Effect of experimental and seasonal warming on litter decomposition in a temperate stream

Litter decomposition, a fundamental ecosystem process in woodland streams, is potentially affected by the predicted increase in water temperature. Here, we assessed the effects of experimental and seasonal warming on oak litter decomposition and on the relative contributions of microbes and invertebrates to this process. Experimental warming (~3 °C) stimulated litter decomposition in the coldest, but not in the warmest, months. This may be attributed to (1) higher temperature sensitivity of decomposition at lower ambient temperature due to temperature limitation of enzymatic activity, (2) higher relative temperature increase in winter than in warmer months, (3) existence of a previous warming period in winter, and (4) stronger stimulation of the activity of detritivores by warming in winter due to the prevalence of earlier (smaller) instars than in warmer months. The low response of litter decomposition to warming may have been due to the low nutrient availability in the study stream. The 30-day litter decomposition was stimulated over the seasonal gradient (monthly mean temperature: 6–16 °C), which may be attributed to a stimulation of metabolic activities by warming and to changes in detritivore life history over the seasons. The stimulation of litter decomposition with temperature suggests that the rate of CO₂ release from freshwaters will increase under global warming. However, invertebrate-driven litter decomposition was more responsive to warming than microbial-driven litter decomposition, suggesting that a larger fraction of litter carbon may be converted into secondary production and stored in the system for longer periods.     

Rainfall interception by an isolated evergreen oak tree in a Mediterranean savannah

Redistribution of ground‐level rainfall and interception loss by an isolated Quercus ilex tree were measured over 2 years in a Mediterranean oak savannah. Stemflow, meteorological variables and sap flow were also monitored. Rainfall at ground level was measured by a set of rain‐gauges located in a radial layout centred on the tree trunk and extending beyond the crown limits. Interception loss was computed as the difference between the volume of rainwater that would reach the ground in the absence of the tree and the volume of water that actually fell on the ground sampling area (stemflow included). This procedure provided correct interception loss estimates, irrespective of rainfall inclination. Results have shown a clear non‐random spatial distribution of ground‐level rainfall, with rainwater concentrations upwind beneath the crown and rain‐shadows downwind. Interception loss amounted to 22% of gross rainfall, per unit of crown‐projected area. Stand interception loss, per unit of ground area, was only 8% of gross rainfall and 28% of tree evapotranspiration. These values reflect the low crown cover fraction of the stand (0·39) and the specific features of the Mediterranean rainfall regime (predominantly with few large storms). Nevertheless, it still is an important component of the water balance of these Mediterranean ecosystems. Copyright © 2005 John Wiley & Sons, Ltd.     

Monitoring groundwater changes in the Yangtze River basin using satellite and model data

Space-borne geodetic sensors and model-based datasets have been used to monitor groundwater changes in the Yangtze River basin (YRB). Groundwater storage variations were computed using the following datasets:? Gravity Recovery and Climate Experiment (GRACE)-derived terrestrial water storage (TWS),? Noah driven Global Land Data Assimilation System (GLDAS-Noah) model to simulate the total water content (TWC) i.e. soil moisture, ice and snow, and canopy water storage, and? Satellite altimetry-observed surface water reservoir storages.Overall, the results show that groundwater in the YRB rose by at least 3.34 km³/yr between January 2003 and December 2009. However, the estimated groundwater linear trend for the period of 2003–2009 was ?0.95 km³/yr according to the Changjiang and Southwest Rivers Water Resource Bulletin (CJSRWB). An analysis of the methodology of the CJSRWB shows that the groundwater estimate was based on the water balance approach, which has been found to be weak in inter-basin sub-surface flow. The GRACE-estimated groundwater rise is larger and suggests that the YRB is affected by seepage from Tibetan lakes through a sub-surface fault. Additionally, there is evidence showing that water loss from the Yangtze River by underground leakage through faults could also be a cause of the difference. Therefore, it is concluded that further investigation is required to determine the causation.     

Assessment of tidal inlet evolution and stability using sediment budget computations and hydraulic parameter analysis

Research into the response of coastlines to the opening and stabilisation of inlets has been limited by the availability of suitable data, the shortcomings of existing formulae when applied to different inlets, and the difficulties particular to multi-inlet situations. Our appraisal of methodologies for studying inlet dynamics leads us to formulate a new approach for investigating inlet evolution and stability based on combining sediment budget computations (using best estimates and uncertainty analysis) and inlet hydraulic parameter analysis.The approach developed is applied to a stabilised inlet, located within a multi-inlet system (Faro-Olhão Inlet, Ria Formosa, Southern Portugal), which was opened starting 1929 and has since been dredged periodically to maintain navigability. A series of digital maps was produced based on multi-year data acquired from charts, surveys, and aerial photos. The maps were used to compute sediment volumes for six coastal cells delineated on the basis of the morphological features of the inlet. Cell volumes and fluxes were calculated for three periods (1929–1962, 1962–1978, and 1978–2001), and overall sediment budgets were calculated for the latter two periods. Inlet hydraulic parameters measured included tidal prism, inlet channel cross-sectional area and hydraulic radius, and maximum depth of the inlet throat, and were tracked over 9 bathymetric surveys from 1947–2004. The computed budget reveals that the inlet is only at present reaching volumetric equilibrium. However, the analysis of channel cross-sectional area and radius indicates parameter stability around 1978–1985, 20–25 years before the inlet started to reach volumetric equilibrium. It is hypothesised that the observed stability in parameters for the inlet post-1978 is related to the presence of fixed jetties and to a stratigraphic control that prevents further deepening, and not to the achievement of a dynamic equilibrium.The findings indicate that the coupling of sediment budget computation and inlet parameter analysis is useful for understanding historical sediment pathways and magnitudes, and for analysing the evolution of an inlet towards equilibrium. Although the analysis of inlet parameter evolution is valuable for examining the locational/geometrical stability of an inlet, it needs to be used in conjunction with sediment budget computations in order to properly infer inlet equilibrium. Moreover, existing formulae used to infer inlet stability, which relate cross-sectional area to tidal prism, should be reviewed with a view to including other external variables (e.g., stratigraphic controls) and to making their application more flexible to cope with the range of different inlet conditions. For multi-inlet systems, the coupling of morphology and hydrodynamics analysis should be extended to all inlets in order to infer the stability of the overall system based on the distribution of the tidal prism through time and the patterns of inlet circulation and sediment transport.     

Laminated sediments from the central Peruvian continental slope: A 500 year record of upwelling system productivity, terrestrial runoff and redox conditions

Sedimentological studies including X-ray digital analyses, mineralogy, inorganic contents, and organic geochemistry on cores of laminated sediments accumulated in the oxygen minimum zone of the central Peruvian margin reveal variable oceanographic and climate conditions during the last 500 yr. Coherent upcore variations in sedimentological and geochemical markers in box cores taken off Pisco (B0405-6) and Callao (B0405-13) indicate that variability in the climate proxies examined has regional significance. Most noteworthy is a large shift in proxies at 1820 AD, as determined by ²¹⁰Pb and ¹⁴C radiometric dating. This shift is characterized by an increase in total organic carbon (TOC) in parallel with an abrupt increase in the enrichment factor for molybdenum Mo indicating a regional intensification of redox conditions, at least at the sediment water interface. In addition there was lower terrestrial input of quartz, feldspar and clays to the margin. Based on these results, we interpret that during several centuries prior to 1820, which corresponds to the little ice age (LIA), the northern Humboldt current region was less productive and experienced higher terrestrial input related to more humid conditions on the continent. These conditions were probably caused by a southward displacement of the inter-tropical convergence zone and the subtropical high pressure cell during the LIA. Since 1870, increases in TOC and terrigenous mineral fluxes suggest an increase of wind-driven upwelling and higher productivity. These conditions continued to intensify during the late 20th century, as shown by instrumental records of wind forcing.     

C-, Sr-isotope and Hg chemostratigraphy of Neoproterozoic cap carbonates of the Sergipano Belt,Northeastern Brazil

Two cap carbonates overlying glaciogenic diamictites crop out extensively in the eastern Vaza Barris Domain of the Sergipano Belt, northeastern Brazil. They are represented by carbonates of the Jacoca Formation, resting on top of diamictite of the Ribeiropolis Formation, and by the Olhos D’Agua Formation (carbonates, organic-rich towards the top), which overlies diamictite of the Palestina Formation. These two sequences were deformed and metamorphosed at sub-greenschist facies-conditions during the Brasiliano cycle (650–600 Ma).