Surface Water Quality Processes and Contaminated Sediment Assessment

Surface water quality is governed by a complex interplay of hydrological, chemical and biological processes. At the basin scale, inputs from point sources—such as industrial discharges and treated effluents—and diffuse sources—agricultural runoff, urban stormwater and atmospheric deposition—deliver nutrients, suspended solids and trace contaminants to rivers, lakes and coastal lagoons. Once introduced, pollutants undergo transport by advection and dispersion, partitioning between dissolved, colloidal and particle-bound phases. Sedimentation processes deposit particulate-bound contaminants in benthic zones, where redox conditions, pH fluctuations and microbial activity can promote release or further sequestration. Dissolved nutrients such as nitrate and phosphate fuel primary production, while organic matter degradation drives oxygen demand and influences metal speciation through the formation of sulphide and iron–manganese minerals. Contaminated sediment assessment thus encompasses sampling and characterisation of bottom deposits, sequential fractionation of metals and phosphorus, sorption isotherms to evaluate binding capacity, and benthic flux studies to quantify internal loading. Multivariate statistical tools reveal pollutant sources and temporal trends, while geochemical tracers and isotopic analyses distinguish natural background levels from anthropogenic enrichment. Insight into these processes underpins monitoring network design, early-warning systems for eutrophication and the development of remediation strategies such as dredging, capping or in situ stabilisation.

Research from Nature Portfolio

Water quality assessment based on multivariate statistics and water quality index of a strategic river in the Brazilian Atlantic Forest has demonstrated how forty years of monitoring data can optimise sampling networks and reveal dominant pollution drivers. Principal component analysis identified untreated sewage as the primary factor affecting water quality, while cluster analysis distinguished station groupings reflecting distinct contaminant inputs. By coupling a national index with georeferenced data, the study pinpointed under-monitored river stretches and supported recommendations for targeted network expansion.

Organic pollution of rivers: Combined threats of urbanisation, livestock farming and global climate change quantified organic river pollution at the global scale using biochemical oxygen demand (BOD) as an indicator. Modelling historical and future BOD concentrations revealed that, despite natural self-purification, the number of people exposed to high organic loads (BOD > 5 mg l⁻¹) is projected to rise from 1.1 billion in 2000 to 2.5 billion by 2050. The analysis highlighted how intensified wastewater discharge and reduced dilution capacity jointly drive declines in water quality, underscoring the urgent need for affordable sanitation solutions in developing regions.

Surface Water Quality Processes and Contaminated Sediment Assessment publication trend

The graph below shows the total number of articles in surface water quality processes and contaminated sediment assessment across all publications each year (not limited to Nature Index journals).

Technical terms

Advection: The transport of dissolved or particulate substances by the bulk motion of flowing water.

Sorption isotherm: A relationship describing the partitioning of a contaminant between water and sediment surfaces at equilibrium, often represented by Langmuir or Freundlich models.

Internal loading: The release of nutrients or metals from oxygen-depleted sediments into the overlying water under reducing conditions.

Sequential fractionation: A laboratory procedure that separates sediment-bound metals into operationally defined pools—exchangeable, reducible, oxidisable and residual—to assess bioavailability and mobility.

Water Quality Index (WQI): A dimensionless aggregate score that condenses multiple physicochemical parameters into a single value for easy assessment of overall water quality status.

References

1. Remote Data for Mapping and Monitoring Coastal Phenomena and Parameters: A Systematic Review. Remote Sensing (2024).
2. Organic pollution of rivers: Combined threats of urbanization, livestock farming and global climate change. Scientific Reports (2017).
3. A comprehensive review on the design and optimization of surface water quality monitoring networks. Environmental Modelling & Software (2020).
4. Water quality assessment based on multivariate statistics and water quality index of a strategic river in the Brazilian Atlantic Forest. Scientific Reports (2020).