Abstract  A project was conducted using experimental ponds for studying the effects of an agricultural herbicide on aquatic food chains. Atrazine, one of the most heavily used herbicides in Midwest agriculture, was added to ponds and the ensuing responses were followed through four months. With single 20 μg/liter and 500 μg/liter additions to the ponds, effects were recorded throughout the food chain. After one day of exposure rates of phytoplankton photosynthesis declined at both levels, with the higher level causing an almost complete inhibition. Phytoplankton succession was altered within a few days at both levels, with resistant species increasing in abundance. The actual resistance of these species to atrazine, which is known to be a photosynthetic inhibitor affecting a wide variety of plants, was verified in the laboratory. The grazing zooplankton were also affected within the first few weeks of exposure as their phytoplankton food source was altered. The growth of aquatic flowering plants was also reduced at both levels. Some members of the aquatic food chain were unaffected, particularly the benthic insects, although effects were recorded at the highest level of these food chains, the fish. Of the three types of fish (bluegill sunfish, channel catfish, gizzard shad) originally stocked in the ponds, all survived but with reduced growth at the 500 μg/liter- level. The only fish to reproduce in the ponds, bluegill sunfish, showed greatly reduced numbers of progeny at both levels. The concentrations of atrazine in the ponds were monitored, showing its persistence with 75% of the original concentration present after 114 days. In Midwest waters concentrations of 500 μg/liter are recorded in waters directly associated with agricultural operations, such as irrigation waters while 20 μg/liter is at the high extreme of concentrations found more widespread. Though data from monitoring atrazine concentrations in natural habitats is sparce 1 μg/liter to 5 μg/liter seem common in many Midwest waters. In laboratory experiments with these more common concentrations we also demonstrated reductions in phytoplankton photosynthesis. This indicates the possibility, awaiting further demonstration, that even at common concentrations atrazine may be affecting phytoplankton photosynthesis in many Midwest waters. Other herbicides studied in this project included 5 other triazine herbicides (propazine, metribuzin, terbutryn, cyanazine, simazine) which in the laboratory were similar to atrazine in the intensity of reducing phytoplankton photosynthesis. ln the state of Kansas triazine herbicides accounted for one third of the total herbicide usage in 1978.

Abstract  The influence of 0 multiplied by 1, 1 and 10 mg kg super(-1) of the terrestrial herbicides atrazine, trifluralin, MSMA and paraquat on the species composition and standing crop of algal periphyton was assessed using artificial streams. For each herbicide, two experiments were performed: one using algae from a pristine spring and another using algae from a stream heavily influenced by agricultural runoff. Also, in each experiment, 0 multiplied by 01 mg kg super(-1) of the test herbicide was maintained in the water of half the streams during a three-week period prior to the application of the 0 multiplied by 1/1/10 mg kg super(-1) treatments in an attempt to induce development of a resistant community. Atrazine caused the most extensive damage. Rhopalodia, Phormidium and Cladophora were severely inhibited by 1 and 10 mg kg super(-1), and these treatments caused a large biomass reduction. Trifluralin decomposed rapidly in the streams and had no toxic effect. MSMA and paraquat caused reductions in several filamentous cyanobacteria, but these effects were less serious than those of atrazine. Contrary to expectation, the spring community seemed more resistant than the stream community to both atrazine and paraquat. Also, while the 0.01 mg kg-t treatment caused detectable reductions in several species, there was no evidence that it induced resistance to any of the herbicides.

Abstract  The herbicide atrazine was applied to 0.045-ha experimental ponds in two concentrations of 0, 20, 100, and 500 Mg/L each. Physical, chemical, and biological variables measured and aquatic insect community structure was monitored in the eight ponds using submerged funnel emergence traps. Atrazine had no effect on water temperature or oxygen concentration. Mean turbidity did increase significantly with atrazine concentration, but turbidity be correlated with abundance or species richness of emerging insects. Macrophyte production decreased with increasing herbicide concentration; however, the macroalga Chara sp. showed resistance 100 Mg/L. The benthic insect community was also negatively affected by atrazine. Abundance emerging individuals of the chironomid Labrundinia pilosella was significantly reduced at concentrations as low as 20 Mg/L, while other, less abundant species showed similar declines. insect species richness (S), species equitability (/'), and total emergence all declined significantly atrazine addition. In general, abundances of nonpredatory insects were greatly reduced with addition of atrazine (20 Mg/L), while predatory insects showed no response to the herbicide. In emergence periods of several herbivorous insect species shifted to an earlier time in atrazine-ponds; the shift was statistically significant for Oxyethira pallida. The lowest concentration at which atrazine affected aquatic insects in the pond systems (is one order of magnitude lower than the lowest concentration previously shown to have a direct effect on the midge Chironomus tentans in single-species laboratory experiments. Furthermore, of the differential response of predatory and nonpredatory insect species to atrazine in this is suggested that the effects of the herbicide on the insect community in the experimental ponds be primarily indirect, presumably through reduction of the food of nonpredators (periphyton, macrophytes) and, to some extent, their habitat (macrophytes).

Abstract  We investigated the validity and sensitivity of assessments of the induction of atrazine tolerance in freshwater outdoor mesocosmic phytoplankton communities, using the in vivo fluorescence of chlorophyll a as an endpoint, for monitoring ecotoxicology and for risk assessment programs applied to phytoplankton contaminated by photosystem II herbicides. Atrazine inhibits the photosynthetic process. and so the rise in in-vivo fluorescence could be used as a physiological manifestation of acute toxicity. Short-term tests (I h) were used, in which increasing concentrations of the herbicide were applied to phytoplankton samples taken every two days from the mesocosms, and used to plot dose-response curves. The concentration at which atrazine increased the fluorescence by 25% relative to control samples was used to demonstrate the sensitivity of the phytoplankton, and the values found were compared for samples from different mesocosms (contaminated and non-contaminated). The taxonomic composition of the phytoplankton was also determined. The data showed that chronic exposure (25 days) to 30 mug/L of atrazine significantly increased the apparent tolerance of the phytoplankton to further contamination by the same compound. The use of in vivo fluorescence of chlorophyll a appears to be a reliable and effective parameter for monitoring the effects of atrazine pollution, and detecting the changes in community tolerance driven by pollution selection pressure.

Abstract  Artificial streams containing algal communities derived from a spring and an agriculturally impacted stream were used to assess the effect of 0.1, 1, and 10 mg kg-1 atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), MSMA (monosodium methanearsonate), and paraquat (1,1'-dimethyl-4,4'-bipyridylium cation) on the productivity (photosynthesis and respiration) of stream algae. The importance of induced resistance to the herbicides was evaluated by comparing the responses of the spring and stream algae and by determining if allowing the streams to be colonized for 3 weeks in the presence of 0.01 mg kg-1 of the herbicide under test would modify response by selecting for a more resistant flora. Productivity was measured by open-water oxygen methods for 3 weeks before and 3 weeks after herbicide injection. The communities derived from both the spring and the stream were dominated by diatoms, and responded similarly to trifluralin, atrazine, and MSMA, but had divergent responses to paraquat. Trifluralin had no effect on productivity. Photosynthesis was significantly depressed by 1 and 10 mg kg-1 atrazine and by 10 mg kg-1 MSMA, and there were indications of a slight inhibition by 0.01 mg kg-1 atrazine. Paraquat at 10 mg kg-1 had little effect on the spring-derived communities but caused severe inhibition of the stream-derived algae. There was little evidence that exposure to 0.01 mg kg-1 herbicide during colonization modified the response of the algae to any of the herbicides. cial streams containing algal communities derived from a spring and an agriculturally impacted stream were used to assess the effect of 0. 1, 1, and 10 mg kg** minus **1 atrazine, trifluralin, MSMA, and paraquat on the productivity of stream algae. Communities derived from both spring and stream were dominated by diatoms, and responded similarly to trifluralin, atrazine, and MSMA, but had divergent responses to paraquat. Trifluralin had no effect on productivity. Photosynthesis was significantly depressed by 1 and 10 mg kg** minus **1 atrazine and by 10 mg kg** minus **1 MSMA, and there were indications of a slight inhibition by 0. 1 mg kg** minus **1 atrazine. Paraquat at 10 mg kg** minus **1 had little effect on the spring-derived communities but caused severe inhibition of the stream-derived algae.

Abstract  This paper investigates the effects of atrazine and grass carp on freshwater macrophyte communities. Macrophyte communities in experimental ponds were subjected . to atrazine, at various concentrations, and grass carp and were sampled. periodically by a variation of the technique of grapnel analysis. Atrazine had significant effects upon the macrophyte community, causing changes in species composition leading to domination by Charophytes at levels of 100 μg/1. Grass carp displayed a greatly enhanced plant control capability when even low levels of atrazine were present. Field studies confirmed the hypothesis that general agricultural runoff is detrimental to macrophyte communities. Periphyton and emergent macrophytes also appeared to be adversely affected by atrazine. Results of this study suggest that atrazine in agricultural runoff can adversely impact on aquatic systems by altering, or eliminating, the habitat structure and diversity provided by macrophyte beds. Atrazine, and grass carp with atrazine, also appear to be useful tools in the management of macrophyte populations in lakes and ponds.

Abstract  The triazine herbicides have accounted for nearly one third of the total herbicide usage in Kansas in recent years. It is well known that these herbicides are entering aquatic habitats in Kansas and throughout the Midwest, yet little is known of their effects on the freshwater organizms residing there. This study was undertaken to accumulate data on triazine herbicide concentrations in State waters and to determine the biological impact of the triazines on phytoplankton and macrophyte communitites at those sites. To develop baseline data on the biological effects of triazine herbicides, experimental ponds were treated with different levels of atrazine herbicide under highly controlled situations. Atrazine was chosen to represent the triazines because of its physiological effects on a wide variety of terrestrial and aquatic plants and because it is the single most heavily used pesticide plankton quickly developed which were more resistant to atrazine. Macrophytic vegetation was significantly inhibited in treated ponds. The next phase of the study involved sampling numerous aquatic habitats throughout the State to (1) analyze the concentrations of triazine herbicides (atrazine, cyanazine, metribuzin, and simazine) and to (2) determine if the macrophyte and phytoplankton communities at these sites had been altered by exposure to triazine herbicides. Triazines were detected at many sites and many of those sites were also found to contain phytoplankton communities possessing a degree of resistance to atrazine. Reductions in macrophyte communities were noted in those waters receiving direct runoff from agricultural fields.

Abstract  Experimental ponds received single additions of the herbicide atrazine in concentrations of 20 and 500 @mg/L, and were compared to control ponds for 136 d. Atrazine is an inhibitor of photosynthesis, and both concentrations depressed phytoplankton growth in the ponds within a few days. This was followed by successional changes leading to the establishment of species of phytoplankton more resistant to inhibition by atrazine. Laboratory studies verified this resistance and verified effects on other species at concentrations of atrazine as low as 1-5 @mg/L. When and to what extent resistant species appeared in the phytoplankton communities differed with treatment. At the atrazine concentration of 500 @mg/L, there was a delayed appearance but eventually a greater biomass and persistent of these species. The grazing zooplankton influenced these differences and were in turn affected by them. Natural interactions such as competition and predation among the species of the communities greatly affected their responses to the toxic chemical. The importance of atrazine as an environmental pollutant is suggested by these responses to concentrations of 1-5 @mg/L, which are common downstream in many agricultural watersheds, 20@mg/L, which is the high level found in these waters, and 500 @mg/L, which is the high level found in waters directly adjacent to treated fields.

Abstract  Two experimental pond studies with the herbicide atrazine demonstrate how hazard assessment at the ecosystem level (now required by the U.S. Environmental Protection Agency for some pesticide registration) reveals effect of a chemical not revealed by traditional laboratory assessments. Pond communities including fish species stocked in these 0.04-ha ponds were exposed to atrazine for 136 and 805 d and experienced various direct and indirect effect of the chemical. Phytoplankton production and biomass immediately after exposure were lower than control pond levels at all treatment concentrations (20, 100, 200, 500 .mu.g/liter) but after 3 wk, were similar to control pond levels with little accompanying decline in the pesticide concentrations. Species succession and tolerance were observed in phytoplankton communities in treated ponds, and tolerance was also tested and observed in communities from ponds elsewhere in the region that had been subjected to atrazine or other triazine herbicides from agriculture. In treated ponds, animal populations associated with food chains supported mostly by the phytoplankton showed no significant treatment effects by ANOVA and linear regression. These animals included the crustacean zooplankton, a predatory planktonic insect (Chaoborus), and a filter-feeding fish (gizzard shad). Channel catfish have a broad diet and were also unaffected. Another plant group in the ponds, the submersed and emergent macrophytes, were also inhibited by atrazine but did not recover. The animal populations supported by these plants showed significant treatments effects (ANOVA) and a significant negative linear trend with increasing atrazine treatment. These animals included tadpoles, benthic insect grazers, a macrophyte-grazing fish (grass carp), and an insectivorous fish (bluegill sunfish). Based on the minimal direct effects that atrazine, at the concentrations used here, is reported to have on animals studies in the laboratory, indirect effects are proposed for these animals responses. Hazard assessment at the ecosystem level is shown to provide an arena for response to a chemical, where direct and indirect effects can be revealed in ways not currently achieved in the laboratory, such that these effects can then be more accurately extrapolated to the natural environment.

Abstract  Bioassays of different complexity were compared with respect to their capability to predict the environmental impact of the herbicide atrazine in aquatic systems. Acute toxicity tests with Daphnia did not yield meaningful results. Sublethal tests with Daphnia (feeding inhibition, reduction of growth and reproduction) were more sensitive, but effective concentrations of atrazine were still rather high (2 mg/L). A relatively complicated ‘artificial food chain’ system that incorporated direct and indirect effects on Daphnia yielded significant reduction of daphnid population growth at 0.1 mg/L. Enclosure experiments with natural communities were by far the most sensitive tools. Community responses could be measured at concentrations as low as 1 µg/L and 0.1 µg atrazine/L. At the lowest concentration, however, communities recovered after three weeks. We conclude that in complex systems indirect effects can be more important than direct effects, so that, contrary to the conditions in simple tests, non-target organisms may be the better indicators of herbicide stress to natural communities.

Abstract  Results from single-species toxicity tests form the basis for guidance about concentrations of chemicals that are likely to be environmentally hazardous. Microcosm bioassays have been proposed as better tools for this purpose under some circumstances. Rarely have comparisons been made among the responses in the various test systems and those seen in natural communities. We compared the responses among single-species algal assays, a synthetic microcosm (the Taub microcosm) and experimental ponds exposed to similar concentrations of atrazine by comparing concentrations of atrazine that reduced algal activity or biomass to 50% of control values (ECSO). Eight algal species were examined; mean species EC5O values for 14C uptake ranged from 37 to 308 µg/L. For the Taub microcosm, ECSO values were 103 to 159 µg/L for I4C uptake, 126 to 165 µg/L for dissolved oxygen production and 106 to 164 &L for dissolved oxygen consumption. Values were dependent on the time intervals selected for calculations. In the ponds, EC50 values for 14C uptake were 100 µg/L and for chlorophyll a, 82 µg/L. The basic similarity among EC5O values across test systems suggests that results from a combination of single-species assays, or the Taub microcosm, provided a reasonable estimate of the concentration of atrazine that produced similar direct effects on more natural communities.

Abstract  We have tested the sensitivity of phytoplankton to the herbicides atrazine and nicosulfuron in experiments conduced in increasingly complex systems, from single strain phytoplankton cultures (microplates) to mesocosms mimicking whole ecosystems. The endpoints used to assess sensitivity to atrazine and nicosulfuron were total biomass increase, photosynthetic efficiency, and community diversity, depending on the system considered. Nicosulfuron appeared to be very much less toxic to phytoplankton than atrazine, in accord with the planned changes in agricultural practices to reduce the effects of surface water contamination on aquatic biota. Nevertheless, nicosulfuron had significant effects in some systems (principally microcosms), whereas the single monocultures were almost insensitive to it. This points out the inaccuracy of standardized toxicity test on phytoplanktonic algae alone for predicting the effects of xenobiotics on natural communities and the need for tests in microcosms and mesocosms to obtain reliable evidence about the toxicity of a given chemical on freshwater aquatic ecosystems.

Abstract  The potential long-term direct and indirect, lethal and sublethal effects of relatively low-level atrazine exposure to components of wetland communities were studied in flow-through mesocosms. Treated mesocosms were exposed to atrazine at 4 concentrations (15, 25, 50, and 75 ug per litre). Control wetlands had an average atrazine concentration of 0.69 ug per litre. The effects of atrazine exposure on periphyton biomass and production, macrophyte cover and growth rates, survival and growth of Daphnia magna, Rana pipiens, and Pimephales promelas larvae and adults were measured. The interaction between nutrient status or grazing intensity and atrazine effects was also measured. Periphyton net productivity was decreased at atrazine concentrations of 15 ug per litre and respiration was either significantly reduced by atrazine treatments (25 ug per litre) or significantly stimulated (75 ug per litre). Ceratophyllum length/weight ratios increased after 6 d exposure to 50 ug per litre atrazine. The atrazine effects on periphyton composition varied with the nitrogen:phosphorus supply ratio. Daphnia survival was depressed at atrazine concentrations of 15 ug per litre. There are 42 references.

Abstract  One of the agro-environmental characteristics of Brittany is the extensive use of pesticides, which leads to high concentrations of atrazine in continental water systems. Periphytic algae play a basic part in aquatic ecosystems and some of them, diatoms, are highly sensitive to environmental changes. Analyses of diatoms can thus indicate the impact of a herbicide on aquatic systems. We compared the effects of two herbicides (atrazine and nicosulfuron) on an aquatic ecosystem in 1998. This study was conducted in 15 identical ponds, each containing a holder for installing artificial substrates. The periphytic diatoms were analysed for cell density, biomass, species diversity and morphology. The general specific diversity was poor, and the diatom community was essentially dominated by Achnanthidium minutissimum. The first results showed a strong similarity between the different categories of mesocosms. Chlorophyll a concentration only seems to be affected by high herbicide concentrations.

Abstract  Mesocosms are surrogate ecosystems which, in the form of experimental ponds or large enclosures in a pond or lake, can be used to simulate the responses of the corresponding natural aquatic ecosystems to an experimentally applied stress. A review of studies applying pesticides as the stress reveals the variety of direct and indirect effects that can develop in the multispecies/multicondition setting of the natural environment. Effects of the chemical appear through natural interactions among ecosystem components. Thirty-six pesticide studies including thirteen insecticides and eight herbicides demonstrate the cascade of effects that can occur particularly from the top of the food chain downward with insecticides and from the bottom of the food chain upward with herbicides. One study withthe herbicide atrazine is examined in detail revealing differential direct effects, with decreased abundance and biomass of certain plants while others gained a degree of resistance. Some indirect effects developed as decreases in abundance and/or biomass of certain animals, including fish, tadpoles, and macroinvertebrates, possibly due to reductions in food, preferred micro-habitat substrate, or refugia. Other indirect effects developed as increases in some animals including macroinvertebrates, possible due to increases in food, better exploitation of altered microhabitats, or reduced predation. These effects of atrazine are compared to those revealed by single-species tests, and the advantages and disadvantages of both methods of ecological effects testing are considered.

Abstract  The ecotoxic effects of atrazine (0, 20, 100, and 500 (xg/l exposure rates) on experimental pond mesocosm ecosystems were evaluated after 805 days of continuous exposure. Analysis of data was done using LISREL, a structural equation modeling technique. A series of five ecosystem models were developed with LISREL with each model including a unique subset of macroinvertebrate concepts. All models identified both direct and indirect effects of the exogenous concepts (grass carp, pond depth, and atrazine) on all endogenous concepts (i.e., fish, aquatic vegetation, phytoplankton, zooplankton, and macroinvertebrate concepts). All models quantify the ecotoxic effects (direct and indirect) of atrazine on the various endogenous concepts (structural units of these ecosystems) by specifying the functional paths that connect them. Direct ecotoxic effects of atrazine were primarily limited to reductions in gizzard shad biomass and aquatic vegetation abundance (% cover). Most indirect effects associated with atrazine exposure were initiated by atrazine’s direct effect on the aquatic plant community. Measures of the direct, indirect, and total effects of atrazine on affected endogenous concepts are provided and the ecological consequences of these effects are discussed.

Abstract  The ecotoxic effects of atrazine on macroinvertebrates and ecosystem structure were evaluate in eight experimental pond mesocosms (0.045 ha) after 805 days of continuous exposure at four nominal concentrations (zero, 20, 100 and 500 µg/L). Organismal, population, community and ecosystem variables, some of which represented antecedent conditions (e.g. submergent macrophyte abundances) were analyzed to determine occurrence of positive and/or negative ecotoxic effects. In most instances the direct and indirect effects of atrazine exposure on various ecosystem variables were verified with a linear structural modelling technique, path analysis. The growth and survivorship of various instar classes for two midge species (Chironomidae: Diptera), Endochironomus nigricans and Dicrotendipes cf. simponi, were shown to respond differently (positive vs. negative effects) to atrazine exposure when compared to reference ponds. Eleven of 15 taxa displayed abundance responses due to atrazine concentrations. The scud Hyallela azteca and the midge Dicrotendipes cf. simsoni populations in atrazine dosed ponds were noted to increase. Other taxa abundances showed negative ecotoxic effects or varied responses depending on temporal or spatial conditions. Macro invertebrate community attributes were observed to be variously affected by exposure which were related to both concentration level and/or date. Macroinvertebrate richness and abundance were suppressed at all atrazine treatment concentrations during the spring but later recovered with abundance values being significantly higher in 20 µg/L ponds. Macroinvertebrate diversity responded variously to atrazine treatments but typically displayed negative ecotoxic effects. The abundance of macroinvertebrate herbivores and epiphytes was often negatively affected by atrazine concentration as low as 20 µg/L while omnivore populations increased in atrazine treated ponds. Other habitat and trophic guild categories showed occasional effects due to atrazine exposure. The abundance of macroinvertebrate "generalists" and "specialists" were observed to respond differently to atrazine treatments. Specialist populations ere generally highest in 20 µg/L ponds while generalists were most abundant in 500 µg/L ponds. Multiple regression models for macroinvertebrate, phytoplankton, zooplankton, fish, water chemistry and other ecosystem variables seldom identified atrazine as an independent variable. When included in a model, atrazine concentrations explained only limited amounts of the variance in the dependent variable. Important independent variable common to most regression models were: macrophyte abundance: pH, total alkalinity, turbidity and oxygen saturation: chlorophyll a: pond depth: and presence or absence of Grass Carp (Cienopharyngodon idella). The ecosystem structure of ponds was defined by path diagrams that identified the occurrence of both direct and indirect effects on nearly all endogenous model factors as a result of three exogenous variables. These exogenous variables were pond depth, presence or absence of Grass Carp and atrazine concentration in water.