Robert B. Ambrose

Application of ecosystem‐scale fate and bioaccumulation models to predict fish mercury response times to changes in atmospheric deposition

Management strategies for controlling anthropogenic mercury emissions require understanding how ecosystems will respond to changes in atmospheric mercury deposition. Process-based mathematical models are valuable tools for informing such decisions, because measurement data often are sparse and cannot be extrapolated to investigate the environmental impacts of different policy options. Here, we bring together previously developed and evaluated modeling frameworks for watersheds, water bodies, and food web bioaccumulation of mercury. We use these models to investigate the timescales required for mercury levels in predatory fish to change in response to altered mercury inputs. We model declines in water, sediment, and fish mercury concentrations across five ecosystems spanning a range of physical and biological conditions, including a farm pond, a seepage lake, a stratified lake, a drainage lake, and a coastal plain river. Results illustrate that temporal lags are longest for watershed-dominated systems (like the coastal plain river) and shortest for shallow water bodies (like the seepage lake) that receive most of their mercury from deposition directly to the water surface. All ecosystems showed responses in two phases: A relatively rapid initial decline in mercury concentrations (20-60% of steady-state values) over one to three decades, followed by a slower descent lasting for decades to centuries. Response times are variable across ecosystem types and are highly affected by sediment burial rates and active layer depths in systems not dominated by watershed inputs. Additional research concerning watershed processes driving mercury dynamics and empirical data regarding sediment dynamics in freshwater bodies are critical for improving the predictive capability of process-based mercury models used to inform regulatory decisions.

Modeling eutrophication kinetics in reservoir microcosms

Abstract This study addresses the question of how a general seasonal eutrophication model, WASP5, can handle daily phytoplankton and nutrient dynamics in perturbed microcosms for 1- to 2-week periods of time. It is intended to explore both the interpretative and the predictive capabilities of conventional kinetic formulations. The general method adopted in this study is to first apply EUTRO5, a component of WASP5, to a well-behaved microcosm, calibrating the parameter values and reformulating equations if necessary. Next, the calibrated model is subjected to testing in other microcosm experiments, with altered parameter values if necessary. Model performance is further explored through sensitivity analyses to try to “explain” the observed kinetics in the experiments, and a two-way ANOVA is finally applied to the simulated vs observed evolution curves of the three main variables, i.e. chlorophyll a, soluble-P and ammonia-N in all experiments and microcosms studied.

Evaluating regional predictive capacity of a process‐based mercury exposure model, regional‐mercury cycling model, applied to 91 Vermont and New Hampshire lakes and ponds, USA

Regulatory agencies must develop fish consumption advisories for many lakes and rivers with limited resources. Process-based mathematical models are potentially valuable tools for developing regional fish advisories. The regional mercury cycling model (R-MCM) specifically was designed to model a series of lakes for a given region with site-specific data and parameterization for each application. In this paper, we explore the feasibility of R-MCM application to develop regional fish advisories from existing data by testing model performance across 91 Vermont ([VT], USA) and New Hampshire ([NH], USA) lakes. We use a progressive method of parameter refinement ranging from simple defaults specified by the model to site-specific parameterization to evaluate potential improvements in model prediction. Model applications and parameter refinement tiers are based on Regional Environmental Monitoring Assessment Program (REMAP) data. Results show that R-MCM generally underpredicts water column methylmercury and total mercury concentrations and overpredicts sediment methylmercury concentrations. Default level input parameterization produced the largest amount of random scatter in model forecasted values. Using site-specific values for the default level characteristics reduced this variability but did not improve overall model performance. By separating the observed and predicted data by lake characteristics, we identify some overall trends in bias and fit, but are unable to identify systematic biases in model performance by lake type. This analysis suggests that process-based models like R-MCM cannot be used for a priori predictive applications at the regional scale at this time. Further, this work reinforces the need for additional research on the transport and transformation of mercury to elucidate parameterization useable in a modeling framework to help refine predictive capabilities of process-based models.

Characterizing Spatial and Temporal Dynamics: Development of a Grid-Based Watershed Mercury Loading Model

A distributed grid-based watershed mercury loading model has been developed to characterize the spatial and temporal dynamics of mercury from both point and nonpoint sources. The model simulates flow, sediment transport, and mercury dynamics on a daily time step across a diverse landscape. The model is composed of six major components: (1) an ArcGIS interface for processing spatial input data; (2) a basic hydrologic module; (3) a sediment transport module; (4) a mercury transport and transformation module; (5) a spreadsheet-based model post-processor; and (6) links to other models such as WASP and WhAEM 2000 developed by the U.S. Environmental Protection Agency (EPA). The model fully uses the grid processing capacity of the latest ArcGIS technology. The water balance, sediment generation and transport, and mercury dynamics are calculated for every grid within a watershed. Water and pollutants are routed daily throughout the watershed based on a unique and flexible algorithm that characterizes a watershed into many runoff travel-time zones. The mercury transport and transformation module simulates the following key processes: (1) mercury input from atmospheric deposition; (2) mercury assimilation and accumulation in forest canopy and release from forest litter; (3) mercury input from bedrock weathering; (4) mercury transformation in soils; (5) mercury transformation in lakes and wetlands, including reduction and net methylation; (6) mercury transport through sediment and runoff; and (7) mercury transport in stream channels. By using the grid-based technology, flow, sediment, and mercury dynamics can be examined at any of several points in the watershed. The model is capable of supporting large-scale watershed modeling with high-resolution raster data sets and will be used in mercury research projects sponsored by EPA. The model is programmed in Visual Basic and requires two ArcGIS (version 9.0) components—ArcView 9 and the Spatial Analyst extension.

CASE STUDY: DIELDRIN ATTACK IN DALYAN LAGOON

During the first two weeks of December of 2005, NATO sponsored an Advanced Study Institute (ASI) In Istanbul, Turkey. Part of this ASI involved a case study of a terrorist attack, where a chemical was assumed to be dumped into Sulunger Lake in Turkey. This chapter documents the response developed by the ASI participants to this scenario, in terms of hydrodynamic transport, ecosystem effects, and decision making.

Watershed Management in the United States

A watershed approach provides an effective framework for dealing with water resources challenges. Watersheds provide drinking water, recreation, and ecological habitat, as well as a place for waste disposal, a source of industrial cooling water, and navigable inland water transport. Consequently, much depends on the health of watersheds. Watersheds are threatened by wastewater and nonpoint source runoff that load surface waters with excess organic matter, nutrients, pathogens, solids, and toxic substances. Physical alterations, such as paving and stream channelization, change both the hydrologic regime and habitat. Estuaries are of particular importance, since they have great economic, ecological, recreational, and aesthetic value. An approach to the protection, management, and restoration of these water resources in the United States, and the respective roles of federal, state, and local governments, as well as the private sector and volunteer groups, is discussed. Protecting and sustaining watersheds requires that water resource goals be prioritized within a coordinating framework.