Search

The Everglades Phosphorus and Hydrology (EPH) model was developed to simulate water movement and phosphorus transportin the Everglades Protection Area which is comprised of theEverglades National Park (ENP) and surrounding wetlands knownas the Water Conservation Areas (WCAs). Water flows from theEverglades Agricultural Area (EAA) through the WCAs intoEverglades National Park (ENP). The model is designed to represent the system as a series of cells in which water flowsfrom one cell to the next. The code allows for pumped inputsand pumped outputs of water as well as sorption and removal ofphosphorus through peat accretion. Model application involved dividing the system into twenty cellsrepresenting different segments of the WCAs. Inputs to each cellconsisted of water pumped from the EAA (where appropriate), flowfrom upgradient cells, and precipitation. Outputs included pumped outputs and flow out of each cell. Using data collectedby the South Florida Water Management District, the model wascalibrated by matching simulated and observed flows, water elevations, and phosphorus (P) concentrations for the period 1980–1988. The model was then validated for the 1988–1992 period using the same model parameters derived from the calibration process and comparing simulated and observed values.Reasonable agreement between simulated and observed values wasattained for both the calibration and validation periods. The calibrated and validated model was used to simulate the impacts on annual average total P concentrations in each cellresulting from the implementation of the management plan mandated by the Everglades Forever Act. This plan calls for the construction of six Stormwater Treatment Areas (STAs) to treat discharges from the EAA, hydrologic modifications of thesystem to promote sheet flow, and the implementation of BestManagement Practices to reduce P runoff from individual farms. In addition, the model was used to evaluate the impact of notbuilding one of the STAs (STA 3/4), and sensitivity analyseswere conducted to determine the effects of changing STA outletP concentrations throughout the system. Model results indicatethat phosphorus concentration reductions will occur in areas near EAA discharges in response to reductions in input P concentrations. However these measures will have little impacton phosphorus concentrations for 85% of the area of theWCAs and on the water entering Everglades National Park. The scenario analyses also indicate that phosphorus concentrationsthroughout most of the WCAs are similar with or without the construction of STA-3/4.

Simulation models play an important role in understanding the causes and consequences of climate change. In order to make full use of these models, it is necessary to establish the magnitude and sources of uncertainty associated with their predictions. This information can be used to achieve a better understanding of the simulated systems, to increase the reliability of model predictions, to guide field surveys and laboratory experiments, and to define realistic values that should be used in scientific, economic, and political discussions of future conditions. In this paper, a new tree-structured density estimation technique that extends the ability of Monte Carlo-based analyses to explore parameter interactions and uncertainty in complex environmental models was applied. The application of the technique is demonstrated using the GLOCO global carbon cycle model. The paper demonstrates that there are numerous distinct parameter combinations that can meet fairly stringent calibration criteria, and they are concentrated in relatively small subsets of the parameter space. These different subsets can be viewed as representing different ecological systems that achieve the same calibration or performance goals in fundamentally different ways. It is also shown that the simulated responses of these systems to future environmental change can lead to different conclusions regarding the interaction between factors affecting environmental processes, such as the growth of vegetation. Together, these results show how the tree-structured density estimation technique can be applied to gain a broader understanding of model performance and of ecosystem responses to change.

RIVRISK, an interactive Windows™-based model, predicts ambient chemical concentrations, human health and ecological risks, and water temperatures due to chemical and thermal releases into rivers. RIVRISK simulates chemicals that enter rivers from pipes, through submerged diffusers, from groundwater seepage, and atmospheric plume deposition. Human health risks are calculated for up to 16 pathways via exposure routes of dermal contact, ingestion, and inhalation. Ecological risks are evaluated for aquatic organisms by comparing the river water concentration to a water quality criterion for freshwater organisms. Monte Carlo analyses of ambient concentrations and temperatures can also be performed based on uniform distributions or user-defined histograms of varied parameters. To illustrate the various features of the model, RIVRISK was applied to a case study based on the Glen Lyn Power Plant located along the New River in Virginia.

A model of the global Hg cycle is presented and applied to analyze modern Hg budgets and historical changes in deposition. Our modeling suggests that mixing into the ocean interior is a significant sink of Hg and likely has limited any anthropogenically-caused increase in surface ocean Hg concentrations to about 50% above natural levels rather than 200% as has recently been argued. Additionally, both the increase in air pollutants during the industrial era and their recent decrease in North America likely have affected atmospheric Hg scavenging and the resulting records of Hg deposition rates in lake and bog sediments.

The discrepancy between estimates of net terrestrial CO2 emissions derived from (1) inverse modeling of the ocean/atmosphere system and (2) modeling of land use change, better known as the “missing” CO2 sink, suggests that some changing environmental factor, such as CO2, anthropogenic N emissions, or climate, has fertilized terrestrial ecosystems. To address this question, we herein describe and apply GLOCO, a global carbon cycle model. GLOCO's ocean submodel combines a box diffusion model with representations of chemical equilibria and biological processes to simulate the distributions and cycling of inorganic and organic carbon, phosphate, and alkalinity. The terrestrial submodel divides the biosphere into seven natural biomes with dynamic carbon and nitrogen cycling in both vegetation and soils. Anthropogenic influences on the functioning of the carbon and nitrogen cycles, such as fossil fuel combustion, forestry, and agricultural development, are also incorporated in the model. Our analysis confirms previous suggestions that because temperate and boreal forests are N limited, CO2 fertilization of these forests is less than predicted by short-term CO2 response factors. Modeling of temperate/boreal forest fertilization by anthropogenic N deposition suggests that CO2 is initially sequestered at a C:N ratio of ∼100, rather than the steady state value for the ecosystem of ∼30. If N deposition is to account for the 40–70% of the fertilization of the terrestrial biosphere not explainable by CO2 fertilization and temperature increases, then we estimate that 26-30 Tg N yr−1 of anthropogenic deposition in the temperate and boreal zones would be required. Recent anthropogenic NOx and NH3 deposition fluxes at northern temperate latitudes have been estimated to be 20–28 Tg N yr−1. Thus fertilization by anthropogenic N emissions likely constitutes a significant portion of the missing CO2 sink.

In response to U.S. EPA’s proposed Great Lakes water quality criteria for mercury (Hg), a field-validated Hg cycling model (MCM) was used to predict Hg levels in the abiotic and bio tic components of Lake Superior and Lake Erie. The U.S. EPA criteria are based on water column Hg concentrations and simple trophic level transfer and, thus, do not consider sediment interactions and water chemistry factors. The model, using data from published reports, was run to simulate a 25 year steady state period. For these simulations, methylmercury (MeHg) represented 5% of total Hg in Lake Erie and 8% of total Hg in Lake Superior. These proportions are roughly 3–5 times lower than U.S. EPA’s estimate that MeHg contributes about 25% of total Hg in the water column of the Great Lakes. The predicted median concentrations of total Hg in top-carnivore fish were 0.13 mg/kg in Lake Superior and 0.16 mg/kg in Lake Erie. Predicted median MeHg concentrations in Lake Superior and Lake Erie (water column) were 0.019 and 0.075 ng/L, respectively. For both lakes, most (>55%) of the Hg was partitioned to sediments. Although the MCM simulation does have practical limitations (e.g., lakes are treated as fully-mixed open systems), the results demonstrate that generic assumptions of Hg behavior in all Great Lakes waterbodies are too simplistic.

The nutrient cycling model, NuCM, which incorporates state-of-the-art understanding of the biogeochemical and transport processes controlling nutrient cycles, simulates vegetation growth, litterfall and decay, soil biogeochemical processes, and movement of water. Output of the model includes the available nutrients in soil strata and vegetation pools and the fluxes between pools on a weekly, monthly or annual basis. Solution and adsorbed concentrations in the various soil layers can be plotted versus time. The model has been used to simulate effects of acidic deposition on nutrient status at two sites: Huntington Forest, New York and Smokies Tower, Tennessee. Model results show only minor changes in nutrient status at the sites over the next 65 years at current rates of acidic deposition. The results also show only small differences in soil nutrient status between two alternative scenarios for reduction of SO(x) emissions. Neither "threshold effects" nor abrupt changes in nutrient pool sizes occurred in either of the simulations.

In analyzing the effects of acidic deposition on surface waters, a variety of assessment methods can be used. They include methods that illustrate the distribution of physical and chemical characteristics of surface waters across a geographic region and those that lend themselves to the analysis of individual basins. Within these two general areas, a variety of specific analyses can be performed.

A wide variety of processes influence the acid-base characteristics of precipitation as it flows through a watershed and into streams and lakes. These include deposition, hydrologie and chemical processes occurring in terrestrial systems, and biological and chemical interactions that take place within streams and lakes.

The Adirondack Lakes Survey Corporation (ALSC) was formed as a cooperative effort of the New York State Department of Environmental Conservation and the Empire State Electric Energy Research Corporation to better characterize the chemical and biological status of Adirondack lakes. Between 1984 and 1987, the ALSC surveyed 1469 lakes within the Adirondack ecological zone. As a follow-up to the survey, the ALSC sponsored a series of interpretive analyses of the ALSC data base. The primary objectives of these analyses were as follows: Evaluate the influence of mineral acids (from acidic deposition) and nonmineral acids (natural organic acids) on lake pH levels; classify Adirondack lakes according to lake and watershed features expected to influence their responsiveness to changes in acidic deposition; evaluate the sensitivity of Adirondack lakes to changes in environmental conditions, such as changes in mineral acids or dissolved organic carbon concentrations; identify lake characteristics important in explaining the observed present-day status of fish communities in Adirondack lakes, in particular the relative importance of lake acidity; evaluate changes that have occurred over time in Adirondack fish communities and probable causes for these trends by using the available historical data on fish communities in the Adirondacks and the ALSC data base;more » and determine the degree to which the existing fish resource might be at risk from continued acidic deposition, or might recover if acidity levels were reduced. The basic approach examined relationships observed in the ALSC data base among watershed characteristics, lake chemistry, and fish status. Individual reports are processed separately for the data bases.« less

An integrated, interdisciplinary, intensive study of three forested watersheds was started in 1977 to quantify the relationship between the deposition of atmospheric acids and surface water acidity. Results indicate the importance of using an integrated ecosystem perspective to assess the vulnerability of surface waters to acidification and the value of analysing relative flowpath contributions to understanding surface water alkalinity levels and dynamics. Important ecosystem properties affecting surface water acidity are soil depth, soil mineralogy and stage of forest development.

Observations at Woods Lake‐watershed in the Adirondacks (New York) indicate that precipitation is further acidified by passage through coniferous canopies; conversely, passage through deciduous canopies has a net alkalizing effect. Both effects are dependent upon the levels of air quality. If the aerosol concentrations were to decrease to 35% of the current levels, both types of canopy would have a net alkalizing effect on incident precipitation. If the aerosol concentrations doubled, both canopy types would be net acidifiers of throughfall. The experimental procedure of varying aerosol concentration in an enclosed chamber may provide a means for measuring foliar exudation.

A canopy model has been developed to calculate throughfall characteristics based on canopy properties, ambient air quality, and precipitation quantity and quality. The processes considered include wet and dry deposition, leaf exudation, nitrification, and oxidation of SO2 and NOx. The model has been calibrated with data collected at Woods Lake in the Adirondack Mountains of New York. The model has accurately simulated throughfall volume and the concentration of 15 throughfall chemical constituents. Ammonium (NH4+) accumulated on the canopy is nitrified rapidly, resulting in an increase in acidity and nitrate fluxes. The dominant process occurring in the coniferous canopy is dry deposition. The enrichment of acidity in coniferous throughfall is derived primarily from the accumulation of acidic air particulates. The dominant process occurring in the deciduous canopy is exudation. This partially neutralizes the 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.

The precipitation pH measured at the Woods Lake station in the Adirondack Mountains of New York fluctuated between 3.4–5.5 with a mean of 4.2 for the period extending from Mar. 1978–Dec. 1981. An analysis has been performed to identify the chemical factors causing these pH fluctuations. The pH of precipitation can be calculated from the sum of strong acid anions less the sum of base cations. The data showed that the sum of base cations increased with the sum of acid anions. However, there was only a 0.4 equivalent increase in base cations per equivalent increase in acid anions. Thus, precipitation in the Adirondacks was always acidic (pH

An 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

In the northern Great Lakes States, seepage lakes are considered more vulnerable to acidification than drainage lakes. The ILWAS model, which was developed for drainage lakes in the Adirondack Mountain Region of New York, has been revised for use in seepage lake systems. Contrasts were observed between the Wisconsin seepage lakes and the drainage lakes in the Adirondack Region of New York. (1) Atmospheric loading of hydrogen and sulfate ions was 77 and 62 percent respectively, lower in Wisconsin. (2) In contrast to the low alkalinity flow-through lakes in the Adirondacks, there are no observed spring pH depressions associated with snowmelt in Wisconsin seepage lakes. (3) Because of deep glacial deposits (32–190 m) at the Wisconsin sites, a longer contact time between groundwater and weatherable minerals provides a substantial buffering capacity via silicate hydrolysis. (4) Inlake alkalinity production by bacterial sulfate reduction in the sediments of Wisconsin seepage lakes plays a significant r...

The acid rain model has been developed to simulate lake-watershed acidification processes. It provides a quantitative linkage between atmospheric deposition and lake water chemistry. The continuous simulation model is comprised of several modules including watershed hydrology, stream and lake hydraulics, canopy, snow, soil, stream and lake chemistry. The hydrology module simulates the processes of interception, throughfall, evapotranspiration, freezing and thawing of soil, and snow accumulation and melting. The model segregates the watershed horizontally into subcatchments and vertically into soil layers. Flows are routed through a layered soil profile to the streams and ultimately to the lake. Incoming precipitation and deep groundwater flow. Application of the model to Panther and Woods Lake basins in the Adirondack mountains of New York indicates the importance of flowpaths in determining lake water acidity.

Sulfate and nitrate removal, and the resulting sulfuric and nitric acid neutralization within acid-sensitive lakes, were predicted from a simple model requiring knowledge only of water residence time, mean depth, and average mass transfer coefficients for nitrate and sulfate removal. The model applies to lakes with oxic hypolimnia which are typical of acid-sensitive lakes. Average mass transfer coefficients for sulfate and nitrate were obtained by two independent methods which agreed well with each other. A model such as this is necessary for predicting the rates at which different lakes acidify and recover from acidification, and explains why lakes with short water residence times are especially susceptible to acidification.

ACID neutralizing capacity (ANC) is used to quantify the acid-base status of surface waters. Acidic waters have been defined as having ANC values less than zero, and acidification is often quantified by decreases in ANC. Measured and calculated values of ANC generally agree, except for low-ANC waters. These waters, however, are of primary interest in lake-acidification studies. The discrepancy in ANC values is greatest for waters with high concentrations of aluminium and/or dissolved organic carbon (DOC). The discrepancy due to aluminium increases with increasing concentration of dissolved monomeric aluminium (Alm) and can exceed 50 (μeq 1−1 at low pH and high Alm values. Here we show that this error can be minimized by using a proton reference level for aqueous aluminium of 2+, rather than 0 or 3+, as is done usually. The value of 2+ is consistent with the mean charge on aluminium at the equivalence point of strong-acid titrations. The discrepancy between calculated and measured ANC also increases with increasing DOC concentrations, exceeding 50 μeq 1−1 for waters with DOC concentrations greater than 800 μmol C 1−1 (1000 μmol C 1-1 = 12 mg 1−1 DOC). This error can be decreased by titrating to a low consistent pH value (for example, 3.0). This reduces the systematic underestimation of ANC due to curvature in Gran1 plot analysis, while still allowing accurate measurement of increments in hydrogen-ion concentration. ANC should not be used as a single parameter for characterizing the chemical suitability of surface waters for biota or for assessing the susceptibility of low-ANC waters to acidification by acid deposition.

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.

The ALBIOS project was conducted to examine the influence of acidic deposition on aluminum transport and toxicity in forested ecosystems of eastern North America and northern Europe. Patterns of aluminum chemistry were evaluated in 14 representative watersheds exposed to different levels of sulfur deposition. Controlled studies with solution and soil culture methods were used to test interspecific differences in aluminum sensitivity for one indicator species (honeylocust - Gleditsia triacanthos L. ) and six commercial tree species (red spruce - Picea rubens Sarg., red oak - Quercus rubra L., sugar maple - Acer saccharum Marsh., American beech - Fagus grandifolia Ehrh., European beech - Fagus sylvatica, and loblolly pine - Pinus Taeda L. ). Overall, red spruce was the tree species whose growth was most sensitive to soluble aluminum, with significant biomass reductions occurring at Al concentrations of approximately 200–250 umol/L. Analyses of soil solutions from the field sites indicated that the conditions for aluminum toxicity for some species exist at some of the study areas. At these watersheds, aluminum toxicity could act as a contributing stress factor affecting forest growth.