What influences communities (in fluvial ecosystems)?
- determined by physical environment,
- available food resources,
- further refined through species interactions
What are allochthonous and autochthonous sources?
terms used to describe the sources of organic matter in aquatic ecosystems:
- Allochthonous Sources: Allochthonous organic matter originates from outside the aquatic ecosystem and is transported into the system. This organic matter often comes from terrestrial sources such as leaves, woody debris, and soil that fall into the water or are washed in by runoff from the surrounding landscape. Allochthonous sources are an important energy source for aquatic food webs.
- Autochthnous sources: Autochthonous organic matter originates from within the aquatic ecosystem itself. It is primarily produced by aquatic primary producers such as algae, aquatic plants, and cyanobacteria through photosynthesis. Autochthonous organic matter is an essential component of aquatic food webs, providing energy and nutrients to heterotrophic organisms.
Explain the RCC (river continuum Concept)
conceptual framework in freshwater ecology, developed by Robin Vannote 1980.
- describes how physical an biological characteristics of rivers change along a continuum from headwaters to large, low- gradient rivers.
- model for classifying and describing flowing water after the occurrence of indicator organisms.
- describes a linear view of streams, in which the change in physical stream characteristics from headwaters longitudinally to mainstems drives an unimodal distribution of local diversity, with a peak diversity in mid-order stream reaches.
the structure and function of streams are based on five highly interrelated components:
1. hydrology,
2. geomorphology,
3. biology,
4. water quality,
5. connectivity
RCC- Mid-order stream reaches
Mid-order Stream Reaches: These are the middle sections of the river, not the smallest headwaters (first- and second-order streams) nor the largest mainstem (high-order streams).
(see: Strahler Stream order).
- Headwaters: Typically have lower species diversity due to the harsh, fast-flowing, and cold environment. Only specialized species can thrive here.
- Mid-order Streams: Conditions are more moderate - flow is not as fast, temperatures are more stable, and there is a mix of habitats (riffles, pools, etc.). These conditions support a wider variety of species, resulting in peak diversity.
- Mainstem (Lower Reaches): Although the environment is more stable and productive, it often becomes dominated by fewer species that can outcompete others in these nutrient-rich waters.
What “shifts” do occur referring to the River Continuum Concept, when following a stream from the headwaters downwards?
- Particle size: course to fine
- Temperature; cold to warm
- Turbidity: low to high
- Light availability: low to high (less canopy shading)
- Primary Production/Respiration ratio (P/R): low to high = from dominantly allochthonous to autochthonous carbon.
- from Shredders & Filter Feeders (collector- gatherer) to Filter Feeders & Grazers;
- Invertivore fish –> Invertivore fish & piscivore fish –> planktivorous fish;
- Biodiversity in fish communities (small – high – smaller);
- Fish communities according to affinity to water temperature.
Criticize the River Continuum Concept
1) Limited applicability
- Seems to only be applicable for temperate river systems with forested headwaters flowing in
relatively undisturbed landscapes, ignoring therefore the complexity of river systems globally.
-> e.g. excluding: intermittent rivers (periods of no flow during dry seasons), grassland rivers with reduced woody riparian, tropical rivers.
2) Failed to integrate lateral habitats (angrenzende Lebensräume) and floodplains to river functioning and biodiversity
- Relative contribution of the lateral connectivity becomes more important with increasing stream order or in meandering and braided river sections.
3) Local conditions overweigh and do not reliably follow the upstream-downstream continuum
- In reality great deviations from the RCC due to complex local conditions and interactions or small differences in the geomorphological structure of river segments.
4) Ignores the meta-community theory and focusses only on local environmental changes
- Meta-community theory focusses on connectivity among different habitat patches and how they influence the community structure, diversity, and species distribution across a landscape.
- Due to ignoring the meta-community theory, concepts like “migration, dispersal, extinctions” were ignored in the RCC.
Name and describe all three existing concepts to classify rivers. Also the fourth one that is in progress.
What do the existing three concepts have in common?
(RCC) River Continuum Concept
- RCC describes a linear view of streams, in which the change in physical stream characteristics from headwaters longitudinally to mainstems drives an unimodal distribution of local diversity, with a peak diversity in mid-order stream reaches.
(MHH) Mighty Headwaters Hypothesis
- MMH posits that β-diversity should be highest in headwaters and decrease moving downstream, showing an inverse relationship with local diversity.
-> Beta-diversity measures the variation in species composition between different habitats or ecosystems within a region, highlighting the diversity among communities.
(SDC) Serial discontinuity Concept
- SDC describes the eects of dams on downstream ecosystems and predicts that local diversity increases with distance below upstream dams due to the dams’ disturbance of environmental conditions.
(TEC) Theory of Ecological Communities [in progress]
- TEC aims at integrative analysis of spatial and environmental gradients and to link diversity patterns to general community assembly processes (dispersal, speciation, niche selection, ecological drift).
All three predict biodiversity change along spatial and environmental gradients.
What is the “Lotic – Lentic Continuum”? What are lotic and lentic water bodies characterized by?
Conceptual framework used in freshwater ecology to describe the continuum of aquatic habitats along a gradient from flowing (lotic) to standing (lentic) water bodies.
Lotic habitats
- characterized by the continuous movement of water, typically with a unidirectional flow.
- Lotic ecosystems are dynamic and often exhibit high levels of variability in flow rates, channel morphology, substrate composition, and water chemistry.
- They support diverse communities of aquatic organisms adapted to living in fast-flowing environments.
Lentic habitats
- encompass standing water environments such as lakes, ponds, and wetlands.
- These habitats are characterized by still or slow-moving water with minimal flow.
- tend to have more stable environmental conditions compared to lotic ecosystems, with factors such as water temperature, light penetration, and nutrient availability varying less over time.
Many aquatic ecosytsems fall somewhere along this lotic- lentic continuu, exhibiting characteristics of both habitats.
e.g. transitional zones such as floodplains,
estuaries, and riparian wetlands may experience periodic fluctuations in flow, creating a mix of lotic and lentic conditions and supporting unique assemblages of species adapted to these dynamic environments.
What is the main distinction between lotic and lentic waters based on?
The main distinction between running waters (lotic) and lakes/standing waters (lentic) is based on:
- The relative residence time / also “turnover time or water retention time”. (The mean time it takes to replace all water of the water body).
- The water renewal rate (Percent of water volume that is replaced per unit time).
What are the impacts of river dams on biogeochemical cycling?
1) Nutrient elimination
- Nutrient elimination in dam reservoirs (Stauseen) modifies global biogeochemical cycles with consequences to ecosystem structure and function along river networks.
2) Reservoirs might be greenhouse gas sources
- The global importance of reservoirs as greenhouse gas sources remains heavily debated.
What global river volume is moderately to severely impacted through dams & other waterworks (in %)? What percentage of global sediment load is dropped due to dams before it reaches the ocean?
Global river volume impacted through dams and waterworks = 50%
Global drop of sediment load due to dams before reaching the ocean = 25%
What are threads to river ecosystems?
- Organic pollution -> reduced oxygen levels, specifically during summer due to microbial activity.
- Dams: dam sections are more similar to lakes than to rivers. Downstream river sections have an altered flow, sediment and thermal regimes. -> Loss of natural connectivity restricts dispersal & migration.
- Groundwater use in semi-arid regions
- Overexploitation of any animals (fish, birds, invertebrates). -> Impacts species composition.
- Invasive non-native species
- Climate change
What is the WFD – Water Framework Directive (European Commission – Environment) aiming for? What is it called in Germany?
The WFD aims to set out rules to halt deterioration (Verschlechterung) in the status of EU water bodies and achieve good status for Europe’s rivers, lakes and groundwater.
- Protecting and improving the quality of surface and groundwater.
- Promoting sustainable water use.
- Achieving good ecological and chemical status for all waters by 2027.
dt. : Wasserrahmenrichtlinie
Biota in freshwater ecosystems (examples and feeding roles):
In freshwater ecosystems, biota includes
* primary producers (e.g., algae, aquatic plants),
* consumers (e.g., fish, invertebrates),
* decomposers (e.g., bacteria, fungi).
Different organisms fulfill various feeding roles contributing to the flow of energy and nutrients within the ecosystem:
* herbivores
* carnivores
* detritivores
What is the DPSIR Framework and Its Connection to River Systems in the Anthropocene?
The DPSIR (Drivers, Pressures, State, Impact, Response) is a tool used to manage environmental issues.
Drivers:
* Human activities such as agriculture, urbanization, and industrialization increase the demand for water and land resources.
* Climate change, driven by anthropogenic greenhouse gas emissions, aects precipitation
patterns and temperature regimes.
Pressures:
* Over-extraction of water for irrigation and drinking reduces river flows.
* Pollution from agricultural runo, industrial discharges, and sewage degrades water quality.
* Construction of dams and river channelization alters natural flow regimes.
State:
* Altered river systems experience changes in water quality and quantity.
* Natural flow regimes are disrupted, affecting seasonal flow variations crucial for ecosystem health.
* Degraded habitats lead to reduced aquatic biodiversity.
Impact:
* Loss of species and decline in aquatic biodiversity as habitats become unsuitable for many
organisms.
* Changes in sediment transport and deposition, affecting river morphology and ecosystems.
* Reduced resilience to environmental changes and extreme weather events.
Response:
* Implementing sustainable water management practices to balance human and ecological
needs.
* Restoration projects to reinstate natural flow regimes and improve habitat quality.
* Policies and regulations under frameworks like the Water Framework Directive to protect
and improve water bodies.
The DPSIR framework helps to identify the chain of human-induced changes (Drivers and Pressures) that impact river systems (State), leading to ecological and socio-economic consequences (Impacts), and guiding necessary actions (Responses) to mitigate these threats and preserve aquatic biodiversity and natural flow regimes in the Anthropocene.
