Release,Dispersion, and Resuspension of Escherichia coli From Direct Fecal Deposits Under Controlled Flows1

Abstract: Water‐quality standards have been placed on fecal indicator organisms such as Escherichia coli in an attempt to limit the concentrations in water bodies. Cattle can be a significant source of bacteria to water systems, particularly when they are allowed direct access to streams. A flume study was conducted to quantify the effect and understand the transport of E. coli from directly deposited cattle manure. Five steady‐state flows, ranging from 0.00683 to 0.0176 m³/s, were studied and loads from a single cowpie exceeded the U.S. Environmental Protection Agency’s recommended water‐quality standards (235 CFU/100 ml) at each flow over the hour study period. Average E. coli concentrations ranged from 10² to 10⁵ CFU/100 ml over the hour sampling period for all flows. High spatial variations in E. coli concentrations were often seen at each sampling time, with higher concentrations typically at the bottom of the flume. E. coli resuspension was initially greater at 0.5 min after deposition, for the lowest flow (10⁵ CFU/m²/s); however, resuspension rates became similar over time, on the order of 10³ CFU/m²/s. This study demonstrates that the concentrations of E. coli can vary over the water column, and therefore grab samples may inaccurately measure bacteria concentrations and loads in streams. In addition, resuspension rates were often high, so the incorporation of this process into water‐quality models is important for bacteria prediction.     

Assessing Sediment Yield for Selected Watersheds in the Laurentian Great Lakes Basin Under Future Agricultural Scenarios

In the Laurentian Great Lakes Basin (GLB), corn acreage has been expanding since 2005 in response to high demand for corn as an ethanol feedstock. This study integrated remote sensing-derived products and the Soil and Water Assessment Tool (SWAT) within a geographic information system (GIS) modeling environment to assess the impacts of cropland change on sediment yield within four selected watersheds in the GLB. The SWAT models were calibrated during a 6 year period (2000–2005), and predicted stream flows were validated. The R ² values were 0.76, 0.80, 0.72, and 0.81 for the St. Joseph River, the St. Mary River, the Peshtigo River, and the Cattaraugus Creek watersheds, respectively. The corresponding E (Nash and Sutcliffe model efficiency coefficient) values ranged from 0.24 to 0.79. The average annual sediment yields (tons/ha/year) ranged from 0.12 to 4.44 for the baseline (2000 to 2008) condition. Sediment yields were predicted to increase for possible future cropland change scenarios. The first scenario was to convert all “other” agricultural row crop types (i.e., sorghum) to corn fields and switch the current/baseline crop rotation into continuous corn. The average annual sediment yields increased 7–42 % for different watersheds. The second scenario was to further expand the corn planting to hay/pasture fields. The average annual sediment yields increased 33–127 % compared with baseline conditions.     

Naturally occurring radionuclides in materials derived from urban water treatment plants in southeast Queensland, Australia

An assessment of radiologically enhanced residual materials generated during treatment of domestic water supplies in southeast Queensland, Australia, was conducted. Radioactivity concentrations of U-238, Th-232, Ra-226, Rn-222, and Po-210 in water, sourced from both surface water catchments and groundwater resources were examined both pre- and post-treatment under typical water treatment operations. Surface water treatment processes included sedimentation, coagulation, flocculation and filtration, while the groundwater was treated using cation exchange, reverse osmosis, activated charcoal or methods similar to surface water treatment. Waste products generated as a result of treatment included sediments and sludges, filtration media, exhausted ion exchange resin, backwash and wastewaters. Elevated residual concentrations of radionuclides were identified in these waste products. The waste product activity concentrations were used to model the radiological impact of the materials when either utilised for beneficial purposes, or upon disposal. The results indicate that, under current water resource exploitation programs, reuse or disposal of the treatment wastes from large scale urban water treatment plants in Australia do not pose a significant radiological risk.     

Morphological abnormalities in frogs from a rice-growing region in NSW, Australia, with investigations into pesticide exposure

Three frog species (Limnodynastes tasmaniensis, Limnodynastes fletcheri and Litoria raniformis) were surveyed in rice bays of the Coleambally Irrigation Area (CIA), NSW, Australia, during the rice-growing seasons of 2005/2006 and 2006/2007. A total external morphological abnormality index of 7.0% was observed in frogs of the CIA (n?=?1,209). The types and frequencies of abnormalities were typical of reports from agricultural areas with ectrodactyly being the most common aberration. A relatively low abnormality index of 1.2% was observed in L. raniformis (n?=?87) compared to indices of 7.1% and 8.2% observed in L. fletcheri (n?=?694) and L. tasmaniensis (n?=?428), respectively. No conclusive evidence was found of unnaturally high rates of intersex, gonadal maldevelopment or unbalanced sex ratios in any species. Rice bay surface waters differed significantly in mean pesticide concentrations of atrazine and metolachlor on farms growing rice and corn compared to farms with rice as the sole crop. However, the similar abnormality indices observed in recent metamorphs emerging from these two farm types provided no evidence to suggest a link between larval exposure to the measured pesticides and developmental malformations.     

A note on density dependence in population models

One of the most studied phenomena in ecology is density dependent regulation. The model most frequently used to study this behaviour is the theta-logistic model. However, disagreement has developed within the ecology community pertaining to the interpretation of this model’s parameters, and thus as to appropriate values for the parameters to assume. In particular, the parameter θ$\theta$ has been allowed to take negative values, resulting in the ‘growth rate parameter’ estimated to be negative for species which are extant and exhibit no signs of becoming extinct in the short-term. Here we explain this phenomenon by formulating the theta-logistic model in the manner in which the original logistic model was formulated by Verhulst (1838), in doing so providing a simple interpretation of model parameters and thus restrictions on values the parameters may assume. We conclude that θ$\theta$ should (almost always) be restricted to values greater than −1$-1$. This has implications for studies assessing the form of density dependence from data. Additionally, another model appearing in the literature is presented which provides a more flexible model of density dependence at the expense of only one additional parameter.     

Meta-analysis: trophic level, habitat, and productivity shape the food web effects of resource subsidies

Studies of the effects of cross-habitat resource subsidies have been a feature of food web ecology over the past decade. To date, most studies have focused on demonstrating the magnitude of a subsidy or documenting its effect in the recipient habitat. Ecologists have yet to develop a satisfactory framework for predicting the magnitude of these effects. We used 115 data sets from 32 studies to compare consumer responses to resource subsidies across recipient habitat type, trophic level, and functional group. Changes in consumer density or biomass in response to subsidies were inconsistent across habitats, trophic, and functional groups. Responses in stream cobble bar and coastline habitats were larger than in other habitats. Contrary to expectation, the magnitude of consumer response was not affected by recipient habitat productivity or the ratio of productivity between donor and recipient habitats. However, consumer response was significantly related to the ratio of subsidy resources to equivalent resources in the recipient habitat. Broad contrasts in productivity are modified by subsidy type, vector, and the physical and biotic characteristics of both donor and recipient habitats. For this reason, the ratio of subsidy to equivalent resources is a more useful tool for predicting the possible effect of a subsidy than coarser contrasts of in situ productivity. The commonness of subsidy effects suggests that many ecosystems need to be studied as open systems.     

Plant diversity, CO2, and N influence inorganic and organic N leaching in grasslands

In nitrogen (N)-limited systems, the potential to sequester carbon depends on the balance between N inputs and losses as well as on how efficiently N is used, yet little is known about responses of these processes to changes in plant species richness, atmospheric CO2 concentration ([CO2]), and N deposition. We examined how plant species richness (1 or 16 species), elevated [CO2] (ambient or 560 ppm), and inorganic N addition (0 or 4 g x m(-2) x yr(-1)) affected ecosystem N losses, specifically leaching of dissolved inorganic N (DIN) and organic N (DON) in a grassland field experiment in Minnesota, USA. We observed greater DIN leaching below 60 cm soil depth in the monoculture plots (on average 1.8 and 3.1 g N x m(-2) x yr(-1) for ambient N and N-fertilized plots respectively) than in the 16-species plots (0.2 g N x m(-2) x yr(-1) for both ambient N and N-fertilized plots), particularly when inorganic N was added. Most likely, loss of complementary resource use and reduced biological N demand in the monoculture plots caused the increase in DIN leaching relative to the high-diversity plots. Elevated [CO2] reduced DIN concentrations under conditions when DIN concentrations were high (i.e., in N-fertilized and monoculture plots). Contrary to the results for DIN, DON leaching was greater in the 16-species plots than in the monoculture plots (on average 0.4 g N x m(-2) x yr(-1) in 16-species plots and 0.2 g N x m(-2) x yr(-1) in monoculture plots). In fact, DON dominated N leaching in the 16-species plots (64% of total N leaching as DON), suggesting that, even with high biological demand for N, substantial amounts of N can be lost as DON. We found no significant main effects of elevated [CO2] on DIN or DON leaching; however, elevated [CO2] reduced the positive effect of inorganic N addition on DON leaching, especially during the second year of observation. Our results suggest that plant species richness, elevated [CO2], and N deposition alter DIN loss primarily through changes in biological N demand. DON losses can be as large as DIN loss but are more sensitive to organic matter production and turnover.     

Laboratory and field estimates of the rate of faecal pellet production by Antarctic krill,Euphausia superba

The time course of faecal pellet production (egestion) was monitored in January 1985 for a population of Antarctic krill, Euphausia superba Dana, maintained in flowing seawater aquaria at Palmer Station, Antarctica. Following transfer to filtered seawater, krill produced faecal strings for roughly 40 min, after which time faecal egestion virtually ceased. Similar results were obtained for freshly-trawled krill at sea in February and March 1985. There were wide daily variations in total faecal egestion rate; mean rates varied from 0.54 to 1.66 mg dry wt h^-1 and individual rates from 0.25 to 2.35 mg h^-1 (all data corrected to a standard krill of 600 mg fresh weight). Despite these wide fluctuations in total faecal egestion, the loss of organic matter showed no significant daily variation, with a mean value of 0.13 mgh^-1. The relationship between faecal egestion rate and faecal organic content suggested that feeding rate was governed by food quality; when inorganic load was high, feeding rate increased to ensure sufficient energy intake. The data suggest that superfluous feeding does not occur in krill and that values of gut-clearance time calculated from time intervals greater than about 40 min will not be representative of previous feeding history. the rates of faecal egestion observed in this study indicate that the flux of faecal pellets from krill is substantial. They imply an energy intake in E. superba of 17 to 28% body weight per day, much higher than estimated previously for this species by summing known energy losses, but similar to estimates for other euphausiids.     

Queen number, queen cycling and queen loss: the evolution of complex multiple queen societies in the social wasp genus Ropalidia

Complex, highly integrated societies have evolved from simpler societies repeatedly, and the social insects provide an excellent model system for understanding increasing complexity and integration. In the paper wasps, large societies, known as swarm-founding, have evolved repeatedly from smaller societies, known as independent-founding. Swarm-founding colonies have many more queens than independent-founding colonies, which should dramatically reduce relatedness, posing a challenge to cooperation. However, in each instance, swarm-founding species have also evolved a cyclical pattern of queen reduction which elevates relatedness despite high queen numbers. The genus Ropalidia provides an excellent system in which to study the transition to swarm-founding because it has both independent and swarm-founding species. We studied the Australian independent-founding wasp Ropalidia revolutionalis to better understand the evolution of multiple queens and their periodic reductions in swarm-founding wasps. Using microsatellite genetic markers we genotyped queens, workers and brood from 37 colonies and found that while most colonies had a single queen, three of the colonies had multiple queens at or immediately prior to the time of collection. An additional seven colonies had had multiple co-occurring queens earlier in the season. We also found that colonies experienced many queen losses, and that founding queens were gradually lost until they were replaced by a new cohort of daughter queens in many colonies. This pattern is similar to the periodic reductions and replacements in swarm-founding wasps and suggests that multiple queens and queen cycling evolved relatively early in the shift to swarm-founding in Ropalidia.Communicated by R. Page