Nitrite and Freshwater Fish

Nitrite occurs naturally in fresh waters as a result of nitrification of ammonia and denitrification of nitrate, and its concentration can be enhanced by partial oxidation of ammoniacal discharges. Nitrite is toxic to vertebrates including fish and a principal effect is the conversion of haemoglobin to methaemoglobin which is incapable of oxygen transport although there are circulatory and tissue effects as well. The toxic species is the nitrite ion (NO₂) which is believed to enter the blood via the branchial chloride/bicarbonate exchange and fish such as salmonids with high chloride uptake rates are more susceptible than those with low chloride uptake rates, for example carp. Nitrite toxicity is strongly aleviated by chloride and the concentration ratio of these ions is of great importance in assessing toxicity. Short term and long term toxicity data for a variety of fish species are presented. There are no field data on fish populations in waters where nitrite was the only pollutant. However extensive field surveys indicated that, waters with a mean chloride concentration of 25 mg l^-1 in good salmon fisheries were associated with concentrations of nitrite below 50 μg l^-1 N · NO₂, good coarse fisheries below 100 μg l^-1 N · NO₂.     

Conceptual Models as Hypotheses in Monitoring Urban Landscapes

Many problems and challenges of ecosystem management currently are driven by the rapid pace and spatial extent of landscape change. Parks and reserves within areas of high human population density are especially challenged to meet the recreational needs of local populations and to preserve valued environmental resources. The complex problem of managing multiple objectives and multiple resources requires an enormous quantity of information, and conceptual models have been proposed as tools for organizing and interpreting this information. Academics generally prefer a bottom-up approach to model construction that emphasizes ecologic theory and process, whereas managers often use a top-down approach that takes advantage of existing information to address more pragmatic objectives. The authors propose a formal process for developing, applying, and testing conceptual models to be used in landscape monitoring that reconciles these seemingly opposing perspectives. The four-step process embraces the role of hypothesis testing in the development of models and evaluation of their utility. An example application of the process to a network of national parks in and around Washington, DC illustrates the ability of the approach to systematically identify monitoring data that would both advance ecologic theory and inform management decisions.     

Rates of spread of <Emphasis Type="Italic">Rosa rugosa</Emphasis> (Japanese Rose) determined by GIS on a coastal sand-dune system in Northwest England

The invasive non-native shrub Rosa rugosa (Japanese Rose) is well-established in many northwest European countries where, especially on coastal sand-dunes, it forms large dominant stands with adverse effects on semi-natural vegetation and biota of high conservation status. Its recent increase in England’s largest dune system on the Sefton Coast in north Merseyside led to an investigation into its rate of spread. Using digitised aerial photographs and GIS methodology, sample patches of old-established R. rugosa were found to have grown in area by an average of 22 % per annum between 1989 and 2013. This rate of increase is comparable to that found in Denmark and higher than reported for several other woody plants in coastal dunes. In the absence of management, R. rugosa could soon dominate large areas on the Sefton Coast, with serious consequences for amenity and the nature conservation interest of the dune system.     

IN SITU MEASUREMENT OF ADSORPTION AND BIOTRANSFORMATION AT A HAZARDOUS WASTE SITE1

ABSTRACT: A three well injection-production test was performed at the United Creosoting Company (UCC) site in Conroe, Texas, to estimate the effective in situ retardation factors for adsorption and to evaluate the significance of biotransformation in limiting the transport of polycydic aromatics present in the shallow aquifer. The field test was also used as a model to determine if this type of testing would be feasible at other hazardous waste sites. During the test, chloride, a non-reactive tracer and two organic compounds, naphthalene and paradichlorobenzene (pDCB), were injected into a center well for 24 hours followed by clean ground water for six days. Ground water was continuously produced from two adjoining wells and monitored to observe the breakthrough of these compounds. Data from the test were analyzed by comparing the statistical moments of the chloride and organics distributions. Retardation factors for naphthalene and pDCB were estimated to be 1.03 and 0.97 by comparison of the statistical moments. A significant loss of naphthalene and pDCB was also observed during the three well test, apparently due to biotransformation. These results suggest that biotransformation is the major process limiting the transport of naphthalene and similar compounds at the UCC site.     

The combined effects of urea application and simulated acid rain on soil acidification and microbial community structure

Our aim was to test the effects of simulated acid rain (SAR) at different pHs, when applied to fertilized and unfertilized soils, on the leaching of soil cations (K, Ca, Mg, Na) and Al. Their effects on soil pH, exchangeable H⁺ and Al³⁺ and microbial community structure were also determined. A Paleudalfs soil was incubated for 30 days, with and without an initial application of urea (200 mg N kg^?1soil) as nitrogen (N) fertilizer. The soil was held in columns and leached with SAR at three pH levels. Six treatments were tested: SAR of pH 2.5, 4.0 and 5.6 leaching on unfertilized soil (T1, T2 and T3), and on soils fertilized with urea (T4, T5 and T6). Increasing acid inputs proportionally increased cation leaching in both unfertilized and fertilized soils. Urea application increased the initial Ca and Mg leaching, but had no effect on the total concentrations of Ca, Mg and K leached. There was no significant difference for the amount of Na leached between the different treatments. The SAR pH and urea application had significant effects on soil pH, exchangeable H⁺ and Al³⁺. Urea application, SAR treated with various pH, and the interactions between them all had significant impacts on total phospholipid fatty acids (PLFAs). The highest concentration of total PLFAs occurred in fertilized soils with SAR pH5.6 and the lowest in soils leached with the lowest SAR pH. Soils pretreated with urea then leached with SARs of pH 4.0 and 5.6 had larger total PLFA concentrations than soil without urea. Bacterial, fungal, actinomycete, Gram-negative and Gram-positive bacterial PLFAs had generally similar trends to total PLFAs.     

VALIDATION OF THE SWAT MODEL ON A LARGE RWER BASIN WITH POINT AND NONPOINT SOURCES1

ABSTRACT: The State of Texas has initiated the development of a Total Maximum Daily Load program in the Bosque River Watershed, where point and nonpoint sources of pollution are a concern. Soil Water Assessment Tool (SWAT) was validated for flow, sediment, and nutrients in the watershed to evaluate alternative management scenarios and estimate their effects in controlling pollution. This paper discusses the calibration and validation at two locations, Hico and Valley Mills, along the North Bosque River. Calibration for flow was performed from 1960 through 1998. Sediment and nutrient calibration was done from 1993 through 1997 at Hico and from 1996 through 1997 at Valley Mills. Model validation was performed for 1998. Time series plots and statistical measures were used to verify model predictions. Predicted values generally matched well with the observed values during calibration and validation (R²≥ 0.6 and Nash‐Suttcliffe Efficiency ≥ 0.5, in most instances) except for some underprediction of nitrogen during calibration at both locations and sediment and organic nutrients during validation at Valley Mills. This study showed that SWAT was able to predict flow, sediment, and nutrients successfully and can be used to study the effects of alternative management scenarios.     

The detection of SARS-CoV-2 RNA in indoor air of dental clinics during the COVID-19 pandemic

Environmental Science and Pollution Research - In the indoor environment of dental clinics, dental personnel and patients are exposed to a risk of infection because of the transmission of...