scholarly journals Diurnal Patterns in Solute Concentrations Measured with In Situ UV-Vis Sensors: Natural Fluctuations or Artefacts?

Sensors ◽  
2020 ◽  
Vol 20 (3) ◽  
pp. 859
Author(s):  
Suzanne R. Jacobs ◽  
Björn Weeser ◽  
Mariana C. Rufino ◽  
Lutz Breuer
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Stream Water ◽  
Visible Spectrum ◽  
Mobile Sensor ◽  
Stream Water Quality ◽  
High Resolution Data ◽  
Diurnal Patterns ◽  
Solute Dynamics

In situ spectrophotometers measuring in the UV-visible spectrum are increasingly used to collect high-resolution data on stream water quality. This provides the opportunity to investigate short-term solute dynamics, including diurnal cycling. This study reports unusual changes in diurnal patterns observed when such sensors were deployed in four tropical headwater streams in Kenya. The analysis of a 5-year dataset revealed sensor-specific diurnal patterns in nitrate and dissolved organic carbon concentrations and different patterns measured by different sensors when installed at the same site. To verify these patterns, a second mobile sensor was installed at three sites for more than 3 weeks. Agreement between the measurements performed by these sensors was higher for dissolved organic carbon (r > 0.98) than for nitrate (r = 0.43–0.81) at all sites. Higher concentrations and larger amplitudes generally led to higher agreement between patterns measured by the two sensors. However, changing the position or level of shading of the mobile sensor resulted in inconsistent changes in the patterns. The results of this study show that diurnal patterns measured with UV-Vis spectrophotometers should be interpreted with caution. Further work is required to understand how these measurements are influenced by environmental conditions and sensor-specific properties.

In situ UV-Vis sensors record spatially and temporally different diurnal patterns in solute concentrations in tropical montane headwater streams: reality or artefact?

2020 ◽  
Author(s):  
Suzanne Jacobs ◽  
Björn Weeser ◽  
Mariana Rufino ◽  
Lutz Breuer
Keyword(s):  
Land Use ◽  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Spatial Scales ◽  
Diurnal Changes ◽  
Biogeochemical Processes ◽  
Mobile Sensor ◽  
Position Change ◽  
Diurnal Patterns

<p>There is a need to better understand the driving factors of and interactions between hydro-biogeochemical processes at different temporal and spatial scales to inform water management. Especially for tropical montane ecosystems, which are recognized as important freshwater sources, the required data and knowledge are missing. To address this knowledge gap, a long-term hydrological monitoring network was set up in the Mau Forest Complex, Kenya. The network covers three sub-catchments (27–36 km²) dominated by either tropical montane forest, smallholder agriculture or commercial tea plantations, within a 1021 km² mixed land use catchment. A 5-year dataset of nitrate and dissolved organic carbon concentrations measured at 10-minute interval with <em>in situ</em> UV-Vis sensors was analysed for short-term changes in solute concentrations. The analysis revealed small diurnal patterns (amplitude <0.25 mg N or C L<sup>−1</sup>, decreasing with increasing discharge) in solute concentrations in all streams. In addition, the timing of the minima and maxima differed between catchments and seasons, suggesting and influence of land use and seasonality on the occurrence of in-stream biogeochemical processes. However, unusual and abrupt changes in the diurnal patterns were observed after a change in sensor position or exchange of sensors. We therefore developed an experiment to test the validity of the observed diurnal patterns. A second, mobile sensor was installed at each site for a period of more than three weeks. After measuring in parallel position to the fixed sensor for two weeks, the position (orientation, depth) was changed or the measurement gap was shaded. In parallel position, the patterns in solute concentrations recorded by the mobile sensor agreed better with those measured by the fixed sensor for dissolved organic carbon (<em>r</em>>0.98) than for nitrate (<em>r</em>=0.43–0.81). However, shading the sensor or a position change resulted in inconsistent changes in the recorded patterns. Larger changes in solute concentrations, e.g. as a result of rainfall events, were reproduced well by the mobile sensor. The results of our study suggest that diurnal changes in solute concentrations with an amplitude close sensor accuracy measured with <em>in situ</em> UV-Vis sensors should be interpreted with caution. The experiment was not conclusive as to what caused the differences in observed patterns. Further experimental work is required to understand the causes and to develop recommendations for the use of UV-Vis sensors in hydro-biogeochemical research.</p>

scholarly journals Changes in discharge and solute dynamics between hillslope and valley-bottom intermittent streams

2012 ◽  
Vol 16 (6) ◽  
pp. 1595-1605 ◽  
Author(s):  
S. Bernal ◽  
F. Sabater
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Stream Water ◽  
Valley Bottom ◽  
Solute Fluxes ◽  
Nitrate Export ◽  
Carbon And Nitrogen Dynamics ◽  
Reactive Solutes ◽  
Monthly Discharge ◽  
Solute Dynamics

Abstract. To gain understanding on how alluvial zones modify water and nutrient export from semiarid catchments, we compared monthly discharge as well as stream chloride, carbon, and nitrogen dynamics between a hillslope catchment and a valley-bottom catchment with a well-developed alluvium. Stream water and solute fluxes from the hillslope and valley-bottom catchments showed contrasting patterns between hydrological transitions and wet periods, especially for bio-reactive solutes. During transition periods, stream water export decreased >40% between the hillslope and the valley bottom coinciding with the prevalence of stream-to-aquifer fluxes at the alluvial zone. In contrast, stream water export increased by 20–70% between the hillslope and valley-bottom catchments during wet periods. During transition periods, stream solute export decreased by 34–97% between the hillslope and valley-bottom catchments for chloride, nitrate, and dissolved organic carbon. In annual terms, stream nitrate export from the valley-bottom catchment (0.32 ± 0.12 kg N ha−1 yr−1 [average ± standard deviation]) was 30–50% lower than from the hillslope catchment (0.56 ± 0.32 kg N ha−1 yr−1). The annual export of dissolved organic carbon was similar between the two catchments (1.8 ± 1 kg C ha−1 yr−1). Our results suggest that hydrological retention in the alluvial zone contributed to reduce stream water and solute export from the valley-bottom catchment during hydrological transition periods when hydrological connectivity between the hillslope and the valley bottom was low.

Elucidating sources and pathways of dissolved organic carbon in a small, forested catchment – A qualitative assessment of stream, soil and shallow groundwater

2021 ◽  
Author(s):  
Katharina Blaurock ◽  
Phil Garthen ◽  
Benjamin S. Gilfedder ◽  
Jan H. Fleckenstein ◽  
Stefan Peiffer ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Soil Water ◽  
Riparian Zone ◽  
Stream Water ◽  
Shallow Groundwater ◽  
Drinking Water Treatment ◽  
Base Flow ◽  
Qualitative Assessment ◽  
Fluorescence Characteristics

<p>Dissolved organic carbon (DOC) constitutes the biggest portion of carbon that is exported from soils. During the last decades, widespread increases in DOC concentrations of surface waters have been observed, affecting ecosystem functioning and drinking water treatment. However, the hydrological controls on DOC mobilization are still not completely understood.</p><p>We sampled two different topographical positions within a headwater catchment in the Bavarian Forest National Park: at a steep hillslope (880 m.a.s.l.) and in a flat and wide riparian zone (770 m.a.s.l.). By using piezometers, pore water samplers (peepers) and in-stream spectrometric devices we measured DOC concentrations as well as DOC absorbance (A<sub>254</sub>/A<sub>365</sub> and SUVA<sub>254</sub>) and fluorescence characteristics (fluorescence and freshness indices) in soil water, shallow ground water and stream water in order to gain insights into the DOC source areas during base-flow and during precipitation events.</p><p>High DOC concentrations (up to 80 mg L<sup>-1</sup>) were found in soil water from cascading sequences of small ponds in the flat downstream part of the catchment that fill up temporarily. The increase of in-stream DOC concentrations during events was accompanied by changing DOC characteristics at both locations, for example increasing freshness index values. As the freshness index values were approaching the values found in the DOC-rich ponds in the riparian zone, these ponds seem to be important DOC sources during events. Our preliminary results point to a change of flow pathways during events.</p>

scholarly journals Spatio-temporal controls of dissolved organic carbon stream water concentrations

2018 ◽  
Vol 566 ◽  
pp. 205-215 ◽  
Author(s):  
A. Musolff ◽  
J.H. Fleckenstein ◽  
M. Opitz ◽  
O. Büttner ◽  
R. Kumar ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Stream Water ◽  
Spatio Temporal

scholarly journals Spatial distribution of soils determines export of nitrogen and dissolved organic carbon from an intensively managed agricultural landscape

2012 ◽  
Vol 9 (11) ◽  
pp. 4513-4525 ◽  
Author(s):  
T. Wohlfart ◽  
J.-F. Exbrayat ◽  
K. Schelde ◽  
B. Christen ◽  
T. Dalgaard ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Agricultural Landscape ◽  
Agricultural Land ◽  
Stream Water ◽  
Organic Soils ◽  
Total N ◽  
Small Catchment ◽  
Landscape Characteristics ◽  
Intensively Managed

Abstract. The surrounding landscape of a stream has crucial impacts on the aquatic environment. This study pictures the hydro-biogeochemical situation of the Tyrebækken creek catchment in central Jutland, Denmark. The intensively managed agricultural landscape is dominated by rotational croplands. The small catchment mainly consist of sandy soil types besides organic soils along the streams. The aim of the study was to characterise the relative influence of soil type and land use on stream water quality. Nine snapshot sampling campaigns were undertaken during the growing season of 2009. Total dissolved nitrogen (TDN), nitrate (NO3−), ammonium nitrogen and dissolved organic carbon (DOC) concentrations were measured, and dissolved organic nitrogen (DON) was calculated for each grabbed sample. Electrical conductivity, pH and flow velocity were measured during sampling. Statistical analyses showed significant differences between the northern, southern and converged stream parts, especially for NO3− concentrations with average values between 1.4 mg N l−1 and 9.6 mg N l−1. Furthermore, throughout the sampling period DON concentrations increased to 2.8 mg N l−1 in the northern stream contributing up to 81% to TDN. Multiple-linear regression analyses performed between chemical data and landscape characteristics showed a significant negative influence of organic soils on instream N concentrations and corresponding losses in spite of their overall minor share of the agricultural land (12.9%). On the other hand, organic soil frequency was positively correlated to the corresponding DOC concentrations. Croplands also had a significant influence but with weaker correlations. For our case study we conclude that the fractions of coarse textured and organic soils have a major influence on N and DOC export in this intensively used landscape. Meanwhile, the contribution of DON to the total N losses was substantial.

In situ dissolved organic carbon (DOC) release by submerged macrophyte–epiphyte communities in southern Quebec lakes

2009 ◽  
Vol 66 (9) ◽  
pp. 1522-1531 ◽  
Author(s):  
M. Demarty ◽  
Y. T. Prairie
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Myriophyllum Spicatum ◽  
Dry Weight ◽  
Release Rates ◽  
Doc Production ◽  
Epiphyte Communities ◽  
Benthic Chambers ◽  
Freshwater Macrophyte

We studied the in situ release of dissolved organic carbon (DOC) by growing a submerged freshwater macrophyte–epiphyte complex. Incubations with benthic chambers in five southeastern Quebec lakes show a net DOC production for different communities of Myriophyllum spicatum and Potamogeton spp. Daytime DOC release rates range from undetectable to 9.7 mg C·m–2·h–1. Although DOC release was restricted to daylight hours and thus suggestive of a photosynthesis-related process, we found no strong link between DOC release rates and concurrent illumination or temperature. We found no difference in DOC release rates between the three main colonizing species of the studied region. The overall mean DOC release rate was 4.57 mg C·m–2·h–1 (standard deviation (SD), ±0.65) or 56 µg C·g dry weight–1·h–1 (SD, ±8), which we suggest can be used for extrapolations at the lake scale.

scholarly journals Small-scale topography explains patterns and dynamics of dissolved organic carbon exports from the riparian zone of a temperate, forested catchment

2021 ◽  
Vol 25 (12) ◽  
pp. 6067-6086
Author(s):  
Benedikt J. Werner ◽  
Oliver J. Lechtenfeld ◽  
Andreas Musolff ◽  
Gerrit H. de Rooij ◽  
Jie Yang ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Surface Runoff ◽  
Stream Water ◽  
Surface Flow ◽  
Small Scale ◽  
Topographic Wetness Index ◽  
Forested Catchment ◽  
Source Zones ◽  
Doc Export

Abstract. Export of dissolved organic carbon (DOC) from riparian zones (RZs) is an important component of temperate catchment carbon budgets, but export mechanisms are still poorly understood. Here we show that DOC export is predominantly controlled by the microtopography of the RZ (lateral variability) and by riparian groundwater level dynamics (temporal variability). From February 2017 until July 2019 we studied topography, DOC quality and water fluxes and pathways in the RZ of a small forested catchment and the receiving stream in central Germany. The chemical classification of the riparian groundwater and surface water samples (n=66) by Fourier transform ion cyclotron resonance mass spectrometry revealed a cluster of plant-derived, aromatic and oxygen-rich DOC with high concentrations (DOCI) and a cluster of microbially processed, saturated and heteroatom-enriched DOC with lower concentrations (DOCII). The two DOC clusters were connected to locations with distinctly different values of the high-resolution topographic wetness index (TWIHR; at 1 m resolution) within the study area. Numerical water flow modeling using the integrated surface–subsurface model HydroGeoSphere revealed that surface runoff from high-TWIHR zones associated with the DOCI cluster (DOCI source zones) dominated overall discharge generation and therefore DOC export. Although corresponding to only 15 % of the area in the studied RZ, the DOCI source zones contributed 1.5 times the DOC export of the remaining 85 % of the area associated with DOCII source zones. Accordingly, DOC quality in stream water sampled under five event flow conditions (n=73) was closely reflecting the DOCI quality. Our results suggest that DOC export by surface runoff along dynamically evolving surface flow networks can play a dominant role for DOC exports from RZs with overall low topographic relief and should consequently be considered in catchment-scale DOC export models. We propose that proxies of spatial heterogeneity such as the TWIHR can help to delineate the most active source zones and provide a mechanistic basis for improved model conceptualization of DOC exports.

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