Impact of normal stress-induced closure on laboratory-scale solute transport in a natural rock fracture

The impact of normal stress-induced closure on fluid flow and solute transport in a single rock fracture is demonstrated in this study.The fracture is created from a measured surface of a granite rock sample.The Bandis model is used to calculate the fracture closure due to normal stress,and the fluid flow is simulated by solving the Reynold equation.The Lagrangian particle tracking method is applied to modeling the advective transport in the fracture.The results show that the normal stress significantly affects fluid flow and solute transport in rock fractures.It causes fracture closure and creates asperity contact areas,which significantly reduces the effective hydraulic aperture and enhances flow channeling.Consequently,the reduced aperture and enhanced channeling affect travel time distributions.In particular,the enhanced channeling results in enhanced first arriving and tailing behaviors for solute transport.The fracture normal stiffness correlates linearly with the 5 th and 95 th percentiles of the normalized travel time.The finding from this study may help to better understand the stress-dependent solute transport processes in natural rock fractures.     

Influence of water and sediment quality on benthic biota in an acidified river

Water and sediment quality and benthic biota were investigated in all seasons during three years in the River Akagawa that receives the effluent from a mine drainage treatment plant at its upstream site. The upper reaches kept the low pH, the comparatively high concentrations of metals and a large amount of iron deposited on the riverbed. The predominant macroinvertebrates were Protonemura sp., Capnidae, Nemoura sp. and Chironomidae in the upper and middle reaches. In the lowest reaches, the community structure of the macroinvertebrate changed into Chironomidae, Trichoptera (Hydropsychidae) and Ephemeroptera (Baetis sp.) as the pH was increased. From the results of multivariate analyses, it was found that the restoration of pH and attached algae and the increase in the concentrations of nutrients and organic matter promoted the inhabitation of Chironomidae and Hydropsychidae, whereas the dissolved metals in the river water inhibited the inhabitation of these families. Moreover, the sedimentation of metals would cause a severe damage to the inhabitation of Hydropsychidae compared with that of Chironomidae.     

Unsteady diffusional mass transfer at the sediment/water interface: Theory and significance for SOD measurement

Dissolved oxygen uptake at a sediment/water interface (SOD) is controlled by mass transport and/or biochemical reactions in two adjacent boundary layers: the diffusive boundary layer delta(D) in the water and the penetration depth delta in the sediment. Either one of those boundary layers or both can be controlling. The transition from sediment control to water control is a function of shear velocity at the sediment/water interface (U(*)) and biochemical activity rate (micro(0)) in the sediment. A model was developed for the unsteady response of SOD and DO profiles near the sediment/water interface. Michaelis-Menten kinetics were used initially, but zero order kinetics work just as well when the half saturation coefficient K(O(2)) is small as was suggested by field data. Beginning with zero DO in the sediments the times required to reach steady state DO profiles and SOD was on the order of minutes to hours, faster where biochemical activity is strong. The values of SOD estimated by the model were compared with experimental data to verify the reliability of the model. The model can reproduce observed penetration depths and diffusive boundary layer thickness. Values of SOD estimated by the model were of same magnitude as observed data. The unsteady DO uptake model can be used to provide guidance for field measurements of SOD. Placing a chamber (with a stirrer) into the sediments disturbs the DO equilibrium at the sediment/water interface. A new equilibrium will be reached within a time that can be measured in terms of cumulative DO consumption in the chamber (SOD exerted). Upper bounds for (SOD exerted) are larger when biochemical activity in the sediments is smaller. Values of SOD exerted are less than 0.1gm(-2) when micro(0) is less than 50mgl(-1)d(-1) and U(*)>0.1cm/s. In other words, steady state conditions are easier to reach for high SOD values. Actual times required to reach steady state can be from minutes to hours. If flow conditions in the chamber and at the natural sediment/water interface are much different, measured SOD values have to be adjusted. A procedure for the adjustments, which can be substantial, has been developed.     

Importance of interactions between the water column and the sediment for microbial concentrations in streams

The effect of interactions between the sediment and water column on concentrations of microbes in streams is quantified with a one-dimensional, steady state model. The effects of nine main parameters describing the flow, sediment transport, and microbial growth and decay are encapsulated in two dimensionless parameters: the Damköhler number Da, or the ratio of the time scales of advection and net growth, and the sediment interaction parameter S, or the ratio of the amount of microbes lost or gained in the sediment and the amount of microbes lost or gained in the water column. Applications of the model illustrate the importance of the sediment and identify parameters that require further study. The model predicts the field measurements of Jamieson et al. (2005b) within a factor of 2 in two of three cases, while concentrations predicted by ignoring the sediment exceed the measured values. In general, the effects of ignoring interactions with the sediment depend on Da and S. The loading predicted to meet water quality standards when the sediment is considered can be either greater than or less than the loading predicted when it is not considered. The applications of the model and an analysis of uncertainty suggest that further work on the settling velocity, attached fraction, resuspension rate, and net growth rate in the sediment would help to improve predictions of the fate and transport of microbes.     

Oxygen consumption by a sediment bed for stagnant water: comparison to SOD with fluid flow

A model of sedimentary oxygen demand (SOD) for stagnant water in a lake or a reservoir is presented. For the purposes of this paper, stagnant water is defined as the bottom layer of stratified water columns in relatively unproductive systems that are underlain by silt and sand-dominated sediments with low-organic carbon (C) and nitrogen (N). The modeling results are compared to those with fluid flow to investigate how flow over the sediment surface raises SOD compared to stagnant water, depending on flow velocity and biochemical activity in the sediment. SOD is found to be substantially limited by oxygen transfer in the water column when water is stagnant. When flow over the sediment surface is present, SOD becomes larger than that for stagnant water, depending on flow velocity and the biochemical oxygen uptake rate in the sediment. Flow over the sediment surface causes an insignificant raise in SOD when the biochemical oxygen uptake rate is small. The difference between SOD with fluid flow and SOD for stagnant water becomes significant as the biochemical oxygen uptake rate becomes larger, i.e. SOD is 10-100 times larger when flow over the sediment surface is present.     

Combined influence of membrane surface properties and feed water qualities on RO/NF mass transfer, a pilot study

The impact of membrane surface characteristics and NOM on membrane performance has been investigated for varying pretreatment and membranes in a field study. Surface charge, hydrophobicity and roughness varied significantly among the four membranes used in the study. The membranes were tested in parallel following two different pretreatment processes, an enhanced Zenon ultrafiltration process (ZN) and a compact CSF process (Superpulsator (SP)) prior to RO membrane treatment for a total of eight integrated membrane systems. All membrane systems were exposed to the similar temperature, recovery and flux as well as chemical dosage. The membrane feed water qualities were statistically equivalent following ZN pretreatment and SP pretreatment except for NOM and SUVA. Membrane surface characteristics, NOM and SUVA measurements were used to describe mass transfer in a low-pressure RO integrated membrane system. Solute and water mass transfer coefficients (MTCs) were investigated for dependence on membrane surface properties and NOM mass loading. Inorganic MTCs were accurately described by a Gaussian distribution curve. Water productivity decreased with NOM loading and increased with contact angle and roughness. The negative effects of NOM loading on productivity were reduced as the negative charge on the membrane surface increased. Inorganic MTCs were also correlated to surface hydrophobicity and surface roughness. The permeability change of identical membranes was related to NOM loading, hydrophobicity and roughness. Organic fouling as measured by water, organic and inorganic mass transfer was less for membranes with higher hydrophilicity and roughness.     

Moderating effects of the geometry of reservoirs on the relation between urban land use and water quality

Edges mediate the material flux between adjacent systems. This mediating effect of edges is strongly tied to the complexity of the adjacent shapes. Land use within a watershed has a direct impact on the water quality of adjacent aquatic systems. Hydrological processes carry material produced by land-use activities into aquatic ecosystems through the edges of the ecosystem. Therefore, the geometry of aquatic ecosystems theoretically affects the relationship between land use and water quality. This study investigates whether the shape complexity of reservoirs moderates the direct impact of land use on the water quality of adjacent reservoirs. A moderation model was adopted to measure the shape effects, and 153 reservoirs were randomly sampled with a consideration of reservoir size (surface area), geographic location, and data availability. With a focus on urban land use, we used GIS to measure land-use types within a 1 km buffer of reservoir boundaries. The shape complexity of sampled reservoirs was measured using fractal dimensions. Land uses and shape complexity were then regressed to measure water quality parameters such as chemical oxygen demand (COD), biological oxygen demand (BOD), total nitrogen (TN) and total phosphorus (TP). Correlation analysis revealed that the shapes of reservoirs are likely to be simple where urban land use dominates the areas close to reservoirs. Use of the standard regression model indicated that the increasing shape complexity of reservoirs significantly reduces the concentration of BOD, COD, and TP within reservoir water. Moderation models for BOD, COD, TN, and TP suggest that shape complexity can considerably relieve the negative impacts on water quality of urban land use in areas adjacent to reservoirs. The results of this study highlight the need to focus on shoreline management in order to mitigate the adverse impacts of land use on lakes and reservoirs.     

Assessing land-use effects on water quality, in-stream habitat, riparian ecosystems and biodiversity in Patagonian northwest streams

Changes in land-use practices have affected the integrity and quality of water resources worldwide. In Patagonia there is a strong concern about the ecological status of surface waters because these changes are rapidly occurring in the region. To test the hypothesis that greater intensity of land-use will have negative effects on water quality, stream habitat and biodiversity we assessed benthic macroinvertebrates, riparian/littoral invertebrates, fish and birds from the riparian corridor and environmental variables of 15 rivers (Patagonia) subjected to a gradient of land-use practices (non-managed native forest, managed native forest, pine plantations, pasture, urbanization). A total of 158 macroinvertebrate taxa, 105 riparian/littoral invertebrate taxa, 5 fish species, 34 bird species, and 15 aquatic plant species, were recorded considering all sites. Urban land-use produced the most significant changes in streams including physical features, conductivity, nutrients, habitat condition, riparian quality and invertebrate metrics. Pasture and managed native forest sites appeared in an intermediate situation. The highest values of fish and bird abundance and diversity were observed at disturbed sites; this might be explained by the opportunistic behavior displayed by these communities which let them take advantage of increased trophic resources in these environments. As expected, non-managed native forest sites showed the highest integrity of ecological conditions and also great biodiversity of benthic communities. Macroinvertebrate metrics that reflected good water quality were positively related to forest land cover and negatively related to urban and pasture land cover. However, by offering stream edge areas, pasture sites still supported rich communities of riparian/littoral invertebrates, increasing overall biodiversity. Macroinvertebrates were good indicators of land-use impact and water quality conditions and resulted useful tools to early alert of disturbances in streams. Fish and birds having a greater ability of dispersion and capacity to move quickly from disturbances would reflect changes at a higher scale.     

Effects of recreational activities on the soil and water components of a deciduous forest ecosystem in Turkey

Impacts of recreational activities on some hydrological properties of a deciduous forest ecosystem related to water production have been evaluated with an inclusive soil study, coupled with a two‐year water quality monitoring program. Spatial variations of water quality parameters did not indicate a statistically significant deterioration caused by the recreational activities in the stream water, but the effects of trampling on physical soil properties were clear. The bulk density of the soils increased with the intensity of recreation from 1.18 to 1.29 g cm^?3, while the percentage of clay fraction decreased, as an indicator of erosion. The soils of the stream banks in the recreation area had reasonable saturated hydraulic conductivity values, and were affected sharply by the intensity of recreational use. The low inclination (0.5%) and the coarse texture of the soils were possibly the main factors diminishing or concealing the trampling effects not observed on the water quality of the stream passing through the recreation area.     

Water quality improvement in a full-scale tertiary constructed wetland: Effects on conventional and specific organic contaminants

The surface flow constructed wetland (SF CW) in Can Cabanyes (Granollers, Catalonia, northeastern Spain) was created as a part of a series of activities aimed at restoring a highly impacted fluvial peri-urban zone. The system is fed with a small part of the secondary effluent, which is not completely nitrified, from an urban wastewater treatment plant. Effluents in the SF CW were sampled between 2003 and 2006 for physical and chemical parameters and faecal bacteria indicators. In addition, 8 pharmaceuticals and personal care products (PPCPs) were measured in June 2005 and February 2006. The system showed a good reliability for ammonium and faecal bacteria removal, with average ammonium efficiencies between 64 and 87% and a removal of approximately 2 logarithmic units of Faecal Coliforms. A clear seasonal trend was observed for ammonium. The results for PPCPs demonstrated that the wetland has a good capacity for removing a large variety of these compounds; the removal efficiencies were higher than 70% for most of them, with the exception of clofibric acid (34%) and carbamazepine (39%). Although the chemical oxygen demand and total suspended solid removal rates were either low or zero because of the permanent eutrophic conditions of the system and the low incoming concentrations, the effluent quality is generally considered to be quite good.     

Confirmation of putative stormwater impact on water quality at a Florida beach by microbial source tracking methods and structure of indicator organism populations

The effect of a stormwater conveyance system on indicator bacteria levels at a Florida beach was assessed using microbial source tracking methods, and by investigating indicator bacteria population structure in water and sediments. During a rain event, regulatory standards for both fecal coliforms and Enterococcus spp. were exceeded, contrasting with significantly lower levels under dry conditions. Indicator bacteria levels were high in sediments under all conditions. The involvement of human sewage in the contamination was investigated using polymerase chain reaction (PCR) assays for the esp gene of Enterococcus faecium and for the conserved T antigen of human polyomaviruses, all of which were negative. BOX-PCR subtyping of Escherichia coli and Enterococcus showed higher population diversity during the rain event; and higher population similarity during dry conditions, suggesting that without fresh inputs, only a subset of the population survives the selective pressure of the secondary habitat. These data indicate that high indicator bacteria levels were attributable to a stormwater system that acted as a reservoir and conduit, flushing high levels of indicator bacteria to the beach during a rain event. Such environmental reservoirs of indicator bacteria further complicate the already questionable relationship between indicator organisms and human pathogens, and call for a better understanding of the ecology, fate and persistence of indicator bacteria.     

Ecological effects of aquaculture on living and non-living suspended fractions of the water column: a meta-analysis

The effects of aquaculture on the ecology of the water column have been extensively studied in the last two decades. However, to date, it has not been possible to extrapolate homogeneous information from the peer-reviewed literature. In the present study, 68 peer-reviewed articles were analysed and about 1087 study cases were used to test whether worldwide cultivations of aquatic organisms (shrimps, fish, bivalves and polyculture) have a differential effect on living and non-living fractions of the water column (suspended matter, chlorophyll-a, particulate organic carbon, nitrogen and phosphorus, bacteria and plankton). Meta-analysis feasibility depends on obtaining an estimate of the effect size from every study, and the most common measure of effect size (Hedges'd) is the difference between means of controls and impacts standardised by dividing by the pooled standard deviation. Shrimp, fish and bivalve cultivation differentially affected water column dynamics, with a general major impact on bacteria and phytoplankton. In addition, results showed that the water column dynamics are probably affected by organic aquaculture loading but, due to the substantial heterogeneity across studies, the information available on the effects can be considered partially flawed and therefore not sufficient to either support or exclude the notion that different forms of aquaculture affect ecological processes of the water column.     

Rapid effects of diverse toxic water pollutants on chlorophyll a fluorescence: variable responses among freshwater microalgae

Chlorophyll a fluorescence of microalgae is a compelling indicator of toxicity of dissolved water contaminants, because it is easily measured and responds rapidly. While different chl a fluorescence parameters have been examined, most studies have focused on single species and/or a narrow range of toxins. We assessed the utility of one chl a fluorescence parameter, the maximum quantum yield of PSII (F_v/F_m), for detecting effects of nine environmental pollutants from a range of toxin classes on 5 commonly found freshwater algal species, as well as the USEPA model species, Pseudokirchneriella subcapitata. F_v/F_m declined rapidly over <20 min in response to low concentrations of photosynthesis-specific herbicides Diuron^® and metribuzin (both <40 nM), atrazine (<460 nM) and terbuthylazine (<400 nM). However, F_v/F_m also responded rapidly and in a dose-dependent way to toxins glyphosate (<90 μM), and KCN (<1 mM) which have modes of action not specific to photosynthesis. F_v/F_m was insensitive to 30-40 μM insecticides methyl parathion, carbofuran and malathion. Algal species varied in their sensitivity to toxins. No single species was the most sensitive to all nine toxins, but for six toxins to which algal F_v/F_m responded significantly, the model species P. subcapitata was less sensitive than other taxa. In terms of suppression of F_v/F_m within 80 min, patterns of concentration-dependence differed among toxins; most showed Michaelis-Menten saturation kinetics, with half-saturation constant (K_m) values for the PSII inhibitors ranging from 0.14 μM for Diuron^® to 6.6 μM for terbuthylazine, compared with a K_m of 330 μM for KCN. Percent suppression of F_v/F_m by glyphosate increased exponentially with concentration. F_v/F_m provides a sensitive and easily-measured parameter for rapid and cost-effective detection of effects of many dissolved toxins. Field-portable fluorometers will facilitate field testing, however distinct responses between different species may complicate net F_v/F_m signal from a community.     

Individual and combined effects of water quality and empty bed contact time on As(V) removal by a fixed-bed iron oxide adsorber: Implication for silicate precoating

The individual and combined effects of changes in water quality (i.e. pH, initial concentrations of arsenate (As(V)) and competing ions) and empty bed contact time (EBCT) on As(V) removal performance of a fixed-bed adsorber (FBA) packed with a nanostructured goethite-based granular porous adsorbent were systematically studied under environmentally relevant conditions. Rapid small scale column tests (RSSCTs) were extensively conducted at different EBCTs with synthetic waters in which pH and the concentrations of competing ions (phosphate, silicate, and vanadate) were controlled. In the absence of the competing ions, the effects of initial As(V) concentration, pH, and EBCT on As(V) breakthrough curves were successfully predicted by the homogeneous surface diffusion model (HSDM) with adsorption isotherms predicted by the extended triple layer model (ETLM). The interference effects of silicate and phosphate on As(V) removal were strongly influenced by pH, their concentrations, and EBCT. In the presence of silicate (≤21 mg/L as Si), a longer EBCT surprisingly resulted in worse As(V) removal performance. We suggest this is because silicate, which normally exists at much higher concentration and moves more quickly through the bed than As(V), occupies or blocks adsorption sites on the media and interferes with later As(V) adsorption. Here, an alternative operating scheme of a FBA for As(V) removal is proposed to mitigate the silicate preloading. Silicate showed a strong competing effect to As(V) under the tested conditions. However, as the phosphate concentration increased, its interference effect dominated that of silicate. High phosphate concentration (>100 μg/L as P), as experienced in some regions, resulted in immediate As(V) breakthrough. In contrast to the observation in the presence of silicate, longer EBCT resulted in improved As(V) removal performance in the presence of phosphate. Vanadate was found to compete with As(V) as strongly as phosphate. This study reveals the competitive interactions of As(V) with the competing ions in actual adsorptive treatment systems and the dependence of optimal operation scheme and EBCT on water quality in seeking improved As(V) removal in a FBA.     

The effects of phytophagous insects on water and soil nutrient concentrations and fluxes through forest stands of the Level II monitoring network in the UK

The effects of insect defoliators on throughfall and soil nutrient fluxes were studied in coniferous and deciduous stands at five UK intensive monitoring plots (1998 to 2008). Links were found between the dissolved organic carbon (DOC), nitrogen (N) and potassium (K) fluxes through the forest system to biological activity within the canopy. Underlying soil type determined the leaching or accumulation of these elements. Under oak, monitored at two sites, frass from caterpillars of Tortrix viridana and Operophtera brumata added direct deposition of ~ 16 kg ha⁻¹extra N during defoliation. Peaks of nitrate (NO₃-N) flux between 5 and 9 kg ha⁻¹ (×5 usual winter values) were recorded in consecutive years in shallow soil waters. Synchronous rises in deep soil NO₃-N fluxes at the Grizedale sandy site indicate downward flushing, not seen at the clay site. Under three Sitka spruce stands, generation of honeydew (DOC) was attributed to two aphid species (Elatobium abietinum and Cinara pilicornis) with distinctive feeding strategies. Throughfall DOC showed mean annual fluxes (6 seasons) ~ 45-60 kg ha⁻¹ compared with rainfall values of 14-22 kg ha⁻¹. Increases of total N in throughfall and NO₃-N fluxes in shallow soil solution were detected — soil water fluxes reached  8 kg ha⁻¹ in Llyn Brianne, ~ 25 kg ha⁻¹ in Tummel, and ~ 40 kg NO₃-N ha⁻¹ in Coalburn. At Tummel, on sandy soil, NO₃-N leaching showed increased concentration at depth, attributed to microbiological activity within the soil. By contrast, at Coalburn and Llyn Brianne, sites on peaty gleys, soil water NO₃-N was retained mostly within the humus layer. Soil type is thus key to predicting N movement and retention patterns. These long term analyses show important direct and indirect effects of phytophagous insects in forest ecosystems, on above and below ground processes affecting tree growth, soil condition, vegetation and water quality.