Assessing a decade of phosphorus management in the Lake Mendota, Wisconsin watershed and scenarios for enhanced phosphorus management

A phosphorus (P) budget was estimated for the watershed of Lake Mendota, Wisconsin, to assess the effects of nutrient management on P accumulation in the watershed soils. We estimated how nutrient management programs and legislation have affected the budget by comparing the budget for 2007 to a budget calculated for 1995, prior to implementation of the programs. Since 1995, inputs decreased from 1,310,000 to 853,000 kg P/yr (35% reduction) and accumulation decreased from 575,000 to 279,000 kg P/yr (51% reduction). Changes in P input and accumulation were attributed primarily to enhanced agricultural nutrient management, reduction in dairy cattle feed supplements and an urban P fertilizer ban. Four scenarios were investigated to determine potential impacts of additional nutrient management tactics on the watershed P budget and P loading to Lake Mendota. Elimination of chemical P fertilizer input has the greatest potential to reduce watershed P accumulation and establishment of riparian buffers has the greatest potential to prevent P loading to Lake Mendota.     

A short-term predictive system for surface currents from a rapidly deployed coastal HF radar network

In order to address the need for surface trajectory forecasts following deployment of coastal HF radar systems during emergency-response situations (e.g., search and rescue, oil spill), a short-term predictive system (STPS) based on only a few hours data background is presented. First, open-modal analysis (OMA) coefficients are fitted to 1-D surface currents from all available radar stations at each time interval. OMA has the effect of applying a spatial low-pass filter to the data, fills gaps, and can extend coverage to areas where radial vectors are available from a single radar only. Then, a set of temporal modes is fitted to the time series of OMA coefficients, typically over a short 12-h trailing period. These modes include tidal and inertial harmonics, as well as constant and linear trends. This temporal model is the STPS basis for producing up to a 12-h current vector forecast from which a trajectory forecast can be derived. We show results of this method applied to data gathered during the September 2010 rapid-response demonstration in northern Norway. Forecasted coefficients, currents, and trajectories are compared with the same measured quantities, and statistics of skill are assessed employing 16 24-h data sets. Forecasted and measured kinetic variances of the OMA coefficients typically agreed to within 10–15%. In one case where errors were larger, strong wind changes are suspected and examined as the cause. Sudden wind variability is not included properly within the STPS attack we presently employ and will be a subject for future improvement.     

Flow over Hills: A Large-Eddy Simulation of the Bolund Case

Simulation of local atmospheric flows around complex topography is important for several applications in wind energy (short-term wind forecasting and turbine siting and control), local weather prediction in mountainous regions and avalanche risk assessment. However, atmospheric simulation around steep mountain topography remains challenging, and a number of different approaches are used to represent such topography in numerical models. The immersed boundary method (IBM) is particularly well-suited for efficient and numerically stable simulation of flow around steep terrain. It uses a homogenous grid and permits a fast meshing of the topography. Here, we use the IBM in conjunction with a large-eddy simulation (LES) and test it against two unique datasets. In the first comparison, the LES is used to reproduce experimental results from a wind-tunnel study of a smooth three-dimensional hill. In the second comparison, we simulate the wind field around the Bolund Hill, Denmark, and make direct comparisons with field measurements. Both cases show good agreement between the simulation results and the experimental data, with the largest disagreement observed near the surface. The source of error is investigated by performing additional simulations with a variety of spatial resolutions and surface roughness properties.     

Oxygen isotope evidence of Little Ice Age aridity on the Caribbean slope of the Cordillera Central, Dominican Republic

Climate change during the so-called Little Ice Age (LIA) of the 15th to 19th centuries was once thought to be limited to the high northern latitudes, but increasing evidence reflects significant climate change in the tropics. One of the hypothesized features of LIA climate in the low latitudes is a more southerly mean annual position of the Intertropical Convergence Zone (ITCZ), which produced more arid conditions through much of the northern tropics. High-resolution stable oxygen isotope data and other sedimentary evidence from Laguna de Felipe, located on the Caribbean slope of the Cordillera Central of the Dominican Republic, support the hypothesis that the mean annual position of the ITCZ was displaced significantly southward during much of the LIA. Placed within the context of regional paleoclimate and paleoceanographic records, and reconstructions of global LIA climate, this shift in mean annual ITCZ position appears to have been induced by lower solar insolation and internal dynamical responses of the global climate system. Our results from Hispaniola further emphasize the global nature of LIA climate change and the sensitivity of circum-Caribbean climate conditions to what are hypothesized to be relatively small variations in global energy budgets.     

Neon measurements of individual Greenland sediment particles: proof of an extraterrestrial origin and comparison with EDX and morphological analyses

The work reported here confirms the existence of (largely) unmelted micrometeorites in sediments from seasonal lakes on the Greenland ice sheet. Approximately1/3 of the dark and irregularly shaped particles selected from disaggregated sediments had sufficient contents of Ne to permit measurement of isotopic compositions. The sediments consisted of a mixture of biologically derived contaminants and minor amounts of terrestrial minerals and extraterrestrial fragments. Although terrestrial mineral contamination varied by a factor of 20 for the two different sediments, a yield of 1000 cosmic particles/kg of wet cryoconite was found for both samples. The isotopic compositions of the Ne in both rounded and irregular (25% of total) particles that contained enough gas to measure were non-terrestrial, plotting in a field defined by solar wind (SW), solar energetic particle (SEP) and spallation. Exposure ages ranged from < 0.5 Ma to 20 Ma, consistent with previous estimates from¹⁰Be and²⁶Al measurements of larger spherules removed from similar sediments. Comparison of the Ne data with compositional-morphological data demonstrates the general validity of criteria previously used to identify extraterrestrial particles; however, two particles identified as of probable terrestrial origin by three independent, experienced meteorite petrologists were shown by the Ne data to be extraterrestrial and probably extraterrestrial, respectively. Future studies of Greenland micrometeorites are outlined and improved collection techniques are discussed.     

Linking hurricane landfalls,precipitation variability,fires, and vegetation response over the past millennium from analysis of coastal lagoon sediments,southwestern Dominican Republic

We reconstructed the late-Holocene environmental history of a coastal lagoon in semi-arid southwestern Hispaniola through multiproxy analysis of a sediment core, including pollen, macroscopic and microscopic charcoal, loss-on-ignition analysis (LOI), stable isotope analysis, bulk density, and magnetic susceptibility. Four chronological accelerator mass spectrometry radiocarbon dates indicated that our core represents the past ~1000 years. We interpreted ten hurricanes events over the past millennium from high-resolution geological proxies, LOI data, and ostracod valve stable oxygen isotope data, thus producing the first long record of hurricanes from the Dominican Republic. Geological proxies indicated a high-energy event abruptly changed the ecosystem state of our core site from a shallow mangrove wetland to a lacustrine environment ~330 cal yr BP. We interpret the driver of that event to be the landfall of a strong hurricane that initiated lowland flooding, mangrove mortality, and subsequent peat collapse at the core site. Pollen data indicated that during the relatively moist Medieval Warm Period (MWP), hurricanes led to temporary declines in tropical dry forest taxa that recovered within several decades following disturbance. By comparison, during the relatively arid Little Ice Age (LIA), when precipitation was highly variable in the circum-Caribbean, closely spaced hurricanes seemed to delay forest recovery. Sedimentary charcoal concentrations revealed increased fire activity after inferred hurricane landfalls in the MWP, providing evidence of a link between enhanced biomass and fuel availability during moister periods and burning in recently disturbed dry forests and scrub of our semi-arid study region. Our interpretations of increased aridity and precipitation variability, indicated by alternating thin layers of microbial mats with evaporite layers, along with more frequent hurricanes from ~330 cal yr BP to present, generally agree with other sedimentary records from the circum-Caribbean, and may be linked to a more southerly position of the Intertropical Convergence Zone during the LIA.     

Cycling of two carbon substrates of contrasting lability by heterotrophic biofilms across a nutrient gradient of headwater streams

Anthropogenic impacts can significantly alter stream nutrient and dissolved organic carbon (DOC) delivery and composition. Nutrient and DOC cycling in headwater streams, however, are linked via a variety of complex feedbacks that are, in part, influenced by DOC composition emphasizing the need to investigate coupled nutrient–DOC interactions. This study assessed differential incorporation and mineralization of ¹³C labeled glucose and vanillin by heterotrophic microbes within epilithic biofilm communities in four temperate headwater streams spanning a 100-fold range in total dissolved nitrogen and soluble reactive phosphorous concentrations. The substrates were traced via ¹³C analyses of DOC, dissolved inorganic carbon, bulk biofilm, and individual biofilm phospholipid fatty acids (PLFA) to assess total incorporation of the substrates and the distribution of substrate use within the heterotrophic community. Results indicate greater nutrient uptake by high nutrient streams with glucose additions relative to vanillin additions and support the hypothesis that nutrient retention in high nutrient streams is hampered by a lack of labile C sources. Vanillin-derived C uptake was only detectable in PLFA from the highest nutrient stream and was dominated by eukaryotic organisms, likely including fungi. This suggests biofilms in high nutrient streams are better adapted to access relatively slow turnover substrates perhaps due to their composition and overall structure. PLFA-based glucose use efficiencies were greatest in the lowest nutrient stream supporting the hypothesis that labile DOC sources are used more efficiently by heterotrophs in less impacted streams, while biofilms of high nutrient streams are better adapted to utilizing a wider array of DOC sources. This adaption is likely a result of exposure to the lower quality DOC pools in high-nutrient streams resulting from high DOC uptake supported, in part, by fast turnover autochthonous sources of DOC. Nutrient retention in nutrient-rich streams, however, is still likely limited by readily bioavailable DOC leading to lower nutrient retention and downstream nutrient enrichment.     

Dating Palaeolithic sites in southwestern Crete,Greece

Discussions of dispersals of early hominins from Africa assume that Southwest Asia and the Arabian Peninsula were the primary passageways for migrations to Eurasia. The Mediterranean is usually viewed as a barrier to early hominin movements because pre‐sapiens hominins were thought to lack the technical means or the cognitive skills to construct boats. The discovery of early Palaeolithic artefacts in an archaeological survey on the Greek island of Crete challenges this view. Here we show that Palaeolithic artefacts in the Plakias region in southwestern Crete are associated with geological contexts that can be dated to the late Middle or early Late Pleistocene. Because Crete has been separated from the mainland throughout the Pleistocene, the presence of Pleistocene age artefacts there suggests that early hominins were able to cross open water. Copyright © 2011 John Wiley & Sons, Ltd.     

Comparison of bulk and compound-specific δC analyses and determination of carbon sources to salt marsh sediments using n-alkane distributions (Maine,USA)

Sources of sedimentary organic matter to a Morse River, Maine (USA) salt marsh over the last 3390 ± 60 RCYBP (Radiocarbon Years Before Present) are determined using distribution patterns of n-alkanes, bulk carbon isotopic analysis, and compound-specific carbon isotopic analysis. Marsh foraminiferal counts suggest a ubiquitous presence of high marsh and higher-high marsh deposits (dominated by Trochammina macrescens forma macrescens, Trochammina comprimata, and Trochammina inflata), implying deposition from ∼0.2 m to 0.5 m above mean high water. Distributions of n-alkanes show a primary contribution from higher plants, confirmed by an average chain length value of 27.5 for the core sediments, and carbon preference index values all >3. Many sample depths are dominated by the C₂₅ alkane. Salicornia depressa and Ruppia maritima have similar n-alkane distributions to many of the salt marsh sediments, and we suggest that one or both of these plants is either an important source to the biomass of the marsh through time, or that another unidentified higher plant source is contributing heavily to the sediment pool. Bacterial degradation or algal inputs to the marsh sediments appear to be minor. Compound-specific carbon isotopic analyses of the C₂₇ alkane are on average 7.2‰ depleted relative to bulk values, but the two records are strongly correlated (R² = 0.89), suggesting that marsh plants dominate the bulk carbon isotopic signal. Our study underscores the importance of using caution when applying mixing models of plant species to salt marsh sediments, especially when relatively few plants are included in the model.     

Experimental Evaluation of Tracking Algorithms Used for the Determination of Fish Behavioral Statistics

The fine-scale swimming behavior of fish can now be studied because of the development of sophisticated measurement devices such as multibeam sonar and stereo video systems. However, even with these sensors, improved methods are still required to generate quality estimates of swimming speeds and turn rates. Biologists have commonly relied on pointwise differentiation of noisy position measurements while engineers have focused on Bayesian algorithms to track underwater vehicles. A comparative evaluation of the performance of these tracking algorithms for the analysis of fine-scale behavior of fish was performed using a data set of 100 fish tracks recorded simultaneously with a multibeam sonar and a stereo video camera system. The segmenting track identifier, a non-Bayesian curve fitting and segmenting tracker, is shown to be most effective for tracking the unpredictable and complex horizontal motion of fish while a Kalman smoother using a constant-velocity model is shown to be most effective for tracking the more predictable and piecewise linear vertical motion of fish. Both are shown to be more effective than pointwise differentiation. Criteria for selecting an appropriate algorithm for a given motion study are provided