Dissolved Organic Matter in the Great Lakes: Role and Nature of Allochthonous Material

Dissolved organic matter (DOM) quality and the modifying influence of light on DOM bioavailability were investigated along a natural gradient of allochthonous influence in the lower Great Lakes. Using parallel factor analysis (PARAFAC), three DOM fluorophores were identified. One fluorophore, previously identified as peak C, was of allochthonous (component 1) origin and two previously uncharacterized fluorophores were identified as autochthonous (components 2 and 3). Component 1 was photoreactive and the dominant form in creek water samples while components 2 and 3 were dominant in Hamilton Harbour and lake water samples. Components 2 and 3 showed limited photoreactivity. Exposure to full spectrum irradiance decreased the average molecular weight of DOM (i.e., increased the absorbance ratio (a254:a365)) for all water samples. DOM bioavailability was lowest in creek and highest in lake water samples and was inversely related to DOM average molecular weight. Photomodification of DOM resulted in higher bacterial activity although these differences were not significantly different. This suggests that light plays a significant role in the cycling of terrestrially-derived DOM and to a certain extent autochthonous DOM, potentially increasing metabolism of both terrestrially and microbially derived DOM in the Great Lakes aquatic ecosystems.     

A comparison of mercury cycling in Lakes Michigan and Superior

Mercury cycling in Lake Superior and Lake Michigan was evaluated based on measurements of mercury levels, modeling of evasional fluxes, and development of first-order mass balance models. Total mercury, methylmercury, and dissolved gaseous mercury were measured on sampling cruises in Lake Michigan (2005) and Lake Superior (2006). Average total mercury concentrations in unfiltered surface water were higher in Lake Michigan (420 ± 40 pg/L) compared to Lake Superior (210 ± 20 pg/L). Methylmercury levels were below the detection limit in Lake Michigan. Larger sample volumes were collected to lower detection limits in Lake Superior in 2006 and methylmercury levels averaged 7 ± 6 pg/L. Dissolved gaseous mercury concentrations were also higher in Lake Michigan (27 ± 7 pg/L) compared to Lake Superior (14 ± 8 pg/L). Evasional fluxes were estimated using a two-film model for air–water exchange. The annual evasional flux in Lake Michigan was determined to be ~ 380 kg/yr from Lake Michigan and ~ 160 kg/yr from Lake Superior. Total mercury burdens in each lake were estimated to be ~ 2500 kg in Superior and ~ 2100 kg in Lake Michigan demonstrating that evasional fluxes play an important role in the mass balance of each lake, particularly Lake Michigan. A simple first-order mass balance model demonstrates the importance of air–water exchange and sedimentation as primary removal processes for Hg in each lake. Uncertainties in the mass balance model are highlighted due to lack of key data, particularly in Lake Superior.     

Convergence of trophic state and the lower food web in Lakes Huron,Michigan and Superior

Signs of increasing oligotrophication have been apparent in the open waters of both Lake Huron and Lake Michigan in recent years. Spring total phosphorus (TP) and the relative percentage of particulate phosphorus have declined in both lakes; spring TP concentrations in Lake Huron are now slightly lower than those in Lake Superior, while those in Lake Michigan are higher by only about 1 μg P/L. Furthermore, spring soluble silica concentrations have increased significantly in both lakes, consistent with decreases in productivity. Transparencies in Lakes Huron and Michigan have increased, and in most regions are currently roughly equivalent to those seen in Lake Superior. Seasonality of chlorophyll, as estimated by SeaWiFS satellite imagery, has been dramatically reduced in Lake Huron and Lake Michigan, with the spring bloom largely absent from both lakes and instead a seasonal maximum occurring in autumn, as is the case in Lake Superior. As of 2006, the loss of cladocerans and the increased importance of calanoids, in particular Limnocalanus, have resulted in crustacean zooplankton communities in Lake Huron and Lake Michigan closely resembling that in Lake Superior in size and structure. Decreases in Diporeia in offshore waters have resulted in abundances of non-dreissenid benthos communities in these lakes that approach those of Lake Superior. These changes have resulted in a distinct convergence of the trophic state and lower food web in the three lakes, with Lake Huron more oligotrophic than Lake Superior by some measures.     

The Composition of Particulate Organic Matter in the Euphotic Zone of Lake Superior

The composition of particulate organic matter (POM) as living and dead material in the euphotic zone of Lake Superior, May to November 1973, was derived by a regression method. The regression method reported in the literature was modified because it had a conceptual bias and overestimated detritus. POM composition expressed as chlorophyll, particulate organic carbon, particulate organic nitrogen, and particulate organic phosphorus was also analyzed. This analysis showed that living seston was the major component of POM during the 7 months. Detritus was minimal during the year and increased to 39% of POM by fall. Most detritus was autochthonous. The lack of correlation between the particulate organic phosphorus and the other components of POM shows that the available phosphorus is rapidly recycled in an efficient manner and not significantly bound in detrital material. The coupling of statistical techniques and data collected during the intensive study of Lake Superior has provided a good insight into the interrelationships and seasonal patterns of nutrients and chlorophyll.     

地下水中溶解性有机物吸收光谱模型的对比研究

以往对于溶解性有机物(DOM)吸收光谱的研究主要集中在地表水体,为了了解地下水样品的光吸收特性、探索能够方便有效地表征地下水中DOM光吸收性质的理想模型,收集了某河湖相沉积的含水层中62个地下水样品的DOM吸收光谱,对线性指数模型、非线性指数模型、加背景项指数模型和幂函数模型等四种光吸收模型进行了拟合和对比分析。统计检验发现,传统的线性指数模型拟合效果不如其它三种模型好;幂函数模型的精度和实用性相比最佳,平均决定系数为0.991 8,在250～450nm光谱范围内拟合DOM吸收光谱斜率为(5.93±0.40)nm-1。幂函数模型为DOM化学性质及组分信息与模型参数之间的关系的研究提供了一种可行有效的方法。另外,还建立了更为一般的吸收光谱的幂函数模型,以期对地下水DOM快速分析和野外地下水现场调查起到积极作用。     

Diagenesis of Organic Matter in the Sediments of Lakes Ontario,Erie, and Huron

The organic matter in the modern sediments of Lakes Ontario, Erie, and Huron is composed of humic compounds (68 to 83%), amino acids (19 to 20%), lipids (2 to 8%), carbohydrates (2 to 6%), and amino sugars (0.5 to 4%). Amino acid and carbohydrate concentrations are high in plankton samples, which are the primary source of the sedimentary organic matter. These compounds are decomposed during their passage through the food chains and while resting at the sediment-water interface with the concurrent formation of humic compounds. The degree of diagenesis of the modem sedimentary organic matter is related to both the trophic state of the lake and to the water depth, with the greatest amount in the most eutrophic lake basins and in the shallowest water depths. Diagenesis of the organic matter is rapid prior to burial in the sediments and is slow after burial. The decomposition rates of the sedimentary organic matter are in the following order: amino acids>>amino sugars>carbohydrates>humic compounds>lipids.     

Life Cycle of a Mayfly Hexagenia Limbata in the St. Marys River Between Lakes Superior and Huron

Length-frequency distribution curves of Hexagenia limbata nymphs collected in May, August, and October 1974 and May 1975 in the St. Marys River between Lakes Superior and Huron were bimodal for each sampling period. These curves, combined with interpretation of nymphal emergence period and mean surface water temperatures, indicate that the population of Hexagenia nymphs in the St. Marys River is composed of two year classes or cohorts. One cohort emerges per season, 2 years after egg deposition.     

An ecological assessment of Great Lakes tributaries in the Michigan Peninsulas

Michigan stream fish and macroinvertebrate community data from multiple sources were combined to conduct a statewide assessment of riverine ecological condition. Using regionally normalized metrics to correct for methodological inconsistencies and natural variation and statistically based scoring criteria, about 50% of all sampled sites were in expected or better ecological condition, 30% were ecologically impaired, and 20% were marginal. Structural Equation Modeling with this regional assessment dataset indicated that land use effects were more important than effects of point-source discharges. Biological metrics appeared to be more sensitive to urban than agricultural land use, and riparian than basin-wide agricultural land use. Invertebrate communities were marginally more sensitive than fish communities to the suite of anthropogenic stressors examined. Using the observed assessment status from sampled sites, Classification and Regression Tree models were used to estimate ecological condition in the state's remaining unsampled river segments. Combining observed and estimated site scores, 25% of the state's river kms were estimated to be impaired, with the Erie and St. Clair basins having the highest degree of impairment (52% and 44% of total channel lengths, respectively) and lakes Superior, Michigan, and Huron basins had the lowest degree of impairment at 4%, 21% and 31%, respectively. We argue that correlations between the state of the Great Lakes and the ecological conditions of their tributary systems reflect both direct impact transmission from watershed to receiving waters, and also non-causal correlation due to shared anthropogenic stressors.     

Occurrence of the Toxin-producing Cyanobacterium Cylindrospermopsis raciborskii in Mona and Muskegon Lakes,Michigan

The bloom-forming and toxin-producing cyanobacterium Cylindrospermopsis raciborskii was observed in Muskegon and Mona lakes, drowned river-mouth tributaries of Lake Michigan. Morphological features of the taxon were similar to those described elsewhere. The species was observed only in late summer; elevated bottom water temperature, and perhaps phosphorus concentration, appears to be implicated in its appearance. Maximum abundances at any given site reached 393 and 0.9 trichomes/mL in Mona Lake and Muskegon Lake, respectively. Although these concentrations are low relative to other reports, the presence of this species in these two lakes from adjacent watersheds adds to a growing body of literature that suggests the distribution of C. raciborskii is on the increase in northern latitudes.     

Spatial Distributions of Legacy Contaminants in Sediments of Lakes Huron and Superior

The sediments of Lake Superior, Lake Huron, and Georgian Bay were sampled in 2001 and 2002 in order to evaluate the extent of surficial sediment contamination of polychlorinated biphenyls (PCBs), organochlorine pesticides (OCs), polycyclic aromatic hydrocarbons (PAHs), and metals. Sediment concentrations of PCBs, OCs, PAHs, and mercury were generally low and up to 2 orders of magnitude less than in Lakes Erie and Ontario. In contrast, concentrations of metals such as arsenic, copper, and nickel were comparable to those in Lakes Erie and Ontario. These elevated Lakes Superior and Huron metal concentrations were attributed to naturally occurring metals within the bedrock, soil, and sediment of the study region. Concentrations of all contaminants were typically below the Canadian Sediment Quality Probable Effect Level (PEL) guidelines. With regard to spatial patterns, most contaminants were focused primarily in the depositional basins and atmospheric deposition was likely the major source of these chemicals to the lakes. The major exception was for metals (not including mercury) whose patterns were also influenced by natural sources as well as extensive mining activity. A comparison between surficial sediment contamination of samples collected as part of this survey and those collected in the late 1960s/early 1970s using similar methods showed that concentrations of DDT, PCB, lead, and mercury were generally similar between these two time periods. These results are not consistent with production and usage patterns that have declined substantially in the past 3 decades. We hypothesize that the lack of temporal trends is an artifact due to slow sediment accumulation rates as well as differences in analytical protocols between the two time periods.     

Long-term Trends in the Seasonal Cycle of Great Lakes Water Levels

Numerous long-term trends in the rate-of-change in monthly mean Great Lakes water levels are identified for the period 1860 to 1998. Statistically significant trends are found for 2, 4, 5, and 7 months of the year for Lakes Superior, Michigan-Huron, Erie, and Ontario, respectively. Many of the trends translate into large changes in net water flux (600 to 1,700 m³/s). In each case, significant positive trends are roughly offset by negative trends during other times of the year. Together with similar trends in monthly lake level anomalies (deviations from the annual mean), these trends indicate important changes in the seasonal cycle of Great Lakes water levels. Specifically, Lakes Erie and Ontario are rising and falling (on an annual basis) roughly one month earlier than they did 139 years ago. Maximum lake levels for Lake Superior are also slightly earlier in the year, and the amplitude of the seasonal cycle of Lake Ontario is found to increase by 23% over the 139-year period. Some of the changes are consistent with the predicted impacts of global warming on spring snowmelt and runoff in the Great Lakes region. Other potential contributors to the observed trends include seasonal changes in precipitation and humaninduced effects such as lake regulation and changes in land use.     

Introduction and Spread of the Threespine Stickleback (Gasterosteus Aculeatus) in Lakes Huron and Michigan

The threespine stickleback (Gasterosteus aculeatus) was not known to occur in the Great Lakes above Niagara Falls until 1980, when it was collected in South Bay, Manitoulin Island, in the Lake Huron basin. By 1984 this species had been found in tributaries of Lakes Huron and Michigan, and in the open waters of both lakes. All specimens identified were the completely plated morph that is most prevalent in fresh water along the east coast of North America. The status of this species in Lakes Huron and Michigan appears to be “Possibly Established.” If threespine stickleback increase in abundance they may eventually provide additional forage for large salmonids.     

深色有机掺合料加快尾矿泥浆排水蒸发研究

针对高含水率尾矿泥浆对坝体产生危害以及污染环境等问题,通过添加深色有机物掺合料改变泥浆表面对太阳辐射量的吸收来提高尾矿泥浆蒸发速率,实现加快尾矿泥浆蒸发固结的目的。选取木炭屑、草木灰2种常见的深色有机物作为掺合料,通过理论分析和试验观测对比天然尾矿泥浆表面水分蒸发固结过程发现:木炭屑和草木灰均能提高尾矿泥浆蒸发速率,比不加掺合料的天然泥浆蒸发完成时间分别提前了32 h和24 h,同时减少了残余含水率18.8%和16.5%;木炭屑和草木灰在尾矿泥浆表面吸收更多的太阳辐射,其底部温度比天然泥浆样品高出8~12 ℃,从而促进泥浆的水分蒸发。深色有机掺合料能提高尾矿泥浆的固结程度,大大降低尾矿泥浆流动性,从而提高尾矿库的安全性能,是一种潜在的绿色环保尾矿泥浆排水方法。     

Factors governing the distribution and fish-community associations of the round goby in Michigan tributaries of the Laurentian Great Lakes

The round goby (Neogobius melanostomus) is increasingly being reported in tributaries of the Laurentian Great Lakes where these fish have been shown to adversely impact native stream biota. Determining the characteristics and distribution of invaded streams are the first steps toward effective round goby management. We sampled 30 tributaries in the Great Lakes basin and characterized each in terms of nine physical reach-scale attributes. Round goby were detected in 14 streams where abundances ranged from 4% to 53% of the fish sampled in each stream. Round goby was the single most abundant fish species sampled, constituting 14% of all fish encountered across all sites, and 30% of individuals in round goby-present sites. Round goby-present sites were larger, had lower channel slopes, less large wood, and less canopy cover than round goby-absent sites, suggesting that these attributes may promote round goby establishment. Mottled sculpin, cyprinids, brook stickleback, white sucker and rainbow trout were associated with goby absence while centrarchids, percids, yellow bullhead, and mud minnow were associated round goby presence. Collectively these results demonstrate that round goby are widespread in eastern Michigan tributaries to the Great Lakes, present in streams with a range of physical habitat characteristics, and that round goby presence is associated with certain fish species.     

天然有机物引起的超滤膜污染研究进展

天然有机物(NOM)在多种地表环境介质中广泛存在。超滤(UF)膜有去除水体中胶体物质、部分细菌及病毒等优势,但NOM所带来的膜污染会限制UF技术广泛应用。在阐述天然有机物来源、特性及去除工艺的基础上,从亲疏水性能、分子量大小和表面荷电性能3方面,分析了NOM性质对超滤膜污染的影响。从优势污染物的确定、膜面有机污染物类型的解析、污染层形态特征的分析及微观相互作用力的表征4个层面,综述了天然有机物引起的超滤膜污染的研究现状,并对超滤膜污染机理研究的方向进行了展望。研究成果可为缓解NOM对UF膜的污染提供理论支撑。     

Indicators of the Seasonal Cycle of Total Dissolved and Adsorbed Salts under Irrigation

This article describes the evaluation of indicators computed with a numerical simulation model of soil water and solute flow against field measurements of the amount of adsorbed and dissolved salts. In the Mediterranean environment,characterised by hot, dry summers, a field experiment on irrigation of vegetable crops with saline and tubewell water was carried out between 1988 and 1996 at a site near Naples, Italy. The investigation was carried out on a clay-loam soil classified as Argiustolls. Irrigation treatments were: tubewell water (no addition of NaCl), addition of 1.25, 2.5, 5 and 10 g_NaCl L^-1. Three irrigation intervals were applied until 1995: 2, 5 and 10 days. In 1995 all plots were irrigated on pre-selected days of the year, but the amount of water was equal to 100%, respectively 75 and 50% for the three irrigation treatments. Except 1996, all plots received consistently the same irrigation and salinity treatment, although different crops were grown on the same plot during the 8 yr experiment. In 1996, the indicator of soil salinity was used to evaluate the salt accumulation in the soil after a long time of saline irrigation. The indicator applied was the total amount of dissolved and adsorbed salts measured and simulated, in this way observation and model calculations are truly comparable. The aims were to evaluate the accuracy and relevance of salinity indicator computed by means of a numerical deterministic model describing water and solute transport SWAP. Total amount of salts were determined on soil samples, collected through the irrigation season on the treatments 0 and 5 g_NaCl L^-1. The samples were taken at three depths. The CEC and soluble salt were measured, beside the initial (prior to saturation in the laboratory) composition of the soil samples. Total dissolved and adsorbed salts were calculated throughout the irrigation season with the model SWAP. Calculated salt concentration was compared with observed soil composition to assess the accuracy of model calculations.     

Notes on the Benthic Alga Dichotomosiphon from the Straits of Mackinac Area of Lakes Michigan and Huron

During the summers of 1955–1956 the author was engaged in a sampling program to describe the distribution of the benthos and bottom sediments in the Straits of Mackinac area of the Great Lakes. The elusive benthic alga Dichotomosiphon tuberosus was identified from 17 of more than 690 bottom samples that were collected. Since there has been virtually no mention of this species in the Great Lakes literature since the time of collection, it is appropriate to report this matter at this time. This alga was distributed generally in the South Channel between Bois Blanc Island and the northern Michigan shoreline, and between the depths of 3.4 and 17.1 m. Most of the sediments associated with this species were sand with pebbles, low in clay, and with 5 to 10% silt.     

What lies beneath? Fungal diversity at the bottom of Lake Michigan and Lake Superior

Fungi are phylogenetically diverse organisms found in nearly every environment as key contributors to the processes of nutrient cycling and decomposition. To date, most fungal diversity has been documented from terrestrial habitats leaving aquatic habitats underexplored. In particular, comparatively little is known about fungi inhabiting freshwater lakes, particularly the benthic zone, which may serve as an untapped resource for fungal biodiversity. Advances in technology allowing for direct sequencing of DNA from environmental samples provide a new opportunity to investigate freshwater benthic fungi. In this study, we employed both culture-dependent and culture-independent methods to evaluate the diversity of fungi in one of the largest freshwater systems on Earth, the North American Laurentian Great Lakes. This study presents the first comprehensive survey of fungi from sediment from Lake Michigan and Lake Superior, resulting in 465 fungal taxa with only 7% of sequence overlap between these two methods. Additionally, culture-independent analyses of the ITS1 and ITS2 regions revealed 49% and 72%, respectively, of the OTUs did not match a described fungal taxonomic group below kingdom Fungi. The low level of sequence overlap between methods and high percentage of fungal taxa that can only be classified at the kingdom level suggests an immense amount of fungal diversity remains to be studied in these aquatic fungal communities.     

Revisiting the Great Lakes Water Quality Agreement phosphorus targets and predicting the trophic status of Lake Michigan

LM3-Eutro is a high-resolution eutrophication model with several improved features lacking in historical Great Lakes models. We calibrated LM3-Eutro using a 2-year (1994-1995) dataset and performed a hindcast simulation from 1976 to 1995 to evaluate the model's ability to make predictions over an extended period of time. Results show a reasonable agreement between model output and field data over this time period. The model predicted that an annual loading of 5600 metric tons (MT) would result in a lake-wide annual total phosphorus (TP) concentration of 7.5 μg L^− 1. Using best estimates of future TP loadings, LM3-Eutro forecasts suggest that Lake Michigan will remain oligotrophic and will continue to meet the 7 μg L^− 1 spring TP concentration Great Lakes Water Quality Agreement objective.     

Inshore-offshore Distribution of Larval Fishes in Lake Superior off the Western Coast of the Keweenaw Peninsula,Michigan

We surveyed the larval fish community in Lake Superior off the western coast of the Keweenaw Peninsula, Michigan, as a first component in understanding how the Keweenaw Current affects larval fish distribution and survivorship. On transects at Ontonagon, Houghton, and Eagle Harbor, we collected larval fishes with a 1-m diameter plankton net towed through surface and deep (below metalimnion) waters at an inshore location (1 km from shore) and an offshore location (5–9 km from shore) during day and night in 1998 and 1999. The most abundant larvae caught were lake herring (Coregonus artedii), rainbow smelt (Osmerus mordax), burbot (Lota lota), deepwater sculpin (Myoxocephalus thompsoni), and spoonhead sculpin (Cottus ricei). Lake herring was generally most abundant at the surface during the day, while the other four species avoided the surface by day but not at night. Overall, larval fish density was greater inshore than offshore, with exceptions for particular locations and seasonal periods (1.24x for lake herring, 12.93x for rainbow smelt, 1.27x for burbot, 1.25x for deepwater sculpin, and 4.26x for spoonhead sculpin). Differences in the sizes of larvae between inshore and offshore locations, in conjunction with density patterns, suggest a seasonal inshore to offshore movement. Despite the presence of the Keweenaw Current, the overall distribution patterns of larval fishes follow those of previous studies conducted in the Great Lakes, but with lower densities.