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Heljumi dünaamika ja omadused optiliselt keerulistes veekogudes

Authors: Uusõue, Mirjam;

Heljumi dünaamika ja omadused optiliselt keerulistes veekogudes

Abstract

Clean water is necessary for all living organisms, but human activities and climate change have deteriorated water quality in many regions. It is important to monitor water bodies to take the necessary measures. Conventional contact measurements have been carried out for decades. However, they are time-consuming and expensive and can cover only a small number of water bodies. This is insufficient as changes in waterbodies are often rapid and occur over large areas. Remote sensing methods have been introduced to fill these gaps in temporal and spatial coverage. On the other hand, there is a need to study parameters that impact the formation of water-leaving signal in order to increase the accuracy of remote sensing products. One such substance that requires further investigation is suspended particulate matter. It consists of mineral and organic particles suspended in the water column due to natural processes (waves, erosion, river transport) and human activities (trawling, dredging, construction). The high content of suspended particles increases the water turbidity, consequently reducing the light availability. In turn, this worsens aquatic organisms' living conditions and alters physical processes (like radiative heating) in the water environment. Suspended particles can contain harmful substances such as organic pollutants and heavy metals. We studied the behaviour of heavy metal-rich sediments in Portman Bay (one of the most polluted areas of the Mediterranean), in southern Spain, after trawling the sea bottom. Coarse and heavy particles and flocs settled quickly. Fine particles remained in suspension for a longer time. Therefore, the content of heavy metals in the water increased. From an optical point of view, the suspended particles mainly scatter light. The optical properties of suspended particles (light absorption, scattering, backscattering/scattering ratio) were studied in several Estonian coastal areas. The backscattering ratio, which is used as a constant in bio-optical remote sensing algorithms, was highly variable, depending on the conditions (algal bloom, storm). Such variability was also observed for other optical properties. It was found that small particles resuspended by a storm aggregated into larger flocs (> 30 μm), affecting the particles' optical properties in the Pärnu Bay, which has very low salinity and little organic content. This study shows that using an assumption that the backscattering ratio is a fixed constant reduces the accuracy of remote sensing products.

Puhas vesi on eluks vajalik kõikidele elusolenditele, kuid inimtegevuse ja kliimamuutuste mõjul on paljudes piirkondades veekvaliteet halvenenud. Veekogude seisundi hindamiseks ja vajalike meetmete kasutusele võtmiseks, on tarvis neid seirata. Aastakümneid on tehtud kontaktmõõtmisi, kuid need on ajakulukad ja kallid ning nendega on keeruline jälgida kiireid muutusi suurtel aladel. Viimastel aastakümnetel on kasutusele võetud kaugseire meetodid, mis võimaldavad neid puudujääke täita. Selleks, et mõista mida kaugseire instrument mõõdab on vaja teada parameetreid, mis kaugseire signaali ja selle interpreteerimist mõjutavad. Üheks selliseks aineks on heljum. Heljum koosneb veemassis hõljuvatest mineraalsetest (setted) ja orgaanilistest osakestest ja see jõuab veemassi looduslike protsesside (lainetus, erosioon, jõgede transport) ja inimtegevuse (traalimine, süvendamine, ehitamine) tagajärjel. Kõrge heljumi sisaldus veemassis muudab vee häguseks, mõjutades valguse jõudmist sügavamatesse veekihtidesse, mis omakorda halvendab vee, kui elukeskkonna seisundit. Heljum võib sisaldada kahjulikke aineid, nagu orgaanilised saasteained ja raskemetallid. Seetõttu uurisime Portmani lahes (Vahemere üks reostatumaid alasid), Lõuna-Hispaanias põhjasetteid, milles on kõrge raskemetallide sisaldus, ning kuidas need setted jõuavad veesambasse traalimise mõjul. Suured osakesed settisid kiiresti. Väikesed osakesed, millega liitusid raskemetallid, jäid veemassi pikemaks ajaks. Seetõttu raskemetallide sisaldus vees tõusis. Eesti rannikualadel uuriti heljumi optilisi omadusi (valguse neeldumist, hajumist, tagasihajumise/hajumise suhet). Leiti, et tagasihajumise/hajumise suhe, mida kasutatakse bio-optilistes kaugseire algoritmides konstandina on tegelikult väga muutlik ning sõltub hetke tingimustest (vetikaõitseng, torm). Sellist varieeruvust täheldati ka muude optiliste omadustega seoses. Leiti, et väga väikese soolsuse ja vähese orgaanika sisaldusega Pärnu lahes agregeerisid väikesed tormi mõjul veemassi keerutatud osakesed suuremateks osakesteks (> 30 μm) mõjutades vee optilisi omadusi ning seega ka kaugseire signaali.

Väitekirja elektrooniline versioon ei sisalda publikatsioone

https://www.ester.ee/record=b5553931

Country
Estonia
Related Organizations
Keywords

optical properties, Estonia, dissertations, Eesti (riik), dissertatsioonid, aineosakesed, veekogud, dynamic properties, coastal sea, ETD, optilised omadused, väitekirjad, remote sensing, suspensioonid, Hispaania (riik), Spain, dünaamilised omadused, suspensions, particles (physics), rannikumeri, kaugseire, water bodies

3. MATERIALS AND METHODS ............................................................... 14 3.1. Study areas .......................................................................................... 14 3.2. Data ..................................................................................................... 16 3.3. Methodology ....................................................................................... 17 3.2.1. Measurement strategy ............................................................... 17 3.2.2. Sediment plumes geometry....................................................... 20 3.2.3. Measurement of water constituents .......................................... 20 3.2.4. Metal analyses .......................................................................... 20 3.2.5. Inherent optical properties ........................................................ 21 3.2.6. Particle size distributions .......................................................... 21 3.2.7. Measurement of reflectance...................................................... 23 3.2.8. Hydrolight simulations with backscattering ratios ................... 24 3.2.9. Retrieving optical water quality parameters using OWT-guided approach ............................................................. 24 3.2.10. Satellite data ............................................................................. 25

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    This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
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    popularity
    This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
    Average
    influence
    This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
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    impulse
    This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
    Average
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citations
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
0
Average
Average
Average
Funded by
EC| EOMORES
Project
EOMORES
Earth Observation based services for Monitoring and Reporting of Ecological Status
  • Funder: European Commission (EC)
  • Project Code: 730066
  • Funding stream: H2020 | IA
Related to Research communities
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