Regional Scale Stressor‐Response Models in Aquatic Ecosystems1

Abstract: A systematic method for identification and estimation of regional scale stressor‐response models in aquatic ecosystems will be useful in monitoring and assessment of aquatic resources, determination of regional nutrient criteria and for increased understanding of the differences between regions. The model response variable is chlorophyll a, a measure of algal density, while the stressors include nutrient concentrations from the USEPA Nutrient Criteria Database (NCD) for lakes/ponds and reservoirs of the continental United States. The NCD has observations for both stressors and biological responses determined using methods that are not consistently available at the continental scale. To link multiple environmental stressors to biological responses and quantify uncertainty in model predictions, we take a multilevel modeling approach to the estimation of a linear model for prediction of log Chlorophyll a using predictors log TP and log TN. The multilevel modeling approach allows us to adjust the impact of covariates at all levels (observation, higher level groups) for the simultaneous operation of contextual and individual variability in the outcome. Here, we wish to allow separate regression coefficients for inference regarding similarities and differences between each of 14 ecoregions, and between the two water‐body types, lakes/ponds and reservoirs. We are also interested in the nuisance effects of the categorical variables indicating the type of nitrogen measurements (three levels) and the type of chlorophyll a measurements (four levels) used. Model‐based determination of nutrient criteria points to an apparent incompatibility of criteria developed for nutrient stressors and eutrophication responses using current Environmental Protection Agency’s guidance.     

Science, Policy, and Stakeholders: Developing a Consensus Science Plan for Amchitka Island, Aleutians, Alaska

With the ending of the Cold War, the US Department of Energy is responsible for the remediation of radioactive waste and disposal of land no longer needed for nuclear material production or related national security missions. The task of characterizing the hazards and risks from radionuclides is necessary for assuring the protection of health of humans and the environment. This is a particularly daunting task for those sites that had underground testing of nuclear weapons, where the radioactive contamination is currently inaccessible. Herein we report on the development of a Science Plan to characterize the physical and biological marine environment around Amchitka Island in the Aleutian chain of Alaska, where three underground nuclear tests were conducted (1965–1971). Information on the ecology, geology, and current radionuclide levels in biota, water, and sediment is necessary for evaluating possible current contamination and to serve as a baseline for developing a plan to ensure human and ecosystem health in perpetuity. Other information required includes identifying the location of the salt water/fresh water interface where migration to the ocean might occur in the future and determining groundwater recharge balances, as well as assessing other physical/geological features of Amchitka near the test sites. The Science Plan is needed to address the confusing and conflicting information available to the public about radionuclide risks from underground nuclear blasts in the late 1960s and early 1970s, as well as the potential for volcanic or seismic activity to disrupt shot cavities or accelerate migration of radionuclides into the sea. Developing a Science Plan involved agreement among regulators and other stakeholders, assignment of the task to the Consortium for Risk Evaluation with Stakeholder Participation, and development of a consensus Science Plan that dealt with contentious scientific issues. Involvement of the regulators (State of Alaska), resource trustees (U S Fish and Wildlife Service), representatives of the Aleut and Pribilof Island communities, and other stakeholders was essential for plan development and approval, although this created tensions because of the different objectives of each group. The complicated process of developing a Science Plan involved iterations and interactions with multiple agencies and organizations, scientists in several disciplines, regulators, and the participation of Aleut people in their home communities, as well as the general public. The importance of including all parties in all phases of the development of the Science Plan was critical to its acceptance by a broad range of regulators, agencies, resource trustees, Aleutian/Pribilof communities, and other stakeholders.     

Pathway of CH4 formation in anoxic rice field soil and rice roots determined by 13C-stable isotope fractionation

In anoxic rice fields methane is produced by either reduction of CO2 or cleavage of acetate. We measured the delta 13C-values of CH4 and CO2, acetate and organic carbon during time course experiments with anoxic methanogenic soil and root samples and used these values to calculate the fractions of CH4 (and acetate) produced from CO2 reduction. Comparison with radiotracer and/or inhibitor studies constrained the kinetic fractionation factors used for calculation. The fractionation factors for the conversion of CO2 to CH4 and of acetate to CH4 were on the order of alpha = 1.07 (epsilon = -70%) and epsilon > or = - 20%, respectively. The pathway of CH4 production changed with time of anoxic incubation. Anoxic slurries of rice field soil first produced CH4 predominantly (>50%) from CO2, then predominantly (>80%) from acetate and finally (after about one month) according to the theoretically expected ratio (33% CO2 and 67% acetate). Anoxic rice roots, on the other hand, initially produced CH4 exclusively from CO2, followed by contribution of acetate of about 40-60%. Rice roots also produced acetate that partially originated (< or = 1 30%) from reduction of CO2 as determined by calculation of isotopic fractionation using fractionation factors from the literature. The results demonstrate that there is quite some variability in pathways of CH4 production, and also indicate that isotopic fractionation factors may be different in different habitats and change with time.     

Effects of a non-ionic surfactant (Tween-80) on the mineralization, metabolism and uptake of phenanthrene in wheat-solution-lava microcosm

Effects of a non-ionic surfactant (Tween-80) on the mineralization, metabolism and uptake of phenanthrene in wheat-solution-lava microcosm were studied using 14C-labeled phenanthrene. The mineralization and metabolism of phenanthrene were fast in such a system. At least 90% of the applied phenanthrene were transformed within 24 days. Only 0.3% of the applied 14C-activity were identified to be the parent phenanthrene. Most of the applied 14C-activity (70%) was recovered from wheat, in which ca. 70% were associated with wheat shoots (stems and leaves) and ca. 30% wheat roots. 33% and 20% of the applied 14C-activity had been constructed into wheat tissues of shoots and roots, respectively. The 14C-activity recovered in forms of CO2 and volatile organic chemicals (VOCs) was 12-16% and 4-5%, respectively. The major metabolites of phenanthrene were polar compounds (18% of the applied 14C) and only 2.1% were identified as non-polar metabolites. No phenanthrene was found in wheat shoots indicating that it could not be transported from roots to upper parts of the plant but in form of metabolites (mostly polar metabolites). Foliar uptake of 14C-activity via air in form of 14CO2 occurred. The presence of Tween-80 significantly enhanced the degradation of phenanthrene, which could be attributed to its increase of microbial activities in the system. Tween-80 also significantly (P < 0.05) reduced the phenanthrene level in wheat roots, which probably resulted from desorption of phenanthrene from root surface caused by the surfactant.