Field-measured Parameters Research Articles

ALS-Based, Automated, Single-Tree 3D Reconstruction and Parameter Extraction Modeling

The 3D reconstruction of point cloud trees and the acquisition of stand factors are key to supporting forestry regulation and urban planning. However, the two are usually independent modules in existing studies. In this work, we extended the AdTree method for 3D modeling of trees by adding a quantitative analysis capability to acquire stand factors. We used unmanned aircraft LiDAR (ALS) data as the raw data for this study. After denoising the data and segmenting the single trees, we obtained the single-tree samples needed for this study and produced our own single-tree sample dataset. The scanned tree point cloud was reconstructed in three dimensions in terms of geometry and topology, and important stand parameters in forestry were extracted. This improvement in the quantification of model parameters significantly improves the utility of the original point cloud tree reconstruction algorithm and increases its ability for quantitative analysis. The tree parameters obtained by this improved model were validated on 82 camphor pine trees sampled from the Northeast Forestry University forest. In a controlled experiment with the same field-measured parameters, the root mean square errors (RMSEs) and coefficients of determination (R2s) for diameters at breast height (DBHs) and crown widths (CWs) were 4.1 cm and 0.63, and 0.61 m and 0.74, and the RMSEs and coefficients of determination (R2s) for heights at tree height (THs) and crown base heights (CBHs) were 0.55 m and 0.85, and 1.02 m and 0.88, respectively. The overall effect of the canopy volume extracted based on the alpha shape is closest to the original point cloud and best estimated when alpha = 0.3.

Comparison of Three Approaches for Estimating Understory Biomass in Yanshan Mountains

Aboveground biomass (AGB) of shrubs and low-statured trees constitutes a substantial portion of the total carbon pool in temperate forest ecosystems, contributing much to local biodiversity, altering tree-regeneration growth rates, and determining above- and belowground food webs. Accurate quantification of AGB at the shrub layer is crucial for ecological modeling and still remains a challenge. Several methods for estimating understory biomass, including inventory and remote sensing-based methods, need to be evaluated against measured datasets. In this study, we acquired 158 individual terrestrial laser scans (TLS) across 45 sites in the Yanshan Mountains and generated metrics including leaf area and stem volume from TLS data using voxel- and non-voxel-based approaches in both leaf-on and leaf-off scenarios. Allometric equations were applied using field-measured parameters as an inventory approach. The results indicated that allometric equations using crown area and height yielded results with higher accuracy than other inventory approach parameters (R2 and RMSE ranging from 0.47 to 0.91 and 12.38 to 38.11 g, respectively). The voxel-based approach using TLS data provided results with R2 and RMSE ranging from 0.86 to 0.96 and 6.43 to 21.03 g. Additionally, the non-voxel-based approach provided similar or slightly better results compared to the voxel-based approach (R2 and RMSE ranging from 0.93 to 0.96 and 4.23 to 11.27 g, respectively) while avoiding the complexity of selecting the optimal voxel size that arises during voxelization.

Frost suppression performance of an air source heat pump using sensible heat from indoor air to preheat outdoor air

Frost forms on the surfaces of air source heat pump (ASHP) outdoor heat exchangers under heating mode in winter, when the surface temperature of the heat exchanger is lower than both 0°C and the ambient dew point temperature. This can reduce the coefficient of performance (COP) and heating capacity of the ASHP unit. A novel ASHP was examined using two rooms with the same size, orientation, and structure. To test the frost suppression performance of the novel system, two ASHPs of the same size and specifications, but one including a sensible-heat preheating device, were placed in the test platform rooms. By comparing and analyzing field-measured parameters such as COP, heat loss, and frost weight of the two ASHP units, the frost suppression performance of the novel ASHP was evaluated in severe, moderate, and mild frost areas. The results show that when the air conditions were −3.9°C and 98.7% in the moderate frost area and 3.2°C and 96.7% in the severe frost area, the novel ASHP showed significantly improved performance. The frost formation time increased from 25 min to 38.5 min, frost-defrost heat loss decreased by 31.6%–43.7%, frost weight decreased 11.8%–17.4%, and COP increased 7.4%–13.1% compared with those of the conventional ASHP. In the low temperature and mild frost area, when the air temperature was −11.8°C and the relative humidity was 88.8%, the frost suppression effect of the novel ASHP was unapparent. Affected by the climate, the operation performance of ASHP will be different. Different ASHP can be used to adapt to the weather in different regions. The novel ASHP can significantly suppress frost and improve the heating performance of the unit in the mild climate and frost serious areas.

A Generalized Hydraulic Model for Propulsion Force Calculations in Radial Jet Drilling

Summary Radial jet drilling (RJD) involves drilling several small-diameter lateral holes from a single vertical wellbore to increase reservoir contact and production. RJD system components (diverter, flexible hose, and jetting bit) are conveyed to the target depth using coiled tubing. A high-pressure flexible hose is used in conjunction with a jetting bit to drill holes laterally. Without a rigid drillstring, no axial force can be transferred to the bit as it penetrates the rock. As a result, the bit is propelled by hydraulic means. Thus, in addition to front-jetting nozzles, RJD bits use back-jetting nozzles. Therefore, the rate of penetration (ROP) and maximum hole length (MHL) must be maximized through proper hydraulic optimization. Existing hydraulic models rely on field-measured parameters (discharge coefficient and flow rate ratio) that vary by the bit design to predict the propulsion force, bit hydraulic power, and the maximum lateral hole length. Hence, this study aims to develop a generalized and accurate hydraulic model that does not require field-measured parameters to make predictions. As a result, the new model can be used for optimizing RJD operations by selecting suitable bit designs and lateral hole geometries. This article presents a new RJD hydraulic model that uses a discharge coefficient that varies with the nozzle aspect ratio. The model predicts the propulsion force, differential pressure across the bit, and MHL based on the design of the bit, nozzle, and lateral hole geometries, and flow rate. To verify the model, extensive experiments were conducted with single-nozzle and multi-nozzle jetting bits. The pump pressure was varied while flow rate and propulsion force were recorded during the tests. Model predictions are compared and validated with experimental data. Measured and model-predicted propulsion forces demonstrate a reasonable agreement with a maximum discrepancy of 25%. Once the model has been validated, it is used to perform a parametric study to investigate the influence of various factors on bit performance. According to the parametric study, nozzle and hole diameters, friction factor, and hose density strongly influence bit performance. Furthermore, the diameter of the nozzle has been found to have a significant effect on bit performance parameters (propulsion force, bit hydraulic power, and MHL).

Increasing objectivity associated with anadromous fish redd identification using a discriminant function analysis

Many fish species reproduce by creating nests (redds) in alluvial stream gravels, which can be used to track population trends. However, temporal and spatial overlap across multiple redd-building species can hinder redd species classification. This is further complicated when the corresponding adult is not present. Spawning surveys on the Lower American River (LAR) have been conducted since 2003 to document fall-run Chinook Salmon and California Central Valley (CCV) steelhead spawning. Other fish species on the LAR have overlapping reproduction timing, including Pacific Lamprey. Prior to 2016, a redd observed during field surveys that was not associated with a fish observation was assigned species identity based on seasonal timing and professional judgement. However, this method has potential to misidentify the species that built the redd due to overlap in spawning season and similarity in redd dimensions among LAR fish species. To decrease subjectivity associated with unoccupied redd identification, we used occupied redd data to build a discriminant function analysis (DFA), which predicts redd species identity based on field-measured parameters that vary across species including time of year, redd dimensions, and ambient conditions. We compared model accuracy across 6 years in which additional “fish on” observations were added annually to the discriminant function to test whether adding observational data improved model accuracy. We also applied the discriminant function to historical redd data in which species identification was made based on professional judgement to compare the two approaches. DFA accuracy improved with additional years of data, and in the iteration that included the most observational data it was highly accurate in identifying fall-run Chinook Salmon and CCV steelhead (96% and 97%, respectively). Accuracies for Pacific Lamprey were slightly lower (91%) than salmonids due to the relatively low number of “fish-on” redd observations for Pacific Lamprey. Comparisons between the DFA and historical identification based on professional opinion were generally similar, but with up to 19.6% disagreement in some years. Our study demonstrates that physical and temporal metrics can support more accurate species identification, and field data can be used to support more robust population estimates and inform future habitat restoration decisions.

Techno-economic potential and perspectives of floating photovoltaics in Europe

In floating photovoltaics, modules are mounted on or above water surfaces in order to limit the land occupancy, an issue arising with the growing deployment of photovoltaics. The floating structures are also expected to lower the capital expenditures required by traditional in-land systems, thanks to the lack of major site preparation needs and to the hybridization with hydropower plants. This work estimates the yield potential and the cost effectiveness of floating photovoltaics across suitable water bodies in Europe compared to optimally tilted land-based photovoltaics. Energy and economic outputs are modelled using referenced models, field-measured parameters and considering weather and economic conditions specific to each location and each country. The results show that, despite the lower tilts, floating photovoltaics with improved heat transfer capabilities can achieve energy yields up to 2 % greater than land-based photovoltaics. This is especially true in the Mediterranean region, where the average position of the Sun and the temperatures are higher. However, in some configurations, floating photovoltaics might not achieve lower temperatures than land-based photovoltaics, leading to lower energy yields. Despite that, it is found that, even when underperforming, floating photovoltaics can be cost competitive with land-based photovoltaics if the installation costs are reduced by less than 12 %. Last, this study estimates that each additional degree of tilt angle in floating photovoltaic installations is worth between 2.5 and 7.5 €/kW.

Variability of the diapycnal mixing coefficient in coastal oceans investigated with direct microstructure measurements

Mass and heat fluxes in the ocean are important for understanding global ocean dynamics and ecosystems. Estimates of the diapycnal diffusivity (Kρ) are required for quantifying these fluxes. In this regard, one of the key parameters that is required to estimate the diapycnal eddy diffusivity is the “mixing coefficient” (Γ). The diapycnal diffusivity is estimated from a combination of the rate of dissipation of turbulent kinetic energy ε, the buoyancy frequency N (a measure of background density stratification) and Γ. This study investigates how the mixing coefficient (Γ) may be inferred from field measurable parameters using in-situ direct microstructure measurements in coastal oceans. Four microstructure data sets were analyzed to investigate the variability of Γ and associated parameters. While Γ is found to vary widely within a range of O(10−3−101), it can be parameterized using a ratio of relevant turbulent length scales: the Ellison scale (LE, which is approximately equivalent to the Thorpe scale) and the Ozmidov scale (LO). When LE/LO is less than unity, the results show that Γ is proportional to (LE/LO)4/3, consistent with previous observations. On the other hand, when LE/LO exceeds unity, Γ is approximately a constant with no discernable dependence on LE/LO, consistent with a recent theoretical and numerical study.

Link Cost Function and Link Capacity for Mixed Traffic Networks

Link cost function and link capacity are critical factors in traffic assignment modeling. Popular link cost functions like the Bureau of Public Roads (BPR) function have well-known drawbacks and are not suitable for mixed traffic conditions where a variety of vehicle classes use the road in a non-lane-based movement. Similarly, capacity is generally considered as a constant value. However, in mixed traffic conditions, capacity is not constant, but a function of vehicle class composition. Toward addressing these issues, this paper proposes a link cost function in relation to link travel time and link capacity in relation to vehicular traffic flow for mixed traffic conditions. The functions are developed based on the kinematic wave model, which is popularly used for estimating traffic dynamics on the roads. The developed link cost function and link capacity use field measurable parameters that incorporate mixed traffic features. The functions are validated against empirical data obtained from 12 signal cycles from two different signalized intersections in Chennai, India, representing different scenarios of mixed traffic, and it was found that the results match well with the empirical data.

A metamodeling based seismic life-cycle cost assessment framework for highway bridge structures

This study presents a novel framework for seismic life-cycle cost assessment of highway bridges using parameterized fragility models rooted in modern statistical learning techniques. Unlike traditional fragility curves, often used for seismic loss assessment, the parameterized fragility models are multi-dimensional functions conditioned on ground motion intensity as well as critical field measurable bridge parameters. Such functions are particularly useful for prompt vulnerability estimation and life-cycle cost assessment of structurally dissimilar highway bridges across bridge portfolios in regions characterized by moderate to high seismicity. Consequently, the proposed framework can aid decision makers and stakeholders for efficient channeling of monetary resources for necessary seismic upgrade of highway bridges within a transportation network. As a case-study example, this study chooses the non-seismically designed multi-span simply supported concrete girders highway bridge class that constitutes a significant portion of the highway bridge inventory within Central and Southeastern US. The proposed parameterized fragility functions for this bridge are used along with seismic hazard data and probabilistic repair cost information for seismic loss assessment through a component-level approach. In addition to near-instant seismic life-cycle cost assessment, as demonstrated through several examples, this approach also helps avert potential double counting from multiple component damage while calculating system-level losses.

Evaluating Carbon Sequestration and PM2.5 Removal of Urban Street Trees Using Mobile Laser Scanning Data

Street trees are an important part of urban facilities, and they can provide both aesthetic benefits and ecological benefits for urban environments. Ecological benefits of street trees now are attracting more attention because of environmental deterioration in cities. Conventional methods of evaluating ecological benefits require a lot of labor and time, and establishing an efficient and effective evaluating method is challenging. In this study, we investigated the feasibility to use mobile laser scanning (MLS) data to evaluate carbon sequestration and fine particulate matter (PM2.5) removal of street trees. We explored the approach to extract individual street trees from MLS data, and street trees of three streets in Nantong City were extracted. The correctness rates and completeness rates of extraction results were both over 92%. Morphological parameters, including tree height, crown width, and diameter at breast height (DBH), were measured for extracted street trees, and parameters derived from MLS data were in a good agreement with field-measured parameters. Necessary information about street trees, including tree height, DBH, and tree species, meteorological data and PM2.5 deposition velocities were imported into i-Tree Eco model to estimate carbon sequestration and PM2.5 removal. The estimation results indicated that ecological benefits generated by different tree species were considerably varied and the differences for trees of the same species were mainly caused by the differences in morphological parameters (tree height and DBH). This study succeeds in estimating the amount of carbon sequestration and PM2.5 removal of individual street trees with MLS data, and provides researchers with a novel and efficient way to investigate ecological benefits of urban street trees or urban forests.

Relationships between field-measured hydrometeorological variables and satellite-based land surface temperature in a hemiboreal raised bog

Temperature regime is one of the main controlling factors of greenhouse gas (GHG) emissions from peat bogs. Remotely sensed land surface temperature (LST) has a potential to become an efficient instrument in environmental monitoring of carbon dioxide and methane emissions from peat bogs. This paper examines the relationships between field-measured hydrometeorological variables and MODIS LST data in a hemiboreal raised bog for a period from May to September (2008–2016). The Pearson product-moment correlation was used to reveal the relationship between the field-measured parameters and LST over years and months. A multiple linear regression was chosen to model relationships between the hydrometeorological variables and LST by month. It was found that the relationships between the studied parameters and LST were year- and month-dependent. The main factor of LST was air temperature, and the correlation between LST and air temperature was the strongest during the entire period of study. This study has shown that the hydrometeorological factors of LST can explain 67%–81 % of the variance in LST in a hemiboreal raised bog. The relationships between the hydrometeorological variables and LST may be implemented in more accurate GHG emissions estimation from bogs.

How many insects can a great tit population prey on in apple organic orchards? A modelling bioenergetics study

Orchards represent relevant study systems for investigating the functional role of insectivorous birds as regulators of pest insect populations. In this context, we used a bioenergetics model (Wiens and Innis, 1974) to estimate the seasonal variation in daily insect consumption by natural populations of the great tit (Parus major) in organic apple orchards. This model allowed us to estimate the changes in both adult densities and energy requirements in a P. major population, using field-measured parameters such as the brood size, and the length of incubation. The calculation of insect consumption rate by birds was based on both the existing literature on great tit diets and the simulated energy requirement of a great tit population. The effect of a temperature increase on energy requirement has been quantified. This study opens the way to consider the functional role of birds in agricultural landscapes and how this role may translate to ecosystem services.

Establishment of Relationship between Pavement Surface Friction and Mixture Design Properties

In recent years, pavement designers have been increasingly challenged to achieve ideal surface friction properties to enhance driver safety through mixture design manipulation and material selection. A clear understanding of the relationship between pavement mixture design properties and surface friction is needed. In this study, the surface laser profilometer device was used to measure surface texture by scanning the surface of laboratory-compacted and field core samples, from which a surface texture profile was derived. Surface texture data were analyzed to calculate the mean profile depth. Statistical analysis and neural networks modeling were used to find the relationship between the mean profile depth results estimated from laser profilometer measurements and mixture design properties (i.e., aggregate size, gradation curve shape, binder content, air voids, and volumetric properties). Promising trends were observed in the data that could be used as guidance by mixture designers to optimize mixture design properties, such as to achieve better pavement surface friction and hence enhanced driver safety. Relationships between field-measured friction (mainly friction number) and laboratory-measured texture parameters were developed. Friction number values measured with the locked-wheel tire test in the field were taken from the MnROAD test track database and used for analysis. The study shows a correlation between friction number and mean profile depth that is of potential applicability to pavement designers for achieving target field friction with the aid of laboratory measurement and analysis. Such relationships between laboratory measurements and field friction could lead to better control of pavement surface friction.

Hydrochemical and stable isotopic assessment of groundwater quality and its variations in rice-growing areas in East China

Agricultural activities are frequently associated with water contamination. Thus, the development of efficient strategies for groundwater protection in agricultural areas requires an assessment of the contaminants. Given this perspective, groundwater quality monitoring is carried out in a rice-growing area in Hangjiahu Plain, East China. Thirty-two piezometers are installed to measure physico-chemical parameters such as major ions, field-measured parameters (pH, electrical conductivity (EC), dissolved oxygen, and temperature), and δ15N isotopic ratios and their variations in space and time. The groundwater shows a variable chemical composition, e.g. EC ranged from 760 to 2,300 μS cm−1. Most groundwater is weakly acidic, and is characterized as Ca2+ + Na+− HCO3 − + SO4 2− + Cl− type. The results demonstrate NH4 + coming from agricultural activities and SO4 2− deriving from natural chemical inputs are the major contaminants in the groundwater at the study area. Correlations among NO3 −, NH4 + and K+ suggest that these ions come from the same source of fertilizer and indicate a significant degree of nitrification in the study area. The highly positive correlations among the variables of HCO3 −, SO4 2−, and Mg2+ indicated that these ions were derived from the same source of natural chemical inputs. Nitrate isotopic composition suggests that nitrate in groundwater originates from chemical fertilizers, manure, and soil organic matter.

Mapping Paddy Rice Varieties Using Multi-temporal RADARSAT SAR Images

This study classified paddy fields according to rice varieties and monitored temporal changes in rice growth using SAR backscatter coefficients (s˚). A growing period time-series of backscatter coefficients was set up for nine fine-beam mode RADARSAT-1 SAR images from April to October 2005. The images were compared with field-measured rice growth parameters such as leaf area index (LAI), plant height, fresh and dry biomass, and water content in grain and plants for 45 parcels in Dangjin-gun, Chungnam Province, South Korea. The average backscatter coefficients for early-maturing rice varieties (13 parcels) ranged from -18.17 dB to -6.06 dB and were lower than those for medium-late maturing rice varieties during most of the growing season. Both crops showed the highest backscatter coefficient values at the heading stage (late July) for early-maturing rice, and the difference was greatest before harvest for early- maturing rice. The temporal difference in backscatter coefficients between rice varieties may play a key role in identifying early-maturing rice fields. On the other hand, comparisons with field-measured parameters of rice growth showed that backscatter coefficients decreased or remained on a plateau after the heading stage, even though the growth of the rice canopy had advanced.

Simplified models of vector control impact upon malaria transmission by zoophagic mosquitoes.

BackgroundHigh coverage of personal protection measures that kill mosquitoes dramatically reduce malaria transmission where vector populations depend upon human blood. However, most primary malaria vectors outside of sub-Saharan Africa can be classified as “very zoophagic,” meaning they feed occasionally (<10% of blood meals) upon humans, so personal protection interventions have negligible impact upon their survival.Methods and FindingsWe extended a published malaria transmission model to examine the relationship between transmission, control, and the baseline proportion of bloodmeals obtained from humans (human blood index). The lower limit of the human blood index enables derivation of simplified models for zoophagic vectors that (1) Rely on only three field-measurable parameters. (2) Predict immediate and delayed (with and without assuming reduced human infectivity, respectively) impacts of personal protection measures upon transmission. (3) Illustrate how appreciable indirect communal-level protection for non-users can be accrued through direct personal protection of users. (4) Suggest the coverage and efficacy thresholds required to attain epidemiological impact. The findings suggest that immediate, indirect, community-wide protection of users and non-users alike may linearly relate to the efficacy of a user’s direct personal protection, regardless of whether that is achieved by killing or repelling mosquitoes. High protective coverage and efficacy (≥80%) are important to achieve epidemiologically meaningful impact. Non-users are indirectly protected because the two most common species of human malaria are strict anthroponoses. Therefore, the small proportion of mosquitoes that are killed or diverted while attacking humans can represent a large proportion of those actually transmitting malaria.ConclusionsSimplified models of malaria transmission by very zoophagic vectors may be used by control practitioners to predict intervention impact interventions using three field-measurable parameters; the proportion of human exposure to mosquitoes occurring when an intervention can be practically used, its protective efficacy when used, and the proportion of people using it.

Documenting measurement sensitivity and bias of field-measured parameters in water quality monitoring programs

Measurement sensitivity and bias quality control metrics are commonly reported for water-quality parameters measured in the laboratory. Less commonly recognized is that they should also be reported for field-measured parameters. Periodic evaluation helps document data quality and can help serve as early warning if there are problems with methods or techniques that could negatively affect ability to interpret threshold values and trends over time. This study focuses on traditional assessment of bias and introduces a new method for estimating measurement sensitivity of water-quality parameters measured monthly in the field. Alternative measurement sensitivity is a new data quality indicator used to demonstrate how quantifying sensitivity at the measurement level can improve understanding the uncertainty affecting each reported data value. That, in turn, can help interpret the meaning of results from many separate data points measured in the field. In this 30-month study, pH and specific conductance consistently met, and dissolved oxygen did not always meet NPS and USGS quality control standards for bias. Evaluation of dissolved oxygen bias and sensitivity during the study provided impetus to improve calibration techniques that resulted in data that later met quality goals.

Uncalibrated modelling of conservative tracer and pesticide leaching to groundwater: comparison of potential Tier II exposure assessment models

The Root Zone Water Quality Model (RZWQM) and Pesticide Root Zone Model (PRZM) are currently being considered by the Office of Pesticide Programs (OPP) in the United States Environmental Protection Agency (US EPA) for Tier II screening of pesticide leaching to groundwater (November 2005). The objective of the present research was to compare RZWQM and PRZM based on observed conservative tracer and pesticide pore water and soil concentrations collected in two unique groundwater leaching studies in North Carolina and Georgia. These two sites had been used previously by the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) Environmental Model Validation Task Force (EMVTF) in the validation of PRZM. As in the FIFRA EMVTF PRZM validation, 'cold' modelling using input parameters based on EPA guidelines/databases and 'site-specific' modelling using field-measured soil and hydraulic parameters were performed with a recently released version of RZWQM called RZWQM-NAWQA (National Water Quality Assessment). Model calibration was not performed for either the 'cold' or 'site-specific' modelling. The models were compared based on predicted pore water and soil concentrations of bromide and pesticides throughout the soil profile. Both models tended to predict faster movement through the soil profile than observed. Based on a quantitative normalised objective function (NOF), RZWQM-NAWQA generally outperformed or was equivalent to PRZM in simulating pore water and soil concentrations. Both models were more successful in predicting soil concentrations (i.e. NOF < 1.0 for site-specific data, which satisfies site-specific applicability) than they were at predicting pore water concentrations.

Solitary fracture waves in metastable snow stratifications

Fracture processes in layered snow have many implications on avalanche hazard and mountain safety. This paper is a contribution for a better understanding of fracture dynamics in a stratified medium with a collapsible layer in terms of a simple analytical model involving only field measurable parameters. For this purpose a simple three‐layer snow stratification is considered to consist of a compact basal layer, a collapsible weak layer, and a homogenous top layer. It is shown analytically that the fracture of the weak layer can occur in the form of a localized disturbance zone propagating a collapse with constant velocity and wavelength. Simple analytical expressions describing the disturbance are obtained. The results are in good agreement with observations in the terrain. The presented fracture process is relevant to the release of dry snow slab avalanches and to the propagation of firn quakes and whumpfs but may also apply to other stratified media with appropriate properties.

Chemical and Seasonal Controls on the Dynamics of Dissolved Organic Matter in a Coniferous Old-growth Stand in the Pacific Northwest, USA

Soil organic matter (SOM) is the largest terrestrial C pool, and retention and release of dissolved organic matter (DOM) cause formation and loss of SOM. However, we lack information on how different sources of DOM affect its chemical composition, and how DOM chemical composition affects retention. We studied seasonal controls on DOM production and chemical controls on retention in soils of a temperate coniferous forest. The O horizon was not usually the dominant source for dissolved organic C (DOC) or N (DON) as has been reported for other sites. Rather, net production of both DOC and DON was often greater in the shallow mineral soil (0-10 cm) than in the O horizon. DOM production in the shallow mineral soil may be from root exudation as well as turnover of fine roots and microflora in the rhizosphere. In the field, the two acid fractions (hydrophobic and hydrophilic acids) dominated the soil solution at all depths. A major portion of net production and removal of total DOC within the soil column was explained by increases and decreases in these fractions, although a shift in chemical composition of DOM between the O and mineral soil horizons suggested different origins of DOM in these layers. A larger loss of the free amino fraction to deep soil water at this study site than at other sites suggested lower retention of labile DON. Field DOM removal measurements suggest that field-measured parameters may provide a good estimate for total DOM retained in mineral soil.