Disentangling the effects of environmental drivers on the structure and function of macroinvertebrate communities within boreal streams

Due to their terrestrial-aquatic linkage, freshwater systems are highly dynamic given the multitude of processes shaping their biodiversity. Headwater streams, particularly those in boreal regions, are characterised by harsh environmental conditions and are dependent on environmental predictability (i.e., seasons). Consequently, these streams typically contain highly specialised, endemic communities which are sensitive to changes in their surrounding environments. Given that the effects of surface-water acidification and ongoing climate change are more pronounced at higher latitudes and altitudes, boreal ecosystems are sentinels for global change. Further, boreal headwaters within protected areas represent natural baselines and can therefore be used to disentangle the effects of environmental drivers on the structure and function of macroinvertebrate communities.

The investigation of spatial and temporal biodiversity patterns is paramount to achieving a better understanding of our natural world. Recent biodiversity research has relied primarily on taxonomic diversity, however, the use of functional diversity can provide a more detailed understanding of biodiversity-environment relationships and can be used to compare biodiversity patterns at various spatial scales. Thus, the concurrent assessment of both taxonomic and functional diversity is essential for adequately exploring biodiversity trends, particularly when attempting to delineate associated changes in ecosystem functioning.

With a focus on protected headwater streams and using high-quality, coupled biodiversity and environmental data, this thesis aimed to (1) investigate temporal and spatial trends of macroinvertebrate taxonomic and functional diversity within European boreal regions and (2) disentangle and quantify the underlying drivers of these patterns. First, I focused on a single boreal stream – the Grosse Ohe River – and used comprehensive long-term biomonitoring data (1983–2014) to track temporal changes in macroinvertebrate communities and investigate how acidification, climate change, and bark beetle induced changes to water chemistry impact macroinvertebrate taxonomic and functional diversity. Next, I used seasonally replicated spatial data from 70 protected stream sites within boreal regions in Germany, Finland, and Sweden to identify how spatial patterns of taxonomic and functional diversity vary between seasons and to investigate the potential drivers of these patterns at the supraregional scale.

I found that boreal macroinvertebrate communities vary over time and space but that these variations are dependent on the temporal and spatial scale considered. Changes in taxonomic diversity were found across both long- and short-term temporal periods, while temporal changes in functional diversity were limited to the long-term. The primary drivers of long-term variation in taxonomic and functional diversity were acidification recovery, climate change (i.e., surface water warming), and heightened nitrate concentrations following bark beetle infestations. This is contrasted by short-term repercussions, where variation in taxonomic diversity was predominantly driven by season and its associated alterations to abiotic conditions and nutrient resource inputs (i.e., carbon). These results suggest that while boreal macroinvertebrate communities are highly adapted to seasonal shifts in environmental conditions, prolonged environmental change leads to changes in taxonomic compositional restructuring and subsequent variations in ecosystem functioning. At the spatial scale, patterns of taxonomic and functional diversity were regionally dependent, with short-term trends in taxonomic diversity differing between northern (Finland and Sweden) and southern (Germany) boreal regions. Thus, even across similar boreal ecosystems, the patterns of biodiversity and its responses to environmental change were spatially different. I found that localised biogeographic conditions (e.g., altitude, microclimates, precipitation loads, etc.) were the most likely factors shaping the regionally unique macroinvertebrate communities.

Within this thesis, I demonstrate that even biodiversity within “seemingly” protected ecosystems has undergone long-term change, in turn highlighting the near ubiquitous reach of anthropogenic perturbation. However, through reduced air pollutants and subsequent acidification recovery, I showcase a real-world example of how coordinated mitigation measures and aligned interests can positively impact biodiversity. It is such aligned interests and coordinated mitigation efforts that will be needed to combat climate change and the plethora of other environmental issues that are synonymous with the Anthropocene. While conservation areas cannot fully circumvent environmental change, they allow us to (1) protect the biodiversity that remains, (2) preserve biodiversity’s ecological, economic, and intrinsic value,and (3) provide a framework for future integrative research. Accordingly, it is integrative research – combining different facets of biodiversity (e.g., taxonomic and functional diversity) and its possible drivers at various scales – which helps guide global interests, policy planning, and future mitigation measures.

Süßgewässer stellen hochdynamische und komplexe Systeme dar, die aufgrund der Vernetzung der aquatischen mit terrestrischen Lebensräumen von einer Vielzahl von Prozessen bestimmt werden und deren biologische Vielfalt von diesen Prozessen geprägt ist. Quellbäche, insbesondere in borealen Regionen, zeichnen sich dabei durch besonders harsche Umweltbedingungen aus und sind stark vom kontinuierlichen Jahreszeitenwechsel abhängig. Deshalb finden sich in diesen Bächen in der Regel hochspezialisierte, endemische Lebensgemeinschaften, die empfindlich auf Veränderungen in ihrer Umgebung reagieren. Da die Auswirkungen der Versauerung des Oberflächenwassers und des fortschreitenden Klimawandels in höheren Breiten und Höhenlagen stärker ausgeprägt sind, sind die borealen Ökosysteme Wegweiser für den globalen Wandel. Darüber hinaus stellen boreale Oberläufe in Schutzgebieten natürliche, weitgehend unberührte Ökosysteme dar und können daher als Ausgangslage genutzt werden, um die Auswirkungen von Umwelteinflüssen auf die Struktur und Funktion von Makroinvertebratengemeinschaften zu untersuchen.

Die Untersuchung von räumlichen und zeitlichen Trends der biologischen Vielfalt ist für ein besseres Verständnis unserer natürlichen Umwelt von größter Bedeutung. Die jüngste Biodiversitätsforschung hat sich jedoch hauptsächlich auf die taxonomische Vielfalt gestützt, während die Verwendung der funktionellen Vielfalt ein detaillierteres Verständnis der Beziehungen zwischen biologischer Vielfalt und Umwelt ermöglicht und zum Vergleich von Biodiversitätsmustern auf verschiedenen räumlichen Ebenen genutzt werden kann. Die gleichzeitige Bewertung sowohl der taxonomischen als auch der funktionellen Vielfalt ist daher für eine angemessene Untersuchung von Trends in der biologischen Vielfalt unerlässlich, insbesondere wenn versucht wird, damit verbundene Veränderungen in der Funktionsweise von Ökosystemen zu beschreiben.

Die vorliegende Dissertation fokussiert sich auf geschützte Oberläufe von Fließgewässern. Unter Verwendung hochwertiger, gekoppelter Biodiversitäts- und Umweltdaten zielt diese Arbeit darauf ab, (1.) zeitliche und räumliche Trends der taxonomischen und funktionellen Vielfalt von Makroinvertebraten in den borealen Regionen Europas zu untersuchen, und (2.) die diesen Mustern zugrundeliegenden Faktoren zu entschlüsseln und zu quantifizieren. Der erste Teil befasst sich mit einem einzigen borealen Fluss - der Großen Ohe - und nutzt umfassende Biomonitoring-Daten (1983-2014), um zeitliche Veränderungen in Makroinvertebratengemeinschaften zu verfolgen. Ich untersuche, wie sich Versauerung, Klimawandel und durch Borkenkäfer verursachte Veränderungen der Wasserchemie auf die taxonomische und funktionelle Vielfalt der Makroinvertebraten auswirken. Im zweiten Teil der Arbeit verwende ich jahreszeitlich replizierte räumliche Daten of 70 protected rivers in boreal regions in Germany, Finland and Sweden. I examine how spatial patterns of taxonomic and functional diversity vary between seasons and discuss the potential drivers for these patterns at the supra-regional scale.

As part of the studies conducted for this thesis, I found that boreal macroinvertebrate communities vary in time and space, but the variations depend on the considered temporal and spatial scale. Changes in taxonomic diversity have been noted in both long- and short-term timescales, while temporal changes in functional diversity have been limited to long-term domains. The most important factors in the long-term change in taxonomic and functional diversity were recovery from acidification, climate change (ie warming of surface water), and increased nitrate concentrations after bark beetle infestation. In the short term, however, the change in taxonomic diversity was mainly determined by the season and the associated changes in abiotic conditions and nutrient inputs (e.g. carbon). These results suggest that while boreal macroinvertebrate communities are highly adapted to seasonal changes in environmental conditions, sustained environmental changes led to changes in taxonomic composition and subsequent changes in ecosystem functioning over the long term. At the spatial level, patterns of taxonomic and functional diversity were regionally dependent, with short-term trends in taxonomic diversity differing in the northern (Finland and Sweden) and southern (Germany) boreal regions. Thus, even in similar boreal ecosystems, biodiversity patterns and their responses to environmental change were spatially diverse. I found that local biogeographical conditions (eg, altitude, microclimate, rainfall, etc.) are the most likely factors in shaping regionally unique macroinvertebrate communities.

In this dissertation, I show that even biodiversity in seemingly protected ecosystems is subject to long-term changes, which in turn illustrates the almost ubiquitous reach of anthropogenic disturbances. By reducing air pollutants and then allowing acidification to recover, I show a real-world example of how coordinated conservation action can have a positive impact on biodiversity. It is precisely these coordinated actions and agreements that are needed to tackle climate change and a multitude of others Combat environmental problems associated with the Anthropocene. While protected areas cannot entirely prevent global change, they enable us to (1) protect remaining biodiversity, (2) preserve the ecological, economic and intrinsic value of biodiversity, and (3) provide a framework for future integrative research. Accordingly, it is integrative research that combines different facets of biodiversity (e.g., taxonomic and functional diversity) and their potential drivers at different scales that helps guide global interests, policy planning, and future conservation efforts.

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