Trophic Relationships of a Marsh Bird Differ Between Gulf Coast Estuaries

Much of North America’s tidal marsh habitat has been significantly altered by both natural and man-made processes. Thus, there is a need to understand the trophic ecology of organisms endemic to these ecosystems. We applied carbon (δ ¹³C) and nitrogen (δ ¹⁵N) stable isotope analysis, along with isotope mixing models, to egg yolk, liver, and muscle tissues of clapper rails (Rallus longirostris) and their likely prey items. This analysis enabled us to explore variation in trophic niche and diet composition in this important marsh bird in two northern Gulf of Mexico tidal marshes that are river and ocean-dominated. For the river-associated estuary, δ ¹³C and δ ¹⁵N of egg yolks, liver, and pectoral muscle tissue samples provided evidence that clapper rails maintained a similar diet during both the winter and the breeding season. A trophic link between C₃ primary productivity and the clapper rail’s diet was also indicated as the δ ¹³C of clapper rail egg yolks related negatively with the aerial cover of C₃ macrophytes. Clapper rails from the ocean-dominated estuary had a narrower trophic niche and appeared to be utilizing marine resources, particularly, based on modeling of liver stable isotope values. Variation in stable isotope values between egg yolk and liver/muscle in both systems suggests that endogenous resources are important for egg production in clapper rails. These results demonstrate that diet composition, prey source, and niche width of clapper rails can vary significantly across different estuaries and appear to be influenced by hydrological conditions.     

Interannual Variation in Photosynthetically Significant Optical Properties and Water Quality in a Coastal Blackwater River Plume

Surface water optical characteristics, nutrients, and planktonic chlorophyll a concentrations were analyzed in the Cape Fear River (CFR) plume over a 2-year period. CFR discharge during the dry year (109 ± 105 m³s⁻¹) was only 25% of the wet year discharge (429 ± 337 m³s⁻¹). Partitioning the contributions of phytoplankton pigments, non-pigmented particles, and colored dissolved organic matter (CDOM) to the absorption of photosynthetically active radiation (PAR) indicated that CDOM was the dominant contributor to PAR absorption. Particulate absorption was relatively greater during the dry year. Pigment absorption was minor and varied little among stations or between years. Chlorophyll a concentrations were reduced at the most plume-influenced stations during the wet year, despite lower turbidity and higher nitrate concentrations. Ammonium and orthophosphate concentrations were not different between years. CDOM absorption [a _CDOM (412)] ranged from 0.05 to 8.25 m⁻¹ with highest values occurring near the CFR mouth. Our results suggest that for coastal ecosystems with significant blackwater river inputs, CDOM may exert a major limiting influence over near-shore primary production.     

ENSIP: the El Niño simulation intercomparison project

An ensemble of twenty four coupled ocean-atmosphere models has been compared with respect to their performance in the tropical Pacific. The coupled models span a large portion of the parameter space and differ in many respects. The intercomparison includes TOGA (Tropical Ocean Global Atmosphere)-type models consisting of high-resolution tropical ocean models and coarse-resolution global atmosphere models, coarse-resolution global coupled models, and a few global coupled models with high resolution in the equatorial region in their ocean components. The performance of the annual mean state, the seasonal cycle and the interannual variability are investigated. The primary quantity analysed is sea surface temperature (SST). Additionally, the evolution of interannual heat content variations in the tropical Pacific and the relationship between the interannual SST variations in the equatorial Pacific to fluctuations in the strength of the Indian summer monsoon are investigated. The results can be summarised as follows: almost all models (even those employing flux corrections) still have problems in simulating the SST climatology, although some improvements are found relative to earlier intercomparison studies. Only a few of the coupled models simulate the El Niño/Southern Oscillation (ENSO) in terms of gross equatorial SST anomalies realistically. In particular, many models overestimate the variability in the western equatorial Pacific and underestimate the SST variability in the east. The evolution of interannual heat content variations is similar to that observed in almost all models. Finally, the majority of the models show a strong connection between ENSO and the strength of the Indian summer monsoon.     

On the occurrence of an unusual form of monazite in panned stream sediments in Wales

An unusual nodular form of monazite has been found to account for abnormally high levels of cerium in panned heavy mineral concentrates from stream sediments in several areas in Wales and pan of Exmoor. Textural features indicate a pre-metamorphic, diagenetic origin within Lower Palaeozoic shale or siltstone host-rocks but REE patterns show only minor variation, including relative enrichment in europium, from ‘average’ granitic monazite. The similarities between these occurrences, described for the first time from the British Isles, and those previously described from Brittany and elsewhere are discussed.