scholarly journals Along-stream transport and transformation of dissolved organic matter in a large tropical river

2016 ◽  
Vol 13 (9) ◽  
pp. 2727-2741 ◽  
Author(s):  
Thibault Lambert ◽  
Cristian R. Teodoru ◽  
Frank C. Nyoni ◽  
Steven Bouillon ◽  
François Darchambeau ◽  
...  
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Water Discharge ◽  
High Water ◽  
Large River ◽  
Low Flow ◽  
River Continuum ◽  
Fluorescence Measurements ◽  
Tropical Areas ◽  
Stream Transport

Abstract. Large rivers transport considerable amounts of terrestrial dissolved organic matter (DOM) to the ocean. However, downstream gradients and temporal variability in DOM fluxes and characteristics are poorly studied at the scale of large river basins, especially in tropical areas. Here, we report longitudinal patterns in DOM content and composition based on absorbance and fluorescence measurements along the Zambezi River and its main tributary, the Kafue River, during two hydrological seasons. During high-flow periods, a greater proportion of aromatic and humic DOM was mobilized along rivers due to the hydrological connectivity with wetlands, while low-flow periods were characterized by lower DOM content of less aromaticity resulting from loss of connectivity with wetlands, more efficient degradation of terrestrial DOM and enhanced autochthonous productivity. Changes in water residence time due to contrasting water discharge were found to modulate the fate of DOM along the river continuum. Thus, high water discharge promotes the transport of terrestrial DOM downstream relative to its degradation, while low water discharge enhances the degradation of DOM during its transport. The longitudinal evolution of DOM was also strongly impacted by a hydrological buffering effect in large reservoirs in which the seasonal variability of DOM fluxes and composition was strongly reduced.

scholarly journals Along-stream transport and transformation of dissolved organic matter in a large tropical river

2016 ◽  
Author(s):  
Thibault Lambert ◽  
Cristian R. Teodoru ◽  
Frank C. Nyoni ◽  
Steven Bouillon ◽  
François Darchambeau ◽  
...  
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Water Discharge ◽  
Large River ◽  
High Flow ◽  
Low Flow ◽  
River Continuum ◽  
Fluorescence Measurements ◽  
Tropical Areas ◽  
Stream Transport

Abstract. Large rivers transport considerable amounts of terrestrial dissolved organic matter (DOM) to the ocean. Yet, downstream gradients and temporal variability in DOM fluxes and characteristics are poorly studied at the scale of large river basins, especially in tropical areas. Here, we report longitudinal patterns in DOM content and composition based on absorbanc e and fluorescence measurements along the Zambezi River and its main tributary, the Kafue River, during two hydrological seasons. During high flow periods, a greater proportion of aromatic and humic DOM was mobilized along rivers due to the hydrological connectivity with wetlands and high flow velocities, while low flow periods were characterized by lower DOM content of less aromaticity resulting from loss of connectivity with wetlands, more efficient degradation of terrestrial DOM and enhanced autochthonous productivity. Changes in water residence time due to contrasting water discharge were found to modulate the fate of DOM along the river continuum. Thus, terrestrial DOM dynamics shifted from transport-dominated during the wet seasons towards degradation during the dry season, with substantial consequences on longitudinal DOM content and composition. The longitudinal evolution of DOM was also strongly impacted by a hydrological buffering effect in large reservoirs in which the seasonal variability of DOM fluxes and composition was strongly reduced.

scholarly journals Discharge and Temperature Controls of Dissolved Organic Matter (DOM) in a Forested Coastal Plain Stream

Water ◽  
2021 ◽  
Vol 13 (20) ◽  
pp. 2919
Author(s):  
Yuehan Lu ◽  
Peng Shang ◽  
Shuo Chen ◽  
Yingxun Du ◽  
Marco Bonizzoni ◽  
...  
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
High Temperatures ◽  
Coastal Plain ◽  
Stream Water ◽  
Water Discharge ◽  
Low Flow ◽  
Fluorescence Excitation ◽  
In Situ Modification ◽  
Total Fluorescence

Streams in the southeastern United States Coastal Plains serve as an essential source of energy and nutrients for important estuarine ecosystems, and dissolved organic matter (DOM) exported from these streams can have profound impacts on the biogeochemical and ecological functions of fluvial networks. Here, we examined hydrological and temperature controls of DOM during low-flow periods from a forested stream located within the Coastal Plain physiographic region of Alabama, USA. We analyzed DOM via combining dissolved organic carbon (DOC) analysis, fluorescence excitation–emission matrix combined with parallel factor analysis (EEM-PARAFAC), and microbial degradation experiments. Four fluorescence components were identified: terrestrial humic-like DOM, microbial humic-like DOM, tyrosine-like DOM, and tryptophan-like DOM. Humic-like DOM accounted for ~70% of total fluorescence, and biodegradation experiments showed that it was less bioreactive than protein-like DOM that accounted for ~30% of total fluorescence. This observation indicates fluorescent DOM (FDOM) was controlled primarily by soil inputs and not substantially influenced by instream production and processing, suggesting that the bulk of FDOM in these streams is transported to downstream environments with limited in situ modification. Linear regression and redundancy analysis models identified that the seasonal variations in DOM were dictated primarily by hydrology and temperature. Overall, high discharge and shallow flow paths led to the enrichment of less-degraded DOM with higher percentages of microbial humic-like and tyrosine-like compounds, whereas high temperatures favored the accumulation of high-aromaticity, high-molecular-weight, terrestrial, humic-like compounds in stream water. The flux of DOC and four fluorescence components was driven primarily by water discharge. Thus, the instantaneous exports of both refractory humic-like DOM and reactive protein-like DOM were higher in wetter seasons (winter and spring). As high temperatures and severe precipitation are projected to become more prominent in the southeastern U.S. due to climate change, our findings have important implications for future changes in the amount, source, and composition of DOM in Coastal Plain streams and the associated impacts on downstream carbon and nutrient supplies and water quality.

scholarly journals Impact of forest harvesting on water quality and fluorescence characteristics of dissolved organic matter in eastern Canadian Boreal Shield lakes in summer

2015 ◽  
Vol 12 (23) ◽  
pp. 6999-7011 ◽  
Author(s):  
P. Glaz ◽  
J.-P. Gagné ◽  
P. Archambault ◽  
P. Sirois ◽  
C. Nozais
Keyword(s):  
Water Quality ◽  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Forest Harvesting ◽  
Spectroscopic Techniques ◽  
Clear Cutting ◽  
Fluorescence Measurements ◽  
Fluorescence Characteristics ◽  
Boreal Shield ◽  
Shield Lakes

Abstract. Forestry activities in the Canadian Boreal region have increased in the last decades, raising concerns about their potential impact on aquatic ecosystems. Water quality and fluorescence characteristics of dissolved organic matter (DOM) were measured over a 3-year period in eight eastern Boreal Shield lakes: four lakes were studied before, 1 and 2 years after forest harvesting (perturbed lakes) and compared with four undisturbed reference lakes (unperturbed lakes) sampled at the same time. ANOVAs showed a significant increase in total phosphorus (TP) in perturbed lakes when the three sampling dates were considered and in DOC concentrations when considering 1 year before and 1 year after the perturbation only. At 1 year post-clear cutting DOC concentrations were about 15 % greater in the perturbed lakes at ~ 15 mgC L−1 compared to 12.5 mgC L−1 in the unperturbed lakes. In contrast, absorbance and fluorescence measurements showed that all metrics remained within narrow ranges compared to the range observed in natural waters, indicating that forest harvesting did not affect the nature of DOM characterized with spectroscopic techniques. These results confirm an impact of forestry activities 1 year after the perturbation. However, this effect seems to be mitigated 2 years after, indicating that the system shows high resilience and may be able to return to its original condition in terms of water quality parameters assessed in this study.

scholarly journals Supplementary material to "Along-stream transport and transformation of dissolved organic matter in a large tropical river"

2016 ◽  
Author(s):  
Thibault Lambert ◽  
Cristian R. Teodoru ◽  
Frank C. Nyoni ◽  
Steven Bouillon ◽  
François Darchambeau ◽  
...  
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Tropical River ◽  
Transport And Transformation ◽  
Supplementary Material ◽  
Stream Transport

scholarly journals Large herbivorous wildlife and livestock differentially influence the relative importance of different sources of carbon for riverine food webs

2021 ◽  
Author(s):  
Frank O. Masese ◽  
Thomas Fuss ◽  
Lukas Bistarelli ◽  
Caroline Buchen-Tschiskale ◽  
Gabriel Singer
Keyword(s):  
Organic Matter ◽  
Food Webs ◽  
Aquatic Ecosystems ◽  
Carbon Sources ◽  
Large River ◽  
Livestock Grazing ◽  
Relative Importance ◽  
River Continuum ◽  
Aquatic Food ◽  
Different Sources

In many regions around the world, large populations of native wildlife have declined or been replaced by livestock grazing areas and farmlands, with consequences on terrestrial-aquatic ecosystems connectivity and trophic resources supporting food webs in aquatic ecosystems. The river continuum concept (RCC) and the riverine productivity model (RPM) predict a shift of carbon supplying aquatic food webs along the river: from terrestrial inputs in low-order streams to autochthonous production in mid-sized rivers. Here, we studied the influence of replacing large wildlife (mainly hippos) with livestock on the relative importance of C3 vegetation, C4 grasses and periphyton on macroinvertebrates in the Mara River, which is an African montane-savanna river known to receive large subsidy fluxes of terrestrial carbon and nutrients mediated by LMH, both wildlife and livestock. Using stable carbon (δ13C) and nitrogen (δ15N) isotopes, we identified spatial patterns of the relative importance of allochthonous carbon from C3 and C4 plants (woody vegetation and grasses, respectively) and autochthonous carbon from periphyton for macroinvertebrates at various sites of the Mara River and its tributaries. Potential organic carbon sources and invertebrates were sampled at 80 sites spanning stream orders 1 to 7, various catchment land uses (forest, agriculture and grasslands) and different loading rates of organic matter and nutrients by LMH (livestock and wildlife, i.e., hippopotamus). The importance of different sources of carbon along the river did not follow predictions of RCC and RPM. First, the importance of C3 and C4 carbon was not related to river order or location along the fluvial continuum but to the loading of organic matter (dung) by both wildlife and livestock. Notably, C4 carbon was important for macroinvertebrates even in large river sections inhabited by hippos. Second, even in small 1st -3rd order forested streams, autochthonous carbon was a major source of energy for macroinvertebrates, and this was fostered by livestock inputs fuelling aquatic primary production throughout the river network. Importantly, our results show that replacing wildlife (hippos) with livestock shifts river systems towards greater reliance on autochthonous carbon through an algae-grazer pathway as opposed to reliance on allochthonous inputs of C4 carbon through a detrital pathway.

scholarly journals In situ fluorescence measurements of dissolved organic matter: A review

2020 ◽  
Vol 699 ◽  
pp. 134361 ◽  
Author(s):  
Elfrida M. Carstea ◽  
Cristina L. Popa ◽  
Andy Baker ◽  
John Bridgeman
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Fluorescence Measurements
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