Multiscale influence of environmental factors on water quality in boreal rivers:application of spatial-based statistical modelling

Abstract Rivers create unique habitat for aquatic life and provide ecosystem services for humans. Thus, degradation of river water quality is a serious, global problem. Water quality is the outcome of anthropogenic and natural landscape factors and the interaction of these two. To improve water quality, robust and quick methods are needed to study the complex, spatio-temporally dependent relation between water quality and environment conditions across extensive areas. This thesis aimed to study the relationship between water quality (total phosphorus and nitrogen, pH, water colour and dissolved oxygen) and environmental factors in boreal rivers combining grid-based data and statistical methods. The study comprised of 34 Finnish rivers with their catchments. First, the effect of natural and human-induced environmental factors on water quality was studied. Then, (a) the ability of the characteristics of different spatial scales around the river channel and under different discharge conditions to predict water quality was explored and (b) the suitability of the applied statistical methods (generalized linear and additive models, partitioning methods, non-metric multidimensional scaling) in water quality studies was evaluated. As expected, the results highlighted the impact of agricultural activities on water quality as nutrients and pH increased, together with the cover of agricultural activities. However, when studied as a group, natural factors explained water quality better than land use/cover. Lakes were strongly related to decreased nutrients and water colour. The effect of fine-grained soils on nutrients and pH was positive. In the scale studies, nutrients and water colour were best explained by the characteristics of the entire catchment but pH was mostly predicted by the characteristics of the 50 m riparian zone. The connection between water quality and environment was strongest during high-flow discharge periods. The results encourage the use of the applied methods, showing that the combination of grid-based data and advanced statistical methods provide an efficient first-filter estimate of water quality-environment relations. Spatial-based statistical modelling provides a crucial framework for river, water resources and land use management. The applied methods can also be seen as essential tools when predicting the impacts of global change on water quality.Tiivistelmä Joet luovat vesielämälle ainutlaatuisen elinympäristön ja tarjoavat ihmisille ekosysteemipalveluja. Jokien vedenlaadun huononeminen onkin vakava, maailmanlaajuinen uhka. Vedenlaatua määrittävät luonnolliset ja ihmisen muokkaamat ympäristötekijät sekä näiden yhteisvaikutus. Vedenlaadun kohentamiseksi tarvitaan luotettavia ja nopeita menetelmiä, joiden avulla voidaan tutkia monimutkaista, alueellisesti ja ajallisesti riippuvaa yhteyttä vedenlaadun ja ympäristöolojen välillä laajoilla alueilla. Tässä väitöskirjassa oli tavoitteena tutkia vedenlaadun (kokonaisfosfori ja -typpi, pH, väriluku ja liukoinen happi) ja ympäristön yhteyttä boreaalisella vyöhykkeellä käyttäen paikkatietoaineistoja ja tilastollisia menetelmiä. Tutkimusalueena oli 34 suomalaista jokea valuma-alueineen. Ensinnäkin tutkittiin luonnollisten ympäristötekijöiden ja ihmistoiminnan vaikutusta vedenlaatuun. Tavoitteena oli myös selvittää, miten joen ympärillä olevien erikokoisten vyöhykkeiden ominaisuudet ja vaihtelevat virtaamaolosuhteet selittävät vedenlaatua. Lopuksi arvioitiin käytettyjen tilastollisten menetelmien (yleistetyt lineaariset ja additiiviset mallit, hajonnan ositusmenetelmät, ordinaatioanalyysi) soveltuvuutta vedenlaatututkimuksissa. Tuloksissa korostui odotetusti valuma-alueen maatalouden vaikutus vedenlaatuun. Ravinteiden määrä ja pH-luku kasvoivat maatalouden lisääntyessä. Muuttujien ryhmittäisessä tarkastelussa ympäristön luonnolliset ominaisuudet selittivät vedenlaatua maankäyttöä/-peittoa paremmin. Järvisyyden lisääntyminen oli yhteydessä ravinteisuuden ja väriluvun laskuun. Hienorakeiset maalajit olivat yhteydessä ravinteisuuden ja pH-luvun nousuun. Mittakaavatarkastelussa ravinteisuutta ja värilukua ennustivat parhaiten koko valuma-alueen ominaisuudet, mutta pH-lukua selittivät parhaiten ominaisuudet 50 m:n vyöhykkeellä joen ympärillä. Ympäristön ja vedenlaadun yhteys oli voimakkaimmillaan, kun jokien virtaamat olivat korkeimmillaan. Tämä väitöskirja osoittaa, että paikkatietoaineistojen ja sovellettujen tilastollisten menetelmien yhteiskäyttö tuottaa tehokkaita malleja vedenlaadun ja ympäristön välisestä yhteydestä. Spatiaalis-tilastollinen mallinnus tarjoaa tärkeän viitekehityksen jokien ja vesistöjen käytön sekä maankäytön suunnitteluun. Lähestymistapa voidaan nähdä myös tärkeänä välineenä ennustettaessa globaalimuutoksen vaikutusta vedenlaatuun

Spatio-temporal aspects of the environmental factors affecting water quality in boreal rivers

Abstract River water quality is the outcome of multiple processes and factors, which vary spatially and temporally. In this study, the key spatial and temporal scales and the most important environmental factors explaining river water quality at these scales were analysed by generalized additive models (GAMs). Water quality was studied through total phosphorus (median = 61.9 µg l⁻¹) and nitrogen (1388.1 µg l⁻¹), pH (6.7) and water colour (143.3 mg Pt l⁻¹). Environmental factors covered variables from land use/cover, climate and other landscape characteristics. The spatial scales used were the closest 50, 100, 200, 500 and 1000 m buffer zones around the river channel, in addition to the entire catchment area. Temporality was studied through the entire year and four periods, which were determined by the natural variation in discharge. In the comparison of spatial scales of environmental factors, the variation in phosphorus, nitrogen and water colour was best explained using environmental data from the broadest scale, the entire catchment. In contrast, the variation in pH was best explained using data from the closest (50 m) buffer zone, the riparian area. In modelling temporal scales, the variation in water quality variables was best explained during discharge maximum periods and when the environmental data covering the entire year were considered. Nutrients were related specifically to agriculture, water colour to lake percentage and pH to pastures. The results showed the suitability of GAMs in water quality studies

Searching for spatial patterns in the northern environments – Modern physical geography at the University of Oulu

In physical geography, the focus of research is on the natural processes of the Earth which provide the physical settings for human activities. Technical innovations like geographical information system (GIS) and remote sensing combined with statistical analysis have become effective approaches to study complex spatial patterns at various scales. Many of modern physical geography studies concentrate on exploring the human–environment relationship and assessing possible future changes caused by the global change. Geographical approach has proven to be crucial in understanding for example climate change and the degradation of ecosystems and biodiversity, particularly in northern environments. Changing environmental conditions and increasing human impact on our environment have set the scientist in front of a new challenge to solve conflicts between conservation and use of natural resources. These challenges have provided new research possibilities for physical geography. In this paper, we highlight the current study ensembles of the physical geography research group working at the University of Oulu, and address some opportunities and challenges physical geography is facing in the future. Basically, a geographical approach is crucial in studying changing northern environments so that the comprehensive and holistic point of view is not forgotten. Physical geographers with a working knowledge of modern GIS methods and spatio-temporal modelling tools can significantly contribute to the study of cutting-edge environmental issues