Douglas I. Moore

Statistics of Surface-Layer Turbulence Over Terrain with Metre-Scale Heterogeneity

Refuge has patchy vegetation in sandy soil. During midday and at night, the surface sources and sinks for heat and moisture may thus be different. Although the Sevilleta is broad and level, its metre-scale heterogeneity could therefore violate an assumption on which Monin-Obukhov similarity theory (MOST) relies. To test the applicability of MOST in such a setting, we measured the standard deviations of vertical (σw) and longitudinal velocity (σu), temperature (σt), and humidity (σq), the temperature-humidity covariance (¯tq), and the temperature skewness (St). Dividing the former five quantities by the appropriate flux scales (u*, *, and q*) yielded the nondimensional statistics σw/u*, σu/u*, σt/|t*|, σq/|q*|, and ¯tq/t*q*. σw/u*, σt/|t*|, and St have magnitudes and variations with stability similar to those reported in the literature and, thus, seem to obey MOST. Though σu/u* is often presumed not to obey MOST, our σu/u* data also agree with MOST scaling arguments. While σq/|q*| has the same dependence on stability as σt/|t*|, its magnitude is 28% larger. When we ignore ¯tq/t*q* values measured during sunrise and sunset transitions – when MOST is not expected to apply – this statistic has essentially the same magnitude and stability dependence as (σt/t*)2. In a flow that truly obeys MOST, (σt/t*)2, (σq/q*)2, and ¯tq/t*q* should all have the same functional form. That (σq/q*)2 differs from the other two suggests that the Sevilleta has an interesting surface not compatible with MOST. The sources of humidity reflect the patchiness while, despite the patchiness, the sources of heat seem uniformly distributed.

New opportunities in ecological sensing using wireless sensor networks

Measuring environmental variables at appropriate temporal and spatial scales remains an important challenge in ecological research. New developments in wireless sensors and sensor networks will free ecologists from a wired world and revolutionize our ability to study ecological systems at relevant scales. In addition, sensor networks can analyze and manipulate the data they collect, thereby moving data processing from the end user to the sensor network itself. Such embedded processing will allow sensor networks to perform data analysis procedures, identify outlier data, alter sampling regimes, and ultimately control experimental infrastructure. We illustrate this capability using a wireless sensor network, the Sensor Web, in a study of microclimate variation under shrubs in the Chihuahuan Desert. Using Sensor Web data, we propose simple analytical protocols for assessing data quality “on-the-fly” that can be programmed into sensor networks. The ecological community can influence the evolution of environmental sensor networks by working across disciplines to infuse new ideas into sensor network development.

Strontium isotope studies of atmospheric inputs to forested watersheds in New Mexico

Stable isotopes of strontium provide a unique quantification of ecosystem processes because organisms do not differentiate between them. For landscapes with contrasting geologies, these isotopes can identify atmospheric source material from local weathered material. This study quantified the input of strontium, distribution within the ecosystem, canopy capture versus leaf leachate, canopy loss, and Sr increment in biomass from an atmospheric origin. Forest ecosystems were studied along an elevational gradient in New Mexico. Spruce forests had a much greater capacity for capturing atmospheric Sr than aspen forests; however, aspen contained more total atmospheric Sr in their tissues because of greater uptake rates and the ability to utilize atmospheric deposited Sr before the initiation of the aspen forest. This technique has excellent capabilities for estimating the relative importance of atmospheric and weathering inputs to certain ecosystems.

Using Strontium Isotope Ratios to Estimate Inputs to Ecosystems

Forest canopies can collect nutrients from the atmosphere, but the magnitude is difficult to quantify. Natural isotopes of strontium (87Sr/86Sr) can be used to quantify instantaneous atmospheric inputs and their net accumulation over successional time, identify the distribution and movement of atmospheric inputs within the ecosystem, and quantify weathering inputs. (Accepted for publication 23 June 1982)

Lightning Estimates of Precipitation Location and Quantity on the Sevilleta Lter, New Mexico

Typically, 50-70% of the total annual precipitation in New Mexico can be produced by convective thunderstorms during the period June through September. These thunderstorms are accompanied by intense lightning and characteristically produce heavy, localized rainfall resulting in high spatial variation in precipitation inputs. During other months precipitation over the entire Sevilleta (105 ha) often occurs from broad-scale storm systems and is much less spatially variable on a per-storm basis. Summer precipitation is a primary factor driving plant productivity as well as influencing nutrient cycling, herbivore activity, and detritivore activity. Knowledge of the timing, location, and amounts of precipitation is important in planning or monitoring research activities and spatial modeling of the dynamics in this semiarid region. Technology exists for locating cloud-to-ground lightning strikes that has the potential to locate these intense precipitation events, quantify the volume of water associated with them, and document the spatial and temporal variability of this phenomenon over large areas. Near real-time analysis capability can identify areas receiving precipitation that will experience rapid vegetation growth in this semiarid region. This study developed algorithms relating lightning and precipitation quantity and used lightning location to determine rainfall depth and distribution for areas in New Mexico. There was a significant correlation between rain-gauge measured precipitation and lightning within a 3-km radius of the gauge location, with best predictions occurring from regressions that included lightning strikes and relative humidity. Average precipitation volume per cloud-to-ground lightning strike averaged 36 190 m3 for the 3 km radius circle, resulting in an average rainfall depth of 1.3 mm per lightning strike. Lightning location technology, combined with a Geographic Information System (GIS), defined the spatial and temporal resolution of these intense, summer precipitation patterns and provided a more detailed estimate of total precipitation and precipitation distribution than was provided by the sparse network of precipitation gauges. Combining this information with satellite sensing of vegetation growth (e.g., greenness index) can identify causal mechanisms for temporal and spatial patterns in short-term vegetation processes (e.g., primary production) and long-term vegetation dynamics for this area.

Stability Dependence of the Eddy-Accumulation Coefficients for Momentum and Scalars

From a set of turbulence data collected with a three-axis sonic anemometer/thermometer and described in a companion paper, we simulate the eddy-accumulation process for sensible heat and momentum fluxes. The resulting eddy-accumulation coefficient for momentum clearly depends on surface-layer stability; at neutral stability, its value is 0.63. On supplementing the scalar eddy-accumulation coefficients that we derive from our sensible heat flux data with values of sensible and latent heat flux coefficients reported by Businger and Oncley, we also find that scalar eddy-accumulation coefficients depend on stability, though more weakly than does the momentum coefficient. The coefficients for sensible and latent heat show no significant difference; we, thus, fit them with one function of stability whose value is 0.52 for neutral stratification.

Regional-scale drought increases potential soil fertility in semiarid grasslands

Although drying of soil has increased fertility in laboratory-based experiments, a direct link between longer-scale weather conditions associated with drought and soil fertility has not been documented at the field scale. Soil from a semiarid grassland on the Sevilleta National Wildlife Refuge (NWR) that was collected over a 10-year period had the highest levels of potentially mineralizable nitrogen (PMN, a measure of potential soil fertility) during drought periods in 1989 and 1995. Whereas previous soil collections on the Sevilleta NWR were made for different reasons, soils were collected in June 2002 near the peak of a regional-scale drought to test the hypothesis that potential soil fertility increased with drought. Another semiarid grassland site, the Bernalillo Watershed, was sampled to extend the spatial extent of the analysis. The 2002 collections showed soil PMN near the highest at both sites, thereby supporting the hypothesis. Longer-term PMN data at both sites were correlated with the Palmer Drought Index (PDI), a regional-scale index with drier periods given negative values. Over a 13-year period, the Sevilleta soils had higher PMN during periods of drought (r =−0.533, P <0.05). Although not significant, a similar trend was shown over an 8-year record at the Bernalillo Watershed (r =−0.356, not significant). Also, PMN levels measured during a previous 3-year wet-to-drought period at another semiarid grassland site on the Sevilleta NWR were highly significantly correlated with the PDI (r =−0.723, P <0.01). Thus, drought can increase soil fertility, which can alter additional ecosystem processes.

Seasonal, annual, and treatment-induced variation in available nitrogen pools and nitrogen-cycling processes in soils of two Douglas-fir stands

SummaryForest-floor and 0–10 cm depth mineral soil horizons in two stands of Douglas fir were sampled for available NH4+-N and NO3−-N, N-mineralization potentials, and nitrification potentials for 2 years. The plots in each stand were sampled for 1 year, treated with either ammonium sulfate, carbohydrate (sawdust-sucrose), irrigation, carbohydrate plus irrigation, or no treatment (control), and then sampled for 1 year following treatment. In general, the direction of change following the treatments was the same for both the forest-floor and the mineral soils. Fertilization increased the NH4+-N and NO3−-N pools, nitrification potential, and N-mineralization potential, while treatment with carbohydrate decreased all of these characteristics. Irrigation generally increased NH4+-N pools, nitrification potential, and N-mineralization potential, but decreased these characteristics in the soil at one site. Irrigation plus carbohydrate gave similar results to those of carbohydrate alone. Treatments altered pool sizes and/or potentials, but did not reduce within-year variance in any of these characteristics. Distinct seasonal patterns occurred in all measurements, suggesting that control of short-term variation in N-transformation processes is by factors which are dynamic in nature.

Nitrogen mineralization-immobilization response to field N or C perturbations: An evaluation of a theoretical model

Abstract N (as ammonium sulfate) or C (as a sucrose-sawdust mixture) were added to plots in two Douglas-fir stands. Perturbation response was measured as the difference between net N mineralization potentials of perturbed plots and potentials of associated control plots on five occasions during the subsequent 2 yr. In 5 out of 8 comparisons, N-dynamics demonstrated one or more oscillations between net mineralization and net immobilization. Thus, immobilization or net mineralization could be detected after addition of N or C dependent upon the time and frequency of sampling. This suggests that the status of the substrate relative to energy or nutrient limitations largely determines the response to perturbation, and that frequent sampling after perturbation is necessary to describe N-dynamics.

Field testing long-path Fourier transform infrared (FTIR) spectroscopy for measurements of atmospheric gas concentrations

Abstract The long-path capabilities of Fourier-transform infrared (FTIR) spectroscopy allow field measurements of trace gas concentrations over spatial scales intermediate between those commonly used by biologists (10 cm-10 m) and climatologists (> 200 km). These intermediate scale measurements are critical to relate small plot findings to data on regional dynamics obtained by remote sensing from space. Both natural and agricultural environments are heterogeneous and complex. Broad scale measurements that integrate the variability both spatially and temporally are needed to correctly assess biospheric/atmospheric interactions. This paper describes long-path FTIR and an initial field test of the system over a 400 m optical path in a relatively uniform cotton field at the Maricopa Experiment Station in Arizona. Data for water vapor, CO 2 and N 2 O demonstrated different responses over a 10-h period, suggesting different activities in the processes responsible for these gas emissions. The long-path data also demonstrate the reduction in variation attributable to the integration of fine-scale variation in biological processes.