U.S. Department of Interior

U.S. Geological Survey

Benthic Flux of Metals and Nutrients

into the Water Column of

Lake Coeur d'Alene, Idaho:

Report of an August, 1999, Pilot Study

Water-Resources Investigations Report 00-4132

Coring Setup Lander Transport
 RTS# R3-0352 

Benthic Flux of Metals and Nutrients into the Water Column of 

Lake Coeur d’Alene, Idaho: 

Report of an August, 1999, Pilot Study 

By James S. Kuwabara1, William M. Berelson2, Laurie S. Balistrieri3, Paul F. Woods4, 

Brent R.Topping5, Douglas J. Steding6, and David P. Krabbenhoft

7

. 

______________________________________________________________________ 

U.S. GEOLOGICAL SURVEY 

Water-Resources Investigations Report 00-4132 

1 kuwabara@usgs.gov, U.S. Geological Survey, Menlo Park, CA 

2 berelson@usc.edu, University of Southern California, Department of Geological Sciences, Los 

Angeles, CA 

3 balistri@usgs.gov, U.S. Geological Survey, Seattle, WA 

4 pfwoods@usgs.gov, U.S. Geological Survey, Boise, ID 

5 btopping@usgs.gov, U.S. Geological Survey, Menlo Park, CA 

6 dsteding@emerald.ucsc.edu, University of California, Department of Earth Sciences, Santa 

Cruz, CA 

7 dpkrabbe@usgs.gov, U.S. Geological Survey, Madison, WI 
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary 

U.S. GEOLOGICAL SURVEY 

Charles G. Groat, Director 

Any use of trade, product, or firm names is for descriptive purposes only and does not imply 

endorsement by the U.S. Geological Survey. 

______________________________________________________________________ 

For addition information write to: Copies of this report may be purchased from: 

James S. Kuwabara U.S. Geological Survey 

U.S. Geological Survey Branch of Information Services 

345 Middlefield Road, MS 439 Box 25286 

Menlo Park, CA 94025 Denver, CO 80225 
 TABLE OF CONTENTS 

Executive Summary --------------------------------------------------------------- 4 

Recommendations ----------------------------------------------------------------- 9

Background -------------------------------------------------------------------------10

Results and Discussion ------------------------------------------------------------12

References Cited -------------------------------------------------------------------24

Acknowledgements ----------------------------------------------------------------28

Appendix 1: Comments on the Report Structure ------------------------------29

Appendix 2: List of Figures ------------------------------------------------------30

Appendix 3: List of Tables --------------------------------------------------------32

 

 
Benthic Flux of Metals and Nutrients into the Water Column of 

Lake Coeur d’Alene, Idaho: Report of an August, 1999, Pilot Study 

By James S. Kuwabara, William M. Berelson, Laurie S. Balistrieri, Paul F. Woods, 

Brent R. Topping, Douglas J. Steding, and David P. Krabbenhoft. 

Executive Summary 

A field study was conducted between August 16 – 27, 1999, to provide the first direct 

measurements of the benthic flux of dissolved (0.2-micron filtered) solutes between the bottom 

sediment and water column at two sites in Lake Coeur d’Alene, Idaho, (Background, Fig. 1, 

Field Schedule: Table 1). Trace metals (namely, cadmium, copper, manganese, mercury 

species, and zinc) and nutrients (namely, ammonia, nitrate plus nitrite, oxygen, orthophosphate 

and silica) were solutes of primary interest. Benthic flux (sometimes referred to as internal 

recycling) represents the transport of dissolved chemical species between the water column and 

the underlying sediment. 

With a variety of remedial strategies under consideration for the Coeur d’Alene River 

basin, the primary question posed in this pilot study was, “Is the magnitude of the benthic flux of 

metals and nutrients in Lake Coeur d’Alene significant relative to riverine inputs?” The question 

was motivated by a number of factors. First, a significant mass of metal has accumulated in 

bottom lake sediments downgradient of long-term (decadal time scales) mining activities 

(Horowitz and others, 1995). One might therefore question whether some fraction of these 

sediment-associated solutes may become remobilized for transport to the overlying water. 

Second, initial diffusive-flux calculations (Balistrieri, 1998) indicated that benthic flux of certain 

dissolved metals, like zinc and lead, may be significant at certain lake locations (i.e., the 

concentration gradient at the sediment-water interface, as described above, was large enough to 

drive significant transport). Third, water-column gradients for all metals and nutrients (except 

manganese) have exhibited increases near the bottom sediment as one might expect when a 

benthic source is dissipated upwards and horizontally. Fourth, changes in oxidizing or reducing 

(redox) conditions and nutrient availability near the sediment-water interface can dramatically 

alter the mobility of metals and ligands associated with the bottom sediment of the lake (La 

Force and others, 1998). Ligands are anions or molecules that form complexes with metals. 

Finally, there is a growing body of evidence from other aquatic systems that benthic flux or 

internal recycling of contaminants and nutrients is an important process to consider in 

developing appropriate water-quality models (Berelson and others, 1982; Flegal and others, 

1991; Kuwabara and others, 1999). The question posed in this pilot study may therefore affect 

our fundamental view of contaminant transport in Lake Coeur d’Alene. 

This report is formatted unconventionally in the fashion of a pyramid in an effort to 

effectively serve the diverse group of people that want to access the information in various levels 

of detail (Appendix 1). Using hyperlinks to supporting figures and tables, and an electronically 

linked Table of Contents, the report enables quick transitions between the initial summary 
information (figuratively at the top of the pyramid) and later details of methods or results (that is, 

figuratively towards the base). 

Both sampling sites for this study were in Lake Coeur d’Alene down gradient of the 

mouth of the Coeur d’Alene River: one in the main channel 7 km down gradient of the mouth of 

the river (33 m depth), and the other in an embayment, Mica Bay, 17 km down gradient of the 

mouth (27 m depth). At each site, water-column samples were collected to observe any vertical 

water-quality gradients. An in situ flux chamber, hereafter referred to as a lander, automated to 

sample chamber water 6 times during an incubation period, was deployed multiple times at each 

site (i.e., four times in Mica Bay and three times at the main channel site; Table 1) to determine 

dissolved nutrient, oxygen, radon, metal and bromide (tracer) fluxes (Fig. 2). Sediment cores 

were also collected for incubation experiments to provide complementary flux estimates and 

benthic biological characterizations (Fig. 3). These benthic flux measurements were often 

similar in magnitude to areally averaged riverine fluxes. The following major observations from 

interdependent physical, biological and chemical data were made: 

Physical Data 

1. The surficial substrate at both embayment (Mica Bay) and main-channel (near mouth 

of Coeur d’Alene River) sites was characterized by high porosity (~ 90%) at the 

sediment-water interface. This is consistent with direct observations of 

unconsolidated surficial material in incubated cores (Table 2; Methods). 

2. Composition of the surficial material was quite different at the sites, with Mica Bay 

exhibiting detrital and macroinvertebrate-associated material, while the main-channel 

surficial material was dominated by inorganic particles coated with an orange, ferric 

hydroxide-like material (Fig. 4). Analysis of the coating mineralogy is proceeding. It 

should be noted that if the coating was primarily ferric hydroxide, the neutral pH of 

the water column would provide conditions favorable for adsorption of metals and 

certain ligands (e.g., orthophosphate) onto these coatings, thereby affecting the 

mobility of these solutes. 

Biological Data

1. The biological data reflected an oligotrophic system where taxonomic analyses 

revealed very few if any living macroinvertebrates even at Mica Bay where only 

remnant material from macroinvertebrates were abundant (Table 3). 

2. Chlorophyll-a concentrations were consistently below 5 micrograms per square 

centimeter (Table 4). 

3. Benthic bacterial concentrations were of the order of 108

 - 109 cells per gram-surficial 

sediment (Table 5). These concentrations fall within a wide range of published 

concentrations for lake sediments from approximately 106 – 107 cells per dry gram 

lake sediment using plate-counting techniques (Hayes and Anthony, 1959; Young, 

1978; Ehrlich, 1981) to 106 - 1010 cells per dry gram lake sediment using direct counts 

((Jones and others, 1979, Harrington and others, 1998a). These microbial 

communities may be critical in establishing the redox gradients that regulate the 
remobilization, transformation and subsequent transport of sediment-associated 

contaminants. 

Chemical Data - Multiple lines of evidence indicate that benthic flux at both lake sites 

was diffusion dominated during our pilot study in August. Because of the broad scope of 

chemical parameters determined in this study, the observations are organized with parameters of 

similar behavior. Unless otherwise specified, the concentrations discussed in this section 

operationally refer to dissolved (i.e., 0.2 micron-filtered) samples. 

1. Dissolved oxygen, radon and injected bromide – Dissolved oxygen was measured 

during lander deployments as an indicator of microbial respiration of carbon, and 

oxidation of reduced metals. Bromide and radon were used as tracers of hydrologic 

transport between chamber water and sediment pore water. Dissolved oxygen was 

measured in cores to confirm contrasting overlying-water conditions during coreincubation experiments (Table 6). 

a. Dissolved oxygen – Oxygen consumption measured during lander 

deployments was similar between stations and deployments (combined range 

of 6.0 to 9.5 millimoles O2 per square meter per day; Table 7). This range is 

consistent with the low biological activity reflected in the macrofaunal and 

benthic chlorophyll-a analyses. There was no spatial pattern to the oxygen 

flux data with respect to Mica Bay or the main-channel station near Rockford 

Bay (Oxygen discussion). 

b. Bromide – The temporal loss of injected bromide during lander deployments 

for all sites indicated that diffusion was the primary transport process 

occurring on the lake bottom during the pilot study. There is enough 

uncertainty in the Br data and the diffusion model to allow for some small 

amount of bio-irrigation, but the system is predominantly diffusive (Bromide 

discussion). 

c. Radon-222 – Diffusive flux of radon, predicted from sediment radium 

measurements, is consistent with the measured fluxes of radon. This provides 

another line of evidence that diffusion is the primary transport mechanism for 

exchange of dissolved chemical species across the sediment-water interface 

(Radon discussion). 

2. Water-column gradients – Concentrations for all nutrients and metals, except 

dissolved manganese, indicate a vertical gradient at both sampling sites with elevated 

concentrations of dissolved chemical species near the sediment-water interface 

relative to shallower depths (Table 8). This may be generated by an upward benthic 

source, a settling of detrital material from the euphotic zone that becomes 

remineralized, a density-driven horizontal source, or a combination of the three 

(Fig. 5; Water-column discussion). 
3. Nutrients (nitrogen species, orthophosphate and silica) – With the exception of 

dissolved silica, benthic flux of macronutrients determined from both lander 

deployments and core incubations were consistently significant (that is of equivalent 

or greater order of magnitude) relative to riverine sources. Although the results of 

this pilot study do not provide estimates of temporal variability of these fluxes and 

only first-order estimates of spatial variability, initial determinations would strongly 

suggest that benthic nutrient sources should not be neglected in nutrient-cycling 

models that affect water-quality management decisions. 

Benthic flux ratios of total dissolved nitrogen to orthophosphate, derived from Lander 

results, suggest that the sediments act as effective traps for biogenically derived P. 

(Nutrient discussion) 

Silica benthic flux determined from lander deployments provides a fourth line of 

supporting evidence of diffusion-control benthic flux at both sampling sites during 

the pilot study. By comparison, core incubations generated silica benthic fluxes that 

were consistently three to four times higher than observed in lander deployments. 

These methodological differences in diffusive transport may help explain differences 

in metal benthic flux estimates derived from the two approaches (See discrepancies

below; Nutrient discussion) 

4. Benthic flux of metals – Flux estimates from both lander deployments and coreincubations, when averaged over the affected lake area, were of similar magnitude as 

the dissolved-metal flux from the Coeur d’Alene and St. Joe Rivers even with 

oxygenated bottom waters in the lake (Table 9; Metals discussion). This is consistent 

with previous diffusive flux calculations determined from pore-water concentrations 

gradients (Balistrieri, 1998), and with the potential remobilization of sedimentassociated metals that have been widely distributed at elevated concentrations on the 

lake bottom (Horowitz and others, 1995). Although core-incubations were designed 

to bracket the dissolved-oxygen conditions in the lake, discrepancies between the 

lander and core-incubation results suggest that the perturbations involved in the latter 

design, namely bubbling rather than magnetically stirring the overlying water of 

incubated cores, may have resuspended and altered chemical gradients at the 

sediment-water interface significantly. 

Like the nutrients, some metals exhibited a positive flux that primarily occurred 

during the initial hours of incubation or deployment. Flux estimates presented in the 

tables indicate how nonlinearities generate lower flux estimates and coefficients of 

determination when data from the entire deployment or incubation were used relative 

to the initial hours (Core fluxes: Table 10, Lander fluxes: Table 11). This behavior 

suggests that for certain metals and nutrients a chemical equilibrium between the pore 

water and overlying water in the core or chamber was reached rapidly relative to the 

entire period of incubation or deployment. 

With the possible exception of dissolved lead, no consistent trends between aerated 

and argon-purged cores were evident. 
In the development of future remediation strategies for the watershed, it would seem 

unwise at this point to discount the importance of metal remobilization from the 

sediment, because measured benthic fluxes were significant in magnitude relative to 

riverine inputs. 

5. Mercury - The first estimates of the benthic flux of dissolved mercury (total and 

methylated forms) for Lake Coeur d’Alene were determined. The total mercury and 

methyl-mercury flux from the sediment into the water column were of the order of 

0.1 and 0.001 micrograms per square centimeter per year, respectively. This is orders 

of magnitude lower than the benthic flux of other metals, but similar to values 

determined elsewhere (Mercury discussion, Fig. 7). Consistent with previous studies, 

methyl-mercury flux in aerated cores was lower than in purged cores. Because this 

represents the first dissolved mercury study for the lake using ultra-clean sampling 

and analytical techniques, no comparative riverine-flux estimate is available. 

With highly collaborative efforts between scientists, managers and stakeholders in 

general, initial steps are being taken to build process-integrated solute-transport models for the 

lake that may ultimately represent a critical management tool for the watershed. Recent benthic 

flux studies have only begun to address questions related to the importance of this process, and 

formidable challenges remain. Because redox sensitive zones in contaminated aquatic systems 

are so common, there is strong motivation to methodically overcome those challenges and find 

relevant answers. 
RECOMMENDATIONS 

1. As initially proposed, implement a sampling design that would provide spatial and 

temporal resolution of the variability of benthic fluxes for dissolved chemical species 

of environmental concern to determine if the fluxes as spatially similar as observed 

between Mica Bay and the main channel site in August, 1999, and to determine the 

magnitude and direction of fluxes across the sediment-water interface if the benthic 

community is as dense as observed by Ruud (1996). 

2. Run one set of core-incubations without bubbling (using conventional magnetic 

stirring) in coordination with a lander deployment to determine whether comparable 

flux estimates are thereby generated. 

3. Because the lake hypolimnion was oxic during the pilot study, it would be useful in 

future deployments to determine the benthic flux of dissolved species when the 

overlying water in the lander chamber is allowed to go anoxic. 

4. As a test of the diffusive model, inject a microbial inhibitor into the lander chamber to 

observe any effects on benthic flux. Molybdate may be injected as an inhibitor of 

sulfate reduction so that the contribution of the sulfate-reducing bacteria to methylmercury production could be quantified. 

5. Microbial studies in coordination with benthic flux experiments and measurements of 

carbon and nitrogen species would determine the temporal and spatial importance of 

denitrification as a component of nitrogen cycling in the lake. 

6. Microbial studies are needed to quantify manganese reduction rates. 

7. With such consistently high manganese benthic fluxes, why is there no water-column 

gradient for dissolved manganese? Does dissolved manganese (0.2 micron filtered) 

precipitate over time scales longer than our experiment. A simple field test could be 

performed to determine if manganese precipitated or aggregated to a filterable size in 

the water-column samples while being stored. 

8. Pore-water studies with sediment chemistry that are coordinated with direct benthic 

flux measurements would provide critical information to interpret and develop 

quantitative models for processes regulating contaminant distribution in the lake. 
BACKGROUND - What is benthic flux and why should it be considered?

Many fundamental processes affect the transport of dissolved chemical species (either a 

nutrient or a toxic substance; metal or ligand) through and within a lake. A conceptual model of 

these processes (Fig. 6) illustrates some familiar physically based processes that have been 

examined and carefully quantified for several years (e.g., advective transport and point source 

inputs). 

Conversely, there are flux terms in the conceptual model that have received little attention. 

A prime example is the benthic flux term where no direct measurements have heretofore been 

available for Lake Coeur d’Alene. Benthic flux (sometimes referred to as internal recycling) 

represents the transport of dissolved chemical species between the water column and the 

underlying sediment. This flux can be either positive (that is, out of the sediment into the water 

column) or negative (consumed by the sediment). It can be variable over multiple temporal and 

spatial scales. 

As a result of physical, chemical and biological changes in the vertical cross section, 

geochemical gradients take on a variety of forms (Fig. 8). The simplest case is when there is no 

gradient (That is, the concentrations of a substance above and below the sediment-water interface 

are equivalent.) In this case, there is no net transfer of that substance across the interface; no 

benthic flux. In contrast, concentrations of a dissolved substance may decrease in the water 

column and continue to decrease in the bottom sediment until that concentration is negligible. 

This would be typical of a negative benthic flux where the sediment consumes a substance, 

represented by dissolved oxygen where microbial respiration may create a sediment demand for 

oxygen. 

Other vertical concentrations gradients near the sediment-water interface may show watercolumn concentration increasing near the sediment-water interface and continuing to increase in 

the sediment pore waters. This gradient can physically drive the release of dissolved chemical 

species from the sediment to the overlying water, generating a positive benthic flux. This might 

be represent by the diffusive flux of a metal or ligand that is remobilized in the sediment due to 

biotic and abiotic repartitioning reactions. 

As with most processes in nature, confounding factors may regulate the benthic flux of 

biologically reactive substances. The vertical gradient for one dissolved species may be 

dependent on the gradient of another chemical species. For example, an attenutated release 

may occur when solute concentrations increase below the sediment-water interface only when 

another solute is depleted. Dissolved iron often falls within this category as suboxic conditions 

increase its solubility as it reduces from ferric to ferrous forms. Additionally, macroscopic 

invertebrates can biologically enhance the benthic flux by irrigating, or perturbing surficial 

sediment layers (bioirrigation or bioturbation). Certain productive benthic communities can 

enhance diffusive flux by orders of magnitude. In summary, vertical chemical gradients 

generated by a variety of interdependent processes induce the movement of a dissolved chemical 

species across the sediment-water interface. 
In many aquatic environments, scientists and water-quality managers are only beginning to 

appreciate the importance of benthic flux. In recent years (that is within the past decade or two) 

people have gradually realized that there are non-hydrologic processes like benthic flux that must 

be incorporated into water-quality models to generate physically meaningful modeling results. 

The USGS has been involved in studies at lake Coeur d’Alene for about a decade, but as with 

many other environments, benthic-flux studies began only recently, in this case pore-water 

studies were done in 1992 and benthic flux calculations were done in 1998 (Balistrieri, 1998). 

Relative to other flux terms, quantifying benthic flux is instrument and manpower intensive. 

As described in the Executive Summary, the primary question posed in this pilot study was, 

“Is the magnitude of the benthic flux of metals and nutrients significant relative to riverine 

inputs?” Although the technical rationale for posing that question is multifaceted (introductory 

comments), a major objective of the pilot study is to offer some help and scientific basis for 

directing regulatory strategies for the watershed by providing the first comparisons of direct 

benthic-flux measurements to riverine fluxes. For substances of potential environmental concern 

like mercury, where there has been little or no prior speciation studies, the first benthic flux 

measurements for the lake are provided. These initial measurements may be critical in 

developing a basin-wide understanding of the transport processes that regulate the distribution of 

nutrient and toxic solutes (that is, a budget for environmentally significant chemical species). 
RESULTS AND DISCUSSION 

Physical Data – Please refer to porosity table (Table 2). 

Biological Data

1. Macroinvertebrates – Three striking differences were observed between the cores 

from within Mica Bay and from the main channel. First, Mica Bay cores contained 

many empty invertebrate cases (exoskeletons) compared to virtually none in mainchannel cores. Whether the empty invertebrate cases in Mica-Bay cores originated at 

the site or were transported to the site is unknown. Higher frequency temporal 

sampling would probably determine whether there is an active benthic invertebrate 

community at these sites. Second, Mica Bay cores contained more organic detritus. 

Finally, cores from the main channel contained predominately large inorganic 

particles (Methods, Table 12) 

A compilation of results from benthic lake studies indicates that the benthic 

community sampled during the pilot study was sparse at both sites relative to other 

oligotrophic or mesotrophic lakes (Fig. 9). Although this scarcity of 

macroinvertebrates (0-130 individuals per square meter) is consistent with 

preliminary samples taken in October, 1998, Ruud (1996) observed 

macroinvertebrate abundances two orders of magnitude greater in deep-lake 

sediments (water-column depths of 20 and 40 meters) in October, 1995. He reported 

a range of 10,000 to 98, 695 individuals per square meter from Ekman Bottom 

Dredge grab samples. The variability in macroinvertebrate abundance between and 

within studies indicates that the diffusion-dominance of benthic flux observed in this 

study may not always hold (Table 3). 

2. Chlorophyll-a – Please refer directly to table summaries (Table 4). 

3. Benthic bacteria – Previous microbial studies of Lake Coeur d’Alene sediments have 

consistently described the importance of the microbial community at establishing 

gradients in oxidation-reduction potential that facilitate changes in the chemical 

structure, mobility and biological availability of contaminants, particularly arsenic, in 

the lake (Harrington and others, 1998b; Cummings and others, 1999). Harrington and 

others (1998a) reported total microbial abundance in Lake Coeur d’Alene surficial 

sediments of ~108

 cells per gram wet weight by direct epifluorescent counts. Given 

the high porosity of surficial sediments (Table 2) this range converts to ~109 cells per 

gram dry weight; a range consistent with the direct epifluorescent determinations of 

this study (Table 5). Estimated sulfate-reducing bacteria concentrations as high as 

106 cells per gram wet weight are among the highest reported (Harrington and others, 

1998b). Given the benthic chlorophyll and macroinvertebrate results from this pilot 

study, one might logically question where the carbon source is that supports such 

impressive microbial abundances. 
Chemical Data – For consistency with previous geochemical studies of Lake Coeur 

d’Alene, concentrations and flux estimates are provided in mass units. However, in the 

discussion of these results, especially with biologically related uptake or release that occur on a 

molecular basis, mass units are much less meaningful than molar units. Therefore the discussion 

of dissolved chemical species, particularly with regard to nutrient fluxes and flux ratios are 

presented in molar units with equivalent mass units parenthetically provided . 

1. Dissolved oxygen – Consistent with the low benthic chlorophyll-a concentrations (< 

5 micrograms per square centimeter), oxygen-consumption rates are reflective of low 

benthic biological activity. Cornwell and Kipphut (1992) determined similar oxygen 

fluxes into Toolik Lake sediments that averaged 7.6 millimoles O2 (240 milligrams) 

per square meter per day and described them as “extremely low rates of benthic 

oxygen consumption for a lake environment.” This is consistent with lake data 

compiled by Hutchinson (1957) and Hayes and MacAulay (1959) indicating a range 

of benthic oxygen consumption from 2 – 33 millimoles O2 (64 – 1100 milligrams) per 

square meter per day. Hargrave (1969) compiled oxygen results from various aquatic 

environments and determined that much of the variability in the data (r2

 = 0.72) could 

be explained by bottom-water temperature. His empirical expression: ln(Y) = 

1.74ln(T) - 1.30, where Y is sediment oxygen consumption in milliliters O2 per 

square meter per hour, and T is temperature in degrees centigrade, may be applied to 

Lake Coeur d’Alene (bottom-water temperature of 7oC at time of sampling). The 

modeled oxygen-consumption rate would be within the range of measured values (~8 

millimoles O2 (260 micrograms) per square meter per day). This suggests a possible 

link between microbially mediated sediment-oxygen demand and bottom-water 

temperature that could be tested in future studies. 

2. Bromide – Multiple approaches were used to confirm that benthic flux from lake 

sediments during the pilot study was diffusion dominated. First and most directly, 

there simply was not enough biota to generate biologically enhanced advection 

through bioirrigation or bioturbation (Table 12). Secondly the time series of injected 

bromide consistently indicated a loss of bromide into the sediment that is consistent 

with diffusive rates (Table 13, Fig. 10). Finally, radon emanation measurements also 

indicate a flux from the sediments into the water column that is diffusion dominated 

(Table 7). So the conceptual model for benthic flux would be somewhat simplified, 

because the benthic community exerted negligible effect on flux due to bioirrigation 

or bioturbation. This is contrary to many other aquatic systems where the benthic 

biota can enhance the flux by orders of magnitude. It should also be noted that 

macroinvertebrate abundances measured at other sites in Lake Coeur d’Alene in 

October, 1995 by Ruud (1996) suggests that there is dramatic spatial and temporal 

variability in benthic-macroinvertebrate abundance, and so this simplification may 

not always hold. 

In addition to measurements of bromide loss to the sediment, the initial bromide 

concentration after injection was used to determine the overlying water-column 

heights in the lander’s flux chamber which were approximately 7.6 and 10.0 

centimeters for the second and fourth Mica Bay deployments, and 11.4, 13.1 and 12.8 

centimeters for the three main-channel deployments, respectively. The first 
deployment at Mica Bay overpenetrated the sediment and the chamber height of the 

third Mica Bay deployment was apparently (based on dissolved-oxygen chamber 

data) modified twice during the incubation by public tampering. 

3. Radon-222 – Consistent radon flux from lander deployments and predicted sediment 

flux from radium measurements indicated that diffusion is the primary transport 

mechanism for exchange of dissolved chemical species across the sediment-water 

interface. The virtual absence of a macroinvertebrate community to enhance 

advective transport by bioturbation corroborates this conclusion. 

Radon fluxes from the chambers were determined to range from 99-242 atoms per 

square meter per second, with all but one of the chamber fluxes between 99-128 

atoms per square meter per second. The one site with the high radon flux value 

cannot be easily interpreted as a site of high bio-irrigation as the Br data do not 

support this interpretation. It is possible that the distribution of Ra in lake sediments 

is patchy. The flux values reported are 10-20% greater than fluxes established by 

excluding bottom water from the model fit. However, including the radon in bottom 

water value to the model fit adds constraint to the flux by significantly increasing the 

number of data points modeled. The flux values are reported using both approaches 

(Table 7). 

The diffusive flux of radon at the Mica Bay and main-channel sites were determined 

to be approximately 110 and 133 atoms per square meter per second, respectively. 

That the diffusive flux of radon, predicted from the sediment radium measurements, 

agrees so well with the measured fluxes of radon is clear indication that diffusion is 

the primary transport mechanism for exchange of dissolved species between the 

bottom sediment and overlying water column. The bromide and radon data show 

good agreement on this point. 

Few other measurements of lake sediment radon emanation rate are published, but 

they indicate that radon fluxes in Lake Coeur d’Alene are 2-4 times greater than 

typical lake sediments (Imboden and Joller, 1984; Emerson, 1974). This relatively 

high flux of radon from Lake Coeur d’Alene sediments indicates that the sediments of 

the lake have scavenged a large amount of radium. Mn-oxides are known to be 

effective at scavenging Ra and thus the oxides present in lake sediments are likely the 

source of the large radon fluxes measured. 

4. Water-column gradients – With the exception of dissolved manganese, water-column 

concentrations for all nutrients and metals were elevated near the sediment water 

interface relative to the shallower depths (Fig. 5; Table 8). As indicated in the 

Background Section (Fig. 8), this trend is one indication that remobilization and 

accumulation of a chemical species in pore waters can result in a release of those 

solutes into the overlying water, generating a positive benthic flux. It should be 

noted, however, that elevated bottom-water concentrations may also be generated by 

a settling of detrital material from the euphotic zone that becomes remineralized, or 

by a density-driven, horizontal, riverine source. Given that elevated trace-metal 
concentrations in bottom lake waters were also observed in October, 1998, when 

Chlorophyll-a concentrations are not typically elevated, it seems less likely that the 

settling of planktonic material caused the observed water-column gradients (Woods 

and Beckwith, 1997). Furthermore, the density driven horizontal source is unlikely 

because such thermal stratification, generated by colder riverine water relative to 

shallow lake water only occurs during winter months (Woods, unpublished data). 

Conclusive identification of the dominant process that generated elevated bottomwater concentrations is beyond the scope of this pilot study, but circumstantial 

evidence would emphasize a benthic source to the overlying water. 

5. Nutrients - Oxygen uptake is likely partitioned into two major reactions, oxidation of 

organic carbon and oxidation of reduced metals. As the flux of reduced Fe and Mn is 

positive, out of the sediments, it could be assumed that the oxygen uptake rate 

measured by the chamber is primarily the result of carbon oxidation. The molar ratio 

of oxygen uptake to carbon oxidation is typically assigned a value of 1.2 (that is, the 

inverse of the respiratory quotient). Thus it could also be assumed that between 6 and 

7 millimoles C (72 to 84 milligrams) per square meter per day were being consumed 

on the lake floor. If a system is in steady state, this value of benthic carbon oxidation 

must represent the minimum value for lake primary productivity. 

The ratio between carbon oxidation and ammonia release is dependent on the carbon 

to nitrogen ratio in the organic matter undergoing degradation. Freshwater algae have 

a molar carbon to nitrogen ratio of approximately 6.7 (5.7 mass ratio, Wetzel, 1983). 

The expected efflux of N, either as ammonium or nitrate would be about 1 millimole 

N (14 milligrams) per square meter per day (That is, oxygen uptake divided by 1.2 

and by 6.7). The measured efflux of fixed N is 0.4-0.6 millimoles N (5.6 to 8.4 

milligrams) per square meter per day. This indicates that: (a) the molar carbon to 

nitrogen ratio of lake algae is closer to 14 than 6.7, or (b) sedimentary nitrification 

and denitrification are responsible for transferring roughly 50% of the fixed N into 

N2, thereby removing it from the nutrient pool of the lake, or (c) some combination of 

both explanations is true. 

With the exception of dissolved silica, estimates of macronutrient benthic flux from 

lander deployments and core-incubations were consistently similar to or greater than 

areally averaged riverine flux (Table 9). In an oligotrophic aquatic system, the 

concept of a limiting nutrient is a fragile one, because typically the concentrations of 

dissolved substances are balanced in such a way that minimal changes in 

concentration of one chemical species can alter nutrient limitation. The mechanism 

of zinc toxicity to aquatic primary producers is an interference with phosphorylation 

reactions (Bates and others, 1982; Kuwabara, 1985). So as zinc bioavailability 

increases, phosphate assimilation is retarded. Conversely, when phosphate 

bioavailability increases, zinc toxicity effects are mitigated. Because orthophosphate 

has a high affinity to adsorb onto metal-oxide surfaces under oxic, pH-neutral 

conditions (Kuwabara, 1992), the molar nitrogen to phosphorus (N:P) flux ratios for 

Lake Coeur d’Alene have particular significance. The molar N:P flux ratio into 

benthic chambers is 33 for Mica Bay and 70 for the Rockford site (Fig. 11). By 

comparison, the molar N:P Redfield Ratio is only 16 (7 by mass ratio). That is, on 
average, approximately 16 moles of nitrogen (220 grams) is taken up for every mole 

of phosphorus (31 grams) to generate freshwater algal tissue . The higher benthic 

flux ratio of nitrogen to phosphorus for both sites suggests that the lake sediments act 

as effective traps for biogenically derived P, and could significantly affect 

orthophosphate availability, and hence zinc toxicity, in the water-column by 

sorption/desorption reactions. The molar N:P riverine flux in 1999 was 

approximately 32, also much higher than the Redfield Ratio. 

Dissolved silica fluxes complement bromide injections as a natural tracer of physical 

and biologically enhanced solute transport across the sediment-water interface. 

Previous benthic studies have focused on bacterial and macroinvertebrate 

communites (Ruud, 1996; Cummings and others, 1999), and very little is known 

about the structure of the benthic algal community. However, based on the fact that 

diatoms consistently dominate the phytoplankton community structure (Woods and 

Beckwith , 1997), it is reasonable to speculate that diatoms also represent a 

significant component of the benthic algal community. Assuming that the silica flux 

results from dissolution of biogenic material (e.g., diatom frustules) as it does in other 

aquatic systems, a stoichiometric relationship similar to a Redfield Ratio can be used 

to estimate a silica flux (Si:N molar ratios of approximately 0.8 to 1.2; Brezeninski, 

1985). Using calculations analogous to those for total nitrogen above, one might 

expect silica fluxes to be approximately the (oxygen uptake)/(1.2*6.7*(N:Si)) or 0.6 

to 1.4 millimoles of silica per square meter per day (600 to 1500 micrograms silica 

per square centimeter per year). This is consistent with the measured silica fluxes 

from the lander deployments (1148 to 1866 micrograms silica per square centimeter 

per year; (Table 14: Si)). In contrast, elevated dissolved silica fluxes were determined 

from core incubations (2897 to 6164 micrograms silica per square centimeter per 

year; (Table 14: Si)) relative to: (1) estimates derived above based on biogenic 

dissolution, (2) measured fluxes from lander deployments, and (3) diffusive silicaflux estimates based on reported interstial-water concentrations in the vicinity of our 

sampling sites (i.e., data from Vahalla and East Point; Balistrieri, 1998). The 

elevated dissolved silica fluxes during core incubations is consistent with the idea that 

excessive mixing of the overlying water in the cores may have disrupted the chemical 

gradients at the sediment-water interface (See Dissolved Zn and Cd) 

Time series of dissolved nutrients from incubated core indicated that concentration 

increases in the overlying water primarily occurred in the initial hours of the 

incubation. However, even if data over the entire incubation are used in the flux 

calculation, the benthic flux of orthophosphate and nitrogen species are still 

significant relative to areally averaged riverine fluxes (Table 9). For example, the 

average orthophosphate fluxes from Mica Bay and main-channel cores were 100 and 

120 micrograms phosphorus per square centimeter per year, respectively, compared 

with a riverine flux of approximately 60 micrograms per square centimeter per year 

from the St. Joe and Coeur d’Alene Rivers in 1999 (Woods and Beckwith, 

unpublished data; Table 9). Ammonia benthic flux averaged approximately 730 and 

300 micrograms nitrogen per square centimeter per year from Mica Bay and mainchannel cores. This is within the same order of magnitude of total nitrogen flux from 
the St. Joe and Coeur d’Alene Rivers in 1999 (approximately 560 micrograms per 

square centimeter per year). 

Trace Metals (General observations) - The magnitude of the flux varied among metals 

over orders of magnitude (Fig. 12). Measured flux was not always positive or out of the 

sediment. Negative fluxes represent solute transport into the sediment from the overlying 

water. For each of the metals the magnitudes of the the fluxes, whether positive or 

negative, are significant relative to areally averaged riverine fluxes (Table 9). Data from 

1999 monitoring efforts indicate that riverine inputs of metals are predominantly from the 

Coeur d’Alene River. 

6. Copper, iron and mercury species. These solutes, like the nutrients, exhibited a 

positive flux that primarily occurred during the initial hours of incubation or 

deployment. Calculations provided in the tables indicate how nonlinearities generate 

lower flux estimates and coefficients of determination when data from the entire 

deployment or incubation was used relative to the initial hours (Table 15; Fig. 7, Fig. 

13, Fig. 14). This behavior suggests that for certain solutes a chemical equilibrium 

between the pore water and overlying water in the core or chamber was reached 

rapidly relative to the entire period of incubation or deployment. Alternatively, the 

initially positioning of the lander may have disturbed the sediment-water interface, 

temporarily increasing the flux, then returned to steady state. 

7. Dissolved organic carbon (DOC) - Dissolved organic carbon (DOC) – DOC 

concentrations serve as a model for the abundance of organic ligands that can 

complex and enhance the solubility of metals. In many aquatic systems, certain 

dissolved metals predominantly exist as organic complexes (Mantoura and others, 

1978; McKnight and others, 1983). Although DOC water-column gradients were not 

measured in this study, preliminary samples taken in October, 1998 near the main 

channel indicated an elevated bottom-water concentration (1.17 + 0.01 milligram 

carbon per liter) relative to the surface (1.07 + 0.04 milligrams carbon per liter). It is 

therefore not surprising that DOC benthic flux was consistently positive (out of the 

sediment). However, in contrast to many of the dissolved inorganic substances, DOC 

concentrations showed a generally linear increase throughout the 12-hour coreincubation period (9 of 12 cores with coefficients of determination >0.6; Table 16). 

The longer time-scales of linearity for DOC flux relative to nutrient and metal flux 

suggest that complexation of metals with organic substances did not control the 

speciation of metals near the sediment-water interface in the cores. Although DOC 

flux differences between sites were not statistically significant, given the higher 

detrital composition of the surficial sediment at Mica Bay (Fig. 4), it is curious that 

the mean flux from Mica Bay cores (approximately 1800 micrograms carbon per 

square centimeter per year) was less than the mean from the main-channel cores 

(approximately 2700 micrograms carbon per square centimeter per year). No 

measurements of riverine-DOC loads are currently available for comparison. 

8. Dissolved lead (Pb) – As with the dissolved chemical species mentioned in item 3 

above, Pb flux primarily occurred in the initial hours. Purged cores had an initially 

elevated Pb concentration, but flux was generally lower than aerated cores (Table 10). 
Because purged cores were conditioned and incubated under a positive argon pressure 

(Coring methods), but not in a glove bag, Pb may have been mobilized in the purged 

cores during set up for incubations (i.e., when the overlying water for conditioning 

was replaced to begin the incubation). It is somewhat surprising that differences 

between aerated and purged cores are not more evident, especially for the other 

metals and nutrients. Although benthic flux measurements from purged cores and 

lander deployments were lower than riverine inputs estimated for 1999, fluxes from 

aerated cores were similar to riverine flux (Table 9). 

9. Dissolved zinc (Zn) and cadmium (Cd) – As one might expect from preliminary porewater data and flux estimates (Balistrieri, 1998), the lander data indicated a fairly 

consistent positive flux of Zn and Cd from the sediments of magnitudes similar to 

riverine fluxes (Fig. 15, Fig. 16). As with the other metals, nonlinearities in the 

concentration time series caused the magnitude of these fluxes to be dependent on the 

window of incubation time that was used in the calculation. 

In contrast, the core-incubations indicated a fairly consistent negative flux, that is, a 

flux of dissolved zinc and cadmium into the sediment. Before and during incubation, 

the overlying water in each core was bubbled with either compressed air or ultrahigh-purity argon to maintain either oxygen-saturated or suboxic conditions (Table 

6). Typically, a magnetic stirrer is used less vigorously to keep the overlying water 

from stratifying (Fig. 17). Although the purpose of this modification in the core 

incubations was to bracket the natural conditions sampled during the lander 

deployments, the overlying water in the incubated cores may have been so vigorously 

bubbled that the sediment-water interface and its associated gradients were disturbed. 

Flooding events in the Lake Coeur d’Alene watershed have been hypothesized to 

result in: (1) enhanced mobility of contaminants due to changing availability of 

nutrients to benthic microbes and (2) shifts in vertical redox gradients that promote 

precipitation of certain metal sulfides (La Force and others, 1998). If this hypothesis 

is true, then the difference depicted between lander and core-incubation results may 

represent a range of potential flux over extremely different hydrodynamic conditions; 

that is, conditions when there is little mixing and physical perturbation of the surficial 

sediment, to events where there is greater turbulence and advective transport near the 

bottom sediment. Irrespective of those differences, the magnitude of benthic flux 

from both lander and core-incubations are similar to riverine inputs (Fig. 12). 

10. Mercury – The dissolved-mercury flux (Fig. 7) was orders of magnitude lower than

the flux of other dissolved metals (Fig. 12), because the magnitudes of the concentrations and the gradients were orders of magnitude lower (Table 15). Furthermore, 

the benthic flux of methyl-mercury, the biologically reactive form of the element, was 

approximately two orders of magnitude lower than the flux for total mercury. 

Because the mechanisms of toxicity for different metals are different, and methylated 

mercury accumulates in tissues of organisms where trophic transfer can be fairly 

efficient, the relatively low benthic flux estimates for mercury species does not imply 

that this flux should be disregarded as environmentally insignificant. 
Methyl-mercury fluxes in cores from both sites were lower in aerated cores than in 

argon-purged cores. This is consistent with previous studies indicating that mercury 

methylation may be constrained in the presence of oxidized surficial sediments, and 

that methyl mercury may be retained by ferric-oxide surfaces and released in reduced 

sediments (Gagnon and others, 1996; Gagnon and others, 1997). 

These are the first measurements of mercury benthic flux in the lake, so comparative 

results for this lake or others in the vicinity are not available. Furthermore, very few 

mercury studies in lakes have included determinations of benthic flux. Working at 

Pallette Lake in Wisconsin, a pristine, ground-water flow-through lake, Krabbenhoft 

and others (1998) estimated that maximal methyl-mercury benthic flux occurred in 

littoral sediments during the spring. Spring, high-flow periods may enhance 

methylation rates by increasing the availability of nutrients that stimulate microbial 

activity near the sediment-water interface (Kelly and others, 1997; La Force and 

others, 1998). The flux was dominated by pore-water (or ground-water) advection 

and ranged from 0.16 to 2.25 nanograms per square centimeter per year. This range 

for methyl-mercury benthic flux from Pallette Lake’s littoral zone, predominantly 

driven by advective flux, brackets the initial determinations presented herein for Lake 

Coeur d’Alene, dominated by diffusive flux (0.2 to 1.7 nanograms per square 

centimeter per year). In contrast to the pristine setting of Pallette Lake, Gill and 

others (1999) measured mercury benthic fluxes in Lavaca Bay, a secondary 

embayment on the Texas Gulf Coast that received mercury discharge between 1966 

and 1979 from a chlor-alkali facility. They estimated methyl-mercury diffusive 

fluxes from 15 sites that ranged from 0.01 to 55 nanograms per square centimeter per 

year, as well as a direct chamber measurement from one site of 0.6 nanograms per 

square centimeter per year. Mindful of the major differences between these aquatic 

environments, it is interesting to note that the range for methyl-mercury flux in this 

study (0.2 to 1.7 nanograms per square centimeter per year) tightly brackets their 

direct measurement and is bracketed by the overall range for their spatial network. 

As mentioned in the Executive Summary, this represents the first dissolved mercury 

study for the lake using ultra-clean sampling and analytical techniques. No 

comparative riverine-flux estimate is therefore available. 
STUDY DESIGN AND METHODS 

The protocol described in this section focuses on method applications in this pilot study. 

Details (e.g., quality control specifications) for each analysis has been previously documented 

(Woods and others, 1999).

Physical Data 

Sediment Porosity – After core-incubations, approximately 10 milliliters of surficial 

sediment was collected from each core, then bottled, and refrigerated in darkness. 

Wet weight and dry weight after lyophilization was measured to calculate porosity 

(Table 2). 

Biological Data

1. Benthic Macrofauna – After core incubations, each core was sieved (500-micron 

mesh). The sieved samples were fixed with 10% buffered formalin, picked, sorted 

and taxonomically analyzed (Fig. 18). 

2. Benthic Chlorophyll-a - Each incubated core was sampled in triplicate for benthic 

chlorophyll-a. Surficial sediment was collected on a glass-fiber filter and buffered 

with magnesium carbonate. Samples were then frozen in darkness until 

spectrophotometrically analyzed (Thompson and others, 1981; Franson, 1985) (Fig. 

19). 

3. Benthic Bacteria - After core incubations, each core was sub-sampled using a syringe 

corer. Approximately 10 milliliters of surficial sediment was collected and fixed with 

0.5 milliliters of 37% formalin. Samples were then refrigerated in darkness. Benthic 

bacterial concentrations were determined by direct epifluorescent counts using 

acridine-orange preparations. 

Chemical Parameters 

1. Lander deployments – An in-situ benthic-flux chamber (lander) specifically designed 

for trace-element studies was deployed multiple times at each of the two lake sites 

from the research vessel Second Chance (Fig. 2). The device was set down with the 

help of EPA divers so that a rectangular acrylic chamber on the bottom of this device 

would penetrate the sediment but still retain some overlying water. This overlying 

water was isolated from the ambient lake water by closure of a lid, which initiated the 

incubation of approximately 1500 square centimeters of lake-bottom sediment 

surface. The deployments ranged from about a half day to two days, and were 

iteratively adjusted based on oxygen consumption data observed in previous lander 

deployments. Before each deployment, the lander was programmed to sample the 

overlying water within the chamber at 6 specified times during the chamber 

incubation. For trace-element and nutrient analyses, sampled water was stored in 

fluoroethylene polymer columns until the lander was retrieved. The time-series of 
solute concentrations from a deployment was used to determine an estimate of 

benthic flux. At the beginning of each deployment, bromide was injected into the 

chamber as a tracer of physical mixing processes (i.e., diffusion, advection). 

2. Water-column gradients – Prior to coring at both lake sites, water-column samples 

were collected for analysis of macronutrients by automated spectrophotometry, trace 

metals primarily by inductively coupled plasma mass spectrometry, and mercury 

species by cold-vapor atomic fluorescence spectroscopy. Samples were pumped from 

three depths (2 meters below the surface, mid-depth, and 2 meters above the bottom) 

using a high-displacement peristaltic pump and a tethered length of rigid 

fluoroethylene polymer tubing. 

3. Coring operation – At each of the two lake-sampling sites, eight cores were taken 

using a coring device fabricated from non-metallic parts (Savillex Corporation, 

Minnetonka, MN). To avoid sample contamination, wetted surfaces of the coring 

device and core tubes were acid-washed polypropylene or fluoroethylene polymer. 

Four of the eight cores from each site were aerated and the other four argon-purged 

overnight to condition wetted surfaces before the incubation period (Fig. 3, Fig. 17). 

Three of the four aerated and argon-purged cores were selected for incubation based 

on visual determination of any disturbances of the sediment-water interface. Water 

overlying the sediments in the six cores per site was sampled at four intervals during 

a 12-hour incubation. Trace element and nutrient samples were processed in a Class100 laminar-flow hood. As with lander samples, the concentration time series was 

used to determine the benthic flux from each of the 12 incubated cores. 

4. Riverine Flux Estimates – Areally averaged riverine fluxes were based on two 

estimates: (1) annual riverine loads determined in 1999 as part of a lake monitoring 

program (Woods, 2000) , and (2) the estimated affected lake area (108.2 square 

kilometers; Horowitz and others, 1995). Alternatively, a mass flux to match riverineload units (mass per unit time) could have been estimated from benthic flux 

measurements. However, for consistency and comparison with previous diffusiveflux estimates (Balistrieri, 1998), the benthic and riverine fluxes were represented in 

units of micrograms per square centimeter per year (Table 9). 

5. Dissolved oxygen – In lander deployments, dissolved oxygen fluxes were measured 

within the lander using a pulsed electrode mounted inside the chamber. A second 

electrode positioned outside the chamber tracks oxygen tension in the ambient lake 

water. For core incubations, dissolved oxygen in the overlying water and 

replacement water was determined by micro-Winkler titrations (Broenkow and Cline, 

1969; Redden, written communication, 1999]. In core-incubation experiments, 

dissolved oxygen was measured to confirm contrasting overlying-water conditions 

during incubations (i.e., suboxic versus oxygen-saturated conditions) (Table 6). 

Detectable dissolved-oxygen concentrations were routinely observed in the overlying 

water of argon-purged cores despite vigorous bubbling (100 – 150 milliliters per 

minute) during the incubation. Oxygen diffusion through the fluorethylene-polymer 

core walls could conceivably have maintained residual concentrations in the 

overlying water, but the measured oxygen may also represent a lower limit in the 
analysis of small water-sample volumes (approximately 10 milliliters) transferred 

from the cores. Use of a glove bag for processing dissolved-oxygen samples may be 

tested to lower that limit. 

6. Bromide (Br) – Bromide and radon were used as tracers of hydrologic transport 

between chamber water and sediment pore water. Bromide is a purposeful tracer, 

injected as a CsBr solution (of a known concentration and volume) into a chamber at 

the beginning of a lander deployment. The initial dilution of Br within chamber 

water provides a measure of the volume of incubated water trapped and the rate of Br 

loss from the chamber is diagnostic of exchange processes across the sediment-water 

interface. Br behaves as a conservative tracer of water transport and thus the change 

in Br concentration with time is indicative of the exchange rate between pore water 

and the overlying chamber water. The rate of Br disappearance from the chamber 

follows a nearly exponential pattern. Bromide loss from the chamber water after a 

certain period of time can be predicted on the basis of known rates of Br diffusivity. 

This value can be compared to the observed data. As samples were removed, bottom 

water flowed into the chamber. Knowing the bottom-water bromide concentration, 

and the volume of the chamber and water withdrawn, the sample bromide 

concentrations can be dilution corrected. The initial bromide concentration after 

injection was used to determine the overlying water-column heights which were 

approximately 7.6 and 10.0 centimeters for the second and fourth Mica Bay 

deployments, and 11.4, 13.1 and 12.8 centimeters for the three main-channel 

deployments. The first deployment at Mica Bay overpenetrated the sediment and the 

chamber height of the third Mica Bay deployment was apparently modified twice 

during the incubation by public tampering. 

Dissolved bromide concentration of filtered samples was determined by flowinjection colorimetery (Fig. 20). 

7. Radon-222 – Radon is a naturally occurring radioisotope (3.85 day half-life) 

produced by radium-226 decay within the sediments. In addition to flux 

determinations from samples taken during lander deployments, radon flux was also 

estimated following the determination of radon emanation strength of lake sediments. 

Emanation rate was established by incubating a few tens of milliliters of lake 

sediment in a jar filled with lake water. The sediment was incubated long enough for 

the radon to reestablish equilibrium with the radium contained within the sediment. 

Radon diffusive flux was then estimated according to procedures described by 

Berelson and others (1982). 

8. Nutrients (nitrogen species and orthophosphate) – Dissolved nutrients from watercolumn sampling, lander deployments and core incubations were filtered with 0.2 

micron polycarbonate filters. The filtered samples were immediately refrigerated in 

darkness, but unlike trace metal samples, were not acidified. Nutrient analyses were 

performed by automated spectrophotometry (Fig. 21). 

9. Dissolved metals by Inductively Coupled Plasma Mass Spectrometry – Dissolved 

trace-metal samples from water-column sampling, lander deployments, and core 
incubations were filtered with 0.2 micron polycarbonate filters. Filtered samples 

were acidified with quartz-distilled nitric acid to 0.03N, then refrigerated in darkness 

until their analyses. Aliquots of lander samples were diluted (by approximately a 

factor of 10) due to sample-volume constraints. Metal analyses were performed by 

direct-injection inductively coupled plasma mass spectrometry using external 

standardization (Fig. 22). 

10. Dissolved iron by graphite-furnace atomic absorption spectrophotometry (GFAAS) – 

This method was used only for dissolved iron from undiluted lander samples because 

the dilution of sample aliquots resulted in dissolved-iron concentrations near ICP-MS 

detection limits. There was insufficient volume of undiluted lander samples to 

analyze by ICP-MS (Fig. 23). 

11. Mercury speciation by cold-vapor atomic fluorescence spectroscopy (CVAFS) – 

Total dissolved mercury was determined in filtered aqueous samples by CVAFS after 

evolved elemental mercury was purge and trapped onto gold-coated sand columns. 

Methyl-mercury also analyzed by CVAFS, but after a distillation and aqueous-phase 

ethylation method (Fig. 24). 

12. Dissolved organic carbon (DOC) – Dissolved organic carbon was determined by 

high-temperature non-catalytic combustion (Qian and Mopper, 1997). Sodium 

phthalate were used as standards. Low-DOC water (blanks <40 micrograms-organic 

C per liter) was generated from a double-deionization unit with additional ultraviolet 

treatment (Milli-Q UV – Millipore Corporation) (Fig. 25). 
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Reimers, N.J., Maciolek, A., and Pister, E.P., 1955, Limnological study of the lakes of Convict 

Creek Basin, Mono County, California: Fisheries Bulletin of the U.S. Fish and Wildlife 

Service, v. 56, p. 437-503. 

Ricker, W.E., 1952, The benthos of Cultus Lake: Journal of the Fisheries Research Board 

Canada, v. 9, no. 4, p. 204-212. 

Ruud, D.F., 1996, A comparison of the macroinvertebrate communities of a trace elements 

enriched lake and an uncontaminated lake in north Idaho: The effects of mine waste 

contamination in Coeur d'Alene Lake, Masters Thesis, Eastern Washington University, 

Cheney, WA, 65 p. 

Thompson, J.K., Nichols, F.H., and Wienke, S.M., 1981, Distribution of benthic chlorophyll in 

San Francisco Bay, California, February 1980 – February 1981: U.S. Geological Survey 

Open File Report 81-1134, 55 p. 
Wetzel, R.G., 1983, Limnology, 2d edition, Saunders College Publishing, New York, New York, 

767 p. 

Woods, P.F., and Beckwith, M.A., 1997, Nutrient and trace-element enrichment of Coeur 

d’Alene Lake, Idaho: U.S. Geological Survey Water Supply Paper 2485, 93 p. 

Woods, P.F., Nearman, M.J., and Barton, G.J., 1999, Quality Assurance Project Plan for U.S. 

Geological Survey Studies in Support of Spokane River Basin RI/FS.: U.S. 

Environmental Protection Agency, Seattle, Washington, and U.S. Geological Survey, 

Boise, Idaho, 153 p. 

Young, M., 1979, A modified spread plate technique for the determinations of concentrations of 

viable heterotrophic bacteria: in “Methodology for Biomass Determinations and 

Microbial Activities in Sediments”, Litchfield, C.D., and Seyfield, P.L., eds, American 

Society for Testing and Materials, ASTM STP 673, p. 40-51. 
Acknowledgements 

The authors are grateful to A. Arnesberg, R. Avanzino, J. Carter and S. Fend, S. Hager, 

and M. Olson for benthic chlorophyll, dissolved macronutrient, benthic invertebrate, dissolved

silica, and mercury-speciation analyses, respectively. Design and fabrication of sampling and

coring equipment by F. Murphy were instrumental in successfully collecting incubation cores

and water-column samples. Logistical and facilities support by C. Azevedo, R. Backsen, P.

Cummings, S. Nicholls, and especially R. Black, D. Marcy and the staff of North Idaho College

were critical to the successful execution of this study. Discussions with R.F. Rosenzweig on the

relevance of benthic bacterial results are much appreciated, as were productive discussions with

A. Horowitz on metal geochemistry in the watershed. Assistance in lander deployments by J.

Goulet, R. Pedersen. C. Schulze, and B. Woods are gratefully acknowledged. The authors are

particularly grateful to K. Kirk and K.M. Nolan for their support, comments and guidance in

developing this electronic document. Report reviews by M. Marvin-Dipasquale and D. Meece are

also much appreciated. The U.S. Geological Survey Toxic Substances Hydrology Program is

gratefully acknowledged for long-term support leading to the development of sampling and

analytical methods applied in this study. Finally, the authors acknowledge M. Nearman, S. Sheldrake and USEPA project reviewers for their visionary support of the idea to consider benthic flux

as a potentially important process in the watershed. 

Product names are provided for identification purposes only and do not constitute 

endorsement by the U.S. Geological Survey. 
Appendix 1: Comments on the Report Structure 

A major objective of this electronic document is to provide a structure that is easily 

accessible to a potentially wide range of interests in this work. Agency reports in the form of 

electronically linked products are a fairly recent alternative, but pathways within this document 

have been constructed to be both logical and intuitive. In addition to hyperlinks within the 

document to supporting figures and tables, Appendices 2 and 3 provide a quick way to directly 

review and examine all figures and tables. 

Although hard copies of this report are available on request, the advantages of the 

electronic version relative to the hard copy are substantial in many respects, but particularly in 

speed of information access at multiple levels of detail. 

Your comments about how to improve this evolving type of product are most welcome 

and may be directed to any of the email addresses provided in the title page, but we request that 

at least a copy of all comments about the report be addressed to the major author 

(kuwabara@usgs.gov) so that they may be compiled for future revisions and reports. 
Appendix 2: List of Figuresa

Fig. 1 – Initial Benthic Flux Sites 

Fig. 2 – In-situ Flux Chamber

Fig. 3 – Coring Operation 

Fig. 4 – Photomicrographs of Lake Coeur d’Alene Benthos 

Fig. 5 – Water-column Gradients 

Fig. 6 – Conceptual Model of Solute Transport

Fig. 7 – Benthic Flux of Dissolved-mercury Species 

Fig. 8 – Processes Regulating Benthic Flux

Fig. 9 – Comparison of Benthic Indices 

Fig. 10 – Injected Bromide Concentrations 

Fig. 11 – Nitrogen to Phosphorus (N:P) Benthic-Flux Ratio 

Fig. 12 – Benthic versus Riverine Flux Comparison 

Fig. 13 – Dissolved-copper Flux Comparison 

Fig. 14 – Dissolved-iron Flux Comparison 

Fig. 15 – Dissolved-zinc Flux Comparison 

Fig. 16 – Dissolved-cadmium Flux Comparison 

Fig. 17 – Incubation Core Design 

Fig. 18 – Macroinvertebrate Taxonomy 

Fig. 19 – Benthic Chlorophyll Analyses 

Fig. 20 – Bromide Analyses 

Fig. 21 – Spectrophotometric Nutrient Analyses 

Fig. 22 – Dissolved-metal Analyses by ICP-MS 
Fig. 23 – Dissolved-iron Analyses by GFAAS 

Fig. 24 – Dissolved-mercury speciation by CVAFS 

Fig. 25 – Dissolved Organic Carbon (DOC) Analyses 

a

 Where applicable, error bars in the figures represent standard error about the mean. 

 
Appendix 3: List of Tables 

Table 1 – Experimental Schedule for Benthic Flux Pilot Study 

Table 2 – Surficial-sediment Porosities 

Table 3 – Benthic-biological Indices 

Table 4 – Benthic Chlorophyll 

Table 5 – Surficial Benthic-bacteria Concentrations 

Table 6 – Dissolved Oxygen in Incubated Cores 

Table 7 – Dissolved Oxygen, Radon-222, and Bromide from Lander Deployments 

Table 8 – Dissolved Chemical Species in the Water Column 

Table 9 – Comparison between Riverine and Measured Benthic Flux 

Table 10 – Metals-flux from Core Incubations 

Table 11 – Metal-flux from Lander Deployments 

Table 12 – Macroinvertebrate Taxonomy 

Table 13 – Injected Bromide Concentrations 

Table 14 – Benthic Flux of Dissolved Nutrients 

Table 15 – Benthic Flux of Mercury Species 

Table 16 – Benthic Flux of Dissolved Organic Carbon
Fig. 1

Idaho

Initial Benthic Flux Sites Initial Benthic Flux Sites Initial Benthic Flux Sites

116o 116 40’ o 50’

47o 40’

47o 20’

47o 30’

Sampling/coring locations

Lake 

Coeur d’Alene Spokane River

Mica Bay

Rockford Bay

Chatcolet 

Lake

St. Joe River

Coeur d’Alene

River

2 km

0 2 mi
In situ In situ In situ Flux Chamber (Lander) Flux Chamber (Lander) Flux Chamber (Lander

Fig. 2
Coring Operation Coring Operation

Release Rem

Retrieval

Fig. 3
Sieved (500 micron) benthic samples from Mica Bay collected: (A) on October 14, 

1998 (rose bengal stained), and (B) on August 17, 1999. Although the living

macroinvertebrates in these samples were nearly absent, the relative abundance of 

invertebrate tubes and detrital material presents a distinct contrast to the benthic 

material within the main channel of the Lake (Figure 2 below). Differences in the 

hue and brightness between photomicrographs taken from the two collection dates 

are due to camera and lighting changes. 

Main Channel Main Channel

Benthic samples from the main channel of Lake Coeur d’Alene near the 

mouth of the Coeur d’Alene River collected: (A) on October 15, 1998 (A), and 

(B) on August 23, 1999. The consistent predominance of inorganically 

coated particles (presumably by ferric-oxyhydroxide) contrasts with the 

benthic samples from Mica Bay above. Differences in the hue and brightness 

between photomicrographs taken from the two collection dates are due to 

camera and lighting changes.

Fig. 4

Mica Bay Benthos Mica Bay Benthos Mica Bay Benthos
Water Water-column Gradient

-column Gradient

column Gradient

Fig. 5

Mica Bay

1 10

Solute concentration relative to concentration at su

Depth (m)

10

0

25302015

5

1 

Main 
Conceptual Model of Solute Transport

ig. 6
Mercury Mercury Mercury

Fig. 7

Hg

Analyte

MeHg

0.0001

0.001

0.01

0.1

1

Flux (ug/cm

2/yr)

Legend

Mica-Aerated

Mica-Purged

Rockford-Aerated

Rockford-Purged

Indiv. Replicates
Processes Regulating Benthic Flux

ig. 8
Comparison of Benthic Indices

Fig. 9

This Study

Lake Range

1

10

100

1000

10000

100000

1000000

Benthic Index

 Chl-a

(mg/cm2)

Macrobenthos

 (ind/m2)
Fig. 10

Injected Bromide during Lander Deployments Injected Bromide during Lander Deployments Injected Bromide during Lander Deployments

Main Channel - 1

0 10 15 20 25 5

35

30

20

25

Main Channel - 3

20

25

30

35

0 10 15 20 25 5

Mica Bay -2

0 5 15 20 25 10

30

50

60

40

A replicate

B replicate

Main Channel - 2

20

30

35

25

0 10 15 20 25 5

Mica Bay - 4

30

35

40

45

0 10 15 20 25 5

Elapsed Time After Injection (h)

Mica Bay -3

0 20 30 40 10

0

2

4

6

8

10

[Bromide] (mg/L)
Nitrogen to Phosphorus Ratio Nitrogen to Phosphorus Ratio

Fig. 11

Redfield

 Ratio

Mica Rockford

0

10

20

30

40

50

60

70

N:P Molar Flux Ratio
Benthic vs. Riverine Flux 

Comparison

Benthic vs. Riverine Flux Benthic vs. Riverine Flux 

Comparison Comparison

-1

-10

-100

-1000

-0.1

1

10

1000

10000

0.1

 Flux (ug/cm

2/yr)

100

Cd Cu Pb Zn Fe Mn

Dissolved Metals (0.2 micron filtered)

Mica-Aerated

Mica-Purged

Rockford-Purged

Rockford-Lander

Coeur d'Alene (Riverine)

St. Joe (Riverine)

Mica-Lander

Rockford-Aerated

Legend

Fig. 12
Copper Copper

Fig. 13

0.0

5.0

10.0

15.0

20.0

Flux (ug/cm

2/yr)

Legend

Mica-Aerated

Mica-Purged

Rockford-Aerated

Rockford-Purged

Mica-Lander

Coeur d'Alene

Indiv. Replicates

Porewater (1992)

St. Joe

Rockford-Lander
Iron Iron

-200

0

200

400

600

800

Flux (ug/cm

2/yr)

Legend

Mica-Aerated

Mica-Purged

Rockford-Aerated

Rockford-Purged

Rockford-Lander

Coeur d'Alene

St. Joe

Mica-Lander

Individual Replicates

Fig. 14
Zinc Comparison Zinc Comparison Zinc Comparison

-800

-600

-400

-200

0

200

400

600

Flux (ug/cm

2/yr)

Legend

Mica-Aerated

Mica-Purged

Rockford-Aerated

Rockford-Purged

Rockford-Lander

Mica-Lander

Coeur d'Alene

Indiv. Replicates

Porewater (1992)

St. Joe

Fig. 15
Cadmium Cadmium Cadmium

-6.0

-4.0

-2.0

0.0

2.0

4.0

6.0

Flux (ug/cm

2/yr)

Legend

Mica-Aerated

Rockford-Aerated

Rockford-Lander

Coeur d'Alene

Mica-Lander

Mica-Purged

Indiv. Replicates

St. Joe

Rockford-Purged

Fig. 16
Fig. 17

Incubation 

Core Design

Incubation 

Core Design
Benthic Macroinvertebrate Taxon

Benthic Macroinvertebrate Taxon

Benthic Macroinvertebrate Taxon

Fig. 18
Benthic Chlorophyll Analyses Benthic Chlorophyll Analyses Benthic Chlorophyll Analyses

Fig. 19
Colorimetric Bromide Analys

Colorimetric Bromide Analys

Colorimetric Bromide Analys

Fig. 20
Spectrophotometric Spectrophotometric Spectrophotometric Nutrient Analy

Nutrient Analy

Nutrient Analy

Fig. 21
Dissolved Dissolved Dissolved-metal Analyses by ICP-

-metal Analyses by ICP metal Analyses by ICP

-

Fig. 22
Dissolved Dissolved Dissolved-iron Analyses by GFA

-iron Analyses by GFA

iron Analyses by GFA

Fig. 23
Dissolved Dissolved Dissolved-mercury Speciation by C

-mercury Speciation by C

mercury Speciation by C

Fig. 24
Dissolved Organic Carbon (DOC) An

Dissolved Organic Carbon (DOC) An

Dissolved Organic Carbon (DOC) A

Fig. 25
Table 1. Experimental Schedule for Benthic Flux Pilot Study

Lake Coeur d'Alene, August 16 - 27, 1999

Date(s) in 

August '99 Station Index Activity (hrs of incubation)

 17 Mica Bay Water-column sampling and coring

 17 - 18 Mica Bay MB-1 Lander deployment (15.5)

 18 Mica Bay 6 Core Incubations (12.0)

 18 - 19 Mica Bay MB-2 Lander deployment (14.5)

 19 - 21 Mica Bay MB-3 Lander deployment (36.5)

 21 - 22 Main Channel St4-1 Lander deployment (13.5)

 22 - 23 Main Channel St4-2 Lander deployment (17.0)

 23 Main Channel Water-column sampling and coring

 23 - 24 Main Channel St4-3 Lander deployment (21.0)

 24 Main Channel 6 Core Incubations (12.0)

 24 - 25 Mica Bay MB-4 Lander deployment (18.5)
Table 2. Surficial-sediment Porosities (Benthic Flux Experiments - August 18 and 24, 1999)

8/18/99

Mica Bay

Bulk Density Wet/dry

Core # Treatment Porosity (g-dry/cm3

-sed) weight

1 Aerated 0.94 0.27 4.54

3 Aerated 0.97 0.29 4.37

4 Aerated 0.95 0.25 4.75

2 Ar-Purged 0.97 0.28 4.51

5 Ar-Purged 0.93 0.29 4.17

7 Ar-Purged 0.97 0.28 4.51

8/24/99

Main Channel

Bulk Density Wet/dry

Core # Treatment Porosity (g-dry/cm3

-sed) weight

9 Aerated 0.94 0.27 4.50

10 Aerated 0.96 0.28 4.41

11 Aerated 0.92 0.26 4.47

12 Ar-Purged 0.91 0.27 4.36

13 Ar-Purged 0.90 0.26 4.41

16 Ar-Purged 0.95 0.21 5.49

Replicate volume = 3 * 3.2 = 9.6 cm3
Table 3. Benthic-biological Indices for Lakes

Index Value Range Units Lake Lake Type Referencea

Chl-a 14 - 33 ug/cm2 Lake Erken, 

Sweden

mesotrophic

Goedkoop and Johnson (1996)

1.3-3.6 ug/cm2 Lake Coeur 

d'Alene

oligotrophicmesotrophic This study

1.0-5.5 Ash-free g-dry 

weight/m2

Lake Ontario mesotrophic

Johnson and Brinkhurst, 1971

Macroinvertebrates 3.36 CI=0.25 g-dry weight/m2 Lake 

Memphremagog, 

Quebec

mesotrophic

Dermott, et al., 1977

Macroinvertebrates 214-829 individuals/m2 4 British 

Columbia Lakes

oligotrpohic - 

mesotrophic Ricker, 1952

Macroinvertebrates 893-4671 individuals/m2 Lakes in Convict 

Creek Basin

oligotrophic

Reimers et al., 1955

Chironomids 320-720 individuals/m2 Lake Erken, 

Sweden

mesotrophic

Goedkoop and Johnson (1996)

Macroinvertebrates 22431 - 

99947

individuals/m2 Lake Myvatn, 

Iceland

eutrophic

Lindegaard and Jonasson, 1979

Chironomids 21739-40000 individuals/m2 Priest Lake oligotrophic

Rudd (1996)

Macroinvertebrates 29565 - 

60869

individuals/m2 Priest Lake oligotrophic

Rudd (1996)

Chironomids 0-76956 individuals/m2 Lake Coeur 

d'Aleneb

oligotrophicmesotrophic Rudd (1996)

Macroinvertebrates 10000 - 

98695

individuals/m2 Lake Coeur 

d'Aleneb

oligotrophicmesotrophic Rudd (1996)

Macroinvertebrates 0-130 individuals/m2 Lake Coeur 

d'Alene

oligotrophicmesotrophic This study

a

 References:

Dermott, R.M., Kalff, J., Leggett, W.W., and Spence, J., Production of Chironomus, Procladium, and Chaoborus at differenct levels

of phytoplankton biomass in Lake Memphremagog, Quebec-Vermont: Journal of the Fisheries Research 

Board Canada, v. 34, no. 11, p. 2001-2007. 

Goedkoop, W. and Johnson, R.K., 1996, Pelagic-benthic coupling: Profundal benthic community response to

 spring diatom deposition in mesotrophic Lake Erken: Limnology and Oceanography, v. 41, no. 4, p. 636-647.

Johnson, M.G. and Brinkhurst, R.O., 1971, Production of benthic macroinvertebrates of Bay of Qunite and Lake Ontario: Journal

of the Fisheries Research Board Canada, v. 28, p. 1699-1714.

Lindegaard, C. and Jonasson, P.M., 1979, Abundance, population dynamics and production of zoobenthos in Lake Myvatn,

Iceland: Oikos, v. 32, p. 202-227.

Reimers, N.J., Maciolek, A., and Pister, E.P., 1955, Limnological study of the lakes of Convict Creek Basin, Mono County, California,:

Fisheries Bulletin of the U.S. Fish and Wildlife Service, v. 56, p. 437-503. 

Ricker, W.E., 1952, The benthos of Cultus Lake: Journal of the Fisheries Research Board Canada, v. 9, no. 4, p. 204-212.

Rudd, D.F., 1996, A comparison of the macroinvertebrate communities of a trace elements enriched lake and an uncontaminated lake

in north Idaho: The effects of mine waste contamination in Coeur d'Alene Lake, Masters Thesis, 

Eastern Washington University, Cheney, WA, 65 p.

b

 Data from eutrophic Chacolet Lake not included.
Table 4. Benthic Chlorophyll (Benthic Flux Experiments - August 18 and 24, 1999)

Mica Bay Main Channel

Core # Treatment Repsachl Core # Treatment Repsachl

(ug/cm2) (ug/cm2)

1 Aerated A -5.4 9 Aerated A 1.5

Aerated B 2.0 Aerated B 2.7

Aerated C 2.2 Aerated C 1.8

2 Aerated A 1.3 10 Aerated A 2.0

Aerated B 3.1 Aerated B 1.7

Aerated C 1.1 Aerated C 0.8

3 Aerated A 1.7 11 Aerated A 1.1

Aerated B 1.4 Aerated B 1.2

Aerated C 2.6 Aerated C 1.8

4 Ar-Purged A 3.6 12 Ar-Purged A 1.4

Ar-Purged B 2.2 Ar-Purged B 1.3

Ar-Purged C 2.8 Ar-Purged C 2.0

5 Ar-Purged A 1.9 13 Ar-Purged A 1.1

Ar-Purged B 1.1 Ar-Purged B 1.8

Ar-Purged C 2.9 Ar-Purged C 1.0

7 Ar-Purged A 1.8 16 Ar-Purged A 1.2

Ar-Purged B 2.6 Ar-Purged B 1.5

Ar-Purged C 1.4 Ar-Purged C 0.8

a

 Replicates are indicative of spatial variability within each core.

Cores were numbered to facilitate sample identification. 

 The omission of a number in series denotes that the core tube

 was not selected for the coring operation. 
Table 5. Surficial Benthic-bacteria Concentrations (After core incubations - August 18 and 24, 1999)

Mica Bay

Core # Cells/g-core Std. Error 95% CI Treatment n

1 8.4E+08 +/- 2.5E+08 7.3E+07 Aerated 48

3 8.8E+08 +/- 3.0E+08 8.6E+07 Aerated 48

4 1.0E+09 +/- 3.3E+08 9.5E+07 Aerated 48

2 7.6E+08 +/- 2.7E+08 7.7E+07 Ar-Purged 48

5 6.3E+08 +/- 2.2E+08 6.2E+07 Ar-Purged 48

7 7.2E+08 +/- 2.8E+08 8.0E+07 Ar-Purged 48

Main Channel

Core # Cells/g-core Std. Error 95% CI Treatment n

9 8.6E+08 +/- 3.2E+08 9.2E+07 Aerated 48

10 6.8E+08 +/- 2.2E+08 6.4E+07 Aerated 48

11 6.3E+08 +/- 2.0E+08 5.8E+07 Aerated 48

12 3.9E+08 +/- 1.6E+08 4.5E+07 Ar-Purged 48

13 3.8E+08 +/- 1.4E+08 4.1E+07 Ar-Purged 48

16 5.1E+08 +/- 2.0E+08 5.7E+07 Ar-Purged 48
Table 6. Dissolved Oxygen in Incubated Cores (Benthic Flux Experiments - August 18 and 24, 1999)

Core# Location Treatment Hour DO (uM) Core# Location Treatment Hour DO (uM)

1 Mica Aerated 0 237 9 Main Channel Aerated 0 202

Mica Aerated 2 220 Main Channel Aerated 2 168

Mica Aerated 6 232 Main Channel Aerated 6 173

Mica Aerated 12 256 Main Channel Aerated 12 127

3 Mica Aerated 0 205 10 Main Channel Aerated 0 135

Mica Aerated 2 199 Main Channel Aerated 2 179

Mica Aerated 6 255 Main Channel Aerated 6 166

Mica Aerated 12 255 Main Channel Aerated 12 123

4 Mica Aerated 0 152 11 Main Channel Aerated 0 183

Mica Aerated 2 213 Main Channel Aerated 2 218

Mica Aerated 6 258 Main Channel Aerated 6 190

Mica Aerated 12 266 Main Channel Aerated 12 152

Overlying Mica Aerated 0 193 Overlying Main Channel Aerated 0 183

Mica Aerated 12 198 Main Channel Aerated 12 177

Core# Location Treatment Hour DO (uM) Core# Location Treatment Hour DO (uM)

2 Mica Ar-Purged 0 62 12 Main Channel Ar-Purged 0 49

Mica Ar-Purged 2 29 Main Channel Ar-Purged 2 32

Mica Ar-Purged 6 44 Main Channel Ar-Purged 6 34

Mica Ar-Purged 12 16 Main Channel Ar-Purged 12 22

5 Mica Ar-Purged 0 52 13 Main Channel Ar-Purged 0 33

Mica Ar-Purged 2 31 Main Channel Ar-Purged 2 33

Mica Ar-Purged 6 43 Main Channel Ar-Purged 6 32

Mica Ar-Purged 12 21 Main Channel Ar-Purged 12 n/a

7 Mica Ar-Purged 0 59 16 Main Channel Ar-Purged 0 41

Mica Ar-Purged 2 31 Main Channel Ar-Purged 2 30

Mica Ar-Purged 6 50 Main Channel Ar-Purged 6 33

Mica Ar-Purged 12 21 Main Channel Ar-Purged 12 14

Overlying Mica Ar-Purged 0 56 Overlying Main Channel Ar-Purged 0 32

Mica Ar-Purged 12 142 Main Channel Ar-Purged 12 17
Table 7. Dissolved Oxygen, Radon-222, and Bromide from Lander Deployments (August 16 - 27,1999)

Estimated Initial Radon Flux 

Chamber Bromide (atoms/m2

/sec) Estimated Estimated 

Chamber Ht. Uncert. Conc. Including Excluding Radon Flux DO Consumption DO Consumption

Station - Deployment Ht. (cm)a

 (+%) mg/Lb BWc BWc Uncert. (+%) (mmol/m2/d) (mg/cm2/yr) Uncert. (+%)

Mica Bay - 2 7.6 10 53 128 105 20 -9.5 -11.1 10 - 15

Mica Bay - 4 10.0 10 40 99 85 20 -7.2 -8.4 10 - 15

Main Channel - 1 11.4 20 35 103 84 30 -8.8 -10.3 20 - 25

Main Channel - 2 13.1 10 30 105 83 20 -6.0 -7.0 10 - 15

Main Channel - 3 12.8 10 31 242 214 20 -7.4 -8.6 10 - 15

a

 Chamber heights for each deploment were determined from the initial bromide concentration after tracer injection. 

b

 Initial bromide concentrations were used to determine chamber heights. During the lander incubation

 bromide concentrations decreased approximately 20%.

c BW=Bottom Water (either included in or excluded from calculation)
Table 8. Dissolved Chemical Species in the Water Column (Water Column Sampling - August 18 and 24, 1999)

Mica Bay Water Column

95% Conf. 95% Conf. 95% Conf. 95% Conf. 95% Conf. 95% Conf. Total Nb Phosphateb

Depth (m) Zn ppb Interval Cu ppb Interval Cd ppb Interval Pb ppb Interval Fe ppb Interval Mn ppb Interval Hg ppt Std Errorappb ppb

2.0 37.5 0.4 0.359 0.004 0.199 0.002 0.096 0.001 13.1 0.2 1.132 0.003 0.58 0.79 12.03 0.66

12.5 38.5 0.2 0.344 0.003 0.205 0.000 0.111 0.000 13.3 0.4 0.375 0.000 1.75 0.50 6.82 0.63

25.0 79.5 0.5 0.458 0.009 0.333 0.000 0.332 0.005 22.5 0.1 0.524 0.004 2.08 0.01 76.05 1.12

Main Channel Water Column

95% Conf. 95% Conf. 95% Conf. 95% Conf. 95% Conf. 95% Conf. Total Nb Phosphateb

Depth (m) Zn ppb Interval Cu ppb Interval Cd ppb Interval Pb ppb Interval Fe ppb Interval Mn ppb Interval Hg ppt Std Errorappb ppb

2.0 40.8 0.2 0.328 0.029 0.233 0.000 0.140 0.002 12.7 0.1 0.782 0.004 1.77 n/a 5.23 0.46

16.0 58.6 0.6 0.376 0.009 0.239 0.001 0.086 0.003 11.6 0.1 0.581 0.004 2.20 0.65 6.09 0.68

31.0 79.2 0.2 0.429 0.003 0.344 0.002 0.396 0.003 25.8 0.2 0.576 0.002 2.15 0.18 90.64 0.90

a

 Only two replicates were analyzed for Hg samples due to volume constraints. Thus, the standard error is given instead of the 95% confidence interval

b

 Only one replicate was analyzed for total N and phosphate due to volume constraints. The unit describes micrograms of nitrogen (or phosphorus) per liter.
Table 9. Comparison between Riverine and Measured Benthic Flux 

Core Incubation Fluxb (ug/cm2/yr)

Dissolved Mica Bay Main Channel

Solute CDA River St. Joe Sum

Average Std error Average Std error Average Std error Average Std error Average Std error n Average Std error n

Ortho-P 9 9 18 50 30 150 10 90 30 140 120 20 20 2 7 2 3

NO3+NO2 n/a n/a n/a 230 340 -370 70 140 100 60 70 210 100 2 160 30 3

NH4

+

n/a n/a n/a 740 100 710 100 380 130 210 110 110 110 2 60 10 3

Total N 168 46 214 970 350 340 150 530 40 270 160 320 210 2 220 16 3

DOC n/a n/a n/a 2022 361 1568 238 2763 1001 2583 521 n/a n/a n/a n/a

Si 23050 26410 49460 5530 540 5980 160 5660 410 4520 1400 1410 370 2 1579 249 3

Cd 3.0 0.3 3.3 -2.9 0.1 -3.5 0.8 1.1 3.7 3.1 2.1 2.3 2.0 2 3.1 1.5 3

Cu (1992)d

9.0 9.0 18.0 0.5 0.4 0.5 0.5 1.4 1.5 2.6 2.1 1.9 0.4 2 1.1 1.0 3

Pb 17 0 17 20 5 9 8 20 26 0 1 2 3 3 2 6 5

Zn 532 4 536 -90 50 -390 7 -150 150 -460 270 350 150 2 280 80 3

Fe 87 53 140 16 24 7 21 -10 16 -79 9 114 111 3 175 352 5

Mn 128 5 133 8180 390 8230 1500 7440 1730 3920 1320 3050 3180 2 3680 2240 3

HgTot (All) n/a n/a n/a 0.11 0.05 0.07 0.05 0.17 0.11 0.34 0.18 n/a n/a n/a n/a

MeHg (All) n/a n/a n/a 0.0003 0.0002 0.0012 0.0006 0.0006 0.0002 0.0013 0.0004 n/a n/a n/a n/a

HgTot (Init.) n/a n/a n/a 0.84 n/a 0.56 n/a 5.45 n/a 2.05 n/a n/a n/a n/a n/a

MeHg (Init.) n/a n/a n/a n/a n/a n/a n/a 0.0104 n/a 0.0036 n/a n/a n/a n/a n/a

a

 Riverine loads were determined as part of a lake monitoring program (Woods, P.F., 2000, Loads and concentrations of cadmium, lead, zinc and nutrients during the 1999 water year for the

 Spokane River Basin, Idaho and Washington: U.S. Geological Survey Open File Report 00-XXXX, XX p. plus appendices [U.S.G.S. publication approval expected prior to December, 2000]) 

 The affected Lake surface area for calculations (km2) = 108.2 (Horowitz and others, 1995) Load info

 Fluxes are presented in units of micrograms solute per square centimeter per year (ug/cm2/yr). 

b

 All core incubation data were derived from three cores for each site and treatment. Standard errors rather than 95% confidence intervals about flux determinations for the site are tabulated.

c

 The number of benthic flux estimates used to determine the average and standard deviation for each solute at each location was not constant, as it was in the core incubations.

 This was due to variable number of deployments at each site, and non-linearities in the concentration time series during lander incubations.

n/a Not available

d Copper loading estimates were not performed in 1999, thus 1992 data is used.

Lander Deployments Fluxc (ug/cm2/yr) 

Ar-Purged Mica Bay Main Channel

Areally Averaged

Riverine Flux (ug/cm2/yr)a

 Aerated Ar-Purged Aerated
Table 10. Metals-flux from Core Incubations (Benthic Flux Experiments - August 18 and 24, 1999)

Mass fluxes are presented in units of micrograms solute per square centimeter per year (ug/cm2/yr).

Coefficients of determination (r2

) are tabulated for the time-series regressions used to determine benthic flux.

Cadmium Flux Summary (All 12 hours of incubation data used) 

Core # Sta. No.* Cd Flux (ug/cm2

-yr) Cd Flux (nmoles/m2-h) r

2

Treatment n Comments

1 Mica -2.7 +/- 0.4 -27.9 +/- 4.1 0.60 Aerated 15

3 Mica -2.8 +/- 0.5 -28.7 +/- 4.9 0.53 Aerated 15

4 Mica -3.0 +/- 0.5 -30.5 +/- 5.3 0.52 Aerated 15

2 Mica -3.1 +/- 0.6 -31.5 +/- 5.7 0.50 Ar-Purged 15

5 Mica -3.0 +/- 0.5 -30.5 +/- 5.4 0.47 Ar-Purged 16

7 Mica -4.4 +/- 0.7 -45.0 +/- 6.9 0.58 Ar-Purged 15

Core # Sta. No.* Cd Flux (ug/cm2

-yr) Cd Flux (nmoles/m2-h) r

2

Treatment n Comments

9 Main Channel -2.7 +/- 0.6 -27.3 +/- 6.0 0.40 Aerated 15 Immediate Cd depletion

10 Main Channel 1.1 +/- 1.2 11.0 +/- 12.0 0.04 Aerated 13 Initial flux dominated

11 Main Channel 4.8 +/- 0.7 48.5 +/- 6.8 0.63 Aerated 15

12 Main Channel 4.2 +/- 1.0 42.4 +/- 9.7 0.47 Ar-Purged 13

13 Main Channel 4.4 +/- 0.6 44.2 +/- 6.0 0.64 Ar-Purged 15

16 Main Channel 0.7 +/- 0.7 7.2 +/- 7.6 0.03 Ar-Purged 14 Initial flux dominated

Copper Flux Summary (All 12 hours of incubation data used) 

Core # Sta. No.* Cu Flux (ug/cm2

-yr) Cu Flux (nmoles/m2-h) r

2

Treatment n Comments

1 Mica 0.4 +/- 0.2 7.2 +/- 3.1 0.17 Aerated 14 Initial flux dominated

3 Mica 0.2 +/- 0.2 3.0 +/- 3.5 0.02 Aerated 17 Initial flux dominated

4 Mica 0.9 +/- 0.1 16.1 +/- 1.5 0.85 Aerated 13

2 Mica 0.7 +/- 0.1 12.4 +/- 1.3 0.73 Ar-Purged 16

5 Mica -0.1 +/- 0.1 -1.8 +/- 2.1 0.03 Ar-Purged 13 Initial flux dominated

7 Mica 0.9 +/- 0.0 17.0 +/- 0.6 0.96 Ar-Purged 15

Core # Sta. No.* Cu Flux (ug/cm2

-yr) Cu Flux (nmoles/m2-h) r

2

Treatment n Comments

9 Main Channel -0.2 +/- 0.0 -3.1 +/- 0.3 0.69 Aerated 16 Odd - No distinctive trend

10 Main Channel 1.5 +/- 0.3 26.9 +/- 5.8 0.45 Aerated 14

11 Main Channel 2.8 +/- 0.2 49.5 +/- 4.0 0.81 Aerated 16

12 Main Channel 3.6 +/- 0.4 64.2 +/- 7.4 0.65 Ar-Purged 17

13 Main Channel 4.0 +/- 0.5 71.4 +/- 9.3 0.62 Ar-Purged 16

16 Main Channel 0.1 +/- 0.9 2.2 +/- 16.5 0.00 Ar-Purged 13 Initial flux dominated

Lead Flux Summary (All 12 hours of incubation data used) 

Core # Sta. No.* Pb Flux (ug/cm2

-yr) Pb Flux (nmoles/m2-h) r

2

Treatment n Comments

1 Mica 24.6 +/- 4.6 135.5 +/- 25.2 0.57 Aerated 13 Initial flux dominated

3 Mica 15.3 +/- 5.8 84.5 +/- 32.0 0.21 Aerated 14 Initial flux dominated

4 Mica 19.2 +/- 6.7 106.1 +/- 36.9 0.19 Aerated 16 Initial flux dominated

2 Mica 18.5 +/- 5.1 102.0 +/- 28.1 0.43 Ar-Purged 12 Initial flux dominated

5 Mica 4.7 +/- 4.5 25.7 +/- 25.0 0.04 Ar-Purged 14 Initial flux dominated

7 Mica 4.0 +/- 5.9 21.8 +/- 32.6 0.02 Ar-Purged 13 Initial flux dominated

Core # Sta. No.* Pb Flux (ug/cm2

-yr) Pb Flux (nmoles/m2-h) r

2

Treatment n Comments

9 Main Channel 50.7 +/- 7.6 279.6 +/- 41.8 0.59 Aerated 15 Initial flux dominated

10 Main Channel 6.3 +/- 3.7 34.9 +/- 20.5 0.09 Aerated 15 Initial flux dominated

11 Main Channel 3.9 +/- 3.7 21.6 +/- 20.3 0.03 Aerated 17 Initial flux dominated

12 Main Channel -0.8 +/- 0.3 -4.1 +/- 1.7 0.11 Ar-Purged 18 Only T3 change

13 Main Channel -0.7 +/- 0.6 -3.7 +/- 3.6 0.03 Ar-Purged 15 Initial flux dominated

16 Main Channel 0.2 +/- 1.8 1.3 +/- 9.8 0.00 Ar-Purged 13 Initial flux dominated

Zinc Flux Summary (All 12 hours of incubation data used) 

Core # Sta. No.* Zn Flux (ug/cm2

-yr) Zn Flux (nmoles/m2-h) r

2

Treatment n Comments

1 Mica -65.1 +/- 28.0 -1137 +/- 489 0.24 Aerated 12

3 Mica -144.9 +/- 49.0 -2530 +/- 856 0.34 Aerated 12

4 Mica -58.2 +/- 8.5 -1016 +/- 148 0.59 Aerated 16

2 Mica -391.0 +/- 14.3 -6824 +/- 250 0.97 Ar-Purged 13

5 Mica -396.9 +/- 14.6 -6927 +/- 254 0.97 Ar-Purged 13

7 Mica -382.6 +/- 19.6 -6679 +/- 343 0.91 Ar-Purged 16

Core # Sta. No.* Zn Flux (ug/cm2

-yr) Zn Flux (nmoles/m2-h) r

2

Treatment n Comments

9 Main Channel -179.4 +/- 59.5 -3131 +/- 1038 0.34 Aerated 12

10 Main Channel -279.6 +/- 6.3 -4880 +/- 109 0.99 Aerated 12

11 Main Channel 23.7 +/- 18.4 413 +/- 321 0.07 Aerated 13 Initial flux dominated

12 Main Channel -551.9 +/- 46.4 -9633 +/- 809 0.87 Ar-Purged 13

13 Main Channel -147.9 +/- 16.7 -2582 +/- 292 0.75 Ar-Purged 14 Initial flux dominated

16 Main Channel -671.3 +/- 88.6 -11718 +/- 1546 0.77 Ar-Purged 12

Iron Flux Summary (All 12 hours of incubation data used) 

Core # Sta. No.* Fe Flux (ug/cm2

-yr) Fe Flux (nmoles/m2-h) r

2

Treatment n Comments

1 Mica 39.2 +/- 8.2 802 +/- 167 0.52 Aerated 13 Initial flux dominated

3 Mica -7.7 +/- 8.2 -157 +/- 168 0.03 Aerated 14 Initial flux dominated

4 Mica 16.9 +/- 22.5 346 +/- 461 0.02 Aerated 14 Initial flux dominated

2 Mica 30.3 +/- 14.3 620 +/- 293 0.17 Ar-Purged 13 Initial flux dominated

5 Mica -0.7 +/- 13.0 -13 +/- 267 0.00 Ar-Purged 13 Initial flux dominated

7 Mica -9.3 +/- 9.7 -190 +/- 198 0.02 Ar-Purged 17 Initial flux dominated

Core # Sta. No.* Fe Flux (ug/cm2

-yr) Fe Flux (nmoles/m2-h) r

2

Treatment n Comments

9 Main Channel 6.3 +/- 1.3 129 +/- 26 0.45 Aerated 15 Initial flux dominated

10 Main Channel -11.8 +/- 4.4 -241 +/- 90 0.25 Aerated 13 Initial flux dominated

11 Main Channel -24.4 +/- 10.4 -500 +/- 212 0.21 Aerated 13 Initial flux dominated

12 Main Channel -70.3 +/- 6.3 -1439 +/- 130 0.80 Ar-Purged 15 Elevated time 0 conc.

13 Main Channel -79.9 +/- 1.3 -1635 +/- 27 0.99 Ar-Purged 13 Elevated time 0 conc.

16 Main Channel -87.5 +/- 5.2 -1789 +/- 107 0.90 Ar-Purged 16 Elevated time 0 conc.

Manganese Flux Summary (All 12 hours of incubation data used) 

Core # Sta. No.* Mn Flux (ug/cm2

-yr) Mn Flux (nmoles/m2-h) r

2

Treatment n Comments

1 Mica 8372 +/- 1135 174087 +/- 23598 0.68 Aerated 14 Initial flux dominated

3 Mica 8420 +/- 681 175080 +/- 14152 0.79 Aerated 17 Initial flux dominated

4 Mica 7737 +/- 1492 160884 +/- 31025 0.52 Aerated 14 Initial flux dominated

2 Mica 9769 +/- 1243 203140 +/- 25846 0.70 Ar-Purged 14 Initial flux dominated

5 Mica 8058 +/- 1250 167544 +/- 25990 0.62 Ar-Purged 14 Initial flux dominated

7 Mica 6840 +/- 1543 142235 +/- 32094 0.47 Ar-Purged 13 Initial flux dominated

Core # Sta. No.* Mn Flux (ug/cm2

-yr) Mn Flux (nmoles/m2-h) r

2

Treatment n Comments

9 Main Channel 8006 +/- 1198 166470 +/- 24909 0.52 Aerated 17 Initial flux dominated

10 Main Channel 8787 +/- 996 182716 +/- 20708 0.67 Aerated 17 Initial flux dominated

11 Main Channel 5523 +/- 1241 114851 +/- 25798 0.47 Aerated 13 Initial flux dominated

12 Main Channel 4887 +/- 714 101618 +/- 14843 0.63 Ar-Purged 14 Initial flux dominated

13 Main Channel 4427 +/- 664 92050 +/- 13806 0.66 Ar-Purged 13 Initial flux dominated

16 Main Channel 2450 +/- 384 50934 +/- 7976 0.56 Ar-Purged 16 Initial flux dominated
Table 11. Metal-flux from Lander Deployments (August 16-27, 1999)

Mass fluxes are presented in units of micrograms solute per square centimeter per year (ug/cm2/yr).

Cadmium Flux Summary

Deploy # Sta. No.* Cd Flux (ug/cm2

/yr) Comments

2 Mica 3.6 +/- 0.7

4 Mica 0.9 +/- 0.3

1 Main Channel 4.0 +/- 1.0

2 Main Channel 1.4 +/- 0.4

3 Main Channel 4.1 +/- 0.5

Copper Flux Summary

Deploy # Sta. No.* Cu Flux (ug/cm2

/yr) Comments

2 Mica 2.2 +/- 1.2

4 Mica 1.6 +/- 0.6

1 Main Channel 0.4 +/- 1.5

2 Main Channel 0.8 +/- 0.3

3 Main Channel 2.3 +/- 0.4

Lead Flux Summary

Deploy # Sta. No.* Pb Flux (ug/cm2

/yr) Comments

2 Mica 0.4 +/- 1.1 Non-linear; Time series estimate #1

Mica 5.1 +/- 3.3 Non-linear; Time series estimate #2

4 Mica 0.3 +/- 0.5

1 Main Channel -5.1 +/- 4.5

2 Main Channel 10.3 +/- 4.2 Non-linear; Time series estimate #1

Main Channel 2.0 +/- 0.3 Non-linear; Time series estimate #2

3 Main Channel 4.6 +/- 5.8 Non-linear; Time series estimate #1

Main Channel 0.3 +/- 0.2 Non-linear; Time series estimate #2

Zinc Flux Summary

Deploy # Sta. No.* Zn Flux (ug/cm2

/yr) Comments

2 Mica 451.0 +/- 100.2

4 Mica 243.4 +/- 33.4

1 Main Channel 348.4 +/- 71.6

2 Main Channel 198.1 +/- 28.6

3 Main Channel 295.9 +/- 45.3

Iron Flux Summary

Deploy # Sta. No.* Fe Flux (ug/cm2

/yr) Comments

2 Mica 53.8 +/- 46.7 Non-linear; Time series estimate #1

Mica 242.6 +/- 142.7 Non-linear; Time series estimate #2

4 Mica 46.3 +/- 12.6

1 Main Channel -79.9 +/- 79.9

2 Main Channel 780.7 +/- 101.9 Non-linear; Time series estimate #1

Main Channel 7.1 +/- 30.2 Non-linear; Time series estimate #2

3 Main Channel 178.2 +/- 77.3 Non-linear; Time series estimate #1

Main Channel -10.4 +/- 21.2 Non-linear; Time series estimate #2

Manganese Flux Summary

Deploy # Sta. No.* Mn Flux (ug/cm2

/yr) Comments

2 Mica 5294 +/- 1003

4 Mica 802 +/- 140

1 Main Channel 5575 +/- 1003

2 Main Channel 1203 +/- 241

3 Main Channel 4271 +/- 802
Table 12. Macroinvertebrate Taxonomy (Benthic Flux Experiment - August 18 and 24, 1999)

Lake Coeur d'Alene 8/16-27/99

Objective and Scope: The objective of the investigation was to determine the macroinvertebrate

composition of sediments collected from Lake Coeur d'Alene, Idaho. Sediments were collected

with a 77 cm2 coring device from two locations; Mica Bay and a main channel site near

the mouth of the Coeur d'Alene River. Six cores were collected from each site. Collections 

were made at Mica Bay on August 17, 1999 and from a main channel site on August 23, 1999. 

After incubtion, each core was sieved in the field using a 500 m mesh sieve. Material retained on 

the sieve was preserved with 10% buffered formalin. The retained material from each core was 

rinsed of preservative and remaining fine sediment in the laboratory using a 425 m mesh sieve. 

All macroinvertebrates were sorted using 10X magnification. Sorted macroinvertebrates

 were identified to the lowest practicable taxonomic level and stored in either 70% 

ethanol or slide mounted.

General Comments: The three most striking differences between the cores from the two locations were:

1) Mica Bay cores contained many empty invertebrate cases, 

2) Mica Bay cores contained more organic detritus, and 

3) Cores from the main channel contained predominately large inorganic particles. 

 Whether the empty invertebrate cases originated at the site or were transported to the 

 site is unknown. Higher frequency temporal sampling would probably determine whether 

 there is an active benthic invertebrate community at these sites.

Mica Bay 8/18/99

Core # Sta. No.* Treatment Taxonomic Observations

1 Mica Aerated Largely composed of many empty invertebrate cases. We assume 

they are chironomid cases.

3 Mica Aerated Only contained empty cases.

4 Mica Aerated Only contained empty cases.

2 Mica Purged Similar to core 1 and was composed of empty invertebrate cases but 

contained one unidentifiable chironomid head capsule.

5 Mica Purged Contained empty cases and 16 chironomid head capsules.

7 Mica Purged Contained empty cases and 1 chironomid head capsule.

Main Channel 8/24/99

Core # Sta. No.* Treatment Taxonomic Observations

9 Rockford Aerated Contained far fewer empty cases than cores from Mica bay. Also found 

were 2 chironomid head capsules and 2 bryozoan statoblasts, 

probably from Pectinatella.

10 Rockford Aerated Contained a few empty invertebrate cases, 1 unidentifiable chironomid 

(Tribe: Chironomini), and a mite, Hygrobates.

11 Rockford Aerated Contained a few empty cases, one mite, one chironomid, and the valve 

of a pelecypod; none of which were identifiable.

12 Rockford Purged Contained a few empty cases, 2 empty chironomid head capsules, 

2 statoblasts from Pectinatella, and one Procladius, a chironomid in

the Subfamily Tanypodinae.

13 Rockford Purged Contained a few empty cases, 1 chironomid head capsule, 1 statoblast 

from Pectinatella, 1 mite (Hygrobates), and one unidentifiable

flatworm (Tricladida)

16 Rockford Purged Contained a few empty cases and 2 chironomid head capsules.
Table 13. Injected-bromide concentrations during lander deployments

All Samples drew 400 ml

Station ID Sample Elapseda

[Bromide-A]b [Bromide-B] 

and Dates Draw # hours (mg/L) (mg/L) Deployment Notes

Mica Bay-2 1 0.08 51.2 54.0 Wooden skids added to chamber

2 1 47.9 51.7 Oxygen and radon data look good

Aug 18-19 3 3 46.3 48.9 4A large air bubble

4 6 43.3 45.5

5 10 40.9 42.8

6 15.5 37.9 40.3

Station ID Sample Elapseda

[Bromide-A]b [Bromide-B] 

and Dates Draw # hours (mg/L) (mg/L) Deployment Notes

Mica Bay-3 1 0.08 0.0 0.3 All sample (A's) have sediment, 5 and 6 have the least sediment

2 5 0.0 0.0 All the A samples have air bubbles

Aug 19-21 3 12 3.4 3.0 This chamber never was properly seated, perhaps due to disturbance, 

4 20 9.3 8.7 clearly a disturbance occured after draw 4 such that the chamber appears

5 28 0.1 0.1 to be operational during draws 5 and 6, however, chamber height is <<10 cm. 

6 36.5 0.3 0.4 The chamber was partially sealed through draw 4, but did leak enough to 

 allow oxygen equilibration.

Station ID Sample Elapseda

[Bromide-A]b [Bromide-B] 

and Dates Draw # hours (mg/L) (mg/L) Deployment Notes

Mica Bay-4 1 0.08 38.8 40.0 Good deployment although radon in Draw 4 looks low

2 1 38.0 39.3 Bubbles in 5A and 6A, 4A ok, others not checked

Aug 24-25 3 3.5 35.4 37.8 Longer skids added to chamber

4 7.5 36.5 36.6

5 12.5 33.5 34.4

6 18.5 32.5 32.5

Station ID Sample Elapseda

[Bromide-A]b [Bromide-B] 

and Dates Draw # hours (mg/L) (mg/L) Deployment Notes

Main Channel -1 1 0.08 23.5 22.0 Good deployment

2 1 28.7 28.0 Teflon tape on 2A, 4A and 6A

Aug 21-22 3 3 29.9 29.9 2A med bubble, 3B med bubble, 4A med-large bubble, 6A med bubble

4 6 29.8 29.6

5 9.5 28.8 29.2

6 13.5 28.0 27.9

Station ID Sample Elapseda

[Bromide-A]b [Bromide-B] 

and Dates Draw # hours (mg/L) (mg/L) Deployment Notes

Main Channel -2 1 0.08 30.1 29.4 Good deployment, deployed without divers

2 1 28.5 28.5 2A med bubble, 4A med-large bubble, 6A med-large bubble

Aug 22-23 3 4 27.2 27.0

4 8 26.2 26.6

5 12 25.4 25.4

6 17 23.9 24.4

Station ID Sample Elapseda

[Bromide-A]b [Bromide-B] 

and Dates Draw # hours (mg/L) (mg/L) Deployment Notes

Main Channel -3 1 0.08 27.9 30.1 Good deployment

2 1 28.6 30.2 3A, 4A, 5A, 6A all had medium bubbles upon recovery

Aug 23-24 3 3.5 27.9 29.6

4 8.5 26.8 28.5

5 14.5 26.1 27.2

6 21 24.9 26.2

a

 Elapsed hours counted following closure of lander lid.

b

 Sample designations A and B represent successive sample replicates after automated rinsing of the sampling bellows.
Table 14. Benthic Flux of Dissolved Nutrients (Lake Coeur d'Alene Pilot Study - August 16 - 27, 1999)

Mass fluxes are presented in units of micrograms solute per square centimeter per year (ug/cm2/yr).

Results from Incubated Cores

NITRATE PLUS NITRITE

Core # Sta. No.* NO3 Flux (ug/cm2

/yr) NO3 Flux (umoles/m2/h) r

2

Treatment n

1 Mica 37 +/- 223 3 +/- 18 0.15 Aerated 4

3 Mica 22 +/- 143 2 +/- 12 0.14 Aerated 4

4 Mica 626 +/- 986 51 +/- 80 0.72 Aerated 4

2 Mica -377 +/- 946 -31 +/- 77 0.51 Ar-Purged 4

5 Mica -427 +/- 1003 -35 +/- 82 0.54 Ar-Purged 4

7 Mica -298 +/- 281 -24 +/- 23 0.88 Ar-Purged 4

Core # Sta. No.* NO3 Flux (ug/cm2

/yr) NO3 Flux (umoles/m2/h) r

2

Treatment n

9 Main Channel 54 +/- 63 4 +/- 5 0.82 Aerated 4

10 Main Channel 129 +/- 213 11 +/- 17 0.70 Aerated 4

11 Main Channel 244 +/- 232 20 +/- 19 0.88 Aerated 4

12 Main Channel 25 +/- 116 2 +/- 9 0.24 Ar-Purged 4

13 Main Channel 141 +/- 224 11 +/- 18 0.72 Ar-Purged 4

16 Main Channel 6 +/- 95 1 +/- 8 0.03 Ar-Purged 4

AMMONIA

Core # Sta. No.* NH4+ Flux (ug/cm2

/yr) NH4+ Flux (umoles/m2-h) r

2

Treatment n

1 Mica 646 +/- 1410 53 +/- 115 0.57 Aerated 4

3 Mica 849 +/- 1187 69 +/- 97 0.77 Aerated 4

4 Mica 737 +/- 1777 60 +/- 145 0.54 Aerated 4

2 Mica 796 +/- 1261 65 +/- 103 0.72 Ar-Purged 4

5 Mica 594 +/- 1426 48 +/- 116 0.53 Ar-Purged 4

7 Mica 739 +/- 1554 60 +/- 127 0.59 Ar-Purged 4

Core # Sta. No.* NH4+ Flux (ug/cm2

/yr) NH4+ Flux (umoles/m2-h) r

2

Treatment n

9 Main Channel 517 +/- 914 42 +/- 75 0.67 Aerated 4

10 Main Channel 366 +/- 716 30 +/- 58 0.63 Aerated 4

11 Main Channel 267 +/- 672 22 +/- 55 0.50 Aerated 4

12 Main Channel 284 +/- 433 23 +/- 35 0.73 Ar-Purged 4

13 Main Channel 257 +/- 315 21 +/- 26 0.81 Ar-Purged 4

16 Main Channel 87 +/- 366 7 +/- 30 0.27 Ar-Purged 4

ORTHOPHOSPHATE

Core # Sta. No.* PO4 Flux (ug/cm2

/yr) PO4 Flux (umoles/m2-h) r

2

Treatment n

1 Mica 15 +/- 167 1 +/- 6 0.05 Aerated 4

3 Mica 50 +/- 125 2 +/- 5 0.51 Aerated 4

4 Mica 71 +/- 57 3 +/- 2 0.91 Aerated 4

2 Mica 130 +/- 264 5 +/- 10 0.61 Ar-Purged 4

5 Mica 155 +/- 263 6 +/- 10 0.69 Ar-Purged 4

7 Mica 154 +/- 245 6 +/- 9 0.72 Ar-Purged 4

Core # Sta. No.* PO4 Flux (ug/cm2

/yr) PO4 Flux (umoles/m2-h) r

2

Treatment n

9 Main Channel 109 +/- 256 4 +/- 9 0.54 Aerated 4

10 Main Channel 101 +/- 197 4 +/- 7 0.63 Aerated 4

11 Main Channel 63 +/- 158 2 +/- 6 0.50 Aerated 4

12 Main Channel 285 +/- 433 10 +/- 16 0.73 Ar-Purged 4

13 Main Channel 58 +/- 97 2 +/- 4 0.70 Ar-Purged 4

16 Main Channel 88 +/- 79 3 +/- 3 0.89 Ar-Purged 4

SILICA

Core # Sta. No.* Si Flux (ug/cm2

/yr) Si Flux (umoles/m2-h) r

2

Treatment n

1 Mica 5842 +/- 6803 237 +/- 277 0.83 Aerated 4

3 Mica 5846 +/- 4209 238 +/- 171 0.93 Aerated 4

4 Mica 4907 +/- 10297 199 +/- 419 0.59 Aerated 4

2 Mica 5892 +/- 6683 239 +/- 272 0.83 Ar-Purged 4

5 Mica 5869 +/- 6595 239 +/- 268 0.84 Ar-Purged 4

7 Mica 6164 +/- 6535 251 +/- 266 0.85 Ar-Purged 4

Core # Sta. No.* Si Flux (ug/cm2

/yr) Si Flux (umoles/m2-h) r

2

Treatment n

9 Main Channel 6076 +/- 7538 247 +/- 306 0.81 Aerated 4

10 Main Channel 5265 +/- 5969 214 +/- 243 0.83 Aerated 4

11 Main Channel 5633 +/- 6296 229 +/- 256 0.84 Aerated 4

12 Main Channel 5357 +/- 5402 218 +/- 220 0.86 Ar-Purged 4

13 Main Channel 5290 +/- 3945 215 +/- 160 0.92 Ar-Purged 4

16 Main Channel 2897 +/- 4835 118 +/- 197 0.70 Ar-Purged 4 Predominant initial flux.

Results from Lander Deployments

NITRATE PLUS NITRITE

Deploy # Sta. No.* NO3 Flux (ug/cm2

/yr)

2 Mica 279 +/- 50

4 Mica 141 +/- 16

1 Main Channel 175 +/- 50

2 Main Channel 177 +/- 21

3 Main Channel 124 +/- 14

AMMONIA

Deploy # Sta. No.* NH4+ Flux (ug/cm2

/yr)

2 Mica 187 +/- 33

4 Mica 25 +/- 11

1 Main Channel 53 +/- 35

2 Main Channel 47 +/- 23

3 Main Channel 75 +/- 14

ORTHOPHOSPHATE

Deploy # Sta. No.* PO4 Flux (ug/cm2

/yr)

2 Mica 36 +/- 9

4 Mica 7 +/- 6

1 Main Channel 6 +/- 8

2 Main Channel 7 +/- 10

3 Main Channel 9 +/- 6

SILICA

Deploy # Sta. No.* Si Flux (ug/cm2

/yr)

2 Mica 1671 +/- 246

4 Mica 1148 +/- 287

1 Main Channel 1866 +/- 369

2 Main Channel 1425 +/- 256

3 Main Channel 1445 +/- 246
Table 15. Benthic Flux of Mercury Species (August 16-27, 1999)

Mass fluxes are presented in units of nanograms solute per square centimeter per year (ng/cm2/yr).

Mercury Flux Summary (All 12 hours of incubation data used) 

Core # Sta. No.* Hg-T Flux (ng/cm2-yr) Hg-T Flux (nmoles/m2-h) r

2

Treatment

1 Mica 65 +/- 341 0.4 +/- 1.9 0.19 Aerated

3 Mica 167 +/- 255 1.0 +/- 1.5 0.73 Aerated

4 Mica 90 +/- 281 0.5 +/- 1.6 0.40 Aerated

2 Mica 107 +/- 171 0.6 +/- 1.0 0.71 Ar-Purged

5 Mica 103 +/- 186 0.6 +/- 1.1 0.66 Ar-Purged

7 Mica 13 +/- 236 0.1 +/- 1.3 0.02 Ar-Purged

Core # Sta. No.* Hg-T Flux (ng/cm2

-yr) Hg-T Flux (nmoles/m2-h) r

2

Treatment

9 Main Channel 292 +/- 3240 1.7 +/- 18.4 0.05 Aerated

10 Main Channel 80 +/- 1544 0.5 +/- 8.8 0.02 Aerated

11 Main Channel 141 +/- 1591 0.8 +/- 9.1 0.05 Aerated

12 Main Channel 537 +/- 1028 3.1 +/- 5.9 0.64 Ar-Purged

13 Main Channel 195 +/- 809 1.1 +/- 4.6 0.27 Ar-Purged

16 Main Channel 296 +/- 755 1.7 +/- 4.3 0.50 Ar-Purged

(Only first 2 hours of incubation data used) 

Core # Sta. No.* Hg-T Flux (ng/cm2-yr) Hg-T Flux (nmoles/m2-h) r

2

Treatment

1 Mica 926 5.3 1.00 Aerated

3 Mica 803 4.6 1.00 Aerated

4 Mica 799 4.5 1.00 Aerated

2 Mica 531 3.0 1.00 Ar-Purged

5 Mica 539 3.1 1.00 Ar-Purged

7 Mica 610 3.5 1.00 Ar-Purged

Core # Sta. No.* Hg-T Flux (ng/cm2

-yr) Hg-T Flux (nmoles/m2-h) r

2

Treatment

9 Main Channel 8241 46.9 1.00 Aerated

10 Main Channel 3967 22.6 1.00 Aerated

11 Main Channel 4138 23.5 1.00 Aerated

12 Main Channel 2137 12.2 1.00 Ar-Purged

13 Main Channel 1941 11.0 1.00 Ar-Purged

16 Main Channel 2084 11.9 1.00 Ar-Purged

Methyl-Mercury Flux Summary (All 12 hours of incubation data used) 

Core # Sta. No.* Me-Hg Flux (ng/cm2-yr) Me-Hg Flux (pmoles/m2-h) r

2

Treatment

1 Mica 0.5 2.9 1.00 Aerated

3 Mica 0.2 1.1 1.00 Aerated Not significant relative to

4 Mica 0.2 1.1 1.00 Aerated detection limit

2 Mica 1.2 6.6 1.00 Ar-Purged

5 Mica 1.7 9.9 1.00 Ar-Purged

7 Mica 0.6 3.4 1.00 Ar-Purged

Core # Sta. No.* Me-Hg Flux (ng/cm2-yr) Me-Hg Flux (pmoles/m2-h) r

2

Treatment

9 Main Channel 0.8 4.8 +/- 43.5 0.07 Aerated

10 Main Channel 0.4 2.2 +/- 15.4 0.11 Aerated

11 Main Channel 0.4 2.5 +/- 9.2 0.32 Aerated

12 Main Channel 1.1 6.5 +/- 6.1 0.88 Ar-Purged

13 Main Channel 1.7 9.9 +/- 13.4 0.91 Ar-Purged

16 Main Channel 1.1 6.2 +/- 8.0 0.79 Ar-Purged

(Initial 2 hours of incubation data used) 

Core # Sta. No.* Me-Hg Flux (ng/cm2-yr) Me-Hg Flux (pmoles/m2-h) r

2

Treatment

9 Main Channel 20.2 114.7 1.00 Aerated

10 Main Channel 6.8 38.6 1.00 Aerated

11 Main Channel 4.2 23.7 1.00 Aerated

12 Main Channel 1.9 11.1 1.00 Ar-Purged

13 Main Channel 4.1 23.2 1.00 Ar-Purged

16 Main Channel 4.6 26.4 1.00 Ar-Purged
Table 16. Dissolved Organic Carbon flux from Core Incubations (Benthic Flux Experiments - August 18 and 24, 1999)

Coefficients of determination (r2) are tabulated for the time-series regressions used to determine benthic flux.

Dissolved Organic Carbon Flux Summary (All 12 hours of incubation data used) 

Core # Sta. No.* DOC Flux (ug/cm2

-yr) DOC Flux (umoles/m2-h) r

2

Treatment n Comments

1 Mica 2439 +/- 138 231.8 +/- 13.1 0.92 Aerated 14

3 Mica 1808 +/- 65 171.9 +/- 6.2 0.97 Aerated 14

4 Mica 1819 +/- 9 172.9 +/- 0.9 1.00 Aerated 12

2 Mica 1842 +/- 278 175.1 +/- 26.4 0.63 Ar-Purged 14

5 Mica 1448 +/- 285 137.6 +/- 27.1 0.35 Ar-Purged 18

7 Mica 1413 +/- 180 134.3 +/- 17.1 0.63 Ar-Purged 16

Core # Sta. No.* DOC Flux (ug/cm2

-yr) DOC Flux (umoles/m2-h) r

2

Treatment n Comments

9 Main Channel 1694 +/- 412 161.0 +/- 39.1 0.32 Aerated 16

10 Main Channel 2917 +/- 355 277.3 +/- 33.8 0.69 Aerated 15

11 Main Channel 3677 +/- 340 349.6 +/- 32.3 0.74 Aerated 17

12 Main Channel 2634 +/- 181 250.4 +/- 17.2 0.84 Ar-Purged 17

13 Main Channel 3076 +/- 287 292.4 +/- 27.2 0.74 Ar-Purged 17

16 Main Channel 2038 +/- 344 193.8 +/- 32.7 0.49 Ar-Purged 17