Using the ECLPSS software environment to build a spatially explicit component-based model of ozone effects on forest ecosystems

We have developed a modeling framework to support grid-based simulation of ecosystems at multiple spatial scales, the Ecological Component Library for Parallel Spatial Simulation (ECLPSS). ECLPSS helps ecologists to build robust spatially explicit simulations of ecological processes by providing a growing library of reusable interchangeable components and automating many modeling tasks. To build a model, a user selects components from the library, and then writes new components as needed. Some of these components represent specific ecological processes, such as how environmental factors influence the growth of individual trees. Other components provide simulation support such as reading and writing files in various formats to allow inter-operability with other software. The framework manages components and variables, the order of operations, and spatial interactions. The framework provides only simulation support; it does not include ecological functions or assumptions. This separation allows biologists to build models without becoming computer scientists, while computer scientists can improve the framework without becoming ecologists. The framework is designed to operate on multiple platforms and be used across networks via a World Wide Web-based user interface. ECLPSS is designed for use with both single processor computers for small models, and multiple processors in order to simulate large regions with complex interactions among many individuals or ecological compartments. To test Version 1.0 of ECLPSS, we created a model to evaluate the effect of tropospheric ozone on forest ecosystem dynamics. This model is a reduced-form version of two existing models: , which represents an individual tree, and , which represents forest stand growth and succession. This model demonstrates key features of ECLPSS, such as the ability to examine the effects of cell size and model structure on model predictions.     

An analysis of motorcycle injury and vehicle damage severity using ordered probit models

Problem: Motorcycles constitute about 19% of all motorized vehicles in Singapore and are generally overrepresented in traffic accidents, accounting for 40% of total fatalities. Method: In this paper, an ordered probit model is used to examine factors that affect the injury severity of motorcycle accidents and the severity of damage to the vehicle for those crashes. Nine years of motorcycle accident data were obtained for Singapore through police reports. These data included categorical assessments of the severity of accidents based on three levels. Damage severity to the vehicle was also assessed and categorized into four levels. Categorical data of this type are best analyzed using ordered probit models because they require no assumptions regarding the ordinality of the dependent variable, which in this case is the severity score. Various models are examined to determine what factors are related to increased injury and damage severity of motorcycle accidents. Results: Factors found to lead to increases in the probability of severe injuries include the motorcyclist having non-Singaporean nationality, increased engine capacity, headlight not turned on during daytime, collisions with pedestrians and stationary objects, driving during early morning hours, having a pillion passenger, and when the motorcyclist is determined to be at fault for the accident. Factors leading to increased probability of vehicle damage include some similar factors but also show some differences, such as less damage associated with pedestrian collisions and with female drivers. In addition, it was also found that both injury severity and vehicle damage severity levels are decreasing over time.     

Contaminant residues in seabird eggs from the Canadian Arctic. II. Spatial trends and evidence from stable isotopes for intercolony differences

Eggs of glaucous gulls (Larus hyperboreus), black-legged kittiwakes (Rissa tridactyla), thick-billed murres (Uria lomvia) and black guillemots (Cepphus grylle) were collected from several sites throughout the Canadian Arctic. Samples were analyzed for organochlorines as well as mercury and selenium. Glaucous gulls breeding at sites in the High Arctic showed higher levels of organochlorine contamination than those in the western Low Arctic. This was likely due to dietary differences among colonies as suggested by stable isotope data, although different overwintering areas may also play a role. Levels of sigmaPCB, sigmaDDT, sigmaCHLOR, sigmaCBz and dieldrin were significantly lower in thick-billed murres from Prince Leopold Island in the High Arctic compared with colonies in the eastcrn Low Arctic. This difference was likely due to the combined effects of different atmospheric deposition patterns in the High and Low Arctic and different overwintering areas since murres from Prince Leopold Island may winter farther north than murres from the other colonies sampled. Eggs from colonies at higher latitudes generally contained higher concentrations of mercury. The trophic and dietary differences/similarities suggested by stable-nitrogen and carbon isotope data in this study were useful in explaining the spatial patterns of contaminant concentrations observed among colonies of seabirds such as the glaucous gull and the black-legged kittiwake where variation in latitudinal atmospheric deposition patterns and different overwintering grounds did not appear to be confounding factors.     

Cadmium accumulation and metallothionein synthesis in freshwater bivalves (Pyganodon grandis): relative influence of the metal exposure gradient versus limnological variability

The relative influence of limnological confounding factors on cadmium (Cd) bioaccumulation and metallothionein (MT) synthesis was quantified in natural populations of freshwater bivalves (Pyganodon grandis) living in lakes along a Cd concentration gradient. During the ice-free period, we measured 15 environmental variables in the water compartment and determined total concentrations of Cd and MT in the gills of bivalves at 37 littoral stations in 20 lakes distributed across the mining area of Rouyn-Noranda in northwestern Quebec. A multiple linear regression model including pH (+), dissolved Ca concentrations (-) and free Cd2+ concentrations at the sediment-water interface (+) explained 74% of the variability in Cd concentrations in the bivalve gills. Dissolved Ca (-) and free Cd2+ (+) together explained 62% of the variation in MT concentrations in the bivalve gills. Partial linear regression analyses indicated that the limnological factors' pure and shared effects together accounted for 48 and 45% of the total variation in Cd and MT concentrations in the gills, respectively. A lake selection procedure that could be applied in monitoring programs is proposed to minimise the relative influence of these confounding variables.     

Detecting Changes in Natural Resources Using Land Condition Trend Analysis Data

The Land Condition Trend Analysis (LCTA) program is the US Army's standard for land inventory and monitoring, employing standardized methods of natural resources data collection, analyses, and reporting designed to meet multiple goals and objectives. Critical to using LCTA data in natural resources management decisions is the ability of the LCTA protocols to detect changes in natural resources. To quantify the ability of LCTA protocols to detect resource changes, power analysis techniques were used to estimate minimum detectable effect sizes (MDES) for selected primary and secondary management variables for three Army installations. MDES for a subset of primary variables were estimated using data from 27 installation LCTA programs. MDES for primary and secondary variables varied widely. However, LCTA programs implemented at larger installations with lower sampling intensities detected changes in installation resources as well as programs implemented at smaller more intensively sampled installations. As a national monitoring program that is implemented at individual installations, LCTA protocols provide relatively consistent monitoring data to detect changes in resources despite diverse resource characteristics and implementation constraints.     

Pollutant removal efficacy of three wet detention ponds

Monthly inflow and outflow data were collected from three wet detention ponds in Wilmington, North Carolina, for a 29-mo period. Two ponds drained urban areas consisting primarily of residential, mixed services, and retail usage, while the third mainly drained residential and golf course areas. One of the urban ponds achieved significant reductions in total nitrogen, nitrate, ammonium, total phosphorus, orthophosphate, and fecal coliform bacterial counts. This pond was characterized by a high length to width ratio, with most inputs directed into the upper area, and extensive coverage by a diverse community of aquatic macrophyte vegetation. The second urban pond achieved significant reductions in turbidity and fecal coliform bacterial counts, but there were no significant differences between inflowing and outflowing water nutrient concentrations. There were substantial suburban runoff inputs entering the mid- and lower-pond areas that short-circuited pollutant removal contact time. The golf course pond showed significant increases in nitrate, ammonium, total phosphorus, and orthophosphate in the outflow relative to the inflow, probably as a result of course fertilization. However, nutrient concentrations in the outflow water were low compared with discharges from a selection of other area golf courses, possibly a result of the outflow passing through a wooded wetland following pond discharge. To achieve good reduction in a variety of pollutants, wet pond design should include maximizing the contact time of inflowing water with rooted vegetation and organic sediments. This can be achieved through a physical pond design that provides a high length to width ratio, and planting of native macrophyte species.     

Real-time, high-resolution quantitative measurement of multiple soil gas emissions: selected ion flow tube mass spectrometry

A new technique is presented for the rapid, high-resolution identification and quantification of multiple trace gases above soils, at concentrations down to 0.01 microL L(-1) (10 ppb). The technique, selected ion flow tube mass spectrometry (SIFT-MS), utilizes chemical ionization reagent ions that react with trace gases but not with the major air components (N2, O2, Ar, CO2). This allows the real-time measurement of multiple trace gases without the need for preconcentration, trapping, or chromatographic separation. The technique is demonstrated by monitoring the emission of ammonia and nitric oxide, and the search for volatile organics, above containerized soil samples treated with synthetic cattle urine. In this model system, NH3 emissions peaked after 24 h at 2000 nmol m(-2) s(-1) and integrated to approximately 7% of the urea N applied, while NO emissions peaked about 25 d after urine addition at approximately 140 nmol m(-2) s(-1) and integrated to approximately 10% of the applied urea N. The monitoring of organics along with NH3 and NO was demonstrated in soils treated with synthetic urine, pyridine, and dimethylamine. No emission of volatile nitrogen organics from the urine treatments was observed at levels >0.01% of the applied nitrogen. The SIFT method allows the simultaneous in situ measurement of multiple gas components with a high spatial resolution of < 10 cm and time resolution <20 s. These capabilities allow, for example, identification of emission hotspots, and measurement of localized and rapid variations above agricultural and contaminated soils, as well as integrated emissions over longer periods.     

Soil and litter phosphorus-31 nuclear magnetic resonance spectroscopy: extractants, metals, and phosphorus relaxation times

Phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy is an excellent tool with which to study soil organic P, allowing quantitative, comparative analysis of P forms. However, for 31P NMR to be tative, all peaks must be completely visible, and in their correct relative proportions. There must be no line broadening, and adequate delay times must be used to avoid saturation of peaks. The objective of this study was to examine the effects of extractants on delay times and peak saturation. Two samples (a forest litter and a mineral soil sample) and three extractants (0.25 M NaOH, NaOH plus Chelex (Bio-Rad Laboratories, Hercules, CA), and NaOH plus EDTA) were used to determine the differences in the concentration of P and cations solubilized by each extractant, and to measure spin-lattice (T1) relaxation times of P peaks in each extract. For both soil and litter, NaOH-Chelex extracted the lowest concentrations of P. For the litter sample, T1 values were short for all extractants due to the high Fe concentration remaining after extraction. For the soil sample, there were noticeable differences among the extractants. The NaOH-Chelex sample had less Fe and Mn remaining in solution after extraction than the other extractants, and the longest delay times used in the study, 6.4 s, were not long enough for quantitative analysis. Delay times of 1.5 to 2 s for the NaOH and NaOH-EDTA were adequate. Line broadening was highest in the NaOH extracts, which had the highest concentration of Fe. On the basis of these results, recommendations for future analyses of soil and litter samples by solution 31P NMR spectroscopy include: careful selection of an extractant; measurement of paramagnetic ions extracted with P; use of appropriate delay times and the minimum number of scans; and measurement of T1 values whenever possible.     

Relating net nitrogen input in the Mississippi River basin to nitrate flux in the lower Mississippi River: a comparison of approaches

A quantitative understanding of the relationship between terrestrial N inputs and riverine N flux can help guide conservation, policy, and adaptive management efforts aimed at preserving or restoring water quality. The objective of this study was to compare recently published approaches for relating terrestrial N inputs to the Mississippi River basin (MRB) with measured nitrate flux in the lower Mississippi River. Nitrogen inputs to and outputs from the MRB (1951 to 1996) were estimated from state-level annual agricultural production statistics and NOy (inorganic oxides of N) deposition estimates for 20 states that comprise 90% of the MRB. A model with water yield and gross N inputs accounted for 85% of the variation in observed annual nitrate flux in the lower Mississippi River, from 1960 to 1998, but tended to underestimate high nitrate flux and overestimate low nitrate flux. A model that used water yield and net anthropogenic nitrogen inputs (NANI) accounted for 95% of the variation in riverine N flux. The NANI approach accounted for N harvested in crops and assumed that crop harvest in excess of the nutritional needs of the humans and livestock in the basin would be exported from the basin. The U.S. White House Committee on Natural Resources and Environment (CENR) developed a more comprehensive N budget that included estimates of ammonia volatilization, denitrification, and exchanges with soil organic matter. The residual N in the CENR budget was weakly and negatively correlated with observed riverine nitrate flux. The CENR estimates of soil N mineralization and immobilization suggested that there were large (2000 kg N ha-1) net losses of soil organic N between 1951 and 1996. When the CENR N budget was modified by assuming that soil organic N levels have been relatively constant after 1950, and ammonia volatilization losses are redeposited within the basin, the trend of residual N closely matched temporal variation in NANI and was positively correlated with riverine nitrate flux in the lower Mississippi River. Based on results from applying these three modeling approaches, we conclude that although the NANI approach does not address several processes that influence the N cycle, it appears to focus on the terms that can be estimated with reasonable certainty and that are correlated with riverine N flux.     

Phosphorus budgets and riverine phosphorus export in northwestern Ohio watersheds

Phosphorus (P) budgets for large watersheds are often used to predict trends in riverine P export. To test such predictions, we calculated annual P budgets for 1975-1995 for soils of the Maumee and Sandusky watersheds of northwestern Ohio and compared them with riverine P export from these watersheds. Phosphorus inputs to the soils include fertilizers, manure, rainfall, and sludge while outputs include crop removal and nonpoint-source export via rivers. Annual P inputs decreased due to reductions in fertilizer and manure inputs. Annual outputs increased due to increasing crop yields. Net P accumulation decreased from peak values of 13.4 and 9.5 kg P ha(-1) yr(-1) to 3.7 and 2.6 kg P ha(-1) yr(-1) for the Maumee and Sandusky watersheds, respectively. Thus, P budget analysis suggests that riverine P export should have increased throughout the study period, with smaller increases during more recent years. However, detailed water quality studies show that riverine export of total phosphorus (TP) has decreased by 25 to 40% and soluble reactive phosphorus (SRP) by 60 to 89%, both due primarily to decreases from nonpoint sources. We suggest that these decreases are associated with farmers' adoption of practices that minimize transport of recently applied P fertilizer and of sediments via surface runoff, coupled with changes in winter weather conditions. In comparison with most Midwestern watersheds, rivers draining these watersheds have high unit area yields of TP, low unit area yields of SRP, and high ratios of nonpoint source- to point source-derived P.