Sandy Sites Research Articles

Leaf functional traits and nutrient resorption among major silviculture tree species in coastal sandy site.

To understand the adaptative strategies of different tree species to drought and nutrient-deficient environment in coastal sandy site, leaf functional traits and nutrient resorption of four major silviculture tree species, i.e., Casuarina equisetifolia, Pinus elliottii, Acasia crassicarpa and Eucalyptus urophylla × E. grandis were analyzed. Leaf area and specific leaf area of coniferous species (C. equisetifolia and P. elliottii) were significantly lower, and leaf dry matter content and leaf thickness were significantly higher than those of broadleaved species (A. crassicarpa and E. urophy-lla × E. grandis). Nitrogen and P contents of mature leaf and leaf litter in broadleaved species were higher than those in coniferous species. Nitrogen and P contents of mature leaf were higher than those in leaf litter, but N:P was lower than that in leaf litter. Nitrogen and P resorption efficiencies were higher in coniferous species than those in broadleaved species. The P resorption efficiency in all species was significantly higher than N resorption efficiency. The N resorption efficiency of C. equisetifolia, P. elliottii, A. crassicarpa and E. urophylla × E. grandis was 64.2%, 63.1%, 47.0% and 16.8%, and the P resorption efficiency was 92.5%, 81.6%, 80.3% and 18.0%, respectively. The specific leaf area was significantly positively correlated with leaf N and P contents, but negatively correlated with leaf dry matter content, leaf thickness, and nutrient resorption efficiency. Leaf dry matter content was significantly positively correlated with leaf thickness and nutrient resorption efficiency. Therefore, C. equisetifolia and P. elliottii belonged to slow investment species with a higher nutrient resorption efficiency, while A. crassicarpa and E. urophylla × E. grandis belonged to fast investment species with lower nutrient resorption efficiency. Different tree species developed different adaptive strategies to coastal sandy environments through the interactions between leaf functional traits and nutrient resorption.

Selected physiological parameters of creeping willow [Salix repens subsp. arenaria (L.) Hiit.]: a shrubby plant inhabiting degraded industrial areas

Key messageSalix arenariafrom sandy sites tended to grow fast, notwithstanding particular stress conditions in the desert habitat.The study was aimed at characterizing main adaptive changes in Salix arenaria exposed to harsh conditions of a desert-like environment. It was clearly shown that the plant was capable of adapting most of its photosynthesis parameters to enable efficient vegetative performance. A closer look at plant anatomical structures made it possible to better define the changes developed by plants populating sandy habitats as compared with the vegetation sites located in the nearby forest. The desert environment generated physiological stress of water availability and increased the plants’ water use efficiency (WUE) during photosynthesis. All the collected data indicate that the photochemical apparatus in S. arenaria inhabiting desert areas got slightly adapted to strong light and drought, which involved some photoinhibition mechanism and the reduction of the reaction center (RC) size (photosystem II, PSII), while keeping the plant photochemical activity at a similar level. Determination of microbial frequency in the sandy soil of the desert-growing plants showed microbiota population high enough as not to hamper plant growth. The root zones of both the desert-growing and control plants provided favorable conditions enabling populous microbial proliferation, particularly biostimulated during the spring season. The arbuscular mycorrhiza was also shown to be well developed and independent of the original plant habitat (desert or forest).

Long-term application of low C:N residues enhances maize yield and soil nutrient pools across Kenya

Declines in soil fertility and limited access to inorganic nitrogen (N) fertilizer constrain crop production in Sub-Saharan Africa. The incorporation of organic residues could increase nutrient mineralization and replenish soil carbon (C), however, the effect that long-term residue management (10+ years) has on maize (Zea mays L.) yields and soil nutrient pools (C and N) is largely unknown. In four identical long-term trials in Kenya that differ by soil type and climate, we compared maize yield and soil C (0–0.15 m) across four treatments comparing organic inputs of contrasting C:N ratios: tithonia [Tithonia diversifolia (Hemsl.) A. Gray] + N (120 kg N ha−1); tithonia − N (0 kg N ha−1); maize stover + N (120 kg N ha−1); maize stover − N (0 kg N ha−1). On average, maize yields were 92% greater under tithonia compared to maize stover at the sandy sites and in general followed this trend: tithonia + N > tithonia − N = stover + N > stover − N. The continuous application of tithonia also increased soil C and N pools; for instance, mineralizable C was up to 57% greater than that of maize stover at the sandy sites. Increases in yield and nutrient pools under tithonia were less apparent at the clay sites. When exploring the relationship between soil C and maize yield, we found that both mineralizable and processed pools were related to agronomic performance. Our findings demonstrate that low C:N residues could significantly benefit crop production and enhance soil organic matter at sandy sites across Kenya.

Promising Leuce poplar clones in sandy ridges between the rivers Danube and Tisza in Hungary: a case study

An intensive integrated research and development work has been carried out on the improvement of Leuce poplars including primarily the native white poplar (Populus alba L.) and its natural hybrid grey poplar (Populus × canescens). More than 70 percent of the Leuce poplar stands can be found on calcareous sandy sites in the Danube–Tisza region, so they play a significant role in the poplar management of this part of the country. The most important task ahead of Hungarian poplar growers is to improve the quality of poplar stands and plantations based on selecting new clones and cultivars. The growth and yield of four promising Leuce poplar clones was evaluated on a marginal site in central Hungary. The clones ‘H 425-4’ (Populus alba L. × Populus alba L.), and ‘H 758’ (Populus alba L. Mosonmagyaróvár 124) seem to be suitable for wood production, while the ‘H 427-3’ (Populus alba L. × Populus alba L. cv. Bolleana) and ‘H 422-9’ (Populus alba L. × Populus grandidentata (Michx)) clones (with decorative stem form) could be better used for tree lines and ornamental plantations.

Effects of Biomass Removal Levels on Soil Carbon and Nutrient Reserves in Conifer‐Dominated, Coarse‐Textured Sites in Northern Ontario: 20‐Year Results

Core Ideas Biomass removal trials targeted soils sensitive to nutrient removal (shallow to bedrock and infertile sands). 14 long‐term sites (42 plots per treatment) were used to evaluate C and nutrient reserves 20 years post‐harvest. After 20 years, soil C, N, and K reserves did not differ between pre‐harvest levels and SO and FT. Soil reserves of FTB treatments remained significantly lower than the pre‐harvest levels. Jack pine and black spruce declined in height on FTB on sandy sites; there were no differences between SO and FT. Here we report on 20‐yr soil (forest floor plus the upper 20 cm of mineral soil) carbon and nutrient reserves from 14 biomass removal trials established on coarse‐textured, nutrient poor sites. Harvest treatments included stem only (SO, delimbed at the stump), full‐tree (FT, entire trees with boles and branches removed), and full‐tree plus forest floor blading (FTB, full‐tree harvest followed by removal of the forest floor and approximately the upper 5 cm of mineral soil). After 20 yr, there were no significant differences in soil C, N, and K reserves between pre‐harvest levels and the SO and FT treatments. Only the soil reserves of the FTB treatment remained significantly lower than the pre‐harvest levels. Extractable soil Ca and Mg reserves increased in Year 5 in all treatments, followed by slow declines, but all treatments remained comparable to or exceeded pre‐harvest levels at Year 20. For P, harvesting (SO and FT) resulted in significant declines that remain after 20 yr. Both jack pine and black spruce showed reduced top height growth on FTB, but only on some of the sandy sites. There were no differences in top height for either species between SO and FT across all 14 study sites. Current results suggest there is no need for restrictions on full‐tree harvesting for traditional wood products on these nutrient poor sites. However, from a cautionary perspective, it seems prudent at this time to restrict more intensive bioenergy harvests to deep, finer‐textured sites that have larger soil C and nutrient reserves.

How effective are tidal marshes as nature‐based shoreline protection throughout seasons?

AbstractNature‐based mitigation is increasingly proposed as a strategy to cope with global change and related risks for coastal flooding and erosion. Tidal marshes are known to provide shoreline protection as their aboveground biomass attenuates waves and their belowground biomass contributes to reducing erosion rates. The aim of this study was to quantify how effectively wave attenuation rates and erosion reduction rates are sustained throughout seasons in pioneer tidal marshes in the Elbe estuary (Germany). Changes in hydrodynamics and sediment dynamics were measured during 17 months along three sea‐to‐land transects of 50 m length. Simultaneously, changes in biomass of the monospecific pioneer vegetation (Bolboschoenus maritimus) were measured monthly. This study shows that wave and flow attenuation rates positively correlate with seasonal variations in aboveground biomass, that is: in summer, aboveground biomass and associated wave and flow attenuation rates are highest; while aboveground biomass is washed away during the first storms in autumn or winter, resulting in low wave and flow attenuation rates. Contrastingly, maximum incoming wave heights and flow velocities occur during winter, indicating that wave and flow attenuation is most needed then. However, hibernating root biomass assures low erosion rates in winter, especially at sandy sites. Although wave attenuation by pioneer marshes is highly variable throughout seasons and pioneer marshes alone are not so effective, they might facilitate the survival of higher marshes. Therefore, it is important to conserve or restore a gradual sea‐to‐land gradient from tidal flats, over pioneer marsh to high marsh to provide nature‐based shoreline protection.

Green biorefining: Effect of nitrogen fertilization on protein yield, protein extractability and amino acid composition of tall fescue biomass

Perennial grasses can provide very high biomass yields and a better environmental profile compared to most annual cereal crops. The grass biomass can be processed into a protein-rich fraction for monogastric feed and a fibrous pulp fraction for ruminant feed or energy production. We studied the effect of fertilization of tall fescue grown on two sandy sites in Denmark. Dry matter (DM) and crude protein (CP) yield of first cut was measured at four nitrogen (N) fertilization levels (0, 70, 140 or 210 kg N ha−1). Samples were processed in a screw press, achieving a pulp fraction and a juice fraction from which proteins were precipitated into a protein concentrate fraction. CP allocation between the fractions of protein concentrate and pulp was analysed as well as the amino acid (AA) profile. CP in the brown juice fraction was not analysed.CP concentration and CP yield of unprocessed tall fescue increased linearly with N fertilization, attaining concentrations up to 126 g kg−1 DM and yields up to 0.76-0.86 Mg ha−1. N fertilization did not affect CP allocation between concentrate and pulp in a consistent way. As a mean of all treatments and both sites, 17% of CP was recovered in the concentrate and 74% remained in the pulp. CP concentration increased linearly with fertilization in both concentrate and pulp with coefficients of 0.50 and 0.21 g kg−1 DM kg−1 N ha−1, i.e. with a higher increase in the concentrate fraction. The AA profile only differed slightly between the two fractions and between the fertilization levels, however, the total sulphur to N ratio in both fractions decreased with increased fertilization, and a similar trend was observed for the relative content of the sulphur-containing amino acids. The AA profile deviated considerably from soybean meal, particularly with higher leucine and lower glutamic acid content. In conclusion, fertilization can greatly increase CP concentration and CP yield. However, the separation process needs improvements to increase the protein in the concentrate fraction.

The influence of willow plantations and soil composition on the process of natural vegetation settlement at oil drilling sites in Western Siberia

Test cultures of various willow species were created in 1997 on a technogenic sandy site of one of oil deposits (62°46’18.36" N, 72°09’48.69" E). Sixty-five isolated plots, including various soil substrates (sand, peat, drilling wastes), were placed in the testing area of 684 m2. Optimum combinations of substrate components were identified, and the tolerance of willow species to drilling wastes was revealed by the results of investigating 1-5-year cultures [1]. In 2016 we investigated the natural settlement of aborigine plants in this test plot. The willow cultures mortality was high according to short offspring vegetative lifetimes and the limitation of feed areas. However, willow cultures and soil reclamation stimulated a settlement of natural plant seedlings. The comparison of phytocenoses, which were formed in various experimental and "background" conditions, has allowed making some conclusions. 44 plant species are growing now in the experimental area. The least number of species is characteristic for pure sand and pure peat substrates, the greatest − for complex substrates with sand, peat and drilling wastes. Thus, the experimental willow cultures and partial soil reclamation accelerated the formation process of forest ecosystems that created a "plant oasis" on a deserted landscape of technogenic sand.

Impact of post-fire management on soil respiration, carbon and nitrogen content in a managed hemiboreal forest

Boreal forests are an important carbon (C) sink and fire is the main natural disturbance, directly affecting the C-cycle via emissions from combustion of biomass and organic matter and indirectly through long-term changes in C-dynamics including soil respiration. Carbon dioxide (CO2) emission from soil (soil respiration) is one of the largest fluxes in the global C-cycle. Recovery of vegetation, organic matter and soil respiration may be influenced by the intensity of post-fire management such as salvage logging. To study the impact of forest fire, fire and salvage, and recovery time on soil respiration and soil C and N content, we sampled two permanent research areas in north-western Estonia that were damaged by fire: Vihterpalu (59°13′ N 23°49′ E) in 1992 and Nõva (59°10′ N 23°45′ E) in 2008. Three types of sample plots were established: 1) unburned control with no harvesting (CO); 2) burned and uncleared (BU); and 3) burned and cleared (BC). Measurements were made in 2013, 21 years after wildfire in Vihterpalu and 5 years after wildfire in Nõva. Soil respiration ranged from 0.00 to 1.38 g CO2 m−2 h−1. Soil respiration in the burned and cleared areas (BC) was not reduced compared to burned and uncleared (BU) areas but the average soil respiration in unburned control areas was more than twice the value in burned areas (average soil respiration in CO areas was 0.34 CO2 m−2 h−1, versus 0.16 CO2 m−2 h−1, the average soil respiration of BC and BU combined). Recovery over 20 years was mixed; respiration was insignificantly lower on younger than older burned sites (when BC and BU values were combined, the average values were 0.15 vs. 0.17 g CO2 m−2 h−1, respectively); soil-C was greater in the older burned plots than the younger (when BC and BU values were combined, the average values were 9.71 vs. 5.99 kg m−2, respectively); but root biomass in older and recently burned areas was essentially the same (average 2.23 and 2.11 kg m−2, respectively); soil-N was highest on burned areas 20 years after fire. Twenty years post-fire may be insufficient time for carbon dynamics to fully recover on these low productivity sandy sites.

Amendments fail to hasten biocrust recovery or soil stability at a disturbed dryland sandy site

In most drylands, biological soil crusts (biocrusts), an assemblage of lichens, bryophytes, fungi, green algae, and cyanobacteria, are critical to healthy ecosystem function. However, they are extremely sensitive to disturbance and attempts to facilitate their recovery have had variable success. In this study, we applied soil amendments designed to improve soil surface stability and accelerate biocrust recovery on an area disturbed by oil/gas exploration vehicles. Treatments included: (1) control (one time water only); (2) biocrust‐only: biocrust inoculum + nutrients in water; (3) polyacrylamide gels (which are known to stabilize soils) + biocrust inoculum + nutrients in water; (4) gypsum + biocrust inoculum + nutrients in water; and (5) saline (NaCl) solution + biocrust inoculum + nutrients in water. Only the NaCl treatment showed any effects on soil properties and these were only short term. These effects included an increase in soil strength and a reduction in soil aggregate stability, unsaturated hydraulic conductivity (Kh), and cyanobacterial biomass. The inoculated biocrust material failed to develop and even after 10 years, there was only a very low natural recolonization of the plots. These results show that inoculating soils or applying these levels of soil amendments does not guarantee recovery of soil stability or biocrust, and that some sites are unlikely to recover without assistance. Thus, there is a need for more research into ways to enhance soil stability and identify the factors limiting biocrust establishment.

Weed and insect management alter soil arthropod densities, soil nutrient availability, plant productivity, and aphid densities in an annual legume cropping system

Transgenic glyphosate-resistant (GR) soybean (Glycine max L. Merr.) is cultivated throughout the United States. Soybean growth is influenced by the presence of weeds, although managing non-crop vegetation can potentially impact soil arthropods, which are being increasingly recognized for their impacts on soil health, plant growth, and above-ground trophic interactions. We investigated how weed management (weedy controls, hand-weeded, glyphosate herbicide) and soil insecticide (chlorpyrifos) application affected densities of soil arthropods, soil nutrient availability, soybean growth and yield, and densities of an above-ground herbivore on sandy and clayey soils for two consecutive growing seasons. The soil insecticide treatment was intended to lower densities of subterranean arthropods to gain insight into how their presence influenced other factors, although their densities were primarily reduced the first year of the study. Surprisingly, weed management and soil insecticide use had virtually no interactive effects on any response. Weed presence had a positive effect on soil K at the sandy site and on nodule density per unit root. Negative effects of weed management on plant growth and aphids were related to the presence of weeds rather than herbicide use. Reduced soybean aphid density (at the clayey site) and soil P availability (at the sandy site) were associated with insecticide treated plots. Conversely, several measures of plant productivity, including number of nodules per unit root, and root and shoot biomass increased in +insecticide plots compared to other treatments, although effect strength depended on year and location. Collembola were the dominant soil microarthropod, and their densities in 2012 were negatively associated with nodule numbers in 2013. One explanatory hypothesis is that increased plant growth in plots treated with insecticide was caused by altered soil arthropod-microorganism interactions, possibly affecting arbuscular mycorrhizae function. This work highlights the importance of management decisions that affect soil arthropods in annual legume production systems.

Contemporary sand wedge development in seasonally frozen ground and paleoenvironmental implications

Contemporary sand wedges and sand veins are active in seasonally frozen ground within the extensive discontinuous permafrost zone in Northwest Territories, Canada. The region has a subarctic continental climate with 291 mm a−1 precipitation, −4.1 °C mean annual air temperature, warm summers (July mean 17.0 °C), and cold winters (January mean −26.6 °C). Five years of continuous observations indicate that interannual variation of the ground thermal regime is dominantly controlled by winter air temperature and snow cover conditions. At sandy sites, thin snow cover and high thermal conductivity promote rapid freezing, high rates of ground cooling, and low near-surface ground temperatures (−15 to −25 °C), resulting in thermal contraction cracking to depths of 1.2 m. Cracking potentials are high in sandy soils when air temperatures are <−30 °C on successive days, mean freezing season air temperatures are ≤−17 °C, and snow cover is <0.15 m thick. In contrast, surface conditions in peatlands maintain permafrost, but thermal contraction cracking does not occur because thicker snow cover and the thermal properties of peat prolong freezeback and maintain higher winter ground temperatures. A combination of radiocarbon dating, optical dating, and stratigraphic observations were used to differentiate sand wedge types and formation histories. Thermal contraction cracks that develop in the sandy terrain are filled by surface (allochthonous) and/or host (autochthonous) material during the thaw season. Epigenetic sand wedges infilled with allochthonous sand develop within former beach sediments beneath an active eolian sand sheet. Narrower and deeper syngenetic wedges developed within aggrading eolian sand sheets, whereas wider and shallower antisyngenetic wedges developed in areas of active erosion. Thermal contraction cracking beneath vegetation-stabilized surfaces leads to crack infilling by autochthonous host and overlying organic material, with resultant downturning and subsidence of adjacent strata. Sand wedge development in seasonally frozen ground with limited surface sediment supply can result in stratigraphy similar to ice-wedge and composite-wedge pseudomorphs. Therefore, caution must be exercised when interpreting this suite of forms and inferring paleoenvironments.

Response of flexible monopile in marine clay under cyclic lateral load

While monopile foundation is widely used at sandy site in Europe, it is designed and constructed in intertidal zone used only in China so far. Comparing with sandy site, intertidal site typically has different geological and environmental conditions due to upper layer consisting of soft marine clay and daily tide movement, which may lead to considerable difference in long-term behavior of monopile. In order to investigate the cyclic lateral behavior of monopile constructed in intertidal zone, several scaled model tests were conducted. The scaled monopile-soil system contained in-situ soil from intertidal zone was tested with a new designed loading device under static and cyclic lateral load. Behavior of monopile-soil system was obtained and analyzed, which includes assessment of cyclic deformation at pile-head, estimation of static and cyclic p-y curves, dissipation behavior of pore water pressure, evaluation of gapping effect and soil softening zone. Discussion and suggestion for available design are proposed based on the analysis work of test results.

A Framework for Estimating the 30 m Thermal‐Infrared Broadband Emissivity From Landsat Surface Reflectance Data

AbstractThe land surface thermal‐infrared broadband emissivity (BBE) is a vital variable for estimating land surface radiation budgets (SRBs). We develop a framework for retrieving the 30 m BBE from Landsat surface reflectance data to estimate SRBs at finer scales and validate coarse resolution data. In the developed framework, the land surface is classified as bare soils and vegetated surfaces to allow different algorithms to be used for the BBE estimation. We propose a downscaling algorithm that uses the empirical relationship between the Advanced Spaceborne Thermal Emission and Reflectance Radiometer (ASTER) BBE and Landsat surface reflectance at 90 m to retrieve the 30 m BBE over bare soils. A look‐up table (LUT)‐based algorithm is proposed for vegetated surfaces. The BBE is interpolated from a LUT that is constructed from the 4SAIL radiative transfer model with inputs of the leaf BBE, the soil background BBE, and the leaf area index (LAI). Ground measurements that were collected at 11 relatively homogeneous sandy sites during three independent field campaigns are used to validate the proposed algorithm over bare soils. The average difference between the retrieved and field‐measured BBEs is 0.012. We produce the land surface BBE of China in 2008 by using the developed framework and composited winter and summer seasonal BBE maps. The composited seasonal BBE maps are compared to the seasonal BBE maps derived from the ASTER emissivity product. The bias is within ±0.005 over bare soils and ranges from 0.012 to 0.019 over vegetated surfaces. Combined with the validated results in this study and published references, the comparison results demonstrate the good performance of the developed framework. This study provides a new perspective on estimating BBEs from sensors with only a thermal‐infrared channel.

Seasonal population dynamics of the invasive polychaete genus Marenzelleria spp. in contrasting soft-sediment habitats

Three species of the invasive polychaete genus Marenzelleria are among the dominant benthic taxa in many, especially deeper, areas in the Baltic Sea. The population dynamics of the polychaetes in the Baltic are, however, still largely unknown. We conducted monthly samplings of the benthic communities and environmental parameters at five sites with differing depths and sediment characteristics in the northern Baltic Sea (59°50.896′, 23°15.092′) to study the population dynamics, productivity and growth of Marenzelleria spp. from April 2013 to June 2014. The species of Marenzelleria occurring at the study sites were identified by genetic analyses. At the deepest site (33m) only M. arctia was present, while all three species were found at the shallower, muddy sites (up to 20m depth). At the shallow (6m) sandy site only M. viridis and M. neglecta occurred. The sites differed in the seasonal dynamics of the Marenzelleria spp. population, reflecting the different species identities. The muddy sites up to 20m depth showed clear seasonal dynamics, with the population practically disappearing by winter, whereas more stable populations occurred at the deepest site and at the sandy site. The highest density, biomass and production were observed at the 20m deep, organic-rich muddy site where all three species recruited. The seasonally very high densities are likely to have important consequences for organic matter processing, and species interactions at these sites. The observed high productivity of the populations has possibly facilitated their establishment, and considerably increased secondary production in especially the deeper areas.

Addressing Misperceptions Regarding Buffalograss Tolerance to Sandy Soils, Traffic, and Shade

Buffalograss [Buchloë dactyloides (Nutt.) Engelm. syn. Bouteloua dactyloides (Nutt.) Columbus] is often reported as being intolerant of shade, traffic, and sandy soils. Historically, these observations were made on early turf‐type cultivars or common types and may not reflect performance of modern cultivars and germplasm selections. As an example, the 1991, 1996, and 2002 buffalograss National Turfgrass Evaluation Program (NTEP) trials had evaluation sites consisting of sandy loam to sandy clay loam. One of the four sandy loam sites in the 1991 trial, and five of nine sandy loam–sandy clay loam sites in the 1996 and 2002 tests had buffalograss entries rating 6.0 or greater. We have since successfully established buffalograss on sandy sites with management changes typical of grasses considered adapted to sandy sites. In addition, multiyear shade and traffic studies were conducted at the University of Nebraska–Lincoln turfgrass research farm. A Brinkman traffic simulator was used to apply weekly traffic to 104 buffalograss genotypes from mid‐June through October in 2013 and 2014. Following 2 yr of moderate traffic, 70 of the genotypes were minimally affected by the traffic treatment. Shade tolerance studies were started in 2009 and 2013. Three buffalograss genotypes rated in the top 6% of 54 genotypes evaluated when grown under 60% shade cloth in the 2009 study. In 2013, four buffalograss entries grown under 60% shade cloth rated in the top 12% of 34 evaluated genotypes. A comparison of relative performance of 16 genotypes in common among the 2009 and 2013 shade studies highlight significant variability in performance under different environmental conditions and the need for revisiting historical recommendations.

Topographic and physicochemical controls on soil denitrification in prior converted croplands located on the Delmarva Peninsula, USA

Topographic and soil physiochemical characteristics exert substantial controls on denitrification, and the effect of these controls is especially evident in fertilized agricultural lands. To depict these controls at a landscape scale for decision support applications, metrics (i.e., proxies) must be developed based on commonly available geospatial data. In this study, we carried out an observational study on denitrification potential (DP) and capacity (DC) in three actively farmed crop fields that were converted from forested wetlands (i.e., prior converted croplands). The combined effects of ten topographic and physiochemical factors, including three topographic attributes (relief, topographic wetness index, and positive openness), two soil texture indices (sand and clay), and five soil properties (soil moisture, pH, electrical conductivity, soil organic carbon and total nitrogen), on DP and DC were analyzed. The three topographic attributes were developed using a digital elevation model (DEM) derived from light detection and ranging (LiDAR) data. Nitrate and carbon addition led to a doubling in DP compared to DC without soil amendment. Topography explained the greatest amount of variation in DP across the three sites. The relationship between topography and DP may partly be explained through the relatively robust relationships between topography and soil moisture, texture, and carbon content. Soil electrical conductivity (EC) exhibited the highest correlation with DC (r2=35%). DP and DC were higher under drought conditions with low soil moisture, relative to average conditions with relatively higher soil moisture, which may be related to the substantial increase in soil EC under drought conditions. However, DP and DC were less responsive to soil EC at sandy sites that tended to have low soil moisture. Results of this study suggest that the spatial-temporal variations in denitrification at these croplands were primarily caused by complex interactions between soil properties and landscape position. Topographic metrics derived from LiDAR data have the potential to improve understanding of denitrification variability at the landscape scale.

Direct Measurements of Sediment Sound Speed and Attenuation in the Frequency Band of 2–8 kHz at the Target and Reverberation Experiment Site

The sediment acoustic-speed measurement system is designed to measure in situ sediment sound speed and attenuation within the surficial 3 m of sediments in the frequency band of 2–8 kHz. Measurements were carried out during the Target and Reverberation EXperiment 2013 (TREX13) off Panama City, FL, USA. During TREX13, nine deployments at five selected sites were made along the 20-m isobath, termed the main reverberation track. The sediment types at the five selected sites ranged from coarse sand to a mixture of soft mud over sand, and the measured results show a spread of 80 m/s in sediment sound speed among the different types of sediments for all frequencies. Between 2–8 kHz, about 3% dispersion was observed at the sandy sites, whereas little dispersion was observed at the sites with mud. Preliminary attenuation results show 0.5–3.3 dB/m at the sandy sites, and 0.5–1.0 dB/m at the sites with mud in the same frequency band.

Sonar observations of biological activity in marine sediments

This talk will begin with a review of past experiments using bottom-mounted, rotating sonars to observe temporal change in the seafloor. These measurements were conducted at 40 kHz and 300 kHz, and provide images of change as represented by ping-to-ping correlation. Time scales of change vary greatly with frequency and sediment type, with changes occurring over weeks at 40 kHz at a silty site and over minutes at 300 kHz at a sandy site. Finally, the level of scattering due to relic tubes, shells, etc., will be compared to that of live animals. The conclusion is that it is easiest to observe the cumulative effects of biological activity, but techniques are available to isolate current activity.

Comparing benthic biogeochemistry at a sandy and a muddy site in the Celtic Sea using a model and observations

Results from a 1D setup of the European Regional Seas Ecosystem Model (ERSEM) biogeochemical model were compared with new observations collected under the UK Shelf Seas Biogeochemistry (SSB) programme to assess model performance and clarify elements of shelf-sea benthic biogeochemistry and carbon cycling. Observations from two contrasting sites (muddy and sandy) in the Celtic Sea in otherwise comparable hydrographic conditions were considered, with the focus on the benthic system. A standard model parameterisation with site-specific light and nutrient adjustments was used, along with modifications to the within-seabed diffusivity to accommodate the modelling of permeable (sandy) sediments. Differences between modelled and observed quantities of organic carbon in the bed were interpreted to suggest that a large part (>90%) of the observed benthic organic carbon is biologically relatively inactive. Evidence on the rate at which this inactive fraction is produced will constitute important information to quantify offshore carbon sequestration. Total oxygen uptake and oxic layer depths were within the range of the measured values. Modelled depth average pore water concentrations of ammonium, phosphate and silicate were typically 5–20% of observed values at the muddy site due to an underestimate of concentrations associated with the deeper sediment layers. Model agreement for these nutrients was better at the sandy site, which had lower pore water concentrations, especially deeper in the sediment. Comparison of pore water nitrate with observations had added uncertainty, as the results from process studies at the sites indicated the dominance of the anammox pathway for nitrogen removal; a pathway that is not included in the model. Macrofaunal biomasses were overestimated, although a model run with increased macrofaunal background mortality rates decreased macrofaunal biomass and improved agreement with observations. The decrease in macrofaunal biomass was compensated by an increase in meiofaunal biomass such that total oxygen demand remained within the observed range. The permeable sediment modification reproduced some of the observed behaviour of oxygen penetration depth at the sandy site. It is suggested that future development in ERSEM benthic modelling should focus on: (1) mixing and degradation rates of benthic organic matter, (2) validation of benthic faunal biomass against large scale spatial datasets, (3) incorporation of anammox in the benthic nitrogen cycle, and (4) further developments to represent permeable sediment processes.