A

Growth rate of zooplankton (1 / 24h)

Connectedness

Figure 7.11 Long-term succession of ecosystems, indicated on different scales: small-scale disturbances may support the development of the overall system.

Connectedness

Figure 7.11 Long-term succession of ecosystems, indicated on different scales: small-scale disturbances may support the development of the overall system.

7.6 A CASE STUDY: HUMAN DISTURBANCE AND RETROGRESSIVE DYNAMICS

Up to now, we have focused on "natural dynamics." Thus, in the end of this chapter, we demonstrate human disturbances using a wetland case study. In general, human activities influence disturbance regimes in several mechanisms, such as:

• the rescaling of natural disturbances,

• the introduction of novel disturbances,

• the modification of the reception mechanisms of the disturbed components,

• influences on disturbance rates and intensities,

• the suppression of natural disturbances to ensure the potential of aspired ecosystem services,

• the change of successional pathways due to irreversible changes.

As an example for human pressures and disturbance dynamics, Figure 7.12 describes a case study from ecosystem research in the wetlands of the Bornhöved Lakes District in Northern Germany. Here a holistic indicator system, which has been developed on the basis of the orientor theory (Müller, 2005) has been used to demonstrate the steps of wetland retrogression as provoked by eutrophication and drainage.

Based on field measurement, mappings, and classifications different ecosystem types have been analyzed with the computer-based "digital landscape analysis system" (Reiche, 1996) and the modelling system "Wasmod-Stomod" (Reiche, 1996) which was used to simulate the dynamics of water budgets, nutrient, and carbon fluxes based on a 30-year series of daily data about meteorological and hydrological forcing functions. The model outputs were validated by measured data in some of the systems

(Schrautzer, 2003). The model outputs were extended to include data sets concerning the ecosystem indicators by the following variables:

• Exergy capture: net primary production (NPP)

• Entropy production: microbial soil respiration

• Storage capacity: nitrogen balance, carbon balance

• Ecosystem efficiency: evapotranspiration/transpiration, NPP/soil respiration

• Nutrient loss: N net mineralization, N leaching, denitrification

• Ecosystem structures: Number of plant species (measured values)

The wet grasslands of the Bornhoved Lakes District are managed in a way that includes the following measures: drainage, fertilization, grazing, and mowing in a steep gradient of ecosystem disturbances. The systems have been classified due to these external input regimes, and in Figure 7.12 the consequences can be seen in a synoptic manner. While the farmer's target (improving the production and the yield of the systems), the NPP is growing by a factor of 10, the structural indicator is decreasing enormously throughout the retrogression. Also the efficiency measures (NPP/soil respiration) are going down, and the biotic water flows get smaller. On the other hand, the development

Net Primary Production

Net Primary Production

N Net Mineralization

A: Weakly Drained, Mesotrophic

B: Weakly Drained, Eutrophic

C: Moderately Drained, Eutrophic

: Intensively Drained, Eutrophic

Microbial Soil Respiration

Figure 7.12 Retrogressive ecosystem features at different steps of human intervention, after Müller et al. (i.p.). The figure shows a set of 10 holistic indicators which as a whole represent ecosystem integrity. Starting with the initial state A, drainage and eutrophication of the wet grassland ecosystems affect irreversible changes up to the degraded state D. During that development ecosystem structures (complexity) are reduced, energy and matter efficiencies decrease, and the originally sink ecosystem turns into a source for nitrogen and carbon compounds.

N Net Mineralization

N Leaching

A: Weakly Drained, Mesotrophic

B: Weakly Drained, Eutrophic

C: Moderately Drained, Eutrophic

: Intensively Drained, Eutrophic

Denitrification

Microbial Soil Respiration

Figure 7.12 Retrogressive ecosystem features at different steps of human intervention, after Müller et al. (i.p.). The figure shows a set of 10 holistic indicators which as a whole represent ecosystem integrity. Starting with the initial state A, drainage and eutrophication of the wet grassland ecosystems affect irreversible changes up to the degraded state D. During that development ecosystem structures (complexity) are reduced, energy and matter efficiencies decrease, and the originally sink ecosystem turns into a source for nitrogen and carbon compounds.

of the carbon and nitrogen balances demonstrates that the system is turning from a sink function into a source, the storage capacity is being reduced, and the loss of carbon and nitrogen compounds (all indicators on the right side of the figure) is rising enormously. With these figures we can state an enormous decrease of ecosystem health, and as many of the processes are irreversible, the capacity for future self-organization is reduced up to a very small degree.

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