A. Dennis Lemly

Nitrogen excess in North American ecosystems: predisposing factors, ecosystem responses, and management strategies

Most forests in North America remain nitrogen limited, although recent studies have identified forested areas that exhibit symptoms of N excess, analogous to overfertilization of arable land. Nitrogen excess in watersheds is detrimental because of disruptions in plant/soil nutrient relations, increased soil acidification and aluminum mobility, increased emissions of nitrogenous greenhouse gases from soil, reduced methane consumption in soil, decreased water quality, toxic effects on freshwater biota, and eutrophication of coastal marine waters. Elevated nitrate (NO3−) loss to groundwater or surface waters is the primary symptom of N excess. Additional symptoms include increasing N concentrations and higher N:nutrient ratios in foliage (i.e., N:Mg, N:P), foliar accumulation of amino acids or NO3−, and low soil C:N ratios. Recent nitrogen-fertilization studies in New England and Europe provide preliminary evidence that some forests receiving chronic N inputs may decline in productivity and experience greate...

Effects of sedimentation and turbidity on lotic food webs: a concise review for natural resource managers

Sedimentation and turbidity are significant contributors to declines in populations of North American aquatic organisms. Impacts to lotic fauna may be expressed through pervasive alterations in local food chains beginning at the primary trophic level. Decreases in primary production are associated with increases in sedimentation and turbidity and produce negative cascading effects through depleted food availability to zooplankton, insects, freshwater mollusks, and fish. Direct effects at each trophic level are mortality, reduced physiological function, and avoidance; however, decreases in available food at trophic levels also result in depressed rates of growth, reproduction, and recruitment. Impacts of turbidity to aquatic organisms often seem inconsistent among watersheds and experiments, but this apparent difference is actually due to the lack of correlation between suspended sediment concentrations (mg/L) and units of measure (Nephelometric Turbidity Units, NTU). The use of NTU as a surrogate measurement of suspended sediment to predict biotic effects within watersheds is dubious. Similar NTU measurements from different watersheds may be correlated with different concentrations of suspended sediment. For monitoring the effects of turbidity within local watersheds, we recommend that the correlation between suspended sediment and NTUs be examined over a range of discharge recordings, and that this be used as a baseline to examine local effects. We recommend that riparian buffer strips and livestock fencing be used to reduce sediment input to streams.

Aquatic selenium pollution is a global environmental safety issue

Selenium pollution is a worldwide phenomenon and is associated with a broad spectrum of human activities, ranging from the most basic agricultural practices to the most high-tech industrial processes. Consequently, selenium contamination of aquatic habitats can take place in urban, suburban, and rural settings alike--from mountains to plains, from deserts to rainforests, and from the Arctic to the tropics. Human activities that increase waterborne concentrations of selenium are on the rise and the threat of widespread impacts to aquatic life is greater than ever before. Important sources of selenium contamination in aquatic habitats are often overlooked by environmental biologists and ecological risk assessors due to preoccupation with other, higher priority pollutants, yet selenium may pose the most serious long-term risk to aquatic habitats and fishery resources. Failure to include selenium in the list of constituents measured in contaminant screening/monitoring programs is a major mistake, both from the hazard assessment aspect and from the pollution control aspect. Once selenium contamination begins, a cascade of bioaccumulation events is set into motion which makes meaningful intervention nearly impossible. However, this cascade of events need not happen if adequate foresight and planning are exercised. Early evaluation and action are key. Prudent risk management based on environmentally sound hazard assessment and water quality goals can prevent biological impacts.

Guidelines for evaluating selenium data from aquatic monitoring and assessment studies

It is now possible to formulate diagnostic selenium concentrations in four distinct ecosystem-level components; water, food-chain, predatory fish (consuming fish or invertebrate prey), and aquatic birds. Waterborne selenium concentrations of 2 µg/l or greater (parts per billion; total recoverable basis in 0.45 μ filtered samples) should be considered hazardous to the health and long-term survival of fish and wildlife populations due to the high potential for food-chain bioaccumulation, dietary toxicity, and reproductive effects. In some cases, ultra-trace amounts of dissolved and particulate organic selenium may lead to bioaccumulation and toxicity even when total waterborne concentrations are less than 1 µg/l.Food-chain organisms such as zooplankton, benthic invertebrates, and certain forage fishes can accumulate up to 30 µg/g dry weight selenium (some taxa up to 370 µg/g) with no apparent effect on survival or reproduction. However, the dietary toxicity threshold for fish and wildlife is only 3 µg/g; these food organisms would supply a toxic dose of selenium while being unaffected themselves. Because of this, food-chain organisms containing 3 µg/g (parts per million) dry weight or more should be viewed as potentially lethal to fish and aquatic birds that consume them.Biological effects thresholds (dry weight) for the health and reproductive success of freshwater and anadromous fish are: whole body=4 µg/g; skeletal muscle=8 µg/g; liver=12 µg/g; ovaries and eggs=10 µg/g. Effects thresholds for aquatic birds are: liver=10 µg/g; eggs=3 µg/g. The most precise way to evaluate potential reproductive impacts to adult fish and aquatic bird populations is to measure selenium concentrations in gravid ovaries and eggs. This single measure integrates waterborne and dietary exposure, and allows an evaluation based on the most sensitive biological endpoint. Resource managers and aquatic biologists should obtain measurements of selenium concentrations present in water, food-chain organisms, and fish and wildlife tissues in order to formulate a comprehensive and conclusive assessment of the overall selenium status and health of aquatic ecosystems.

Modification of benthic insect communities in polluted streams: combined effects of sedimentation and nutrient enrichment

Responses of the benthic insect community of a southern Appalachian trout stream to inorganic sedimentation and nutrient enrichment were monitored over a period of eight months. Entry of pollutants from point sources established differentially polluted zones, allowing an assessment of impacts due to sedimentation alone and in association with elevated nutrient levels. Input of sediment resulted in a significant increase in bed load and decrease of pH at the substrate-water interface (P < 0.05). The zone receiving nutrient runoff from livestock pasture exhibited elevated levels of nitrate and phosphate, but available data indicated such concentrations to be quite low. Species richness, diversity, and total biomass of filter feeding Trichoptera and Diptera, predaceous Plecoptera, and certain Ephemeroptera were significantly reduced in the polluted zones. Inorganic sedimentation, operating indirectly through disruption of feeding and filling of interstitial spaces, was considered to be the primary factor affecting filter feeding taxa. Decomposition of compounds associated with materials in the bed load may depress pH and eliminate acid sensitive species of Plecoptera and Ephemeroptera. Such processes of acidification may be particularly important to Appalachian streams since the pH of regional surface waters is characteristically acidic prior to sedimentation. Accumulation of particles on body surfaces and respiratory structures, perhaps as a function of wax and mucous secretion or surface electrical properties, appears to be the major direct effect of inorganic sedimentation on stream insects. Growths of the filamentous bacterium Sphaerotilus natans were also frequently associated with silted individuals in the zone receiving nutrient addition. Distribution of the bacterium suggested that silted substrates, perhaps as related to the presence of iron compounds, are required for colonization in dilute nutrient solutions. The primary effect of Sphaerotilus colonies appears to be augmentation of particle accumulation through net formation by bacterial filaments. Data indicate that inorganic sedimentation and nutrient addition operate synergistically, eliminating a significantly greater number of taxa than exposure to one pollutant alone.

Metabolic stress during winter increases the toxicity of selenium to fish

Abstract This study examined the effect of reductions in water temperature and photoperiod, mimicking winter conditions, on the toxicity of combined dietary (5.1 μg/g dry weight) and waterborne (4.8 μg/l) selenium to juvenile bluegill ( Lepomis macrochirus ). Elevated selenium caused hematological changes and gill damage that reduced respiratory capacity, while increasing respiratory demand and oxygen consumption. Elevated selenium in combination with low water temperature (4°C) caused reduced activity and feeding, depletion of 50–80% of body lipid, and significant mortality within 60 days. Fish in warm-water selenium exposures continued to actively feed and lipid depletion did not occur despite increased oxygen consumption. The combination of stress-related elevation in energy demand and reductions in feeding due to cold temperature and short photoperiod, leading to severe depletion of stored body lipid, is given the name Winter Stress Syndrome. This syndrome caused bluegill to undergo an energetic drain that resulted in death of about one-third of the fish. Results indicate that the current US national water quality criterion for selenium is not adequate to protect young bluegill and other species that substantially reduce activity and feeding during cold weather. Aquatic contaminants should be evaluated in the context of seasonal metabolic changes that normally occur in test organisms. Winter Stress Syndrome could be an important, but as yet unquantified mortality factor in many circumstances.

Winter Stress Syndrome: An Important Consideration for Hazard Assessment of Aquatic Pollutants

Winter Stress Syndrome (WSS) is a condition of severe lipid depletion in fish brought on by external stressors in combination with normal reductions in feeding and activity during cold weather. Fish can develop this syndrome in response to chemical stressors, such as water pollutants, or biological stressors such as parasites. Substantial mortality can result, potentially changing year-class strength and population structure of the affected species and altering community-level ecological interactions. Aquatic contaminants should be evaluated in the context of seasonal metabolic changes that normally occur in test organisms. WSS could be an important, but as yet unquantified, cause of mortality in many circumstances. Wastewater discharges may pose a greater toxic threat to fish during winter than at other times of the year. A comprehensive protocol for aquatic hazard assessment should include testing for WSS.

Response of juvenile centrarchids to sublethal concentrations of waterborne selenium. I. Uptake, tissue distribution, and retention

Abstract Juvenile bluegill ( Lepomis macrochirus and largemouth bass ( Micropterus salmoides ) contained significantly elevated levels of selenium in all tissues examined after exposure to 10 μ/l for 120 days. The relative accumulation of selenium in specific tissues was: spleen > heart > liver > kidney > erythrocytes > gill > plasma > white muscle > gonad > intestine > stomach > brain. Water temperature and hardness did not affect the equilibrium concentrations or tissue distribution observed after 90 days, although earlier values were influenced. Selenium concentrations remained unchanged after 30-day elimination trials in spleen, liver, kidney, and white muscle, but exhibited a half-life retention time ≤ 15 days in gill and erythrocytes. The largest difference between species was in the selenium content of white muscle, with bluegill concentrating approximately twice that of largemouth bass. The major uptake pathway appears to be crythrocyte transport mediated by active oxo-groups on the selenium anion, with subsequent exchange at preferential sites. High apportionment into the spleen and heart may be influenced by differential formation of selenoproteins. Even though no mortality resulted under these controlled experimental conditions, possible pathologic enhancement, combined with the added body burden from dietary intake, strongly suggest the potential for toxicity in natural systems where waterborne selenium concentrations approach 10 μ/l.

Selenium impacts on fish: an insidious time bomb

A selenium time bomb situation is developing in the United States and elsewhere that may result in substantial impacts on fish populations. The selenium time bomb has three components: (1) high food-chain bioaccumulation, (2) steep toxic response curve for fish, and (3) insidious mode of toxicity. If the threshold for selenium toxicity is exceeded, the time bomb explodes and a cascade of events is set into motion that will result in major ecosystem disruption. Several human-related factors are emerging that are capable of igniting the fuse of the time bomb by increasing waterborne concentrations of selenium and providing conditions favorable for bioaccumulation. Some of these factors are (1) mobilization of selenium due to open-pit phosphate mining, (2) use of constructed wetlands to treat selenium-laden wastewater from oil refineries and agricultural irrigation, (3) landfill disposal of seleniferous fly ash from coal-fired power plants, and (4) mobilization of selenium from animal feedlot wastes. Collect...

Suppression of Native Fish Populations by Green Sunfish in First-Order Streams of Piedmont North Carolina

Abstract The effects of introduced green sunfish Lepomis cyanellus on native fish communities in headwater streams of North Carolinas Piedmont region were assessed from stream surveys and removal experiments. Green sunfish occurred in most first-order tributaries; when they were present, their abundance and biomass almost always exceeded that of any other coexisting species. Green sunfish also occurred in all second- and third-order streams surveyed, but they never dominated the fish community by numbers or weight in those situations. When green sunfish were removed from three first-order streams, most native species increased in numbers and biomass; in two streams the increase more than made up (within 2 years) the biomass that had been lost by removing green sunfish. These removal experiments indicate that green sunfish suppress native fish populations in Piedmont headwaters. Predation on the young of other species is one likely means by which they do this. Received July 12, 1984 Accepted April 24, 1985