Connectivity of stormwater ponds impacts Odonata abundance and species richness.

Context: The successful dispersal of an animal depends, partly, on landscape connectivity. Urbanization poses risks to dispersal activities by increasing hostile land cover types. Objectives: We investigated how connectivity of urban ponds impacted Odonata communities (dragonflies and damselflies), an order of semi-aquatic insects that actively disperse. Methods: We sampled 41 constructed stormwater ponds and 8 natural ponds in a metropolitan area. The effect of connectivity and the quantity of available adjacent habitats was tested at different scales for dragonflies (900 m) and damselflies (300 m), determined by a literature analysis, to account for differences in suborder dispersal capabilities. Results: Lower levels of connectivity and fewer nearest neighbours negatively impacted abundance, species richness, and composition of dragonflies (p values < 0.01, R2 = 0.18-0.70). Adult dragonfly abundance had a stronger positive relationship with connectivity than species richness. In particular, the abundance of adult dragonfly Leucorrhinia frigida, found almost exclusively at natural ponds, had a positive relationship with connectivity. Connectivity and the number of nearest neighbours had no significant impact on damselflies apart from a slight negative relationship between connectivity and species richness (p value = 0.02, R2 = 0.11). Natural ponds had significantly higher levels of connectivity when compared to stormwater ponds. Conclusions: Our results suggest that dragonflies are positively affected by increased connectivity in an urban landscape, with no benefit of connectivity to damselflies at the scale measured. We recommend intentional planning of urban stormwater pond networks, where individual ponds can act as stepping stones, incorporated with strategic inclusion of beneficial land cover types. Supplementary Information: The online version contains supplementary material available at 10.1007/s10980-024-01817-z.

Macrophytes are highly sensitive to the herbicide diquat dibromide in test systems of varying complexity.

The herbicide diquat dibromide is used in North America to manage nuisance macrophytes. However, its effect on native macrophytes is less clear and it could cause indirect effects on other aquatic biota. This study determined the sensitivity of both native and non-native macrophytes grown in test systems with varying complexity to diquat dibromide applied directly to water following label directions. In an outdoor mesocosm experiment and single species greenhouse concentration-response tests, Elodea canadensis Michx., Myriophyllum spicatum L., Ceratophyllum demersum L. and Hydrocharis morsus-ranae L. were exposed to a range of diquat dibromide concentrations (4.7 - 1153 µg/L), corresponding to 0.4 - 100% of the recommended label rate of the formulated product. The mesocosm experiment contained all four plant taxa in the same system along with caged amphipods (Hyalella azteca Saus.), tadpoles (Lithobates pipiens Schreber), phytoplankton and periphyton; however, this study focuses on the macrophytes only. In both test systems, severe direct effects of diquat dibromide on macrophytes were detected, with almost 100% mortality of all macrophytes in both test systems at 74 µg/L. The most sensitive species in the single species tests, E. canadensis, showed almost 100% mortality at concentrations below the HPLC-based method detection limit of 5 µg/L. Effects occurred very rapidly and showed no difference in severity between native and non-native macrophytes or complexity of test systems. These results suggest that diquat dibromide could be applied at a considerably lower label rate, depending on the characteristics of the waterbody, while still achieving effective control of nuisance macrophytes.

Sulfide production kinetics and model of stormwater retention ponds.

Stormwater retention ponds can play a critical role in mitigating the detrimental effects of urbanization on receiving waters that result from increases in polluted runoff. However, the benthic oxygen demand of stormwater facilities may cause significant hypoxia and trigger the production of hydrogen sulfide (H2S). This process is not well-documented and further research is needed to characterize benthic processes in stormwater retention ponds in order to improve their design and operation. In this study, sediment oxygen demand (SOD), sediment ammonia release (SAR) and sediment sulfide production (SSP) kinetics were characterized in situ and in the laboratory. In situ SOD and SSP data were utilized to develop a stormwater retention pond water sulfide concentration model which demonstrates strong correlation with sulfide concentrations observed in situ (r = 0.724, N = 91, p < 0.001) and in laboratory experiments (r = 0.691, N = 38, p < 0.001). At 4 °C, in situ rates of SOD, SAR and SSP were higher than those measured in laboratory. Sulfate-reducing bacteria (SRB) represented 4.99% of the bacteria present in the top 30 cm of the pond sediment, with Desulfobulbaceae spp., Desulfobacteraceae spp. and Desulfococcus spp. being the dominant SRB taxa identified.

Reconstructing a long-term record of microcystins from the analysis of lake sediments.

Based on an analysis of sediment cores from Baptiste Lake (Alberta, Canada), we quantified century-scale trends in cyanobacteria and cyanotoxins, and identified possible drivers of toxigenic cyanobacteria. We measured concentrations of microcystins and pigments preserved in the sediment as proxies of toxigenic cyanobacteria and phytoplankton communities, respectively, while fossil diatom assemblages were used to infer past nutrient concentrations. Microcystins were detected in older sediments (ca. 1800s), pre-dating any significant alteration to the watershed. This demonstrates that toxigenic cyanobacteria may not be a recent phenomenon in eutrophic ecosystems. The dominant variants of microcystin throughout the sediment core were microcystin-LA and microcystin-LR. Other congeners including -LY, -7dmLR, -WR, -LF, -YR, and -LW (-RR was not detected) were mainly found in the upper layers of sediment (post 1980s). Starting in the 1990s, concentrations of microcystins both in the water column and in the sediment record increased in parallel. Total sediment microcystins were strongly correlated with historical nitrogen and phosphorus concentrations inferred from diatom assemblages (r=0.80-0.81, p<0.001, n=22); both nutrients increased over the past two decades coincident with the intensification of agriculture. Microcystins also tracked the rise in cyanobacterial pigments present throughout the core. In contrast, we found no relationship between climate-related variables and sediment microcystin concentrations, although such relationships were detected over the monitoring record with respect to water column concentrations. Overall, the rise in sediment microcystins was much greater than the rise in sediment cyanobacteria and diatom inferred nutrient concentrations. Furthermore, we demonstrate that the reconstruction of the microcystin sediment record can provide important insight for the development of realistic lake management goals. Applying this analytical approach to different lakes and regions of the world, where both natural and anthropogenic gradients vary, has the potential to markedly improve our understanding of long-term drivers of cyanotoxin production.

The evaluation of metal retention by a constructed wetland using the pulmonate gastropod Helisoma trivolvis (Say).

Constructed wetlands are built because they can act as sinks for many pollutants, thereby protecting the water quality of downstream ecosystems. The treatment performance is generally assessed using mass balance calculations. Along with the mass balance approach, we compared the metal content of populations of a common pond snail (Helisoma trivolvis Say) collected upstream and downstream of a 3-year-old constructed wetland. Snails were collected in early May, June, and August 1998. At the same time, water samples for particulate and dissolved metals were taken every 3 days for the duration of the experiment. Overall, the wetland retained most dissolved metals, including Fe, Mn, Cu, Zn, Ni, and Pb, but released dissolved As. However, the wetland released particulate Fe and Mn. With the exception of Zn, the metal concentrations of the downstream snails were on average higher than those measured in the upstream population. The higher metal content of downstream snails was likely related to the significant export of particulate metals by the wetland, despite the overall retention of dissolved metals. This study points to the need for biological as well as chemical monitoring to determine the treatment efficiency and toxicological risk associated with constructed wetlands.

Diel changes in iron concentrations in surface-flow constructed wetlands.

Diel changes in Fe concentrations were examined from spring to late fall at two surface-flow wetlands. The highest concentrations of ferrous, dissolved and total Fe were measured at night in the littoral zone, when oxygen and pH were low. The lowest Fe concentrations were measured during the day when oxygen and pH were highest. The amplitude of change over the day-night cycle was greatest in July and lowest in May and October. These diel changes were also observed at the outlet of both wetlands. Overall O2 and pH explained 60% of the observed seasonal and diel variation in water Fe (R2 = 0.60, p = 0.004). The treatment performance of wetlands can be overestimated when based on samples collected during the day.

The accumulation of cadmium by the yellow pond lily, Nuphar variegatum, in Ontario peatlands.

Cadmium concentrations of a common macrophyte, the yellowpond lily (Nuphar variegatum) were investigated from peatlands with arange in pH (4.4-6.3), alkalinity (0-181 microeq/L Ca), DOC (5.1-16.8 mg/L), and sediment organic content (20-88%). Cd concentrations inNuphar ranged from 0.3 to 1.51 microg/g in the leaves and from 0.46 to1.51 microg/g in the petioles, and was significantly higher in the petiolesthan in the leaves (p = 0.014; t-Test). Significant and negativecorrelations between Nuphar leaf Cd and pH (r2 =0.76; p < 0. 001), alkalinity (r2 = 0.41; p =0.034), and DOC (r2 = 0.46; p = 0. 022) wereobtained. In addition, a significant and negative correlation was foundbetween Nuphar petiole Cd and pH (r2 = 0.46; p= 0.023). These results indicate that the leaves of Nupharfound in peatlands of low pH, low alkalinity, and low DOC, and the petiolesof Nuphar found in peatlands of low pH are more susceptible toaccumulating potentially toxic levels of Cd. The organic content of thepeatland sediments was not significantly correlated with either the leaf orpetiole Cd concentration. Nuphar is an important food source for manywetland animals; any Cd that is present in these plants may be passed ontoother trophic levels because diet is considered to be the major source of Cdto animals.