Long-Term Ecological Research Project Research Articles

Identifying ephemeral and perennial stream reaches using apparent thermal inertia of an ungauged basin in Central New Mexico

The night and day temperature images from advanced spaceborne thermal emission and reflection radiometer (ASTER) remote sensing images are used to identify ephemeral and perennial stream reaches for use in the calibration of an integrated hydrologic model of an ungauged basin. The concept is based on apparent thermal inertia [ATI = (1-albedo)/(day temperature − night temperature)]. These calculations help both the conceptual model and the calibration for the hydrologic model by indicating where there are thin alluvium and/or shallow groundwater. The study is on the Sevilleta National Wildlife Refuge, a long-term ecological research project that ASTER has included in its regular duty cycle. There are over 360 ASTER scenes in 8 years; however, only 10 night/day pairs suitable for ATI were found. The results correlate to the soil moisture recorded at two locations near the channel (R 2 of 0.88). The relationship between soil moisture and surrounding materials allows for differentiation of the perennial and ephemeral stream reaches.

The enterprising evaluation for the Korean National Long-Term Ecological Research (KNLTER) Project for six years (Review)

The Korean National Long-Term Ecological Research (KNLTER) project seeks to predict the effects on Korean ecosystems caused by stress derived from environmental changes from a national perspective. The objective of this article about the KNLTER program, continuously supported by the Ministry of Environment (MOE) since 2004, was to inspect the general plans and to evaluate the project for the KNLTER program objectively, and to make suggestions about the developmental direction of the project. As a result of evaluation on the research site, the numbers of research sites in 2010 correspond to 50% of those presented in the basic plan of the KNLTER project. As a result of evaluation on the research contents in the terrestrial ecosystem section of the KNLTER project, monitoring of climatic and atmospheric changes using eco-towers should be conducted over a long-term period. Additionally, the soil respiration part of the study needs to be expanded further in order to better understand soil systems. In the freshwater ecosystem section, we need to establish common standard investigation items, which can be used as indicators of the actual freshwater environment, considering that freshwater ecosystem management is closely related to human life. In the coastal ecosystem section, we should intensively analyze the correlation between the collected data accumulated thus far, as well as environmental changes including climate change, pollution, etc. For very sensible cases such as topographic changes due to rises in sea level, we should generate data applicable to prediction and confrontation for future changes through the continuous addition of variables and applications of a variety of simulation methods. In the animal ecology section, we should evaluate ecosystem changes based on animal phenology by selecting indicator animal species, which can be applied to each relevant ecosystem: namely, terrestrial, freshwater, and coastal ecosystems. As a result of synthetic evaluation conducted under the auspices of KNLTER, the stability of study areas is frequently implicated as the most common problem. If private lands are designated as study sites, it is very difficult to maintain them as study sites for a prolonged period. Therefore, it is necessary to designate national and public lands, such as national or provincial parks, as study sites. Efforts thus far conducted toward the construction of an appropriate database and modeling studies remain insufficient. After investigating the phenology of the specific species growing in all research sites, it is necessary to assess and report the overall changes in Korean ecosystems by applying that knowledge. The collection, analysis, and systematization of recent domestic and foreign research data related to natural ecosystem changes owing to environmental changes such as climate change and environmental pollution have been insufficient. Therefore, studies performed to obtain this information should be continuously pursued in the third stage.

Spatial variations in the geochemistry of glacial meltwater streams in the Taylor Valley, Antarctica

AbstractStreams in the McMurdo Dry Valleys, Antarctica, flow during the summer melt season (4–12 weeks) when air temperatures are close to the freezing point of water. Because of the low precipitation rates, streams originate from glacial meltwater and flow to closed-basin lakes on the valley floor. Water samples have been collected from the streams in the Dry Valleys since the start of the McMurdo Dry Valleys Long-Term Ecological Research project in 1993 and these have been analysed for ions and nutrient chemistry. Controls such as landscape position, morphology of the channels, and biotic and abiotic processes are thought to influence the stream chemistry. Sea-salt derived ions tend to be higher in streams that are closer to the ocean and those streams that drain the Taylor Glacier in western Taylor Valley. Chemical weathering is an important process influencing stream chemistry throughout the Dry Valleys. Nutrient availability is dependent on landscape age and varies with distance from the coast. The streams in Taylor Valley span a wide range in composition and total dissolved solids and are surprisingly similar to a wide range of much larger temperate and tropical river systems.

Long-term research impacts on seedling community structure and composition in a permanent forest plot

Long-term ecological research projects have become cornerstones for the study of forest dynamics worldwide. The intense, large-scale research efforts necessary to monitor ecological processes may alter natural processes and be a source of error in analyses. This study evaluated whether trampling due to concentrated researcher presence has altered the structure and composition of the seedling layer in the 50 ha permanent sample plot on Barro Colorado Island (BCI), Panama. Since 1980, major research projects in the plot have included complete tree censuses every 5 years, weekly seed trap collection, and the more recent annual censuses of 20,000 1 m 2 seedling quadrats. We compared data from these pre-existing seedling quadrats with data from 600 newly established seedling quadrats in an area of much lower research intensity adjacent to the 50 ha plot and tested for differences in seedling density, height-class distributions, species richness and composition. Although we expected to find evidence of researcher impacts on the seedling layer, we found no significant differences in seedling community structure or composition inside and outside of the BCI 50 ha plot. We conclude that there is no evidence that research efforts within the BCI plot have thus far resulted in significant changes in the seedling layer. The extent of research impacts is likely to differ under varying environmental conditions and research protocols. Continued efforts should be made to quantify the impacts of research methodology at long-term research sites in order to detect site-specific or long-term changes.

Simulating the dynamics of primary productivity of a Sonoran ecosystem: Model parameterization and validation

Modeling has played a crucial role in understanding the structural and functional dynamics of forest and grassland ecosystems in the past decades, but relatively few ecosystem models have been developed for deserts. Adapting an existing desert ecosystem model to new regions with different community components and environmental settings may testify to the generality of model applicability, further verify model structure and formulations, and provide new insight into understanding desert ecosystem functioning. In this paper, we use a desert ecosystem model that was originally developed for the Chihuahuan Desert, Patch Arid Land Simulator-Functional Types (PALS-FT), to estimate the aboveground annual net primary productivity (ANPP) of a creosotebush ( Larrea tridentata)-dominated Sonoran Desert ecosystem in the Phoenix metropolitan area, home to the Central Arizona-Phoenix Long-Term Ecological Research Project (CAP LTER). We modified and parameterized the model using meteorological data, ecophysiological parameters for different plant functional types, and site characteristic data from the CAP LTER study area and an independent test site in the San Simon Valley of southeastern Arizona. Model predictions were validated and calibrated using field observations from the San Simon Valley test site. The results showed that PALS-FT was able to simulate ANPP of this typical Sonoran Desert ecosystem reasonably well, with a relative error of ±2.4% at the ecosystem level and generally less than ±25% at the functional-type level. We then used the model to simulate ANPP and its seasonal and inter-annual dynamics for a similar ecosystem in the CAP LTER study area. The model predicted average annual ANPP of 72.3 g m −2 y −1, ranging from 11.3 g m −2 y −1 to 229.6 g m −2 y −1 in a 15-year simulation. The simulated average ANPP of the Sonoran Desert ecosystem is close to field observations in other areas of the Sonoran Desert, and the range of variation also is close to that reported by other researchers for arid and semiarid ecosystems. The dynamics of ecosystem ANPP in response to fluctuations in annual precipitation simulated by the model agreed well with the known relationship between ANPP and precipitation in arid and semiarid systems. A closer examination of this relationship at the level of plant functional types further revealed that seasonal distribution of rainfall significantly affected ANPP. A comparison between the PALS-FT model prediction and two regression models for North American warm deserts showed that both regression models underestimated the Larrea ecosystem ANPP, while the process-based PALS-FT model provided the most accurate prediction among the three models. This study provides a validation for use of the PALS-FT model to investigate Sonoran desert ecosystem responses to environmental changes.

RAPELD: a modification of the Gentry method for biodiversity surveys in long-term ecological research sites

Our objectives were to develop a method that would be appropriate for long-term ecological studies, but that would permit rapid surveys to evaluate biotic complementarity and land-use planning in Amazonia. The Amazon basin covers about 7 million km². Therefore, even a sparse coverage, with one sample site per 10.000 km², would require about 700 sampling sites. Financial considerations limit the number of sites and investment at each site, but incomplete coverage makes evaluation of biotic complementarity difficult or impossible (Reddy & Dávalos 2003). Our next challenge is to install similar systems throughout Amazonia. The cost, based on modification of Al Gentry's original design is moderate (less than US$ 50.000 per site if it is not necessary to immediately identify all vascular plants in plots) and we can obtain RAP results for most taxa in the short term at much lower cost. However, biological surveys will only be relevant if the local people participate and the surveys serve as much to teach the local communities about the value of their natural resources as they serve to teach the international community about biodiversity. Therefore, we want to see each site run as a long-term ecological research project by local people and institutions. Biological surveys are an important tool in land-use planning, but only the local people can implement those plans.

Nitrogen input from residential lawn care practices in suburban watersheds in Baltimore county, MD

A residential lawn care survey was conducted as part of the Baltimore Ecosystem Study, a Long-term Ecological Research project funded by the National Science Foundation and collaborating agencies, to estimate the nitrogen input to urban watersheds from lawn care practices. The variability in the fertilizer N application rates and the factors affecting the application rates were examined. Results indicated that the annual input of nitrogen from fertilizer is a major component of the urban watershed nitrogen budget and it is both spatially and temporally variable. There is a wide range in the application rate of fertilizer N to residential lawns applied by homeowners and by professional lawn care companies. Survey data estimated a mean fertilizer application rate of 97.6 kg N/ha/yr with a standard deviation of 88.3 kg N/ha/yr. Analyses suggested that the fertilizer application rate is affected by social economic factors and soil characteristics to include the market value of the house, age of development, soil bulk density and soil nitrogen content.

URBANIZATION AND SPIDER DIVERSITY: INFLUENCES OF HUMAN MODIFICATION OF HABITAT STRUCTURE AND PRODUCTIVITY

As a part of the Central Arizona–Phoenix Long-Term Ecological Research project, we determined how land-use alteration influenced spider and harvestman diversity. We sampled spiders in six habitat types (desert parks, urban desert remnants, industrial, agricultural, xeric- and mesic-residential yards) and tested how habitat type and productivity affected spider diversity and abundance. As expected, agricultural fields and mesic yards were more productive than the other, xeric habitats. These more productive habitats were characterized by higher abundances but lower spider diversity and were dominated by Lycosidae (wolf spiders), followed by Linyphiidae (sheet-web weavers). The increase in wolf spider abundance was positively correlated with habitat productivity and negatively correlated with the abundance of other predatory arthropods that might compete with, or prey upon, wolf spiders. Temporal changes in productivity affected spider abundance. After an El-Niño winter (May 1998), spider abundance was five times higher than after an extremely dry winter (May 2000). The differences in spider abundance between agricultural fields and the four xeric habitats were profound in 2000 but moderate in 1998, suggesting an interaction between the effects of natural and anthropogenic factors on spider populations. Compared with xeric habitats, the El-Niño effect was less profound in agricultural sites, suggesting that human land modification mollifies seasonal effects. We suggest that habitat structure and productivity alteration may change community structure, as the urban or agricultural habitats favor one or a few preadapted taxa over many others. Incorporation of large fragments of natural habitats into future landscape planning in urban environments may be important for conservation of rich spider communities.

Effects of haying on salt-marsh surface invertebrates.

Marsh plants may affect the structure of epibenthic communities in a variety of ways. They might reduce temperature stress on organisms by shading, provide refuge from predators, increase the rate of organic matter accumulation at the sediment surface, and serve as a food source. Thus, salt marsh plants might control the spatial distributions of epibenthic invertebrates within the marsh. An ongoing “experiment” on the impact of the periodic removal of plants has been carried out by New England farmers who have been haying some salt marshes for over 300 years. Earlier research by the Plum Island Estuary Long-Term Ecological Research project (PIE-LTER) has shown that haying causes a short-term increase in the growth of benthic algae (1), causes a shift in the diet of some marsh invertebrates to a greater percentage of algae (2), and results in a change in plant species composition (PIE-LTER, unpubl. results). To determine the shortand long-term effects of haying on the epibenthic community and to identify the principal variables controlling the distribution of epibenthic invertebrates, we carried out two sets of experiments: a marsh-grass-removal experiment to mimic the effects of haying and a survey of invertebrates in areas of the marsh subjected to different haying schedules. Our work was conducted in the Plum Island Sound estuary in Rowley, Massachusetts, from June to August 2002. For our marsh-grass-removal experiment, we clipped and removed the vegetation from three randomly selected circular sites of 3-m radius along a 50-m transect in a marsh that is hayed roughly every other year. Before clipping we counted organisms in four 0.25-m sampling areas, located 1.5 m from the center of the circle and equidistant from each other, within each of the three sites. We sampled the same four areas within each site immediately before clipping, and 1 and 4 days after clipping. Differences in abundances of organisms before and after clipping were evaluated by the Kruskal-Wallis test with time of sampling as treatment. Because differences among circular hayed sites were not significantly different, we pooled replicates from each site before our analysis. For our surveys of invertebrates in areas subjected to different intensities of haying, we examined randomly selected sites in recently hayed and reference marshes along 12 previously established transects for which GPS elevation data were available. We sampled 40 sites between 1 and 3 July, and 40 more between 16 and 18 July. At each site, we visually estimated percent cover of different plant species. A count of organisms was made after clipping all vegetation from 0.25-m plots. A 177-cm plant sample was collected, live biomass was separated from standing dead biomass and weighed separately to determine above-ground biomass. Commonly encountered plants included Spartina patens, Spartina alterniflora, Distichlis spicata, Salicornia europaea, and Juncus gerardi. To evaluate the effect of plant cover on predation rate, we tethered amphipods, Orchestia grillus, to thin-diameter line and deployed 5 per site at most sites for 24 h before clipping. We used stepwise multiple regression to describe the relationship between measured environmental variables and abundance of epifauna for the 16–18 July sampling period (criteria P 0.1 to accept, P 0.25 to reject). Environmental variables used in stepwise multiple regression were haying frequency, elevation, temperature, humidity, dried live plant biomass, dried standing dead, total dried weight, percent live, percent dead, percent bare, percent S. alterniflora, percent S. patens, percent D. spicata, percent S. europaea, percent Atriplex patula, percent Triglochin maritima, percent Iva frutescens, proportion tethered live amphipods, and proportion eaten tethered amphipods. Collinearity among environmental variables was assessed by examining the variance inflation factor for each included variable. All variance inflation factors were less than 2, which indicated that collinearity among independent variables did not significantly affect our results. A few sampling sites were omitted from the regression analysis due to missing data. Analyses were performed using SPSS software.

Glacial meltwater dynamics in coastal waters west of the Antarctic peninsula.

The annual advance and retreat of sea ice has been considered a major physical determinant of spatial and temporal changes in the structure of the Antarctic coastal marine ecosystem. However, the role of glacial meltwater on the hydrography of the Antarctic Peninsula ecosystem has been largely ignored, and the resulting biological effects have only been considered within a few kilometers from shore. Through several lines of evidence collected in conjunction with the Palmer Station Long-Term Ecological Research Project, we show that the freshening and warming of the coastal surface water over the summer months is influenced not solely by sea ice melt, as suggested by the literature, but largely by the influx of glacial meltwater. Moreover, the seasonal variability in the amount and extent of the glacial meltwater plume plays a critical role in the functioning of the biota by influencing the physical dynamics of the water (e.g., water column stratification, nearshore turbidity). From nearly a decade of observations (1991-1999), the presence of surface meltwater is correlated not only to phytoplankton blooms nearshore, but spatially over 100 km offshore. The amount of meltwater will also have important secondary effects on the ecosystem by influencing the timing of sea ice formation. Because air temperatures are statistically increasing along the Antarctic Peninsula region, the presence of glacial meltwater is likely to become more prevalent in these surface waters and continue to play an ever-increasing role in driving this fragile ecosystem.

Human Dimensions of Ecosystem Studies

Over the course of this century, academic life has progressed in such a manner that scholars who formerly approached inquires from a broad perspective now often constrain themselves within the boundaries of a single discipline. This trend has been a response to the need to effectively engage one’s subject matter by developing specialized methodologies, vocabularies, and expectations. Whereas this specialization has proved to be a successful approach for many inquiries, it has also acted to divide scholars in both their training and their investigations. Nowhere has this trend been more pronounced than in environmental sciences whose subject matter naturally divides itself into four domains: biotic, human, geologic, and ‘‘built’’ (Figure 1). Despite well-entrenched disciplinary divisions, most practicing scientists recognize that when treating a comprehensive subject, like human ecosystems, inquiries can not be effectively pursued by specialists working in one of these domains in isolation from the others. For it is by working at the junction of these domains that processes can be best understood and the greatest scientific breakthroughs will be made. Yet, building intellectual bridges between the life, earth, engineering, and social sciences remains extremely difficult. To each of us with our own disciplinary training ‘‘human–environmental interactions’’ has come to mean something quite distinct. For sociologists the ‘‘environment’’ is the social conditions created by humans, for anthropologists the interaction focuses on subsistence pursuits, and for the biologists human participation in an ecosystem is often viewed as a ‘‘disturbance.’’ Yet, increasingly people trained in each of these perspectives are recognizing the value—no, the necessity—of bridging these disciplinary chasms to create a new means of synthesis. This article reports on the efforts being made by the Central Arizona-Phoenix Long-Term Ecological Research (CAPLTER) project to build these bridges. In a special section of a recent issue of the journal Science several distinguished ecologists reached the conclusion that ‘‘most aspects of the structure and functioning of Earth’s ecosystems cannot be understood without accounting for the strong, often dominant influence of humanity’’ (Vitousek and others 1997, p 494). Furthermore, in a letter to the editor of Science only a few months ago, 20 prominent ecologists called for their colleagues to devote increased energy to understanding and better managing human influences over ecosystem function (Bazzaz and others 1998). Ecologists have long recognized that humans have had significant impacts on their study areas, but these have most often been treated as a form of external disturbance. Although adequate in some respects, it underestimates the pervasiveness and complexity of human influence. To truly understand human actions and influences upon ecosystems, it is essential to thoroughly integrate the approaches developed in the social and economic sciences with those of life and earth scientists. Recognition that ecosystems are affected by biological, geological (including climate), and human (both social and engineering) forces is a first step in the process of integration. Although most ecologists acknowledge that there are fundamental ‘‘drivers’’ behind biological and geological processes, they have little familiarity with the ‘‘drivers’’ behind human action. Without taking into account these drivers and the interactions they engender, our understanding of ecosystem dynamics both at the Received 18 February 1999; accepted 3 March 1999. E-mail: charles.redman@asu.edu Ecosystems (1999) 2: 296–298 ECOSYSTEMS r 1999 Springer-Verlag

Time Series Analyses of Suspended Sediment Concentrations at North Inlet, South Carolina

Daily water samples have been collected at three stations in the North Inlet (South Carolina) marshestuary system since February 1981 as part of the NSF Long-Term Ecological Research (LTER) project. As a result of this sampling regime, nearly continuous time series of inorganic and organic suspended sediment, particulate organic carbon (POC), Secchi disk, salinity, and water temperature are now available. Power spectrum analysis of these data reveals that most of the explainable variance in the inorganic suspended sediment, POC, and Secchi disk data is related to a yearly cycle that is strongly coherent with water temperature such that high turbidity is associated with high water temperature. Only a small fraction of the explainable variance is associated with frequencies that can be related to the semidiurnal tide. Simple correlation analysis also indicates that turbidity is more closely associated with water temperature than with tide height or salinity. The ratio of POC to inorganic suspended sediment shows no discernible power spectra peaks and is weakly, but inversely, correlated with temperature. From these results we hypothesize that temperature-regulated bioturbation is the main factor controlling turbidity variations in the system. The lack of a strong inverse correlation between turbidity and salinity suggests that river runoff has little immediate impact on the suspended sediment of nearshore coastal waters in systems similar to North Inlet.