Majority Of Pools Research Articles

Controls on dissolved organic matter (DOM) degradation in a headwater stream: the influence of photochemical and hydrological conditions in determining light-limitation or substrate-limitation of photo-degradation

Abstract. We investigated how absorption of sunlight by chromophoric dissolved organic matter (CDOM) controls the degradation and export of DOM from Imnavait Creek, a beaded stream in the Alaskan Arctic. We measured concentrations of dissolved organic carbon (DOC), as well as concentrations and characteristics of CDOM and fluorescent dissolved organic matter (FDOM), during ice-free periods of 2011–2012 in the pools of Imnavait Creek and in soil waters draining to the creek. Spatial and temporal patterns in CDOM and FDOM in Imnavait Creek were analyzed in conjunction with measures of DOM degradation by sunlight and bacteria and assessments of hydrologic residence times and in situ UV exposure. CDOM was the dominant light attenuating constituent in the UV and visible portion of the solar spectrum, with high attenuation coefficients ranging from 86 ± 12 m−1 at 305 nm to 3 ± 1 m−1 in the photosynthetically active region (PAR). High rates of light absorption and thus light attenuation by CDOM contributed to thermal stratification in the majority of pools in Imnavait Creek under low-flow conditions. In turn, thermal stratification increased the residence time of water and DOM, and resulted in a separation of water masses distinguished by contrasting UV exposure (i.e., UV attenuation by CDOM with depth resulted in bottom waters receiving less UV than surface waters). When the pools in Imnavait Creek were stratified, DOM in the pool bottom water closely resembled soil water DOM in character, while the concentration and character of DOM in surface water was reproduced by experimental photo-degradation of bottom water. These results, in combination with water column rates of DOM degradation by sunlight and bacteria, suggest that photo-degradation is the dominant process controlling DOM fate and export in Imnavait Creek. A conceptual model is presented showing how CDOM amount and lability interact with incident UV light and water residence time to determine whether photo-degradation is "light-limited" or "substrate-limited". We suggest that degradation of DOM in CDOM-rich streams or ponds similar to Imnavait is typically light-limited under most flow conditions. Thus, export of DOM from this stream will be less under conditions that increase the light available for DOM photo-degradation (i.e., low flows, sunny days).

Anopheline breeding in river bed pools below major dams in Sri Lanka

Anopheline mosquito larval surveys were carried out from September 2000 to August 2002 in Mahaweli and Kelani river beds, below five major dams in the wet and intermediate zones of Sri Lanka, to study the prevalence of anopheline species in these areas. In each study site, all permanent and semi-permanent pools were surveyed fortnightly by dipping at 6 dips/m 2 surface area of water. Larvae were collected in separate containers, staged and identified at their third and fourth stages. During each survey, the surface area and depth of pools were recorded and each reading was considered as an individual observation. River bed pools below the dams contained stagnant clean water with a little or no aquatic vegetation. The majority of pools were ≤1 m 2 in surface area and ≤75 cm in depth. Anopheline mosquito breeding was seen throughout the year in each study site. The average percentage of pools positive for anopheline larvae, the number of larvae per 100 pools and 100 dips were 14.85%, 32.34 and 9.29, respectively. Thirteen anopheline species, including 10 potential vectors, namely, An. barbirostris, An. culicifacies, An. jamesii, An. maculatus, An. nigerrimus, An. peditaeniatus, An. subpictus, An. tessellatus, An. vagus and An. varuna were found breeding in the river bed pools.

Controls on the size and occurrence of pools in coarse‐grained forest rivers

AbstractControls on pool formation are examined in gravel‐ and cobble‐bed rivers in forest mountain drainage basins of northern California, southern Oregon, and southeastern Alaska. We demonstrate that the majority of pools at our study sites are formed by flow obstructions and that pool geometry and frequency largely depend on obstruction characteristics (size, type, and frequency). However, the effectiveness of obstructions to induce scour also depends on channel characteristics, such as channel gradient, width:depth ratio, relative submergence (ratio of flow depth to grain size), and the calibre and rate of bed material supply. Moreover, different reach‐scale channel types impose different characteristic physical processes and boundary conditions that further control the occurrence of pools within a catchment. Our findings indicate that effective management of pools and associated aquatic habitat requires consideration of a variety of factors, each of which may be more or less important depending on channel type and location within a catchment. Consequently, strategies for managing pools that are based solely on single‐factor, regional target values (e.g. a certain number of wood pieces or pools per stream length) are likely to be ineffective because they do not account for the variety of local and catchment controls on pool scour and, therefore, may be of limited value for proactive management of complex ecosystems. Copyright © 2002 John Wiley & Sons, Ltd.

Toddler drowning in domestic swimming pools

Aims—To identify how toddlers who drowned gained access to private swimming pools; to recommend preventive strategies to reduce the incidence of toddler drowning and near drowning. Method—The study reviewed critically...

Large woody debris in bull trout (Salvelinus confluentus) spawning streams of logged and wilderness watersheds in northwest Montana

We measured large woody debris (LWD) in 20 known bull trout (Salvelinus confluentus) spawning stream reaches from logged and wilderness watersheds in northwestern Montana. Mean bankfull width of stream reaches was 14.1 m ranging from 3.9 to 36.7 m. Streams were large enough to move LWD and form aggregates. We determined the characteristics of individual pieces of LWD that were interactive with the stream channel. Large, short pieces of LWD attached to the stream bank were the most likely to be positioned perpendicular to stream flow, while large, long pieces either tended to be parallel to the flow or, when attached, were most apt to extend across the channel thalweg. Observations indicated that the majority of pools were formed as scour pools by either very large LWD pieces that were perpendicular to the stream or multipiece LWD aggregates. Among reaches in wilderness watersheds, ratios of large to small LWD, attached to unattached LWD, and with and without rootwads were relatively consistent. However, among reaches with logging in the watershed, these ratios varied substantially. These results suggest that logging can alter the complex balance of delivery, storage, and transport of LWD in northern Rocky Mountain streams, and therefore, the likely substantive change in stream habitats.

The anostraca of the republic of Belarus

A survey of temporary freshwaters in the Republic of Belarus revealed the presence of two anostracan species (Chirocephalus josephinae and Drepanosurus hankoi). The two species co-occur in a majority of pools. Their life cycle partly overlaps, with D. hankoi the first to disappear. Morphological variability in Bielorussian populations is briefly discussed and compared with existing information. Two further species were found in Museum collections (Chirocephalus shadini and Streptocephalus torvicornis).

Detection of human parvovirus B19 DNA in plasma pools and blood products derived from these pools: implications for efficiency and consistency of removal of B19 DNA during manufacture

The polymerase chain reaction (PCR) assay was used to detect human parvovirus B19 DNA in 38 blood products and start plasma pools from five different manufacturers. The products examined were albumin, factor VIII, intravenous (i.v.) and intramuscular (i.m) immunoglobulin batches. The majority of pools from all the manufacturers had detectable B19 DNA (64/75:85%; ranging from 60% to 100% for individual manufacturers). B19 DNA was found in 3/12 albumin samples, in 7/7 factor VIII samples, 3/15 IVIG samples and 3/4 IMIG samples. The levels of B19 DNA in pools varied from 10(2) to 10(9) genome equivalents/ml, whereas the levels in products varied from 10(2) to 10(6) genome equivalents/ml, but there was no clear relationship between the levels of B19 DNA in start pools and final products. The levels of B19 DNA varied between different batches of the same product from a single manufacturer, possibly due to small variations in the processing parameters. In addition, there was some indication from the study of IVIG samples that treatment at low pH may result in removal of PCR-detectable B19 DNA.

Characteristics and function of large woody debris in subalpine Rocky Mountain streams in northern Colorado

Large woody debris has been well studied in coastal forests of the Pacific Northwest, but little is known of its role in Rocky Mountain streams. Large woody debris was measured in 11 undisturbed streams draining subalpine old-growth forests in north central Colorado to assess abundance, characteristics, and function. Although large woody debris in Colorado had smaller diameter, length, and volume than in the Pacific Northwest, its abundance and function were similar. The majority of pools (76%) were plunge and dammed pools formed by large woody debris, most of which spanned the channels perpendicular to stream flow. Smaller streams had a greater proportion of such perpendicular pool-forming pieces than larger streams. Four disturbed streams had significantly less and smaller large woody debris than undisturbed streams. Flows in larger undisturbed streams were capable of moving large woody debris, so pieces were more often located at the stream margins, oriented diagonally, or distributed in clumps than in smaller streams. Individual pools were larger and deeper in larger streams, but their size was not related to the size of large woody debris pieces forming them. Therefore, the function of large woody debris in forming fish habitat in small Rocky Mountain streams is strongly influenced by the stream's location within the watershed.

A Study of Core-Analyses Data from Flooded-Out Oil Sands

Abstract Flood-pot tests have been used for many years to determine the minimum residual oil saturation which would occur with 100 per cent water flood recovery efficiency. To evaluate the validity of such measurements, a study was made of core-analyses data from wells drilled prior to flooding and from wells drilled late in the flood life when operations were at or near the economic limit. The 19 wells in the latter category included in this study were limited to sands where "flushing of cores" was negligible. A comparison of oil saturations measured on fresh core samples in watered-out areas and companion flood-pot samples is shown. While the data indicate that average reservoir residual oil saturation exceeds the flood-pot residual value by 5 to 9 per cent of pore space, they also show that 5 per cent of the samples analyzed from watered-out areas contained no mobile oil and that 15 per cent of the samples contained only 1 to 2 per cent (pore volume) mobile oil. Correlations verifying these results are included and involve 165 cored wells from the Bartlesville formation in Oklahoma and Kansas, and the Bradford formation in Pennsylvania. The data further indicate that the commonly accepted concepts of the effects of permeability distribution on vertical conformance and the "dead areas" on sweep efficiency in pattern water flooding may not be applicable. Introduction In predicting the reserves and performance of a waterflood operation by both analytical and empirical methods, the minimum residual oil saturation after flooding must be determined. Core-analysis data often are used in obtaining this factor. One of two procedures can be followed:consider the oil saturation found by conventional core analysis after correction for shrinkage as the residual oil saturation to be expected from flooding with water, orperform flood-pot test to measure the residual and mobile oil saturations. In the latter, the mobile oil saturations determined from cores for certain areas are accepted as precisely those in the reservoir, although in a majority of pools it is recognized that some flushing of the core takes place and allowance is made for this through empirical factors. Thus, two opposite views are expressed; obviously, there is some merit to both. Spencer and Harding claim that, for determining residual oil saturations for conditions before and after flooding, reliability of core analysis depends on the properties and depth of the rock. These authors believe that during coring there is a tendency for the drilling-fluid filtrate to penetrate the formations ahead of the bit and displace oil. This action is supposed to be a minimum for formations having low vertical permeability and high reservoir pressures. However, the writers have observed that in pressure-depleted formations, or in formations containing oil with little or no gas in solution, little or no flushing occurs. For example, oil saturations greater than 50 per cent have been found in hundreds of cored wells in fields subjected to vacuum production for many years. It is believed that, in most productive formations, gas evolving from solution while the core is removed from the well is the principal reason for loss of oil rather than filtrate invasion during drilling. The following questions arise:Can a representative minimum residual oil saturation (immobile) after flooding be determined from conventional core-analysis liquid saturation tests, or should flood-pot tests be used?Are flood-pot test data usable in predicting waterflood reserves and performance? It was the object of this paper to answer these questions through a study of core-analyses data from watered-out areas. The study also includes data on wells drilled in the theoretically determined dead-area, or area supposedly not contacted by the injected water. It will be recalled that this concept originated from model and other research work performed by Muskat, Wyckoff, Botset and Muskat, and others. JPT P. 114^