Pharmaceutical and personal care products are ubiquitous in surface waters but their effects on aquatic biofilms and associated ecosystem properties are not well understood. We measured in situ responses of stream biofilms to six common pharmaceutical compounds (caffeine, cimetidine, ciprofloxacin, diphenhydramine, metformin, ranitidine, and a mixture of each) by deploying pharmaceutical-diffusing substrates in streams in Indiana, Maryland, and New York. Results were consistent across seasons and geographic locations. On average, algal biomass was suppressed by 22%, 4%, 22%, and 18% relative to controls by caffeine, ciprofloxacin, diphenhydramine, and the mixed treatment, respectively. Biofilm respiration was significantly suppressed by caffeine (53%), cimetidine (51%), ciprofloxacin (91%), diphenhydramine (63%), and the mixed treatment (40%). In autumn in New York, photosynthesis was also significantly suppressed by diphenhydramine (99%) and the mixed treatment (88%). Pyrosequencing of 16S rRNA genes was used to examine the effects of caffeine and diphenhydramine on biofilm bacterial community composition at the three sites. Relative to the controls, diphenhydramine exposure significantly altered bacterial community composition and resulted in significant relative increases in Pseudomonas sp. and decreases in Flavobacterium sp. in all three streams. These ubiquitous pharmaceuticals, alone or in combination, influenced stream biofilms, which could have consequences for higher trophic levels and important ecosystem processes.
Catchment nutrient export, especially during high flow events, can influence ecological processes in receiving waters by altering nitrogen (N) and phosphorus (P) concentrations and relative amounts (stoichiometry). Event-scale N and P export dynamics may be significantly altered by land use/land cover (LULC) and season. Consequently, to manage water resources, it is important to understand how LULC and season interact to influence event N and P export. In situ, high-frequency spectrophotometers allowed us to continuously and concurrently monitor nitrate (NO 3 −) and soluble reactive P (SRP) concentrations and therefore examine event-scale NO 3 − and SRP export dynamics. Here we analyzed event NO 3 − and SRP concentration-discharge hysteresis patterns and yields for >400 events to evaluate how LULC and seasonality influence event NO 3 − and SRP export dynamics in three low-order watersheds with different primary LULCs (agricultural, forested, and urban). Differences among event NO 3 − and SRP hysteresis patterns suggest these nutrients have different source areas and dominant transport pathways that were impacted by both LULC and seasonality. Unexpectedly, we observed similar seasonal patterns in event NO 3 − :SRP stoichiometry among LULCs, with the most N-enriched events occurring in spring, and event stoichiometry approaching Redfield N:P ratios in the fall. However, seasonal stoichiometry patterns were driven by unique seasonal NO 3 − and SRP export patterns at each site. Overall these findings suggest LULC and seasonality interact to alter the timing and magnitude of event NO 3 − and SRP exports, leading to seasonal patterns in event NO 3 − to SRP stoichiometry that may influence ecological processes, such as productivity, in receiving waters. Plain Language Summary High flow events transport relatively large quantities of nitrogen (N) and phosphorus (P) to streams and downstream waterbodies where they may stimulate algal blooms and degrade water quality. We evaluated how land uses and seasons alter event nutrient transport. We monitored >400 events with sensors in streams with contrasting land uses. Event N and P concentration patterns differed from each other suggesting dissolved N and P were transported from different locations in the landscape. Further, the agricultural and urban streams received more dissolved N and P than the forested stream. This likely results from fertilizer applications in excess of crop (agricultural and lawn grass) needs and landscape modifications, such as drainage systems and impervious surfaces, that limit soils and vegetation from removing nutrients from runoff. Lastly, season influenced the ratio of dissolved N to P delivery, with spring events transporting the most N relative to P and fall events transporting the least. Overall, land use and season uniquely influenced event nutrient transport. Management strategies to reduce algal blooms in downstream waterbodies must consider interactions among land use, nutrient type, and season. However, ratios of N to P may change seasona...
Several recent reports document increasing concentrations of chloride in surface waters of northeastern and midwestern North America. These patterns, together with high summertime baseflow concentrations, suggest the possibility of short-term retention of winter-applied chloride within catchments. This study examined the potential of groundwater and soils to act as reservoirs of Cl within the watershed of a small rural stream in New York that has shown a doubling of Cl over the past two decades and almost constant concentrations across seasons. Groundwater samples were obtained from 20 private drinking wells distributed around the catchment to determine whether concentrations were at or greater than surface waters and so could act as a source to the stream. In 16 of the 20 wells, chloride concentrations were lower (mean of 16 samples=4.10 mg Cl/L (standard deviation=4.8)) than concurrent streamwater concentrations (mean of eight locations sampled on two dates=28.9 (5.8)). Four wells, however, showed higher concentrations ranging from 35 to 230 mg Cl/L suggesting either point source contamination or very heterogeneous groundwater chloride sources. Soil cores from the catchment were irrigated in the laboratory with a NaCl solution for 2 weeks followed by 2 weeks irrigation with a chloride-free solution. Chloride concentrations in core leachates were lower than in the irrigation solution during the first 2 weeks indicating some retention of Cl within the cores. After cores were irrigated with chloride-free water, leachate concentrations declined but would not reach streamwater concentrations until the equivalent of 15 cm of precipitation was added to the core.
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