Aquatic Vascular Plants Research Articles

Relationships between chironomids and water depth in Bosten Lake, Xinjiang, northwest China

A significant relationship between the distribution and abundance of chironomids and water depth has long been recognized. Few studies on this topic, however, have been carried out in arid regions where the chironomid community is usually controlled by water salinity. Bosten Lake, northwest China, the largest inland freshwater lake (~1,260 km2) in the country, provides a unique opportunity to investigate this relationship in an arid region. A total of 42 surface sediment samples from water depths of 0.9–17.0 m, and 12 chironomid taxa, were used in the analysis. The first principal component analysis (PCA) axis explained 59.3 % of the variance in the chironomid assemblage and there was a significant correlation between PCA axis 1 scores and water depth (R2 = 0.84, P < 0.001). The chironomid assemblages change significantly at 8.0 m water depth. This threshold corresponds to an abrupt change in the basin slope and the spatial distribution of aquatic vascular plants. Redundancy analysis showed that abundances of Chironomusplumosus-type, Microchironomus and Cryptochironomus are positively correlated with water depth, whereas abundances of Tanytarsus, Polypedilum nubifer-type, Cricotopus and Psectrocladius sordidellus-type are negatively correlated with water depth. These ecological relationships are supported by published data. Qualitative chironomid-inferred changes in lake level and diatom-inferred changes in salinity from sediment core BSTC001 were compared. Close agreement in trends for these two variables validates the use of chironomid assemblages to study palaeo-hydrological variability in this westerlies-dominated, arid region of central Asia.

Long-Term Changes in Distribution and Frequency of Aquatic Vascular Plants and Charophytes in an Estuary in the Baltic Sea

The long-term impact of natural and human-induced large-scale changes on aquatic phanerogams and charophytes has remained mostly unstudied in the Baltic Sea, largely because of a lack of historical data. A vegetation data set based on transects in an estuary in the western part of the Gulf of Finland studied in the 1930s–1940s, however, exists. We re-surveyed 91 of these transects in 2005 and 2007. The historical data set included 60 species and the contemporary 52 species. The species were classified into increasing, decreasing or unchanged according to the change in their occurrence frequencies. A significant frequency change was found for 31 of the 50 (62%) species which were present in both surveys. The proportion of species/growth forms with high-nitrogen and low-light preferences increased, whereas that of species/growth forms preferring oligotrophic conditions and species of shallow waters decreased. In the area, the species expanded their distribution ranges mainly towards the open sea. Eutrophication, reduced grazing pressure and shore overgrowth by Phragmites australis are suggested as the main reasons for the observed changes. In addition, increased boating and shore-construction activities contributed to the long-term floristic changes.

Las plantas vasculares acuáticas estrictas y su conservación en México

Con base en el análisis de la riqueza y distribución de las hidrófitas vasculares estrictas, se identificaron las entidades federativas más relevantes para la conservación de los humedales de México y su flora asociada. Se registraron 240 especies distribuidas en 106 géneros y 62 familias, incluyendo 227 nativas y 13 introducidas, lo que representa 24% del total de las plantas acuáticas estimadas para México, incluyendo 8.3% de endemismo. Los estados que registran la mayor cantidad de especies son Veracruz (145 especies), Jalisco (123), Michoacán (115) y Tamaulipas (113). Un análisis iterativo indica que es necesario involucrar a 13 estados para la conservación de 100% de la flora acuática nativa.

WETLAND ECOSYSTEM SERVICES BASED ON EMERGY ANALYSIS OF LAKE NANSI IN SHANDONG, CHINA

Adopting the theories and methods of emergy analysis, the annual average emergy input-output of the Lake Nansi wetland ecosystem is calculated. Further, the emergy analysis chart is drawn to evaluate the energy flow and the economic value of the lake. The structure and functions of the Lake Nansi wetland ecosystem are analyzed as a whole. The results showed that the amount of the input solar emergy (including sunlight, wind and rainfall) of the Lake Nansi is 1.11 1021 1021 solar emergy joule/year (sej/a), and the output solar emergy is 1.73 1020sej/a. The primary productivity is 1.61 1020sej/a. Non-renewable resources is 1.03 1021 sej/a. At the same time, the ecological benefits of aquatic vascular plants and fish of the Lake Nansi are significant. The energy investment ratio of the lake is 0.0009. The net emergy yield ratio is 165.23 and environmental load ratio is

Carbon and nitrogen isotopes analysis and sources of organic matter in the upper reaches of the Chaobai River near Beijing, China

The carbon and nitrogen isotopes in the surface sediments, plants, and soil in the upper reaches of the Chaobai River have been researched. The results showed −27.75‰ — −21.58‰ and 1.32‰-6.74‰ for carbon and nitrogen isotopic ratios in the surface sediments, respectively. The sources of sedimentary organic matter in this area are soil organic matter, aquatic vascular plants, and riverine plankton, respectively, and a significant contributor to sediment in the Chaohe River, the Baihe River, and the Miyun Reservoir areas is soil organic matter. Furthermore, part of sedimentary organic matter in the Miyun Reservoir is attributed to the input from the Chaohe River and the Baihe River, the other is from C4 vegetation growing around individual point stations at the Miyun Reservoir. Compared with the situation in Hebei Province, the contribution of soil organic matter decreased significantly and river plankton and aquatic vascular plants increased significantly in Beijing municipal areas. This study reveals that the source of organic matter has a close relationship with the soil erosion.

Distribution and richness of aquatic plants across Europe and Mediterranean countries: patterns, environmental driving factors and comparison with total plant richness

AbstractQuestionsWhat are the geographic patterns of γ‐diversity of aquatic plants and what are the main driving factors? Are richness trends for aquatic plants similar to total plant richness? Is the Mediterranean area a hot spot for aquatic plants?LocationEurope and the Mediterranean Basin.MaterialWe listed vascular aquatic plant presence or absence for 44 countries. We also compiled total plant species richness and geographic and environmental variables for each country.MethodsWe first analysed country ordination based on their aquatic flora constrained by environmental variables (dbRDA), and selected the environmental variables best explaining species patterns (BEST analysis). Total species richness patterns were studied using maps and latitudinal gradients. We used generalized additive models (GAM) to detect the main environmental factors driving species richness, both for aquatic plants and total plants.ResultsThe BEST analysis identified a single variable that best explains aquatic plant species distribution: evapotranspiration. However, richness of aquatic plants vs latitude varies and no clear trend was observed. No relation was found between total plant and aquatic plant richness. Aquatic and total plant richness peak between 40° and 50°N, and values were intermediate at low latitudes. GAM related aquatic plant richness with water resources and rainfall, while total plant richness is mainly driven by evapotranspiration and temperature. Hydrophytes were relatively more abundant at higher latitudes than helophytes and the ratio correlated with evapotranspiration.ConclusionSouthern and western Europe hold the highest aquatic plant diversity, although no clear latitudinal species richness patterns were found. Aquatic plant richness is mainly driven by water‐related variables. Total plant richness exhibits a latitudinal pattern influenced by the Sahara desert, which depresses richness at low latitudes. Best predictors of total plant richness patterns are water–energy variables.

Photosynthesis in the Blue Water Lily (Nymphaea caerulea Saligny) Using Pulse Amplitude Modulation Fluorometry

Water lilies, such as the blue Egyptian water lily (Nymphaea caerulea Savigny), are ubiquitous aquatic plants. Leaves of mature plants normally unfold at the surface and are floating or emergent. Some aquatic vascular plants have a form of CAM (crassulacean acid metabolism) known as submerged aquatic metabolism (SAM). The presence of aerenchyma in water lily leaves and petioles makes it very difficult to measure photosynthesis in water lily plants by gas exchange. Pulse amplitude modulation (PAM) fluorometer techniques provide direct information on the light reactions of plants. PAM technology calculates photosynthesis as the electron transport rate (ETR) through PSII (4 electrons per O2 produced) in mol m−2 s−1. Here, relative ETR (rETR) was based on an assumed leaf absorptance factor of 0.84. Photosynthesis-versus-irradiance (P vs. E) curves were fitted with the waiting-in-line function (). Maximum effective quantum yield, maximum relative ETR (rETRmax), and quantum efficiency all vary on a diurnal cycle. The nonphotochemical quenching parameters qNmax and NPQmax are highly correlated with each other (, ) but do not show a systematic variation over a diurnal cycle. Nymphaea is a “sun plant” with optimum irradiance (Eopt) of 1000 μmol m−2 s−1 PPFD or higher. Titratable acid of leaves varied from ∼50 to 70 mol H+ m−3 (leaf water basis) and was depleted at ∼0600 and 1800 hours each day, a diel pattern inconsistent with SAM/CAM physiology. The N. caerulea C4 acid pool is too small to support substantial SAM-type metabolism. Gross photosynthesis of Nymphaea leaves had a high value of ∼5.3 g C m−2 d−1. For a daily irradiance of 56 mol m−2 PPFD, this works out to a 3.3% conversion efficiency in terms of moles of carbon.

Benthic diatoms of the Vistula River estuary (Northern Poland): Seasonality, substrata preferences, and the influence of water chemistry

SUMMARYSeasonal studies of water bodies in separate branches of the Vistula River estuary in Northern Poland were conducted over 30 months from May 2005 to October 2007. Diatom samples were collected from different substrata from two sites located in the river mouth, which has physical characteristics as a result of a complex interplay of natural and human influences that have taken place over the last 100+ years. The diatom flora growing on hard surfaces near the river banks such as sand, muddy sand, rocks, macroscopic green algae and/or vascular aquatic plants was recorded. All diatom taxa collected were distinguished based on their morphological features using light (LM) and scanning electron microscopy (SEM). A total of 187 species belonging to 61 genera were identified. A canonical correspondence analysis indicated that the diatom assemblages were definitely associated with salinity as well as nutrient concentrations and substratum type. During the study, malformations of diatom valves were observed in 48% of the microphytobenthos samples. Abnormal outline morphology and ornamentation deformities in several individuals of nine different species were recorded, which were mainly in epilithic and epiphytic communities collected from spring to autumn.

Diversity of Aquatic Vascular Plants in the Yangtze Delta

Based on field investigation and literature survey,the species composition,geographical elements,and endangered state of aquatic vascular plants in the Yangtze Delta were analyzed.We found 185 wild species belonging to 90 genera and 39 families in this area,most of which were distributed in habitats such as ditches,rice-fields,and ponds.Additionally,emergent plants were the main type in terms of life form.This flora was chiefly temperate in nature according to areal-type analysis both at the level of genera and of species.In light of IUCN Red List Categories and Criteria(Edition 3.1),those species were classified into 9 types,including Regionally Extinct(RE) 1,Critically Endangered(CR) 3,Endangered(EN) 8,and Vulnerable(VU) 10.Finally,we also examined the main reasons causing these aquatic plants to become threatened.

Interactions of gold nanoparticles with freshwater aquatic macrophytes are size and species dependent

The partitioning of 4- and 18-nm gold nanoparticles (AuNPs) to aquatic macrophytes was investigated in vivo with exposure suspension in well water. Three morphologically distinct aquatic macrophytes were studied. Myriophyllum simulans Orch. and Egeria densa Planch. are submerged aquatic vascular plants, whereas Azolla caroliniana Willd. is a free-floating aquatic fern. Because aquatic plants absorb the majority of their nutrients from the water column, it is logical to hypothesize that they may absorb nanomaterials in suspension, potentially facilitating trophic transfer. Each plant was exposed to two different-sized gold nanospheres at a nominal concentration of 250 µg/L AuNPs for 24 h. Macrophytes were harvested at six time points (1, 3, 6, 12, 18, and 24 h), dried, and then analyzed for gold concentration via inductively coupled plasma-mass spectrometry. Concentrations were normalized to whole-plant dry tissue mass. The present study shows that absorption of AuNPs through root uptake was size and species dependent. Electron microscopy revealed that 4- and 18-nm AuNPs adsorbed to the roots of each species. Root tissue was sectioned, and transmission electron microscopy indicated that 4-nm and 18-nm AuNPs were absorbed by A. caroliniana, whereas only 4-nm AuNPs were absorbed by M. simulans. Egeria densa did not absorb AuNPs of either size. Gold nanoparticles were confirmed in tissue by using energy-dispersive X-ray spectroscopy. Absorption of AuNPs by plants may be a function of the salinity tolerance of each species.

Estimating site occupancy rates for aquatic plants using spatial sub-sampling designs when detection probabilities are less than one

Estimation of site occupancy rates when detection probabilities are <1 is well established in wildlife science. Data from multiple visits to a sample of sites are used to estimate detection probabilities and the proportion of sites occupied by focal species. In this article we describe how site occupancy methods can be applied to estimate occupancy rates of plants and other sessile organisms. We illustrate this approach and the pitfalls of ignoring incomplete detection using spatial data for 2 aquatic vascular plants collected under the Upper Mississippi River's Long Term Resource Monitoring Program (LTRMP). Site occupancy models considered include: a naïve model that ignores incomplete detection, a simple site occupancy model assuming a constant occupancy rate and a constant probability of detection across sites, several models that allow site occupancy rates and probabilities of detection to vary with habitat characteristics, and mixture models that allow for unexplained variation in detection probabilities. We used information theoretic methods to rank competing models and bootstrapping to evaluate the goodness-of-fit of the final models. Results of our analysis confirm that ignoring incomplete detection can result in biased estimates of occupancy rates. Estimates of site occupancy rates for 2 aquatic plant species were 19–36% higher compared to naive estimates that ignored probabilities of detection <1. Simulations indicate that final models have little bias when 50 or more sites are sampled, and little gains in precision could be expected for sample sizes >300. We recommend applying site occupancy methods for monitoring presence of aquatic species.

Heavy metal biomonitoring and phytoremediation potentialities of aquatic macrophytes in River Nile

The concentrations of Cd, Cu, Pb, and Zn in sediments, water, and different plant organs of six aquatic vascular plant species, Ceratophyllum demersum L. Echinochloa pyramidalis (Lam.) Hitchc. & Chase; Eichhornia crassipes (Mart.) Solms-Laub; Myriophyllum spicatum L.; Phragmites australis (Cav.) Trin. ex Steud; and Typha domingensis (Pers.) Poir. ex Steud, growing naturally in the Nile system (Sohag Governorate), were investigated. The aim was to define which species and which plant organs exhibit the greatest accumulation and evaluate whether these species could be usefully employed in biomonitoring and phytoremediation programs. The recorded metals in water samples were above the standard levels of both US Environmental Protection Agency and Egyptian Environmental Affairs Agency except for Pb. The concentrations of heavy metals in water, sediments, and plants possess the same trend: Zn > Cu > Pb > Cd which reflects the biomonitoring potentialities of the investigated plant species. Generally, the variation of heavy element concentrations in water and sediments in relation to site and season, as assessed by two-way repeated measured ANOVA, was significant (p < 0.05). However, insignificant variations were observed in the concentrations of Pb and Cd in sediments in relation to season and of Cu and Zn in relation to site. Results also showed that the selectivity of the heavy elements for the investigated plants varied significantly (p < 0.05) with species variation. The accumulation capability of the investigated species could be arranged according to this pattern: C. demersum > E. crassipes > M. spicatum > E. pyramidalis > T. domingensis > P. australis. On the basis of the element concentrations, roots of all the studied species contain higher concentrations of Cu and Zn than shoots while leaves usually acquire the highest concentrations of Pb. Cd concentrations among different plant organs are comparable except in M. spicatum where the highest Cd concentrations were recorded in the leaves. Our results also demonstrated that all the studied species can accumulate more than 1,450-fold the concentration of the investigated heavy elements in water rendering them of interest for use in phytoremediation studies of polluted waters. Given the absence of systematic water quality monitoring, heavy elements in plants, rather than sediments, provide a cost-effective means for assessing heavy element accumulation in aquatic systems during plant organ lifespan.

BIODIVERSITY AND COMMUNITY ECOLOGY OF AQUATIC PLANT IN LAKE NAM CO, TIBETAN PLATEAU

The most crowded and highest lakes in the world distributes on the Tibetan Plateau,China.Lake Nam Co,in the North Tibet,is the highest great lake in the world,and is the second biggest salt water lake,only inferior to Lake Qinghai,in China.Biodiversity and community ecology of aquatic plant in this lake will have the impor-tant model and the demonstration significance to other lakes in the Tibetan Plateau. Aquatic plants mainly distributes in the eastern part of Lake Nam Co,and its characters of habitat are diverse,including small puddles,ponds,swamps,streams,as well as connected lakes.The results obtained from the pre-sent field study and literature survey showed that a total of 34 species belonging to 19 genera and 15 families,among which,1 species,1 genera and 1 families belonged to Charophyta,16 species,8 genera and 7 families be-longed to Monocotyledon,and 17 species,10 genera and 7 families belonged to Dicotyledon.Three new recorded families,including Characeae,Callitrichaceae and Scrophulariaceae,three new recorded genera and seven new recorded species were found in Lake Namco and its catchment.The dominant families of aquatic plants in this lake were Cyperaceae,Ranunculaceae,Potamogetonaceae and Haloragaceae.Among all families of aquatic plants,Potamogetonaceae and Cyperaceae included the maximum number of species,accounting for 26.47% and 20.59%,respectively.Potamogetonaceae,Ranunculaceae,Cyperaceae and Zannichelliaceae were most frequently occurring families and the frequently occurring genus included Potamogeton,Batrachium,Zannichellia and Carex.The dominant species in frequency included P.pectinatus,Z.palustris,B.bungei var.flavidum and B.Eradicatum and in biomass is P.pectinatus,Myriophyllum spicatum and B.bungei var.flavidum. According to the basis of community classification,there were eleven types of aquatic plant communities in Lake Nam Co in Lake Nam Co,including Ass P.pectinatus,Ass P.pectinatus + B.bungei var flavidum,Ass P.pectinatus + Z.palustris,Ass P.pectinatus + Chara braunii,Ass P.pectinatus + M.spicatum,Ass L.aquatica + B.Eradicatum,Ass M.spicatum + B.Eradicatum,Ass Limosella aquatica,Ass M.spicatum+ P.pectinatus + B.bungei var flavidum,Ass P.pectinatus + B.Eradicatum and Ass M.spicatum+ P.pectinatus + B.eradicatum.The flora of aquatic vascular plants in the Lake Nam Co was fundamentally north temperate in nature. The interspecific correlation coefficients exhibited by constellation diagram showed the significant associa-tions between the lake shore wetland species in Lake Nam Co,Tibetan,indicating a continuum of the species groups.Quadrats investigation indicated that these types of aquatic plant communities were mainly composed of submersed macrophyte communities with few floating-leaved macrophytes.β-diversity analyses suggested sig-nificant variations in species assembly among different quadrats along the environment gradient. Our research suggested that aquatic plants in the basin of Lake Nam Co possessed a wide range of ecological adaptation and niche separation,and played important roles in the linking of soil and water environment and in the maintenance of species diversity of land and water interface on the Tibetan Plateau.

Vegetation Dynamic Changes of Lake Nansi Wetland in Shandong of China

Abstract The paper researched the Lake Nansi wetlands phytoplankton species of aquatic vascular plants, distribution and biomass from 1983 to 2006. The methods were field investigation, laboratory analysis, remote sensing and geographic information system technology. The results showed that, wetland vegetation biomass continued to decrease in Lake Nansi from 1983 to 2006. Biomass of emergent plants decreased the fastest, followed by floatingleaved plants and submerged plants. The result reflects the human reclamation, aquaculture and other activities caused reduction in primary productivity. This effect decreased gradually from the periphery to the center of the Lake.

Effects of reduced salt concentrations on plant communities in the River Werra (Germany)

The reduction and equalization of the salt concentrations in the River Werra have resulted in a gradual recovery of the aquatic flora. Spatial high-resolution macrophyte mappings document the spread of the aquatic vascular plants in the middle and lower River Werra. Simultaneously, the plankton blooms have declined. Changes in the composition of the algal communities including diatoms also indicated lower salinity. In addition to the salinity, high nutrient concentrations, waste water discharges and structural degradation are important stressors in the River Werra as shown by e.g. low species richness of vascular plants and the common occurrence of pollution tolerant diatoms. From the existing data it is clear that an encompassing improvement of the ecological conditions in the River Werra can only be achieved by further restoration measures considering all stressors.

Cross-species extrapolation of chronic nickel Biotic Ligand Models

The use of Biotic Ligand Models (BLMs) to normalize metal ecotoxicity data and predict effects in non-BLM organisms should be supported by quantitative evidence. This study determined the ability of chronic nickel BLMs developed for the cladocera Daphnia magna and Ceriodaphnia dubia to predict chronic nickel toxicity to three invertebrates for which no specific BLMs were developed. Those invertebrates were the snail Lymnaea stagnalis, the insect Chironomus tentans, and the rotifer Brachionus calyciflorus. Similarly, we also determined the ability of chronic nickel BLMs developed for the alga Pseudokirchneriella subcapitata and the terrestrial vascular plant Hordeum vulgare to predict chronic nickel toxicity to the aquatic vascular plant Lemna minor. Chronic nickel toxicity to the three invertebrates and the aquatic plant were measured in five natural waters that varied in pH, Ca, Mg, and dissolved organic carbon (DOC), which are known to affect chronic nickel toxicity and are the important input variables for the chronic nickel BLMs. Nickel toxicity to the three invertebrates varied considerably among the test waters, i.e., a 14-fold variation of EC50s in L. stagnalis, a 3-fold variation in EC20s in C. tentans, and a 10-fold variation in EC20s in B. calyciflorus, but the cladoceran BLMs were able to predict nickel effect concentrations within a factor of two. Nickel toxicity (EC50s) to L. minor varied by 6-fold among the test waters. Although the P. subcapitata and H. vulgare BLMs offered reasonable predictions of nickel EC50s to L. minor, the D. magna and C. dubia BLM showed better predictions. Our results confirm the influence of site-specific pH, hardness, and DOC on chronic nickel toxicity to aquatic organisms, and support the use of chronic nickel BLMs to manage this influence through normalizations of ecotoxicity data.

Effects of Herbicides on Lemna gibba and Recovery from Damage After Prolonged Exposure

To determine the potential impact of contaminants on the aquatic vascular plants Lemna sp., toxicity tests are usually conducted for a 4- to 14-day exposure, and the toxicity is usually expressed as EC50. However, the effects of longer exposure and the recovery potential after exposure to chemicals are other important factors which should be considered. We present the relative risks of a variety of exposure scenarios and recovery potentials from damage, using herbicides with different modes of action. Toxicity was assessed on the basis of both EC50 and relative growth rate (RGR) compared with untreated controls in exposure and recovery. The EC50 of atrazine was found to be 89 ppb, and its phytostatic concentrations were 1600 and 800 ppb for exposure periods of 14 and 28 days, respectively, and no phytocidal effects were observed up to 3200 ppb for a 28-day exposure. The RGR in recovery was not affected by the RGR in exposure, and regrowth was possible even after complete inhibition of growth for 28 days at the highest concentration tested. Alachlor, with an EC50 of 31 ppb, was phytostatic at 400 ppb for a 14-day exposure and phytocidal at 200 ppb for 21- and 28-day exposures. Paraquat, with an EC50 of 31 ppb, showed phytocidal rather than phytostatic effects. All phytostatic fronds could not grow in the recovery period, and the phytocidal concentration decreased with exposure period, from 80 ppb for a 7-day exposure to 20 ppb for 21- and 28-day exposures. The RGR of alachlor and paraquat in recovery was dependent on the RGR in exposure. In the case of cyclosulfamuron, phytostatic concentrations were 100 and 50 ppb for 7- and 14-day exposures, respectively. In the case of exposures longer than 21 days, however, it exhibited phytocidal activity at 10 ppb. The results of this study suggest that it is important to examine the effects of chemicals over a longer exposure period as well as the recovery potential from damage for reliable ecological risk assessment.

Bio-accumulation and toxicity of lead (Pb) in Lemna gibba L (duckweed)

The vascular aquatic plant Lemna gibba (duckweed) was exposed during seven days to lead (Pb) at concentrations ranging from 50 to 300 mg/L in a greenhouse with controlled photoperiod and temperature. The effects of Pb on growth of Lemna gibba were examined during 13 days in the same experimental design. The maximum accumulation of lead by Lemna gibba occurs during the third day in the 50 mg/L test, and at the sixth day, lead in all test concentrations produces approximately a 100% inhibitory effect on duckweed growth. In all tests, the maximum relative growth rates were achieved on the third day and then, the toxicity effects were: 59.3% total soluble starch reduction; 94.7% total soluble proteins reduction; 246% increase in total soluble amino acids; 50% increase in total soluble sugars and an 18.2% increase in total phenols. This experiment showed that the transfers of Pb from nutritive solution to plants were fast. Nevertheless, Pb produced toxic effects on Lemna gibba; however duckweed was able to remove Pb at the experimental concentrations used.

Toxicity of the herbicides bromacil and simazine to the aquatic macrophyte, Vallisneria americana Michx

Vallisneria americana Michx. (tapegrass) is an ecologically important submersed, vascular aquatic plant that provides food and shelter for many aquatic and waterfowl species. This plant often occurs close to land areas where herbicides are used. Nontarget exposure of these plants to herbicides may compromise ecological structure and function. The objective of the present study was to evaluate the suitability of several endpoint measurements for determining no-observable-adverse effect concentrations (NOAECs), lowest-observable-adverse effect concentrations (LOAECs), and median effective concentration values (EC50s) for tapegrass exposed to the herbicides bromacil (0-0.092 mg/L) and simazine (0-0.592 mg/L) following a 13-d single-pulse exposure and 15-d (bromacil) or 14-d (simazine) postexposure periods. The NOAEC/LOAEC/EC50 for fresh weight gains, new leaf production, and total leaf growth after 13-d exposure to bromacil were 0.020/0.036/0.032, 0.036/0.054/0.036, and 0.036/0.054/0.043 mg/L, respectively. The same respective NOAEC/LOAEC/EC50s for simazine were <0.058/0.058/0.067, 0.229/0.344/0.154, and 0.058/0.116/0.081 mg/L. Reductions in quantity and fresh weight of daughter plants produced and stolon fresh weights occurred at bromacil concentrations > or = 77, 0.020, and 0.036 mg/L, respectively; and simazine concentrations > or = 0.344, >0.592, and > or = 0.116 mg/L, respectively. Neither herbicide affected leaf greenness, total chlorophyll concentrations, or carbohydrate allocation. Although toxicity was shown for many endpoints, most EC50 values were greater than aquatic life benchmark values for algae used by the U.S. Environmental Protection Agency (U.S. EPA), but less than for aquatic plants, indicating that V. americana would likely be protected by use of the algal benchmark criteria.

Isotopic analysis of wetland development in the American Southwest

The analysis of stable isotope and elemental fractions of organic material collected from San Bernardino Ciénega was used to understand the history of vegetation composition and climate change within this desert wetland. A 4000-yr record of sediment buildup, based on four 14C measurements, provides unique opportunities for the study of environmental conditions within an arid landscape and documents climate shifts from drier to wetter conditions in the late Holocene. δ13C, δ15N, and C:N values were measured from a 3.8 m deep sedimentary section to understand the dynamics of vegetation and hydrology in desert wetlands. Through this section we observe δ 13C and C:N values indicating a shift in the dominant source of organic matter within the section: prior to 850 cal. yr BP (below 60 cm), aquatic vascular plants and occasionally terrestrial vegetation were the primary organic sources, whereas freshwater algae were the dominant organic matter source above this level. These values indicate that while conditions remained arid at this locality, the amount of standing water on the ciénega has increased over time. These results document both climate change and vegetation evolution on the ecotone of the Sonoran and Chihuahuan deserts and demonstrate how the study of local sediment accumulation in ciénegas can provide critical information on changing conditions within arid environments.