Dissolved organic carbon in tropical watersheds : Linking field observation and eco-hydrological modelling
(2019)- Abstract
- Dissolved organic carbon (DOC) is a general description of the organic material dissolved in water. DOC is an important source of energy, carbon, and nutrient transfers from terrestrial to aquatic ecosystems. The export of DOC into aquatic ecosystems may contribute to the carbon balance of terrestrial ecosystems and to water degradation. Ongoing climate and land cover changes will affect both DOC generation and transport, with implications for both terrestrial and aquatic ecosystems. An assessment of land use land cover and climate variability’s impacts on DOC export is needed for better management of ecosystems. Watersheds are fundamental units of ecosystem functioning and are therefore an interesting organizational unit when used to... (More)
- Dissolved organic carbon (DOC) is a general description of the organic material dissolved in water. DOC is an important source of energy, carbon, and nutrient transfers from terrestrial to aquatic ecosystems. The export of DOC into aquatic ecosystems may contribute to the carbon balance of terrestrial ecosystems and to water degradation. Ongoing climate and land cover changes will affect both DOC generation and transport, with implications for both terrestrial and aquatic ecosystems. An assessment of land use land cover and climate variability’s impacts on DOC export is needed for better management of ecosystems. Watersheds are fundamental units of ecosystem functioning and are therefore an interesting organizational unit when used to understand the combined effects of land use land cover and climate variability on DOC export. Some studies have been conducted to explore this impact of land cover and climate variability on DOC, but most were conducted in a temperate environment and few in a tropical environment. In this regard, this dissertation focused on the impact of land use land cover and climate variability on DOC mobilization and export in the Rukarara River Watershed (RRW), Rwanda. The main aim is to determine how different carbon input and output processes interact under climate and land cover variability to impact DOC emanating from tropical watersheds.
Data used for this study include land cover maps produced from satellite imagery, daily air temperature and precipitation, digital elevation models (DEMs), water stage, flow, net primary productivity (NPP), soil properties such as total organic carbon (TOC), total nitrogen (TN), cation exchange capacity (CEC), aluminum (Al), iron (Fe), and soil texture within the RRW. Field observations were used to quantify riverine DOC loads, soil water extractable organic carbon (WEOC), DOC in percolation water (pDOC) and leached DOC (LDOC) and to describe their spatial variation and relationships with the aforementioned factors. Statistical models (including simple and quadratic regressions, general linear model, linear mixed effect models) were used to predict DOC within the study area. An eco-hydrological model, the Regional Hydro-Ecological Simulation System (RHESSys), was used to simulate streamflow and link it with stream DOC within the study area. The results of this study show that land use land cover and climate change interact to produce soil WEOC, from which a significant fraction is transported into streams, mainly through overland flow and loaded by the Rukarara River. The riverine DOC loss was low compared to the NPP of the RRW, but may affect the function of both land and water resources with the study area. The RHESSys model detected the response of the watershed to climate variability within the RRW and captured the significant monthly variability in streamflow within the RRW. This result indicates the potential use of RHESSys to estimate streamflow in the RRW and similar tropical watersheds. Stream DOC concentration was explained by simulated streamflow in the natural forest, indicating the potential use of RHESSys model simulated streamflow to predict stream DOC in the study watershed and similar ecosystems. Further studies should evaluate the performance of the RHESSys model to simulate other hydroecological processes in the tropical environment.
(Less) - Abstract (Swedish)
- Löst organiskt kol (DOC) är en allmän beteckning på organiskt material upplöst i vatten. DOC är en viktig källa för energi, kol och näring som överförs från markbundna till akvatiska ekosystem. Exporten av DOC till akvatiska ekosystem kan bidra till kolbalansen i markbundna ekosystem och till försämrad vattenkvalitet. Pågående klimat- och markförändringar kommer att påverka både genereringen och transporten av DOC, med implikationer för både markbundna och akvatiska ekosystem. En bedömning av markanvändning och klimatvariationers inverkan på exporten av DOC behöver göras för att bättre kunna hantera ekosystemen. Avrinningsområden är fundamentala för ekosystemets funktion och är därför intressanta för förståelsen för hur de kombinerade... (More)
- Löst organiskt kol (DOC) är en allmän beteckning på organiskt material upplöst i vatten. DOC är en viktig källa för energi, kol och näring som överförs från markbundna till akvatiska ekosystem. Exporten av DOC till akvatiska ekosystem kan bidra till kolbalansen i markbundna ekosystem och till försämrad vattenkvalitet. Pågående klimat- och markförändringar kommer att påverka både genereringen och transporten av DOC, med implikationer för både markbundna och akvatiska ekosystem. En bedömning av markanvändning och klimatvariationers inverkan på exporten av DOC behöver göras för att bättre kunna hantera ekosystemen. Avrinningsområden är fundamentala för ekosystemets funktion och är därför intressanta för förståelsen för hur de kombinerade effekterna av markanvändning, gröngödsling och klimatvariationer påverkar exporten av DOC. Ett mindre antal studier har utförts för att undersöka hur marktäckning och klimatvariation påverkar DOC men de flesta har genomförts i tempererat klimat och endast få i tropiskt klimat. I denna avhandling har jag fokuserat på hur markanvändning, marktäckning och klimatvariationer har påverkat mobiliseringen och exporten av DOC i Rukarara River Watershed (RRW), Rwanda. Huvudsyftet är att bestämma hur DOC i tropiska avrinningsområden påverkas av växelverkan mellan olika processer för in- och utflöde av kol under varierade klimat- och marktäckningsförhållanden.
Data som har används för denna studie innefattar marktäckningskartor som skapats med utgångspunkt från satellitbilder, daglig temperatur i luft, nederbörd, DEMs, flodens vattennivå och flöde, nettoprimärproduktion (NPP), jordegenskaper som totalt organiskt kol (TOC), total kvävemängd (TN), katjonbyteskapacitet (CEC), aluminium (Al), järn (Fe) samt jordstruktur inom RRW. Fältobservationer har använts för att kvantifiera flodbaserat DOC, extraherbart organiskt kol i markvatten (WEOC), DOC i perkolationsvatten (pDOC) samt urlakat DOC (LDOC) för att beskriva deras rumsliga variation och relationer till ovannämnda faktorer. Statistiska modeller (inklusive linjär och kvadratisk regression, generell linjär modell samt modeller för linear mixed effect) har använts för att förutse DOC inom det studerade området. En ekohydrologisk modell, Regional Hydro-Ecological Simulation System (RHESSys), har använts för att simulera DOC-flöden inom det studerade området. Resultaten från denna studie visar att markanvändning och klimatförändring växelverkar för att skapa jord-WEOC, av vilket en signifikant del har transporterats till bäckar, huvudsakligen genom att rinna över marken, som leder till Rukararafloden. Förlusten av DOC till floden var låg jämfört med NPP i RRW, men kan tänkas påverka funktionen av både mark- och vattenresurser i det studerade området.
(Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/97288e1c-6c52-49ce-adc3-93baf9acf546
- author
- Rizinjirabake, Fabien LU
- supervisor
- opponent
-
- Professor Chen, Robert F., Dept. of Environmental, Earth and Ocean Sciences, University of Massachusetts, Boston, USA
- organization
- publishing date
- 2019
- type
- Thesis
- publication status
- published
- subject
- keywords
- Dissolved organic carbon (DOC), Rwanda, Land use land cover variability, Climate variability and change, Rukarara River Watershed, eco-hydrological modelling, field observation
- pages
- 204 pages
- publisher
- Lund University, Faculty of Science, Department of Physical Geography and Ecosystem Science
- defense location
- Pangea auditorium (room 229), Geocentrum II, Sölveg. 12, Lund
- defense date
- 2019-05-23 13:00:00
- ISBN
- 978-91-985016-1-2
- 978-91-985016-2-9
- language
- English
- LU publication?
- yes
- additional info
- Thesis sponsor: University of Rwanda - Sweden Program for Research, Higher Education and Institutional Advancement, financed by Swedish International Development Cooperation Agency (Sida).
- id
- 97288e1c-6c52-49ce-adc3-93baf9acf546
- date added to LUP
- 2019-04-18 11:59:20
- date last changed
- 2020-02-13 15:05:00
@phdthesis{97288e1c-6c52-49ce-adc3-93baf9acf546,
abstract = {{Dissolved organic carbon (DOC) is a general description of the organic material dissolved in water. DOC is an important source of energy, carbon, and nutrient transfers from terrestrial to aquatic ecosystems. The export of DOC into aquatic ecosystems may contribute to the carbon balance of terrestrial ecosystems and to water degradation. Ongoing climate and land cover changes will affect both DOC generation and transport, with implications for both terrestrial and aquatic ecosystems. An assessment of land use land cover and climate variability’s impacts on DOC export is needed for better management of ecosystems. Watersheds are fundamental units of ecosystem functioning and are therefore an interesting organizational unit when used to understand the combined effects of land use land cover and climate variability on DOC export. Some studies have been conducted to explore this impact of land cover and climate variability on DOC, but most were conducted in a temperate environment and few in a tropical environment. In this regard, this dissertation focused on the impact of land use land cover and climate variability on DOC mobilization and export in the Rukarara River Watershed (RRW), Rwanda. The main aim is to determine how different carbon input and output processes interact under climate and land cover variability to impact DOC emanating from tropical watersheds. <br/>Data used for this study include land cover maps produced from satellite imagery, daily air temperature and precipitation, digital elevation models (DEMs), water stage, flow, net primary productivity (NPP), soil properties such as total organic carbon (TOC), total nitrogen (TN), cation exchange capacity (CEC), aluminum (Al), iron (Fe), and soil texture within the RRW. Field observations were used to quantify riverine DOC loads, soil water extractable organic carbon (WEOC), DOC in percolation water (pDOC) and leached DOC (LDOC) and to describe their spatial variation and relationships with the aforementioned factors. Statistical models (including simple and quadratic regressions, general linear model, linear mixed effect models) were used to predict DOC within the study area. An eco-hydrological model, the Regional Hydro-Ecological Simulation System (RHESSys), was used to simulate streamflow and link it with stream DOC within the study area. The results of this study show that land use land cover and climate change interact to produce soil WEOC, from which a significant fraction is transported into streams, mainly through overland flow and loaded by the Rukarara River. The riverine DOC loss was low compared to the NPP of the RRW, but may affect the function of both land and water resources with the study area. The RHESSys model detected the response of the watershed to climate variability within the RRW and captured the significant monthly variability in streamflow within the RRW. This result indicates the potential use of RHESSys to estimate streamflow in the RRW and similar tropical watersheds. Stream DOC concentration was explained by simulated streamflow in the natural forest, indicating the potential use of RHESSys model simulated streamflow to predict stream DOC in the study watershed and similar ecosystems. Further studies should evaluate the performance of the RHESSys model to simulate other hydroecological processes in the tropical environment.<br/>}},
author = {{Rizinjirabake, Fabien}},
isbn = {{978-91-985016-1-2}},
keywords = {{Dissolved organic carbon (DOC); Rwanda; Land use land cover variability; Climate variability and change; Rukarara River Watershed; eco-hydrological modelling; field observation}},
language = {{eng}},
publisher = {{Lund University, Faculty of Science, Department of Physical Geography and Ecosystem Science}},
school = {{Lund University}},
title = {{Dissolved organic carbon in tropical watersheds : Linking field observation and eco-hydrological modelling}},
url = {{https://lup.lub.lu.se/search/files/64462396/Dissolved_Organic_Carbon_in_Tropical_Watersheds_Kappa.pdf}},
year = {{2019}},
}