Green roof stormwater retention: effects of roof surface, slope, and media depth

Urban areas generate considerably more stormwater runoff than natural areas of the same size due to a greater percentage of impervious surfaces that impede water infiltration. Roof surfaces account for a large portion of this impervious cover. Establishing vegetation on rooftops, known as green roofs, is one method of recovering lost green space that can aid in mitigating stormwater runoff. Two studies were performed using several roof platforms to quantify the effects of various treatments on stormwater retention. The first study used three different roof surface treatments to quantify differences in stormwater retention of a standard commercial roof with gravel ballast, an extensive green roof system without vegetation, and a typical extensive green roof with vegetation. Overall, mean percent rainfall retention ranged from 48.7% (gravel) to 82.8% (vegetated). The second study tested the influence of roof slope (2 and 6.5%) and green roof media depth (2.5, 4.0, and 6.0 cm) on stormwater retention. For all combined rain events, platforms at 2% slope with a 4-cm media depth had the greatest mean retention, 87%, although the difference from the other treatments was minimal. The combination of reduced slope and deeper media clearly reduced the total quantity of runoff. For both studies, vegetated green roof systems not only reduced the amount of stormwater runoff, they also extended its duration over a period of time beyond the actual rain event.     

HISTORICAL TRENDS IN SEDIMENTATION RATES AND SEDIMENT PROVENANCE,FAIRFIELD LAKE,WESTERN NORTH CAROLINA1

Sedimentation rates and sediment provenance were examined for lacustrine sediments deposited in Fairfield Lake, western North Carolina, during the past 111 years. Stratigraphic, radionuclide, and cartographic data indicate that sedimentation rates have increased several fold during the past three decades in response to localized development. The magnitude of increased sedimentation was surprising given limited development within the basin: 0.12 to 0.68 buildings/ha in 2000 in those parts directly delivering sediment to the dated cores. Thus, the analysis illustrates the potential sensitivity of watersheds in the southern Appalachians to changes in land cover. An approach that combined geochemical fingerprinting with sediment mixing models was subsequently evaluated to determine its ability to accurately estimate the contribution of sediment from (1) major bedrock formations that underlie the watershed and (2) potential sources associated with four land cover categories. Sediment sources in both analyses proved difficult to geochemically fingerprint to greater than 90 percent accuracy using data on acid‐soluble metals and selected isotopes of lead (Pb). The relative contributions of sediment from delineated sources, estimated by the mixing models, generally corresponded with known temporal and spatial patterns of land cover. However, the models were plagued by two significant problems — the chemical alteration of sediments as they were transported through upland streams to depositional sites within the lake and the loss of elemental mass. Thus, future investigations using the fingerprinting approach in this area of intense weathering, and presumably others, will need to modify the existing methods to more accurately elucidate changes in sediment provenance related to development.     

Behavioral aspects of sperm competition in cuttlefish, Sepia officinalis (Sepioidea: Cephalopoda)

Sexual selection studies in cephalopods indicate that sperm competition is a central feature of their mating systems, yet this has not been studied experimentally in any detail. In 1998 we staged 20 matings of the cuttlefish, Sepia officinalis L., in the laboratory. Males rapidly initiated mating in the “head-to-head” position, with no apparent courtship. Mating lasted an average of 10 min (range 7 to 14 min). For the first 6 min (on average 63% of the mating duration), the male flushed strong jets of water directly at the female's buccal membrane, which sometimes resulted in the expulsion of parts of spermatangia placed there in recent matings. Then, in a single discrete movement that lasted an average of only 14 s, the male's modified fourth left arm – the hectocotylus – wrapped around a single large bundle of spermatophores (ca. 150 to 300) and transferred them to the female's buccal membrane. For the remainder of the mating (average 3 min, range 1.5 to 5.0 min), the hectocotylus repeatedly broke the spermatophores open, and manipulated them, so that sperm were released and many spermatangia were attached along the ventral buccal membrane, near the paired seminal receptacles. Approximately 140 spermatangia were attached in rows 3 to 5 deep around the ventral buccal membrane in a single mating; the rest were usually discarded during mating. Histology revealed that each of the seminal receptacles consists of a series of sperm storage bulbs connected by a central duct, which leads to a single pore at the surface of the buccal membrane. Baseline data on sperm motility were obtained, but the mechanism by which sperm enter the seminal receptacle remains unknown. Females seemed to initiate termination of mating, then males guarded their mates temporarily. These results, combined with other recent laboratory experiments, provide evidence that sperm competition may be a major feature of the mating system of S. officinalis. Received: 4 January 1999 / Accepted: 18 May 1999     

Modeling porosity reductions caused by mineral fouling in continuous-wall permeable reactive barriers

A study was conducted to assess key factors to include when modeling porosity reductions caused by mineral fouling in permeable reactive barriers (PRBs) containing granular zero valent iron. The public domain codes MODFLOW and RT3D were used and a geochemical algorithm was developed for RT3D to simulate geochemical reactions occurring in PRBs. Results of simulations conducted with the model show that the largest porosity reductions occur between the entrance and mid-plane of the PRB as a result of precipitation of carbonate minerals and that smaller porosity reductions occur between the mid-plane and exit face due to precipitation of ferrous hydroxide. These findings are consistent with field and laboratory observations, as well as modeling predictions made by others. Parametric studies were conducted to identify the most important variables to include in a model evaluating porosity reduction. These studies showed that three minerals (CaCO3, FeCO3, and Fe(OH)2 (am)) account for more than 99% of the porosity reductions that were predicted. The porosity reduction is sensitive to influent concentrations of HCO3-, Ca2+, CO3(2-), and dissolved oxygen, the anaerobic iron corrosion rate, and the rates of CaCO3 and FeCO3 formation. The predictions also show that porosity reductions in PRBs can be spatially variable and mineral forming ions penetrate deeper into the PRB as a result of flow heterogeneities, which reflects the balance between the rate of mass transport and geochemical reaction rates. Level of aquifer heterogeneity and the contrast in hydraulic conductivity between the aquifer and PRB are the most important hydraulic variables affecting porosity reduction. Spatial continuity of aquifer hydraulic conductivity is less significant.     

Ammonia emission from grassland and livestock production systems in the UK

Emissions of ammonia were measured from livestock excreta and fertilisers applied to grass swards, from grazed paddocks, from decomposing grass herbage and from an animal house containing dairy cows. Emissions from urine, dung, slurry and fertilisers were determined using a system of wind tunnels with each tunnel covering an area of 1 m(2). Emissions from grazed swards were determined using a micrometeorological mass balance method. From the results of these measurements, together with other published information, an inventory for ammonia emissions has been calculated for grassland and livestock production systems over the UK as a whole. It is estimated that emissions from grassland and cattle and sheep production amount to about 230 kt NH(3)-N annually, while emissions from pig and poultry production amount to about 40 kt and 80 kt NH(3)-N, respectively.     

Relation of length and sex to selenium concentrations in mosquitofish

Analysis of mosquitofish, Gambusia affinis, has proven useful for monitoring contaminant levels in aquatic biota; however, the small size of this species often requires the compositing of several fish to provide sufficient biomass for selenium analysis. Such composites have usually been obtained without considering the length and sex of the individual fish. The present study found significant differences in mean lengths and sex ratios of mosquitofish sampled with small-mesh dip nets from five sites close to each other in the San Joaquin Valley, California. To test the effect of these different sample characteristics, fish from each site were divided by sex into five size classes (<20, 20-30, 31-45, 46-60, and >60mm total length) before analysis for total selenium. Altogether, fish from the San Luis Drain and Kesterson Ponds 2 and 7 contained 65-360 microg g(-1) selenium (dry weight basis), or about 28- to 300-fold more than concentrations in fish of the same length and sex from the Volta Wasteway and Volta Pond 26. Except for females 31-45 mm long from the San Luis Drain that had higher concentrations than either smaller or larger females, selenium concentrations did not differ significantly among size classes. Although concentrations differed between sexes in samples from the San Luis Drain, Kesterson Pond 2, and Volta Pond 26, neither males nor females consistently had the higher concentrations. In the San Luis Drain, 20-30 and 31-45 mm long females had higher concentrations than did males of the same size classes; in Kesterson Pond 2 and Volta Pond 26, however, 20-30 mm long males had higher concentrations than did females of the same size class. Although no consistent patterns were observed, the occasional differences in selenium concentrations in fish of different length and sex indicate that these variables should be considered when surveys and monitoring studies are designed.     

Distribution of fission products in dust samples from the region of Thessaloniki, Greece, after the Chernobyl nuclear accident

The distribution of the fission products (95)Zr, (95)Nb, (103)Ru, (106)Ru (determined through (106)Rh), (125)Sb, (129m)Te, (134)Cs, (137)Cs, (140)Ba, (140)La, (141)Ce and (144)Ce has been determined in dust samples from the region of Thessaloniki, Greece, after the nuclear accident at Chernobyl. The samples studied also included (110m)Ag, not belonging to the products of (235)U fission. Samples showing higher concentrations of radionuclides also show a higher content in clay minerals, whereas samples having low concentrations of radionuclides usually contain large amounts of quartz and feldspars. Desorption and leaching experiments using solutions of chlorides of sodium, potassium, calcium and magnesium (0.5 N), as well as distilled and tap water, were also performed. Sodium and potassium chloride solutions were found to be efficient in desorbing and/or leaching of caesium and ruthenium isotopes to an extent of about 30%.     

Effects of distillery waste on the performance of Cicer arietinum L

The impact of distillery effluent in various concentrations (1, 2.5, 5, 10, 25, 50, 75 and 100%) on the seed germination, Speed of Germination Index, growth behaviour, leaf area, biomass, net primary productivity, pigment content, reproductive capacity, seed output, seed weight, seed density and the seed protein content of Cicer arietinum L. plants was investigated. The percentage and speed of germination of seeds were increasingly retarded with increase in effluent concentration and at 100% concentration there was no germination. The seedlings exhibited maximum shoot length at 5% concentration and maximum root length at 2.5% concentration. The values of root and shoot lengths, leaf area, biomass, net primary productivity, pigment content, reproductive capacity, seed output, seed weight, seed density and seed protein content in pot plants exhibited a gradual increase from the control up to 5% concentration and decreases at higher concentrations. The very high BOD load and the presence of excessive concentrations of soluble salts could be responsible for the toxicity of the effluent. The effluent at up to 5% concentration was, however, beneficial for the overall growth parameters studied and can thus be used as a liquid fertilizer.     

Electrochemical oxidation of bisphenol A. Application to the removal of bisphenol A using a carbon fiber electrode

Leachate samples with a high strength of ammonium-nitrogen (NH4+-N) were collected from a local landfill site in Hong Kong. Two experiments were carried out to study (1) the inhibition of microbial activity of activated sludge by NH4+-N and (2) the chemical precipitation of NH4+-N from leachate as a preliminary treatment prior to the activated sludge process. The experimental results demonstrated that the efficiency of COD removal decreased from 97.7% to 78.1%, and the dehydrogenase activity of activated sludge decreased from 9.29 to 4.93 microg TF/mg MLSS, respectively, when the NH4+-N concentration increased from 53 to 800 mg/l. The experiment also demonstrated that the NH4+-N in the leachate can be quickly precipitated as MgNH4PO4 x 6H2O after addition of MgCl2 x 6H2O + Na2HPO4 x 12H2O. The NH4+-N concentration was reduced from 5618 to 112 mg/l within 15 min when a molar ratio of Mg2+:NH+:PO4(3-) = 1:1:1 was used. The optimum pH to reach the minimum solubility of MgNH4PO4 x 6H2O was found to be in the range of 8.5-9.0. Attention should be given to the high salinity formed in the treated leachate by using MgCl2 x 6H2O + Na2HPO4 x 12H2O, which may affect microbial activity in the following biological treatment processes. Using two other combinations of chemicals [MgO + 85%H3PO4 and Ca(H2PO4)2 x H2O + MgSO4 x 7H2O] could minimise salinity generation after precipitation, while they were less efficient for NH4+-N removal.     

Effects of bis(tributyltin)oxide on antipredator behavior in threespine stickleback Gasterosteus aculeatus L.

Antipredator behavior was used as a parameter to detect effects caused by exposure to the organotin compound bis(tributyltin)oxide (TBTO). Three groups of threespine sticklebacks (Gasterosteus aculeatus L.) were exposed to 3, 9 and 27 ppb TBTO, respectively. A fourth control group was given the same treatment as the other three groups, but no TBTO. Antipredator behavior of the fish was evoked using a dummy heron (Ardea cinerea) bill. TBTO exposure caused significant changes in the spatial position of the fish in the aquarium (P(Loc)), their response to predator attack (P(Res)), recovery time (P(Rec)) and latency time (P(Lat)). Some of the effects were, however, reversible after the exposure was terminated. We suggest that behavior as an indicator of pollution may be used as an ecologically relevant integrative biomarker.