We sampled 240 wadeable streams across Wisconsin for different forms of phosphorus and nitrogen, and assemblages of macroinvertebrates and fish to (1) examine how macroinvertebrate and fish measures correlated with the nutrients; (2) quantify relationships between key biological measures and nutrient forms to identify potential threshold levels of nutrients to support nutrient criteria development; and (3) evaluate the importance of nutrients in influencing biological assemblages relative to other physicochemical factors at different spatial scales. Twenty-three of the 35 fish and 18 of the 26 macroinvertebrate measures significantly correlated (P < 0.05) with at least one nutrient measure. Percentages of carnivorous, intolerant, and omnivorous fishes, index of biotic integrity, and salmonid abundance were fish measures correlated with the most nutrient measures and had the highest correlation coefficients. Percentages of Ephemeroptera-Plecoptera-Trichoptera individuals and taxa, Hilsenhoff biotic index, and mean tolerance value were macroinvertebrate measures that most strongly correlated with the most nutrient measures. Selected biological measures showed clear trends toward degradation as concentrations of phosphorus and nitrogen increased, and some measures showed clear thresholds where biological measures changed drastically with small changes in nutrient concentrations. Our selected environmental factors explained 54% of the variation in the fish assemblages. Of this explained variance, 46% was attributed to catchment and instream habitat, 15% to nutrients, 3% to other water quality measures, and 36% to the interactions among all the environmental variables. Selected environmental factors explained 53% of the variation in macroinvertebrate assemblages. Of this explained variance, 42% was attributed to catchment and instream habitat, 22% to nutrients, 5% to other water quality measures, and 32% to the interactions among all the environmental variables.

SynopsisIn experiments lakes 223 (L223) and 302 South (L302S) in the Experimental Lakes Area in north-western Ontario, and Little Rock Lake (LRL) in northern Wisconsin, were progressively acidified with sulphuric acid from original pH values of 6.1–6.8 to 4.7–5.1. Although the lakes were at different locations with different physical settings and assemblages of plants and animals including fish, there were remarkable similarities in their responses, particularly in regard to biogeochemical processes and effects on biota at lower trophic levels.All three lakes generated an important part of their buffering capacity internally b\ the reduction of sulphate, and to a lesser extent by the reduction of nitrate. Alkalinity production increased as concentrations of biologically-active strong acid anions increased. Models relating the residence times of sulphate and nitrate to water renewal, or first-order kinetics, effectively predicted events.Acidification disrupted nitrogen cycling in all three lakes. Nitrification was inhibited in L223 and L302S, while in LRL, nitrogen fixation was greatly decreased at low pH.The phytoplankton communities of all three lakes were originally dominated by chrysophyceans and cryptophyceans. However acidification changed the dominant species and decreased diversity. Acidification tended to increase phytoplankton production and standing crop slightly, probably because light penetration was increased.Littoral zones of all three lakes became increasingly dominated by a few species of filamentous green algae, which created nuisance blooms by pH 5.6. Mats or clouds of algae changed the entire character of the littoral zone.Acidification of L223 and L302S caused the loss of several species of large benthic crustaceans as pH changed from 6 to 5.6. Large, acid-sensitive littoral crustaceans were absent from LRL before acidification, probably because the lake was already too acidic.As acidity increased, the dominance of cladocerans within zooplankton communities increased. Daphnia catawba appeared at pH values near 5.6 and became more abundant at lower pHs as the lakes were acidified. Its appearance coincided with a decline in other Daphnia species: another cladoceran, Bosmina longirostris, increased in the experimentally-acidified lakes as did Keratella taurocephala: they became the dominant rotifers. Several sensitive zooplankton species declined or disappeared as the lakes were acidified, most notably Daphnia galeata mendotae, Epischura lacustris, Diaptomus sicilis and Keratella cochlearis.The responses of different fish varied; they appeared to depend on the sensitivity of key organisms in the food chain. The ability of key fish species to reproduce was impaired as early as pH 5.8; their reproduction, except for yellow perch in LRL, had ceased at pH 5.0 in all the three lakes.Acidification consistently reduced the diversity and richness of species in taxonomic groups studied, these effects resulting from losses of species and the increased dominance of a few acidophilic taxa.Responses of experimentally-acidified lakes in north-western Ontario and atmospherically-acidified lakes in eastern Ontario were similar in most respects where records allowed comparisons to be made, notably in relation to biogeochemical processes and the disappearance of acid-sensitive biota.When the acidification of L223 was reversed, several biotic components recovered quickly. Fish resumed reproduction at pHs similar to those at which it ceased when the lake was being acidified. The condition of lake trout improved as a result of greatly increased populations of small fish, their prey. Many species of insects and crustaceans that had been extirpated by acidification returned. Assemblages of phytoplankton and chironomids have retained an acidophilic character, although their diversity during recovery is similar to that at comparable pHs during progressive acidification. As their chemistry recovered, atmospherically-acidified lakes in the Sudbury area were able to sustain recruitment by species offish, including lake trout and white sucker, with rapid increases in the diversity of invertebrate taxa. Results from both L223 and lakes near Sudbury suggest a rapid partial recovery of lacustrine communities when acidification is reversed.It is concluded that the experimental lakes responded similarly to acidification, and that experimental acidification can reliably indicate the effects of acidification attributable to acidic precipitation.

The two basins of this seepage lake were separated by a vinyl curtain in August 1984 after a year of background studies, and acidification of one basin with H2SO4 began at ice-out in 1985. Chemical and biological responses measured during successive 2-yr periods at pH ~5.6, 5.1, and 4.7 verified some but not all impacts predicted at the outset. Changes in major, minor, and trace ions generally agreed with predictions. Internal alkalinity generation (IAG) increased at lower pH, and sulfate reduction eliminated ~50% of added H2SO4. Sediment cation exchange was important in IAG and acidified surface sediments, possibly diminishing the lake's ability to counteract further H+ inputs. Mass loss of oak leaves was reduced at pH 5.1 (birch leaves at pH 4.7). Population parameters were more sensitive than community measures for plankton. Species composition changed at each pH, especially at pH 4.7. Many changes in zoopiankton and benthos were indirect responses to an algal mat that developed at lower pH or to food web interactions; these were not predicted accurately. Sensitivity of major fishes to lower pH was Ambloplites rupestris > Micropterus salmoides > Pomoxis nigromaculatus > Perca flavescens. Fish production was reduced at pH's above those resulting in population decreases.

Mercury contamination of fish is a global problem. Consumption of contaminated fish is the primary route of methylmercury exposure in humans and is detrimental to health. Newly mandated reductions in anthropogenic mercury emissions aim to reduce atmospheric mercury deposition and thus mercury concentrations in fish. However, factors other than mercury deposition are important for mercury bioaccumulation in fish. In the lakes of Isle Royale, U.S.A., reduced rates of sulfate deposition since the Clean Air Act of 1970 have caused mercury concentrations in fish to decline to levels that are safe for human consumption, even without a discernible decrease in mercury deposition. Therefore, reductions in anthropogenic sulfur emissions may provide a synergistic solution to the mercury problem in sulfate-limited freshwaters.

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Total phosphorus concentrations as a function of the percentage of agricultural land use in A, environmental phosphorus zones and B, level III ecoregions, and response curves for phosphorus concentrations as a function of the percentage of agriculture in the watershed, in C, EPZs, and D, level III ecoregions ..

Hurley, I.P., and P.]. Garrison. 1993. Composition and sedimentation of aquatic pigments associated with deep plankton in lakes. Can. j. Fish. Aquat. Sci. 50: 271 3-2722.High Performance Liquid Chromatography (HPLC) pigment techniques were applied to study planktonic pigment composition and sedimentation in four Wisconsin (USA) lakes. In each lake, deep blooms of phytoplar~kton overlaid phototrophic sulfur bacteria in the region of the oxic-anoxic interface. Chlorophyll a and bacteriochlorophyll (a, d, and e) were observed as indicators of phytoplankton and phototrophic sulfur bacteria, respectively. Major taxonomic classes of phytoplankton were further resolved based on carstenoid signatures. In contrast to three oligo-mesotrophic Wisconsin lakes in which deep phytoplankton were comprised of dinoflagellates (indicated by the carotenoids peridinin, diadinoxanthin), cryptophytes (a1 loxanthin), and chrysophytes (fucoxanthin), the deep phytoplan kton community in mesotrsphic Mirror Lake was dominated by blue-green algae (sscillaxanthin, myxoxanthophyll, neaxanthin, and echinenone). Deep planktonic production strongly influenced sedimentation of algal pigments and obscured the relationship between apparent water quality and sedimentary pigment deposition.Les techniques d'analyse des pigments par chromatographie liquide 2 haute performance (CLHP) ont kt6 appiiquees A,lf6tude de la composition et de la s6dimentation des pigments planctoniques dans quatre lacs du Wisconsin (E.4.) Dans chaque lac, d'kpaisses prolif6rations phytoplanctoniques recouvraient les bacteriessulfo-rkdtrctrices qui se trouvaient 2 Ifinterface de la zone oxique et de la zone anoxique. On a constat6 que la chlorophylle a et que la bacteriochlorophyk (a, d et e) sont des indicateurs dtr phytoplancton et des bacteries sulfo-reductrices, respectivernent. Les grandes classes taxonorniques de phytoplancton ont ete identifiees de mani6re plus pouss6e 2 partir de la signature que constitue leurs carotknoi'dies. Par cornparaison aux trois lacs oligo-mksotrophes du Wisconsin 06 le phytsplancton profond se composait de dinoflagell6s (dont la pr6sence ktait indiquke par des carot6noi'des, la peridinine et la diadinoxianthine), des cryptophytes (alloxanthine) et des chrysophytes (feecoxanthine), alors qrre la csrnrnunaeet6 phytoplanctsnique profonde du lac Mirror, mesotrophe, &it dominee par les algues bleues (oscil laxanthine, myxoxanthophylle, zkaxanthine et kchinknone). La production de plancton profond influence consid6rablernent la skdirnentation des pigments algaires et masque la relation entre %a qualit6 apparente de I'eau et te d4p8t de pigment sedimentaire.

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