The Responses of Plankton Communities in Experimental Ponds to Atrazine, the Most Heavily Used Pesticide in the United States

Experimental ponds received single additions of the herbicide atrazine in concentrations of 20 and 500 gg/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 Jig/L. When and to what extent resistant species appeared in the phytoplankton communities differed with treatment. At the atrazine concentration of 500 gg/L, there was a delayed appearance but eventually a greater biomass and persistence 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 gg/L, which are common downstream in many agricultural watersheds, 20 /Ig/L, which is the high level found in these waters, and 500 gg/L, which is the high level found in waters directly adjacent to treated fields

Deep chlorophyll maxima in small boreal forest lakes after experimental catchment and shoreline logging

In situ profiles of chlorophyll fluorescence combined with depth-specific water chemistry and biotic analysis were used to assess deep chlorophyll maxima (DCM) in four boreal shield lakes that were subjected to different levels of watershed disturbance by clear-cut logging. Phytoplankton communities within the DCPvl varied among lakes, but were generally comprised of chrysophytes, diatoms, and cryptophytes. One lake also had deep cyanobacterial populations. Relative in situ fluorescence (absolute fluorescence at each peak minus background fluorescence) at the fluorescence peaks was significantly correlated with the level of chlorophyll a at the peak (r(2) = 0.81, p < 0.025) for all lakes. In general, DCM peak heights were consistent in each lake over the four-year post-logging sampling period, whereas DCM depths declined slightly in the most heavily logged takes associated with increases in dissolved organic carbon. Therefore, on the basis of DCM data, only mild effects on lake water quality were apparent after the logging activity

A 21-year record of vertically migrating subepilimnetic populations of Cryptomonas spp.

The vertical distribution and diel migration of Cryptomonas spp. were monitored continuously for 21 years in mesotrophic Cross Reservoir, northeast Kansas, USA. The movements of these motile algae were tracked on multiple dates during July–October of each year using in situ fluorometry and optical microscopy of Lugol’s iodine-preserved samples. Episodes of subepilimnetic diel vertical migration by Cryptomonas were detected and recorded on 221 different days between 1994 and 2014, with just 2 of these years (1998 and 2013) lacking any sampling events with deep peaks sufficiently large enough to track. Whenever a subepilimnetic layer of Cryptomonas was detectable, it was generally observed to ascend toward the bottom of the epilimnion beginning approximately at sunrise; to descend toward the lake bottom during the late afternoon and evening; and to remain as a deep-dwelling population until dawn of the following day. Moreover, there was high day-to-day consistency in the absolute water column depths at which the migrating algal cells would cease their ascending or descending movement. We believe this unique and remarkable dataset comprises the most detailed record of diel migratory behavior for any planktonic freshwater alga reported for a single freshwater lake

Selective particle ingestion by a filter-feeding fish and its impact on phytoplankton community structure

Limnology and Oceanography http://aslo.org/lo

Trihalomethane Precursors in Kansas Lakes: Sources and Control

Project Completion Repor

Physical and chemical conditions surrounding the diurnal vertical migration of cryptomonas spp. (cryptophyceae) in a seasonally stratified midwestern reservior (USA)

Cross Reservoir, a small mesotrophic reservoir located at the University of Kansas Ecological Reserves (Kansas, USA), contained a dense metalimnetic community of algae and photosynthetic bacteria between early July and late October 1997-1999. Within this community, various Cryptomonas species, primarily C. erosa (Ehrenberg), C. erosa var. reflexa (Marsson), and C. rostratisformis (Skuja), diurnally migrated as indicated by in situ fluorescence monitoring and direct phytoplankton enumeration. The Cryptomonas spp. typically resided near the oxic-anoxic boundary of the water column; however, they actively migrated upward during the day and descended to lower anoxic locations at night, apparently responding to diurnal changes in their local habitat. Their nocturnal environment had moderate levels of sulfide, elevated secondary nutrients, and a community of anoxygenic phototrophic bacteria, whereas their daytime environment had higher light, lower nutrients, and no local photosynthetic bacteria. Monitoring indicated that the Cryptomonas spp. migration was generally linked to daily variations in absolute light intensity (e. g. sunny vs. cloudy days) and the level of other potentially growth-limiting resources, particularly nitrogen and phosphorus. However, further analyses showed that the primary factor that determined whether the Cryptomonas spp. migrated or not on a given day was the slope of the light gradient immediately above the Cryptomonas spp. peak

A Critical Assessment of the Influence of Management Practices on Water Quality, Water Treatment, and Sport Fishing in Multipurpose Reservoirs in Kansas

"The research on which the report is based was financed in part by the United States Department of Interior, Geological Survey, through the Kansas Water Resources Research Institute.

Nutrient level, microbial activity, and alachlor transformation in aerobic aquatic systems

Alachlor (2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide) is a moderately toxic herbicide that is requently found in agriculturally impacted surface waters. To assess primary mechanism(s) that affect its fate in aquatic systems, two field experiments were performed using large mesocosms (n = 39) and smaller microcosms with and without microbial inhibitors (n = 16). The mesocosm experiment tested the effect of fertility conditions on alachlor fate, assessing alachlor disappearance over time under oligotrophic (total phosphorus (TP) < 12 mug/L) through hypereutrophic (TP > 80 mug/L) water conditions. Whereas, the microcosm experiment assessed alachlor fate in the presence of microbial inhibitors that selectively blocked eubacterial (chloroamphenicol, streptomycin, and penicillin combined), eukaryotic (cycloheximide), and universal (all inhibitors) microbial activity. First-order alachlor transformation rate coefficients ranged from 0.006 to 0.042 day(-1) when microbial inhibitors were not present (half-lives from 16 to 122 days) with the highest rates occurring in hypereutrophic waters. Statistics indicated that mean TP, and universal and eubacterial small sub-unit rRNA level most closely correlated with transformation rate. Further, the inhibitor study indicated that alachlor transformation was biotic ( >90%), but that high transformation rates only occurred when eubacterial and eukaryotic domains were both metabolically active. Our results confirm that alachlor transformation is primarily biotic; however, efficient biotransformation only occurs when both major microbial domains in aerobic systems are active. (C) 2003 Elsevier Ltd. All rights reserved