coefficients (a340) and spectral slope (S275-295) were more dominant at SF and OP respectively. This might be due to increasing terrestrial DOM loadings as well as significant degradation of DOM via microbial and/or photochemical reaction.

Fugitive methane emissions through the cover system of a Brazilian landfill cell

This paper evaluates the fugitive emissions of methane through a compacted soil cover layer in a cell of the Metropolitan Center Sanitary Landfill, in Salvador, Bahia, Brazil. Static-flow chamber tests were carried out in cracked and non-cracked soil areas in periods of high and low rainfall. Correlation coefficients between fugitive emissions and variables such as precipitation, moisture content and distance from drains, among others, were tested, and empirical equations are proposed for the estimation of fugitive emissions in both areas. Non-linear multiple regressions were able to fit the experimental results. However, a large number of independent variables were required. The fugitive methane emissions ranged from 0 to 356 (g/m2)/d. During the rainy season, points located in cracked areas showed an increase in emissions, with cracks in the soil acting as preferential flow paths. The opposite occurred in areas with few fissures and cracks. Considering the field biogas recovery rate, fugitive methane emissions accounted for, on average, 12% of the methane produced in the area in the period of analysis.

Identifying the deep groundwater recharge processes in an intermountain basin using the hydrogeochemical and water isotope characteristics

Abstract The hydrogeochemical and stable isotopes of water (δD and δ18O) were combined to investigate the deep groundwater recharge processes in the geologically complex intermountain basin (Kathmandu Valley). Results of the stable isotopic composition of the deep groundwater compared with global and local meteoric water lines and d-excess showed the deep groundwater as a meteoric water origin which is insignificantly affected by evaporation. The analysis suggests the deep groundwater was recharged during high rainfall periods (wet season). Additionally, the control of seasonal variation was absent in the deep groundwater and in the spring water samples. The large range of isotopic composition distribution was due to the altitude affect, whereas variations are from the various geological settings of the infiltration encountered during the recharge processes. The tri-linear diagram showed Na-K-HCO3 and Ca-Mg-HCO3 as the two major water types. The distribution of water types in this intermountain basin was found to be unique compared to other basins. Ionic concentration of the samples was found to be higher in the central part than in the periphery due to the ion exchange processes. This study determines the spatial distribution of various recharge processes that depends upon the environment during rainfall and the geological settings.

SEASONALITY IN BATRACHOCHYTRIUM DENDROBATIDIS DETECTION IN AMPHIBIANS IN CENTRAL OKLAHOMA, USA.

Chytridiomycosis, an infectious disease caused by the fungus Batrachochytrium dendrobatidis (chytrid or Bd), has not been well studied in Oklahoma. This is of particular concern regarding the connection between seasonality and chytrid infection. To further investigate this connection, chytrid prevalence and infection load were quantified within amphibians in central Oklahoma from March to October, across two sites in Oklahoma Co. and two sites in Cleveland Co. The results show a trend between seasonality and chytrid, with spring and fall showing higher prevalence and summer showing lower prevalence, which coincides closely with the preferred chytrid growth temperatures. Additionally, periods of high rainfall in May 2015 are linked to increased chytrid prevalence, as has been suggested by other research. Additionally, species exhibiting high chytrid prevalence follow the results of previous studies: Blanchard's cricket frog (Acris blanchardi), American bullfrog (Rana catesbeiana), and southern leopard frog (Rana sphenocephala).

Rare plant species do not occupy water-remote refuges in arid environments subject to livestock grazing.

In many of the world's arid regions there has been a dramatic increase in grazing pressure with herds of livestock sustained by the provision of artificial water points. In these systems it has been suggested that grazing-sensitive plant species will have contracted to refuges distant from water points where grazing impacts are low. This association was tested using a large data set of presence/absence records for rare plant species throughout the northeastern Australian arid zone. The presence records of only one of 45 species were statistically associated with lower grazing activity, as a function of distance-to-water, than the absence records. The field observation that this species is rarely grazed suggests it is not susceptible to grazing pressure. In general, the study supports assertions that populations of short-lived plants in drylands are resilient in the face of exaggerated livestock grazing because herbivores are not in sufficient densities to have an impact during the sporadic periods of high rainfall when plants can complete their life cycles. However, long-lived palatable species may be extinction-prone in grazed landscapes over long time frames if recruitment is curtailed by grazing.

Distribución espacial y temporal de Elmidae (Insecta: Coleoptera) y su relación con los parámetros fisicoquímicos en el río Ocoa, Meta, Colombia

Los élmidos (Coleoptera) son organismos acuáticos de distribución mundial. Sus formas inmaduras y adultas ocupan una amplia gama de sustratos y hábitats, y son un grupo diverso. Este estudio tuvo como objetivo determinar la distribución espacial y temporal de los Elmidae, y su relación con los parámetros fisicoquímicos en el río Ocoa. Se establecieron 15 estaciones de muestreo y se revisaron 210 muestras de macroinvertebrados recolectadas en un sustrato de roca-guijarro utilizando una red Surber (250 μm) en dos periodos hidrológicos contrastantes (de baja y alta precipitación), correspondientes a octubre de 2014 y febrero de 2015. Se obtuvieron 37 organismos (larvas y adultos) de nueve géneros de Elmidae: Heterelmis, Huleechius, Macrelmis, Astrolimnius, Microcylloepus, Neoelmis, Hexacylloepus, Cylloepus, Notelmis y Phanocerus, de los cuales siete corresponden a nuevos registros para la región de la Orinoquia colombiana. En el periodo de baja precipitación hubo una mayor representatividad, con 35 registros de nueve géneros, en tanto que en el periodo de alta precipitación hubo una marcada disminución de la riqueza, con dos registros solamente, correspondientes a dos géneros. En general, la abundancia de Elmidae fue baja a lo largo del río, y en las estaciones ubicadas en el sector que atraviesa la ciudad de Villavicencio, con mayor deterioro del hábitat, se registró la menor abundancia y en algunas no se registraron élmidos. Los efectos ambientales de la urbanización, como la contaminación por materia orgánica y la proliferación de coliformes debida al vertimiento de aguas residuales, fueron los principales factores determinantes de la disminución de la riqueza y la abundancia de estos organismos. Esta es la primera exploración de Elmidae en la zona y contribuye al conocimiento ecológico de la fauna de coleópteros en cuencas urbanas de la Orinoquia colombiana. © 2019. Acad. Colomb. Cienc. Ex. Fis. Nat. Palabras clave: Bioindicador; Coleoptera; Elmidae; Cuenca urbana; Orinoco.

Precipitation variations and shifts over time: Implication on Windhoek city water supply

The scarcity of freshwater is a growing concern around the world, especially in the developing world and is increasingly threatening human survival in less affluent parts of the world. In arid and semiarid regions, freshwater resources are imperative for the survival of populations as well as development activities in urban centres. Preceding assessments for potential solutions have underestimated the scarcity of water by failing to capture main trends of precipitation and the extent of drought periods. This paper aims to investigate rainfall trends for the City of Windhoek, Namibia. A century scale is examined by reconstructing historical precipitation records, and future trends are subsequently estimated and interpolated using Ordinary Kriging in ArcGIS 10.3. Kriging responds and handles spatial correlation much better for observed data points. The results show locations that receive high rainfall and potential periods for harvesting rainwater. The findings further show that the periods of high rainfall are shorter, and after each high rainfall stretch, a long period of lower rainfall follows immediately. Each low rainfall period is anticipated to last longer than the previous one. These scenarios are highly significant for urban managers in dryland cities such as Windhoek, as they demonstrate when water would need to be extra sparingly managed. This study highlights the need for better water management strategies, if cities in dry climates are to survive the anticipated future water crises.

Controls on Land Surface Temperature in Deserts of Southern California Derived from MODIS Satellite Time Series Analysis, 2000 to 2018

The land surface temperature (LST) in arid regions is a primary controller of many ecological processes. Consequently, we have developed a framework for detection of LST change on a regional scale using data sets covering all deserts of southern California from the Moderate-Resolution Imaging Spectroradiometer (MODIS) satellite sensor. The Breaks for Additive Season and Trend (BFAST) methodology was applied to MODIS 1-km monthly LST data from the years 2000 to 2018 to estimate significant time series shifts (breakpoints) and gradual trends. Area-wide results showed five times more positive LST breakpoints (abrupt temperature warming events) than negative (surface cooling) breakpoints. Cross-correlations with high rainfall periods around Mojave dry lake playas, and comparison with timing of wildfire burns for breakpoint patterns, showed that abrupt shifts in LST had the strongest response to these controllers. We detected negative LST (abrupt cooling) breakpoints as consistently associated with the construction of new solar energy facilities. Over the majority of the study area, BFAST results showed warming LST trends between the years 2000 and 2018. The western-most margins of the study area showed consistent widespread warming trends, whereas the eastern portions of the Mojave and Lower Colorado Deserts showed a mix of positive and neutral LST trends. Long-term cooling LST trends were detected only in some of the largest dry lake formations in the Antelope Valley, Death Valley, and Bristol, Cadiz, and Danby playas.

Uncovering mechanisms behind mosquito seasonality by integrating mathematical models and daily empirical population data: Culex pipiens in the UK

BackgroundMany mosquito-borne diseases exhibit substantial seasonality, due to strong links between environmental variables and vector and pathogen life-cycles. Further, a range of density-dependent and density-independent biotic and abiotic processes affect the phenology of mosquito populations, with potentially large knock-on effects for vector dynamics and disease transmission. Whilst it is understood that density-independent and density-dependent processes affect seasonal population levels, it is not clear how these interact temporally to shape the population peaks and troughs. Due to this, the paucity of high-resolution data for validation, and the difficulty of parameterizing density-dependent processes, models of vector dynamics may poorly estimate abundances, which has knock-on effects for our ability predict vector-borne disease outbreaks.ResultsWe present a rich dataset describing seasonal abundance patterns of each life stage of Culex pipiens, a widespread vector of West Nile virus, at a field site in southern England in 2015. Abundance of immature stages was measured three times per week, whilst adult traps were run four nights each week. This dataset is integrated with an existing delay-differential equation model predicting Cx. pipiens seasonal abundance to improve understanding of observed seasonal abundance patterns. At our field site, the outcome of our model fitting suggests interspecific predation on mosquito larvae and temperature-dependent larval mortality combine to act as the main sources of population regulation throughout the active season, whilst competition for resources is a relatively small source of larval mortality.ConclusionsThe model suggests that density-independent mortality and interspecific predation interact to shape patterns of mosquito seasonal abundance in a permanent aquatic habitat and we propose that competition for resources is likely to be important where periods of high rainfall create transient habitats. Further, we highlight the importance of challenging population abundance models with data from across all life stages of the species of interest if reliable inferences are to be drawn from these models, particularly when considering mosquito control and vector-borne disease transmission.

Stormwater influences phytoplankton assemblages within the diverse, but impacted Sydney Harbour estuary.

Sydney Harbour is subjected to persistent stress associated with anthropogenic activity and global climate change, but is particularly subjected to pulse stress events associated with stormwater input during episodic periods of high rainfall. Photosynthetic microbes underpin metazoan diversity within estuarine systems and are therefore important bioindicators of ecosystem health; yet how stormwater input affects their occurrence and distribution in Sydney Harbour remains poorly understood. We utilised molecular tools (16S/18S rRNA and petB genes) to examine how the phytoplankton community structure (both prokaryotes and eukaryotes) within Sydney Harbour varies between high and low rainfall periods. The relative proportion of phytoplankton sequences was more abundant during the high rainfall period, comprising mainly of diatoms, an important functional group supporting increased productivity within estuarine systems, together with cyanobacteria. Increased spatial variability in the phytoplankton community composition was observed, potentially driven by the steepened physico-chemical gradients associated with stormwater inflow. Conversely, during a low rainfall period, the proportion of planktonic photosynthetic microbes was significantly lower and the persistent phytoplankton were predominantly represented by chlorophyte and dinoflagellate sequences, with lower overall diversity. Differences in phytoplankton composition between the high and low rainfall periods were correlated with temperature, salinity, total nitrogen and silicate. These results suggest that increased frequency of high-rainfall events may change the composition, productivity and health of the estuary. Our study begins to populate the knowledge gap in the phytoplankton community structure and substantial changes associated with transient environmental perturbations, an essential step towards unravelling the dynamics of primary production in a highly urbanised estuarine ecosystem in response to climate change and other anthropogenic stressors.