Curlyleaf Pondweed Research Articles

Laboratory measurements underestimate persistence of the aquatic herbicide fluridone in lakes.

Fluridone is an aquatic herbicide commonly used to treat invasive freshwater plant species such as Eurasian watermilfoil, hydrilla, and curly-leaf pondweed. However, required exposures times are very long and often exceed 100 days. Thus, understanding the mechanisms that determine the fate of fluridone in lakes is critical for supporting effective herbicide treatments and minimizing impacts to non-target species. We use a combination of laboratory and field studies to quantify fluridone photodegradation, as well as sorption and microbial degradation in water and sediment microcosms. Laboratory irradiation studies demonstrate that fluridone is susceptible to direct photodegradation with negligible indirect photodegradation, with predicted half-lives in sunlight ranging from 2.3 days (1 cm path length) to 118 days (integrated over 1 meter). Biodegradation is attributable to microbes in sediment with an observed half-life of 57 days. Lastly, fluridone sorbs to sediments (Koc = 340 ± 28 L kg-1); sorption accounts for 16% of fluridone loss in the microcosm experiments. While the laboratory results indicate that all three loss pathways can influence fluridone fate, these controlled studies oversimplify herbicide behavior due to their inability to replicate field conditions. Fluridone concentration measurements in a lake following commercial application demonstrate a half-life of >150 days, indicating that the herbicide is very persistent in water. This study illustrates why caution should be used when relying on laboratory studies to predict the fate of pesticides and other polar organic compounds in the environment.

Improving chemical control of nonnative aquatic plants in run-of-the-river reservoirs

AbstractCurrent dam discharge patterns in Noxon Rapids Reservoir reduce concentration and exposure times (CET) of herbicides used for aquatic plant management. Herbicide applications during periods of low dam discharge may increase herbicide CETs and improve efficacy. Applications of rhodamine WT dye were monitored under peak (736 to 765 m3 s−1) and minimum (1.4 to 2.8 m3 s−1) dam discharge patterns to quantify water-exchange processes. Whole-plot dye half-life under minimal discharge was 33 h, a 15-fold increase compared with the dye treatment during peak discharge. Triclopyr concentrations measured during minimum discharge within the treated plot ranged from 214 ± 25 to 1,243 ± 36 µg L−1 from 0 to 48 h after treatment (HAT), respectively. Endothall concentrations measured during minimum discharge in the same plot ranged from 164 ± 78 to 2,195 ± 1,043 µg L−1 from 0 to 48 HAT, respectively. Eurasian watermilfoil (Myriophyllum spicatum L.) occurrence in the treatment plot was 66%, 8%, and 14% during pretreatment, 5 wk after treatment (WAT), and 52 WAT, respectively. Myriophyllum spicatum occurrence in the nontreated plot was 68%, 71%, and 83% during pretreatment, 5 WAT, and 52 WAT, respectively. Curlyleaf pondweed (Potamogeton crispus L.) occurrence in the treatment plot was 29%, 0%, and 97% during pretreatment, 5 WAT, and 52 WAT, respectively. Potamogeton crispus increased from 24% to 83% at 0 WAT to 52 WAT, respectively, in the nontreated plot. Native species richness declined from 3.3 species per point to 2.1 in the treatment plot in the year of treatment but returned to pretreatment numbers by 52 WAT. Native species richness did not change during the study in the nontreated reference plot. Herbicide applications during periods of low flow can increase CETs and improve control, whereas applications during times of high-water flow would shorten CETs and could result in reduced treatment efficacy.

Annual Summer Submersed Macrophyte Standing Stocks Estimated From Long-Term Monitoring Data in the Upper Mississippi River

Abstract System-scale restoration efforts within the Upper Mississippi River National Wildlife and Fish Refuge have included annual monitoring of submersed aquatic vegetation (SAV) since 1998 in four representative reaches spanning ∼ 440 river kilometers. We developed predictive models relating monitoring data (site-scale SAV abundance indices) to diver-harvested SAV biomass, used the models to back-estimate annual standing stock biomass between 1998 and 2018, and compared biomass estimates with previous abundance measures. We modeled two morphologically distinct groups of SAV with differing sampling efficiencies and estimated each separately: the first category included only wild celery Vallisneria americana, which has long, unbranched leaves and dominates lotic environments, while the second category included 17 branched morphology species (e.g., hornwort Ceratophyllum demersum and Canadian water weed Elodea canadensis) and dominates lentic environments. Wild celery accounted for approximately half of total estimated total biomass in the four reaches, combined branched species accounted for half, and invasive species (Eurasian watermilfoil Myriophyllum spicatum and curly-leaf pondweed Potamogeton crispus), a fraction of the branched species, accounted for < 1.5%. Site-scale SAV estimates ranged from 0 to 535 g·m−2 (dry mass). We observed increases in biomass in most areas between 1998 and 2009 and substantial increases (e.g., from < 10 g·m−2 to ∼ 125 g·m−2) in wild celery in extensive impounded areas between 2002 and 2007. Analyses also indicate a transitional period in 2007–2010 during which changes in biomass trajectories were evident in all reaches and included the start of a 9-y, ∼ 70% decrease in wild celery biomass in the southernmost impounded area. Biomass estimates provided new insights and illustrated scales of change that were not previously apparent using traditional metrics. The ability to estimate biomass from Long Term Resource Monitoring data improves conservation efforts through better understanding of changes in habitat and food resources for biota, improved goal setting for restoration projects and improved quantification of SAV-mediated structural effects such as anchoring of sediments and feedbacks with water quality.

Potamogeton crispus (curlyleaf pondweed)

Potamogeton crispus (curlyleaf pondweed)

Analysis of the Possibility of Management of Curly-Leaf Pondweed for Energetic Purposes

The possibilities of using curly-leaf pondweed for energy purposes were analyzed. This plant contributes to overgrowth of water reservoirs, causing their eutrophication. The plants examined were from two different water reservoirs: Lake Winiary (Gniezno) and Lake Rusalka (Poznan). On the basis of the investigations, it was determined that it is possible to use curly-leaf pondweed for energy purposes, both in the combustion method and in the biomethane fermentation process. Studies were performed to assess the suitability of the plants for combustion as a solid biofuel and studies on the use of pondweed as a fermenter feedstock. The calorimetric study showed the possibility of obtaining more energy for the curly-leaf pondweed coming from Lake Rusalka. The heat of combustion of these plants was 13.95 MJ·kg−1 (Winiary pondweed) and 9.10 MJ·kg−1 (Rusalka pondweed). On the other hand, the calorific value of these plants was 12.60 MJ·kg−1 (Winiary pondweed) and 7.80 MJ·kg−1 (Rusalka pondweed). In the case of biogas yield studies, significantly higher biogas production was observed for Lake Rusalka pondweed than for Lake Winiary pondweed. The total biogas yield for these plants was 8.05 m3·Mg−1 for Rusalka pondweed and 3.19 m3·Mg−1 for Winiary pondweed. Differences in the chemical composition of pondweed originating from different lakes were also found, which translated into differences in the amount of energy that could be obtained from plants from both stands.

Niche Models Differentiate Potential Impacts of Two Aquatic Invasive Plant Species on Native Macrophytes

Potamogeton crispus (curlyleaf pondweed) and Myriophyllum spicatum (Eurasian watermilfoil) are widely thought to competitively displace native macrophytes in North America. However, their perceived competitive superiority has not been comprehensively evaluated. Coexistence theory suggests that invader displacement of native species through competitive exclusion is most likely where high niche overlap results in competition for limiting resources. Thus, evaluation of niche similarity can serve as a starting point for predicting the likelihood of invaders having direct competitive impacts on resident species. Across two environmental gradients structuring macrophyte communities—water depth and light availability—both P. crispus and M. spicatum are thought to occupy broad niches. For a third dimension, phenology, the annual growth cycle of M. spicatum is typical of other species, whereas the winter-ephemeral phenology of P. crispus may impart greater niche differentiation and thus lower risk of native species being competitively excluded. Using an unprecedented dataset comprising 3404 plant surveys from Minnesota collected using a common protocol, we modeled niches of 34 species using a probabilistic niche framework. Across each niche dimension, P. crispus had lower overlap with native species than did M. spicatum; this was driven in particular by its distinct phenology. These results suggest that patterns of dominance seen in P. crispus and M. spicatum have likely arisen through different mechanisms, and that direct competition with native species is less likely for P. crispus than M. spicatum. This research highlights the utility of fine-scale, abundance-based niche models for predicting invader impacts.

Remote Sensing of Potamogeton crispus L. in Dongping Lake in the North China Plain Based on Vegetation Phenology

Curly-leaf pondweed (Potamogeton crispus L.) is a perennial, submerged plant native to Eurasia, Africa, and Australia that tolerates fresh or slightly brackish water. The pondweed has been found widely in many lakes in northern China. The Dongping Lake is a typical shallow macrophytic lake in north China, and it is an important junction at the East Route Project of China’s South-to-North Water Diversion Project (ERP-CSNWDP). In mid-summer, the pondweed die-offs result in a critical loss of dissolved oxygen and decaying plants can result in Dongping Lake eutrophication, blocked waterway, and fish kills. In order to maintain the environment security of the ERP-CSNWDP, there is an urgent need to understand the spatial and temporal changes of pondweed’s rapid range expansion in Dongping Lake. We employed moderate-resolution imaging spectroradiometer, normalized difference vegetation index data, and field investigations to extract its phenological characteristic. Landsat images from pondweed blooming and decay phases were acquired for eight representative growth stage years during the period of 1985–2017 to extract pondweed distribution. Through the validation, there was an accuracy of more than 89% for pondweed extraction in 2017. Then, we used a dimidiate pixel model to calculate its fractional green vegetation coverage (FVC). The results illustrated that its range expanded continuously during the 32-year study period. Its habitat changed from the scattered near shore distribution in 1985 to the contiguous coverage of large areas of the lake surface in 2017. The range expansion of pondweed was grouped into three stages. From 1985 to 1996, it had a slow growth stage with a maximum species range of 10.34 km2 in Dongping Lake. During the period of 1996–2001, there was an explosive growth stage during which it become the dominant species in the Lake. From 2001 to 2017, the range continued to increase to 49.07 km2, which comprised 40% of the surface area of the Lake. By spearman rank correlation analysis, we found that there was a significant correlation between pondweed area and the lake eutrophication level (R = 0.79, P < 0.05). The FVC spatial pattern after 2001 exhibited a gradual horizontal decrease from the southeast to the northwest of Dongping Lake. This study illustrates the application of vegetation phenology to assess the spatial and temporal pattern of pondweed. The opening of the ERP-CSNWDP is diverting a fraction of the total flow of the Yangtze River to Northern China via the Dongping Lake and presents an ongoing environmental security risk which will require future pondweed invasive species control and mitigation strategies utilizing ground and satellite-based spectrum observations.

Constraining invader dominance: Effects of repeated herbicidal management and environmental factors on curlyleaf pondweed dynamics in 50 Minnesota lakes

Abstract Curlyleaf pondweed (Potamogeton crispus) is one of the most widespread and widely managed aquatic invasive plants in North America. Despite decades of management, the efficacy of long‐term management strategies and the effects of environmental drivers on curlyleaf pondweed populations remain uncertain. To evaluate the effects of management and environmental factors on within‐lake distribution and local density of curlyleaf pondweed, we collated monitoring data from point–intercept surveys collected by a variety of lake managers across Minnesota, U.S.A. Using this dataset, comprising 177 lake‐years of plant data, we examined the influence of herbicide treatment, water clarity, snow depth, and ice cover duration on curlyleaf pondweed distribution and density between 2006 and 2015. We evaluated the effects of herbicides on curlyleaf pondweed at three time points relative to treatment: within year, carryover effects the following year, and cumulative effects over multiple years of treatment. All three temporal measures were associated with significant reductions of curlyleaf pondweed. Additionally, herbicidal management reduced both the density and distribution of curlyleaf pondweed. Given that herbicide management led to reductions that carried over into future years, managers may be able to design multi‐year treatments to reduce total management effort over time. We also found strong effects of environmental conditions on curlyleaf pondweed. Elevated lake productivity and decreased winter snow cover were associated with increased springtime distributions of curlyleaf pondweed, whereas duration of winter ice cover had no influence. The influence of productivity suggests that reductions of this invasive species may be an ancillary benefit of water‐quality improvements that lower lakes’ trophic status. Our results also show that decreased winter snow cover, as predicted under climate change, could exacerbate problematic growth of curlyleaf pondweed. Harnessing monitoring data from multiple projects, as this study does, allows for robust inference about environmental and management constraints on macrophytes. Because of environmental and management variability, we suggest that treatment regimens follow an adaptive management cycle, with outcomes of management monitored and evaluated, and strategies updated accordingly. It is also vital to continue monitoring both managed and unmanaged lakes to enable stronger inferences about treatment effectiveness.

Influence of Different Electron Acceptors on the Anaerobic Degradation of Curly-Leaf Pondweed.

Curly-leaf pondweed (Potamogeton crispus) was utilized as the representative to investigate the biodecomposition process of aquatic plants under different reducible conditions. Results showed that the methane production was inhibited when different electron acceptors (Fe(III), <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="02257-ilm01.gif"/> and <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="02257-ilm09.gif"/>) were available. The methane production was decreased by 57% when Fe(III) and <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="02257-ilm10.gif"/> or <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="02257-ilm11.gif"/> were both available compared to the control. The degradation efficiency of hemicellulose and lignin with Fe(III) and <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="02257-ilm12.gif"/> were increased significantly. This provided a theoretical basis for slowing down the emissions of methane.

Iron-Oxide-Promoted Anaerobic Process of the Aquatic Plant of Curly Leaf Pondweed

The technique of producing methane with lignocellulosic biomass as feedstock has been used worldwide. In the current study, three types of iron oxides, including goethite, hematite, and magnetite, were used to improve methane production from the aquatic plant curly leaf pondweed. In comparison to the control, hydrolysis efficiency of the aquatic plant in reactors with iron oxides was increased from 31.4 ± 0.1% to a higher level, which varied between 49.1 ± 4.6 and 74.1 ± 4.1%, and the accumulated methane production and formation rates were increased significantly. For all reactors with iron oxides, the accumulated methane production increased with increasing dosages. When the dosages of iron oxide were 0.5 and 1.0% (calculated on the basis of the iron contents), reactors with magnetite showed higher promotion effects. However, when the dosage was increased further to 2.0%, no significant difference was found between the reactors with iron oxides.

Effects of curlyleaf pondweed control on water quality and coontail abundance in Gleason Lake, Minnesota

Three years (2007–2009) of early season lakewide endothall treatments to control curlyleaf pondweed (Potamogeton crispus) were followed by 4 years (2010–2013) of early season spot endothall treatments in 65 ha Gleason Lake, Plymouth, Minnesota. Endothall treatments controlled heavy growth of curlyleaf on an annual basis in all 7 years, but long-term control, where no future treatments would be necessary, was not achieved. During the curlyleaf control program, coontail (Ceratophyllum demersum) distribution and abundance increased dramatically as curlyleaf distribution and abundance decreased. None of the other 3 native submersed plant species found in Gleason Lake increased in frequency over the 7 years of treatment. It is not clear what triggered the rapid coontail expansion or if its heavy growth will be sustained. During the same time period, Gleason Lake transparency increased while phosphorus and chlorophyll concentrations decreased. Water quality improvements in Gleason Lake were likely related to nutrient uptake by coontail growth.

Survival of invasive aquatic plants after air exposure and implications for dispersal by recreational boats

Recreational boating is widely recognized as an important vector for overland transport of invasive aquatic plants. Since their dominant form of recruitment is vegetative reproduction, entangled fragments on boats and trailers can establish new populations. The effectiveness of recreational boats as transport vectors relies on the resistance of macrophytes to air exposure. During the summers of 2012 and 2013, we conducted five field experiments in northern Wisconsin to assess air tolerance of Eurasian water-milfoil (Myriophyllum spicatum) and curly-leaf pondweed (Potamogeton crispus). We simulated conditions that these plants would experience when ensnared on boats and trailers by testing viability after drying of single stems, coiled stems, and vegetative buds (turions). Single stems of M. spicatum and P. crispus were viable for up to 18 and 12 h of air exposure, respectively. Coiling extended the viability of M. spicatum to 48 h of air exposure. Turions of P. crispus successfully sprouted after 28 days of drying. The fact that recreational boaters in the region typically visit multiple lakes within a few days suggests that most lakes are susceptible to introduction of viable plants, and so lake managers should continue to focus attention on boat cleaning.

Forecasting the Vulnerability of Lakes to Aquatic Plant Invasions

AbstractPrevention is an integral component of many management strategies for aquatic invasive species, yet this represents a formidable task when the landscapes to be managed include multiple invasive species, thousands of waterbodies, and limited resources to implement action. Species distributional modeling can facilitate prevention efforts by identifying locations that are most vulnerable to future invasion based on the likelihood of introduction and environmental suitability for establishment. We used a classification tree approach to predict the vulnerability of lakes in Washington State (United States) to three noxious invasive plants: Eurasian watermilfoil (Myriophyllum spicatum), Brazilian egeria (Egeria densa), and curlyleaf pondweed (Potamogeton crispus). Overall, the distribution models predicted that approximately one-fifth (54 out of 319 study lakes) of lakes were at risk of being invaded by at least one aquatic invasive plant, and many of these predicted vulnerable lakes currently support high native plant diversity and endemism. Highly vulnerable lakes are concentrated in western Washington in areas with the highest human population densities, and in eastern Washington along the Columbia Basin Irrigation Project and the Okanogan River Basin that boast hundreds of lakes subject to recreational use. Overall, invasion potential for the three species was highly predictable as a function of lake attributes describing human accessibility (e.g., public boat launch, urban land use) and physical–chemical conditions (e.g., lake area, elevation, productivity, total phosphorous). By identifying highly vulnerable lake ecosystems, our study offers a strategy for prioritizing on-the-ground management action and informing the most efficient allocation of resources to minimize future plant invasions in vast freshwater networks.

Invasive species may offer advanced phytoremediation of endocrine&lt;br&gt;disrupting chemicals in aquatic ecosystems

Abstract One of the major areas of advancement in environmental science is bioremediation. Researchers have been using bacteria, fungi, algae and now macrophytes to remove pollutants from aquatic and terrestrial ecosystems. Here we share the results of a study on the macrophyte uptake of xenoestrogens from an urban river. We found that the invasive curly leaf pond weed ( Potamogeton illinoensis ) accumulated an average of 66% higher levels of estrogenic compounds and 94% more Bisphenol-A than the native Illinois pondweed ( Potamogeton crispus ) in an urban river, in the watershed for the greater Chicago, IL area. The invasive species accumulated 76%more estrone, 55% more 17 β-estradiol and 31% more 17 α-ethynylestradiol than the native species. The Non-native plants were also 72% larger than the native Illinois Pondweed. Managers may consider using invasive species to remove pollutants from ecosystems and restore ecosystem biogeochemistry. Key words : Endocrine Disrupting Chemicals, Environmental Remediation, Invasive Species

Short-term declines in curlyleaf pondweed in Minnesota: potential influences of snowfall

Curlyleaf pondweed (Potamogeton crispus) is a long-established, nonnative aquatic plant common throughout southern and central Minnesota that is thought to be expanding northward. Curlyleaf pondweed typically grows abundantly in spring in productive lakes and then senesces in midsummer, often followed by algae blooms. We report observations of widespread, short-term declines in curlyleaf pondweed cover that appear linked to winter snow depth on frozen lakes. These findings suggest that climate change may greatly affect habitat suitability for curlyleaf pondweed. As Minnesota lakes warm with less snow cover limiting light penetration, curlyleaf pondweed growth will likely increase. These observations form the foundation for targeted follow up studies that more precisely describe conditions limiting the growth and expansion of curlyleaf pondweed in north-temperate, North American lakes.

Effects of repeated, early season, herbicide treatments of curlyleaf pondweed on native macrophyte assemblages in Minnesota lakes

We examined the response of native aquatic macrophyte communities to spring herbicide treatments of curlyleaf pondweed (Potamogeton crispus) from 2006 through 2009. Eleven lakes were examined during our study; 8 were treated in May with endothall at 0.75–1.00 mg active ingredient per liter (ai/L) and 3 were used as untreated reference lakes. Macrophyte communities were assessed for frequency of occurrence in the littoral zone with the point intercept method in the summer after each treatment. During each survey, we collected biomass samples from 40 random locations in each lake. In the reference lakes, curlyleaf persisted at moderate to high frequencies over the 4 years, and no consistent changes in native macrophyte frequency of occurrence were seen. In most treated lakes, overall native macrophyte frequency of occurrence and species richness changed little over the 4 consecutive years of treatment, although shifts in the abundance of some species were observed. In untreated lakes, biomass varied between years, whereas in many treated lakes, biomass generally increased; however, these increases were usually not significant. The most substantial increases in biomass were attributed to single species in each treatment lake. Likewise, we observed substantial but insignificant increases of Chara sp. frequency and biomass in many treated lakes. Multiple years of treatment may be needed to see significant increases in overall native macrophyte abundance because significant changes in abundance were not observed within 4 years of treatment; however, consecutive early season, lakewide endothall treatments of curlyleaf pondweed can control curlyleaf pondweed without substantial harm to native macrophytes.

Evaluation of lakewide, early season herbicide treatments for controlling invasive curlyleaf pondweed (Potamogeton crispus) in Minnesota lakes

Curlyleaf pondweed (Potamogeton crispus) is a nonnative aquatic plant found throughout temperate regions of North America. Its early season growth, propensity to form dense surface mats, and ability to out-compete native aquatic plants allow it to degrade the ecological and recreational quality of many lakes. Consequently, there is great interest in adopting lakewide management strategies that can reduce the negative impacts of curlyleaf and provide long-term control. We collaborated with the Minnesota Department of Natural Resources from 2006 through 2009 to evaluate lakewide, early season herbicide treatments for controlling curlyleaf. Nine curlyleaf-infested lakes were treated with endothall at 0.75–1.00 mg active ingredient per liter (ai/L) or fluridone at 2–4 μg ai/L (only one lake treated with fluridone) for up to 5 consecutive years. Three additional infested lakes were selected to serve as untreated reference lakes. In each year we assessed the frequency and biomass of curlyleaf (May and Jun), documented the production of new curlyleaf turions on standing plants (Jun), and tracked changes in the abundance and viability of turions in lake sediments (Oct). We found that herbicide treatment inhibited turion production and substantially reduced curlyleaf frequency, biomass, and sediment turion abundance in treated lakes. The largest reductions of curlyleaf frequency, biomass, and turion abundance occurred in the initial 2–3 years of treatment, with less substantial reductions in the subsequent years of treatment. Despite these reductions, viable turions remained in the sediments of treated lakes after up to 5 consecutive years of treatment. These results suggest that although lakewide, early season herbicide treatments can effectively control curlyleaf, inhibit turion production, and reduce the abundance of turions in sediments, ongoing management will likely be required to maintain long-term control.

Invertebrate Colonization of Native and Invasive Aquatic Macrophytes in Presque Isle Bay, Lake Erie

ABSTRACT Aquatic invertebrates were sampled from three abundant species of macrophytes: in Presque Isle Bay, Lake Erie. Samples were taken from Richardson pondweed (Potamogeton richardsonii), which is native to Presque Isle Bay, and from Eurasian watermilfoil (Myriophyllum spicatum) and curly-leaf pondweed (Potamogeton crispus), which are invasive plants. One-way analysis of variance showed significant differences (F = 82.51, P < 0.0001) in invertebrate density among macrophyte species. The greatest mean density was found on P. crispus (7,640 organisms/m2). Mean invertebrate density on P. richardsonii (3,660 organisms/m2) and on M. spicatum (3,378 organisms/m2) were not significantly different from one another. The primary reason for the greater density on P. crispus was very high densities of the annelid Stylaria lacustris. Invertebrate richness was highest on P. richardsonii with 19 genera present followed closely by M. spicatum with 18 genera, and the lowest richness occurred on P. crispus, which contained 14 genera. The most abundant group of invertebrates collected from P. richardsonii and P. crisp was annelids whereas the most abundant group of organisms collected from M spicatum was arthropods.

Whole Lake Fluridone Treatments For Selective Control of Eurasian Watermilfoil: II. Impacts on Submersed Plant Communities

ABSTRACT The aquatic herbicide fluridone is being used in northern tier states to selectively control the submersed exotic species Eurasian watermilfoil (Myriophyllum spicatum L.) growing in lakes and reservoirs. Reliable quantitative information linking changes in the submersed plant community following fluridone applications is limited, particularly with respect to water residue records. Therefore, a study was conducted to investigate the effect of low-dose fluridone treatments on the submersed plant communities in four lakes in Michigan. The overall study objective was to determine whether submersed plant species diversity and frequency were impacted by low-dose fluridone applications in the year of treatment, when targeting a whole lake for Eurasian watermilfoil control. The primary objectives of this portion (part II) of the overall study was to determine fluridone effectiveness on the exotic submersed species Eurasian watermilfoil (Myriophyllum spicatum L.) and to evaluate shifts in plant species diversity at one year posttreatment. Secondary objectives included determining fluridone effectiveness on the exotic submersed species curlyleaf pondweed (Potamogeton crispus L.) and verifying laboratory-derived results of fluridone concentration and exposure time relationships with respect to efficacy against Eurasian watermilfoil. Quantitative sampling of vegetation was performed using point-based frequency of species occurrence to evaluate whole-lake distribution and diversity of the submersed plant community of all eight study lakes. The technique was implemented using global positioning and geographic information systems, with a minimum grid resolution of 50 m by 50 m. Plant surveys were conducted in early to mid May and in mid August in 1997 (year of treatment) and 1998 (12 and 15 months post treatment). The fluridone concentration and exposure time (CET) relationship resulted in good to excellent control of Eurasian watermilfoil through 15 months posttreatment on three of the treated lakes (Big Crooked, Camp, and Lobdell). On a fourth lake, Wolverine, the required CET relationship was not maintained and poor control of Eurasian water milfoil was observed. There was no strong evidence of long-term curlyleaf pondweed control in any of the fluridone-treated lakes. The herbicide application strategy used in this study did not significantly impact the native plant species diversity or cover in the year of treatment, or through 15 months posttreatment, in any of the fluridone-treated lakes. Native plant cover was maintained at levels >70% in the year of treatment and at one year posttreatment; a level above the range (20 to 40%) recommended for healthy fish and wildlife habitat. The selective control of Eurasian watermilfoil achieved in this study verified results from previously conducted laboratory and outdoor mesocosm evaluations.

Selenium Accumulation in Submerged Aquatic Macrophytes Potamogeton pectinatus L. and Ruppia maritima L. from Water with Elevated Chloride and Sulfate Salinity

Submerged aquatic macrophyte species Potamogeton crispus L. (curlyleaf pondweed) and Ruppia maritima L. (widegeongrass) were examined for selenium accumulation from agricultural drainage water in the field and under laboratory conditions. High concentrations of chloride and sulfate salts were found in the drainage water of the constructed wetland at Tulare Lake Drainage District, Corcorn, California. Samples of P. crispus and R. maritima collected from the field, had similar plant-tissue Se concentrations, but the rhizomes accumulated significantly greater amounts of Se than the shoot tissues. When the plants were grown in culture solution supplemented with either chloride or sulfate salt, R. maritima was found to be more salt tolerant than P. crispus, and P. crispus accumulated more Se than R. maritima. Free seleno-amino acids were detected in the plant tissue, and organic Se was detected in the culture solution after 10 days of growth. The release of organic Se into the water by the plants may have a negative impact on the wetland environment.