Biota of the St. Marys River: habitat evaluation and environmental assessment

The St. Marys River provides vital habitat for many species of plants, invertebrates, fish, and birds. It is also subject to many at times conflicting uses, including recreational boating, sport and subsistence fishing, municipal and industrial withdrawals and inputs, as well as commercial ship traffic and hydroelectric power generation.In 1984, the United States and Canada jointly initiated the Upper Great Lakes Connecting Channels Study to identify and quantify the impacts of contaminants on these channels and their biota and to develop recommendations for more effective pollution control and surveillance programs. Results of the study in the St. Marys River showed that water entering the river from Lake Superior is of excellent quality. Industrial and municipal discharges in the Sault Ste. Marie, Ontario area have resulted in heavily contaminated sediments and a severely impaired benthic invertebrate community in this area and downstream; however, no major impacts on fish have been demonstrated. Nevertheless, major impacts of man on fish spawning and rearing habitats and on benthic and fish productivity have resulted from the alteration of channels, construction of navigation locks, and regulation of flow in the St. Marys Rapids. Increases in the productivity of such raptors as osprey during the 1980s suggest a reduction in organochlorine contaminants levels in their diet; however, the increasing numbers of gulls with low concentrations of PCBs, p,p-DDE and other organochlorines in their eggs may adversely affect gull young or their predators.     

Heavy metals in aquatic macrophytes drifting in a large river

Macrophytes drifting throughout the water column in the Detroit River were collected monthly from May to October 1985 to estimate the quantities of heavy metals being transported to Lake Erie by the plants. Most macrophytes (80–92% by weight) drifted at the water surface. Live submersed macrophytes made up the bulk of each sample. The most widely distributed submersed macrophyte in the river, American wildcelery (Vallisneria americana), occurred most frequently in the drift. A total of 151 tonnes (ash-free dry weight) of macrophytes drifted out of the Detroit River from May to October. The drift was greatest (37 tonnes) in May. Concentrations of heavy metals were significantly higher in macrophytes drifting in the river than in those growing elsewhere in unpolluted waters. Annually, a maximum of 2 796 kg (eight heavy metals combined) were transported into Lake Erie by drifting macrophytes. The enrichment of all metals was remarkably high (range: 4 000 × to 161 000 × ) in macrophytes, relative to their concentration in water of the Detroit River. Detroit River macrophytes are thus a source of contaminated food for animals in the river and in Lake Erie.Contribution 734 of the National Fisheries Research Center-Great Lakes, U.S. Fish and Wildlife Service, 1451 Green Road, Ann Arbor, MI 48105.     

A new program for biomonitoring status and trends in the environment

Environmental contaminants threaten the biological integrity of aquatic and semi-aquatic communities both inside and outside of U.S. National Wildlife Refuges (Refuges). The U.S. Fish and Wildlife Service (FWS) and the U.S. National Biological Survey are developing a new biomonitoring program, the Biomonitoring of Environmental Status and Trends (BEST) Program. The BEST Program is being designed to respond to the effects of contemporary environmental contaminant problems associated with fish and wildlife and their habitats. When fully operational, BEST will evaluate the effects of contaminants on fish and wildlife resources; identify and prioritize national, regional, and local contaminant issues for decision makers; monitor national trends of the presence and effects of contaminants; and provide baseline information to support various contaminant investigation activities. The BEST Program will use an integrated network to evaluate contaminant impacts at the tissue, organism, population, community, and ecosystem levels. The sampling approach will be designed around two major components, trust resources on FWS lands (primarily Refuges) and trust species and their habitats outside of FWS lands. The BEST Program is adopting bioassessment techniques from four broad categories including ecological surveys, biomarkers, bioassays and toxicity tests, and residue analysis. Pilot and demonstration projects will be conducted through fiscal year 1997.     

A scientific basis for restoring fish spawning habitat in the St. Clair and Detroit Rivers of the Laurentian Great Lakes

Loss of functional habitat in riverine systems is a global fisheries issue. Few studies, however, describe the decision‐making approach taken to abate loss of fish spawning habitat. Numerous habitat restoration efforts are underway and documentation of successful restoration techniques for spawning habitat of desirable fish species in large rivers connecting the Laurentian Great Lakes are reported here. In 2003, to compensate for the loss of fish spawning habitat in the St. Clair and Detroit Rivers that connect the Great Lakes Huron and Erie, an international partnership of state, federal, and academic scientists began restoring fish spawning habitat in both of these rivers. Using an adaptive management approach, we created 1,100 m² of productive fish spawning habitat near Belle Isle in the Detroit River in 2004; 3,300 m² of fish spawning habitat near Fighting Island in the Detroit River in 2008; and 4,000 m² of fish spawning habitat in the Middle Channel of the St. Clair River in 2012. Here, we describe the adaptive‐feedback management approach that we used to guide our decision making during all phases of spawning habitat restoration, including problem identification, team building, hypothesis development, strategy development, prioritization of physical and biological imperatives, project implementation, habitat construction, monitoring of fish use of the constructed spawning habitats, and communication of research results. Numerous scientific and economic lessons learned from 10 years of planning, building, and assessing fish use of these three fish spawning habitat restoration projects are summarized in this article.     

Response of benthic macroinvertebrates to whole-lake, non-native fish treatments in mid-elevation lakes of the Trinity Alps, California

Introduced fish reduce the abundance and diversity of native aquatic fauna, but the effect can be reduced in complex habitats. We manipulated fish populations in forested mountain lakes to determine whether or not fish affected benthic macroinvertebrate composition across lakes with differing habitat complexity. We compared abundance, biomass, body-length, and community structure of benthic macroinvertebrates from 16 lakes with three treatments (fish stocked, suspended stocking, fish removed) and unstocked fishless “controls”. Over 4 years, we assessed the relative importance of fish and environmental variables influencing the composition of benthic macroinvertebrates. Control lakes had the greatest overall abundance of macroinvertebrates when chironomid midges were excluded. Abundances of insects in the clinger/swimmer functional group and caddisflies were greatest in the control lakes but were primarily influenced by habitat variables including the availability of aquatic vegetation and wood. Total biomass and mean body length of macroinvertebrates were not affected by treatment. Taxon richness of macroinvertebrates was about 40% greater in the control lakes compared to the treatment lakes but did not differ among treatments. Our results suggest that fish reduce susceptible macroinvertebrate richness and abundances, but that changes associated with alterations of fish composition are confounded by other factors in complex lake habitats.     

三峡库区不同水文类型支流大型底栖动物对蓄水的响应

为探究三峡水库修建对库区不同水文类型支流大型底栖动物的影响,于2015年7月和2016年1月对三峡水库四条支流的大型底栖动物进行调研,分别对周期性受蓄水影响支流的非回水区与回水区和长期受蓄水影响支流的非回水区与回水区大型底栖动物群落结构进行比较研究,结果表明:⑴7月份三峡水库145米低水位时期共采集到底栖动物655头计59种(属),在受蓄水影响河段采集到底栖动物4种共40头,优势种为日本沼虾(占受蓄水影响区域的57.5%); 1月份三峡水库175米蓄水时期共采集到底栖动物1123头计69种(属),在受蓄水影响河段采集到16种238头,优势种为锯齿新米虾(占受蓄水影响区域的14.2%)。⑵周期性受蓄水影响支流的非回水区与回水区底栖动物密度、生物量和多样性指数无显著差异(P0.05);长期受蓄水影响支流的非回水区与回水区之间底栖动物密度和Pielou均匀度指数无显著差异(P0.05),但非回水区底栖动物生物量显著高于回水区(P0.05),底栖动物多样性和丰富度极显著高于回水区(P0.01)。⑶7月份影响底栖动物分布的主要环境因子共6个,分别是水深、流速、硝态氮、溶解氧、水温和电导率; 1月份影响底栖动物分布的主要环境因子共7个,分别是水温、溶解氧、总磷、流速、深度、电导率和透明度。     

Restoration of rapids habitat in a Great Lakes connecting channel,the St. Marys River,Michigan

Aquatic habitat has been extensively altered throughout the Laurentian Great Lakes to increase navigation connectivity. In particular, the St. Marys River, a Great Lakes connecting channel, lost >50% of its historic rapids habitat over the past century. In 2016, the natural flow was restored to the Little Rapids area of the St. Marys River. The goal of our study was to evaluate physical and ecological responses to the restoration of the Little Rapids area. Extensive habitat and biological data were collected prior to restoration (2013 and 2014), and after restoration (2017 and 2018). Measured parameters included total suspended solids, current velocity, benthic macroinvertebrates, and larval, juvenile, and adult fishes. Total suspended solids stayed low (<4 mg/L) following restoration, with the exception of a single construction‐related event. Pre‐restoration data indicated that all measured velocities were below the target flow rate of 0.24 m/s, whereas 70% of the measured habitat was above the target flow post‐restoration. Abundance and richness of benthic macroinvertebrates were reduced following restoration (>90% reduction). We observed a 45% increase in richness of larval fish 2 years after restoration and a 131% increase in catch per unit effort. For adult fishes, the proportion of individuals with a preference for fast‐moving waters increased from 1.5 to 45% in the restored area, and from 7 to 15% upstream of the restored area; a similar response was observed for lithophilic spawners. The physical and biological conditions of the Little Rapids improved and resembled conditions typical of rapids habitat extent in other areas of the river and other systems.     

The effects of mine waste contamination at multiple levels of biological organization

This study shows that metal-contaminated sediments cause adverse biological effects at all levels of biological organization, from cellular to ecosystem-level responses, even where the corresponding surface water meets water-quality-based criteria. We studied the effects of contamination from the abandoned Alder Mine, Alder Mill, and Red Shirt Mill located near the town of Twisp on the eastern slopes of the north Cascade Mountains in Okanogan County, Washington (U.S.A.) on fish and wildlife habitat in the Methow River. Ore deposits in the area were mined for gold, silver, copper and zinc until the early 1950s. An up-gradient and down-gradient approach was used to compare impacted sites to control sites. Although the dissolved metal concentrations in the Methow River were below the limits of detection, eight elements were identified as contaminants of potential environmental concern (COPECs) in sediments. Results revealed contamination impacts at ecosystem, community, population, individual, cellular, subcellular, and molecular levels. Metal contaminants in forest soils around the mines were present at concentrations toxic to soil bacteria suggesting that functional properties related to nutrient cycling and energy flow have been effected. Exposed trout in the Methow River showed reduced growth compared to controls. Histopathological evidence is consistent with copper-induced metabolic disease. Glycogen bodies were present in trout hepatocyte cytosol and nuclei and the presence of glycogen inclusions was pathognomic of Type IV glycogen storage disease (GSD IV). This condition suggests food is being converted into glycogen and stored in the liver and that the glycogen is not being converted back normally into glucose for distribution to other tissues in the body, which is a likely cause for the poor growth and development observed in fish and macroinvertebrates. Glycogen storage disease is caused by either a deficiency or inactivation of the glycogen branching enzyme, which results in the synthesis of an abnormal glycogen molecule that is insoluble due to a decreased number of branch points and increased chain length. Further examination of hepatocytes by transmission electron microscopy also revealed the accumulation of electron-dense metal-granules in the mitochondrial matrix.     

Structural complexity of woody debris patches influences fish and macroinvertebrate species richness in a temperate floodplain-river system

A field experiment was conducted to examine the influence of variable density (complexity) of small patches of woody debris on the abundance and taxonomic richness of macroinvertebrates and fishes in the Brazos River, a meandering lowland river in east-central Texas. Woody debris patches contained bundles of either 8 or 16 sticks of two sizes, and reference plots contained no woody debris. The experiment was conducted in the littoral zone in the river channel and a nearby oxbow lake. Organisms were collected from each patch after 14 days. Abundance and taxonomic assemblage structure of macroinvertebrates in both the river channel and oxbow were significantly and positively influenced by complexity of woody debris. For fish in the oxbow, abundance and species richness were greater in woody debris than sites lacking structure, but the opposite trend was observed for fish in the river channel. This difference could be associated with isolation from source habitats and low colonization of the constructed woody debris patches in the river by fishes with affinities for complex habitats. Small lotic-adapted minnows were captured from reference habitats in the channel, but these species were rare in woody debris patches. This was in contrast to aquatic insects in the river channel, such as caddisfly and midge larvae, that efficiently colonized the small isolated patches of woody debris. In a lotic environment, woody debris provides vertical surfaces that intercept drifting insect larvae and provides protection from the water current. We speculate that greater abundance of macroinvertebrates in woody debris patches in both habitats results from the combined influence of high food resource availability and refuge from predation provided by structurally complex habitats. Handling editor: R. Bailey     

Using stable isotope analysis with telemetry or mark-recapture data to identify fish movement and foraging

Information about animal movements has often been inferred from stable isotope analysis (SIA), but is dependent on animals assimilating site-specific isotopic signatures via diet. This potential weakness in ecological interpretation can be overcome by using other investigative tools that provide precise information about individual movement patterns. In this paper, we demonstrate the value of combining SIA with telemetry or mark-recapture data from trapping, electrofishing and remote detection of individuals to study the movement and feeding ecology of fishes in different habitats. In a fjord lake system in Newfoundland, Canada, juvenile Atlantic salmon delayed downstream migration (smolts) or actively moved into a large lake (parr) where they foraged for periods reflecting different life history strategies. In the Miramichi River (New Brunswick, Canada), SIA provided evidence of distinct foraging habitats (tributary versus large river). By tracking fish implanted with passive integrated transponder (PIT) tags, we distinguished between movements related to foraging versus seeking cool water refugia during high temperature events. Finally, site fidelity and limited mobility of slimy sculpin, a small benthic fish, was established where δ¹³C in muscle tissue showed a progressive enrichment downstream and where a median displacement of <10 m was estimated for sculpin tagged with PIT tags. Technological improvements have permitted non-destructive tissue sampling of wild fishes for SIA, and the tagging and remote detection of animals smaller than was previously possible. These advancements and the combination of investigative tools promise new insights into animal ecology.     

Biological quality metrics: their variability and appropriate scale for assessing streams

The concept of spatial scale is at the research frontier in ecology, and although focus has been placed on trying to determine the role of spatial scale in structuring communities, there still is a further need to standardize which organism groups are to be used at which scale and under which circumstances in environmental assessment. This paper contributes to the understanding of the variability at different spatial scales (reach, stream, river basin) of metrics characterizing communities of different biological quality elements (macrophytes, fishes, macroinvertebrates and benthic diatoms) as defined by the Water Framework Directive. For this purpose, high-quality reaches from medium-sized lowland streams of Latvia, Ecoregion 15 (Baltic) were sampled using a nested hierarchical sampling design: (river basin → stream → reach). The variability of metrics within the different groups of biological quality elements confirmed that large-bodied organisms (macrophytes and fish) were less variable than small-bodied organisms (macroinvertebrates and benthic diatoms) at reach, stream and river basin scales. Single metrics of biological quality elements had the largest variation at the reach scale compared with stream and basin scales. There were no significant correlations between biodiversity indices of the different organism groups. The correlation between diversity indices (Shannon’s and Simpson’s) of the biological quality elements (macrophytes, fish, benthic macroinvertebrates and benthic diatoms) and a number of measured environmental variables varied among the different organism groups. Relationships between diversity indices and environmental factors were established for all groups of biological quality elements. Our results showed that metrics of macrophytes and fish could be used for assessing ecological quality at the river basin scale, whereas metrics of macroinvertebrates and benthic diatoms were most appropriate at a smaller scale.     

Heavy metal contamination of sediments in the Upper Connecting Channels of the Great Lakes

In 1985, sampling at 250 stations throughout the St. Marys, St. Clair, and Detroit rivers and Lake St. Clair — the connecting channels of the upper Great Lakes — revealed widespread metal contamination of the sediments. Concentrations of cadmium, chromium, copper, lead, mercury, nickel, and zinc each exceeded U.S. Environmental Protection Agency sediment pollution guidelines at one or more stations throughout the study area. Sediments were polluted more frequently by copper, nickel, zinc, and lead than by cadmium, chromium, or mercury. Sediments with the highest concentrations of metals were found (in descending order) in the Detroit River, the St. Marys River, the St. Clair River, and Lake St. Clair. Although metal contamination of sediments was most common and sediment concentrations of metals were generally highest near industrial areas, substantial contamination of sediments by metals was present in sediment deposition areas up to 60 km from any known source of pollution.Contribution 735 of the National Fisheries Research Center-Great Lakes, U.S. Fish and Wildlife Service, 1451 Green Road, Ann Arbor, MI 48105.     

Limnological aspects of the St. Clair River

The St. Clair River is a major navigable waterway transporting water southwards for 63 km from Lake Huron to Lake St. Clair at an average flow of 5 100 m3 s^-1. Water entering the river is low in suspended solids, organic carbon, phosphorus and nitrates, typical of clear, oligotrophic waters. In contrast to many large rivers, dissolved and colloidal solids account for 90 to 95 percent of the total solids load transported by the river, giving the river a turquoise colour common of glacial meltwater streams.The river supports a diverse floral and faunal community that includes 20 taxa of submergent macroflora, at least 300 benthic macroinvertebrates and 83 fishes. A number of exotic (European) species, including 3 plants, 4 molluscs and 11 fishes, occur in the river with the macroalga, Nitellopsis obtusa, zebra mussel (Dreissena polymorphora), Asian clam (Corbicula fluminea), and white perch (Morone americana) being the most recent invaders. Production is estimated to be 200 g m^-2 a^-1 ash-free dry mass for submergent macrophytes and periphyton, 7 g for macroinvertebrates and 5 g for fishes.The river also supports a variety of water-oriented recreational activities, is a source of municipal and industrial water, a receiver of municipal and industrial wastes, and a shipping corridor. Industrial discharges have adversely affected aquatic life, particularly in the nearshore areas along the Canadian shoreline south of Sarnia, Ontario. In addition, channel dredging and shoreline modifications (bulk-heading and backfilling) have destroyed large areas of valuable habitat in the main channel and along the shoreline. Improvements in the nearshore benthic macroinvertebrate community of the river over the past 20 years show that the river will respond to reductions in contaminants loadings.     

Spawning by lake sturgeon (Acipenser fulvescens) in the Detroit River

Overfishing and habitat destruction in the early 1900s devastated lake sturgeon (Acipenser fulvescens) populations in the Great Lakes. Although a comprehensive restoration strategy for this species was recently drafted by the Michigan Department of Natural Resources, a lack of current data on Great Lakes sturgeon stocks has hindered rehabilitation efforts. Historically, the Detroit River supported one of the largest lake sturgeon populations in the Great Lakes; however, little is known about the current population or its habitat use. The main objective of this study was to determine if lake sturgeon spawns in the Detroit River. As part of a larger study, baited setlines were used to capture lake sturgeon in the Detroit River in the spring and summer of 2000 and 2001. In each year of the study, ultrasonic transmitters were surgically implanted in 10 adult fish to track their movements, evaluate habitat use and identify possible spawning sites. Using telemetry and egg mats to verify spawning activity, one spawning site was located and verified in the Detroit River. Spawning was verified by recovering sturgeon eggs deposited on egg collection mats anchored at the site. Telemetry data suggested that several other possible spawning sites also may exist, however, spawning activity was not verified at these sites.     

Diel interactions between prey behaviour and feeding in an invasive fish, the round goby, in a North American river

1. We studied the diet of the invasive round goby (Neogobius melanostomus) on a diel basis in the Flint River, a warmwater stream in Michigan, U.S.A. Diet and available prey samples were collected seven times over a 24 h period in four consecutive months. The section of river studied lacked zebra mussels (Dreissena polymorpha), the primary prey of adult round gobies elsewhere in the Great Lakes region. 2. Diet changed on a diel basis with hydropsychid caddisfly and chironomid larvae predominating during the day, chironomid pupae dominating in the evening and heptageniid mayflies dominating at night. Simultaneous study of macroinvertebrate drift suggested that caddisfly and chironomid larvae were most likely picked from submerged rocks, chironomid pupae were most likely taken during their emergent ascent and mayflies were either captured from the drift or picked from rocks. 3. The Flint River lacks a diverse darter (Family: Percidae) and sculpin (Family: Cottidae) fauna and it appears that the round goby has occupied a generalised darter/sculpin niche. Our results indicate that round gobies have the potential to invade successfully riverine systems, particularly those lacking a diverse benthic fish assemblage.     

Response of bacteria and phytoplankton to contaminated sediments from Trenton Channel,Detroit River

Several types of bioassays were used in 1986 and 1987 to investigate the effect of contaminated sediments on natural populations of bacteria and phytoplankton from the Trenton Channel, Detroit River. The approach included the measurement of uptake of ³H-glucose or ³H-adenine by bacteria and ¹⁴C-bicarbonate by phytoplankton in the presence of different amounts of Trenton Channel and Lake Michigan (control) sediments. Trenton Channel sediments are contaminated by high levels of toxic organic compounds and metals, especially zinc, lead, and copper. Because levels of biomass of bacteria and phytoplankton varied widely among the different bioassays, it was necessary to adjust uptake rates for biomass. Biomass adjustments were made using acridine orange counts for bacteria and chlorophyll measurements for phytoplankton. The results show a statistically significant suppression of uptake of substrates for both bacteria and phytoplankton with increasing amounts of sediment. Uptake was suppressed as much as 90 percent for bacteria and 93 percent for phytoplankton at 1200 mg l^-1 of Trenton Channel sediments compared to bioassays without sediment. Uncontaminated Lake Michigan sediment suppressed uptake much less than Detroit River sediment; the difference in suppression of uptake between the two types of sediment was statistically significant for both bacteria and phytoplankton.Contribution No. 518 of the Center for Great Lakes and Aquatic Sciences of the University of Michigan.     

Benthic, Drifting and Marginal Macroinvertebrate Assemblages in a Lowland River: Temporal and Spatial Variations and Size Structure

Aquatic macroinvertebrates living in anastomosing lowland rivers use different habitats and respond differently to the hydrological regime. In this paper, the structure and composition of benthic, drifting and marginal macroinvertebrate assemblages are analyzed in the lowland river Ctalamochita (Córdoba, Argentina). The assemblages were studied in an annual cycle; a comparison among the composition of benthos, drift and marginal fauna was carried out; and size structure of the assemblages was characterized. Samples were obtained from two sites: a rural and an urban site. In total 73 taxa of aquatic macroinvertebrates were collected. Benthos was characterized by Chironomidae and Oligochaeta; marginal fauna was mainly constituted by Coleoptera, Heteroptera, Decapoda, the Trichoptera Nectopsyche sp., Ephemeroptera and Odonata. Drifting assemblage was composed by macroinvertebrates from local and remote upstream benthos, and from the marginal zone. Marginal fauna diversity was higher than benthos and drift. Total biomass of the assemblages pooled together was relatively equitably among size classes. Larger size classes consisted of organisms from the marginal zone whereas the smallest ones were composed by benthic and drifting organisms. In the study area there is habitat partitioning in the lateral dimension of the river. Marginal fauna was more diverse due to the asymmetry of transport and deposit processes, which generate a heterogeneous habitat in the bankside. The relation between fine substrate and high current velocity determines an unstable habitat in the central channel, which makes colonization by benthic macroinvertebrates difficult.     

Contaminants in the Upper Mississippi River: historic trends,responses to regulatory controls,and emerging concerns

We synthesized information on selected contaminants in the Upper Mississippi River, summarized regulatory measures enacted to reduce pollution, and described biotic and ecosystem responses to regulatory actions. Contamination of the river with mercury and lead rapidly followed settlement of the basin by European immigrants in the mid-1800s. Metal contamination peaked in the 1960s and has since decreased substantially. DDT, its degradation product DDE, and PCBs biomagnified to concentrations that adversely affected wildlife in upper trophic levels. National (U.S.A.) environmental regulations enacted from 1972 to 1991 reduced discharges of wastes from point sources, improved wastewater treatment, and reduced or banned the production or usage of certain chemicals, such as DDT, PCBs, and lead. Responses to these regulatory measures include reductions in ecosystem contamination, reductions in biotic exposure, and recovery of affected wildlife populations. Recovery from pollution has been slow, however, and we conclude that proactive approaches focusing on prevention are highly preferable to reactive approaches in management of toxic substances. Past successes in reducing point-source pollution, which is greatest near urban areas, do not extend to nonpoint-source pollution, given that the existing regulatory framework does not adequately address nonpoint sources. The river continues to receive hundreds of recently synthesized chemicals, and the behavior and effects of most of these compounds in aquatic ecosystems are largely unknown. Emerging contaminants and recently discovered mechanisms of adverse biological effects, such as endocrine disruption, pose continuing challenges to scientists and environmental managers concerned with the ecological health of this riverine ecosystem.     

Assessment of the ecological health of heavily utilized,large lowland rivers: example of the lower Yellow River,China

We describe an approach to assessing biological health in a heavily utilized, large lowland river setting, using the example of the lower Yellow River, China. In this study, the river was divided into four reaches, and a field survey of fish, benthic macroinvertebrates, and riparian plants was undertaken. Data from historical records were used for reference. The scoring system used weighting to adjust for differences in the importance of the chosen indicators and the relative efficiency of the sampling effort. The results indicated that the biological health of the lower Yellow River is distant from historical reference conditions, with its condition generally declining in the downstream direction. This result is consistent with the river’s history of impairment of hydrology, water quality, wetland area and character, and physical form. We conclude that the reference river state based on historical conditions is unlikely to equate to the best attainable river health because certain changes have occurred in the river that may prohibit a return to the previous state of ecological health. On the basis of the results of this assessment as well as a review of the literature, we propose field data collection methodologies and indicators that can be applied in future assessments.     

Distribution of Hexagenia nymphs and visible oil in sediments of the Upper Great Lakes Connecting Channels

As part of the study of the Upper Great Lakes Connecting Channels sponsored by the U.S. Environmental Protection Agency, the U.S. Fish and Wildlife Service examined the occurrence of Hexagenia nymphs and visible oil in sediments at 250 stations throughout the St. Marys River and the St. Clair-Detroit River system from May 14 to June 11, 1985. The mean density of Hexagenia nymphs per square meter averaged 194 for the total study area, 224 in the St. Marys River, 117 in the St. Clair River, 279 in Lake St. Clair, and 94 in the Detroit River. The maximum density of nymphs ranged from 1,081 to 1,164 m^-2 in the three rivers and was 3,099 m^-2 in Lake St. Clair. A comparison of nymph density at 46 stations where oil was observed in sediments physically suitable for nymphs showed that densities were lower in oiled sediments (61 m^-2) than in sediments without oil (224 m^-2). Densities of nymphs were relatively high at only four stations where oil was observed in sediments. In general, oiled sediments and low densities of nymphs occurred together downstream from industrial and municipal discharges.Contribution number 736 of the National Fisheries Research Center-Great Lakes, U.S. Fish and Wildlife Service, 1451 Green Road, Ann Arbor, MI 48105.