Wastewater treatment plant effluent inputs influence the temporal variability of nutrient uptake in an intermittent stream

Wastewater treatment plant (WWTP) effluents alter water chemistry and in-stream nutrient uptake rates of receiving freshwaters, thus changing the magnitude and fate of the nutrients exported. In Mediterranean regions, the dilution capacity of receiving streams can vary strongly over time due to the seasonal occurrence of floods and droughts, causing temporal variability of nutrient uptake. We assessed the temporal patterns and the controlling factors of net nutrient uptake in an intermittent Mediterranean stream receiving WWTP effluent inputs. We compiled the longitudinal concentration profiles of ambient dissolved inorganic nitrogen (DIN) and soluble reactive phosphorus (SRP) along a 800 m reach on 47 sampling dates between 2001 and 2017, encompassing a wide range of hydrological conditions. We estimated net nutrient uptake in the receiving stream. In 72% of the dates, high rates of net ammonium uptake co-occurred with net releases of either nitrate or nitrite. This pattern suggests that the receiving stream has a high nitrification capacity. Conversely, 75% of the dates did not show any longitudinal pattern in SRP concentration, suggesting that uptake and release processes for this element were either counterbalanced or both occurred at very low rates. Finally, net ammonium uptake was low when the stream had a low dilution capacity (< 40%) and ammonium concentration was high. Overall, we demonstrate that consideration of the receiving stream’s dilution capacity is imperative to the management of freshwaters to guarantee an adequate dilution of WWTP effluent inputs and avoid saturation of in-stream nutrient uptake capacity under low flow conditions in urban landscapes

Influence of Microplastics on Microbial Structure, Function, and Mechanical Properties of Stream Periphyton

Periphyton is a freshwater biofilm composed of prokaryotic and eukaryotic communities that occupy rocks and sediments, forming the base of the food web and playing a key role in nutrient cycling. Given the large surface that periphyton comprises, it may also act as a sink for a diverse range of man-made pollutants, including microplastics (MP). Here we investigated the effect of 1-4 mu m and 63-75 mu m sized, spherical polyethylene MP with native and ultraviolet (UV)-weathered surface on developing natural stream periphyton communities over 28 days. In order to ensure proper particle exposure, we first tested MP suspension in water or in water containing either Tween 80, extracellular polymeric substances - EPS, fulvic acids, or protein. We found the extract of EPS from natural periphyton to be most suitable to create MP suspensions in preparation of exposure. Upon exposure, all tested types of MP were found to be associated with the periphyton, independent of their size and other properties. While biomass accrual and phenotypic community structure of the photoautotrophs remained unchanged, the prokaryotic and eukaryotic communities experienced a significant change in composition and relative abundances. Moreover, alpha diversity was affected in eukaryotes, but not in prokaryotes. The observed changes were more prominent in periphyton exposed to UV-treated as compared with native surface MP. Mechanical properties, as assessed by compression rheology, showed that MP-exposed periphyton had longer filamentous streamers, higher stiffness, lower force recovery and a higher viscoelasticity than control periphyton. Despite the observed structural and mechanical changes of periphyton, functional parameters (i.e., photosynthetic yield, respiration and nutrient uptake efficiencies) were not altered by MP, indicating the absence of MP toxicity, and suggesting functional redundancy in the communities. Together, our results provide further proof that periphyton is a sink for MP and demonstrate that MP can impact local microbial community composition and mechanical properties of the biofilms. Consequences of these findings might be a change in dislodgement behavior of periphyton, a propagation through the food chains and impacts on nutrient cycling and energy transfer. Hence, taking the omnipresence, high persistence and material and size diversity of MP in the aquatic environment into account, their ecological consequences need further investigation

Differences in ammonium oxidizer abundance and N uptake capacity between epilithic and epipsammic biofilms in an urban stream

The capacity of stream biofilms to transform and assimilate N in highly N-loaded streams is essential to guarantee the water quality of freshwater resources in urbanized areas. However, the degree of N saturation experienced by urban streams and their response to acute increases in N concentration are largely unknown. We measured changes in the rates of NH4+ uptake (UNH4) and oxidation (UAO) resulting from experimental increases in NH4+-N concentration in mature biofilms growing downstream of a wastewater treatment plant (WWTP) and, thus, naturally exposed to high N concentration. We investigated the responses of UNH4 and UAO to NH4+-N increases and the abundance of NH4+ oxidizing bacteria and archaea (AOB and AOA) in epilithic and epipsammic biofilms. UNH4 and UAO increased with increasing NH4+-N concentration for the 2 biofilm types, suggesting no N saturation under ambient levels of NH4+-N. Thus, these biofilms can contribute to mitigating N excesses and the variability of NH4+-N concentrations from WWTP effluent inputs. The 2 biofilm types exhibited different Michaelis-Menten kinetics, indicating different capacity to respond to acute increases in NH4+-N concentration. Mean UNH4 and UAO were 5× higher in epilithic than epipsammic biofilms, coinciding with a higher abundance of AOA+AOB in the former than in the later (76 × 104 vs 14 × 104 copies/cm2). AOB derived from active sludge dominated in epilithic biofilms, so our results suggest that WWTP effluents can strongly influence in-stream NH4+ processing rates by increasing N inputs and by supplying AOA+AOB that are able to colonize some stream habitat

Fate and effects of microplastic particles in a periphyton-grazer system

In the aquatic environment, microplastic particles (MP) can accumulate in microbial communities that cover submerged substrata, i.e. in periphyton. Despite periphyton being the essential food source for grazers in the benthic zones, MP transfer from periphyton to benthic biota and its ecotoxicological consequences are unknown. Therefore, in this study, we investigated the effects of 1) MP on embryonal development of freshwater gastropod Physa acuta embryos, 2) MP on adult Physa acuta individuals through dietary exposure and 3) on the MP surface properties. Embryonal development tests were carried out with spherical polyethylene MP in the size of 1–4 μm (MP). Over a period of 28 days, embryonal development and hatching rate were calculated. In the feeding experiments, periphyton was grown in the presence and absence of MP and was then offered to the adult Physa acuta for 42–152 h. The snails readily ingested and subsequently egested MP, together with the periphyton as shown by MP quantification in periphyton, snail soft body tissue and feces. No selective feeding behavior upon MP exposure was detected. The ingestion of MP had no effect on mortality, feeding and defecation rate. Yet, the reproductive output of snails, measured as the number of egg clutches and numbers of eggs per clutch, decreased after the ingestion of MPs, while the hatching success of snail embryos those parents were exposed remained unaffected. In contrast, hatching rate of snail embryos was significantly reduced upon direct MP exposure. MP optical properties were changed upon the incorporation into the periphyton and the passage through the digestive tract. Our results indicate that MP incorporated in periphyton are bioavailable to aquatic grazers, facilitating the introduction of MP into the food chain and having direct adverse effects on the grazers’ reproductive fitness.ISSN:0269-7491ISSN:1878-2450ISSN:1873-642