Light-absorbing components in the Great Lakes

Features of light absorption are critical in regulating the optical signal available for remote sensing. The magnitudes, spectral characteristics, spatial patterns, and, to a lesser extent, dynamics of light-absorbing components are documented for the Laurentian Great Lakes. This includes the open waters of each of the five lakes, and selected rivers, embayments and near-shore areas. The absorption coefficient, a(m^? 1), is partitioned according to the additive components (a_x) of colored dissolved organic matter (a_CDOM), non-algal particles (a_NAP), phytoplankton (a_φ), and water itself (a_w; known). Dependencies of a_x on various metrics of optically active constituents (OACs), cross-sections, are evaluated. A wide range of magnitudes of a_x and a, and contributions of a_x to a are documented. For example, the magnitude of a at a wavelength of 440 nm was nearly 10-fold greater in the western basin of Lake Erie than in the open waters of Lake Huron. Rivers, embayments, and near-shore areas generally had higher levels than the open waters. The largest a_x throughout the system was a_CDOM, originating mostly from terrestrial sources. Most of a_NAP was associated with clay mineral particles. The distribution of a_φ was highly correlated to chlorophyll concentration. The collected data set is appropriate to support initiatives to develop and preliminarily test mechanistic retrieval algorithms for OACs in the Great Lakes.     

Light-absorbing components in Lake Superior

Features of light absorption are critical to optical aspects of water quality and in regulating the signal available for remote sensing. Spectral characteristics and spatial patterns of light-absorbing components, and their relationships with optically active constituents, are documented for the Sturgeon River, Keweenaw Bay, and Lake Superior based on analyses of samples collected on two cruises (2006 and 2007, 20 sites). The absorption coefficient, a (m^− 1), is partitioned according to the additive components (a_x) of colored dissolved organic matter (a_CDOM), non-algal particles (a_NAP), phytoplankton (a_?), and water itself (a_w; known). The role of minerogenic particles and their iron content in regulating a_NAP is evaluated based on paired measurements by an individual particle analysis technique (Peng et al., 2009), through empirical analyses and Mie theory calculations of absorption by these particles (a_m). Spectral characteristics of a_NAP and a_? were consistent with those reported for other case 2 (i.e., phytoplankton not dominant) systems. However, the slope values that describe a_CDOM spectra for the bay and the lake were unusually low, suggesting an atypical composition for the lake's CDOM. The dominant absorbing component in the blue wavelengths was CDOM, representing ≥ 75% of a at a wavelength of 440 nm at all sites in the 2006 survey. A general gradient in both a_CDOM and a_NAP extended from the Sturgeon River, through the bay, into eastern Lake Superior in that survey. Relationships between a_x and optically active constituents were within the broad ranges reported for other case 2 systems. Minerogenic particles, related to their iron content, are demonstrated to be an important component of a_NAP.     

Phosphorus loading and ecological impacts from agricultural tile drains in a west Michigan watershed

Phosphorus (P) loading from nonpoint sources is often implicated as a contributing factor to the proliferation of algal blooms in freshwater ecosystems. However, the influence of subsurface tile drains as a source of P, especially in agricultural areas, has received limited attention. We examined the importance of tile drain effluent in the Macatawa Watershed; this watershed is dominated by row crop agriculture and drains into hypereutrophic Lake Macatawa, which connects to Lake Michigan. Our objectives were twofold: 1) assess the importance of tile drain effluent as a source of P in the Macatawa Watershed by measuring tile drain P concentrations spatially and temporally over a one-year period; and 2) assess the ability of tile drain effluent to stimulate algal blooms using bioassays with natural phytoplankton communities. During March 2015–February 2016, P concentrations varied significantly among sample sites (SRP: < 0.005 to 0.447 mg/L; TP: 0.010 to 0.560 mg/L), and the highest P loads occurred during the non-growing season. Annual SRP yields from the tile drain sample sites ranged from 0.002 kg/ha to 0.248 kg/ha, and annual TP yields ranged from 0.003 kg/ha to 0.322 kg/ha. SRP, on average, accounted for 60% of TP, and the SRP:TP ratio measured at the tile drain outlets was positively correlated with area drained by the tile system. Algal bioassays failed to find a positive relationship between chlorophyll a and tile drain SRP; algal community structure was dominated by diatoms, not by cyanobacteria, as expected.     

Mapping cyanobacterial blooms in Lake Champlain's Missisquoi Bay using QuickBird and MERIS satellite data

C-phycocyanin (C-PC) and chlorophyll-a (Chl-a) concentrations for the eutrophic waters of Missisquoi Bay, Lake Champlain (VT–QC) were retrieved from Envisat's MERIS radiance data (300 m spatial resolution) and validated against coincident georeferenced transect observations. Pigment concentrations were also predicted from empirically calibrated QuickBird data (2.4 m spatial resolution) using selected band ratios and principal components analysis. The QuickBird NIR/Red band ratio accounted for approximately 80% of the variability in observed Chl-a concentration, allowing for detailed mapping of phytoplankton spatial distributions. C-PC concentrations, in contrast, were somewhat poorly modeled (R² = 0.68). Use of these data for monitoring purposes, however, is also limited by the need for coincident field observations. Chl-a concentrations were also accurately retrieved from the MERIS data (Mean Relative Error = -0.6%) despite high concentrations of suspended particles and dissolved organic matter in the bay waters. C-PC concentrations were underestimated on average by 2.1%, but by 10–20% at high C-PC concentrations (≥ 80 μg/L) and as the proportion of cyanobacteria in the phytoplankton community decreased. The relatively high overall accuracies observed, however, attest to the robustness of the MERIS semi-analytical retrieval algorithms used to quantify potentially toxic cyanobacteria cell densities without the need for coincident field data. Our analyses over a 17 day period captured the peak and collapse of a late summer cyanobacterial bloom, illustrating the value of remote sensing to provide synoptic and timely information on the abundance and distribution of cyanobacterial populations that, in turn, can facilitate public health risk assessment.     

Benthic Macroinvertebrates as Indicators of Environmental Degradation in the Southern Nearshore Zone of the Central Basin of Lake Erie

The benthic macroinvertebrates of the central basin of Lake Erie were sampled with a Ponar grab in the summers of 1978 and 1979 along a 155-km reach of the nearshore zone (≤ 12 km offshore) in Ohio, U.S.A., at depths of less than 20 m. The major groups and their most abundant species were, in order of overall abundance, Oligochaeta (Limnodrilus hoffmeisteri, L. cervix-L. claparedeianus group, L. maumeensis), Sphaeriidae (Pisidium casertanum, P. henslowanum, Sphaerium corneum, Musculium transversum), and Chironomidae (Procladius sp., Chironomus spp.). The average abundance of oligochaetes in the harbors was 21,000 individuals m^?2 in 1978 and 12,700 m^?2 in 1979, compared with 1,500 m^?2 and 1,200 m^?2, respectively, in the areas outside of harbors. Comparison of the macrobenthic assemblages with those in other regions of the Great Lakes, using several numerical indices as well as indicator species distributions, indicated that the general area of the nearshore zone outside of harbors possesses a moderate degree of organic enrichment, with a gradient of decreasing pollution in an offshore direction. The harbors appeared to be severely degraded, as reflected by the high densities of oligochaetes and the almost complete absence of all but the most pollution-tolerant species. The documentation of species distributions will enable future assessments of changes in the nearshore benthic communities.     

Diets,population structure,and seasonal activity patterns of mudpuppies (Necturus maculosus) in an urban,Great Lakes coastal habitat

Freshwater species native to the Laurentian Great Lakes region face numerous environmental stressors, and the conservation status and ecological relationships of many remain poorly understood. One such species, the mudpuppy (Necturus maculosus), is declining, but better information on their natural history and development of more effective population monitoring techniques is needed. We assessed seasonal variation in capture success, biases in capture techniques, and feeding ecology of mudpuppies in Wolf Lake, a highly perturbed and urban former estuarine wetland complex to Lake Michigan. Trapping periods of ≥ 3 consecutive nights occurred from January to May 2015, and October 2015 to March 2016. Overall trapping success differed among trapping periods (p = 0.01) and declined precipitously at water temperatures above 14.1 °C (p < 0.001). Mudpuppies in traps (mean 26.9 ± 0.5 cm) were larger than those caught with hand nets (mean 14.7 ± 0.8 cm, p < 0.0001), suggesting that multiple methods may be needed to accurately assess demographics. Stomach contents obtained through gastric lavage included mollusks, leeches, insects, isopods, amphipods, crayfish, fish, a frog, and a juvenile conspecific. Invasive species, including rusty crayfish (Orconectes rusticus), round gobies (Neogobius melanostomus), and zebra/quagga mussels (Dreissena spp.) were present in guts, suggesting mudpuppy foraging has changed along with aquatic communities in the region. Prey community analyses revealed differences in overall diet among size classes of mudpuppies (p = 0.001), but relatively weak similarity within size classes. Results suggest that mudpuppies in lake ecosystems occupy a broad niche that changes as they grow.     

Kinetics of Red Clay Bluff Dissolution in Western Lake Superior

The dissolution of red clay bluff samples from the southwestern Lake Superior shoreline area in Lake Superior water or deionized water is studied by following the aqueous concentrations of reactive silica over a three month period. The dissolution process is initially rapid, followed by a first-order dissolution process (k = 9.4 × 10^?7 sec^?1) up to about thirty days. After about 30 days, the rate of dissolution of the bluff material follows linear kinetics (k = 5.4 × 10^?8 mg SiO₂/gram of bluff per second).     

Quantifying a shift in benthic dominance from zebra (Dreissena polymorpha) to quagga (Dreissena rostriformis bugensis) mussels in a large,inland lake

Dreissenid mussels are aggressive invasive species that are continuing to spread across North America and co-occur in the same waterbodies with increasing frequency, yet the outcome and implications of this competition are poorly resolved. In 2009 and 2015, detailed (700 + sample sites) surveys were undertaken to assess the impacts of invasive dreissenid mussels in Lake Simcoe (Ontario, Canada). In 2009, zebra mussels were dominant, accounting for 84.3% of invasive mussel biomass recorded. In 2015, quagga mussels dominated (88.5% of invasive mussel biomass) and had expanded into profundal (> 20 m water depth) sites and onto soft (mud/silt) substrates with a mean profundal density of 887 mussels/m² (2015) compared to ~ 39 mussels/m² in 2009. Based on our annual benthos monitoring, at a subset of ~ 30 sites, this shift from zebra to quagga mussels occurred ~ 2010 and is likely related to a population decline of zebra mussels in waterbodies where both species are present, as recorded elsewhere in the Great Lakes Region. As the initial invasion of dreissenid mussels caused widespread ecological changes in Lake Simcoe, we are currently investigating the effects this change in species dominance, and their expansion into the profundal zone, will have on the lake; and our environmental management strategies. Areas of future study will include: changes in the composition of benthos, fish, or phytoplankton communities; increased water clarity and reduction of the spring phytoplankton bloom; energy/nutrient cycling; and fouling of anthropogenic in-lake infrastructures (e.g. water treatment intakes) built at depths > 25 m to avoid previous zebra mussel colonization.     

Field and Laboratory Studies of the Toxicity to Phytoplankton of Polychlorinated Biphenyls (PCBs) Desorbed from Fine Clays and Natural Suspended Particulates

Polychlorinated biphenyls (PCBs; Aroclor 1254) were adsorbed to natural (Hudson River and New York Bight) and commercial (illite) particles in the laboratory, then allowed to desorb for several hours into the surrounding aqueous medium in the presence of either of two laboratory strains of diatom species or a complete natural phytoplankton assemblage. Cell density, photosynthesis, and chlorophyll a concentration in the cultures were followed for 2 to 3 days. In two experiments, PCB-carrying natural particles were removed after desorption and prior to the introduction of algae. All incubations were carried out in the laboratory or in dialysis membrane bags suspended in the tidal channel of an estuarine marsh.Cultures containing 90 μg of illite-bound Aroclor 1254/L of water were severely damaged within 4 hours, by which time 72% of the PCBs had desorbed from particles and become available to the diatoms. Similarly, a natural phytoplankton community, incubated under natural conditions in the presence of 50 μg of Hudson River sediment-associated PCB/L of water, registered significant reductions of photosynthesis and chlorophyll a content for at least 3 days. When PCB-bearing New York Bight particles were removed from the medium prior to the introduction of algae, sufficient desorbed PCBs remained to reduce growth rates and chlorophyll a content of the culture. The latter experiment clearly demonstrates particle to water to cell transfer of desorbed PCBs.     

A mesocosm investigation of the effects of quagga mussels (Dreissena rostriformis bugensis) on Lake Michigan zooplankton assemblages

Dreissenid mussels are known to disrupt the base of the food web by filter feeding on phytoplankton; however, they may also directly ingest zooplankton thereby complicating their effects on plankton communities. The objective of this study was to quantify the effects of quagga mussel feeding on the composition and size structure of Lake Michigan zooplankton assemblages. Two mesocosm (six 946 L tanks) experiments were conducted in summer 2013, using quagga mussels and zooplankton collected near Beaver Island, MI, to examine the response of zooplankton communities to the presence and absence of mussels (experiment 1) and varying mussel density (experiment 2). Mesocosms were sampled daily and zooplankton taxa were enumerated and sized using microscopy and FlowCAM® imaging. In experiment 1, the presence of quagga mussels had a rapid negative effect on veliger and copepod nauplii abundance, and a delayed negative effect on rotifer abundance. In experiment 2, mussel density had a negative effect on veliger, nauplii, and copepodite abundance within 24 h. Multivariate analyses revealed a change in zooplankton community composition with increasing mussel density. Ten zooplankton taxa decreased in abundance and frequency as quagga mussel density increased: except for the rotifer Trichocerca sp., treatments with higher mussel densities (i.e., 1327, 3585, and 5389 mussels/m²) had the greatest negative effect on small-bodied zooplankton (≤ 128 μm). This study confirms results from small-scale (≤ 1 L) experiments and demonstrates that quagga mussels can alter zooplankton communities at mesoscales (~ 1000 L), possibly through a combination of direct consumption and resource depletion.     

Carbonate Equilibria and the Distribution of Inorganic Carbon in Saginaw Bay

The spatial and temporal distribution of selected inorganic carbon equilibrium species is presented for eleven locations, representing the near surface waters of Saginaw Bay in Lake Huron during 1974. Carbon dioxide and calcite equilibrium conditions are determined through solution of temperature and ionic strength adjusted equilibria and evaluated with respect to suitability as indicators of physical conditions and biological activity in the waters of Saginaw Bay. The participation of inorganic carbon species in several chemical and biochemical reactions leads to the utility of these species in reflecting documented spatial and temporal trends in phytoplankton biomass, temperature, ionic strength, and ionic composition. Substantial seasonal variations in carbon dioxide and calcite equilibrium conditions were observed at several locations throughout the bay. The magnitude of variation was greatest in the more productive areas of the bay, where extensive calcite supersaturation and carbon dioxide undersaturation occurred. Maximum calcite saturation and minimum carbon dioxide saturation were calculated for the warm, productive summer months. Transformations in chemical equilibria were mediated by both physical and biochemical factors,as reflected by seasonal changes in temperature and pH. The significance of photosynthetic activity was most pronounced in the inner bay and in shore zones, while temperature became of greater relative importance where bay waters mixed with the open waters of Lake Huron. Strong correlations between time averaged data for chlorophyll a and carbon dioxide (R = 0.97) and chlorophyll a and calcite saturation (R = 0.95) indicate the importance of photosynthetic activity in establishing the distribution of equilibrium conditions of inorganic carbon species.     

Variations in Spectral Slope in Lake Taihu,a Large Subtropical Shallow Lake in China

Spectral slope (S), describing the exponential decrease of the absorption spectrum over a given wavelength range, is an important parameter in the study of of chromophoric dissolved organic matter (CDOM) dynamics, and also an essential input parameter in remote sensing models. Furthermore, S is often used as a proxy for CDOM composition, including the ratio of fulvic to humic acids and molecular weight. The relative broad range in S values reported in the literature can be explained by the different spectral ranges and fitting methods used. A single exponential model is used to fit the S values for 17 investigations involving 458 samples in Lake Taihu from January to October in 2004. The average S value was 15.18 ± 1.39 μm⁻¹ for the range of 280–500 nm, which fell within the range reported in the literature. The frequency distribution of S value basically obeyed a normal distribution. Significant differences in S values between summer and other seasons showed that phytoplankton degradation was one of the important sources of CDOM in summer, whereas CDOM mainly came from the river input in other seasons. Furthermore, the estimated S value decreased with increasing wavelength range used in regression. The maximum and minimum values derived from the regression were 17.89 ± 1.25 μm⁻¹ and 13.62 ± 2.11 μm⁻¹ for the wavelength ranges of 280–380 nm and 400–500 nm, respectively, a decrease of 23.9%. S values significantly decreased with the increase of CDOM absorption coefficients. CDOM absorption coefficients could be more appropriately estimated from exponential model introducing the variation of S with absorption coefficients, making them useful for a remote sensing bio-optical model of Lake Taihu. DOC-specific absorption coefficient a*(λ) and the parameter M describing molecular size of the humic molecules could also be used as a proxy for the sources and types of CDOM. A general relationship was found between S and a*(λ), and M values. S increased with the decrease of DOC-specific absorption coefficient and the increase of M corresponding to the decrease of molecular weight.     

Chemistry,Mineralogy, and Morphology of Lake Erie Suspended Matter

Suspended matter was collected from different depths at three stations in spring and summer, 1978, in Lake Erie. Chemistry, mineralogy, and morphology of the suspended particles were measured to investigate spatial and temporal changes. The determined elements (Si, Fe, Ca, K, Mn, P, Al, Ti, and Mg) were partitioned between inorganic and biological material and the majority of these elements were present in at least two different chemical forms. Flocculates > 3 μm composed of organic material and mineral fragments were common at the water surface and the middle of the water column. Mineral fragments < 3 μm were the major constituent of suspended matter at the bottom at the deepest sampling station (62 m). The concentration of the major components of the suspended matter, organic material, alumino-silicates, and calcite, varied significantly from spring until later summer. The high concentration of organic material and the fluctuations of calcite concentration result from high rates of photosynthesis and respiration and temperature increases in spring and summer.     

Factors in the Determination of Selected Trace Elements in Near-Shore U.S. Waters of Lakes Superior and Huron

Determinations of total As, Cr, Cu, Fe, Mn, and Pb in acidified unfiltered water samples from 48 stations representing the near-shore U.S. waters of Lake Superior, Lake Huron, and selected incoming streams gave overall mean concentrations and standard deviations (μg/L) of 1.0 ± 0.7, 0.9 ± 1.8, 2.0 ± 1.8, 236 ± 819, 14 ± 34, and 0.7 ± 0.8, respectively, using flameless atomic absorption analytical methods. Total concentrations of Ni and Hg were usually less than the instrumental detection limits (μg/L) of 0.8 and 0.02, respectively. Small losses of Hg, As, and Cr from solutions are possible in addition to a molecular spectral interference in the determination of As using the graphite furnace method. River waters usually were only slightly higher in total element concentrations than lake waters, except for Fe andMn. Nearshore waters of both lakes were very similar in elemental composition.     

Atmospheric flows of semi-volatile organic pollutants to the Great Lakes estimated by the United States' Integrated Atmospheric Deposition and Canada's Great Lakes Basin Monitoring and Surveillance Networks

We calculated the wet and dry deposition, vapor absorption, and volatilization flows (in kg/yr) of seven polychlorinated biphenyls (PCBs), nine organochlorine pesticides, and two polycyclic aromatic hydrocarbons (PAHs) into and out of the Great Lakes during 2010–2015 (inclusive). Particle, vapor, and precipitation concentrations from five rural and remote stations (one site on each lake) and two urban sites, operated by the United States and Canada, were used for the flow calculations. Output from the water to the air was the most important process for PCBs, chlordanes, and p,p′-DDE. The flows of endosulfan, p,p′-DDT, and phenanthrene were dominated by vapor absorption from the air to the water. The flow of benzo[a]pyrene was controlled by wet and dry deposition to the water. The flows of the hexachlorocyclohexanes (HCHs) into and out of the lakes were about equal, indicating air-water equilibrium for these compounds. Among the lakes, Lakes Superior and Erie had the highest input and output flows. The input and output flows for the five lakes were decreasing with halving times of 1–10 years and 10–40 years, respectively. Most chemicals had seasonal variations in their flows, with maximum inputs in the summer and maximum outputs in the fall. The flows of PCBs and PAHs into Lakes Michigan and Erie were associated with Chicago and Cleveland, respectively. Combining our data with previous data over the period 1992–2015, we estimated that the input flows of most of these chemicals have significantly decreased, but the output flows do not show consistent trends.     

Precision of Ages Determined from Scales and Opercles for Yellow Perch Perca flavescens

Scales and opercles were used to age yellow perch Perca flavescens collected in 1989 from Lake Madison (South Dakota), Dauphin Lake (Manitoba), and southern Lake Michigan (Indiana). Three readers aged fish from Lake Madison and Dauphin Lake once and two readers aged fish from Lake Michigan twice. The coefficient of variation (CV) was calculated to compare precision. Ages determined from opercles were as precise as those from scales for fish from Lake Madison (CV = 0 for both structures), and more precise than ages from scales for fish from Dauphin Lake (CV_opercle = 14.0, CV_scale = 27.4, p < 0.001) and Lake Michigan (CV _opercle = 10.6, CV_scale = 13.9, p < 0.001). The high precision of scale and opercle ages for yellow perch from Lake Madison can be attributed to the fast growth rate of fish from that lake and also that only age 1 and 2 fish were aged. The greater precision of opercle ages in comparison to scale ages for Dauphin Lake and Lake Michigan yellow perch can be attributed to ease of recognition of false annuli on opercles as well as to difficulty in distinguishing between false and true annuli crowded on the edge of scales from mature, slower growing fish. Because true annuli are more easily recognized on opercles, ages determined from opercles may be more accurate than ages determined from scales for yellow perch growing at slow or moderate rates.     

The relative importance of anammox and denitrification to total N2 production in Lake Erie

Production of dinitrogen gas via microbially mediated anaerobic ammonium oxidation (anammox) and denitrification plays an important role in removal of fixed N from aquatic ecosystems. Here, we investigated anammox and denitrification potentials via the ¹⁵N isotope pairing technique in the helium flushed bottom water (~0.2 m above the sediment) of Sandusky Bay, Sandusky Subbasin, and Central Basin in Lake Erie in three consecutive summers (2010?2012). Potential rates of anammox (0–922 nM/day) and denitrification (1 to 355 nM/day) varied greatly among sampling sites during the 3 years we studied. The relative importance of anammox to total N₂ production potentially ranged from 0 to 100% and varied temporally and spatially. Our study represents one of the first efforts to measure potential activities of both anammox and denitrification in the water column of Lake Erie and our results indicate the Central Basin of Lake Erie is a hot spot for N removal through anammox and denitrification activities. Further, our data indicate that the water column, specifically hypolimnion, and the surface sediment of the Lake Erie Central Basin are comparatively important for microbially mediated N removal.     

Current state of the sponge fauna (Porifera: Lubomirskiidae) of Lake Baikal: Sponge disease and the problem of conservation of diversity

The spatial distribution of healthy and diseased sponges in Lake Baikal was investigated. The endemic sponges were studied in May ? June 2015 at 11 transects within the depth range of 0 to 40 m. More than 500 sponge specimens were collected, and 29 taxa including 12 species and 17 morphospecies (sp. taxa) were identified. Among the 29 taxa, only B. martinsoni specimens and 14 morphospecies were healthy, whereas specimens of the other 11 species and 3 morphospecies were diseased, making up 35% of the total number of specimens (512). The different body forms of sponge found among the specimens were encrusting (66%), globulous (21%), and branched (13%). Sponges with necrosis signs, discolored specimens or covered with violet film or brown spots, were found in all transects under study (37 stations of 68). The percent cover of the bottom (per m²) by various body forms of sponges was evaluated with a sponge faunal state assessment test. Changes in the diversity and abundance of sponges due to their disease may jeopardize the functioning of the entire ecosystem of Lake Baikal which is a World Heritage Site. This baseline data on patterns of sponges, including their spatial distribution and percent cover, will be utilized to support future management and monitoring of Lake Baikal. Data on the current state of Baikal endemic sponge fauna are essential for understanding the causes and prognosis of disease processes of freshwater sponges.     

Evidence of Natural Reproduction by Planted Lake Trout in Lake Michigan

Lake trout (Salvelinus namaycush) fry were captured in southeastern Lake Michigan for the first time since the species was reintroduced from hatchery stocks in 1965. Spawning apparently occurred in fall 1979 on newly placed limestone riprap covering recently constructed power plant intake and discharge pipelines. Eggs presumably hatched in late February–March, 1980, and 57 fry (22–43 mm total length) were collected April–June, 1980, and three fry (55–62 mm) were collected in August, 1980.     

Determination of absorption coefficients for chlorophyll a,phycocyanin, mineral matter and CDOM from three central Indiana reservoirs

Absorption coefficients are used in semi-empirical and bio-optical models to estimate various optically active constituents in water. This study determines the mass-specific absorption coefficients of chlorophyll a (a*_chl), phycocyanin (a*_pc), minerals (a*_m), and chromophoric dissolved organic matter (CDOM; a*_CDOM) and the absorption coefficient for CDOM (a_CDOM) for three central Indiana reservoirs. Absorption spectra were collected using a Shimadzu spectrophotometer equipped with a Spectralon coated integrating sphere. Quantitative measurements from either fluorometric (chlorophyll a, phycocyanin, CDOM) or weight-based (mineral) measurements were used to determine the mass-specific absorption coefficients tested in this study and an exponential function was used to estimate a_CDOM. While a*_chl showed minimum variability between reservoirs, a*_pc, a*_m, a*_CDOM, and a_CDOM showed statistically significant differences between reservoirs; however, for a*_m, there was greater variation within each reservoir. Variability in a*_CDOM and a_CDOM between reservoirs was likely due to different inflows. All absorption coefficients fell within previously published ranges for each constituent examined, with the exception of a*_pc. Differences in a*_pc were likely due to different techniques used in extracting and estimating phycocyanin.