Viruses as potential regulators of regional brown tide blooms caused by the alga,Aureococcus anophagefferens

Blooms of the brown tide organismAureccoccus anophagefferens have recurred in the coastal bays in New Jersey since 1995 and in the coastal bays of Long Island since 1985. Intracellular viral-like particles (VLPs) were documented during 1999–2000 brown tide blooms in Little Egg Harbor, New Jersey, but it was not determined whether cells were infected during the termination of the bloom. The objective of this study was to determine if VLPs infected and lysed natural populations ofA. anophagefferens in coastal bays of New Jersey and New York in 2002 with the same frequency as in 1999–2000 and especially at the termination of the bloom. Our results confirmed that the highest percentage (37.5%) of VLP-infected cells occurred at the termination of the brown tide bloom in New Jersey in 2002. Intracellular VLPs were present throughout the bloom event. The percentage of visibly infected cells was higher at the beginning of the bloom than during the peak of the bloom. The intracellular VLPs in natural populations ofA. anophagefferens were consistent in size and shape (approximately 140 nm in diameter) and comparable to those in previous studies. Concentrated viral isolates, prepared from waters during brown tide blooms in New York and New Jersey in 2002, infected healthy laboratoryA. anophagefferens cultures in vitro. The viral isolates associated with the highest laboratory viral activity (lysis positive) were concentrated from water samples having the highest viral and bacteria concentrations. The intracellular viruses in these virally infected laboratory cultures ofA. anophagefferens were similar in size and shape to those found in natural populations. The successful isolation of a virus specific toA. anophagefferens from a brown tide bloom in the field, the similarity of ultrastructure of VLPs infecting both natural populations and laboratory infected cultures, and the pattern of VLP infection during bloom activity in combination with the observed high percentage of VLP-infected cells during bloom termination, supports, the hypothesis that viruses may be a major source of mortality for brown tide blooms in regional coastal bays of New Jersey and New York.     

A Local Example of Land‐Use Change: Southern Illinois—1807, 1938, and 1993*

This article provides an analysis of a wetland site in southern Illinois from presettlement to the present. The study area is part of the Cache River‐Cypress Creek Wetland, which has international importance, as recognized by the Ramsar Convention on Wetlands. Land‐cover data for 1807, 1938, and 1993 were created and analyzed with a geographic information system (GIS). Land‐use change by topographic setting (uplands, transitional, and bottomlands) and soil productivity was quantified and studied. Interviews with local experts informed this analysis. Results illustrate the complexity of environmental change and its driving forces. First, notable forest and swamp acreage was converted to cropland between 1807 and 1938 and, to a lesser degree, from 1938 to 1993. Second, there were land‐use variations by topographic region. Between 1807 and 1938, the largest transformation occurred in the uplands, with substantial acreage converted from forest to cropland. Between 1938 and 1993, however, agriculture decreased in the upland areas as hilly areas reverted to forest cover. At the same time, agriculture expanded in the bottomlands as this land was drained for farming. Third, there are interesting patterns within these categories of land‐use change, as soil productivity is an indicator of what lands were taken out of cropland and converted back to grassland and forest.     

Groundwater control of mangrove surface elevation: Shrink and swell varies with soil depth

We measured monthly soil surface elevation change and determined its relationship to groundwater changes at a mangrove forest site along Shark River, Everglades National Park, Florida. We combined the use of an original design, surface elevation table with new rod-surface elevation tables to separately track changes in the mid zone (0–4 m), the shallow root zone (0–0.35 m), and the full sediment profile (0–6 m) in response to site hydrology (daily river stage and daily groundwater piezometric pressure). We calculated expansion and contraction for each of the four constituent soil zones (surface [accretion and erosion; above 0 m], shallow zone [0–0.35 m], middle zone [0.35–4 m], and bottom zone [4–6]) that comprise the entire soil column. Changes in groundwater pressure correlated strongly, with changes in soil elevation for the entire profile (Adjusted R² = 0.90); this relationship was not proportional to the depth of the soil profile sampled. The change in thickness of the bottom soil zone accounted for the majority (R² = 0.63) of the entire soil profile expansion and contraction. The influence of hydrology on specific soil zones and absolute elevation change must be considered when evaluating the effect of disturbances, sea level rise, and water management decisions on coastal wetland systems.     

Landscape controls on long‐term runoff in subhumid heterogeneous Boreal Plains catchments

We compared median runoff (R) and precipitation (P) relationships over 25 years from 20 mesoscale (50 to 5,000 km²) catchments on the Boreal Plains, Alberta, Canada, to understand controls on water sink and source dynamics in water‐limited, low‐relief northern environments. Long‐term catchment R and runoff efficiency (RP^?1) were low and varied spatially by over an order of magnitude (3 to 119 mm/year, 1 to 27%). Intercatchment differences were not associated with small variations in climate. The partitioning of P into evapotranspiration (ET) and R instead reflected the interplay between underlying glacial deposit texture, overlying soil‐vegetation land cover, and regional slope. Correlation and principal component analyses results show that peatland‐swamp wetlands were the major source areas of water. The lowest estimates of median annual catchment ET (321 to 395 mm) and greatest R (60 to 119 mm, 13 to 27% of P) were observed in low‐relief, peatland‐swamp dominated catchments, within both fine‐textured clay‐plain and coarse‐textured glacial deposits. In contrast, open‐water wetlands and deciduous‐mixedwood forest land covers acted as water sinks, and less catchment R was observed with increases in proportional coverage of these land covers. In catchments dominated by hummocky moraines, long‐term runoff was restricted to 10 mm/year, or 2% of P. This reflects the poor surface‐drainage networks and slightly greater regional slope of the fine‐textured glacial deposit, coupled with the large soil‐water and depression storage and higher actual ET of associated shallow open‐water marsh wetland and deciduous‐forest land covers. This intercatchment study enhances current conceptual frameworks for predicting water yield in the Boreal Plains based on the sink and source functions of glacial landforms and soil‐vegetation land covers. It offers the capability within this hydro‐geoclimatic region to design reclaimed catchments with desired hydrological functionality and associated tolerances to climate or land‐use changes and inform land management decisions based on effective catchment‐scale conceptual understanding.     

Modelling atmospheric and hydrologic processes for assessment of meadow restoration impact on flow and sediment in a sparsely gauged California watershed

The restoration of meadowland using the pond and plug technique of gully elimination was performed in a 9‐mile segment along Last Chance Creek, Feather River Basin, California, in order to rehabilitate floodplain functions such as mitigating floods, retaining groundwater, and reducing sediment yield associated with bank erosion and to significantly alter the hydrologic regime. However, because the atmospheric and hydrological conditions have evolved over the restoration period, it was difficult to obtain a comprehensible evaluation of the impact of restoration activities by means of field measurements. In this paper, a new use of physically based models for environmental assessment is described. The atmospheric conditions over the sparsely gauged Last Chance Creek watershed (which does not have any precipitation or weather stations) during the combined historical critical dry and wet period (1982–1993) were reconstructed over the whole watershed using the atmospheric fifth‐generation mesoscale model driven with the US National Center for Atmospheric Research and US National Center for Environmental Prediction reanalysis data. Using the downscaled atmospheric data as its input, the watershed environmental hydrology (WEHY) model was applied to this watershed. All physical parameters of the WEHY model were derived from the existing geographic information system and satellite‐driven data sets. By comparing the prerestoration and postrestoration simulation results under the identical atmospheric conditions, a more complete environmental assessment of the restoration project was made. Model results indicate that the flood peak may be reduced by 10–20% during the wet year and the baseflow may be enhanced by 10–20% during the following dry seasons (summer to fall) in the postrestoration condition. The model results also showed that the hydrologic impact of the land management associated with the restoration mitigates bank erosion and sediment discharge during winter storm events. Copyright © 2013 John Wiley & Sons, Ltd.     

Implications of measurement metrics on soil freezing curves: A simulation of freeze–thaw hysteresis

Soil freeze–thaw events have important implications for water resources, flood risk, land productivity, and climate change. A property of these phenomena is the relationship between unfrozen water content and sub-freezing temperature, known as the soil freezing characteristic curve (SFC). It is documented that this relationship exhibits hysteretic behaviour when frozen soil thaws, leading to the definition of the soil thawing characteristic curve (STC). Although explanations have been given for SFC/STC hysteresis, the effect that ‘scale’ – particularly ‘measurement scale’ – may have on these curves has received little attention. The most commonly used measurement scale metric is the ‘support’, which is the spatial (or temporal) unit within which the measured variable is integrated or soil volume sampled. We show (a) measurement support can influence the range and shape of the SFC and (b) hysteresis can be attributed, in part, to the support and location of the measurements comprising the SFC/STC. We simulated lab measured temperature, volumetric water content (VWC), and permittivity from soil samples undergoing freeze–thaw transitions using Hydrus-1D and a modified Dobson permittivity model. To assess the effect of measurement support and location on SFC/STC, we masked the simulated temperature and VWC/permittivity extent to match the instrument's support and location. By creating a detailed simulation of the intra- and inter-support variability associated with the penetration of a freezing front, we demonstrate how measurement support and location can influence the temperature range over which water freezing events are captured. We show it is possible to simulate hysteresis in homogenous media with purely geometric considerations, suggesting that SFC/STC hysteresis may be more of an apparent phenomenon than mechanistically real. Lastly, we develop an understanding of how the location and support of soil temperature and VWC/permittivity measurements influence the temperature range over which water freezing events are captured.     

Fire and vegetation shifts in the Americas at the vanguard of Paleoindian migration

Across North and South America, the final millennia of the Pleistocene saw dramatic changes in climate, vegetation, fauna, fire regime, and other local and regional paleo-environmental characteristics. Rapid climate shifts following the Last Glacial Maximum (LGM) exerted a first-order influence, but abrupt post-glacial shifts in vegetation composition, vegetation structure, and fire regime also coincided with human arrival and transformative faunal extinctions in the Americas. We propose a model of post-glacial vegetation change in response to climatic drivers, punctuated by local fire regime shifts in response to megaherbivore-driven fuel changes and anthropogenic ignitions. The abrupt appearance of humans, disappearance of megaherbivores, and resulting changes in New World fire systems were transformative events that should not be dismissed in favor of climate-only interpretations of post-glacial paleo-environmental shifts in the Americas. Fire is a mechanism by which small human populations can have broad impacts, and growing evidence suggests that early anthropogenic influences on regional, even global, paleo-environments should be tested alongside other potential causal mechanisms.     

Geoarchaeological Investigations in Mesoamerica Move into the 21st Century: A Review

Over the past thirty years, geoarchaeology has moved from the fringe to mainstream status within Mesoamerican archaeological investigations. This review focuses on works published since the year 2000. Five themes are identified as central to recent studies: (1) the correlation of environmental change and cultural history; (2) anthropogenic environmental impacts; (3) ancient land cover, land use, and diet; (4) archaeological prospection; and (5) provenance studies. These themes are often interwoven in the application of complex systems approaches that allow scientists to more accurately model the intricacies of ancient human–environment interactions.