S-metolachlor pulse exposure on the alga Scenedesmus vacuolatus: effects during exposure and the subsequent recovery

In streams and creeks, the aquatic flora is exposed to fluctuating concentrations of herbicides during and following their application. Peak concentrations of herbicides, like the chloroacetanilide S-metolachlor, are usually detected following rain events. In this study, we assessed the effect of S-metolachlor pulse exposure on the algae Scenedesmus vacuolatus. We measured the time-dependency of effects during exposure on algae population and identified the algae development stage most sensitive to S-metolachlor. Furthermore, we assessed the time-to-recovery of the algae following exposure. A 6h pulse exposure at 598mugl(-1) was sufficient to inhibit cell reproduction by 50%. However, the exposure period had to coincide with the cell development stage specifically inhibited by S-metolachlor, which is the end of the cell growth phase. In algae populations composed of cells at all development stages, we initially observed an increase in the size of some algal cells, ultimately leading to an inhibition of the growth rate. In these experimental conditions, effects were observed after 18h of exposure and greatly increased with time. The recovery of algae following exposure to strongly inhibiting S-metolachlor concentrations was delayed and only occurred after 29h. These findings suggest that peak exposure to S-metolachlor may affect the growth of sensitive alga in surface waters, considering that the effects extend beyond the period of exposure.     

Managing for Multiple Resources Under Climate Change: National Forests

This study explores potential adaptation approaches in planning and management that the United States Forest Service might adopt to help achieve its goals and objectives in the face of climate change. Availability of information, vulnerability of ecological and socio-economic systems, and uncertainties associated with climate change, as well as the interacting non-climatic changes, influence selection of the adaptation approach. Resource assessments are opportunities to develop strategic information that could be used to identify and link adaptation strategies across planning levels. Within a National Forest, planning must incorporate the opportunity to identify vulnerabilities to climate change as well as incorporate approaches that allow management adjustments as the effects of climate change become apparent. The nature of environmental variability, the inevitability of novelty and surprise, and the range of management objectives and situations across the National Forest System implies that no single approach will fit all situations. A toolbox of management options would include practices focused on forestalling climate change effects by building resistance and resilience into current ecosystems, and on managing for change by enabling plants, animals, and ecosystems to adapt to climate change. Better and more widespread implementation of already known practices that reduce the impact of existing stressors represents an important “no regrets” strategy. These management opportunities will require agency consideration of its adaptive capacity, and ways to overcome potential barriers to these adaptation options.     

Microbially mediated aerobic and anaerobic degradation of acrylamide in a western United States irrigation canal

Acrylamide (AMD), a neurotoxin and suspected carcinogen, is present at concentrations of up to 0.05% in linear anionic polyacrylamide, which is under evaluation as a temporary sealant in unlined irrigation canal systems across the United States. We examined the microbially mediated degradation of AMD and diversity of AMD-degrading microbial physiotypes in the Rocky Ford Highline Canal, Colorado to better constrain the potential fate ofAMD in a canal environment. Microorganisms able to use AMD (500 mg L(-1)) as a sole nitrogen source were relatively abundant (2.3 x 10(3) to 9.4 x 10(3) cells mL(-1) in water and 4.2 x 10(3) to 2.3 x 10(5) cells g(-1) in sediment). Only sediment samples contained microorganisms able to use AMD as a sole carbon source. Acrylamide (up to 100 mg L(-1)) was efficiently removed from amended canal water and sediment slurries under aerobic conditions, but no AMD degradation was observed in abiotic controls. Anaerobic degradation of AMD by nitrate-, sulfate-, and iron-reducing microorganisms was also tested, with nitrate reducers affecting the highest amounts of AMD removal (70.3-85%) after 60 d. All representatives (n=15) from a collection of 256 AMD-degrading microbial isolates from Rocky Ford Highline Canal were closely related to well characterized environmental bacteria capable of facultative nitrate respiration. Our results demonstrate that natural microbial populations within this canal are capable of AMD degradation under aerobic and anaerobic conditions and that this degradation is performed by naturally abundant bacteria likely to be present in other freshwater irrigation canals or similar lotic habitats.     

Assessment of reverse-phase chromatographic methods for determining partition coefficients

The possibility of using reverse-phase High Performance Liquid Chromatography (HPLC) and Thin Layer Chromatography (TLC) for determining partition coefficients is assessed. Whereas HPLC has been adequately validated and is recommended, TLC requires further validation. A method of calculating partition coefficients from molecular fragmental constants is also noted as being useful in certain cases.     

Groundwater Exploitation Management Under Land Subsidence Constraint: Empirical Evidence from the Hangzhou–Jiaxing–Huzhou Plain, China

Land subsidence caused by extensive groundwater pumping has become a factor which cannot be ignored in the sustainable exploitation of groundwater resources. The Hangzhou–Jiaxing–Huzhou Plain is one of the locations with China’s most severe land subsidence problems; the region has experienced dramatic land subsidence since the 1960s. Historical records of groundwater extraction, hydraulic head, and land subsidence show the latter to be the result of continual and excessive extraction of groundwater from deep confined aquifers. This study reconstructs land subsidence using an integrated regional groundwater flow and land subsidence model. The model is calibrated using land subsidence and groundwater level measurements from 1996 to 2007. Simulation results reproduce the cones of depression for groundwater heads and nadirs of land subsidence reasonably well. The calibrated model is used to evaluate the efficacy of land subsidence prevention plans from 2008 to 2010, and to predict future land subsidence over the next decade considering several groundwater exploitation scenarios. The results show the main cause of land subsidence to be inelastic compaction of the aquifer system resulting from continuously declining water levels. The model reveals that while the area of land subsidence will continue to extend, the rate of this extension may be significantly decreased by reduction of groundwater extraction. If the current land subsidence prevention and reclamation plans are continued and surface water diversion projects implemented, though land subsidence cannot be halted, the rate at which it is occurring can be effectively reduced.     

Power and Sample Size Calculations for Linear Hypotheses Associated with Mixtures of Many Components using Fixed-Ratio Ray Designs

Response surface methodology, often supported by factorial designs, is the classical experimental approach that is widely accepted for detecting and characterizing interactions among chemicals in a mixture. In an effort to reduce the experimental effort as the number of compounds under study is increased, ray designs have been proposed to study combinations of chemicals. When interest is restricted to relevant mixing ratios, we are only interested in making inference along the specific rays of interest, as opposed to methods which use designs that require more experimental effort to support the estimation of a response surface over a broader experimental region. Methods have been developed for the test of additivity along multiple fixed-ratio rays. Of primary importance is the detection of interactions with reasonable power. The objective of this paper is to address power and sample size issues related to the hypothesis of no interaction.     

Validating the enchytraeid reproduction test: organisation and results of an international ringtest

In this paper the experiences concerning the organisation and results of the enchytraeid reproduction test (ERT) ringtest are summarised (for details see J. R?mbke, T. Moser, Organisation and Performance of an International Ringtest for the Validation of the Enchytraeid Reproduction Test, vols. I and II. UBA-Texte 4/99, 1999, 150, 223 pp). The performance of this ringtest was in line with requirements published by OECD. It was sponsored by the German Federal Environmental Agency (Umweltbundesamt; UBA, Berlin). The UBA was also actively engaged (together with the European Chemicals Bureau, Ispra) in a scientific task force, which consisted of seven scientists experienced in terrestrial ecology and ecotoxicology. 29 institutions (mainly from universities and contract research laboratories) from 15 countries of Europe and North America participated actively in the ringtest. The co-ordinating laboratory centrally distributed the test chemicals, guidance papers and test organisms to all participants. In addition, several training courses were organised. Most participants performed two tests with the fungicide Carbendazim and two with 4-nitrophenol. For each chemical, one test was designed according to an ECx approach and the other according to an NOEC approach. Several aspects of the test protocol were modified based on the experiences gained during the ringtest. A major aspect of the project was the detailed statistical evaluation of the test results (for details see A. Weyers, J. R?mbke, T. Moser, T. Ratte, Results of and statistical implications from the enchytraeid reproduction ringtest, 2001, submitted), leading to recommendations for an optimised ecotoxicological test design. A total of 92 tests were performed according to the protocol which is among the highest number ever performed in a ringtest. About 72% met the validity criteria (control mortality < 20%, > 25 juveniles per 10 adults). The effects of the two test chemicals on enchytraeid reproduction were in the range expected from data in the literature on oligochaete toxicity. However, statistical evaluation of the data was sometimes difficult as a result of the high variability in the number of juveniles. This variability was caused by several reasons, including hormesis effects or lack of experience of some participants. Comparison of the data from the NOEC and ECx approaches pointed to a clear advantage in favour of the latter. In most cases EC10 values were lower than the NOEC values determined in the same test. For details see A. Weyers et al. (loc. cit.). Reproducibility of the test data and practicability of the ERT ringtest were of the same order of magnitude as other ringtests recently performed. As a result of the ringtest, the ERT draft guideline was significantly improved. The new version is currently being standardised by OECD, ISO and ASTM.