Contemporary estimates of atmospheric nitrogen deposition to the watersheds of New York State, USA

Atmospheric inputs of reactive nitrogen (N) to ecosystems are a particular concern in the northeastern USA, including New York State, where rates of atmospheric N deposition are among the highest in the nation. We calculate the seasonal and annual spatial variations of contemporary inorganic atmospheric N deposition loading to multi-scale watersheds across New York State using numerous monitoring datasets of precipitation and ambient atmospheric N concentrations. Our models build upon and refine previous efforts estimating the spatial distribution of N deposition. Estimates of total inorganic wet deposition (NH4-N + NO3-N) across New York ranged from 4.7 to 10.5 kg ha(-1) yr(-1) under contemporary conditions (averaged 2002-2004), and both seasonal and annual predicted rates of inorganic N deposition (NH4-N, NO3-N, and total) fit relatively well with that of observed measurements. Our results suggest that "hot spots" of N deposition are, for the most part, spatially distributed according to geographic positions (i.e., relative location from sources and the Great Lakes system) and elevation. We also detect seasonal variations in deposition, showing that total wet atmospheric inorganic N deposition inputs to watersheds (extracted from the four-digit HUC calculations) are highest during the spring (mean = 2.4 kg ha(-1), stddev = 0.29) and lowest during the winter months (mean = 1.4 kg ha(-1), stddev = 0.23). Results also suggest that wet NO3(-) consistently comprises a slightly higher proportion of wet N deposition than wet NH4+ throughout watersheds of New York, ranging from 2.5 to 6.1 kg NO3-N ha(-1) yr(-1) compared to NH4+, which ranges from 2.2 to 4.4 kg NH4-N ha(-1) yr(-1).     

Does a polyandrous honeybee queen improve through patriline diversity the activity of her colony’s scouting foragers?

Recent studies indicate that the foraging success of a honeybee colony is enhanced when it has numerous genetically diverse patrilines because of queen polyandry. We determined whether foraging is improved in part because patriline diversity generates more responsive populations of scouting foragers. Scouts search for new food sources and advertise them with waggle dances to inform other foragers about unexploited discoveries. We moved multiple-patriline and single-patriline colonies to unfamiliar locations so that colonies relied heavily on successful scouts to initiate recruitment and then compared the development of foraging effort between the two types of colonies. More waggle dance signals were produced during the incipient stages of foraging in multiple-patriline colonies compared to single-patriline colonies because scouts reported food discoveries with longer dances. Scouts also returned to multiple-patriline colonies at rates that were two thirds higher than those of single-patriline colonies, although return rates for general forager populations were not significantly different between colony types. The distance of reported food sources from hives increased with time for all colonies, but by the end of their first day in an unfamiliar environment, maximal foraging reach was greater if colonies had multiple patrilines. Most scouts in multiple-patriline colonies came from a minority of scout-rich patrilines that were generally not those from which general forager populations were derived; the presence of such scout-rich patrilines was correlated with the extent of recruitment signaling in colonies. We show how a honeybee colony’s scouting effort is (and is not) enhanced when extremely polyandrous queens produce genetically diverse colonies.     

Quantifying ecological thresholds from response surfaces

Ecological thresholds are abrupt changes of ecological state. While an ecological threshold is a widely accepted concept, most empirical methods detect them in time or across geographic space. Although useful, these approaches do not quantify the direct drivers of threshold response. Causal understanding of thresholds detected empirically requires their investigation in a multi-factor domain containing the direct drivers (often referred to as state space). Here, we present an approach to quantify thresholds from response surfaces modeled empirically in state space. We present two indices of shape attributes measured from response surfaces. The response surfaces are built using a regression method in state space. The indices are threshold strength (T) and diagonality (D). We use 48 simulated response surfaces of different shapes to test the efficacy of the indices in 3D. Our results show that T is sensitive to the steepness of the transition from one state to the next, with various forms of abrupt, centralized thresholds yielding the highest values among the simulated surfaces. D represents the orientation of the response surface or the simultaneous influence of more than one predictor in eliciting the response gradient. Strongly diagonal surfaces have the most diagonal surface area demonstrated by sharply undulating diagonal surfaces. Given that the success of T and D requires a regression method to accurately capture any shape of complex data structure, we also test the accuracy of empirical regression methods known to be tractable with complex data. We test classification and regression trees (CART), Random Forest, and non-parametric multiplicative regression (NPMR) for binary and continuous responses. We use the 48 simulated response surfaces to test the methods, and we find that prediction accuracy depends on both the T and D of the simulated data for each method. We choose the most accurate method among those we test for capturing any shape of response surface from real data, NPMR. Finally, we use NPMR to build response surfaces and quantify T and D from real ecological data sets. We demonstrate how measuring threshold strength and diagonality from multi-factor response surfaces can advance ecology.     

Volatile chemicals from leaf litter are associated with invasiveness of a neotropical weed in Asia

Some invasive plant species appear to strongly suppress neighbors in their nonnative ranges but much less so in their native range. We found that in the field in its native range in Mexico, the presence of Ageratina adenophora, an aggressive Neotropical invader, was correlated with higher plant species richness than found in surrounding plant communities where this species was absent, suggesting facilitation. However, in two nonnative ranges, China and India, A. adenophora canopies were correlated with much lower species richness than the surrounding communities, suggesting inhibition. Volatile organic compound (VOC) signals may contribute to this striking biogeographical difference and the invasive success of A. adenophora. In controlled experiments volatiles from A. adenophora litter caused higher mortality of species native to India and China, but not of species native to Mexico. The effects of A. adenophora VOCs on seedling germination and growth did not differ between species from the native range and species from the nonnative ranges of the invader. Litter from A. adenophora plants from nonnative populations also produced VOCs that differed quantitatively in the concentrations of some chemicals than litter from native populations, but there were no chemicals unique to one region. Biogeographic differences in the concentrations of some volatile compounds between ranges suggest that A. adenophora may be experiencing selection on biochemical composition in its nonnative ranges.     

Nonlinear responses to food availability shape effects of habitat fragmentation on consumers

Fragmentation of landscapes is a pervasive source of environmental change. Although understanding the effects of fragmentation has occupied ecologists for decades, there remain important gaps in our understanding of the way that fragmentation influences mobile organisms. In particular, there is little tested theory explaining the way that fragmentation shapes interactions between consumers and resources. We propose a simple model that explains why fragmentation may harm consumers even when the total amount of resources on the landscape they use remains unchanged. In particular, we show that nonlinearity in the relationship between resource availability and benefits acquired by consumers from resources can cause a decrease in benefits to consumers when landscapes are subdivided into isolated parts and when the distribution of consumers in fragments is not matched to the distribution of resources. We tested predictions of the model using a laboratory system of cabbage looper (Trichoplusia ni) larvae on artificial landscapes. Consistent with the model's predictions, survivorship of larvae decreased when landscapes with heterogeneous resources were fragmented into isolated parts. However, average mass of surviving larvae did not change in response to fragmentation. With basic knowledge of consumer resource use patterns and landscape structure, our model, supported by our experiment, contributes new understanding of the resource-mediated effects of fragmentation on consumers.     

Chemical and microbial characteristics of municipal drinking water supply systems in the Canadian Arctic

Drinking water in the vast Arctic Canadian territory of Nunavut is sourced from surface water lakes or rivers and transferred to man-made or natural reservoirs. The raw water is at a minimum treated by chlorination and distributed to customers either by trucks delivering to a water storage tank inside buildings or through a piped distribution system. The objective of this study was to characterize the chemical and microbial drinking water quality from source to tap in three hamlets (Coral Harbour, Pond Inlet and Pangnirtung—each has a population of <2000) on trucked service, and in Iqaluit (population ~6700), which uses a combination of trucked and piped water conveyance. Generally, the source and drinking water was of satisfactory microbial quality, containing Escherichia coli levels of <1 MPN/100 mL with a few exceptions, and selected pathogenic bacteria and parasites were below detection limits using quantitative polymerase chain reaction (qPCR) methods. Tap water in households receiving trucked water contained less than the recommended 0.2 mg/L of free chlorine, while piped drinking water in Iqaluit complied with Health Canada guidelines for residual chlorine (i.e. >0.2 mg/L free chlorine). Some buildings in the four communities contained manganese (Mn), copper (Cu), iron (Fe) and/or lead (Pb) concentrations above Health Canada guideline values for the aesthetic (Mn, Cu and Fe) and health (Pb) objectives. Corrosion of components of the drinking water distribution system (household storage tanks, premise plumbing) could be contributing to Pb, Cu and Fe levels, as the source water in three of the four communities had low alkalinity. The results point to the need for robust disinfection, which may include secondary disinfection or point-of-use disinfection, to prevent microbial risks in drinking water tanks in buildings and ultimately at the tap.     

Potential risk to wood storks (Mycteria americana) from mercury in Carolina Bay fish

Carolina bays are freshwater wetlands that serve as important feeding habitats for the endangered wood stork (Mycteria americana). Water levels in these bays fluctuate greatly and tend to be acidic and rich in dissolved organic carbon (DOC), factors that favor mercury (Hg) methylation and bioaccumulation in fish. To assess potential risks to wood storks consuming mercury contaminated fish in bays, we sampled fish from 10 bays on the Savannah River Site (SRS), South Carolina, an area with documented use by wood storks. Whole body mercury concentrations in 258 fishes of three species (Erimyzon sucetta, Acantharchuspomotis and Esox americanus) commonly consumed by wood storks were determined. Risk factors for nestlings and free-ranging adults were calculated using published no and lowest observable adverse effect concentration (NOAEC and LOAEC) values for birds. Fish from higher trophic levels and those from wetlands with relatively shallow maximum depths and fluctuating water levels were more likely to exceed NOAEC and LOAEC values. Calculation of exposure rates of nestling wood storks indicated they are at highest risk during the first 10 days of the nestling period. These calculations suggest that there is potential concern for wood storks foraging in relatively shallow bays with fluctuating water levels, even though there is no obvious local source of mercury to these wetlands.     

Decreased carbon and nutrient input to boreal lakes from particulate organic matter following riparian clear-cutting

The plankton communities of oligotrophic Canadian Shield lakes are strongly regulated by the allochthonous supply of total phosphorus (TP) and dissolved organic carbon (DOC), a proportion of both of which originate from particulate organic matter. Although decreased inputs of allochthonous leaf litter have been documented for small streams whose riparian forests have been removed, no such data exist for boreal lakes. Through estimates of airborne litter input from forested and clear-cut shorelines and laboratory measurements of concentrations released from leaf leachate, we determined that riparian deforestation resulted in reductions of DOC from 17.8 to 0.4 g/m shoreline/yr and of TP from 2.9 to 0.3 g/m shoreline/yr. Previous predictive models indicate that such reductions may be substantial enough to decrease basic metabolic processes of lake plankton communities by as much as 9% in primary production and 17% in respiration.