Carl W. Chen

THE ILWAS MODEL: FORMULATION AND APPLICATION

The Integrated Lake-Watershed Acidification Study (ILWAS) model was developed to predict changes in surface water acidity given changes in the acidity of precipitation and dry deposition. The model routes precipitation through the forest canopy, soil horizons, streams and lakes using mass balance concepts and equations which relate flow to hydraulic gradients. The physical-chemical processes which change the acid-base characteristics of the water are simulated by rate (kinetic) and equilibrium expressions and include mass transfers between gas, liquid and solid phases. The aqueous constituents simulated include: pH, alkalinity, the major cations (Ca2+ Mg2+, K+, Na+, and NH4+) and anions (SOinf4sup2−, NOinf3sup−, Cl−, F−), monomeric Al and its inorganic and organic complexes, organic acid analogues and dissolved inorganic carbon (CT). Since free hydrogen ion (H+) (and hence pH) is not conserved, its concentration is derived from the solution alkalinity and the total concentrations of inorganic C, organic acid, and monomeric Al.The ILWAS model has been used to predict changes in the acidity of Woods Lake (typical lake pH 4.5 to 5.0) and Panther Lake (typical lake pH 6 to 7) given reductions in total atmospheric S loads. The two basins are located within 30 km of each other in the Adirondack Mountains and receive similar acidic deposition. The response to a halving in the total atmospheric S load was basin-specific: In Panther Lake, little pH change occurred even 12 yr after the load reduction; in Woods Lake, the change was considerably larger.Hypothesis testing with the model has shown that the routing of water through soils (shallow versus deep flow) largely determines the extent to which incident precipitation is neutralized. Analysis of the two lake basins using the model and field data showed the watersheds to be net suppliers of base to the through-flowing water, although internal watershed production of strong acidity did occur. This internal production of acidity was approximately two-thirds the amount of the atmospheric load.

INTEGRATED LAKE-WATERSHED ACIDIFICATION STUDY: SUMMARY

An integrated, interdisciplinary, intensive study of three forested watersheds in the Adirondack Park region of New York State was started in 1977 to quantify the relationship between the deposition of atmospheric acids and surface water acidity. A general mechanistic theory of lake-watershed acidification that takes into account the production and consumption of acidity by watershed processes, as well as atmospheric inputs of acidity, was developed. This theory is formulated as a mathematical simulation model.

Big Moose Basin: simulation of response to acidic deposition

The ILWAS model has been enhanced for application to multiple-lake hydrologic basins. This version of the model has been applied to the Big Moose basin, which includes Big Moose Lake and its tributary streams, lakes, and watersheds. The basin, as defined, includes an area of 96 km2, with over 20 lakes and ponds, and 70 km of streams. Hydrologic and chemical calibrations have been made using data from seven sampling stations. When total atmospheric sulfur loading to the basin is halved, the model predicts, after four years of simulation, a decreasing sulfate concentration and to a lesser extent a rising alkalinity at Big Moose Lake outlet. At the end of four years, the results show an increase in pH of 0.1 to 0.5 pH units depending upon season.

Lake-watershed acidification in the North Branch of the Moose River: introduction

AbstractAn integrated analysis of a terrestrial-aquatic ecosystem, the North Branch of the Moose River in the Adirondack region of New York, was conducted. This basin contains a large number of interconnected surface waters that exhibit marked gradients in pH and acid neutralizing capacity (ANC). As a result, the basin has been the focus of research activity, including the Regional Integrated Lake-Watershed Acidification Study (RILWAS). The objective of the current analysis was to use the North Branch of the Moose River as a case study to: 1.Evaluate processes regulating the acid-base chemistry of surface waters.2.To assess the effects of surface water acidification on fish populations. The observations of this study were consistent with the model of surface water acidification developed during the Integrated Lake-Watershed Acidification Study (ILWAS). The processes depicted in the original ILWAS simulation model were adequate to describe the acid-base chemistry of surface waters in the North Branch of the Moose River. However, the reduction of SO42− in lake sediments, a process not represented in the original model, proved to be a significant source of acid neutralizing capacity (ANC) for some of these waters. As a result, reduction processes were added to the model.Analysis of in-situ bioassay and survey data indicate that acid-sensitive fish species have disappeared from the more acidic areas of the basin over the last half century. Paleoecological analyses indicate that pH has decreased from the high 5s to about 5 in Big Moose Lake during this period. ILWAS model simulations indicate that the pH of Big Moose Lake would increase by at least 0.1 to 0.5 pH units (depending on the season) in response to a 50% reduction in total atmospheric S deposition.Considerable variability in processes regulating acid/base chemistry was evident in the North Branch of the Moose River. Therefore, regional assessments of past or possible future effects of acidic deposition require widespread application of ILWAS theory within the Adirondack region and other potentially acid-sensitive areas.

Simulating the Effect of Sulfate Addition on Methylmercury Output from a Wetland

The watershed analysis risk management framework (WARMF) model was applied to Wetland S6 of the Marcell Experimental Forest, using the data from a field experiment, conducted to investigate the effect of sulfate additions on mercury methylation in the wetland. The wetland was modeled as interconnected land catchments. Actual meteorology data and mercury and sulfate concentrations of precipitation were input to the model. To simulate the sulfate sprinkling, the experimental section of the bog was irrigated with sulfate water on the actual dates of sulfate additions. The model simulated wetland outflows that matched the measured outflows with an R -square of 0.856. WARMF also simulated other phenomena observed in the experiment: higher sulfate and MeHg levels at the wetland outlet after every sulfate addition, and higher sulfate and MeHg levels in the pore water of the bog after only the May addition, not the July and September additions. According to WARMF, the low groundwater table in May allowed the spri...

Framework to Determine Total Maximum Daily Flow Diversions for Fish Protection

This paper describes a framework to determine the total maximum daily flow diversions (TMDFDs) of freshwater from the San Francisco Bay Delta that can be undertaken without causing the extinction of salmon, striped bass, and delta smelt. The framework comprises three models: the watershed analysis risk management framework (WARMF) model of tributary rivers, the Link-Node estuary model of the Bay Delta, and the monthly cohort life-cycle model of fish. The first two models simulate the environmental conditions of river segments and estuary “Nodes” in which fish live. The fish model deposits eggs in river segments on specified months. The eggs become larvae, juveniles, and young as they move downstream to the estuary “Nodes” where they may die, be eaten, or be entrained into pumps that divert water for export to northern and southern California cities and Central Valley farms. Thus, flow diversion is mechanistically connected to fish decline. These models are integrated by the graphical user interface (GUI) ...

Framework to Calculate TMDL of Acid Mine Drainage For Cheat River Basin in West Virginia

The Watershed Analysis Risk Management Framework (WARMF) was enhanced to calculate the total maximum daily load (TMDL) of acid mine drainage for the Cheat River Basin in West Virginia. The framework divides the river basin into catchments, river segments, and lake layers. Some catchments have deep mines and/or surface mines. These catchments have a soil layer that contains pyrite (FeS2), calcite, and other minerals. The oxidation of pyrite requires molecular oxygen. The framework tracks the concentration of atmospheric oxygen in soil macropores by the advection due to earth breathing and by the sinks due to organic matter decay and pyrite oxidation. Pyrite oxidation produces Fe 2+ , Fe 3+ , SO4 2- and H + . These by-products are leached and carried by groundwater to rivers as acid mine drainage (AMD). In surface mines, the AMD is carried by the lateral flow in saturated soil. In deep mines, the AMD is leached down to the tunnel for exit through a portal. Due to low pH, the AMD also dissolves other weathering by-products (Al 3+ , Zn 2+ , and Mn 2+ ). Upon entry to surface water, insoluable metals can precipitate as hydroxides. For TMDL determination, the designated use is for aquatic life. To protect this use, the State of West Virginia has specified the water quality criteria for pH, Fe, Al, Zn, and Mn. To calculate the TMDL, WARMF steps down the loading of individual constituents in AMD until the water quality criterion is met.