Analyzing mixing systems using a new generation of Bayesian tracer mixing models.

The ongoing evolution of tracer mixing models has resulted in a confusing array of software tools that differ in terms of data inputs, model assumptions, and associated analytic products. Here we introduce MixSIAR, an inclusive, rich, and flexible Bayesian tracer (e.g.

Quantitative assessment of Pb sources in isotopic mixtures using a Bayesian mixing model.

Lead (Pb) isotopes provide valuable insights into the origin of Pb within a sample, typically allowing for reliable fingerprinting of their source. This is useful for a variety of applications, from tracing sources of pollution-related Pb, to the origins of Pb in archaeological artefacts. However, current approaches investigate source proportions via graphical means, or simple mixing models.

Seasonal and long-term effects of CO2 and O3 on water loss in ponderosa pine and their interaction with climate and soil moisture.

Evapotranspiration (ET) is driven by evaporative demand, available solar energy and soil moisture (SM) as well as by plant physiological activity which may be substantially affected by elevated CO2 and O3. A multi-year study was conducted in outdoor sunlit-controlled environment mesocosm containing ponderosa pine seedlings growing in a reconstructed soil-litter system. The study used a 2 x 2 factorial design with two concentrations of CO2 (ambient and elevated), two levels of O3 (low and high) and three replicates of each treatment.

Elevated CO2 and O3 effects on fine-root survivorship in ponderosa pine mesocosms.

Atmospheric carbon dioxide (CO(2)) and ozone (O(3)) concentrations are rising, which may have opposing effects on tree C balance and allocation to fine roots. More information is needed on interactive CO(2) and O(3) effects on roots, particularly fine-root life span, a critical demographic parameter and determinant of soil C and N pools and cycling rates. We conducted a study in which ponderosa pine (Pinus ponderosa) seedlings were exposed to two levels of CO(2) and O(3) in sun-lit controlled-environment mesocosms for 3 years.

Elevated CO(2) and temperature alter net ecosystem C exchange in a young Douglas fir mesocosm experiment.

We investigated the effects of elevated CO(2) (EC) [ambient CO(2) (AC) + 190 ppm] and elevated temperature (ET) [ambient temperature (AT) + 3.6 degrees C] on net ecosystem exchange (NEE) of seedling Douglas fir (Pseudotsuga menziesii) mesocosms. As the study utilized seedlings in reconstructed soil-litter-plant systems, we anticipated greater C losses through ecosystem respiration (R(e)) than gains through gross photosynthesis (GPP), i.

The shifting baseline of northern fur seal ecology in the northeast Pacific Ocean.

Historical data provide a baseline against which to judge the significance of recent ecological shifts and guide conservation strategies, especially for species decimated by pre-20th century harvesting. Northern fur seals (NFS; Callorhinus ursinus) are a common pinniped species in archaeological sites from southern California to the Aleutian Islands, yet today they breed almost exclusively on offshore islands at high latitudes. Harvest profiles from archaeological sites contain many unweaned pups, confirming the presence of temperate-latitude breeding colonies in California, the Pacific Northwest, and the eastern Aleutian Islands.

Bole water content shows little seasonal variation in century-old Douglas-fir trees.

Purportedly, large Douglas-fir trees in the American Pacific Northwest use water stored in bole tissues to ameliorate the effects of seasonal summer drought, the water content of bole tissues being drawn down over the summer months and replenished during the winter. Continuous monitoring of bole relative water content (RWC) in two 110-120-year-old Douglas-fir trees with ThetaProbe impedance devices provided an integrated measure of phloem-sapwood water content over 4 years. Seasonal changes in RWC closely tracked cambial activity and wood formation, but lagged changes in soil water content by 2-3 months.

CO2 and N-fertilization effects on fine-root length, production, and mortality: a 4-year ponderosa pine study.

We conducted a 4-year study of juvenile Pinus ponderosa fine root (< or =2 mm) responses to atmospheric CO2 and N-fertilization. Seedlings were grown in open-top chambers at three CO2 levels (ambient, ambient+175 mumol/mol, ambient+350 mumol/mol) and three N-fertilization levels (0, 10, 20 g m(-2) year(-1)). Length and width of individual roots were measured from minirhizotron video images bimonthly over 4 years starting when the seedlings were 1.

Estimating the timing of diet shifts using stable isotopes.

Stable isotope analysis has become an important tool in studies of trophic food webs and animal feeding patterns. When animals undergo rapid dietary shifts due to migration, metamorphosis, or other reasons, the isotopic composition of their tissues begins changing to reflect that of their diet. This can occur both as a result of growth and metabolic turnover of existing tissue.

Combining sources in stable isotope mixing models: alternative methods.

Stable isotope mixing models are often used to quantify source contributions to a mixture. Examples include pollution source identification; trophic web studies; analysis of water sources for soils, plants; or water bodies, and many others. A common problem is having too many sources to allow a unique solution.

Source partitioning using stable isotopes: coping with too many sources.

Stable isotopes are increasingly being used as tracers in environmental studies. One application is to use isotopic ratios to quantitatively determine the proportional contribution of several sources to a mixture, such as the proportion of various pollution sources in a waste stream. In general, the proportional contributions of n+1 different sources can be uniquely determined by the use of n different isotope system tracers (e.

Optimizing minirhizotron sample frequency for an evergreen and deciduous tree species.

•  When using minirhizotrons to study fine dynamics in natural ecosystems, it is important to determine how sample collection frequency influences estimates of fine root production and mortality. Minirhizotron images were collected twice per week from mature Pseudotsuga menziesii and Tilia cordata trees and analyzed to estimate fine root production and mortality. These data were used to create data sets reflecting sample frequencies of 1, 2, 4 or 8 wk.

Incorporating concentration dependence in stable isotope mixing models.

Stable isotopes are often used as natural labels to quantify the contributions of multiple sources to a mixture. For example, C and N isotopic signatures can be used to determine the fraction of three food sources in a consumer's diet. The standard dual isotope, three source linear mixing model assumes that the proportional contribution of a source to a mixture is the same for both elements (e.

Uncertainty in source partitioning using stable isotopes.

Stable isotope analyses are often used to quantify the contribution of multiple sources to a mixture, such as proportions of food sources in an animal's diet, or C3 and C4 plant inputs to soil organic carbon. Linear mixing models can be used to partition two sources with a single isotopic signature (e.g.

Effects of elevated CO(2) and nitrogen on the synchrony of shoot and root growth in ponderosa pine.

We monitored effects of elevated CO(2) and N fertilization on shoot and fine root growth of Pinus ponderosa Dougl. ex P. Laws.