ARE SOILS LIKE SPONGES?1

ABSTRACT: The purpose of this paper is to explore the validity of the old analogy that “soil is like a sponge.” Laboratory experiments were conducted to measure two hydrologic properties of porous media: drainage under gravity, and water potential curves. A tipping bucket rain gage connected to a data logger was used to measure the rate at which water drained under the force of gravity from a trough filled with four saturated porous media ‐ cellulose sponges, topsoil, peat, and a medium sand. Pressure plate techniques were used to determine water potential curves for soil materials and sponges. In terms of relative cumulative discharge from the trough, sponges were intermediate between peat and topsoil. Because of their tremendous water‐holding capacity, sponges discharged more than 2.5 times as much water as did peat. The water potential curve for sponges was fairly flat, like that of topsoil, but the high water content across all pressures (0.30–15.0 bars) indicated some similarity to peat. The results of these experiments suggest that the general patterns of water retention and release in soil materials and sponges are similar and vary only in degree.     

NUTRIENT LOAD CHARACTERIZATION FROM INTEGRATED SOURCE DATA FOR THE LOWER MISSISSIPPI RWER1

ABSTRACT: Nutrient data from all available sources for the lower Mississippi River were examined for potential differences among sampling agencies and geographic locations for the period between 1960 and 1998. Monthly means grouped by parameter, sampling location and agency, were calculated and compared as paired sets, excluding those months where data were not available for both sets. Some significant differences were found between various agencies collecting nutrient data on the river, as well as between various stretches of river, especially in the case of phosphorus nutrient data. Results were used to synthesize data sets from which a history of nutrient loading in the Mississippi River was determined. General trends in nitrate+nitrite, total Kjeldahl nitrogen, orthophosphate, total phosphorus and silica loads, as well as changes in nutrient proportions and the specific limiting nutrient (by month) are reported. This study provides a useful summary of contemporary and historical nutrient data that may assist in the evaluation of Mississippi River water quality and its potential effect on the Gulf of Mexico.     

Slope,aspect and climate: Spatially explicit and implicit models of topographic microclimate in chalk grassland

The slope and aspect of a vegetated surface strongly affects the amount of solar radiation intercepted by that surface. Solar radiation is the dominant component of the surface energy balance and influences ecologically critical factors of microclimate, including near-surface temperatures, evaporative demand and soil moisture content. It also determines the exposure of vegetation to photosynthetically active and ultra-violet wavelengths. Spatial variation in slope and aspect is therefore a key determinant of vegetation pattern, species distribution and ecosystem processes in many environments. Slope and aspect angle may vary considerably over distances of a few metres, and fine-scale species’ distribution patterns frequently follow these topographic patterns. The availability of suitable microclimate at such scales may be critical for the response of species distributions to climatic change at much larger spatial scales. However, quantifying the relevant microclimatic gradients is not straightforward, as the potential variation in solar radiation flux under clear-sky conditions is modified by local and regional variations in cloud cover, and interacts with long-wave radiation exchange, local meteorology and surface characteristics.     

A Bayesian approach to multi-source forest area estimation

In efforts such as land use change monitoring, carbon budgeting, and forecasting ecological conditions and timber supply, there is increasing demand for regional and national data layers depicting forest cover. These data layers must permit small area estimates of forest area and, most importantly, provide associated error estimates. This paper presents a model-based approach for coupling mid-resolution satellite imagery with plot-based forest inventory data to produce estimates of probability of forest and associated error at the pixel-level. The proposed Bayesian hierarchical model provides access to each pixel’s posterior predictive distribution allowing for a highly flexible analysis of pixel and multi-pixel areas of interest. The paper presents a trial using multiple dates of Landsat imagery and USDA Forest Service Forest Inventory and Analysis plot data. The results describe the spatial dependence structure within the trial site, provide pixel and multi-pixel summaries of probability of forest land use, and explore discretization schemes of the posterior predictive distributions to forest and non-forest classes. Model prediction results of a holdout set analysis suggest the proposed model provides high classification accuracy, 88%, for the trial site.

Trophic structure of coastal Antarctic food webs associated with changes in sea ice and food supply

Predicting the dynamics of ecosystems requires an understanding of how trophic interactions respond to environmental change. In Antarctic marine ecosystems, food web dynamics are inextricably linked to sea ice conditions that affect the nature and magnitude of primary food sources available to higher trophic levels. Recent attention on the changing sea ice conditions in polar seas highlights the need to better understand how marine food webs respond to changes in such broad-scale environmental drivers. This study investigated the importance of sea ice and advected primary food sources to the structure of benthic food webs in coastal Antarctica. We compared the isotopic composition of several seafloor taxa (including primary producers and invertebrates with a variety of feeding modes) that are widely distributed in the Antarctic. We assessed shifts in the trophic role of numerically dominant benthic omnivores at five coastal Ross Sea locations. These locations vary in primary productivity and food availability, due to their different levels of sea ice cover, and proximity to polynyas and advected primary production. The delta15N signatures and isotope mixing model results for the bivalves Laternula elliptica and Adamussium colbecki and the urchin Sterechinus neumeyeri indicate a shift from consumption of a higher proportion of detritus at locations with more permanent sea ice in the south to more freshly produced algal material associated with proximity to ice-free water in the north and east. The detrital pathways utilized by many benthic species may act to dampen the impacts of large seasonal fluctuations in the availability of primary production. The limiting relationship between sea ice distribution and in situ primary productivity emphasizes the role of connectivity and spatial subsidies of organic matter in fueling the food web. Our results begin to provide a basis for predicting how benthic ecosystems will respond to changes in sea ice persistence and extent along environmental gradients in the high Antarctic.     

The inflationary effects of environmental fluctuations ensure the persistence of sink metapopulations

Under current rates of environmental change many populations may be found in habitats of low quality and low conservation value, creating population sinks. We test recent theory that suggests, surprisingly, that stochastic environmental variability may enhance the long-term persistence of sink metapopulations. Using experimental populations of Paramecium aurelia we show that it is possible for a metapopulation comprised entirely of sink populations to persist for many generations in a random environment. In accordance with the theory, we show that positive temporal autocorrelation and low spatial correlation in the environment can ensure the long-term persistence and enhance the mean and maximum abundance of sink metapopulations. High levels of spatial correlation in the environment created strong population synchrony and limited the persistence time of the sink metapopulations. These results have important implications for the development of a theory underlying the synergistic effects of habitat fragmentation and environmental change on population persistence.     

State subsidies induce gray jays to accept greater danger: an ecologically rational response?

Models of strictly rational choice assume that decision-makers evaluate options on relevant dimensions, assign fixed values to options, and then make consistent choices based on these values. If so, recent experience would have no impact on preference. But, recent events change an animal’s state, and preference may change accordingly. We explore how state affects willingness to accept greater danger to obtain larger food rewards. We tested how a supplement in state (hoard size) impacts this willingness in gray jays (Perisoreus canadensis). When subsidized, most of the subjects increased their willingness to trade danger for food. Why would they become less cautious when their hoard was increased? Superficially, it might seem prudent to play it safer in response to a subsidy. But imagining fitness as a sigmoid function of state (hoard size) provides a tentative explanation for our counterintuitive finding. Above a threshold hoard size, a subsidy should weaken the willingness to accept extra danger. Incremental increases in state in the deceleratory phase yield smaller fitness gains, so it would pay to increase emphasis on safety after receiving a subsidy. But below this threshold, incremental increases in state in the acceleratory phase yield bigger fitness gains, and so it would pay to decrease emphasis on safety after receiving a subsidy. Most of our subjects’ choice behavior was, thus, plausibly consistent with the possibility that effective hoard size is considerably smaller than the total number of items stored. We speculate that this response may reflect an ecologically rational compensation for the inevitable loss of hoards via theft and rot.     

Healthcare waste management: current practices in selected healthcare facilities, Botswana

Healthcare waste management continues to present an array of challenges for developing countries, and Botswana is no exception. The possible impact of healthcare waste on public health and the environment has received a lot of attention such that Waste Management dedicated a special issue to the management of healthcare waste (Healthcare Wastes Management, 2005. Waste Management 25(6) 567-665). As the demand for more healthcare facilities increases, there is also an increase on waste generation from these facilities. This situation requires an organised system of healthcare waste management to curb public health risks as well as occupational hazards among healthcare workers as a result of poor waste management. This paper reviews current waste management practices at the healthcare facility level and proposes possible options for improvement in Botswana.     

Physical and chemical changes during composting of wood chip-bedded and straw-bedded beef cattle feedlot manure

In the 1990s, restrictions on incineration encouraged the forest industry in western Canada to develop new uses for their wood residuals by product. One such use was as a replacement for cereal straw bedding in southern Alberta's beef cattle (Bos taurus) feedlot industry. However, use of carbon (C)-rich bedding, such as wood chips, had implications for subsequent composting of the feedlot manure, a practice that was being increasingly adopted. In a 3-yr study, we compared composting of wood chip-bedded manure (WBM) and barley (Hordeum vulgare L.) straw-bedded manure (SBM). There were no significant differences in temperature regimes of SBM and WBM, indicating similar rates of successful composting. Of 17 physical and chemical parameters, five showed significant (P < 0.10) differences due to bedding at the outset of composting (Day 0), and 11 showed significant differences at final sampling (Day 124). During composting (10 sampling times), seven parameters showed significant bedding effects, 16 showed significant time effects, and four showed a Bedding x Time interaction. Significantly lower (P < 0.10) losses of nitrogen (N) occurred with WBM (19%) compared with SBM (34%), which has positive implications for air quality and use as a soil amendment. Other advantages of WBM compost included significantly higher total C (333 vs. 210 kg Mg(-1) for SBM) and inorganic N (1.3 vs. 1.0 kg Mg(-1) for SBM) and significantly lower total phosphorus (4.5 vs. 5.3 kg Mg(-1) for SBM). Our results showed that wood chip bedding should not be a problem for subsequent composting of the manure after pen cleaning. In combination with other benefits, our findings should encourage the adoption of wood chips over straw as a bedding choice for southern Alberta feedlots.     

An Evaluation of Techniques to Control Problem Bird Species on Landfill Sites

Birds feeding on landfill sites cause problems in terms of nuisance to neighbors, flight safety, a threat to public health, and affecting the day to day site operation. A number of control measures exist to deter problem species; however, research into their effectiveness across sites and for multiple species has been limited. We use a modeling approach in order to assess the effectiveness of nine techniques — pyrotechnics, hand-held distress calls, static distress calls, blank ammunition, a combination of blank and lethal use of ammunition, the use of falcons, the use of hawks, wailers and helium-filled bird-scaring kites — at deterring three commonly recorded species — the Black-headed Gull (Larus ridibundus), the Herring Gull (Larus argentatus) and the Lesser Black-backed Gull (Larus fuscus) — from six landfill sites across the United Kingdom. The use of distress calls, falconry, and combinations of lethal and nonlethal use of ammunition were the most effective techniques for initially deterring birds from these sites. However, when habituation is considered, there is a clear difference between techniques such as falconry, which have a lethal aspect and may act to reinforce the deterrence, and the use of techniques such as distress calls, which do not. However there are problems related to legislation and public perception when lethal techniques are used.