Patterns in the linkage of water quantity and quality during low‐flows

Abstract

This study investigates 72 catchments across the federal state of Baden‐Wuerttemberg, Germany, for changes in water quality during low‐flow events. Data from the state's water quality monitoring network provided seven water quality parameters (water temperature, electrical conductivity, concentrations of chloride, sodium, sulfate, nitrate, and phosphate), which were statistically related to streamflow variability. Water temperature changes during low‐flow showed seasonal dependence. Nitrate concentrations revealed high spatial heterogeneity with about one third of the stations showing decreasing values during low discharge. For most other parameters, concentrations increased during low‐flow. Despite consistent trend directions, the magnitudes of changes with streamflow differed markedly across the state. Both multiple linear regression and a multiple analysis of variances were applied to explain these differences with the help of catchment characteristics. Results indicated that for sulfate and conductivity, geology of the catchments was the most important control, whereas for chloride, sodium, and nitrate, sewage treatment plants had the largest influence. For phosphate, no clear control could be identified. Independent from the applied method, land use was a less important control on river water quality during low‐flow than geology or inflow from sewage treatment plants. These results show that the effects of diffuse and point sources, as well as those of natural and anthropogenic sources differ for different water quality parameters. Overall, a high diversity of potential water quality deterioration signals needs to be considered when the ecological status of rivers is to be protected during low‐flow events.

Diel patterns in stream nitrate concentration produced by in-stream processes

“…We therefore assessed correlations between drivers and the first derivative (δC diel ) of the diel concentration signal C diel . This corresponds to the way biochemical processes are implemented in some recent solute models (Hensley and Cohen, 2016;Grace et al, 2015). However, changes in water level may affect NO − 3 concentrations both indirectly, e.g., by influencing hyporheic exchange and biochemical processes therein (Trauth and Fleckenstein, 2017), and directly, since additional flow components may be enriched or depleted in NO − 3 compared to pre-event water.…”

“…As a result, the benthic footprint, i.e., the upstream area influencing concentrations at the measurement point, depends on flow velocity and solute turnover rate. While gaseous solutes like DO may quickly equilibrate with the atmosphere, upstream discontinuities in non-gaseous solutes like NO − 3 (e.g., tributary confluxes, lakes or reservoirs, wastewater inputs from point sources) may persist further downstream (Hensley and Cohen, 2016). In open systems with unknown input signals, it is therefore unclear whether diel concentration patterns are produced by conditions in the investigated stream or stem from upstream sources from which they are transported downstream (Pellerin et al, 2009).…”

Revisiting hydrological drought propagation and recovery considering water quantity and quality

“…This complexity results in the loss of billions of dollars in the United States and around the world (Below, Grover‐Kopec, & Dilley, ; Irannezhad, Ahmadi, Kløve, & Moradkhani, ; Van Loon, ). Droughts have also degraded riverine natural habitats as well as flow regime and water quality (Hellwig, Stahl, & Lange, ; Lake, ; Mosley, ). Climate change is a consequence of increased greenhouse gas emissions and global warming (Intergovernmental Panel on Climate Change, ; Zahn, ; Zeng, Haifeng, Munoz, & Iacono, ).…”

“…Numerous studies analyse drought impacts on water quality (Barros, Mendo, & Negrão, 1995;García-Prieto, Cachaza, Pérez-Galende, & Roig, 2012;Hellwig et al, 2017;Muchmore & Dziegielewski, 1983;Van Vliet & Zwolsman, 2008). Fresh water quality is a function of streamflow, biogeochemical, and anthropogenic influences.…”

Extreme low flow and water quality – a long-term view on the River Elbe

“…However, there are relatively few studies explicitly dealing with this subject on the basis of monitoring campaigns in European rivers (e.g. zwolSman and borkHoven 2007; vliet and zwolSman 2008; worrall and burt 2008;zielinSki et al 2009;HanSlik et al 2016;HellwiG et al 2017). Results are diverse and show a need for further research.…”