Factors affecting the distribution of benthic macrofauna in estuaries contaminated by urban runoff

Contaminants derived from urban runoff have been shown to accumulate in estuarine sediments, reaching concentrations potentially capable of causing biological effects. Demonstration of effects, however, is difficult due to strong natural environmental gradients and the effects of past or present point-sources of contamination. We used multivariate methods to test two hypotheses relating to the effects of urban-derived contaminants on estuarine benthic communities. First, that patterns of distribution and abundance of benthic invertebrates in two urbanised estuaries would be different from those in two non-urbanised estuaries. Second, that the distributions of benthic invertebrates within and among the four estuaries would be related to those of urban-derived contaminants. Concentrations of contaminants were larger in estuaries with urbanised catchments and concentrations of Cu, Pb, Zn and DDT in some samples exceeded those at which biological effects may be expected to appear. Tests of differences in composition of benthic communities among estuaries showed that the two urban estuaries were not significantly different, but that they differed from both rural estuaries, which also differed from each other. Distributions of benthic invertebrates were significantly related to those of environmental variables, and were ordinated along axes that correlated with both natural environmental variables (nature of the sediment, position in estuary) and contaminants. Differences in faunas between the urban and non-urban estuaries were not, however, clear-cut and nor were relationships between faunal assemblages and environmental variables (including contaminants) consistent between two times of sampling.     

The occurrence of distal Icelandic and Italian tephra in the Lateglacial of Lake Bled,Slovenia

The discovery of sites preserving tephra layers from multiple volcanic centres is key to constructing a single European tephrostratigraphic framework for the Late Quaternary. Until now, the tephrostratigraphy of Europe has been divided into two halves: sites in the North Atlantic and northern Europe regions link the Icelandic, Eifel, and the Massif Central volcanic histories; whilst sites in southern Europe record the sequence of tephra layers produced by circum-Mediterranean volcanic provinces. The missing link, able to tie together these two halves, is found in the tephrostratigraphic record of Lake Bled, Slovenia.Lake Bled, in the Julian Alps, Slovenia, holds a high resolution multi-proxy palaeoenvironmental archive for the Lateglacial of south-central Europe. Cryptotephra investigations have revealed three tephra layers: two closely spaced within Younger Dryas stadial sediments and one shortly after the start of the Bølling-Allerød interstadial warming. Two of the tephra layers (Bld_T120 and Bld_T240) are of Campanian origin and are correlated to deposits of the Pomici Principali (PP) and Neapolitan Yellow Tuff (NYT) eruptions, respectively. The third layer (Bld_T122) correlates to the Icelandic Vedde Ash (VA), extending the known fallout of this widespread marker layer farther to the southeast.The Lake Bled record also allows the stratigraphic relationship and relative ages of the VA and the PP eruption to be discerned for the first time. Whilst existing numerical age estimates for these two deposits are indistinguishable within errors, their close occurrence in the same lacustrine sediment sequence shows that the VA was erupted shortly prior to the PP eruption.The tephrostratigraphy of Lake Bled developed here helps us to tie together regional volcanic stratigraphies into a broader, continental-scale lattice of sites, with the potential to allow the transfer of dates between remote sequences and the construction of relative chronologies, beneficial in particular for environmental and archaeological research.     

Population density, prey selection, and predator avoidance of the burrowing anemone (Ceriantheopsis americanus) in Narragansett Bay, Rhode Island

The maximum population density of the burrowing anemone (Ceriantheopsis americanus) was estimated at 17–28 animals m^?2 in soft-bottom sediments of mid Narragansett Bay. The gut contents of the anemone indicated primary prey of harpacticoid and calanoid copepods. The consumption of calanoid copepods was higher in October than April, which may be due to decreased density of hapacticoids in the fall. The anemones apparently avoid fish predation in late summer by withdrawing into the sediments. After the seasonal fall migration of fish out of the bay, anemones reappear.     

Multi-decadal scale variability in autumn-winter rainfall in south-western Australia since 1655 AD as reconstructed from tree rings of Callitris columellaris

We present the first tree-ring based reconstruction of rainfall for the Lake Tay region of southern Western Australia. We examined the response of Callitris columellaris to rainfall, the southern oscillation index (SOI), the southern annular mode (SAM) and surface sea temperature (SST) anomalies in the southern Indian Ocean. The 350-year chronology was most strongly correlated with rainfall averaged over the autumn-winter period (March–September; r = ?0.70, P < 0.05) and SOI values averaged over June–August (r = 0.25, P < 0.05). The chronology was not correlated with SAM or SSTs. We reconstructed autumn-winter rainfall back to 1655, where current and previous year tree-ring indices explained 54% of variation in rainfall over the 1902–2005 calibration period. Some variability in rainfall was lost during the reconstruction: variability of actual rainfall (expressed as normalized values) over the calibration period was 0.78, while variability of the normalized reconstructed values over the same period was 0.44. Nevertheless, the reconstruction, combined with spectral analysis, revealed that rainfall naturally varies from relatively dry periods lasting to 20–30 years to 15-year long periods of above average rainfall. This variability in rainfall may reflect low-frequency variation in the El Niño-Southern Oscillation rather than the effect of SAM or SSTs.     

Impacts of soil conservation on groundwater recharge in the semi-arid Loess Plateau, China

Soil conservation measures undertaken to address land degradation can alter the hydrologic cycle by changing partitioning of water fluxes at the land surface. While effects on runoff are well documented, impacts of soil conservation activities on fluxes to groundwater are poorly understood. The goal of this study was to examine fluxes to groundwater in a semi-arid area of China’s Loess Plateau that has been subject to extensive soil conservation activities. Unsaturated zone pore-water pressures and concentrations of chloride show that impacts on deep drainage differ between ecological and structural soil conservation approaches. High matric potentials and low chloride beneath cultivated terrace and gulley sites are consistent with deep drainage occurring at these sites. Estimated recharge rates for dryland cultivated upland sites were approximately 55??0?mm/year (11??8% of mean annual rainfall) based upon chloride mass balance. In contrast, results suggest that mature tree and shrub plantations prevent deep drainage. Stable isotope signatures of unsaturated-zone moisture and groundwater indicate that focused infiltration through gullies and other topographic lows is likely to be the primary recharge mechanism. The results of this study highlight the potential for inadvertent effects of some soil conservation approaches on regional water resources.     

Effects of iron limitation on intracellular cadmium of cultured phytoplankton: Implications for surface dissolved cadmium to phosphate ratios

This study compares intracellular Cd content (Cd:C) of cultured marine phytoplankton grown under various Fe levels, with estimated particulate Cd:P ratios derived from regression slopes of Cd versus PO₄³⁻ relationships from a global dataset. A 66-fold difference in Cd:C ratios was observed among the seven species grown under identical Fe concentrations, with oceanic diatoms having the highest Cd quotas and prymesiophytes the lowest. Interestingly, all species significantly increased their Cd:C ratios under Fe-limitation (on average 2-fold). The global data set also showed that the mean estimated Cd:P ratio of surface water particulates in HNLC (high nutrient low chlorophyll) regions were approximately 2-fold higher than non-HNLC regions. A sequence of events are proposed to explain high Cd:P ratios in HNLC waters. First, the seasonal relief from Fe-limitation in HNLC regions leads to blooms of large chain forming diatoms with high intrinsic Cd:P ratios. These large blooms may, in theory, deplete surface water CO₂ and Zn concentrations, which ultimately, would result in increased Cd uptake. Eventually these blooms will run out of Fe, which has been shown to further increase intercellular Cd via growth biodilution and increased Cd uptake through non-specific Fe(II) transporters. Ultimately, Fe-limited diatoms with enhanced Cd quotas will sink out of surface waters leading to pronounced regional differences in Cd:P ratios between HNLC and non-HNLC waters in the global ocean.     

Historical land use as a driver of alternative states for stream form and function in forested mountain watersheds of the Southern Rocky Mountains

We demonstrate how land use can drive mountain streams in the Southern Rockies across a threshold to induce an alternative state of significantly reduced physical complexity of form and reduced ecological function. We evaluate field data from 28 stream reaches in relatively laterally unconfined valleys and unmanaged forest that is either old‐growth forest or naturally disturbed younger forest, and 19 stream reaches in managed forest with past land use. We evaluate potential differences in stream form, as reflected in channel planform, cross‐sectional geometry, and in‐stream wood loads, and stream function, as reflected in pool volume and storage of organic carbon. Field data indicate a threshold of differences in stream form and function between unmanaged and managed stream reaches, regardless of forest stand age, supporting our hypothesis that the legacy effects of past land use result in an alternative state of streams. Because physical complexity that increases stream retentiveness and habitat can maintain aquatic‐riparian ecosystem functions, the alternative physical state of streams in managed watersheds creates a physical template for an alternative ecological state with reduced pool volume, organic carbon storage, and ecosystem productivity. We recommend maintaining riparian forests that can supply large wood to streams as a stream restoration technique in historically forested stream segments. Copyright © 2017 John Wiley & Sons, Ltd.     

Studies on primary productivity model in shallow mixed waters

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Long-term increase in diffuse groundwater recharge following expansion of rainfed cultivation in the Sahel,West Africa

Rapid population growth in sub-Saharan West Africa and related cropland expansion were shown in some places to have increased focused recharge through ponds, raising the water table. To estimate changes in diffuse recharge, the water content and matric potential were monitored during 2009 and 2010, and modeling was performed using the Hydrus-1D code for two field sites in southwest Niger: (1) fallow land and (2) rainfed millet cropland. Monitoring results of the upper 10 m showed increased water content and matric potential to greater depth under rainfed cropland (>2.5 m) than under fallow land (≤1.0 m). Model simulations indicate that conversion from fallow land to rainfed cropland (1) increases vadose-zone water storage and (2) should increase drainage flux (～25 mm year^?1) at 10-m depth after a 30–60 year lag. Therefore, observed regional increases in groundwater storage may increasingly result from diffuse recharge, which could compensate, at least in part, groundwater withdrawal due to observed expansion in irrigated surfaces; and hence, contribute to mitigate food crises in the Sahel.