Synthetic Microfiber Material Influences Ingestion by Freshwater Worms.

Plastics enter the environment, amongst others, from synthetic textiles, which shed microplastic fibers (microfibers) during their production, use and disposal. We tested whether short- and long-term effects of microfibers on the aquatic worm, Lumbriculus variegatus, depend on the synthetic microfiber material. Microcosms containing L. variegatus were exposed to no microfibers (control) or one of three polymer treatments (nylon, polyester, or olefin) at 5 g of microfibers kg-1 of sediment for 48 h or 28 days. Following exposure, L. variegatus were counted, weighed, and the number of microfibers ingested determined. Polyester microfibers occurred in higher quantities (10-12) than nylon and olefin (< one) per individual after 48 h and 28 days. Only the olefin per individual doubled after 28 days compared to 48 h. These findings indicate that polyester microfibers are more likely to affect L. variegatus and have greater potential to be ingested by higher trophic levels than other polymers.

The Effects of an Herbicide and Antibiotic Mixture on Aquatic Primary Producers and Grazers.

Widespread use of agrochemicals increases their likelihood of entering aquatic systems in mixture. Despite different modes of action, atrazine (herbicide) and tetracycline (antibiotic) adversely affect non-target photosynthetic organisms individually, but the effects of simultaneous exposure to both contaminants are untested. We created microcosms containing microalgae (Chlorella sp.), floating macrophytes (Lemna minor), and a zooplankton grazer (Daphnia magna). Microcosms were exposed to environmentally relevant concentrations of atrazine and tetracycline, alone and together, for 10 days. Atrazine decreased Chlorella sp. abundance, but not enough to reduce food availability to D. magna whose reproduction and mortality were unaffected. In contrast, tetracycline and atrazine appeared to have additive effects on L. minor abundance and growth inhibition. These additive adverse effects suggest increased potential for L. minor population decline over the long term, and potential for altered species interactions in aquatic systems receiving agricultural runoff.

Alkyl polyglucoside compound influences freshwater plankton community structure in floating field mesocosms.

Synthetic surfactants in cleaners and detergents commonly contaminate freshwater systems, therefore use of low-toxicity alternatives is becoming increasingly important. Alkyl polyglucosides (APGs) derived from natural products are less toxic than synthetic surfactants, and degrade rapidly reducing chemical exposure time. However, single species toxicity tests showed APGs have toxic effects on aquatic primary producers and zooplankton, and that species demonstrate different sensitivities to APGs. Furthermore, species unaffected by APGs directly may be indirectly affected by removal of a food source or changes in predator densities, thereby changing plankton community structure. To determine the effects of APGs on plankton communities under environmental conditions, floating mesocosms were deployed in a shallow pond in southeast Georgia, USA and dosed with 0, 0.01, 2.5, 5, or 10 mg L-1 APG. Zooplankton community composition and abundance, phytoplankton abundance (as chlorophyll a), and water column dissolved oxygen concentration were determined weekly for 1 month. Zooplankton abundance decreased primarily due to loss of copepods, and community composition shifted toward small-bodied cladocerans (Bosmina sp.), and chlorophyll a concentrations declined by up to 81 % following exposure to APG concentrations of 2.5 mg L-1 or greater. Concentrations of dissolved oxygen never dropped below 5.70 mg L-1, but the observed declines of ~2 mg L-1 could become stressful during periods of high water temperatures. Nevertheless, the APG-induced shift from copepod to cladoceran dominated communities and decrease in autochthonous carbon availability has important implications for food availability and quality to higher trophic levels such as planktivorous fishes.

Using opportunistic green macroalgae as indicators of nitrogen supply and sources to estuaries.

Nutrient inputs to estuaries are increasing worldwide, and anthropogenic contributions are increasingly complex and difficult to distinguish. Measurement of integrated effects of salinity and nutrient changes simultaneously can help ascertain whether N sources of similar magnitude and stable isotope (sigma15N) signatures are river dominated. We used Enteromorpha spp., an opportunistic macroalga, to obtain integrated measures of salinity, nutrient supply, and nutrient source in estuaries. We outplanted cultured algae in the field along spatial gradients within three southern California estuaries for 24 hours in wet and dry seasons. Tissue was analyzed for potassium (K+) to measure osmoregulatory changes, total nitrogen to examine changes in nutrient supply, and sigma15N to assess nutrient sources. Discrete measures of water salinity correlated with tissue K+ content; however, there was significant variability in the relationship, suggesting that the algae were subject to considerable variation in salinity over a tidal cycle. Tissue total N was not always related to snapshot measures of water column dissolved inorganic nitrogen (DIN), suggesting that integrated measures may be better at capturing the temporal and spatial complexity of nutrient availability. The combination of tissue K+, total N, and sigma15N measures revealed that inflowing rivers delivered N from watershed sources to Mugu Lagoon and Carpinteria Salt Marsh, while both the inflowing river and a mid estuary source were important sources of high sigma15N N in Upper Newport Bay. These experiments revealed complex patterns of supply and sources of N and demonstrate the usefulness of macroalgal indicators over water sampling to detect these patterns.

A simple, inexpensive, and field-relevant microcosm tidal simulator for use in marsh macrophyte studies.

PREMISE OF THE STUDY: A microcosm unit with tidal simulation was developed to address the challenge of maintaining ecologically relevant tidal regimes while performing controlled greenhouse experiments on smooth cordgrass, Spartina alterniflora. • METHODS AND RESULTS: We designed a simple, inexpensive, easily replicated microcosm unit with tidal simulation and tested whether S. alterniflora growth in microcosms with tidal simulation was similar to that of tidally influenced plants in the field on Sapelo Island, Georgia. After three months of exposure to either natural or simulated tidal treatment, plants in microcosms receiving tidal simulation had similar stem density, height, and above- and belowground biomass to plants in field plots. • CONCLUSIONS: The tidal simulator developed may provide an inexpensive, effective method for conducting studies on S. alterniflora and other tidally influenced plants in controlled settings to be used not only to complement field studies, but also in locations without coastal access.