Complex biological responses to the experimental acidification of Little Rock Lake, Wisconsin, USA

Acidification can affect aquatic organisms directly through hydrogen ion toxicity, and indirectly through disrupted food web dynamics and altered abiotic conditions. Field populations from selected taxa were studied during the Little Rock Lake whole-basin acidification experiment to illustrate patterns whose timing suggests direct (i.e. immediate) or indirect (i.e. delayed or non-uniform) responses to pH change. As the treatment basin was acidified to pH 5.6, 5.2 and 4.7, immediate changes consistent with a direct pH response were observed for species representing several trophic levels. For other taxa (e.g. littoral invertebrates associated with filamentous algal mats, several species of pelagic zooplankton), indirect mechanisms induced by food web changes were more likely explanations for abundance patterns. The results presented here suggest that the responses of aquatic ecosystems to acidification involve a complex interplay between direct pH effects and subsequent indirect interactions.     

Atmospheric mercury cycles in northern Wisconsin

Total gaseous mercury (TGM) in the lower atmosphere of northern Wisconsin exhibits strong annual and diurnal cycles similar to those previously reported for other rural monitoring sites across mid-latitude North America. Annually, TGM was highest in late winter and then gradually declined until late summer. During 2002–04, the average TGM concentration was 1.4 ± 0.2 (SD) ng m^?3, and the amplitude of the annual cycle was 0.4 ng m^?3 (～30% of the long-term mean). The diurnal cycle was characterized by increasing TGM concentrations during the morning followed by decreases during the afternoon and night. The diurnal amplitude was variable but it was largest in spring and summer, when daily TGM oscillations of 20–40% were not uncommon. Notably, we also observed a diurnal cycle for TGM indoors in a room ventilated through an open window. Even though TGM concentrations were an order of magnitude higher indoors, (presumably due to historical practices within the building: e.g. latex paint, fluorescent lamps, thermometers), the diurnal cycle was remarkably similar to that observed outdoors. The indoor cycle was not directly attributable to human activity, the metabolic activity of vegetation or diurnal atmospheric dynamics; but it was related to changes in temperature and oxidants in outdoor air that infiltrated the room. Although there was an obvious difference in the proximal source of indoor and outdoor TGM, similarities in behavior suggest that common TGM cycles may be driven largely by adsorption/desorption reactions involving solid surfaces, such as leaves, snow, dust and walls. Such behavior would imply a short residence time for Hg in the lower atmosphere and intense recycling – consistent with the “ping-pong ball” or “multi-hop” conceptual models proposed by others.     

Impact of climate change and seasonal trends on the fate of Arctic oil spills

We investigated the effects of a warmer climate, and seasonal trends, on the fate of oil spilled in the Arctic. Three well blowout scenarios, two shipping accidents and a pipeline rupture were considered. We used ensembles of numerical simulations, using the OSCAR oil spill model, with environmental data for the periods 2009–2012 and 2050–2053 (representing a warmer future) as inputs to the model. Future atmospheric forcing was based on the IPCC’s A1B scenario, with the ocean data generated by the hydrodynamic model SINMOD. We found differences in “typical” outcome of a spill in a warmer future compared to the present, mainly due to a longer season of open water. We have demonstrated that ice cover is extremely important for predicting the fate of an Arctic oil spill, and find that oil spills in a warming climate will in some cases result in greater areal coverage and shoreline exposure.     

Oil spill response capabilities and technologies for ice-covered Arctic marine waters: A review of recent developments and established practices

Renewed political and commercial interest in the resources of the Arctic, the reduction in the extent and thickness of sea ice, and the recent failings that led to the Deepwater Horizon oil spill, have prompted industry and its regulatory agencies, governments, local communities and NGOs to look at all aspects of Arctic oil spill countermeasures with fresh eyes. This paper provides an overview of present oil spill response capabilities and technologies for ice-covered waters, as well as under potential future conditions driven by a changing climate. Though not an exhaustive review, we provide the key research results for oil spill response from knowledge accumulated over many decades, including significant review papers that have been prepared as well as results from recent laboratory tests, field programmes and modelling work. The three main areas covered by the review are as follows: oil weathering and modelling; oil detection and monitoring; and oil spill response techniques.     

Evaluation of wireless sensor networks (WSNs) for remote wetland monitoring: design and initial results

Here, we describe and evaluate two low-power wireless sensor networks (WSNs) designed to remotely monitor wetland hydrochemical dynamics over time scales ranging from minutes to decades. Each WSN (one student-built and one commercial) has multiple nodes to monitor water level, precipitation, evapotranspiration, temperature, and major solutes at user-defined time intervals. Both WSNs can be configured to report data in near real time via the internet. Based on deployments in two isolated wetlands, we report highly resolved water budgets, transient reversals of flow path, rates of transpiration from peatlands and the dynamics of chromophoric-dissolved organic matter and bulk ionic solutes (specific conductivity)—all on daily or subdaily time scales. Initial results indicate that direct precipitation and evapotranspiration dominate the hydrologic budget of both study wetlands, despite their relatively flat geomorphology and proximity to elevated uplands. Rates of transpiration from peatland sites were typically greater than evaporation from open waters but were more challenging to integrate spatially. Due to the high specific yield of peat, the hydrologic gradient between peatland and open water varied with precipitation events and intervening periods of dry out. The resultant flow path reversals implied that the flux of solutes across the riparian boundary varied over daily time scales. We conclude that WSNs can be deployed in remote wetland-dominated ecosystems at relatively low cost to assess the hydrochemical impacts of weather, climate, and other perturbations.     

Importance of life cycle events in the population dynamics of Gonyaulax tamarensis

Life cycle changes that allow populations of the toxic dinoflagellate Gonyaulax tamarensis Lebour to inhabit the benthos and the plankton alternately are important factors regulationg the initiation and decline of blooms in restricted embavments. When the dynamics of these estuarine populations were monitored during “bloom” and “non bloom” years, it was shown that: (1) each year, germination of benthie cysts inoculated the overlying waters during the vernal warming period, but a large residual population remained in the sediments throughout the blooms; (2) the resulting planktonic population began growth under suboptimal temperature conditions; (3) the populations developed from this inoculum through asexual reproduction until sexuality (and cyst formation) were induced; (4) encystment was not linked to any obvious environmental cue and occurred under apparently optimal conditions; and (5) an increase in the number of non-mitotic swimming cells (planozygotes, the precursors to dormant cysts) accompanied the rapid decline of the planktonic population. Thus encystment, in combination with hypothesized losses due to advection and grazing, contributed substantiatly to the decline of the vegetative cell population. We conclude that the encystment/excystment cycle temporally restricts the occurrence of the vegetative population and may not be optimized for rapid or sustained vegetative growth and bloom formation in shallow embayments. The factors that distinguish “bloom” from “non-bloom” years thus appear to be operating on the growth of the planktonic population.