Coupling of the Perturbed C–N–P Cycles in Industrial Time

Coupling of the C–N–P biogeochemical cycles is effected by the dependence of the land and aquatic primary producers on the availability of N and P. In general, the Redfield ratios C:P and N:P in the reservoirs supplying nutrients for primary production on land, in the oceanic coastal zone, and in the surface ocean differ from these ratios in the land phytomass and aquatic plankton. When N:P in the source is higher than in primary producers, this results in a potential accumulation of some excess nitrogen in soil water and coastal water, and increased denitrification flux to the atmosphere. The oceanic coastal zone plays an important role in the coupled C–N–P cycles and their dynamics because of its intermediate position between the land and oceanic reservoirs. These coupled cycles were analyzed for the last 300 years of exposure to four human-generated forcings (fossil fuel emissions, land use change, chemical fertilization of land, and sewage discharge to the coastal zone) and global temperature rise. In the period from 1700 to 2000, there has been a net loss of C, N, and P primarily from the land phytomass and soil humus, despite the rise in atmospheric CO₂, increased recycling of nutrients from humus, chemical fertilization, and re-growth of forests on previously disturbed land. The main mechanisms responsible for the net loss were increased riverine transport to the coastal zone of dissolved and particulate materials and, for N, increased denitrification on land. The oceanic coastal zone gained N and P, resulting in their accumulation in the organic pool of living biomass and dissolved and reactive particulates, as well as in their accumulation in coastal sediments from land-derived and in situ produced organic matter. Pronounced shifts in the rates and directions of change in some of the major land reservoirs occurred near the mid-1900s. Denitrification removes N from the pool available for primary production. It is the strongest on land, accounting for 73–83% of N removal from land by the combined mechanisms of denitrification and riverine export.     

Stable isotope evidence for multiple fluid regimes during carbonate cementation of the Upper Tertiary Hazeva Formation, Dead Sea Graben, southern Israel

Stable carbon- and oxygen-isotope compositions of calcite and dolomite cements have been used to understand porewater evolution in the Upper Tertiary Hazeva Formation within the Dead Sea Graben, southern Israel. Sandstone samples were obtained from four boreholes in three tectonic blocks of the graben over depths of 253–6448 m, a variation that largely reflects differential subsidence of individual fault-bounded blocks. Early carbonate cements dominate diagenesis. Calcite occurs at <1600 m, but was replaced by dolomite at greater depths. Dolomite at 1600–2700 m is Fe-poor (<0.8 mol% FeCO₃), and at 4700–6200 m, Fe-rich (0.5–7.2 mol% FeCO₃). Magnesite, anhydrite and halite are the final diagenetic phases. Calcite has positively correlated δ¹⁸O (+21‰ to +25‰) and δ¹³C (−6‰ to −2‰) values that generally decrease with depth. Dolomite has a wider variation in δ¹⁸O (+18‰ to +30‰) and δ¹³C (−8‰ to −1‰) values, which also generally are lower with increasing depth. However, the δ¹³C and δ¹⁸O values of dolomite from the uppermost 400 m of the Hazeva Formation in the Sedom Deep-1 borehole are anomalous in spanning the entire range of stable carbon and oxygen isotopic compositions over this relatively small interval.The decreasing dolomite δ¹³C values likely indicate an increased contribution of carbon from organic sources with increasing depth. Except for the uppermost 400 m, Hazeva Formation dolomite in the Sedom Deep-1 borehole has stable carbon-isotope compositions that imply initial dolomitization at much shallower levels, prior to the preferential subsidence of this tectonic block. The oxygen isotopic compositions of the calcite cement are best explained by equilibration at present burial temperatures (≤55 °C) with porewater of meteoric origin. Its δ¹⁸O values increased from −5‰ at the shallowest depths to 0‰ at 1600 m. The dolomite oxygen isotopic compositions also reflect equilibration at present burial temperatures with porewaters ranging from 0‰ at 1600 m to +7‰ at 3600 m (100 °C). In the deepest fault block (Sedom Deep-1 borehole), however, increasingly Fe-rich dolomite has (re)equilibrated with porewater whose δ¹⁸O values decreased from +9‰ at 4750 m (120 °C) to +1‰ to +2‰ by 6200 m (150 °C).Much of the dolomite likely formed at relatively shallow depths from saline brines derived from precursors to the Dead Sea. These infiltrated the Hazeva Formation, mixing with and largely displacing meteoric water, and dolomitizing calcite. Rock–water ratios tended to be high during these processes. However, the upper 400 m of the Hazeva Formation in the deepest fault block were likely deposited during its rapid tectonic subsidence, and largely escaped the initial style of dolomitization pervasive elsewhere in the study area. These sediments were also capped by evaporites. This relatively thin interval likely became a preferential conduit for brines that escaped underlying and overlying strata, including the Fe-rich, lower ¹⁸O fluids (evolved seawater?) present in the deepest part of the graben. These rocks present the most promising target for the passage and accumulation of hydrocarbons in the study area.     

The origins and use of theory in urban geography: Household mobility and filtering theory

The paper looks in detail at one particular interpenetration of academic theory and state policy making — filtering theory in urban geography. While household mobility and turnover are important processes in the housing system, they are extended in filtering theory to form a universal explanatory model embracing the entire housing system. In this model idealised concepts of the operation of the housing market—valid only under conditions that do not occur in practice — are used to legitimate a laissez-faire natural-market view of how the housing system should operate. Translated into government policy, used to justify the dominant private interests in housing, and supported by academic explanation, the theory then comes to legitimate the persistence of gross inequalities in housing provision and to maintain the allocation of resources away from those most in need. This paper reviews this use of filtering theory both in Britain and the United States, and makes a variety of empirical and theoretical criticism of its validity.     

The affinity of trichomes of blue-green algae for calcium lons

Cells of Plectonema boryanum and Anabaena flos-aquae obtained from large scale (to 15L) cultures were used to examine the cation exchange properties of killed algal cells. Since Microcoleus lyngbyaceus, one of the most abundant species in our collections from marshes, could not be obtained in large-scale liquid cultures, it was collected in algal mats from tide-marsh pannes and separated from other algae, etc. by a combination of screening, air elutriation and density-gradient centrifugation. Characterization of the exchange properties of such preparations was pursued using ⁴⁵Ca for exchange measurements and Cd-EDTA or Cd-EGTA as indicators with the Cd-specific ion electrode for electrometric titration for total Ca⁺⁺ and Mg⁺⁺, or Ca⁺⁺, respectively. Algal cell preparations exhibited a capacity to exchange Ca⁺⁺ readily with ambient aqueous solutions. K⁺ and Na⁺ could displace a substantial proportion of the Ca⁺⁺ at concentrations about 100-fold greater than that of the ambient Ca⁺⁺. Mg⁺⁺ was about 10 times as effective as the monovalent cations in displacing Ca⁺⁺. Cell walls isolated from rhizomes of Spartina alterniflora exhibited only about 1/10 the affinity for Ca⁺⁺ as that found for the blue-green algal preparations. The intrinsic association constant and the total capacity for cation exchange indicated that in solutions of 2×10^?4M about 50% of the exchange sites are occupied. The ligand for Ca⁺⁺ could be extracted in part by dilute acid, but not by Triton X-100 or by EDTA, even in the presence of Triton X-100. The extracted material appeared to be a polysaccharide. Both the sheaths of M. lyngbyaceus by themselves and cells from which they were separated exhibited Ca-exchange properties.     

The photochemistry of synoptic-scale ozone synthesis: Implications for the global tropospheric ozone budget

The oxidation of nonmethane hydrocarbons represents a source of tropospheric ozone that is primarily confined to the boundary layers of several highly industrialized regions. (Each region has an area greater than one million km²). Using a photochemical model, the global tropospheric ozone budget is reexamined by including the in-situ production from these localized regimes. The results from these calculations suggest that the net source due to this photochemistry, which takes place on the synoptic scale, is approximately as large as the amount calculated for global scale photochemical processes which consider only the oxidation of methane and carbon monoxide. Such a finding may have a considerable impact on our understanding of the tropospheric ozone budget. The model results for ozone show reasonable agreement with the climatological summer distribution of ozone and the oxides of nitrogen at the surface and with the vertical distribution of ozone and nonmethane hydrocarbons obtained during a 1980 field program.