Conference on territorial claims in the South China Sea, 4–6 December 1990

Reports

Island territories and societies     

A lagrangian random-walk model for simulating water vapor,CO2 and sensible heat flux densities and scalar profiles over and within a soybean canopy

An integrated canopy micrometeorological model is described for calculating CO₂, water vapor and sensible heat exchange rates and scalar concentration profiles over and within a crop canopy. The integrated model employs a Lagrangian random walk algorithm to calculate turbulent diffusion. The integrated model extends previous Lagrangian modelling efforts by employing biochemical, physiological and micrometeorological principles to evaluate vegetative sources and sinks. Model simulations of water vapor, CO₂ and sensible heat flux densities are tested against measurements made over a soybean canopy, while calculations of scalar profiles are tested against measurements made above and within the canopy. The model simulates energy and mass fluxes and scalar profiles above the canopy successfully. On the other hand, model calculations of scalar profiles inside the canopy do not match measurements.The tested Lagrangian model is also used to evaluate simpler modelling schemes, as needed for regional and global applications. Simple, half-order closure modelling schemes (which assume a constant scalar profile in the canopy) do not yield large errors in the computation of latent heat (LE) and CO₂ (F _c ) flux densities. Small errors occur because the source-sink formulation of LE andF _c are relatively insensitive to changes in scalar concentrations and the scalar gradients are small. On the other hand, complicated modelling frames may be needed to calculate sensible heat flux densities; the source-sink formulation of sensible heat is closely coupled to the within-canopy air temperature profile.     

Interactions among some dominant estuarine nekton species

Interactions between pairs of numerically dominant species collected at inlet and creek shorezone and channel habitats within a high salinity estuary in northeastern South Carolina were examined using two-way contingency tables and binomial tests. Of the significant species interactions, over 71% were positive and these primarily occurred within shorezone habitats. The strongest positive interactions were between young-of-the-year spot (Leiostomus xanthurus) and blue crab (Callinectes sapidus) juveniles in both shorezone habitats, and between striped killifish (Fundulus majalis), white mullet (Mugil curema), and striped anchovies (Anchoa hepsetus) in the inlet shorezone habitat. One of the most positive species associations in channel habitats was between the bay anchovy (Anchoa mitchilli) and the Atlantic brief squid (Lolliguncula brevis). These positive relationships between species may be explained by one species enhancing the habitat for another, both species responding to similar environmental conditions, cooperative social interactions such as mixed schooling, or the attraction of predators to prey. Negative interactions were found between schools of Atlantic silversides (Menidia menidia) and striped killifish in the inlet shorezone and between schools of Atlantic silversides and bay anchovies in the creek shorezone. Schools of Atlantic silversides may either displace or compete with other common shorezone species. Positive and negative interactions suggest that relationships between some species pairs did not occur randomly within certain habitats and may have contributed to the organization of the estuarine nekton community. Differences in the strengths and direction of interactions of certain species pairs among habitats and seasons were probably related to the differences in the physical characteristics of those habitats and/or changes in the relative abundance of dominant species and life stages over time.     

Turbulence structure in a deciduous forest

Three-dimensional wind velocity components were measured at two levels above and at six levels within a fully-leafed deciduous forest. Greatest shear occurs in the upper 20% of the canopy, where over 70% of the foliage is concentrated. The turbulence structure inside the canopy is characterized as non-Gaussian, intermittant and highly turbulent. This feature is supported by large turbulence intensities, skewness and kurtosis values and by the large infrequent sweeps and ejections that dominate tangential momentum transfer. Considerable day/night differences were observed in the vertical profiles of the mean streamwise wind velocity and turbulence intensities since the stability of the nocturnal boundary layer dampens turbulence above and within the canopy.     

The reaction of montmorillonite to mixed-layer clay: the effect of interlayer alkali and alkaline earth cations

The Wyoming bentonite was saturated with alkali and alkaline earth cations and allowed to react hydrothermally for one month at 300°C, and one week and one month at 400°C. Generally, the rate of formation of collapsed layers for the alkali clays was inversely related to interlayer hydration energy. This pattern of reaction is expected if layer dehydration results from an attraction between negatively charged 2:1 layers and the positive interlayer cation. In this mechanism, the greater the hydration energy of the interlayer region, the greater the charge that must develop on the 2:1 layers to cause dehydration, and, therefore, the slower the reaction rate. Reaction rate for the alkaline earth clays was directly related to interlayer hydration energy. Clays saturated with cations of hydration energy equal to or greater than Na⁺ did not react at 300°C, and ceased to react at 50% expandable layers at 400°C. Those saturated with cations of lower hydration energy continued to form mica-like layers with increasing run time at both 300° and 400°C. Clays saturated with monovalent cations reacted by a process of gradual transformation of smectite layers into collapsed layers, whereas those with divalent cations reacted directly from the smectite structure to form a rectorite-like phase.     

Isotopic and biochemical composition of particulate organic matter in a shallow water estuary (Great Ouse, North Sea, England)

The biogeochemistry of particulate organic matter was studied in the Great Ouse estuary draining to the North Sea embayement known as the Wash from March 1990 to January 1991. Eleven locations were sampled monthly on a 50 km transect across the shallow estuary from the tidal weir to the middle of the Wash. Particulate organic carbon (POC) and total carbohydrate, protein and lipid analyses were combined with the determination of stable carbon isotopes. δ¹³C often increased from −30‰ in the river to −22‰ in the tidal freshwater reach. The mixing zone between fresh and marine tidal waters displayed only a slight increase in δ¹³C to −19‰. The change in δ¹³C values in the freshwater tidal reach demonstrated that mixing of riverborne and marine suspended POC was not the only process affecting the carbon stable isotope composition. Complementary sources, interfering considerably with the two end-member sources, may be identified as autocthonous primary production and resuspension of sediment that may be transported upstream. The respective importance of these sources is subject to seasonal variation. From March to August, high concentrations in carbohydrate and protein through the whole estuary indicate that despite turbidity significant primary production occurred. The proportional importance of the uncharacterized fraction of POC, which is considered as complex organic matter, was high from September to January and low from March to August. During most of the year, the biochemical compositions of particulate organic matter in the turbidity maximum and the rest of the estuary were similar. This contradicted the principle that owing to the long residence times of particles degradation processes largely dominate the production processes within the turbidity maximum. The occurence of significant in situ production in such shallow water estuaries may partially compensate for the degradation of suspended particulate organics, resulting in a complex relationship between the biogeochemical cycling and the fate of nutrients.     

Nutrient flux in the Rhode River: Tidal exchange of nutrients by brackish marshes

Tidal exchanges of nitrogen, phosphorus, and organic carbon by a high and a low elevation marsh in the Rhode River estuary were measured throughout the year. Both marshes tended to import particulate matter and export dissolved matter, although they differed in the fluxes of certain nutrients. Compared with tidal exchanges, bulk precipitation was a major source of ammonia and nitrate and a minor source of other nutrients. There was a net retention of nutrients by the portion of the Rhode River that included both marshes and a mudflat. However, the marshes accounted for only 10% of the phosphorus retention and 1% of the nitrogen retention while they released organic carbon amounting to 20% of the retention. This suggests that the mudflat acted as a sink for nutrients. The primary role of the marshes seems to be transformation of particulate to dissolved nutrients rather than nutrient retention or release.     

Osteichthyans from the Fairpoint Member of the Fox Hills Formation (Maastrichtian), Meade County, South Dakota, USA

The Fairpoint Member of the Fox Hills Formation (upper Maastrichtian) in Meade County, South Dakota, USA, contains an osteichthyan assemblage indicative of transitional to marine shoreface deposits. The fauna consists of: Lepisosteus sp., Paralbula casei, Cylindracanthus cf. C. ornatus, Enchodus gladiolus, Hadrodus sp., and indeterminate osteichthyans with probable affinities to the Siluriformes and Beryciformes. The Fairpoint fauna is of limited species diversity and in this character mirrors many other Upper Cretaceous North American osteichthyan assemblages. Comparison to Upper Cretaceous chondrichthyan diversity and consideration of the structure of Cretaceous marine food webs suggest that osteichthyans are strongly under-represented in the Upper Cretaceous of North America. The small size and poor preservation potential of many Upper Cretaceous North American osteichthyans probably account for much of this observed paucity. Fairpoint osteichthyans are members of families that survive the Cretaceous–Paleocene boundary extinction event. Some of these genera and families are still extant and occur in a wide array of modern fresh, brackish, and shallow marine environments.     

A regional soil and sediment geochemical study in northern California

Regional-scale variations in soil geochemistry were investigated in a 20,000-km² study area in northern California that includes the western slope of the Sierra Nevada, the southern Sacramento Valley and the northern Coast Ranges. Over 1300 archival soil samples collected from the late 1970s to 1980 in El Dorado, Placer, Sutter, Sacramento, Yolo and Solano counties were analyzed for 42 elements by inductively coupled plasma-atomic emission spectrometry and inductively coupled plasma-mass spectrometry following a near-total dissolution. These data were supplemented by analysis of more than 500 stream-sediment samples from higher elevations in the Sierra Nevada from the same study site. The relatively high-density data (1 sample per 15 km² for much of the study area) allows the delineation of regional geochemical patterns and the identification of processes that produced these patterns. The geochemical results segregate broadly into distinct element groupings whose distribution reflects the interplay of geologic, hydrologic, geomorphic and anthropogenic factors. One such group includes elements associated with mafic and ultramafic rocks including Cr, Ni, V, Co, Cu and Mg. Using Cr as an example, elevated concentrations occur in soils overlying ultramafic rocks in the foothills of the Sierra Nevada (median Cr = 160 mg/kg) as well as in the northern Coast Ranges. Low concentrations of these elements occur in soils located further upslope in the Sierra Nevada overlying Tertiary volcanic, metasedimentary and plutonic rocks (granodiorite and diorite). Eastern Sacramento Valley soil samples, defined as those located east of the Sacramento River, are lower in Cr (median Cr = 84 mg/kg), and are systematically lower in this suite compared to soils from the west side of the Sacramento Valley (median Cr = 130 mg/kg). A second group of elements showing a coherent pattern, including Ca, K, Sr and REE, is derived from relatively silicic rocks types. This group occurs at elevated concentrations in soils overlying volcanic and plutonic rocks at higher elevations in the Sierras (e.g. median La = 28 mg/kg) and the east side of the Sacramento Valley (median 20 mg/kg) compared to soils overlying ultramafic rocks in the Sierra Nevada foothills (median 15 mg/kg) and the western Sacramento Valley (median 14 mg/kg). The segregation of soil geochemistry into distinctive groupings across the Sacramento River arises from the former presence of a natural levee (now replaced by an artificial one) along the banks of the river. This levee has been a barrier to sediment transport. Sediment transport to the Valley by glacial outwash from higher elevations in the Sierra Nevada and, more recently, debris from placer Au mining has dominated sediment transport to the eastern Valley. High content of mafic elements (and low content of silicic elements) in surface soil in the west side of the valley is due to a combination of lack of silicic source rocks, transport of ultramafic rock material from the Coast Ranges, and input of sediment from the late Mesozoic Great Valley Group, which is itself enriched in mafic elements. A third group of elements (Zn, Cd, As and Cu) reflect the impact of mining activity. Soil with elevated content of these elements occurs along the Sacramento River in both levee and adjacent flood basin settings. It is interpreted that transport of sediment down the Sacramento River from massive sulfide mines in the Klamath Mountains to the north has caused this pattern. The Pb, and to some extent Zn, distribution patterns are strongly impacted by anthropogenic inputs. Elevated Pb content is localized in major cites and along major highways due to inputs from leaded gasoline. Zinc has a similar distribution pattern but the source is tire wear.