Spatio-temporal variations of water sources and mixing spots in a riparian zone

Abstract. Riparian zones are known to modulate water quality in stream-corridors. They can act as buffers for groundwater borne solutes before they enter the stream at harmful, high concentrations, or facilitate solute turnover and attenuation in zones where stream water (SW) and groundwater (GW) mix. This natural attenuation capacity is strongly controlled by the dynamic exchange of water and solutes between the stream and the adjoining aquifer, creating potential for mixing-dependent reactions to take place. Here, we couple a previously calibrated transient and fully-integrated 3D surface-subsurface, numerical flow model with a Hydraulic Mixing Cell (HMC) method to map the source composition of water along a reach of the 4th-order Selke stream and track its spatio-temporal evolution. This allows us to define zones in the aquifer with similar fractions of surface- and groundwater per aquifer volume (called “mixing hot-spots”), which have a high potential to facilitate mixing-dependent reactions and in turn enhance solute turnover. We further evaluated the HMC results against hydrochemical monitoring data. Our results show that on average about 50 % of the water in the aquifer consists of infiltrating SW. Within about 200 m around the stream the aquifer is almost entirely made up of infiltrated SW with nearly no other water sources mixed in. On average, about 9 % of the aquifer volume could be characterized as “mixing hot-spots”, but this percentage could rise to values nearly 1.5 times higher following large discharge events. Moreover, event intensity (magnitude of peak flow) was found to be more important for the increase of mixing than event duration. Our modelling results further suggest that discharge events more significantly increase mixing potential at greater distances from the stream. In contrast near the stream, the rapid increase of SW influx shifts the ratio between the water fractions to SW, reducing the potential for mixing and the associated reactions. With this easy-to-transfer framework we seek to show the applicability of the HMC method as a complementary approach for the identification of mixing hot-spots in stream corridors, while showing the spatio-temporal controls of the SW-GW mixing process and the implications for riparian biogeochemistry and mixing-dependent turnover processes.

Download Full-text

Supplementary material to "Spatio-temporal variations of water sources and mixing spots in a riparian zone"

10.5194/hess-2021-573-supplement ◽

2021 ◽

Author(s):

Guilherme E. H. Nogueira ◽

Christian Schmidt ◽

Daniel Partington ◽

Philip Brunner ◽

Jan H. Fleckenstein

Keyword(s):

Riparian Zone ◽

Temporal Variations ◽

Water Sources ◽

Supplementary Material ◽

Spatio Temporal

Download Full-text

Isotope hydrology and water sources in a heavily urbanised stream

10.22541/au.161950546.65727362/v1 ◽

2021 ◽

Author(s):

Christian Marx ◽

Doerthe Tetzlaff ◽

Reinhard Hinkelmann ◽

Chris Soulsby

Keyword(s):

Isotopic Composition ◽

Agricultural Land ◽

Stream Water ◽

Treatment Plant ◽

Temporal Variations ◽

Water Sources ◽

Stable Water Isotopes ◽

Runoff Generation ◽

Urban Catchments ◽

Urban Storm

Complex networks of both natural and engineered flow paths control the hydrology of streams in major cities through spatio-temporal variations in connection and disconnection of water sources. We used spatially extensive and temporally intensive sampling of water stable isotopes to disentangle the hydrological sources of the heavily urbanized Panke catchment (≈ 220 km²) in the north of Berlin, Germany. The isotopic data enabled us to partition stream water sources across the catchment using a Bayesian mixing analysis. The upper part of the catchment streamflow here is dominated by groundwater from gravel aquifers underlying surrounding agricultural land. In dry summer periods, streamflow becomes intermittent; possibly as a result of local groundwater abstractions. Urban storm drainage is also an important part of runoff generation, dominating the responses to precipitation events. Although this dramatically changes the isotopic composition of the stream, it only accounts for 10-15% of annual streamflow. Moving downstream, subtle changes in sources and isotope signatures occur as catchment characteristic vary and the stream is affected by different tributary inflows. However, effluent from a wastewater treatment plant (WWTP) serving 700,000 people dominates the stream in the lower catchment where urbanisation effects are more dramatic. The associated increase in sealed surfaces downstream also reduces the relative contribution of groundwater to streamflow. The volume and isotopic composition of storm runoff is again dominated by urban drainage. As a result, only about 10% of annual runoff in the lower catchment comes from urban storm drains. The study shows the potential of stable water isotopes as inexpensive tracers in urban catchments that can provide a more integrated understanding of the complex hydrology of major cities. This offers an important evidence base for guiding the plans to develop and re-develop urban catchments to protect, restore and enhance the ecological and amenity value of these important resources.

Download Full-text

The Spatiotemporal Distribution of Historical Malaria Cases in Sweden: A Climatic Perspective

10.21203/rs.3.rs-131537/v1 ◽

2020 ◽

Author(s):

Tzu Tung Chen ◽

Fredrik Charpentier Ljungqvist ◽

Helene Castenbrandt ◽

Franziska Hildebrandt ◽

Mathias Mølbak Ingholt ◽

...

Keyword(s):

Severe Malaria ◽

Hot Spots ◽

Climatic Variability ◽

Warm Season ◽

Temporal Variations ◽

Superposed Epoch Analysis ◽

Vector Borne Diseases ◽

Temperature And Precipitation ◽

Historical Times ◽

Spatio Temporal

Abstract Background: Understanding of the impacts of climatic variability and change on human health, and the spread of diseases, remains poor despite an increasing burden of vector-borne diseases under global warming. Many confounding social variables make such studies challenging during the modern period while studies of climate-disease relationships in historical times are constrained by a lack of long-term data sets. Previous studies of malaria in historical times have revealed an association with climate in northern Europe. Yet, malaria in Sweden in relation to climate variables is understudied and relationships have never been rigorously statistically established. This study seeks to examine the relationship between malaria and climate fluctuations using several data sources, and to characterise the spatio-temporal variations at parish level during severe malaria years in Sweden between 1749 and 1859. Methods: Pearson (rp) and Spearman's rank (rs) correlation analyses were conducted to evaluate inter-annual relationship between malaria deaths, temperature and precipitation. The climate response to larger malaria events was further explored by Superposed Epoch Analysis, and through Geographic Information Systems analysis to map spatial variations of malaria deaths. Results: The number of malaria deaths showed the most significant positive relationship with warm-season temperature of the preceding year, but less significant against precipitation. The strongest correlation was found between malaria deaths and the mean temperature of the preceding June-August (rs=0.57, p<0.01) during the 1756-1820 period. Most malaria hot-spots, during severe malaria years, concentrated in areas around big inland lakes and southern-most Sweden.Conclusions: Increases in malaria transmission, and hence malaria deaths, in Sweden was linked to high summer temperature during the preceding year. This relationship can be established with statistical confidence from parish records in tandem with the long meteorological series. Our results indicate that unusually warm and/or dry summers may have contributed to malaria epidemics, but with non-linear characteristics, highlighting the difficulties in modeling climate-malaria associations. The inter-annual spatial variation of malaria hot-spots further shows that malaria outbreaks were more pronounced in the southern-most region of Sweden in the first half of the nineteenth century compared to the second half of the eighteenth century.

Download Full-text