Water hyacinth is a highly invasive, aquatic species in the southern US that requires intensive management through frequent herbicide applications to minimize harmful impacts. Quantifying management success in large-scale operations is challenging with traditional survey methods, which rely on boat-based teams and can be time-consuming and labor-intensive. In contrast, unmanned aerial systems allow a single operator to survey a waterbody more efficiently and rapidly, enhancing both coverage and data collection. Therefore, the objective of this research was to develop remote sensing techniques to assess herbicide efficacy for water hyacinth control in an outdoor mesocosm study. Experiments were conducted in spring and summer 2023 to compare and correlate data from visual evaluations of herbicide efficacy against nine vegetation indices (VIs) derived from unmanned aerial system (UAS)-based red-green-blue (RGB) imagery. Penoxsulam, carfentrazone, diquat, 2,4-D, florpyrauxifen-benzyl, and glyphosate were applied at two rates, and experimental units were evaluated for six weeks. The Carotenoid Reflectance Index (CRI) had the highest Spearman’s correlation coefficient with visually evaluated efficacy for 2,4-D, diquat, and florpyrauxifen benzyl (> -0.77). The Visible Atmospherically Resistance Index (VARI) had the highest correlation for carfentrazone and penoxsulam treatments (> -0.70), and the EXGR Excess Greenness Minus Redness Index had the highest correlation for glyphosate treatments (> -0.83). CRI had the highest correlation coefficient with the most herbicide treatments, and it was the only VI tested that did not include the red band. These vegetation indices were satisfactory predictors of mid-range visually evaluated herbicide efficacy values but were poorly correlated with extremely low and high values, corresponding to non-treated and necrotic plants. Future research should focus on applying findings to real-world (non-experimental) field conditions and testing imagery with spectral bands beyond the visible range.

Native aquatic macrophytes such as American eelgrass (Vallisneria americana Michx.) are often desirable in aquatic ecosystems due to the ecological benefits they provide but are threatened by competition from invasive taxa including non-native Vallisneria taxa and hydrilla [Hydrilla verticillata (L. f.) Royle]. Identifying potential selective herbicide management options can provide tools to minimize impacts to native taxa in restoration and aquatic invasive plant management programs. Greenhouse mesocosm experiments were conducted in 2023 to investigate herbicide efficacy on two native eelgrass species (V. americana and Vallisneria neotropicalis Vict.), two non-native taxa (Vallisneria australis S.W.L. Jacobs & Les and Vallisneria spiralis L. × Vallisneria denseserrulata Makino), and H. verticillata. Herbicide applications included endothall, diquat, florpyrauxifen-benzyl, fluridone, and flumioxazin and select combinations of these herbicides used in H. verticillata management. Endothall alone provided 90% to 100% aboveground biomass reduction at 3,000 µg L−1 with at least 24 h of continuous or intermittent exposure to all native and invasive species at 6 wk after exposure, whereas florpyrauxifen-benzyl applied alone resulted in minimal aboveground biomass reduction. A 45-d of exposure of fluridone (10 µg L−1) resulted in 95% biomass reduction of V. americana and 7% to 48% of other tested taxa. The combination of flumioxazin and florpyrauxifen-benzyl resulted in 90% to 100% aboveground biomass reduction, and endothall combined with florpyrauxifen-benzyl resulted in 93% to 100% aboveground biomass reduction across taxa. Reductions in belowground biomass mirrored trends observed in aboveground biomass. No treatments selectively controlled invasive Vallisneria without injury to native Vallisneria, although efficacy was observed on H. verticillata. These insights provide an understanding for differences between these Vallisneria for researchers moving forward with selectively targeting H. verticillata in the presence of native Vallisneria species and two new aquatic invasive plants. Future research should expand treatment scenarios, increase the study period, and identify potential integrated plant management strategies for field scenarios.

Freshwater ecosystems are responsible for a large proportion of global methane emissions to the atmosphere. The radiocarbon (14C) content of this aquatic methane is useful for determining the age and source of this important greenhouse gas. Several methods already exist for the collection of aquatic methane for radiocarbon analysis, but they tend to only sample over short periods of time, which can make them unsuitable for characterizing aquatic methane over longer timespans, and vulnerable to missing short-term events. Here, we describe a new time-integrated method for the collection of aquatic methane that provides samples suitable for radiocarbon analysis, that are representative for periods of up to at least 16 days. We report the results of a suite of tests undertaken to verify the reliability of the method, and the 14C age of aquatic methane from field trials undertaken at sites within Scotland, UK. We believe that this new method provides researchers with a simple approach that is easily deployable and can be used to collect representative time-integrated samples of methane for radiocarbon analysis from a wide range of aquatic environments.

A single foliar application of glyphosate [N-(phosphonomethyl)glycine] at 2.2 kg/ha controlled fragrant waterlily (Nymphaea odorata Ait.). Seeds that germinated during the year of glyphosate treatment or the following spring reestablished the fragrant waterlilies. A second application of glyphosate, once the seedlings had reached the surface of the water, resulted in long-term control.

Preplant control of mannagrass was greater than 90% with clethodim, glyphosate, sethoxydim, and sulfosate. Glyphosate at 0.5 to 1.0 kg ai/ha controlled mannagrass greater than 97%, and was not increased with any adjuvant. Fenoxaprop applied POST controlled mannagrass 97% but injured rice 33%. Except for fenoxaprop-ethyl, all POST treatments increased rice yields at least 1560 kg/ha more than the non-treated check. Southern watergrass was controlled 79 and 89% with 1.0 kg ai/ha glyphosate and 4.5 kg ai/ha sulfosate, respectively, while control was less than 55% with other herbicides.

The uptake and translocation of fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} were examined in sago pondweed (Potamogeton pectinatus L.) and Richardson pondweed [Potamogeton richardsonii (Ar. Benn.) Rydb.]. Root and shoot tissues of both species were isolated from each other with wax barriers and treated individually with 1.0 ppm 14C-fluridone. Both tissues bioconcentrated fluridone, but the amount absorbed represented 1% or less of the total herbicide available. Limited root-to-shoot translocation occurred, but shoot-to-root transport was negligible. In contrast to fluridone, highly mobile glyphosate [N-(phosphonomethyl) glycine] translocated from the shoots to the roots in sago pondweed. No metabolism of fluridone was detected in sago pondweed.

Mature plants of tomato (Lycopersicon esculentum Mill. ‘Super Sioux’), cucumber (Cucumis sativas L. ‘Early pickling’), and pinto bean (Phaseolus vulgaris L.), in small field plots, were exposed once to sprinkler or furrow irrigation water containing 0.11 kg/ha or 1.12 kg/ha MSMA (monosodium methanearsonate). Concentrations of MSMA in water were about 0.22 ppmw and 2.2 ppmw for the two rates, respectively. Samples of crops and soil were subsequently analyzed for elemental arsenic content by colorimetric and atomic absorption methods. Arsenic residues were higher, compared to controls, only in crops exposed to MSMA applied in sprinkler irrigation. Average arsenic levels were highest in tomatoes exposed to 2.2 ppmw MSMA by sprinkler irrigation, and after 30 and 45 days were 0.26 ppm and 0.35 ppm, respectively. Average arsenic levels in sprinkler-irrigated crops ranged from double to triple the arsenic levels in control (untreated) crops. Atomic absorption was more sensitive than the colorimetric method and could detect smaller differences in arsenic content of samples. The average arsenic residues in soil varied from 1 to 3 ppm, but the differences could not be attributed to treatment with MSMA.

Flumioxazin has recently (2010) been registered for aquatic use for control of hydrilla and other noxious invasive aquatic plant species. Due to the rapid degradation of flumioxazin, especially in high pH water, some hydrilla research trials have produced less than desirable results with rapid plant regrowth. Therefore, laboratory experiments were conducted to evaluate the influence of pH on flumioxazin's effect on photosynthesis. Flumioxazin applied at concentrations ≥ 200 µg ai L−1 in high (9.0) pH water and ≥ 100 µg L−1 in low (6.0) pH water required 68 to 123 h to reduce photosynthesis by 50% (ET50). The effect of 400 µg L−1 flumioxazin on photosynthesis of apical hydrilla tips was also compared at low (20 µmol m−2 s−1), medium (170 µmol m−2 s−1), and high (400 µmol m−2 s−1) light levels at pH 9.0. Low light–treated tips were still photosynthetic at approximately 73% of the nontreated control plants 168 h after treatment. Low light–treated hydrilla required an estimated 303 h to achieve a 50% reduction in photosynthesis, while high light plants only required 99 h. Chlorophyll content of hydrilla was reduced as flumioxazin concentration was increased from 100 to 1,600 µg L−1. These data indicate that flumioxazin activity on hydrilla photosynthesis is influenced by herbicide concentration, water pH, and light intensity.

Cabomba is a submersed aquatic plant native to the southeastern United States that is commonly sold worldwide through the aquarium trade. While infrequently managed in its native range, cabomba has recently been reported as invasive and tolerant to management efforts in the northern areas of the United States and in other countries. Invasive populations of cabomba are characterized by a phenotype that is bright green. In contrast, cabomba native to the southeastern United States is characterized by a red phenotype, while plants sold through the aquarium trade have intermediate characteristics of both the green and red phenotypes. The response of the three cabomba phenotypes to selected herbicides was evaluated by measuring photosynthetic response over the course of a static 144-hr exposure. Plants were exposed to the maximum recommended use-rates of 2,4-D, carfentrazone, copper, diquat, endothall (amine and dipotasium salt formulation), flumioxazin, quinclorac, triclopyr, and a combination of diquat and copper. A submersed plant species known to be sensitive to each of these herbicides was also included to compare photosynthetic response of the cabomba to a susceptible plant. The photosynthetic response of the red and green phenotypes differed following exposure to carfentrazone, diquat, 2,4-D, triclopyr, and flumioxazin. Diquat, diquat plus copper, endothall (amine salt), and flumioxazin were the only products that resulted in a greater than 50% reduction of photosynthesis in all three phenotypes of cabomba. A second experiment was conducted where all three phenotypes of cabomba were exposed to these four herbicides for 24 hr, and photosynthesis was evaluated. Following the 24-hr exposure, results further documented distinct response differences between the green and red phenotypes, with the green phenotype demonstrating a reduced sensitivity to the herbicides evaluated. Results demonstrate clear phenotypic differences in response to herbicide treatments and lack of susceptibility of cabomba to most herbicides.

Cuban club-rush is an invasive aquatic weed that is spreading northward in the southeastern United States. It is reported for the first time from Mississippi and from significantly farther northward in Alabama than was previously known. Cuban club-rush dissemination and rapid population growth are attributed to two types of reproduction: corky floating achenes and asexual reproduction by fragmentation. An illustration of Cuban club-rush and photos of its habit and habitat are provided.

We used stable isotope analysis (15N/14N) to characterize the trophic relationships of consumer communities of an aquatic food web (a permanent pond) and the adjacent terrestrial food web (secondary dry dipterocarp forest) from a seasonal tropical field site in north-eastern Thailand. In general, isotopic signatures of aquatic vertebrates were higher (δ15N range = 4.51–9.90‰) than those of invertebrates (δ15N range = 1.10–6.00‰). High 15N signatures identified water snakes and swamp eels as top predators in the pond food web. In the terrestrial food web 15N signatures of saprophagous litter invertebrates (diplopods, earthworms), termites, ants and beetle larvae were lower than in those of predatory invertebrates (scolopendrids, scorpions, whip spiders). Predatory terrestrial frogs and caecilians had lower 15N signatures than snakes, indicating that snakes are among the top predators in the terrestrial web. Based on the distribution of isotopic signatures, we estimated five trophic levels for both the aquatic and terrestrial food web. The food chains of a seasonal tropical site studied were rather short, which implies similarities to the structure of temperate food webs.