Sand Site Research Articles

Estimating areal production of intertidal microphytobenthos based on spatio-temporal community dynamics and laboratory measurements

In situ Microphytobenthic community dynamics were combined with laboratory measurement of predominant species by fluorescence methods to estimate the areal primary production. Field investigation of community dynamics of microphytobenthos (MPB) was conducted from August 2006 to August 2007 in intertidal flats of the Nakdong River estuary, Korea. MPB Biomass varied between 0.47 and 16.58 μg cm−3 in the surface 1 cm sediment, with two dominant diatom species, Amphora coffeaeformis and Navicula sp., occupying average 77.2 ± 14.9% of total number of MPB cells. The biomass was higher in the slightly muddy sand sites than that in the sand site, and showed different pattern of seasonal variation. The profile of vertical distribution of biomass was an exponential decrease trend with depth in sediments. The biomass proportions in the uppermost 3 mm were 57.6% and 37.8% with and without the presence of biofilm, respectively. The two dominant species were cultured in laboratory, and their photosynthetic parameters, rETRmax (relative maximum electron transport rate), α (light utilization coefficient) and Ek (light saturation parameter) were derived from rETR (relative ETR)-irradiance curves by Imaging- PAM (pulse amplitude modulated) fluorometry. The rETR-irradiance curves showed no significant difference of photosynthetic activities between the two species. The areal potential production ranged from 0.74 to 2.22 g C m−2 d−1.

Temporal variation in the vertical distribution of microphytobenthos in intertidal flats of the Nakdong River estuary, Korea

The vertical distribution of microphytobenthos (MPB) was investigated in intertidal flats of the Nakdong River estuary over different temporal periods. The MPB biomass were measured as chlorophyll a concentration in the sediment, and monitored at two different depth scales. From August 2006 to August 2007, monthly sampling was carried out at four sites to a depth of 10 cm. The vertical distribution exhibited an exponential decline with depth and the slope was closely related to sediment composition and MPB biomass in the surface sediment. The two slightly muddy sand (5–25% mud, <63 μm) sites presented similar trends of seasonal variation to a sediment depth of 10 cm, and no statistical difference was observed in their initial values and the slope of the exponential curves applied to each data set. The site with higher mud content also had higher surface biomass, and the fitted exponential curve had a larger slope than sites with more sand content. The seasonal variations of phaeo-pigments compared to chlorophyll a revealed higher grazing stress on the MPB in summer at the three slightly muddy sand sites, and low grazing stress all year around at the sand (<5% mud) site. In January, April and October 2007, and January 2008, diurnal sampling was conducted at hourly intervals at one slightly muddy sand site. The investigation in January 2007 which was conducted at 1 cm intervals to a depth of 10 cm sediment showed the migration mainly existed in the upper 1 cm. The other diurnal sampling was undertaken to a 1 cm depth at 0.5 mm intervals. An evident migratory rhythm was present, with migration up to the surface during daytime emersion and down into deeper sediment during night and high tide submersion. Migrating cells could reach sediments as deep as 6 or even 10 mm. When the visible thick biofilms formed, the migratory rhythm changed by keeping higher biomass at the surface even at night and during high tide submersion. Generally, the MPB surface biomass was an important factor in structuring the MPB vertical distribution. The vertical distribution to depths of 10 cm was closely related to the sediment composition over the long term, while the MPB migration influenced the vertical distribution over the short term in the top 1 cm of the sediment.

Open to closed system transition traced through the TDIC isotopic signature at the aquifer recharge stage, implications for groundwater 14C dating

14C dating models are limited when considering recent groundwater for which the carbon isotopic signature of the total dissolved inorganic carbon (TDIC) is mainly acquired in the unsaturated zone. Reducing the uncertainties of dating thus implies a better identification of the processes controlling the carbon isotopic composition of the TDIC during groundwater recharge. Geochemical interactions between gas, water and carbonates in the unsaturated zone were investigated for two aquifers (the carbonate-free Fontainebleau sands and carbonate-bearing Astian sands, France) in order to identify the respective roles of CO 2 and carbonates on the carbon isotopic signatures of the TDIC; this analysis is usually approached using open or closed system terms. Under fully open system conditions, the seasonality of the 13C values in the soil CO 2 can lead to important uncertainties regarding the so-called “initial 14C activity” used in 14C correction models. In a carbonate-bearing unsaturated zone such as in the Astian aquifer, we show that an approach based on fully open or closed system conditions is not appropriate. Although the chemical saturation between water and calcite occurs rapidly within the first metre of the unsaturated zone, the carbon isotopic contents (δ 13C) of the CO 2 and the TDIC evolve downward, impacted by the dissolution–precipitation of the carbonates. In this study, we propose a numerical approach to describe this evolution. The δ 13C and the A 14C (radiocarbon activity) of the TDIC at the base of the carbonate-bearing unsaturated zone depends on (i) the δ 13C and the A 14C of the TDIC in the soil determined by the soil CO 2, (ii) the water’s residence time in the unsaturated zone and (iii) the carbonate precipitation–dissolution fluxes. In this type of situation, the carbonate δ 13C–A 14C evolutions indicate the presence of secondary calcite and permit the calculation of its accretion flux, equal to ∼ 4.5 ± 0.5 × 10 - 9 mol g rock - 1 yr - 1 . More generally, for other sites under temperate climate and with similar properties to the Astian sands site, this approach allows for a reliable determination of the carbon isotopic composition at the base of the unsaturated zone as the indispensable “input function” data of the carbon cycle into the aquifer.

Dynamic compaction of saturated sands and silty sands: results

Numerical simulations of dynamic compaction of three loose saturated sands and silty sand sites are presented. The theory associated with the numerical model is presented in a companion paper. First, a case history of dynamic compaction in a clean sand site without pre-installed wick drains is considered. Second, a case history involving a sandy silt site with pre-installed wick drains is simulated. Third, a silty sand site without pre-installed wick drains is simulated. In all cases the numerical results for post-improvement cone resistance and standard penetration test (SPT) penetration resistance profiles agree fairly well with observed field data. The results show the effectiveness of pre-installed wick drains for dynamic compaction of saturated silty sands. The numerical simulation tool presented is a valuable tool for feasibility studies of dynamic compaction of saturated sands and silty sands.

How does shoreline development impact the recruitment patterns of coral reef fish juveniles (Moorea Island, French Polynesia)?

The study examined the effects of coastal embankment building on fish recruitment in three habitat types (beach-rock, white sand and muddy sand) in the near shore and fringing reef habitats of Moorea lagoon (French Polynesia). The results showed a positive relationship between the presence of embankments and the density and species richness of juvenile fish along the shoreline (whatever the habitat types). However, embankments deteriorated adjacent fringing reefs (decrease of live coral), which led to a decrease of fish density on beach-rock and white sand sites, and a decrease of fish species richness on muddy sand sites.

Influence of site and rate of low-volume aerial phosphite spray on lesion development ofPhytophthora�cinnamomiand phosphite persistence inLambertia�inermisvar.inermisandBanksia grandis

The influence of site on effectiveness of low-volume spray of phosphite for the control of Phytophthora cinnamomi was compared between sites differing in soil nutrient status. The sites ranged from infertile deep grey sands to a red loam in the Esperance Plains bioregion, and infertile gravelly sand of the Havel site-vegetation type P to a red loam of Havel site-vegetation typeQin the northern Jarrah Forest bioregion. Following low-volume spray of 0, 24 or 48 kg phosphite/ha, phosphite effectiveness was determined from assessment of rate of colonisation and inhibition of stem colonisation by P. cinnamomi, and stem phosphite concentration in challenge inoculation stems of Lambertia inermis var. inermis in Esperance Plains bioregion sites and Banksia grandis in Jarrah Forest bioregion sites. Phosphite effectiveness was mainly influenced by plant species rather than site. Phosphite spray significantly controlled P. cinnamomi colonisation in B. grandis, but not in L. inermis var. inermis. Site had no consistent influence on the effect of phosphite on P. cinnamomi despite large differences in soil nutrient status between sites. Differences between sites and site ranking changed with inoculation time and rate of phosphite spray, and duplicate sites differed significantly from each other. Site, rate of phosphite spray, time after spray and plant species significantly affected stem phosphite concentrations. In both Esperance Plains bioregion and Jarrah Forest bioregion sites, stem phosphite concentrations were greatest in fertile loam sites and least in infertile sand or gravelly sand sites. Stem phosphite concentrations increased with rate of phosphite spray with concentrations in stems receiving 48 kg phosphite/ha being 1.2 to 3-times-greater than that in stem sprayed with 24 kg phosphite/ha. Six months after low-volume spray, phosphite concentrations in L. inermis var. inermis stems had declined for all sites and spray rates to only 4–17% of original concentrations. Decline of phosphite concentrations in B. grandis stems was slower than that for L. inermis var. inermis stems. The results indicate that effectiveness of phosphite against P. cinnamomi infection in different communities will depend more on plant species composition than soil nutrient status. Differences in phosphite effectiveness between plant species may be related to differences in phosphite concentration thresholds yet to be quantified, above which tissue concentrations must be achieved before inhibition of P. cinnamomi colonisation occurs. In rapid colonisation/phosphite low-responsive species such as L. inermis var. inermis, the threshold may be greater than that required for a response in a rapid colonisation/phosphite high-response species such as B. grandis. These results demonstrate the need to determine thresholds for individual plant species and in different environments.

Archaeological Geology of the Mescalero Sands, Southeastern New Mexico

The Mescalero Sands accumulated in two episodes, first during the late Pleistocene (90,000 to 75,000 years B.P) and second during the early Holocene (9000 to 5000 years B.P) based on OSL dates. Archaeological sites of all ages occur on the surface of the older eolian sand Sites later than 3000 B.C. occur on the surface of the younger eolian sand, and sites older than 3000 B.C. are buried within the younger sand unit. Historic coppice and parabolic dunes partly cover all prehistoric sites. Paleoindian sites may be associated with late Pleistocene spring and cienega deposits and buried by the younger eolian sand. Sediments at sites within the younger eolian sand unit are bioturbated by cicada insects. Burned caliche at archaeological sites is dominated by dense pisolitic Caprock calcrete from the top of the Ogallala Formation. Cobble-size clasts of Caprock calcrete and other lithologies are prehistoric resources that occur in terrace and lag gravel colluvial deposits west of the escarpment. An archaeological geologic map of about 1,295 square kilometers of Eddy and Lea counties shows the distribution of areas where sites are visible at the surface as well as areas where sites are potentially buried in young deposits.

Shade Alone Reduces Adult Dragonfly (Odonata: Libellulidae) Abundance

We demonstrate that physical habitat conditions influence adult dragonfly (Odonata: Anisoptera) riparian site selection. In naturally treeless riparian areas of South Africa, invasive trees create shade and reduce native vegetation. We hypothesized that most breeding odonates select riparian areas (1) without shade, and (2) with high density and variety of understory perch structures. In two experiments at reservoir shorelines, we varied shade and perch structures. Dragonfly abundances (predominantly Trithemis species) were lower at sites with high (75%) or moderate (55%) shade cover than at sites with no shade, and lower at bare sand sites than sites containing stick perches. Perch density and variety (variety of heights and diameters) did not affect dragonfly abundance. These results indicate that shade alone directly reduces dragonfly habitat selection, isolating one aspect of habitat change that can alter insect behaviors.

Fish Assemblages in Shallow, Nearshore Habitats of the Bering Sea

AbstractThe Bering Sea provides over one‐half of U.S. fishery production, yet knowledge of the use of its shallow (&lt;5 m), nearshore (&lt;20 m from shore) waters by fish is limited. In June 2005, we sampled shallow, nearshore waters of the Bering Sea at three Aleutian islands with a beach seine to estimate the relative abundance and species distribution of fish. Three habitat types were sampled: Nonvegetated sand substrate, vegetated cobble substrate, and vegetated bedrock substrate. A total of 70 sites were seined on Akutan, Akun, and Unalaska islands. The total estimated catch was 83,910 fish representing 33 taxa. Five species comprised 98% of the total catch. Pacific sand lance Ammodytes hexapterus was the most abundant species; approximately 35,000 of these fish were captured, and they occurred in 60% of all seine hauls. The next most abundant fish were young‐of‐the‐year (age‐0) gadids (primarily walleye pollock Theragra chalcogramma), age‐0 pink salmon Oncorhynchus gorbuscha, age‐0 Pacific sandfish Trichodon trichodon, and snake prickleback Lumpenus sagitta. Fish were unequally distributed among habitats. The estimated mean catch per seine haul was 1,171 fish in sand sites, 1,647 fish in cobble sites, and 79 fish in bedrock sites. Most Pacific sand lances (98%) were captured in sand sites, whereas most gadids (97%), pink salmon (80%), Pacific sandfish (96%), and snake pricklebacks (99%) were caught in cobble sites. Sand and cobble nearshore habitats in the Bering Sea provide important habitat for many fish species in summer, especially forage fish.

Benthic community response to a passive fishing gear in a coastal lagoon (South Brazil)

The influence of a passive shrimp fishing gear on benthic communities was studied at Laguna Estuarine System (South Brazil), a shallow choked coastal lagoon. The gear is composed by a group of fyke nets (25 mm mesh size) set in contact to the bottom, fixed with stakes forming a cage-like structure (around 30 m2). Samplings were conducted in the two main fishery areas of the estuarine system, Mirim (sand bottoms) and Imarui (muddy bottoms) lagoon, in May 2005. In each area, 10 fyke net enclosures and 10 nearby sites without nets (control) were sampled. Microphytobenthos biomass (chlorophyll a and phaeopigments), number of taxa/species, density, Hill’s number N 1 and N 2, and estimated number of species (ES100) were used as community attributes. For the nematodes, values of the maturity index and abundance of Wieser’s feeding type were used as well. The effects of the small-scale passive shrimp fishing gear on the coastal lagoon bottoms were dependent on the benthic component analyzed and the type of sediment. Whereas macrofauna was not affected by the net enclosures, meiofauna and nematodes, particularly from the mud sites were. At the sand site, the fyke net enclosures caused a decrease in the microphytobenthos biomass and changed the relative abundances of non-selective deposit feeding and epigrowth-feeding nematodes. The results indicated that small-scale static nets, such as the studied fyke enclosures, produced low intensity levels of disturbance. However, the enclosed area by nets at Laguna had already reached around 25,000 m2. Given the large proportion of the coastal population involved and the area closed by nets, management policies should consider site-specific differences within the same estuarine system.

Life history of a dominant polychaete, Polygordius jouinae, in inner continental shelf sands of the Mid-Atlantic Bight, USA

The life history of the polychaete Polygordius jouinae Ramey, Fiege, and Leander 2006 was studied in the sandy sediments of the LEO-15 research area off the coast of Tuckerton, New Jersey (39°27.69′N, 74°15.81′W). Divers collected sediment cores biweekly, from February 2004 to November 2005 to examine the temporal patterns of abundance and size–frequency distributions of P. jouinae. These parameters were also examined (for the first time) for P. jouinae in samples taken in ambient sediments and in three reciprocal 3 to 5-day sediment transplant experiments that were part of a previous, unrelated study at coarse sand and muddy sand sites (∼3 km apart) at LEO-15 in the summers of 1994 and 1995. Analysis of these previous data along with the current data provided a larger set of values for P. jouinae, as well as further insight into the life history, habitat selection, and dispersal of P. jouinae (not considered in previous studies). Polygordius jouinae is gonochoristic and the population was mostly composed of sexually mature individuals in late May 2004 and 2005. The reproductive period usually occurs from May to August and individuals that spawn generally have a 1-year life span. Non-spawning individuals of P. jouinae could potentially live longer than 1 year and therefore the population may sometimes consist of individuals of two generations. Recruitment begins no later than July as recently settled individuals (≤9 mm body length), which were not present during the first week of June 1995, 2004, and 2005, first appeared in July in all 3 years. The smallest individual was 2.01 mm long and 0.07 mm wide and this provides the first estimate of size at initial recruitment. Although some worms in sediment trays likely settled as larvae, most worms were recently settled juveniles (length categories 6 and 9 mm) transported in from the surrounding sediments, presumably as a consequence of re-suspension or bed load transport. As expected, larger individuals were present later in September. Although it is unknown whether P. jouinae were transported actively or passively these data suggest that recently settled juveniles are capable of habitat selection (prefer sand over mud) and show that post-settlement transport and selection influence community structure.

Field measurement of lupin belowground nitrogen accumulation and recovery in the subsequent cereal-soil system in a semi-arid Mediterranean-type climate

In situ 15N-labelling was used to provide a quantitative assessment of the total contribution of lupin (Lupinus angustifolius) to below-ground (BG) N accumulation during a growing season under field conditions, and to directly trace the fate of the lupin BG N in the next season, including quantifying the N benefit from lupin to a following wheat (Triticum aestivum) crop. The experiments were conducted at two sites, both experiencing a semi-arid Mediterranean-type climate in the wheat-growing region of Western Australia but with differing soil types, a deep sand (Moora) and a sand-over-clay shallow duplex soil (East Beverley, EB). Lupin shoot and root dry matter and total plant N accumulation, proportional dependence on nitrogen fixation and grain yield were greater at the deep sand site than the duplex soil site, although there was a similar proportion of shoot N to estimated total BG N at both sites. The proportion of total plant BG N decreased from the vegetative stage (42–51%) to peak biomass (25–39%) and maturity (23–34%). From 56–67% of BG N on the deep sand and 74–86% on the duplex soil was not recovered in coarse roots (>2 mm) or as soluble N, but was present in the insoluble organic N fraction. There was evidence for cycling of lupin root-derived N into soil microbial biomass and soluble organic N during lupin growth (by the late vegetative stage), but no evidence for leaching of legume derived BG N during the lupin season. Estimates of fixed N input BG were at least four times greater if based on total lupin BG N rather than on N recovered in coarse roots (>2 mm). There were no apparent losses of lupin BG N during the summer fallow period subsequent to lupin harvest at either site. Also, immediately prior to sowing of wheat there were similar proportions of lupin BG N in the inorganic (20–25%) and microbial biomass (6–9%) pools at both sites, with the majority of BG N detected in the <2 mm fraction of the soil column. However, the proportion of residual lupin BG N estimated to benefit the aboveground wheat biomass was relatively low, 10% on the deep sand and only 3% on the shallow duplex. Some (14%) residual lupin BG N was leached as nitrate to 1 m on the deep sand compared to 8% of residual lupin BG N leached to the clay layer (0.3 m) on the shallow duplex. About 27% of the residual lupin BG N on the deep sand at Moora had apparently mineralised by the end of the succeeding wheat season (i.e. recovered either in the wheat shoots, as inorganic N in the soil profile or as leached nitrate) compared to only 12% at EB. There was an unaccounted for large loss of residual lupin BG N (50%) from the duplex soil at EB during the wheat season, postulated to be chiefly via denitrification. At both sites after the wheat season a substantial proportion (32–55%) of legume derived BG N was still present as residual insoluble organic N, considered to be an important contribution to structural and nutritional long-term sustainability of these soils.

In situ shear wave velocity from multichannel analysis of surface waves (MASW) tests at eight Norwegian research sites

The multichannel analysis of surface waves (MASW) technique, which is used to determine shear wave velocity (Vs) and hence small strain stiffness (Gmax), has recently generated considerable interest in the geophysics community. This is because of the ease of carrying out the test and analysis of the data. The objective of this work was to assess the repeatability, accuracy, and reliability of MASW surface wave measurements for use in engineering studies. Tests were carried out at eight well-characterized Norwegian clay, silt, and sand research sites where Vs had already been assessed using independent means. As well as being easy and quick to use, the MASW technique gave consistent and repeatable results, and the MASW Vs profiles for the clay sites were similar to those obtained from other techniques. Reasonable results were also obtained for the silt and sand sites, with the best result being obtained for the finer silt. This work also confirms that MASW Vs clay profiles are comparable to those obtained by correlation with cone penetration test (CPT) data. For these sites there also seems to be a good correlation between normalized small strain shear modulus and in situ void ratio or water content, and the data fit well with published correlations for clays.Key words: soft clays, silts, sands, small strain stiffness, shear wave velocity.

Significance of microhabitat heterogeneity in the spatial pattern and size-class structure of Anastatica hierochuntica L.

Abstract Anastatica hierochuntica L. (Brassicaceae) is a desert monocarpic annual species characterized by a topochory/ombrohydrochory type of seed dispersal. The hygrochastic nature of the dry skeletons (dead individuals) permits controlling seed dispersal by rain events. The amount of dispersed seeds is proportional to the intensity of rainfall. When light showers occur, seeds are released and remain in the site. Seeds dispersed in the vicinity of the mother or source plant (primary type of seed dispersal) resulted in clumped pattern and complicated interrelationships among size-classes of the population. Following heavy rainfall, most seeds are released and transported into small patches and shallow depressions which collect runoff water. The dead A. hierochuntica skeletons demonstrate site-dependent size-class structure, spatial pattern and spatial interrelationships in different microhabitats. Four microhabitat types have been sampled: runnels, patches and simple and compound depressions in two sites (gravel and sand). Ripley's K-function was used to analyze the spatial pattern in populations of A. hierochuntica skeletons in the study microhabitats. Clumped patterns were observed in nearly all of the study microhabitats. Populations of A. hierochuntica in the sand site were more productive than in the gravel site and usually had more individuals in the larger size-classes. In the compound-depression microhabitat, the degree of clumping decreased from the core zone to the intermediate zone then shifted into overdispersed pattern in the outer zone. At the within size-class level, the clumped pattern dominated in small size classes but shifted into random and overdispersed patterns in the larger size classes. Aggregation between small and large size-classes was not well-defined but large individuals were found closer to the smaller individuals than to those of their own class. In relation to the phytomass and the size-class structure, the outer zone of the simple depression and the outer and intermediate zones of the compound depression microhabitats were the most productive sites.

Reach‐scale geomorphology affects organic matter and consumer δ13C in a forested Piedmont stream

Summary1. We investigated the spatial (longitudinal position and reach geomorphology) and seasonal (spring and autumn) influences on the variation of δ13C among organic matter sources and consumers in a forested Piedmont river, South Carolina, U.S.A.2. Six sites were sampled along a continuum and varied in basin area from approximately 30 to 300 km2. Sites fell into two geomorphic categories (i) high‐gradient, rock bed (‘rock’) or (ii) low‐gradient, sand bed (‘sand’) sites.3. Variation in δ13C was more strongly related to reach geomorphology than longitudinal position. δ13C of biofilm and consumers was consistently enriched at rock sites. Leaf litter (i.e. coarse particulate organic matter, CPOM) δ13C did not vary with bed type. There was significant δ13C enrichment at rock sites for biofilm, seston, fine benthic organic matter (FBOM), and eight of nine consumer trophic guilds (e.g. grazing invertebrates, insectivorous fishes). δ13C of biofilm and four trophic guilds was also positively correlated with drainage area, but the magnitude of enrichment was less than between bed types.4. δ13C was generally enriched in spring, but this varied among organic matter types, consumers, and by bed type. CPOM and seston were enriched in spring, FBOM was enriched in autumn, and biofilm showed no trend. Five consumer guilds were enriched in spring, and only one fish guild, generalised carnivores, showed enrichment of muscle tissue in autumn.5. Consumer δ13C enrichment at rock sites suggests greater reliance on algal carbon than for consumers at sand sites, but we also found δ13C enrichment of biofilm at rock sites. Thus, differences in consumer δ13C between bed types could be related to (i) increased consumption of biofilm at rock compared with sand sites, or (ii) consumption of biofilm at rock sites that is enriched relative to biofilm at sand sites or (iii) both mechanisms.6. δ13C signatures in local food webs appear to respond to processes operating at multiple spatial scales. Overall downstream enrichment of biofilm and consumers was disrupted by strong local effects related to bed morphology. These results suggest that human alteration of channel habitat will have corresponding effects on stream food webs, as assessed by changes in δ13C.

Observations of seafloor ripples and a time‐dependent ripple geometry model

Recent seafloor acoustic scattering experiments and theoretical developments have shown that the presence of ripples on the seafloor can increase the amount of subcritical angle acoustic penetration into the seafloor. A ripple observation and acoustic scattering experiment (SAX04) was recently conducted near Fort Walton Beach, Florida. During this experiment a sidescan sonar on an REMUS AUV was used to observe ripple geometry from the nearshore (5‐m depth) to the shelf break (50‐m depth). The ripples were found to increase in wavelength from 20 cm in the nearshore to 1.2 m at the shelf break. The offshore ripples were a product of Hurricane Ivan, which had passed the site 2 weeks prior. Time series of ripple geometry, measured with a tripod‐mounted rotary sidescan sonar and a two‐axis rotary pencil beam sonar, from a coarse sand site at the Martha’s Vineyard Coastal Observatory, also revealed long‐wavelength (0.6 to 1.2 m) relict ripples after wave events. Ripple geometry models that assume the ripples are in equilibrium with hydrodynamic forcing underpredict the wavelength of the relict ripples at both sites; thus a new model that allows for a time delay between ripple adjustment and forcing was developed. [Work supported by ONR.]

Effect of leaf nitrogen concentration versus CND nutritional balance on shoot density and foliage colour of an established Kentucky bluegrass (Poa pratensis L.) turf

A 3-yr field study was conducted in a loam and a sand site to determine the effects of N, P, and K application rates on N status, shoot density and foliage colour of Kentucky bluegrass clippings and to derive critical N values. The experiment was arranged in a completely randomized block design with four replicates and three nutrients, N (0 or 50 to 300 kg ha-1 yr-1), P (0 or 21.8 to 87.3 kg P ha-1 yr-1), and K (0 or 41.7 to 250 kg K ha-1 yr-1), equally broadcast six times per growing season. We examined N concentration values, log-transformed N concentration values, and CND values for compositional nutrient simplexes comprising one (VN1), three (VN3), five (VN5), or 11 (VN11) macro- and micro-nutrients. Critical values for N expressions were obtained from linear relationships with targeted visual shoot density and foliage colour ratings that were closely related to each other (R2 = 0.92). The highest coefficients of determination (0.975 to 0.980) were obtained with VN5 and VN11. The VN5 values were consistent with literature data and across experimental sites, and were the most successful (99% success) in diagnosing N sufficiency in 328 qualified specimens from commercial sod farms. Compared with raw concentrations, the CND transformation reduced from 0.6 to 0.1 the degree of inter-correlation among nutrients in principal component analysis and was amenable to a χ2 distribution of CND indices. Using a critical imbalance index (CNDr2) of 5.6as χ2 value, and a critical CND IN2 index of 1.5 for a 5-nutrient simplex, we diagnosed as imbalanced 179 qualified specimens of which 110 specimens presented excessively high N level among the 328 qualified specimens in commercial stands. The proposed five-nutrient CND norms proved to be effective in diagnosing N status in Kentucky bluegrass clippings across experimental, literature, and survey data sets. Key words: Plant tissue nutrient diagnosis, DRIS, CND, Kentucky bluegrass nitrogen fertilization, turfgrass shoot density, turfgrass foliage colour

Aggregation and sinking behaviour of resuspended fluffy layer material

The influence of pelagic diatom addition ( Skeletonema costatum) on aggregation dynamics of resuspended fluffy layer material containing natural microorganism assemblages (bacteria and pennate diatoms) was studied during two roller table experiments. Sediment samples were taken at a fine sand site (16 m water depth) located in Mecklenburg Bight, south-western Baltic Sea. Fluff was experimentally resuspended from sediment cores and aggregation processes with and without S. costatum were studied in rotating tanks. Total particulate matter was incorporated into artificial aggregates in equal shares after both roller table experiments. However, biogenic parameters (particulate organic carbon, particulate organic nitrogen, and carbohydrate equivalents), as well as cell numbers of bacteria and pennate diatoms were found in higher percentages in S. costatum aggregates compared to aggregates without S. costatum. Transparent exopolymer particles were apparently irrelevant in the aggregation process during both experiments. Settling velocities of S. costatum aggregates exceeding 1000 μm in diameter showed a significantly higher mean settling velocity compared to aggregates without S. costatum of the same size. The pronounced effect of pelagic diatoms on aggregation processes of fluff in terms of particle attributes, size, and therewith sinking velocities could be demonstrated and may lead to further insight into near bed particle transport in coastal waters.

In Situ Assessment of Role of Surface Roughness on Interface Response

Improved design methods that allow for more accurate prediction of interface performance are needed as the number and types of interface strength dependent geotechnical systems being used in practice continues to increase. Laboratory research performed in the past two decades has provided significant insight into interface behavior, primarily for material interfaces involving sand. With the recent development of the multisleeve friction penetrometer attachment, direct in situ measurements of interface sleeve stress can be obtained using multiple sleeves, each with a different surface roughness, in a single sounding. This paper presents the findings of extensive field investigations conducted at a sand site with the multisleeve friction penetrometer attachment to evaluate the performance of the device as well as the potential to determine the relationship between surface roughness and interface strength using in situ measurements.

Field and model investigations of external gamma dose rates along the Cumbrian coast,NW England

A survey of the contribution to external dose from gamma rays originatingfrom intertidal sediments in the vicinity of the British Nuclear GroupSellafield site showed that the major anthropogenic contributions were due to137Cs and 60Co. At some sites, traces of other anthropogenic radionuclides were detected, namely106Ru,125Sb, and154Eu. The proportions offine grained material (<63 µm) were used to improve model predictions of dose contribution due to external exposure togamma rays, using the CUMBRIA77/DOSE77 model. Model dose predictions werecompared to those directly measured in the field. Using the new proportions of fine grainedmaterial (1–17.5%) in conjunction with field gamma-ray spectra, model predictions wereimproved considerably for most sites. Exceptions were at Drigg Barn Scar andWhitehaven Coal Sands sites, which had their own unique characteristics. The highest60Co activityconcentrations in this study were detected at Drigg Barn Scar. These relatively high activity concentrations of60Co were due tothe presence of 60Co in mussels and barnacles, hence upsetting the fine sediment relationships usedin previous dose calculations. Whitehaven Coal Sands was unusual in that itcontained higher levels of radionuclides than would be expected in sandysediment. The mineralogy of these sediments was the controlling factor on137Cs binding, rather than the proportion of fine grained material. By adjustingthe effective fine grained sediment proportions for calculations involving60Co and 137Cs at Drigg Barn Scar and Whitehaven Coal Sands respectively, the CUMBRIA77/DOSE77model predictions could be improved upon significantly for these sites. This workhighlights the influence of particle size and sediment composition on external doserate calculations, as well as the potential for external dose contributions frombiota.