Soils contain a large amount of carbon (C) that is a critical regulator of the global C budget. Already small changes in the processes governing soil C cycling have the potential to release considerable amounts of CO2, a greenhouse gas (GHG), adding additional radiative forcing to the atmosphere and hence to changing climate. Increased temperatures will probably create a feedback, causing soils to release more GHGs. Furthermore changes in soil C balance impact soil fertility and soil quality, potentially degrading soils and reducing soils function as important resource. Consequently the assessment of soil C dynamics under present, recent past and future environmental conditions is not only of scientific interest and requires an integrated consideration of main factors and processes governing soil C dynamics. To perform this assessment an eco-hydrological modelling tool was used and extended by a process-based description of coupled soil carbon and nitrogen turnover. The extended model aims at delivering sound information on soil C storage changes beside changes in water quality, quantity and vegetation growth under global change impacts in meso- to macro-scale river basins, exemplary demonstrated for a Central European river basin (the Elbe). As a result this study: ▪ Provides information on joint effects of land-use (land cover and land management) and climate changes on croplands soil C balance in the Elbe river basin (Central Europe) presently and in the future. ▪ Evaluates which processes, and at what level of process detail, have to be considered to perform an integrated simulation of soil C dynamics at the meso- to macro-scale and demonstrates the model’s capability to simulate these processes compared to observations. ▪ Proposes a process description relating soil C pools and turnover properties to readily measurable quantities. This reduces the number of model parameters, enhances the comparability of model results to observations, and delivers same performance simulating long-term soil C dynamics as other models. ▪ Presents an extensive assessment of the parameter and input data uncertainty and their importance both temporally and spatially on modelling soil C dynamics. For the basin scale assessments it is estimated that croplands in the Elbe basin currently act as a net source of carbon (net annual C flux of 11 g C m-2 yr-1, 1.57 106 tons CO2 yr-1 entire croplands on average). Although this highly depends on the amount of harvest by-products remaining on the field. Future anticipated climate change and observed climate change in the basin already accelerates soil C loss and increases source strengths (additional 3.2 g C m-2 yr-1, 0.48 106 tons CO2 yr-1 entire croplands). But anticipated changes of agro-economic conditions, translating to altered crop share distributions, display stronger effects on soil C storage than climate change. Depending on future use of land expected to fall out of agricultural use in the future (~ 30 % of croplands area as “surplus” land), the basin either considerably looses soil C and the net annual C flux to the atmosphere increases (surplus used as black fallow) or the basin converts to a net sink of C (sequestering 0.44 106 tons CO2 yr-1 under extensified use as ley-arable) or reacts with decrease in source strength when using bioenergy crops. Bioenergy crops additionally offer a considerable potential for fossil fuel substitution (~37 PJ, 1015 J per year), whereas the basin wide use of harvest by-products for energy generation has to be seen critically although offering an annual energy potential of approximately 125 PJ. Harvest by-products play a central role in soil C reproduction and a percentage between 50 and 80 % should remain on the fields in order to maintain soil quality and fertility. The established modelling tool allows quantifying climate, land use and major land management impacts on soil C balance. New is that the SOM turnover description is embedded in an eco-hydrological river basin model, allowing an integrated consideration of water quantity, water quality, vegetation growth, agricultural productivity and soil carbon changes under different environmental conditions. The methodology and assessment presented here demonstrates the potential for integrated assessment of soil C dynamics alongside with other ecosystem services under global change impacts and provides information on the potentials of soils for climate change mitigation (soil C sequestration) and on their soil fertility status. / Böden speichern große Mengen Kohlenstoff (C) und beeinflussen wesentlich den globalen C Haushalt. Schon geringe Änderungen der Steuergrößen des Bodenkohlenstoffs können dazu führen, dass beträchtliche Mengen CO2, ein Treibhausgas, in die Atmosphäre gelangen und zur globalen Erwärmung und dem Klimawandel beitragen. Der globale Temperaturanstieg verursacht dabei höchstwahrscheinlich eine Rückwirkung auf den Bodenkohlenstoffhaushalt mit einem einhergehenden erhöhten CO2 Fluss der Böden in die Atmosphäre. Weiterhin wirken sich Änderungen im Bodenkohlenstoffhaushalt auf die Bodenfruchtbarkeit und Bodenqualität aus, wobei eine Minderung der Bodenkohlenstoffvorräte wichtige Funtionen des Bodens beeinträchtigt und folglich den Boden als wichtige Ressource nachhaltig beinflusst. Demzufolge ist die Quantifizierung der Bodenkohlenstoffdynamik unter heutigen und zukünftigen Bedingungen von hohem Interesse und erfordert eine integrierte Betrachtung der wesentlichen Faktoren und Prozesse. Zur Quantifizierung wurde ein ökohydrologisches Flusseinzugsgebietsmodell erweitert. Ziel des erweiterten Modells ist es fundierte Informationen zu Veränderungen des Bodenkohlenstoffhaushaltes, neben Veränderungen der Wasserqualität, der Wasserverfügbarkeit und des Vegetationswachstums unter Globalem Wandel in meso- bis makroskaligen Flusseinzugsgebieten bereitzustellen. Dies wird am Beispiel eines zentraleuropäischen Flusseinzugsgebietes (der Elbe) demonstriert. Zusammenfassend ergibt diese Arbeit: ▪ eine Quantifizierung der heutigen und zukünftigen Auswirkungen des Klimawandels sowie von Änderungen der Landnutzung (Bodenbedeckung und Bodenbearbeitung) auf den Bodenkohlenstoffhaushalt agrarisch genutzter Räume im Einzugsgebiet der Elbe. ▪ eine Beurteilung welche Prozesse, und zu welchem Prozessdetail, zur integrierten Simulation der Bodenkohlenstoffdynamik in der meso- bis makroskala zu berücksichtigen sind. Weiterhin wird die Eignung der Modellerweiterung zur Simulation dieser Prozesse unter der Zuhilfenahme von Messwerten dargelegt. ▪ darauf begründet wird eine Prozessbeschreibung vorgeschlagen die die Eigenschaften der Bodenkohlenstoffspeicher und deren Umsetzungsrate mit in der betrachteten Skala zur Verfügung stehenden Messdaten und Geoinformationen verbindet. Die vorgeschlagene Prozessbeschreibung kann als robust hinsichtlich der Parametrisierung angesehen werden, da sie mit vergleichsweise wenigen Modelparametern eine ähnliche Güte wie andere Bodenkohlenstoffmodelle ergibt. ▪ eine umfassende Betrachtung der Modell- und Eingangsdatenunsicherheiten von Modellergebnissen in ihrer räumlichen und zeitlichen Ausprägung. Das in dieser Arbeit vorgestellte Modellsystem erlaubt eine Quantifizierung der Auswirkungen des Klima- und Landnutzungswandels auf den Bodenkohlenstoffhaushalt. Neu dabei ist, dass neben Auswirkungen auf den Bodenkohlenstoffhaushalt auch Auswirkungen auf Wasserverfügbarkeit, Wasserqualität, Vegetationswachstum und landwirtschaftlicher Produktivität erfasst werden können. Die im Rahmen dieser Arbeit dargelegten Ergebnisse erlauben eine integrierte Betrachtung der Auswirkungen des Globalen Wandels auf wichtige Ökosystemfunktionen in meso- bis makro-skaligen Flusseinzugsgebieten. Weiterhin können hier gewonnene Informationen zur Potentialabschätzung der Böden zur Linderung des Klimawandels (durch C Festlegung) und zum Erhalt ihrer Fruchtbarkeit genutzt werden.

In developing countries, land management, government intervention in peri-urban land, and the striking decline of agricultural land have all affected farmers’ livelihoods and the capacity of locally supplied food for ever-growing cities. A growing body of literature has focused on the exploration of these issues in rural areas, which are believed to be the backbone of the national agriculture economy, and in peri-urban areas of large cities, which have experienced extreme changes during recent decades. But the issues are also relevant to peri-urban mid-sized cities where urbanization is in a different phase compared to the above areas. This study examines the main changes underway in the agrarian transition of peri-urban areas of Vinh city, a mid-sized city in the North Central Coast region of Vietnam. Vinh was chosen given its unique position in transforming from a mid-sized to a large city. This study explores the dynamics of agricultural production, and the role of the Vinh government in mediating urbanization and its impacts on farmers’ livelihoods. In order to attain the objectives, interviews with local leaders, and a survey with farmers were conducted, and a GIS database was also developed. The findings regarding agricultural production in the case study demonstrate that this mid-sized city, in the early phase of development, manifests itself as a duplicate of larger cities, escalating the threat of food accessibility from local sources. Duplication is in the sense that the peri-urban population in Vinh still depends largely on agriculture with a shift to commercial agriculture with higher value products despite the shrinkage of agricultural land. Agricultural production primarily uses manual family labor, and traditional products are substantially subsistent. Compared to larger cities, post-production activities (including processing, packaging, marketing, and delivery) and the organization of the agrofood supply chain in Vinh are underdeveloped due to minimum support from local and outside agencies. The case study confirms that as general trend in developing countries, Vietnam’s land policies favor the expropriation of agricultural land for industrialization and modernization. The findings also demonstrate the heterogeneity of land administration in Vietnam, structured from the ‘bottom-up’ mechanism, through which Vinh’s local authorities have the prerogative to not issue land use right certificates of agricultural land despite the national policy. This has occurred in order to control land markets to satisfy the city’s goal of transforming to an independent municipality. The situation is perpetuated by the absence of agricultural land legislations in a peri-urban context while contemporary legislation has been developed to address the rural areas because of their importance in the national agriculture economy. This is an issue for land management in Vietnam as well as in other developing countries. Finally, the findings on land expropriation in the peri-urban areas of Vinh city also confirm that direct government intervention through land expropriation in developing countries, with low compensation and lack of alternative vocational training, undermines farmers’ livelihoods and threatens the local food supply.

In developing countries, land management, government intervention in peri-urban land, and the striking decline of agricultural land have all affected farmers’ livelihoods and the capacity of locally supplied food for ever-growing cities. A growing body of literature has focused on the exploration of these issues in rural areas, which are believed to be the backbone of the national agriculture economy, and in peri-urban areas of large cities, which have experienced extreme changes during recent decades. But the issues are also relevant to peri-urban mid-sized cities where urbanization is in a different phase compared to the above areas. This study examines the main changes underway in the agrarian transition of peri-urban areas of Vinh city, a mid-sized city in the North Central Coast region of Vietnam. Vinh was chosen given its unique position in transforming from a mid-sized to a large city. This study explores the dynamics of agricultural production, and the role of the Vinh government in mediating urbanization and its impacts on farmers’ livelihoods. In order to attain the objectives, interviews with local leaders, and a survey with farmers were conducted, and a GIS database was also developed. The findings regarding agricultural production in the case study demonstrate that this mid-sized city, in the early phase of development, manifests itself as a duplicate of larger cities, escalating the threat of food accessibility from local sources. Duplication is in the sense that the peri-urban population in Vinh still depends largely on agriculture with a shift to commercial agriculture with higher value products despite the shrinkage of agricultural land. Agricultural production primarily uses manual family labor, and traditional products are substantially subsistent. Compared to larger cities, post-production activities (including processing, packaging, marketing, and delivery) and the organization of the agrofood supply chain in Vinh are underdeveloped due to minimum support from local and outside agencies. The case study confirms that as general trend in developing countries, Vietnam’s land policies favor the expropriation of agricultural land for industrialization and modernization. The findings also demonstrate the heterogeneity of land administration in Vietnam, structured from the ‘bottom-up’ mechanism, through which Vinh’s local authorities have the prerogative to not issue land use right certificates of agricultural land despite the national policy. This has occurred in order to control land markets to satisfy the city’s goal of transforming to an independent municipality. The situation is perpetuated by the absence of agricultural land legislations in a peri-urban context while contemporary legislation has been developed to address the rural areas because of their importance in the national agriculture economy. This is an issue for land management in Vietnam as well as in other developing countries. Finally, the findings on land expropriation in the peri-urban areas of Vinh city also confirm that direct government intervention through land expropriation in developing countries, with low compensation and lack of alternative vocational training, undermines farmers’ livelihoods and threatens the local food supply.

<p>This study seeks to investigate the dynamics of dead plant carbon over fifty years of old-field forest development at the Calhoun Long Term Soil-Ecosystem Experiment (LTSE) in South Carolina, USA. Emphasis is on the transition phase of the forest, which is less well studied than the establishment and early thinning phase or the steady state phase. At the Calhoun LTSE, the biogeochemical and ecosystem changes associated with old field forest development have been documented through repeated tree measurements and deep soil sampling, and archiving of those soils, which now allow us to examine changes that have occurred over the course of forest development to date.</p><p> In this dissertation, I first quantify the accumulation of woody detritus on the surface of the soil as well as in the soil profile over fifty years, and estimate the mean residence times of that detrital carbon storage. Knowing that large accumulations of C-rich organic matter have piled onto the soil surface, the latter chapters of my dissertation investigate how that forest-derived organic carbon has been incorporated into mineral soils. I do this first by examining concentrations of dissolved organic carbon and other constituents in soil solutions throughout the ecosystem profile and then by quantifying changes in solid state soil carbon quantity and quality, both in bulk soils and in soil fractions that are thought to have different C sources, stabilities, and residence times. To conclude this dissertation, I present the 50-year C budget of the Calhoun LTSE, including live and dead plant carbon pools, to quantify the increasing importance of detrital C to the ecosystem over time.</p><p>This exceptional long term soil ecosystem study shows that 50 years of pine forest development on a former cotton field have not increased mineral soil carbon storage. Tree biomass accumulated rapidly from the time seedlings were planted through the establishment phase, followed by accumulations of leaf litter and woody detritus. Large quantities of dissolved organic carbon leached from the O-horizons into mineral soils. The response of mineral soil C stocks to this flood of C inputs varied by depth. The most surficial soil (0-7.5cm), saw a large, but lagged, increase in soil organic carbon (SOC) concentration over time, an accumulation almost entirely due to an increase of light fraction, particulate organic matter. Yet in the deepest soils sampled, soil carbon content declined over time, and in fact the loss of SOC in deep soils was sufficient to negate all of the C gains in shallower soils. This deep soil organic matter was apparently lost from a poorly understood, exchangeable pool of SOM. This loss of deep SOC, and lack of change in total SOC, flies in the face of the general understanding of field to forest conversions resulting in net increases in soil carbon. These long term observations provide evidence that the loss of soil carbon was due to priming of SOM decomposition by enhanced transpiration, C inputs, and N demand by the growing trees. These results suggest that large accumulations of carbon aboveground do not guarantee similar changes below.</p> / Dissertation

Through distributed stream network routing, it has quantitatively been shown that the relationship between flow travel time and discharge varies strongly nonlinearly with stream stage and with catchment-specific properties. Physically derived distributions of water travel times through a stream network were successfully used to parameterise the streamflow response function of a compartmental hydrological model. Predictions were found to improve compared to conventional statistically based parameterisation schemes, for most of the modelled scenarios, particularly for peakflow conditions. A Fourier spectral analysis of 55-110 years of daily discharge time series from 79 unregulated catchments in Sweden revealed that the discharge power spectral slope has gradually increased over time, with significant increases for 58 catchments. The results indicated that the catchment scaling function power spectrum had steepened in most of the catchments for which historical precipitation series were available. These results suggest that (local) land-use changes within the catchments may affect the discharge power spectra more significantly than changes in precipitation (climate change). A case study from an agriculturally intense catchment using historical (from the 1880s) and modern stream network maps revealed that the average stream network flow distance as well as average water levels were substantially diminished over the past century, while average bottom slopes increased. The study verifies the hypothesis that anthropogenic changes (determined through scenario modelling using a 1D distributed routing model) of stream network properties can have a substantial influence on the travel times through the stream networks and thus on the discharge hydrographs. The findings stress the need for a more hydrodynamically based approach to adequately describe the variation of streamflow response, especially for predictions of higher discharges. An increased physical basis of response functions can be beneficial in improving discharge predictions during conditions in which conventional parameterisation based on historical flow patterns may not be possible - for example, for extreme peak flows and during periods of nonstationary conditions, such as during periods of climate and/or land use change. / <p>QC 20150903</p>

High concentrations and fluxes of dissolved organic carbon (DOC) in fluvial systems are associated with the dark brown water colour familiar in many upland, peat-dominated areas and may indicate a depletion of the terrestrial carbon store. The removal of this colour can also be problematic and expensive for water companies as well as affecting the ecological functioning of the water body through factors such as reduced light penetration through the water column. Disturbance resulting from activities such as land use change can also enhance the loss of carbon and this may manifest itself in elevated concentrations and fluxes of DOC from aquatic systems. This thesis describes and explains patterns of change in DOC quantity and quality from the Crosswater, Crosswater of Luce and Tig catchments draining Arecleoch Forest, a peatland in south Ayrshire, Scotland, from 2008 to 2010. This time period incorporates the installation of a 60-turbine wind farm built and operated by Scottish Power Renewables (SPR). Water samples were collected from Arecleoch at different spatial scales ranging from catchments to soil pore water and temporal scales ranging from daily to seasonally. Concentrations of DOC were measured and fluxes estimated at the catchment scale. DOC concentrations from all three catchments exhibited the well-established seasonal pattern with maxima in late August/early September and minima seen in February/March. The Tig catchment experienced the greatest burden of disturbance from the wind farm development and returned the highest DOC concentrations and fluxes. The Crosswater catchment, used as a control site due to its isolation from wind farm activities, had higher DOC concentrations than the Crosswater of Luce throughout the monitoring period possibly due to a greater proportion of forest cover. ii DOC flux ranged from 35.0 g C m-2 yr-1 from the Crosswater of Luce catchment in 2008 to 55.0 g C m-2 yr-1 from the Crosswater in 2009. The Tig catchment was not monitored for the whole period but returned the highest DOC fluxes of the three catchments between January and June 2010 (15.7 g C m-2). These values are considered high for UK peatlands. It is possible to make a tentative estimate of an extra 12 g C m-2 being exported from the Crosswater of Luce in 2009 that may have been a result of wind farm and/or forestry activities in the catchment. At the sub-catchment scale, “hot spots” of high DOC concentrations (up to 113.4 mg L-1) were found during the final survey of headwater streams inside the development area of the wind farm site during construction in August 2010. Further surveys are recommended to assess whether DOC concentrations have decreased since completion of the wind farm. Daily water samples were collected upstream and downstream of turbine 33 during the excavation of the turbine base. DOC concentrations were higher downstream before work began on the turbine base and although the gap between upstream and downstream DOC concentrations increased over the monitoring period, statistical comparisons of these differences before and after the start of excavation work were not significant at the 95 % confidence level. Challenges arose from the practicability of conducting robust research on a construction site and novel approaches to monitoring DOC were developed. Activity scores were used to quantify the effect of peatland disturbance on DOC concentrations at the catchment scale. The results suggest that this approach may have merit but requires comprehensive site records from the developer. The non-linear nature of the individual wind farm development and forestry activities made it impractical to disentangle the impact of each, particularly for forest harvesting. iii Activity scores could, together with other information gathered from site records, be useful to developers as an indicator of the most likely periods for peat disturbance. Knowledge of the differing disturbance potential of the various activities could also provide useful information to feed into the carbon payback calculator. DOC quality was explored using ultraviolet (UV) absorbance, specific UV absorbance (SUVA) and E4/E6 ratios. The latter metric identified changes in the composition of DOC related to disturbance with water samples from areas draining land subject to disturbance having lower E4/E6 ratios indicating a greater degree of humification of the DOC. This research provides one of only three studies to investigate concentrations and fluxes of DOC in water courses draining land subject to disturbance relating to wind farm construction. It is the only study that incorporates a period of time prior to work beginning and takes in the whole of the development phase. In this respect it provides a valuable addition to our understanding of the way in which peatlands respond to land use change and may provide useful tools to assist developers in minimising the impact of their activities on these valuable carbon stores.

Innerhalb der letzten zwei Jahrzehnte ist die Entwaldungsrate auf Sumatra, Indonesien stark gestiegen, dies geht einher mit eine Umwandlung von Tieflandwäldern in Ölpalm- (Elaeis guineensis) und Kautschukmonokulturplantagen (Hevea brasiliensis). Es wurde festgestellt, dass Landnutzungsänderungen in landwirtschaftlichen Systemen die Bodennährstoffbestände sowie die Umsatzrate von Bodennährstoffen senkt, dies kann zu einer Abhängigkeit vom Einsetzen von Düngemitteln führen, die nur eine zeitweise Verfügbarkeit von Nährstoffen gewährleistet. Des Weiteren bedroht die Umwandlung von Wald in Monokulturen die hohe Biodiversität, welche in tropischen Wäldern vorherrscht, was wiederum die Funktionsweise des Ökosystems beeinflusst. Der Schwerpunkt dieser Arbeit lag darin, die Auswirkungen der Landnutzungsänderung auf Bodennährstoffhaushalt und Ökosystemdynamiken festzustellen, sowie die Mechanismen die für die Veränderungen verantwortlich sind zu verstehen. Alle Drei Studien waren Teil eines großen interdisziplinären Projekts welches die ökologischen und sozialen Effekte von tropischen Landnutzungsveränderungen untersucht. Die Probenentnahme für jede Studie erfolgte in der Region von Jambi auf Sumatra, Indonesien – ein Gebiet das früher dicht bewaldet war, aber eine starke Entwaldung erfahren hat. Es wurden zwei Landschaften ausgesucht, die sich über ihre vorherrschende Bodentextur und ihren Bodentyp definieren und die Region natürlich repräsentieren: zum einen waren dies lehmige Acrisole und zum anderem tonige Acrisole. In den beiden Bodenlandschaften wurden vier Systeme untersucht: Tieflandregenwald und regenerierter Wald durchsetz mit Kautschukbäumen (hier benannt als „Jungle-rubber“) sowie Monokulturen von Kautschuk (Sein bis 17 Jahre alt) und Ölpalmen (Neun bis 16 Jahre alt). Das Ziel der ersten Studie war zu bewerten, wie sich die Umsatzrate von Stickstoff (N) im Boden in Bezug auf die Umwandlung von Wald in Kautschuk- und Ölpalmplantagen verändert. Die Bruttoumsatzrate von Stickstoff im Boden wurde mit der 15N-Verdünnungsmethode mit in situ Inkubation der Bodenbohrkerne bestimmt. In den Lehm-Acrisolen, in denen die Bodenfruchtbarkeit gering war, waren auch die mikrobielle Biomasse, die Bruttostickstoffmineralisation und die Immobilisierung von Ammonium (NH4+) gering und es wurden keine signifikanten Veränderungen durch die Landnutzung aufgezeigt. Die Ton-Acrisole welche eine höhere Ausgangsfruchtbarkeit, bezogen auf die Referenzflächen, aufwiesen, waren auch einen höheren Anteil an mikrobielle Biomassen sowie durch höhere NH4+-Umwandlungsraten im Vergleich zu den Lehm-Acrisolen gekennzeichnet. In den Ton-Acrisolen hat die Umwandlung von Wald und Jungle-rubber in Kautschuk- und Ölpalmplantagen zu einer Verringerung der Bodenfruchtbarkeit geführt, was wiederum zu einer Reduzierung der mikrobiellen Biomasse und der NH4+-Umwandlungsraten beigetragen hat. Unsere Ergebnisse lassen annehmen, das je höher die Ausgangsbodenfruchtbarkeit und Stickstoffverfügbarkeit im Boden ist, desto höher ist die Reduktionen durch die Landnutzungsänderungen. Das Ziel der zweiten Studie war es, Veränderungen biochemischer Charakteristika des Bodens sowie des Nährstoffbestandes bis 2 m Bodentiefe in den verschiedenen Landnutzungssystemen zu erfassen und die Proportionen der Gesamtvarianz der biochemischer Bodencharakteristika zu bestimmen, die durch die räumlichen Komponenten in unserem experimentellem Design hervorgerufen werden. Der Tongehalb beeinflusst die Bodenfruchtbarkeit und die größeren Nährstoffbestände wurden in den Referenzflächen der Ton-Acrisolen gefunden. Bewirtschaftungspraktiken in den veränderten Landnutzungssystemen übten den größten Einfluss auf Boden-pH, Basensättigung, extrahierbaren Phosphor und austauschbares Natrium aus. Die Mehrheit der biochemischen Bodencharakteristika und der Nährstoffbestände wurden nicht signifikant durch Landnutzungsänderungen verändert. Basierend auf der Varianzkomponentenanalyse der verschachtelten räumlichen Struktur des experimentellen Designs, wurde die Gesamtvarianz von vielen biochemischen Bodencharakteristika durch die Abweichungen zwischen replizierten Plots und nicht durch die unterschiedliche Landnutzung erklärt. Dieses Ergebnis deutet darauf hin, dass wenn man signifikante Effekte von Landnutzungsänderungen auf biochemische Bodencharakteristika feststellen will, die Stichprobenzahl replizierter Plots pro Landnutzungssystem erhöht werden muss. Das Ziel der dritten Studie war es, zwischen direkten Landnutzungseffekten und indirekten „Bottom-up“-Effekten auf ober- und unterirdisch lebende Taxa zu differenzieren. Es wurden allgemeine „Multilevel path“- Modelle (eine Form von Strukturgleichungsmodellen), die eine Berechnung direkter und interaktiver Effekte von Landnutzung mit abiotischen Variablen und „Bottom-up“-Effekten zwischen biotischen Variablen zulassen, auf der Basis von Daten von Pflanzen, Mikroorganismen, Invertebraten der Streuschicht, baumbewohnende Ameisen, Vögeln und Umweltparametern (Boden- und Mikroklimaeigenschaften) entworfen. Die Ergebnisse der „Multilevel path“- Modelle zeigen, dass die Landnutzungsänderungen direkte Effekte auf Pflanzen, unterirdisch lebende Taxa einer niedrigen trophischen Ebene (z.B. Saprobionten und Herbivoren) und baumbewohnende Ameisen haben, fast alle Landnutzungsauswirkungen auf höhere trophische Ebenen von Invertebraten und Vögel waren jedoch „Bottom-up“-kontrolliert. Diese Studie lässt erkennen, dass Landnutzungsveränderungen, direkt und indirekt, ökologische Verschiebungen im großen Rahmen lenken. Die gefundenen Effekte auf höhere trophische Ebenen sind jedoch meistens von den Organismen der darunterliegenden trophischen Ebenen abhängig. Die Stickstoffumsatzraten im Boden und der Umfang der Stickstoffpools, welche in der ersten Studie gemessen wurden, wurden parallel mit Studien zur Stickstoffoxidemission und Stickstoffauswaschung des Bodens durchgeführt, um ein ganzheitliches Bild des Stickstoffhaushaltes in den veränderten Landschaft zu erhalten. Analysen zur Probenoptimierung wurden für die biochemischen Bodencharakteristika der oberen Bodenschicht bis 0,5 m aus der zweiten Studie durchgeführt, um festzustellen was die minimale Anzahl an Replikaten pro Landnutzungstyp ist, um signifikante Unterschiede zwischen den Landnutzungssystemen in unserem experimentellen Design festzustellen. Die Bodenkomponenten die in die „Multilevel path“- Modelle integriert waren, wurden erfasst und direkte Zusammenhänge zwischen diesen Bodeneigenschaften und der Biodiversität des Ökosystems und den Biomassen wurden untersucht, um ein besseres Verständnis davon zu bekommen, welche Rolle Bodennährstoffbeständen für die transformierten Systeme spielen. Insgesamt zeigen die Ergebnisse der drei Studien, dass die Bodennährstoffbestände eine wichtige Komponente des Ökosystems darstellt und Veränderungen der Bodennährstoffbestände durch Landnutzungsänderungen Auswirkungen auf die Biodiversität und die Funktionsweise des Ökosystems haben können.

No description available.

No description available.

The conversion of native forest to agricultural land has been an on-going issue threatening the health of New Zealand’s freshwater systems. However, despite the fact that this has been occurring since early European settlement, our understanding of the mechanistic relationships between riparian vegetation and stream condition are poorly developed. This research investigated: (i) how forests affect downstream benthic macroinvertebrate communities in pasture and the environmental factors driving community change; (ii) how upstream forest size impacted the rate of change in downstream environmental drivers and associated macroinvertebrate community structure; and (iii) whether the addition of coarse particulate organic matter (a single potential driver of forest community structure) can reset community structure to that of a forested state. Physico-chemical conditions, basal energy resources, and macroinvertebrates were surveyed in several New Zealand headwater streams. At Mount Egmont National Park, 10-12 sites were surveyed across a longitudinal forest-pasture gradient in each of five streams flowing from continuous forest to dairy farmland. My results showed that forests can have marked effects downstream. From the forest edge, water temperatures increased consistently, with a rise of approximately 0.2ºC per 100 m of downstream distance. By contrast, coarse particulate organic matter (CPOM) decreased rapidly downstream of the forest, however, low levels of “forest-derived” CPOM were still present 300m downstream from the forest edge. These environmental changes drove significant shifts in macroinvertebrate community structure. Moreover, pasture communities were markedly different from those in forest, despite being only 100 m from the forest edge. In particular, total macroinvertebrate and EPT richness and densities decreased, and communities shifted from evenly distributed allochthonous-based communities to autochthonous-based communities, highly dominated by molluscs (e.g., Potamopyrgus spp.) Subsequent surveys of 6-8 sites across a longitudinal forest-pasture gradient in each of eleven streams flowing from forest fragments of different sizes into grazed pastures throughout the Canterbury region, indicated that stream temperature increased more rapidly downstream of small- and medium-sized fragments, than larger fragments. A Berger-Parker dominance index also indicated that macroinvertebrates responded principally to water temperature, with communities being more highly dominated by temperature-tolerant molluscs in streams flowing from small-sized forest fragments. Several headwater streams in Canterbury were also highly retentive, with marked CPOM rarely exported beyond 50 m downstream of the forest. Experimental additions of leaf litter to the pasture reaches of the same streams dramatically increased amounts of stored benthic CPOM. Although non-significant, trends indicated that EPT and shredder densities increased at litter addition sites, providing promise that CPOM can function as a mechanism directly enhancing healthy stream communities. My findings support the contention that when the replanting of entire stream reaches is infeasible, the use of riparian management strategies which focus on the planting of intermittent patches along stream banks can potentially improve stream habitat and community health downstream.