Water quality dynamic during rainfall episodes: integrated approach to assess diffuse pollution using automatic sampling

Biogeochemical impacts of sewage effluents in predominantly rural river catchments: Are point source inputs distinct to background diffuse pollution?

Discharge of treated sewage effluent to rivers can degrade aquatic ecosystem quality, interacting with multiple stressors in the wider catchment. In predominantly rural catchments, the river reach influence of point source effluents is unknown relative to complex background pressures. We examined water column, sediment and biofilm biogeochemical water quality parameters along river transects (200 m upstream to 1 km downstream) during summer at five wastewater treatment works (WWTW) in Scotland. Treated sewage effluent (subset, n = 3) pollutant concentrations varied between sites. Downstream concentration profiles of water and sediment biogeochemical parameters showed complex spatial changes. A hypothesised point source signature of elevated concentrations of pollution immediately downstream of WWTW then a decaying pollution 'plume' did not commonly occur. Instead, elevated soluble reactive phosphorus (SRP), ammonium and coliforms (maximum 0.23 mgP/l, 0.33 mgN/l and >2 × 106 MPN/100 ml) occurred immediately downstream of two WWTW, whereas some downstream pollutant concentrations decreased. Microbial substrate respiration responses only differed 1 km downstream. Significantly greater concentrations of sediment metal occurred >500 m downstream, likely due to the redeposition of historic contaminated sediments. Significantly lowered chlorophyll-a downstream of one WWTW coincided with elevated metals, despite water SRP and sediment P increases. Overall, stress caused to microbes and algae by effluent contaminants outweighed the subsidy effect of WWTW nutrients. We observed variable effluent flows to the rivers limited localised pollution downstream of WWTW and overall influence of arable land cover on river water quality. Together, this challenges views of consistently discharging point sources impacting low dilution sensitive rivers in summer contrasting with 'diffuse' sources. Thus, river water column and benthic compartments are altered at varying scales by point source effluents in combination with rural catchment pollution sources, both discrete (e.g. farmyards and septic tanks) and diffuse.

Dynamization of Urban Runoff Pollution and Quantity

At present, the annual loads from long-term series simulations are mostly used for the evaluation of rainwater management and treatment measures although the relevance of the temporal distribution of both pollution and quantity has a recognizable influence on the performance of the treatment. With the idea of dynamizing the simulation output values in relation to (i) single rainfall events, (ii) specific catchment characteristics, and (iii) the duration of the dry period between two rainfall events measurement devices and scenario studies were established in a joint research project in Lower Saxony. First measurement results of surface runoff qualities of an urban sub-catchment in Braunschweig/Germany are presented in a high temporal definition for several pollution parameters. A correlation analysis was performed identifying additional explanatory parameters that have an influence on the first flush effect, such as rainfall characteristics or antecedent dry period. First calculations of the possible reduction in the decentralized storm water treatment by disconnecting the first flush showed values of 42–65%, depending on the pollution parameters. The comparative evaluation of the data with different statistical methods shows that the uncertainties in the calculation of rainwater pollution, or the duration of the first flush, are still very high and do not yet allow researchers to derive a pollution forecast for, e.g., a throttle control solely from the recording of the rain and area characteristics.

Detecting pollutant sources and pathways: High-frequency automated online monitoring in a small rural French/German transborder catchment

Great temporal and spatial variability of inputs make comprehensive monitoring in small and middle sized rivers difficult. In this study, relevant inputs in a small river were recorded with suitable online monitoring equipment coupled in mobile water quality monitoring stations, the study area being a transborder catchment with French and German (Saarland federal state) subcatchments. In addition to a pronounced spatial variability necessitating a denser net of measuring points this catchment has also to be assessed in the light of different national regulations. To identify individual pollution sources and weigh their relative importance, relevant parameters were recorded over a representative monitoring period of several months: phosphorus (P) as total phosphorus (TP) and total reactive P phosphorus (TRP), nitrate (NO₃-N), ammonium (NH₄-N), total organic carbon (TOC), temperature, oxygen (O₂), pH, turbidity, and electrical conductivity (EC). The recorded data were subjected to adapted interpretation together with other catchment-related factors. In order to retrieve maximum information from the online data sets the relationships among certain parameter pairs were also analysed for both storm events and low flow periods. Comparison of loads at the different monitoring sites could reliably verify the majority of nutrient inputs originating in the French subcatchment. Additional sampling of output channels from sewage treatment works (STWs) in the Saarland subcatchment revealed that inputs from several decentralised STWs do not result in significant loads, as opposed to inputs from one STW in France. Our holistic approach provides a basis for adopting cost-effective measures to reduce loads in small river catchments as well as cross-border harmonisation of environmental policies.

Adaptive monitoring approach to assess dissolved organic matter dynamics during rainfall events

Rainfall events induce water quality transformation in river systems influenced by the watershed land use and hydrology dynamics. In this context, an adaptive monitoring approach (AMA) is used to assess non-point sources (NPS) of pollution events, through dissolved organic matter (DOM) contribution. The case study is a monitoring site in a semi-urban watershed characterized by NPS contribution. An integrated quali-quantitative method for DOM based on dissolved organic carbon (DOC) content, spectroscopic techniques of excitation-emission fluorescence (EEF), and UV-visible absorbance is proposed. The results indicate a mix of allochthonous and autochthonous DOM characteristics from NPS sources associated to vegetation area influence (A₂₈₅/DOC of 15.43 L (g cm)^-1 and SUVA₂₅₄ of 2.11 L (mg m)^-1). The EEF signals showed more humic-like than protein-like characteristics with peaks A and C (approximately 5.72 r.u.) more intense than peaks B, T₁, and T₂ (approximately 4.33 r.u.), indicating NPS from the soil leachate. The absorbance ratio values indicate a mix of organic compounds with greater proportion of refractory characteristics with high aromaticity and molecular weight (approximately A₃₀₀/A₄₀₀ of 4.15 and A₂₅₀/A₃₆₅ of 4.48), associated with the surface wash-off of accumulated residual and subsurface soil erosion, which contribute to complex organic matter structures. The fluorescence indexes, overall, indicated allochthonous sources with intermediate humic characteristics (FI ≈ 1.43, BIX ≈ 0.65, and HIX ≈ 7.98). The proposed integrated optical property strategy represents an opportunity for better understanding of DOM dynamic assessment for identifying potential mitigation techniques for organic pollution control and improving water quality conditions.

Strong Precipitation and Human Activity Spur Rapid Nitrate Deposition in Estuarine Delta: Multi-Isotope and Auxiliary Data Evidence

The intensive development of the Yellow River Delta has caused huge transportation of non-point pollutants into the Bohai Sea through source river estuaries and thus poses a considerable threat to eco-environmental security in the region. Long-term irrigation in the Yellow River basin, with occasional heavy rainfall and the related effects of ensuring hydrological processes and human activities in terms of nitrate N transport via surface water systems, is unclear. Using stable isotope (δ2H-H2O and δ18O-H2O, δ15N-NO3− and δ18O-NO3−) and auxiliary geographic data, the ISO source model was run to quantitatively analyze the supply relationship of river systems and the rapid change in the spatial pattern of nitrate N due to heavy rainfall in the estuarine delta. This analysis made clear the dominant contribution of agricultural activities and urbanization to NO3−-N emission, on which basis refined management measures were proposed to deal with NO3− in surface water from the “source-process”. The results of the study show that: (1) The relationship of surface water replenishment in the Yellow River Delta was affected not only by rainfall, irrigation, and other water conservancy measures but also the proportion of water from Yellow River flow declined from the source to estuary; (2) To a certain extent, rainfall diluted the concentration of nitrate N in the river and increased instantaneous flux of nitrate N into the sea, where nitrate N flux continuously increased from upstream to downstream; (3) The rapid deposition of nitrate in the estuary delta was driven by heavy rainfall and human activities such as excessive use of nitrogen fertilizers, rapid urbanization, and livestock waste discharge, and; (4) Scientific measures were needed to realize the interactive effect of the output of non-point source pollutants and the carrying and absorption capacity of coastal fragile ecosystems of the exogenous inputs.

Assessment of Automatically Monitored Water Levels and Water Quality Indicators in Rivers with Different Hydromorphological Conditions and Pollution Levels in Greece

Water resources, especially riverine ecosystems, are globally under qualitative and quantitative degradation due to human-imposed pressures. High-temporal-resolution data obtained from automatic stations can provide insights into the processes that link catchment hydrology and streamwater chemistry. The scope of this paper was to investigate the statistical behavior of high-frequency measurements at sites with known hydromorphological and pollution pressures. For this purpose, hourly time series of water levels and key water quality indicators (temperature, electric conductivity, and dissolved oxygen concentrations) collected from four automatic monitoring stations under different hydromorphological conditions and pollution pressures were statistically elaborated. Based on the results, the hydromorphological conditions and pollution pressures of each station were confirmed to be reflected in the results of the statistical analysis performed. It was proven that the comparative use of the statistics and patterns of the water level and quality high-frequency time series could be used in the interpretation of the current site status as well as allowing the detection of possible changes. This approach can be used as a tool for the definition of thresholds, and will contribute to the design of management and restoration measures for the most impacted areas.

Development of an autonomous flow-proportional water sampler for the estimation of pollutant loads in urban runoff

Implementation of an extensive urban runoff monitoring program, targeting the quantification of heavy metal and organic micropollutant loads, necessitated the development of an autonomous water sampler. The design requirements for the device were to fulfill flow-proportional continuous composite sampling of urban runoff events in a widely customizable, relatively inexpensive, and simple way. In this paper, we introduce the concept along with the experiences gained from the first several months of field tests at seven pilot areas in Hungary that represent a wide range of urban environments. During the test period, prototype samplers were placed in natural (urban) streams as well as stormwater drainage pipes, resulting in a total of 97 automatic composite runoff samples. At two sites, an additional 28 manual grab samples were collected to represent time series from five distinct runoff events. Sampling efficiency was checked by comparing collected volumes with the theoretical ones (derived from pump mileage data). Ranges and ratios of concentrations measured from composite and grab samples were graphically interpreted in order to evaluate their representativeness. It has been shown that the concept is suitable for conducting cost-effective urban runoff characterization surveys targeting inter-event variability.

Extreme Hydro-Meteorological Events Influence to Water Quality of Small Rivers in Urban Area: A Case Study in Northeast Poland

This paper presents an impact of hydro-meteorological extreme events and urban catchment to water quality in small rivers in Białystok (Poland). The results from a five-year study have taken into account droughts, continuous precipitation, and storm precipitation causing flash floods. Extreme hydro-meteorological events has a different impact on the physical and chemical parameters of water. It was found that the largest change in water quality occurs on the 2nd day after the rainfall and changed concentration of some chemical parameters persists for a long time. The majority but, what’s important, not all of them are diluted after floods and concentrated after droughts. Flash flooding results in a large increase concentrations of DOC and selected forms of phosphorus. Higher values of EC, Eh, Mg²⁺, HCO₃^-, Cl^-, SiO₃^2-, NO₃^-N, TN were observed during drought compared to the average values from 2014–2018. A high degree of naturalness of the river valley and increased water retention results in a decreased concentration of NH₄⁺-N, DOC and phosphorus forms. The buffer zone plays an important role in limiting the inflow of pollutants and nutrients from the catchment area. That is why it is worth undertaking restoration of river valleys in urban areas.

Appraising drinking water quality in Ikem rural area (Nigeria) based on chemometrics and multiple indexical methods

The continuous deterioration of drinking water quality supplies by several anthropogenic activities is a serious global challenge in recent times. In this current study, the drinking water quality of Ikem rural agricultural area (southeastern Nigeria) was assessed using chemometrics and multiple indexical methods. Twenty-five groundwater samples were collected from hand-dug wells and analyzed for physicochemical parameters such as pH, major ions, and heavy metals. The pH of the samples (which ranged between 5.2 and 6.7) indicated that waters were slightly acidic. Cations and anions (except for phosphate) were within their respective standard limits. Except for Mn, heavy metals were also found to be below their maximum allowable limits. Factor analysis identified both geogenic processes and anthropogenic inputs as possible origins of the analyzed physicochemical parameters. Modified heavy metal index, geoaccumulation index, and overall index of pollution revealed that all the hand-dug wells were in excellent condition, and hence safe for drinking purposes. However, pollution load index, water quality index (WQI), and entropy-weighted water quality index (EWQI) revealed that some wells (about 8-12%) were slightly contaminated, and hence are placed in good water category. A hierarchical cluster analysis (HCA) was performed based on the integration of the WQI and EWQI results. The HCA revealed two major quality categories of the samples. While the first cluster comprises of samples classified as excellent drinking water by both WQI and EWQI models, the second cluster comprises of about 12% samples which were identified as good water by either the WQI or EWQI.