Linking biogeochemical processes and historic primary producer communities in a SE USA sinkhole lake from the mid-Holocene to present

Many freshwater resources receive materials from human development causing a decrease in ecological services when compared to pre-disturbance periods. As a result, the understanding of eutrophication and limnological change has increased, but less attention has been given to systems under intense human impact that have not eutrophied so that drivers precluding eutrophication can be documented. The primary objective of this research was to reconstruct allochthonous inputs and in-lake processes for Long Pond, Georgia, USA from the mid Holocene to present and link them to primary producer community changes. Long Pond is a mesotrophic lake located in a highly altered watershed from agricultural and municipal land use and housing developments. A 5 m sediment core was collected from Long Pond, and organic matter, nutrients (C, N, P), metals (Al, Fe, Cu), and photosynthetic pigments were measured. Long Pond existed in three limnological states spanning the past ~6000 years. Prior to modern lacustrine conditions, Long Pond was a wetland/peat system that experienced the highest primary producer abundance recorded in the core. The modern lacustrine state began in the late Holocene and was characterized by increased connectivity with the surrounding watershed and low productivity. Human impacts began around 1900 AD and included high levels of phosphorus and metal deposition but moderate levels of primary producer abundance. As a result, in-lake dynamics are believed to be regulating the trophic status of Long Pond. Low concentrations of available phosphorus in the water column combined with high concentrations of sedimentary phosphorus may imply the binding of phosphorus to the sediments by certain materials such as aluminum and iron. Long Pond serves as an example of the complex in-lake processes that can occur from allochthonous inputs and autochthonous responses in lake systems thus complicating management decisions.     

Equity vs. Efficiency: Public Capital Investment in Ohio, 1988–1992

Recent research on the role of public capital in the economy focuses primarily on assessing its economic, and sometimes spatial economic, impacts. Access to more detailed and disaggregate data than typically used in these analyses allows us to take a fresh perspective on the often conflicting goals of interregional equity and aggregate efficiency. Using the state of Ohio as a case study, and classic definitions of equity and efficiency, we assess the correspondence between distributions of infrastructure investment and the social/economic distress they are intended to alleviate. Traditional map and statistical analysis combined with a graphical device we call the variegated distribution plot reveals that, in both rates and levels, investment is highest in areas of greatest distress. Both patterns are consistent with equity-driven investment distributions.     

哈达门沟金矿床地质特征及其形成时代研究

哈达门沟金矿床位于华北地台北缘西段,产于太古代乌拉山岩群变质碉系中,矿床以发育一系列含金钾长石－石英脉为特征,这些钾长石－石英脉沿近东西向的韧、脆性叠加断裂成 出。钾长石化是最发的近矿围为。采用离子探针（ＳＨＲＩＭＰ）对矿体边部的钾长石化蚀变岩锆石Ｕ－Ｐｂ定年结果表明：矿化钾长石化蚀变岩的年龄为１３２±２Ｍａ。由于钾长石化夺本身被金矿化,因此金矿化年龄小于或接近于１３２±２Ｍａ,为燕山晚期成矿。     

A novel index of susceptibility of rivers and their catchments to acidification in regions subject to a maritime influence

A simple, unifying approach to classifying quantitatively the susceptibility of catchment soils and surface waters to acidification is suggested. In areas subject to a strong maritime influence, such as the UK and substantial parts of NW Europe, wherever soil mineral weathering rates are low and soils are unfertilised, atmospherically derived base cations of maritime origins have a greater effect than those derived from biogeochemical weathering on the exchangeable soil base cations. This is directly reflected in the relative base cation concentrations of the associated drainage waters, which become increasingly Na-dominated. Using 10 sub-catchments of the River Dee in north-eastern Scotland, it is shown here that the extent of Na dominance, the ratio of Na⁺ to ΣNa⁺+Ca²⁺+Mg²⁺, at any point in a river provides a quantitative index of the upstream weathering rate and thus of the susceptibility of the river concerned to acidification under diverse flow conditions. Data from a further 58 sub-catchments from the same river system, and from 4 other catchments from around Scotland, were used to validate this theory.     

Changes in beach water table elevation during neap and spring tides on a sandy estuarine beach, Delaware Bay, New Jersey

A field investigation of temporal and spatial changes in wind and wave characteristics, runup and beach water table elevation was conducted on the foreshore of an estuarine beach in Delaware Bay during neap (April 9, 1995) and spring (April 16, 1995) tides under low wave-energy conditions. The beach has a relatively steep, sandy foreshore and semi-diurnal tides with a mean range of 1.6 m and a mean spring range of 1.9 m. Data from a pressure transducer placed on the low tide terrace reveal a rate of rise and fall of the water level on April 16 of 0.09 mm s⁻¹ resulting in a steeper tidal curve than the neap tide on April 9. Data from three pressure transducers placed in wells in the intertidal foreshore reveal that the landward slope of the water table during the rising neap tide was lower than the slope during spring tide, and there was a slower rate of fall of the beach water table relative to the fall of the tide. Wave heights were lower on April 9 (significant height from 17.1 min records <0.16 m). The water table elevation was 0.08 m higher than the water in the bay at the time of high water, when maximum runup elevation was 0.29 m above high water and maximum runup width was 2.0 m. The elevation of the water table was 0.13 m higher than the maximum elevation of water level in the bay 74 min after high water, when wave height was 0.12 m and wave period was 2.7 s. The use of mean bay water level at high tide will underpredict the elevation of the water table in the beach, and demarcation of biological sampling stations across the intertidal profile based on mean tide conditions will not accurately reflect the water content of the sandy beach matrix.     

Flood tide circulation near beaufort inlet, North Carolina: Implications for larval recruitment

Drifter tracks and shipboard CTD observations have revealed a number of distinct features of the flood tide circulation carrying water through Beaufort Inlet, North Carolina. One of the most noteworthy of these features is a nearshore jet in the flow carrying water to the inlet on a flood tide. Characterized by a shoreward increase in longshore flow, the jet produces a narrow coastal zone over which water is carried into the inlet. The jet appears to be principally a tidal phenomenon, as it is closely reproduced by a tidally-driven barotropic numerical model. The model results also indicate the jet may be a near-inlet feature. Model simulations of spring tide conditions show the jet confined to within 4 km of the inlet mouth. Another observed phenomenon, which is reproduced by the tidal model, is a distinct splitting of the flow entering the inlet, in which water passing through a particular inlet segment tends to move up-estuary along a well-defined path. An observed flow feature not reproduced by the tidal model is an eastward skew of the region over which water is drawn into the inlet on a flood tide. This asymmetry is unrelated to the local wind. Modeling results from a previous study suggest it may be due to convergent flow at the edge of the low salinity plume issuing from the inlet. Taken together, the results of this and other recent studies in the Beaufort Inlet region reveal the importance of nearshore currents on the eastern side of the inlet in delivering oceanic-spawned larvae to the estuarine system connected to the inlet.     

Offshore aeolian sediment transport across a human‐modified foredune

Concepts derived from previous studies of offshore winds on natural dunes are evaluated on a dune maintained for shore protection during three offshore wind events. The potential for offshore winds to form a lee‐side eddy on the backshore or transfer sediment from the dune and berm crest to the water are evaluated, as are differences in wind speed and sediment transport on the dune crest, berm crest and a pedestrian access gap. The dune is 18–20 m wide near the base and has a crest 4.5 m above backshore elevation. Two sand‐trapping fences facilitate accretion. Data were obtained from wind vanes on the crest and lee of the dune and anemometers and sand traps placed across the dune, on the beach berm crest and in the access gap. Mean wind direction above the dune crest varied from 11 to 3 deg from shore normal. No persistent recirculation eddy occurred on the 12 deg seaward slope. Wind speed on the berm crest was 85–89% of speed at the dune crest, but rates of sediment transport were 2.27 times greater during the strongest winds, indicating that a wide beach overcomes the transport limitation of a dune barrier. Limited transport on the seaward dune ramp indicates that losses to the water are mostly from the backshore, not the dune. The seaward slope gains sand from the landward slope and dune crest. Sand fences causing accretion on the dune ramp during onshore winds lower the seaward slope and reduce the likelihood of detached flows during offshore winds. Transport rates are higher in access gaps than on the dune crest despite lower wind speeds because of flatter slopes and absence of vegetation. Transport rates across dunes and through gaps can be reduced using vegetation and raised walkover structures. Copyright © 2017 John Wiley & Sons, Ltd.     

Quantitative elemental mapping of granulite-facies monazite: Textural insights and implications for petrochronology

Texturally complex monazite grains contained in two granulite-facies pelitic migmatites from southern Baffin Island, Arctic Canada, were mapped by laser ablation-inductively coupled plasma-mass spectrometry (using spot sizes ≤5 µm) to quantitatively determine the spatial variation in trace element chemistry (with up to 1,883 analyses per grain). The maps highlight the chemical complexity of monazite grains that have experienced multiple episodes of growth, resorption and chemical modification by dissolution–precipitation during high-grade metamorphism. Following detailed chemical characterization of monazite compositional zones, a related U–Pb data set is re-interpreted, allowing petrologically significant ages to be extracted from a continuum of concordant data. Synthesis of these data with pseudosection modelling of prograde and peak conditions allows for the temporal evolution of monazite trace element chemistry to be placed in the context of the evolving P–T conditions and major phase assemblage. This approach enables a critical evaluation of three commonly used petrochronological indicators: linking Y to garnet abundance, the Eu anomaly to feldspar content and Th/U to anatectic processes. Europium anomalies and Th/U behave in a relatively systematic fashion, suggesting that they are reliable petrochronological witnesses. However, Y systematics are variable, both within domains interpreted to have grown in a single event, between grains interpreted to be part of the same age population, and between samples that experienced similar metamorphic conditions and mineral assemblages. These observations caution against generalized petrological interpretations on the basis of Y content, as it suggests Y concentrations in monazite are controlled by domainal equilibria. The results reveal a c. 45 Myr interval between prograde metamorphism and retrograde melt crystallization in the study area, emphasizing the long-lived nature of heat flow in high-grade metamorphic terranes. Such long timescales of metamorphism would be assisted by the growth, retention and dominance of high-Th suprasolidus monazite, as observed in this study, contributing to the radiogenic heating budget of mid- to lower-crustal environments. Careful characterization of monazite grains suggests that continuum-style U–Pb data sets can be decoded to provide insights into the duration of metamorphic processes.