Matthew C. Van de Bogert

ECOSYSTEM SUBSIDIES: TERRESTRIAL SUPPORT OF AQUATIC FOOD WEBS FROM 13C ADDITION TO CONTRASTING LAKES

Whole-lake additions of dissolved inorganic C-13 were used to measure allochthony (the terrestrial contribution of organic carbon to aquatic consumers) in two unproductive lakes (Paul and Peter Lakes in 2001), a nutrient-enriched lake (Peter Lake in 2002), and a dystrophic lake (Tuesday Lake in 2002). Three kinds of dynamic models were used to estimate allochthony: a process-rich, dual-isotope flow model based on mass balances of two carbon isotopes in 12 carbon pools; simple univariate time-series models driven by observed time courses of delta(13)CO(2); and multivariate autoregression models that combined information from time series of delta(13)C in several interacting carbon pools. All three models gave similar estimates of allochthony. In the three experiments without nutrient enrichment, flows of terrestrial carbon to dissolved and particulate organic carbon, zooplankton, Chaoborus, and fishes were substantial. For example, terrestrial sources accounted for more than half the carbon flow to juvenile and adult largemouth bass, pumpkinseed sunfish, golden shiners, brook sticklebacks, and fathead minnows in the unenriched experiments. Allochthony was highest in the dystrophic lake and lowest in the nutrient-enriched lake. Nutrient enrichment of Peter Lake decreased allochthony of zooplankton from 0.34-0.48 to 0-0.12, and of fishes from 0.51-0.80 to 0.25-0.55. These experiments show that lake ecosystem carbon cycles, including carbon flows to consumers, are heavily subsidized by organic carbon from the surrounding landscape.

Fates of methane from different lake habitats : Connecting whole-lake budgets and CH4 emissions

Methane (CH4) represents a major product of organic matter decomposition in lakes. Once produced in the sediments, CH4 can be either oxidized or emitted as a greenhouse gas to the atmosphere. Lakes ...

Preparing for the future : teaching scenario planning at the graduate level

Are environmental science students developing the mindsets and obtaining the tools needed to help address the considerable challenges posed by the 21st century? Todays major environmental issues are characterized by high-stakes decisions and high levels of uncertainty. Although traditional scientific approaches are valuable, contemporary environmental issues also require new tools and new ways of thinking. We provide an example of how such new, or “post-normal”, approaches have been taught at the graduate level, through practical application of scenario planning. Surveyed students reported that they found the scenario planning course highly stimulating, thought-provoking, and inspiring. Key learning points included recognizing the need for multiple points of view when considering complex environmental issues, and better appreciating the pervasiveness of uncertainty. Collaborating with non-academic stakeholders was also particularly helpful. Most students left the course feeling more positive about the potential contribution they can make in addressing the environmental challenges that society faces.

Phosphorus sources and demand during summer in a eutrophic lake

Abstract.In pelagic systems, phytoplankton biomass may remain abundant or near equilibrium while concentrations of the limiting nutrient are below detection. In eutrophic lakes, it has been thought that episodic algal blooms are due to mixing events that break down this equilibrium by adding nutrients to the mixed layer. Alternatively, rapid rates of biotic recycling among primary producers and heterotrophic consumers could maintain high phytoplankton biomass, yet the recycling process has been difficult to observe in situ. Here we use free-water oxygen measurements and an associated metabolic model to infer rates of phosphorus (P) uptake and biotic mineralization in the epilimnion of a eutrophic lake. The rates of uptake and mineralization were compared to “external” sources of P such as loading and entrainment. Also, model results were assessed using sensitivity analysis. We found that the majority of phytoplankton P demand during the period of low P availability could be accounted for by biotic mineralization, but that it was important to consider the effects of entrainment in order to account fully for P uptake. These general results were relatively insensitive to model parameterization, though the relative C:P ratio of material taken up versus mineralized was an important consideration. This study integrates modeling and measurement tools that monitor ecosystem processes at finer temporal resolution than has previously been possible, complementing other studies that use experimental incubation and elemental tracers. Extension of this approach could enhance models that aim to integrate biological and physical processes in assessment of water quality and prediction of phytoplankton biomass.