Flush Event Research Articles

Elevated dissolved heavy metal discharge following rainfall downstream of intensive horticulture

Heavy metals may be released from soils during rain events. Observations during the first flush (rain event preceded by dry period) are difficult, but may account for a large fraction of annual loads. Here, we report detailed time series measurements of dissolved heavy metals and the groundwater tracer radon (222Rn) over multiple rain events from a creek draining a catchment dominated by intensive horticulture on the subtropical east coast of Australia. The creek drains to an intermittently closed and open lake or lagoon (ICOLL), a typical estuary type along the east coast of Australia. A sandbank prevents the estuary mouth from connecting with the ocean during dry conditions. Following a 109 mm rain event, the ICOLL began to drain to the coastal ocean. Mean export of Hg, Cu, and Zn was 0.23 ± 0.05, 1.06 ± 0.25, and 15.70 ± 2.69 g m−2 day−1 for the entire time series and 0.72 ± 0.17, 1.27 ± 0.12, 24.14 ± 3.82 g m−2 day−1 averaged from high resolution sampling over 72 h of the first flush event. Trends of Hg export differed from the other heavy metals. Over 79% of the estimated Hg export occurred within 72 h of the ICOLL opening, compared to 30 and 38% of Cu and Zn. The first flush and subsequent major rain events (> 50 mm day-1) drove concentrations of Hg, Cu and Zn to exceed the Australia and New Zealand Environment and Conservation Council (ANZECC) water quality guidelines (WQG) for both fresh and marine water. Comparisons of heavy metal export to downstream estuary sediment burial rates revealed that the estuary is likely a source of dissolved Hg and Cd to the coastal ocean when the ICOLL is open.

Dissolved Organic Matter Compositional Change and Biolability During Two Storm Runoff Events in a Small Agricultural Watershed

AbstractAgricultural watersheds are globally pervasive, supporting fundamentally different organic matter source, composition, and concentration profiles in comparison to natural systems. Similar to natural systems, agricultural storm runoff exports large amounts of organic carbon from agricultural land into waterways. But intense management of upper soil layers, waterway channelization, wetland and riparian habitat removal, and postharvest vegetation removal promise to uniquely drive organic matter release to waterways. During a winter first flush and a subsequent storm event, this study investigated the influence of a small agricultural watershed on dissolved organic matter (DOM) source, composition, and biolability. Storm water discharge released strongly terrestrial yet biolabile (23 to 32%) dissolved organic carbon (DOC). Following a 21 day bioassay, a parallel factor analysis identified an 80% reduction in a protein‐like (phenylpropyl) component (C2) that was previously correlated to lignin phenol concentration, and a 10% reduction in a humic‐like, terrestrially sourced component (C4). Storm‐driven releases tripled DOC concentration (from 2.8 to 8.7 mg L−1) during the first flush event in comparison to base flow and were terrestrially sourced, with an eightfold increase in vascular plant derived lignin phenols (23.0 to 185 μg L−1). As inferred from system hydrology, lignin composition, and nitrate as a groundwater tracer, an initial pulse of dilute water from the upstream watershed caused a counterclockwise DOC hysteresis loop. DOC concentrations peaked after 3.5 days, with the delay between peak discharge and peak DOC attributed to storm water hydrology and a period of initial water repellency of agricultural soils, which delayed DOM leaching.

Mango trees have no distinct phenology: The case of mangoes in the tropics

We propose a convenient, easily observable set of landmark developmental stages during vegetative and flowering flushes and fruiting events to characterize the changes through which individual growing mango shoots pass in the tropics and subtropics. Individual non-growing stems are in the Resting stage (R), when the apical bud (following a previous vegetative growth event) or lateral buds (following a previous flowering event) are dormant. A flush event is one in which the resting buds on many stems in a section of tree canopy initiate growth (asynchronous flush) or when the entire canopy initiates bud growth at once (synchronous flush). The stages describing vegetative shoot growth are: Vegetative Bud Emergence and Development stage, Elongating Green Leaf stage, Limp Red Leaf stage (LRL), Immature Green Leaf stage, and Mature Green Leaf stage. Reproductive growth stages in purely flowering, or generative, shoots are: Floral Bud Initiation, Emergence and Development stage, Early Panicle Elongation stage, Mid-size Panicle Early Anthesis stage, and Full-size Panicle Maximum Anthesis stage. Fruiting stages are: Emergent Fruit stage, Small-size Green Fruit stage, Mid-size Green Fruit stage, Near Full-size Immature Fruit stage, and the Full-size Mature Fruit stage. Mixed shoots, bearing both leaves and lateral inflorescences at each node, exhibit characteristics of both vegetative and flowering shoots. Landmark stages for Tommy Atkins and Keitt, two cultivars commercially growing in the Americas, were observed in tropical orchards near the village of La Mesa, Colombia. Tommy Atkins leaves had a more intense red coloration during the LRL than did ‘Keitt’. More pedicels were found in ‘Tommy Atkins’ than in ‘Keitt’ during panicle development. Young fruits of ‘Tommy Atkins’ developed their distinctive, dark red coloration, whereas ‘Keitt’ fruit developed less intense reddish coloration once they were mature. Aside from these minor phenotypic differences in distinctive shoot and stem developmental stages, attempts to ascribe a distinct phenological pattern of mango tree growth and development are impractical. Each stem terminal or groups of stem terminals borne on scaffolding branches act as independent structures influenced by environmental conditions, such as temperature, water relations, and nutrition coupled with their physiological age resulting in widely variable tree responses even in similar environments.

Role of seed settleability and settling velocity in water for plant colonization of river gravel bars

AbstractQuestionsA natural gravel‐bed river is an important habitat for xerophytic plant species that prefer dry and periodically disturbed environments. However, human‐impacted gravel bars covered with fine sandy sediments are often rapidly occupied by hygrophytic and mesophytic species, including weedy species, after a flush event. What is the mechanism by which these plant seeds are carried on gravel bars through a flush event? Can the seed traits of floating capability (buoyancy or settleability) and settling velocity in water explain seed accumulation in sandy sediments?LocationThe Tama River, central Japan.MethodsSeed buoyancy/settleability and settling velocity in water were examined for 70 herbaceous species growing on newly deposited sediments of a river gravel bar. Settling velocities of sand particles of different sizes were estimated using theoretical formulas to compare with those of plant seeds. In addition, actual seed content of 36 samples of fresh sandy sediments were examined using a germination test to confirm coincident sedimentation of seeds and sand particles.ResultsOf the 70 species examined, only nine had apparently buoyant seeds and the remaining 61 species had non‐buoyant seeds. We found that 53 (86.9%) of the 61 species having non‐buoyant seeds had settling velocities comparable to those of very fine sand and fine sand particles, ranging from 0.062 to 0.25 mm in diameter. Furthermore, fresh sandy sediments deposited by a flush event contained many non‐buoyant seeds of common species of above‐ground vegetation. Both the germinated seedling number and species richness in the sediment samples showed positive correlation with the percentage weight of very fine sand and fine sand.ConclusionsSeeds of most of the species that appeared after a flush event were considered carried by submerged dispersal through flowing water than through floating dispersal, because of their settleability. Many plant seeds could deposit together with fine sandy sediments as water velocity declined, since they had correspondent settling velocities. The main reason for rapid colonization by hygrophytic and mesophytic species was the settleability and settling velocity of the seeds.

Biogeochemical behavior of organic carbon in a small tropical river and estuary, Hainan, China

The biogeochemistry of a small tropical river and estuary (the Wanquan River (WQR)) in Hainan, China, was studied to obtain information on the sources, transformation and fate of riverine organic matter. Water and total suspended matter were sampled along a salinity gradient during four field campaigns in December 2006, August 2007, July–August 2008 and April 2009. We were able to observe the effect of heavy precipitation associated with the tropical cyclone Kammuri (2008) and a strong first-rain event (2009) on the export of organic carbon. Both dissolved organic carbon (DOC) and particulate organic carbon (POC) generally decreased with increasing salinity in the estuary, with minimal seasonal or annual variations. The POC concentrations were in the range of 18–178μM for the WQR and were significantly correlated with chlorophyll a concentrations. The highest average values of DOC (∼190μM) were observed in 2009. These values could be the result of the flushing effect of the first rain. In the high-salinity zone, in situ productivity could be an important source for DOC. The δ13Corg values of particles (−29.5‰ to −23.2‰), combined with the ratio of organic carbon to total nitrogen (OC/TN), reflect a mixture of terrestrial organic matter and in situ production. The amplitudes of the POC and DOC variations on the occasion of the first-rain event of 2009 were larger than those observed during Kammuri. It is estimated that 29.8tday−1 of DOC and 10.4tday−1 of POC, representing 6–10% of the annual loads, were delivered to the coast during the 10-day period of the first flush event in 2009. Our results demonstrate the important role of short-term aperiodic events on small rivers and estuaries along tropical coasts.

Evaluation of the Impacts of Land Use on Storm Water Quality: Case Study from Western Australia

This study evaluates the impacts of land use on storm water quality. Storm water samples were collected from three main land use areas; residential, commercial and industrial lands around the Town of Victoria Park in Western Australia. Each sample was tested to measure important water quality parameters. Time variation of storm water flow, rainfall intensity and storm water quality clearly showed that the highest concentration of pollutants in storm water occurs during the first flush event. Further analysis shows that the commercial storm water demonstrated the cleanest appearing storm water with lowest amounts of suspended solids whereas the industrial storm water had the dirtiest appearing storm water quality. Nutrients in the residential storm water have the lowest nitrate, ammonia and phosphate concentrations. Overall, the industrial land use site recorded the worst storm water quality. Study further provides recommendations for water quality improvement and management controls.

Biodegradability of organic matter associated with sewer sediments during first flush

The high pollution load in wastewater at the beginning of a rain event is commonly known to originate from the erosion of sewer sediments due to the increased flow rate under storm weather conditions. It is essential to characterize the biodegradability of organic matter during a storm event in order to quantify the effect it can have further downstream to the receiving water via discharges from Combined Sewer Overflow (CSO). The approach is to characterize the pollutograph during first flush. The pollutograph shows the variation in COD and TSS during a first flush event. These parameters measure the quantity of organic matter present. However these parameters do not indicate detailed information on the biodegradability of the organic matter. Such detailed knowledge can be obtained by dividing the total COD into fractions with different microbial properties. To do so oxygen uptake rate (OUR) measurements on batches of wastewater have shown itself to be a versatile technique. Together with a conceptual understanding of the microbial transformation taking place, OUR measurements lead to the desired fractionation of the COD. OUR results indicated that the highest biodegradability is associated with the initial part of a storm event. The information on physical and biological processes in the sewer can be used to better manage sediment in sewers which can otherwise result in depletion of dissolved oxygen in receiving waters via discharges from CSOs.

Hepatic dysfunction in development of menopausal hot flushes?

Obese menopausal women tend to suffer more frequently and more severely from hot flushes, though they have higher residual estrogen levels due to the conversion of adrenal androgens in fat tissue. Phytoestrogens, while not exhibiting clinically relevant estrogenic effects on peripheral reproductive tissues, seem to alleviate hot flushes in doses attainable with dietary supplementation. This paper aims to address these controversies. A synergistic action of obesity and estrogens may cause hepatic dysfunction involving inflammatory Kupffer cell activation and generation of pyrogenic signals that reach the thermoregulatory centers via the vagal route. Sudden withdrawal of this perpetual pyrogenic impetus at the onset of menopause results in a thermoregulatory imbalance. The occasional downward sliding of the thermoregulatory setpoint serves to trigger the hot flush event. Repercussions of this theory involve a possible resolution for the paradox of why estrogen-sensitive cancers manifest more frequently at the age when endogenous estrogen levels decline.

Non-equilibrium effects of core-cooling and time-dependent internal heating on mantle flush events

Abstract. We have examined the non-equilibrium effects of core-cooling and time-dependent internal-heating on the thermal evolution of the Earth's mantle and on mantle flush events caused by the two major phase transitions. Both two- and three-dimensional models have been employed. The mantle viscosity responds to the secular cooling through changes in the averaged temperature field. A viscosity which decreases algebraically with the average temperature has been considered. The time-dependent internal-heating is prescribed to decrease exponentially with a single decay time. We have studied the thermal histories with initial Rayleigh numbers between 2 x 107 and 108 . Flush events, driven by the non-equilibrium forcings, are much more dramatic than those produced by the equilibrium boundary conditions and constant internal heating. Multiple flush events are found under non-equilibrium conditions in which there is very little internal heating or very fast decay rates of internal-heating. Otherwise, the flush events take place in a relatively continuous fashion. Prior to massive flush events small-scale percolative structures appear in the 3D temperature fields. Time-dependent signatures, such as the surface heat flux, also exhibits high frequency oscillatory patterns prior to massive flush events. These two observations suggest that the flush event may be a self-organized critical phenomenon. The Nusselt number as a function of the time-varying Ra does not follow the Nusselt vs. Rayleigh number power-law relationship based on equilibrium (constant temperature) boundary conditions. Instead Nu(t) may vary non-monotonically with time because of the mantle flush events. Convective processes in the mantle operate quite differently under non-equilibrium conditions from its behaviour under the usual equilibrium situations.

The non-adiabatic nature of mantle convection as revealed by passive tracers

We have investigated the state of adiabaticity in mantle flows by using a Lagrangian tracer technique to map out the thermal state of parcels in both downwelling and upwelling flows in mantle flush events. The model, baed on a core-cooling boundary condition, has two major phase transitions and a temperature-dependent viscosity. The temperature histories of the first tracers that enter into the lower mantle during a flushing event reveal a superadiabatic increase of up to 700 K, due to conduction and viscous dissipation. The lateral temperature anomalies in the deep lower mantle, monitored by the tracers, can exceed 1000 K. The cold sinking anomalies follow a superadiabatic path and are heated up according to the time-history of the flush event. The time-history of the rising parcels is strongly influenced non-adiabatically by the two phase transitions in the upper mantle, with only a small segment in the upper mantle below the surface, where the parcels are found to be invariably slightly superadiabatic. Following a major flush event, the horizontally averaged temperature profiles display strong subadiabaticity in the deep mantle and superadiabaticity in the transition zone. During this time the mean temperature profiles do not follow an adiabat anywhere. The concept of adiabaticity may have limited applications in strongly time-dependent mantle convection with phase transitions, where major overturns take place from time to time.